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This PDF file contains the front matter associated with SPIE Proceedings Volume 7747, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.
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This paper describes two topics of our recent studies on ultrafast strong-field interactions with atoms, molecules and
solid surfaces. One is concerned with the high-order harmonic generation (HHG) from molecules nonadiabatically
aligned with intense femtosecond (fs) laser pulses in a pump and probe experiment. The HHG is very sensitive to the
molecular orbital and its spatial orientation with respect to the laser polarization. Experimental and theoretical studies
demonstrate the characteristic properties of HHG from coherently rotating molecules. The other topic is the periodic
nanostructure formation observed in fs laser ablation of dielectric materials. The major interest is in the ultrafast
interaction process of nanostructuring on solid surfaces, for the purposes of potential applications of fs lasers to nanoprocessing.
The experimental results have shown that enhanced near-field initiates the ablation of surface area much
smaller than the laser wavelength and the origin of nanoscale periodicity can be attributed to the excitation of surface
plasmon polaritons in the surface layer.
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Catheters and medicals tubes are widely used to introduce pharmaceuticals and nutrients into arteries and veins, and
to drain fluids or urine from urethra or the digestive organs. It is well known that illuminated TiO2 photocatalysts
can decompose most noxious or toxic organic compounds.
We studied the properties of titanium dioxide layers created by pulsed laser deposition from pure titanium and
titanium dioxide targets with the goal to develop urethral catheter using TiO2 coated plastic tube. To reach
crystalline structure at low substrate temperatures the radio-frequency discharge between the target and the substrate
was implemented. The crystalline structure of layers was determined by X-ray diffraction and Fourier Transform
Infrared Spectroscopy. Morphology was studied by atomic force microscopy (AFM). Using RF discharge, mixture
of anatase and rutile was found at substrate temperature of 90°C (which was reached only by RF discharge).
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This preliminary work explores a technique for processing collagen thin films by femtosecond Ti:Sapphire laser ablation
in order to provide a structured matrix support for cell growth and other tissue engineering applications. The laserinduced
structuring of collagen easily yields an expanded micro foam material with interconnected pores and properties
that mimics the native collagen-based extracellular matrix. The obtained structured matrix is formed by a cavitation and
bubble growth mechanism. The surface properties of collagen thin films before and after Ti-sapphire irradiation with 800
nm were investigated by means of Field Emission Scanning Electron Microscope (FESEM) technique. FESEM analysis
showed that with a single pulse of ultra-short laser radiation is capable of inducing morphological changes in the
irradiated collagen films. The size of the observed features can be controlled by selection of laser fluence and pulse
number. Collagen-based biomaterials were developed and explored for the purposes of tissue engineering. Biomaterials
are expected to function as cell scaffolds to replace native collagen. The ultra-short laser ablation induced nanofoaming
of biomaterials will improve currently available techniques. Artificial collagen nanofibers are increasingly significant in
numerous tissue engineering applications and seem to be ideal scaffolds for cell growth and proliferation.
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Lasers can provide a precious tool to conservation process due to their accuracy and the controlled energy they
deliver, especially to fragile organic material such as paper. The current study concerns laser modification such as paper
cleaning, initially of test papers artificially soiled and then of an original book of the early 20th Century. The test objects
were A4 copier paper, newspaper, and paper Whatman No.1056. During the experiments, ink of a pen, pencil and ink
from a stamp was mechanically employed on each paper surface. Laser cleaning was applied using a Q-switched
Nd:YAG operating at 532 nm and CO2 laser at 10.6 μm for various fluences. The experimental results were presented by
using optical microscopy. Eventually, laser cleaning of ink was performed to a book of 1934, by choosing the best
conditions and parameters from cleaning the test samples, like Nd:YAG laser operating at 532 nm.
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Recently we proposed a novel PLD arrangement, termed inverse pulsed laser deposition (IPLD). Being able to produce
thin films of better surface morphology without any complex instrumentation, this method can represent an alternative to
the traditional PLD technique while preserving versatility. Two configurations of this new target-substrate arrangement,
namely static and co-rotating IPLD were developed. In the static IPLD configuration, the substrate is stationary with
respect to the ablated spot; while in the co-rotating IPLD configuration the substrate is fixed to the target surface and
rotates simultaneously with the target. Co-rotating IPLD proved to be capable of homogenizing the film thickness.
Here we report a model calculation supported by experimental results to describe the radial growth rate variation of corotating
IPLD films. To characterize the homogeneity of CNx, TiOx, and Ti co-rotating IPLD films, a thickness
inhomogeneity index (TII) was introduced, which allows the comparison of thickness homogeneity between films of
different lateral dimensions. The presented semi-analytical, semi-numerical model derives the radial variation of the
growth rate of co-rotating IPLD films from the lateral growth rate distributions measured along the symmetry axes of the
static IPLD films. The laterally averaged growth rate (LAGR) was used to describe how the ambient pressure affects thin
film growth in the 0.5-50 Pa domain. As an example, the absolute error between the measured and calculated radial
growth rate variation of CNx layers grown by co-rotating IPLD at 5 Pa, was less than 3%, while the LAGR was predicted
with 20% accuracy.
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μInterest to the narrow band gap semiconductors for example Pb1-xCdxSe is connected with problem of creation of new
sources of IR radiation. Possibility of control of the properties of polycrystalline films of the lead chemical compounds
by luminescent and Raman methods is considered.
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Colloidal solutions of gold and silver nanoparticles (NPs) were prepared using a method pulsed laser ablation of target in
liquid media. A gold and silver targets immersed in double distilled water are irradiated for 20 min by laser pulses with
duration of 15 ns and repetition rate of 10 Hz. In order to investigate influences of laser wavelength and fluence on the
particle size, shape and optical properties the experiments were preformed by using two different wavelength - the
fundamental and the second harmonic (SH) (λ = 1064 and 532 nm, respectively) of a Nd:YAG laser system. Two
different values of the laser fluence for each wavelength at the experimental conditions chosen were used and thus it was
changed from several J/cm2 to tens of J/cm2. For characterization of the NPs shape and size distribution were used
transmission electron microscope (TEM) and optical transmission spectroscopy in the near UV and in the visible region.
Spherical shape of the nanoparticles at the low laser fluence and appearance of aggregation and building of nanowires at
the SH and high laser fluence is seen. Dependence of the mean particle size at the SH on the laser fluence was
established. The mean diameter of gold NPs became smaller with decrease in laser wavelength.
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Modulated optical reflectance (MOR) technique is employed for defectoscopy and structural analysis of La2/3Sr1/3MnO3(LSMO) ferromagnetic nanolayers. The optical reflectance is affected by the change of free charge carrier density due to
periodic photothermal modulation described by Drude effect. A dual wavelength setup of a pulsed heating laser and a
probe CW laser, whereas the laser focal spots are precisely aligned on the scanned sample surface, provides electrical
signal proportional to the variation of optical reflectance at each measurement point. The probe beam is modulated
selectively by reflection without interference by the substrate properties or external fields. It is shown theoretically and
experimentally that MOR signal is proportional to the thermal derivative of magnetoresistance. The described contactless
measurement may find important application in investigation of a range of new magnetoelectric devices.
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Photomultiplier tubes are widely used detectors of low level light signals; however their performance is often limited,
especially at long wavelengths. Input signals are reduced both by surface reflection and by transmission through the
photocathode layer. Earlier methods of overcoming these weaknesses are summarized. New predictive modelling of the
reflectivity and absorption reveals dependencies that are a function of angle of incidence, cathode thickness and
polarization. Improvements on normal usage using extremely simple and low cost techniques are effective. These are
demonstrated using retrofits that can improve the overall sensitivity of many types of photomultiplier. Examples include
a simple external conical torch reflector, which has raised the efficiency of an S20 multialkali photocathode by between
20 to 10% across the blue to red spectral range. A second example, of a semi-cylindrical glass coupler, improved the
absorption efficiency by exploiting 60 degree, rather than normal incidence of the light. Enhancements are up to 500% at
longer wavelengths. Such gains are particularly valuable as this is the region of lowest quantum efficiency for the
standard operation of the tubes.
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Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to
study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically
induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission
backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows
enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to
overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ
configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate
and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is
also shown.
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Comparison of absorption and fluorescence in a nano-cell containing Rb vapor with other Rb nano-cells with addition of
neon gas is presented. It is shown that the effect of collapse and revival of Dicke-type narrowing occurs for Rb nanocells
containing N2 as buffer gas under 6 and 20 Torr pressure for the thickness L = λ /2 and L = where λ is the resonant λ,
laser wavelength 794 nm (D1 line). Particularly for 6 Torr the line-width of the transmission spectrum for the thickness L
=λ/2 is 2 times narrower than that for L = λ. For an ordinary Rb cell with L = 0.1 - 10 cm with addition of buffer gas, the
velocity selective optical pumping/saturation (VSOP) resonances in saturated absorption spectra are fully suppressed
when the buffer gas pressure > 0.5 Torr. A spectacular difference is that for L = λ, VSOP resonances located at the
atomic transitions are still observable even when Ne pressure is ≥ 6 Torr. Narrowband fluorescence spectra of a nano-cell
with L = λ/2 can be used as a convenient tool for online buffer gas pressure monitoring for the conditions when ordinary
pressure gauges are unusable. Comparison of electromagnetically induced transparency (EIT) effect in a nano-cell filled
with pure (without a buffer gas) Rb with another nano-cell, where buffer gas nitrogen is added, is presented. The use of
N2 gas inside Rb nano-cells strongly extends the range of coupling laser detunings in which it is still possible to form
EIT resonance.
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We present in this paper recent results on Light - Induced Atom Desorption (LIAD) in sealed and open coated cells.
LIAD is defined via the description of an experiment on rubidium atoms stored in a dry - film coated cell, where a few
milliwatts of even non coherent and non resonant light are able to increase the alkali atomic density for more than one
order of magnitude. Modeling of the effect is given. New features become relevant in the case of LIAD in porous
glasses: in fact, although the photodesorption efficiency per unit area in bare glass is much lower, photoatomic sources
can be prepared, due to the huge inner surface of porous samples. We applied LIAD from organic coatings to the
stabilization of alkali densities out of equilibrium: sodium case is here discussed. Finally, we report on fully original,
preliminary measurements of rubidium Magneto - Optical Trap loading via LIAD from a dry - film coated cell.
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We present Hanle electromagnetically induced transparency (EIT) resonances obtained from the outer parts of the
Gaussian laser beam. The signal from the outer parts only was obtained by placing circular opaque masks of different
diameters in the center of the laser beam just in front of the detector. The Hanle EIT resonances obtained in that way are
narrower and for high laser intensities even more contrasted. Suggested explanation for the line narrowing is based on
lower power broadening in the wings of the Gaussian laser beam as well as on the traversing of the coherently prepared
atoms through the beam. The resonance contrast to linewidth ratio, when the central part of the beam is blocked, is
higher or equal to the ratio obtained when the whole laser beam is detected, for all laser intensities used in the
experiment. Due to high ratio of contrast and linewidth, resonances obtained in proposed way could be useful in
frequency metrology and magnetometry.
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In this paper we present our spectroscopic studies on Coherent Population Trapping (CPT) in micro-fabricated Caesium
cells and our evaluation of its application in miniature atomic frequency standards (atomic clocks). We observe the CPT
signal on the Cs D1-line by coupling two hyperfine ground-state Zeeman sub-levels to a common excited state using two
coherent electromagnetic fields created with a modulated DFB laser. Contrarily to double resonance, CPT does not
require any microwave cavity, which should facilitate the miniaturization of a future atomic clock device. We study and
report here on the light shift phenomena at different cell temperatures and laser wavelength. We also present resonance
shifts due to cell temperature variations and clock frequency stability measurements. To the best of our knowledge, this
article is the first report on light shift with Cs D1 line in a CPT vapour-cell atomic clock.
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The fast development of CPT applications and the need of good magnetooptical sensors result in an increased interest in
the Coherent Population Trapping (CPT) resonances and the processes that determine their shape. In this work the shape
and width of the CPT resonances are investigated in two different paraffin-coated Rb vapor cells from point of view of
understanding the processes influencing the shape of the resonances and building of miniature and sensitive detector. The
dependence of the shape of the resonances on the laser power is measured. Narrow resonances on three hyperfine
transitions of the D1 87Rb line are registered. For explanation of the bright structure in the resonance shapes at low laser
powers analysis of the influence of different processes is made.
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In this communication we report the first observation of a narrow, reduced fluorescence dip in the profile of the
completely closed transition on the D2 line of 133Cs vapor, confined in Extremely Thin Cell with nanometric thickness.
The theoretical modeling of the fluorescence based on the Optical Bloch Equation for two-level atomic system, shows
that the narrow dip in the fluorescence could be attributed to a very small loss in the excitation process of the examined
degenerate transition. While the population in the atomic system remains constant, the depolarization of the excited level
can lead to some loss in the efficiency of the optical transition excitation. Under the conditions of our experiment, no dip
in the fluorescence is registered for the cell thickness where a well pronounced Dicke peak in the absorption takes place.
For the cells with nanometric thickness, the previous investigations demonstrate that the fluorescence profiles of optical
transitions differ significantly from the absorption profiles. However, our experiment shows that some traces of the
coherent Dicke process contributing to the absorption line still remain in the fluorescence, which is result of non-coherent
processes.
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Electromagnetically induced transparency (EIT) and Autler-Townes (A-T) effect were studied under conditions of strong
coupling of the hyperfine manifold 5P3/2 (F') with the 5S 1/2 (F=2) ground state of cold 85Rb atoms in MOT. Transmission
spectra of a weak probe beam, at the frequency scanned in the vicinity of the 5S1/2(F=3)→5P3/2(F') resonances were
registered at various frequency settings of the coupling beam. The spectra were interpreted by applying optical Bloch
equations. As a starting point, a 5-level model, accounting for F=2, 3 and F'=1, 2, 3 states was assumed (the noncoupled
state F'=4 being neglected, but the F'=1 state, coupled but not directly probed, included, as its presence was
found to be imprinted in the spectra). Such a model alone does not reproduce all the spectral features observed.
Therefore we have considered the existence of the polarized light induced transitions between Zeeman substates,
involving (F'=2, m') and (F'=3, m') upper states. In order to indirectly account for the m→m' absorption transitions to
the non-coupled m' states, and to the pairs of states with incomplete coupling, we have complemented the results of the
5-level model with the ones of its reduced versions. Satisfactory agreement of the positions of respective modeled and
experimental spectral peaks was achieved.
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An analysis is presented of the high resolution Autler-Townes spectra in a pump-probe cascade 5S1/2(F=3)→5P3/2(F'=4) → 5D5/2(F") experiment in a working 85Rb-MOT. It is shown that despite the complex nature of the spatially
varying interactions of individual atoms with MOT fields, the probed region of the atomic cloud in MOT can be
characterized by effective Rabi frequency, at least for the customary used range of detuning and intensity of the trapping
field. This effective value which relates to the averaged atom interactions, is directly dependent on the trapping laser
power and practically does not depend of detuning. The applied procedure is based on predictions of a three-level model.
The procedure can be used as a method for determination of the effective Rabi frequency experienced by atoms in MOT,
and it also indicates applicability limits of the approach for a given MOT implementation.
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The paper presents a holographic optical element (HOE) for a phase-stepping digital electronic speckle pattern
interferometry with double symmetrical illumination of the object both in vertical and horizontal planes for precision
full-field displacement measurement of objects under loading . More specifically, the proposed HOE allows for
simultaneous reconstruction of four virtual and parallel to the HOE surface reference planes for off-axis illumination
with two pairs of diode lasers emitting at two different wavelengths. In this way we transform a two-beam interferometer
into a multiple beam interferometer with four separate channels. The HOE is constructed as a sandwich structure of two
reflection (Denisuyk type) holograms of a diffuse metal screen illuminated at 30 degrees to the normal. Each of the
holograms comprises two holographic reflection records made successively on a single holographic plate. Recording is
performed in the visible part of the spectrum, and through additional chemical treatment the spectral maximum of the
developed holograms is shifted into the IR region to achieve correct reconstruction for illumination at 790 nm and 830
nm. Super high resolution silver halide emulsion with resolution over 6000 line/mm is used for recording of holograms.
The reconstructed four reference beams interfere with the beam reflected from the object, thus forming four independent
optical channels for two laser beams at 790 nm with S and P polarizations, as well as for two S and P polarized beams at
830 nm.
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Coherent illumination of a diffuse object yields a randomly varying interference pattern, which changes over time at any
modification of the object. This phenomenon can be used for detection and visualization of physical or biological activity
in various objects (e.g. fruits, seeds, coatings) through statistical description of laser speckle dynamics. The present
report aims at non-destructive full-field evaluation of bread by spatial-temporal characterization of laser speckle. The
main purpose of the conducted experiments was to prove the ability of the dynamic speckle method to indicate activity
within the studied bread samples. In the set-up for acquisition and storage of dynamic speckle patterns an expanded
beam from a DPSS laser (532 nm and 100mW) illuminated the sample through a ground glass diffuser. A CCD camera,
adjusted to focus the sample, recorded regularly a sequence of images (8 bits and 780 x 582 squared pixels, sized 8.1 ×
8.1 μm) at sampling frequency 0.25 Hz. A temporal structure function was calculated to evaluate activity of the bread
samples in time using the full images in the sequence. In total, 7 samples of two types of bread were monitored during a
chemical and physical process of bread's staling. Segmentation of images into matrixes of isometric fragments was also
utilized. The results proved the potential of dynamic speckle as effective means for monitoring the process of bread
staling and ability of this approach to differentiate between different types of bread.
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The electron-hole states in the molecular beam epitaxy grown GaAs/In0.5Ga0.5As quantum well, placed into space charge region, have been studied by photoreflectance spectroscopy. The energies of electrons and holes have been calculated in the envelope function model including deformation-induced changes in the band structure of quantum well. It is shown that the best accordance between experimental and theoretical data is achieved in the case of band offset Q = ;Ec/;Ev = 0.62/0.38 at GaAs/In0.5Ga0.5As heterojunction. The most intense transition is observed in this case between 1 electron and 1 light hole energy. This fact is connected with the indium segregation in the GaAs/In0.5Ga0.5Asquantum well. In this case one could obtain the flat bands in the quantum well and realize the parity selection rules for the rectangular potential. The model of the nonsymmetrical rectangular potential is applied to describe the energies of electronic levels in the quantum well. The segregation parameters have been calculated from the segregation-induced shift of the energies of interband transitions in the GaAs/In0.5Ga0.5As quantum well.
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An interferometric phase-shifting photoelasticity is an effective approach to separate the stress components in
engineering structures with mechanical and geometrical complexity, especially when the photoelastic coating method is
applied. A series of photoelastic fringe patterns are recorded with a circular polariscope to obtain the phase map
proportional to the difference of the principal stresses in the tested specimen. In addition, holographic recording of
fringe patterns is applied for retrieval of isopachic fringes which give the sum of the principal stresses. The easiest way
to perform a combined polariscopic and holographic measurement for full-field stress analysis is to use a laser light
source. However, the speckle noise at coherent illumination could severely violate the requirement for high signal-tonoise
ratio in the recorded patterns. Thus, task-oriented preprocessing and denoising algorithms become mandatory for
accurate phase estimation and unwrapping. Development of such algorithms is impossible without an adequate signaland-
noise model, which is the goal of this paper. The paper presents simulation of an interferometric photoelastic
measurement that is based on calculation of the complex amplitudes at the output of a Mach-Zender interferometer
combined with a circular polariscope. The model is used for simulation of speckled fringe patterns for an epoxy disk
under concentrated diametral compression. Comparison with experimental fringe patterns which have been recorded at
pure tensile load for PhotoStress coated samples with a hole as a mechanical stress concentrator is also included.
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We present the results of an experimental study of Coherent Population Trapping (CPT) in potassium, obtained by means
of modulation of laser light amplitude with kHz frequency. The radiation from an external cavity diode laser, matching
the D1 line of K, is modulated by an acousto-optical modulator. In the cell containing buffer gas, the CPT resonance
width is reduced more than three orders of magnitude as compared to the cell containing pure potassium vapor. In K this
resonance narrowing occurs with high resonance contrast; such behavior is not observed in buffered cells containing Rb
or Cs, where the optical pumping to the non-interacting with the light ground level is very effective and depletes the
population of the working ground Zeeman sublevels. The narrow CPT resonance of reduced fluorescence transforms to
the one of enhanced fluorescence with the cell temperature rising. The transformed resonance exhibits higher contrast
and lower width than those of the reduced fluorescence resonance. Hence, beside its scientific importance the resonance
sign reversal can be used for the improvement of the CPT resonance parameters.
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This paper and corresponding seminar given on 20 September 2010 at the 16th International School for Quantum
Electronics in Nesebar, Bulgaria, will describe the key hardware aspects of the Raman-shifted Eye-safe Aerosol
Lidar (REAL) and recent advances in extracting two-component wind vector fields from the images it produces.
The REAL is an eye-safe, ground-based, scanning, elastic aerosol backscatter lidar operating at 1.54 microns
wavelength. Operation at this wavelength offers several advantages compared to other laser wavelengths including:
(1) maximum eye-safety, (2) invisible beam, (3) superior performance photodetectors compared with those
used at longer wavelengths, (4) low atmospheric molecular scattering when compared with operation at shorter
wavelengths, (5) good aerosol backscattering, (6) atmospheric transparency, and (7) availability of optical and
photonic components used in the modern telecommunations industry. A key issue for creating a high-performance
direct-detection lidar at 1.5 microns is the use of InGaAs avalanche photodetectors that have active areas of at
most 200 microns in diameter. The small active area imposes a maximum limitation on the field-of-view of the
receiver (about 0.54 mrad full-angle for REAL). As a result, a key requirement is a transmitter that can produce
a pulsed (>10 Hz) beam with low divergence (<0.25 mrad full-angle), high pulse-energy (>150 mJ), and short
pulse-duration (<10 ns). The REAL achieves this by use of a commercially-available flashlamp-pumped Nd:YAG
laser and a custom high-pressure methane gas cell for wavelength shifting via stimulated Raman scattering. The
atmospheric aerosol features in the images that REAL produces can be tracked to infer horizontal wind vectors.
The method of tracking macroscopic aerosol features has an advantage over Doppler lidars in that two components
of motion can be sensed. (Doppler lidars can sense only the radial component of flow.) Two-component
velocity estimation is done by computing two-dimensional cross-correlation functions (CCFs) and noting the
displacement of the peak of the CCF with respect to the origin. Motion vectors derived from this method are
compared with coincident sonic anemometer measurements at 1.6 km range. Preliminary results indicate the
method performs best when the atmosphere is stable with light winds.
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Aerosols and clouds have significant impact on global climate. In this work experimental results from regular lidar
investigations of tropospheric aerosols and clouds are presented. Examples of calculated atmospheric backscatter
coefficient profiles extracted from four years lidar dataset collected in the city of Sofia (Bulgaria) are offered and
analyzed. They illustrate remote detection of aerosol fields and clouds at different altitudes including Saharan dust
intrusion over the city and highly situated cirrus clouds. The mass temporal evolution and the spatial distribution of
registered atmospheric layers are visualized by 2D-colormaps in height-time coordinates. The ground-based
measurements are performed with a newly developed lidar in the Laser Radar Lab, Institute of Electronics, Bulgarian
Academy of Sciences. The good parameters of all the laser, telescope, photo-receiving modules and software make it
possible the developed lidar to be utilized for carrying out fast and accurate remote atmospheric measurements with high
spatial and temporal resolution.
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Second half of April and beginning of May 2010, were remembered by a big trouble in the airplane traffic over Europe,
due to the eruption of the volcano Eyjafjallajokull in Iceland. The volcanic ash propagated quickly in the atmosphere
traversing most of European countries. Its trajectories were forecasted and observed by many meteorological stations to
prevent unintended consequences of the airplane transport
The lidar stations of the European lidar network EARLYNET-ASOS [1] performed a large campaign of measurements to
identify the position, the height above ground level (AGL) and the thickness of the volcanic aerosols transported in the
air. It was an appreciable work to update meteorological forecasting and to study volcanic distribution directions, power
and sedimentation in continental scale. As partner in EARLINET-ASOS project, Sofia lidar station performed
measurements of the atmospheric aerosol profiling which results where quickly presented on the WEB-page of the
Institute of Electronics - BAS [2]. A more detailed discussion and comments concerning only Sofia-lidar measurements
of the volcanic dust layers observed over the town we present in this work.
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In this work we present an analysis of the response of a compact, simple and inexpensive optoelectronic
sensor system intended to detect spectral shifts of a long-period fiber grating (LPG). The system makes use of a
diffraction grating and a couple of receiving optical fibers that pick up signals at two different wavelengths. This
differential detection system provides the same useful information from an LPG-based sensor as with a conventional
laboratory system using optical spectrum analyzers for monitoring the minimum offset of LPG. The design of the
fiber detection pair as a function of the parameters of the dispersion grating, the pick-up fiber and the LPG
parameters, is presented in detail. Simulation of the detection system responses is presented using real from spectral
shifts in nano-coated LPGs caused by the evaporation of various liquids such as water, ethanol and acetone, which
are examples of corrosive, flammable and hazardous substances. Fiber optic sensors with similar detection can find
applications in structural health monitoring for moisture detection, monitoring the spillage of toxic and flammable
substances in industry etc.
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The potentialities are investigated, by statistical modeling, of deconvolution techniques for high-resolution restoration of
electron temperature profiles in fusion plasma reactors like Joint European Torus (JET) measured by Thomson scattering
lidar using the center-of-mass wavelength approach. The sensing laser pulse shape and the receiving-system response
function are assumed to be exponentially-shaped. The plasma light background influence is taken into account as well as
the Poisson fluctuations of the photoelectron number after the photocathode enhanced in the process of cascade
multiplying in the employed microchannel photomultiplier tube. It is shown that the Fourier-deconvolution of the
measured long-pulse (lidar-response-convolved) lidar profiles, at relatively high and low signal-to-noise ratios, ensures a
higher accuracy of recovering the electron temperature profiles with three times higher range resolution compared to the
case without deconvolution. The final resolution scale is determined by the width of the window of an optimum
monotone sharp-cutoff digital noise-suppressing (noise-controlling) filter applied to the measured lidar profiles.
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Time-resolved measurements of the distribution and dynamics of aerosols in atmospheric layers over complex terrains
differing in their orographic characteristics, performed at two or more wavelengths, offer an opportunity for revealing
peculiarities and evolution of different aerosol fractions, in view of their importance for local climate, air circulations,
rainfalls, ecology, etc. In this work, an investigation of dynamical characteristics of the atmospheric aerosol over
adjacent city-, plain-, and mountain zone is reported. Measurements are carried out at two wavelengths (1064 nm and
532 nm) by using two channels of an aerosol lidar based on a powerful Nd:YAG laser. Representative results of lidar
measurements over the zone of investigation are described, obtained during a winter day. Range profiles of the
atmospheric backscattering coefficient, range-corrected lidar signal, normalized standard deviation, and backscattering-related
Angstrom exponent are presented and analysed, as averaged over the time and/or range of measurements, as well
as in their temporal evolution. Taking advantage of the two-wavelength lidar sounding, statistical quasi-quantitative
analysis of the spatial density distribution and temporal dynamics of both the fine-mode and coarse-mode aerosol
fractions is accomplished in orographic aspect. Domains of most intensive dynamics are determined for the two aerosol
fractions. Obtained results show the strong impact of the heterogenic orography on the atmospheric dynamics, as well as
the ability of the utilised lidar system for investigating the distribution and dynamics of aerosol fractions over large areas
with high spatial and temporal resolution.
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The use of intraocular lenses (IOL) is the most promising method for restoring excellent vision in cataract surgery. In
addition, multifocal intraocular lenses for good distant and near vision are investigated. Several new materials,
techniques and patterns are studied for the formation and etching of intraocular lenses in order to improve their optical
properties and reduce the diffractive aberrations. As pulsed laser ablation is well established as a universal tool for
surface processing of organic polymer materials, this study was focused in using laser ablation with short and ultra short
laser pulses for surface modification of PMMA and intraocular lenses, instead of using other conventional techniques.
The main advantage of using very short laser pulses, e.g. of ns, ps or fs duration, is that heat diffusion into the polymer
material is negligible. As a result high precision patterning of the sample, without thermal damage of the surroundings,
becomes possible.
In this study, laser ablation was performed using commercially available hydrophobic acrylic IOLs, hydrophilic acrylic
IOLs, and PMMA IOLs, with various diopters. We investigated the ablation efficiency and the phenomenology of the
etched patterns by testing the ablation rate, versus laser energy fluence, at several wavelengths and the surface
modification with atomic force microscopy (AFM), or scanning electron microscopy (SEM). The irradiated polymers
have different optical properties, at the applied wavelengths, and therefore, present different ablation behaviour and
morphology of the laser ablated crater walls and surrounding surfaces. The experimental results, some theoretical
assumptions for mathematical modeling of the relevant ablation mechanisms are discussed.
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In this invited paper we focus on the discussion of two recent unique applications of the Finite-Difference Time-Domain
(FDTD) simulation method to the design and modeling of advanced nano- and bio-photonic problems. We will first
discuss the application of a traditional formulation of the FDTD approach to the modeling of sub-wavelength photonics
structures. Next, a modified total/scattered field FDTD approach will be applied to the modeling of biophotonics
applications including Optical Phase Contrast Microscope (OPCM) imaging of cells containing gold nanoparticles (NPs)
as well as its potential application as a modality for in vivo flow cytometry configurations. The discussion of the results
shows that the specifics of optical wave phenomena at the nano-scale opens the opportunity for the FDTD approach to
address new application areas with a significant research potential.
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speed, fibre optic communication or cost per CCD pixel often follow a smooth logarithmic improvement per year. This
seems desirable, but progress is frequently only achievable by introduction of new software, different types of storage
media or new operating conditions. Consequently technologies become outdated. For transient information this is
unimportant, but for long term storage and archiving of information, images, photographs etc, there is an inevitable loss
of earlier records. This is not a new phenomenon as even information on stone or clay tablets has decayed or been lost,
either by physical decay of storage materials or loss of understanding because of changing language and cultural
nuances.
Examples emphasise how technological progress has speeded up information decay and loss. Since logarithmic "laws"
have been proposed to describe the trends for electronic improvements, one may consider if equivalent trends apply to
information loss. It appears that one may propose that the product of three factors is roughly constant. These are the time
needed to write the new information; the quantity of information stored, and the average survival time of the information
before the storage medium has decayed or is obsolete. The reality of such a "law" is that, whereas we may currently have
records and photographs from many earlier generations, our rapidly stored electronic data may be lost within a few years,
and certainly will have vanished in a readable form for the next generation.
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New methods of control of tooth bleaching stages through simultaneous measurements of a reflected light and a
fluorescence signal are proposed. It is shown that the bleaching process leads to significant changes in the intensity of a
scattered signal and also in the shape and intensity of the fluorescence spectra. Experimental data illustrate that the
bleaching process causes essential changes in the teeth discoloration in short time as 8-10 min from the beginning of the
application procedure. The continuation of the treatment is not necessary moreover the probability of the enamel destroy
increases considerably. The proposed optical back control of tooth surface is a base for development of a practical set up
to control the duration of the bleaching procedure.
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A considerable interest, in the recent years, has been allocated in the mid-infrared Er:YAG laser surgery and
microsurgery. This interest has been increased after the development of optical fibers and waveguides, for safe and
efficient transmission of the ~3.0 μm wavelength beams. On the other hand, a laser delivery system based on
common silica glass fibers and caps are not applicable for delivery of the Er:YAG laser light, due to high absorption
losses at the mid-infrared wavelengths. Thus, fluoride glass fibers and sealing quartz caps is a promising
combination for laser delivery due to their low transmission loss. In this study, we investigated the properties of
three sealing quartz caps, suitable for fluoride glass optical fibers, with various distal end geometries, in order to
evaluate the attenuation and the spatial and temporal energy distribution of the transmitted laser radiation. Moreover,
we evaluated the experimental beam divergence of the sealing caps. As a transmission medium, three fluoride glass
optical fibers were used. As a laser source we used a Q-switched Er:YAG laser with a pulse duration of 190 ns and a
repetition rate of 1 Hz. The mean value of the energy loss for dome geometry was found (0.73 ± 0.03), for planoconvex
geometry was found (0.76 ± 0.03) and for ball geometry was found (0.73 ± 0.05). The beam divergence was
found (62.4 ± 0.1) mrad, (156.2 ± 0.3) mrad and (37.5 ± 0.5) mrad for dome, ball and plano-convex geometry,
respectively.
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The propagation is investigated of a continuous laser beam through homogeneous tissue-like turbid media such as diluted
emulsions of Intralipid or milk having presumably sharply forward directed Henyey-Greenstein or Gaussian indicatrices.
The cross sectional radial distributions of the detected forward-propagating light power at different depths along the
beam axis in each medium of interest are experimentally determined. The detected-power spatial distribution, for both
the types of indicatrices, is also described analytically by a solution of the radiative transfer equation in the so-called
small-angle approximation. The experimental results are consistent with the analytical expressions obtained that are
shown to allow one to estimate the extinction ( αt), reduced-scattering (αrs) and absorption (αa) coefficients and the gfactor
of the investigated media. The values obtained of α quite reasonable and
behave, depending on the dilution turbidity, in a way observed formerly in other similar experiments. The comparative
analysis of the estimated characteristics of the dilutions shows that in the case of Henyey-Greenstein indicatrix we have a
smaller value of the g-factor and larger value of αrs with respect to the case of Gaussian indicatrix. At equal g-factors, in
the former case we shall have a narrower forward-propagating scattered-light beam with higher on-axis intensity as
compared with the latter case.
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This investigation is carried out on two groups of patients with corpus alienum corneae. In every group are
included 40 patients (40 eyes). For the first group standard treatment is applied after extraction of the corpus
alienum corneae using antibiotic drugs (Oftaquix®) and epithelizing gel (Corneregel). First group is used as a
control. For the second group of patients immediately after extraction of the corpus alienum corneae, eyes are
irradiated for 3 minutes with He-Ne laser (Mediray 04, Optella Ltd., Sofia, Bulgaria) at emission wavelength at
632 nm and power density 0.1 mW/cm2. Second group of eyes is treated with the same drugs as the control
group. We observed epithelisation of the damaged cornea in the first group - after 24 hours, and in the laser-irradiated
group of eyes significant epithelisation is pronounced the 10th hour after irradiation. Epithelization is
proved by fluorescein reaction to detect the eye cornea recovery. The patient eyes of the both groups were
investigated under bio-microscope in cobalt-blue illumination. For irradiated eyes by LLLT, we have found that
the healing period is shortened significantly by 42 % (p<0,001).
Our results revealed that LLLT application is appropriate and perspective for recovery therapy after corpus
alienum corneae extraction.
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Phthalocyanines of gallium(III) and indium(III) (GaPc1 and InPc1) bearing four methylpyridyloxy groups on the
periphery of the phthalocyanine ring were synthesized. The both phthalocyanines were obtained with a good solubility
in water solutions, which make them suitable for application in the Photodynamic therapy (PDT). The absorbance in
the Uv-vis region of the complexes is typical for MPc with a highly intensive maximum in the far red spectra (681 nm
- 697 nm for GaPc1 and for InPc1, both in DMSO). The fluorescence maxima are red shifted (691 nm/716 nm). The
fluorescence quantum yields of the both complexes are lower than that for the unsubstituted MPcs with values of 0.25
for GaPc1 and much lower for InPc1 (0.012), which suggested a quenching from the substituents. The photochemical
properties of singlet oxygen generation show quenching curves of "Furane" test with a 1O2 formation that increase
significantly in the presence of the heavy atoms such as Ga(III) and especially In(III). Photodynamic efficacy against
C. albicans in planktonic media was evaluated with a high photodynamic effect for GaPc1 at low concentrations (0.5
μM, - 3 μM) at mild irradiation parameters (30-60 J cm-2 and 50 mW cm-2). The inactivation of the fungus cells with
InPc1 was insignificant even at strong treatment conditions (6.8 μM; 60 J cm-2). The water-soluble phthalocyanine
complexes of Ga(III) and In (III) were compared to the recently studied by us water-soluble Zn(II)-phthalocyanine,
which was shown to have a high potential for photodynamic inactivation of variety pathogenic bacterial strains.
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We review the photo-driven directed charge, spin and acoustic phonon transport in dielectrics and semiconductors, in
bulk and hetero-structures, lacking spatial inversion symmetry. We express these photo-galvanic effects in terms of
photo-induced driving forces bilinear in the coherent light field amplitude mediated through the spatial asymmetry of the
medium. We discuss their interrelations with nonlinear optical analogues and also nonlinear optical time resolved
techniques for their study. These issues are of certain relevance in optoelectronics and photonics and in the emerging
fields of phononics and photo-spintronics as they introduce new unidirectional and nonreciprocal photonic
functionalities. They are manifestations of photo-driven ratchet and pawl processes.
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Mathematical similarities and parallels between two different physical objects, optical solitons and matter-wave solitons,
both described by similar mathematical models: the nonlinear Schrodinger equation (NLSE) and the Gross-Pitaevskii
equation (GPE) model, open the possibility to study both systems in parallel and because of the obvious complexity of
experiments with matter-wave solitons, offer outstanding possibilities in studies of BEC system by performing
experiments in the nonlinear optical system and vise versa. In this report we briefly overview recent theoretical studies of
the existence and stability of 3D solitons. With contributions from major groups who have pioneered research in this
field, the report describes the historical development of the subject, provides a background to the associated nonlinear
optical processes, the generation mechanisms of soliton bullets. The main features of nonautonomous matter-wave
solitons near the Feshbach resonance with continuously tuned scattering length are investigated. We focus on the most
physically important situations where the applied magnetic field is varying in time linearly and periodically. In nonlinear
optical applications, this kind of periodic graded-index nonlinear structure with alternating waveguiding and
antiwaveguiding segments can be used to simulate different and complicated processes in the total scenario of matterwave
soliton bullets generation.
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Experimental and numerical results on the interaction of the Raman-soliton continuum and dispersive waves through
inelastic collisions mediated by four wave mixing are presented. In particular the spectral broadening of the continuum to
longer wavelengths beyond a second zero dispersion point through four wave mixing of the dispersive wave produced by
soliton self-frequency shift cancelation and other solitons in the continuum is considered.
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Nonlinear photonic crystals are materials in which the second order susceptibility is modulated. These structures are
often used in nonlinear optics applications for compensating the phase mismatch between interacting waves. The
progress in techniques of modulating the nonlinearity enables to explore new applications, based on all-optical control
of the phase, amplitude and polarization of the nonlinearly generated waves. This enables the realization of functional
nonlinear optical devices, such as nonlinear lenses, switches, polarization rotators, deflectors and beam shapers. Here
we will discuss in detail two applications that are enabled by specially designed nonlinear photonic crystals: All optical
polarization switching, and the generation, nonlinear mixing and manipulation of accelerating Airy beams.
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Edge-pumping is very advantageous for pumping disk lasers because it provides a long absorption path for the pump
compared with end-pumped one. In the current work, we report an edge-pumped Yb:YAG disk laser pumped from four
sides with diode laser stacks. For delivering the pump light into the gain medium, asymmetric hollow ducts have been
employed. For any type of disk laser system, the key criterion is a uniform deposition of absorbed pump power and in
turn a uniform temperature distribution throughout the disk. We try to meet this restriction by designing an appropriate
asymmetric hollow duct. In order to obtain laser output power, a self-consistent numerical model has been developed for
simulating lasing properties of our configuration. A Monte Carlo ray tracing based code and two-dimensional finite
element analysis have been utilized to calculate the absorption power and temperature distribution inside the crystal,
respectively. The model is used to investigate the influence of the effective parameters on the operational efficiency of
the disk laser.
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In real thin disk laser systems, a fraction of absorbed pump power is dissipated as heat. Consequently, the thin disk lasers experience a temperature gradient in the axial direction of the disk which produces inhomogeneous stress and strain distributions. In this paper, we present the numerical calculation of Von Mises stress and the thermal lensing due to temperature gradient, stress gradient and deformation. Based on the results of our numerical study, it was proved that the most dominant parameters, which cause optical path difference and therefore thermal lensing, are temperature-dependent refractive index and deformation of the disk. Moreover, these are both directly related to absolute temperature values within the crystal.
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The thermally induced stress in pulsed pump solid state lasers with super-Gaussian profile has been investigated. An
analytical expression for the thermal stress is introduced. We consider the heat deposited in the crystal due to the pump.
The temperature distribution in the crystal has been calculated by solving the non-steady state heat conduction equation.
A Ti: Sapphire crystal is assumed pumped by a pulse laser. All the stress components have been obtained and discussed
in details. The results show that the non-homogenous temperature distribution is induced by the thermal stress in the
crystal.
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The effect of thermal lensing is a critical factor for resonator design and must be considered to improve the beam quality.
The absorption of the pump radiation by laser material and surface cooling leads to a nonuniform temperature
distribution in the rod. In this letter the temperature distribution in a cylindrical Nd:YAG rod under repetitive flash lamp
pulses is numerically simulated, when pumped by flash lamp with 150 μs pulse width and 10 Hz repetition rate . We
consider Gaussian pump pulse shape in time and redial absorption in laser rod. Our calculations show that the
temperature converges to a finite value and doses evolve in time noticeably. Also by computing the changes of refraction
index, we obtain the focal length of the heat dispersion.
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Propagation of short laser pulses governing by a vector type 3D+1 non-linear Schrödinger equation in Kerr-type medium
with anomalous dispersion and spatial dependence of the nonlinear refractive index is investigated. Finite energy
analytical soliton solutions in spherical coordinates are found. Conditions for experimental observation are discussed.
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In this paper, a careful analysis is provided of the nonlinear propagation of three-dimensional pulses with large spectral
bandwidth in isotropic media. After applying the small parameter method to nonlinear amplitude equation, approximate
analytical solutions up to first order are obtained.
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Optimization of the Petzval objective with various evolution strategies and the damped least squares is presented. All
algorithms are shortly described and their advantages and shortcomings are discussed. Application of evolution strategies
to the optimization of optical systems is outlined. Analysis of the Petzval objective optimizations is given.
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We study theoretically the non-phase-matched degenerate four-wave mixing of type ωs = 2ω1 ωω2 , involving beams
carrying two-dimensional spatial phase dislocations in the form of singly-charged optical vortices (OVs).
Accompanying third-order nonlinear processes in the non-resonant nonlinear medium (NLM), which are accounted
for, are self- and cross-phase modulation. In the case of pump OV beams with identical topological charges the
model predicts the generation of signal beams carrying OVs of the same charge. If the pump beams carry OVs with
opposite charges, the generated signals are predicted to carry triply charged vortices which, in the case of a nonnegligible
initial free-space propagation from the plane of vortex generation to the NLM, decay inside the NLM into
three singly-charged vortices with highly overlapping cores.
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Passive Q-switching of a diode pumped Nd:YVO4 laser with Cr+4:YAG saturable absorber was studied experimentally.
At 3Wof incident pump power, the laser pulses of duration 37 ns and energy 5.2 μJ with peak power of 140 W and
repetition rate of 100 kHz were obtained.
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Based on the generalized nonlinear Schrödinger equation model with sign-reversal varying-in-time harmonic oscillator
potential, we show that conditions of its exact integrability in one-dimensional case (1D) indicate conclusively the way
for solitonlike bullets generation in 3D nonautonomous nonlinear and dispersive systems. It turns out that generation of
matter-wave soliton bullets can be realized if periodic variations of nonlinearity and confining potential are opposite in
phases so that peaks of nonlinearity inside the atomic cloud coincide in time with repulsive character of trapping
potential. In nonlinear optical applications, periodic graded-index nonlinear structures with alternating wave-guiding and
anti-wave-guiding segments open remarkable opportunities in studies of BEC systems by performing experiments in
nonlinear optical systems.
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A detailed study of axicon-based Bessel-Gauss resonator for the thin disk laser has been carried out. A paraxial ray
analysis is performed to find the self-consistency condition to have stable periodic ray trajectory after one or two round
trips.
By using the Fox-Li method, it is possible to find the lowest mode shape and associated optical loss for an arbitrary
optical resonator. Nevertheless, the mentioned routine is very time-consuming and therefore, we make use of a technique
in order to convert the Huygens-Fresnel integral self-consistency equation into a matrix one and then find the
eigenvalues and the eigenfields of the resonator. Here, special attention is paid to investigate the dependence of the
transverse profile and the loss on the cavity length.
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We present two novel applications of optical properties of the interference wedge (compact realization of the Fizeau
Interferometer) for the case of illumination with a small diameter laser beam. The first one is a new and competitive
wavelength division multiplexing structure. The main advantages of the device are the possibility for separate frequency
tuning of each input-output channel as well as its compactness. The made computer simulation proves that the structure
can work with very short laser pulse duration (~ 0.1 ns), which corresponds to pulse repetition rate of order of ten GHz
and more, thus fulfilling the requirements of modern digital communication systems. The theoretical analysis and the
experimental check with laboratory model of a free-optical communication system show a sufficient resonant narrowline
transmission up to 75% with the linewidth of emission from 0.05 nm to few nm. The second proposal is a device
which allows for distant laser measurement of small linear translation of a rigid object for distances from a few meters
up to hundred meters.
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By the method of magnetron sputtering the nanocrystalline films LiNbO3 on the surfaces of (001)Si, (111)Si and of Si-
SiO2 heterostructure have been synthesized. The elemental and phase composition, structure and surface morphology, the
electrical-physical parameters of the heterostructures (001)Si-LiNbO3 and (111)Si-SiO2-LiNbO3 have been studied.
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In this work we study the influence of the additional second- and third-order dispersion introduced in a femtosecond
laser cavity by varying the beam's penetration into a prism of the double-pass intracavity prism compressor on the
output pulse duration, as well as on the emission spectral bandwidth and its central wavelength. The theoretically
calculated pulse durations are found to be in a good agreement with the respective experimental data from
frequency-resolved optical gating and interferometric autocorrelation measurements.
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The discovery of stimulated Raman self-scattering (SRSS) effect of femtosecond optical solitons is acknowledged
to be among the most notable achievements of nonlinear fiber optics. This effect is also often called intrapulse
stimulated Raman scattering (ISRS), or soliton self-frequency shift (SSFS), thereby emphasizing the unusual
regime of stimulated Raman scattering, when the spectrum of a high-power ultrashort laser pulse proves to be so
broad that it covers the band of Raman resonances of the medium. The soliton-like wave packets with continuously
shifted spectrum traveling not only in the ordinary space and time, but also in the spectral space, are known as
colored femtosecond solitons. Colored solitons play an important role in the soliton supercontinuum generation.
The most interesting features of colored optical solitons are connected with the possibility of their tunneling in the
spectral domain through a potential barrier-like spectral inhomogeneity of group velocity dispersion (GVD),
including the forbidden band of positive GVD. This effect is known as soliton spectral tunneling effect (SST).
In this Report, we consider the influence of the soliton binding energy on dynamics of the SST effect assuming that
the amplitude and duration of the tunneling soliton vary in time when the soliton spectrum approaches a forbidden
GVD barrier. We show that soliton self-compressing effect has dramatic impact on the SST through forbidden
spectral region of positive GVD.
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An active volume scaling in bore and length of He-SrBr2 laser excited in nanosecond pulsed longitudinal discharge is
carried out. The optimal temperature regime is found for laser oscillation at several different Sr atom and ion lines.
Optimal discharge conditions, such as active zone diameter, vapor pressure, buffer-gas pressure, electrical excitation
scheme parameters, average input power, pulse repetition frequency, are found. At multiline operation a record average
output power of 4.30 W for the Sr atom lasers is obtained, more than 90 % of which is concentrated on the 6.45-μm Sr
atom line. A new discharge tube with furtherly increased active volume in bore is developed. The effect of neon additive
to the helium buffer gas on the gas and electron temperatures is investigated.
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Recent studies have thrown doubt on the ideal treatment of soliton tunneling. The most important enigmas in this
field can be formulated in the following way: As to whether nonlinear soliton tunneling effect will resemble more
the point like classical particle case or the quantum mechanical behavior in which the particle itself has an internal
structure? How "hidden" degrees of freedom can show up in the process of soliton tunneling? What happens if the
amplitude and duration of the input soliton vary in time when the soliton approaches a classically forbidden
barrier? In particular, what happens in the case of the nonlinear tunneling of self-compressing soliton when its
binding energy is increased? As to whether this case will resemble more the classical particle case or the quantum
mechanical behavior? These questions are taken up in this Report.
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Linear regime of propagation of short optical laser pulses in isotropic dispersive medium with attenuation in the frame
3D+1 non-paraxial model is investigated. The corresponding amplitude equation is solved in ( kx, ky, kz, t ) space and
fundamental solution is found. In case of weak attenuation we found, that the loss term in the equation do not influence
the phase, and change considerably the real amplitude only.
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In this work we study the evolution of dark beams of finite length carrying edge-screw phase dislocations in selffocusing
Kerr nonlinear media aiming to find appropriate conditions to control the process of filamentation of the
background beam. In the case of a single fractional vortex dipole, geometry-controlled conditions for changing the
intensity ratio of the peaks and their offset are found. Depending on their orientation, two parallel or two in-line mixed
phase dislocations carried by a common background beam are predicted to perturb it and to initiate filamentation of
different number of peaks with different spatial distributions.
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