The backscattered light originated when machining with femtosecond laser pulses can be used to accurately measure the processed surface position through an interferometer, as recently demonstrated by our group, in a setup that uses the same laser beam for ablation and inspection. The present work explores the characteristics of the laser light reflected by the target and its interaction with the resulting plasma to better understand its propagation physics and to improve the dynamic focusing system. The origin of this returning radiation was studied and has been traced, mainly, from the peripheral area of the focal spot (doughnut-like). By means of a Mach-Zehnder setup, the interferometric pattern was measured and analyzed aiming to access the influences of the plasma on the laser beam properties, and therefore on the retrieved information. Finally, the wavefront of the laser that creates and propagates through the plasma was characterized using a Shack-Hartmann sensor.
Boron thin films were produced using femtosecond pulsed laser deposition aiming at the development of a neutron detector. As neutrons have no charge, in order to detect this particle converter materials are applied, promoting nuclear reactions that result in the emission of charged particles, allowing the neutrons presence to be indirectly inferred. Among the possible conversion materials, 10B has a considerable cross section for thermal neutrons and accessible cost. Furthermore, the nuclear reaction produces easily detectable alpha particles, making it a rational option to develop a low cost and portable neutron detector. The boron ablation threshold fluence has been measured by the Diagonal Scan (Dscan) technique that resulted in the minimum laser energy value of 17.7 (6) μJ and fluence of 5.63(19) J/cm2. Boron deposition was performed varying the pulse energy and deposition duration. The growth rate, morphological and physical aspects of the boron pulsed laser deposition were characterized by a Scanning Electron Microscope and an optical profilometer. The films surfaces have a flaky aspect with eventual droplets which had decayed overtime to a more smooth surface. The studied parameters allowed producing a boron coating with the optimal thickness in order to minimize self-absorption effect in the film, thus increasing efficiency.
Taking advantage of the inherent characteristics of femtosecond laser used for machining, we developed an interferometric system able to evaluate and correct the focal position with an accuracy of a few microns, implementing a technique based on low coherence interferometry. This approach measures at the exact spot that the laser is machining, in real time, and is sensitive to any sample that acts as a scatterer to the wavelength in use. The experimental evaluation was divided in two steps: in the first a system based on a superluminescent LED was mounted to check the viability and develop the controlling software; in the second part a setup was mounted employing a femtosecond laser, and several kinds of samples using the active focus control, among which the results obtained with glass sample and a bovine tooth are meticulously described in this paper. The system was able to improve the performance in both samples, keeping them in the confocal region for an extended positioning range, resulting in better engraving by the laser.
Metallic nanoparticles are important on several scientific, medical and industrial areas. The control of nanoparticles
characteristics has fundamental importance to increase the efficiency on the processes and applications in which they are
employed. The metallic nanoparticles present specific surface plasmon resonances (SPR). These resonances are related
with the collective oscillations of the electrons presents on the metallic nanoparticle. The SPR is determined by the
potential defined by the nanoparticle size and geometry.
There are several methods of producing gold nanoparticles, including the use of toxic chemical polymers. We already
reported the use of natural polymers, as for example, the agar-agar, to produce metallic nanoparticles under xenon lamp
irradiation. This technique is characterized as a “green” synthesis because the natural polymers are inoffensive to the
environment.
We report a technique to produce metallic nanoparticles and change its geometrical and dimensional characteristics using
a femtosecond laser. The 1 ml initial solution was irradiate using a laser beam with 380 mW, 1 kHz and 40 nm of bandwidth
centered at 800 nm.
The setup uses an Acousto-optic modulator, Dazzler, to change the pulses spectral profiles by introduction of several orders
of phase, resulting in different temporal energy distributions. The use of Dazzler has the objective of change the gold
nanoparticles average size by the changing of temporal energy distributions of the laser pulses incident in the sample. After
the laser irradiation, the gold nanoparticles average diameter were less than 15 nm.
The use of gold nanoparticles (AuNps) as the vehicle for 5-Aminolevulinic acid (ALA) delivery for photodynamic and photothermic plasmonic therapies is a promising approach, especially with the recent demonstration that this photosensitizer immobilization on the particle surface improves reactive oxygen species (ROS) formation, increasing its cytotoxicity. Gold nanorods (AuNRs) present an absorption spectrum shifted to 700 nm, within the tissue transparency window, which allows excitation of the nanoparticles situated deeper in the tissues. Here, we describe a new synthesis method that was applied to control the shape of the gold nanoparticles during its synthesis. To obtain ALA:AuNRs, precursor ALA:AuNps were irradiated by ultrashort laser pulses. The variation of the laser parameters such as pulse energy and duration and irradiation time was assessed. The relevant mechanisms are discussed.
We report the use of the Diagonal Scan (D-Scan) technique to determine the ablation threshold of the AISI 1045 steel, a common engineering material that can be used as a probe for thermal effects, for superpositions ranging from single shot up to more than 10,000 pulses, for three pulses durations (25, 87 and 124 fs). It only took two hours of laboratory time to determine more than 20 ablation thresholds per pulse duration spanning 4 orders of magnitude of superpositions. The large amount of data generated shows a small deviation of the ablation threshold from the expected behavior, which can lead to the use of a model that better describes the dynamics of the ultrashort pulses ablation mechanism in metals.
The diagnosis of dental caries at an early stage enables the implementation of conservative treatments based
on dental preservation. Several diagnostic methods have been developed, like visual-tactile and radiographic
are the most commons but are limited for this application. The Optical Coherence Tomography is a technique
that provides information of optical properties of enamel, which may change due to the decay process. The
objective of this study was to evaluate the ability of OCT to detect different stages of demineralization of tooth
enamel during the development of artificial caries lesions, taking as a reference standard for comparison
sectional microhardness testing. Different stages of caries lesions were simulated using the pH cycling model
suggested Feathestone and modified by Argenta. The samples were exposed to 0 (control group), 5, 10, 15,
20 and 25 days at a daily regimen of three hours demineralization followed by remineralization during 20
hours. It was used an OCT system with at 930nm. Sectional images were generated in all lesion region. The
results obtained from the OCT technique presented similar behavior to microhardness, except for the group
25 days, due to inability to perform indentations reading in areas of more intense demineralization. A linear
relationship was observed between the OCT and microhardness techniques for detection of demineralization
in enamel. This relationship will allow the use of OCT technique in quantitative assessment of mineral loss
and for the evaluation of incipient caries lesions.
The objective of this work was to develop a LIDAR-like equation model to analyze the measured Optical
coherence tomography (OCT) signal and determine the total extinction coefficient of a scattering sample.
OCT is an interferometric technique that explore sample backscattering feature to acquire in depth cross-section
images using a low coherence light source. Although, almost of the OCT applications are intended
to generate images for diagnostic, similar to histological images, but the backscattering signal carries much
more information. The backscattering problem is similar to those found on LIDAR (Light Detection And
Ranging) problem, this similar situation indicate a path that should be followed to solve the OCT problem.
To determine the total extinction coefficient three inversion methods was used: the slope, boundary point
and optical depth methods solutions. These algorithms were used to analyze the OCT signal of a single and
double layer dentist resin polymer. The total extinction coefficient variations along the optical path were
obtained in order to evaluate the potential of this technique to differentiate structures with different optical
properties. The sample optical characteristics extracted from OCT signal can be use as an additional
quantitative method to help clinical diagnoses when applied on biological tissues among others.
The present work developed a Polarization Sensitive Optical Coherence Tomography system capable of perform
birrefringence images and also determine completely the Mueller Matrix of a sample, in depth. In this way many
measurements were needed to be done, with different combinations of polarization states of the incident beam on the
sample and the reference arm of the interferometer. After calibrating the system, a roll of adhesive tape was used as
sample for two main reasons: presents birrefringent and has a periodic structure. Firstly the system was set to gather
data about the horizontal polarization state and then vertical polarization state of light to construct a birrefringence
image. The birrefringence (δn) of ordinary adhesive tape was evaluated as 4.03(26)x10-4. Latter a system capable of
measure any polarization state was implemented and 16 scattering profiles for different polarizations were collected.
Software also was developed to solve a linear equations system. As a result a 4x4 matrix of images were calculated.
Some of the features, as birefringence were easily indentified in some elements of this matrix, others, more subtle,
can be founded in the literature. We also decomposed the matrix as linear combinations of other known optical
elements.
In this work we described the potentiality of the Hypocrellin B (HB) modified with the presence of lanthanum (La3+)
ions, in eliminate Candida albicans in suspension. The results showed that the presence of lanthanum ions promotes a
red shift of the HB absorption band and an enhancement in singlet oxygen quantum yield in 32%. Also in this work we
obtained that the best molar ration between HB and La concentrations was 1:2. No photobleaching was observed in our
experimental conditions. Antimicrobial activity was studied exciting C. albicans suspension with a 460 nm LED and a
660 nm laser both with 330 mW/cm2 irradiance. Best irradiation time, PS concentration and ROS production profile
were determined showing that using 460 nm LED with 10 μM of PS, only 30 s of irradiation time was sufficient to
reduce 100 % C. albicans colonies.
This work presents a compositional characterization of 1939's Thousand "Réis" and 1945's One "Cruzeiro" Brazilian
coins, forged on aluminum bronze alloy.
The coins were irradiated by a Q-switched Nd:YAG laser with 4 ns pulse width and energy of 25mJ emitting at 1064nm
reaching 3.1010Wcm-2 (assured condition for stoichiometric ablation), forming a plasma in a small fraction of the coin. Plasma emission was collected by an optical fiber system connected to an Echelle spectrometer. The capability of LIBS
to remove small fraction of material was exploited and the coins were analyzed ablating layer by layer from patina to the
bulk.
The experimental conditions to assure reproductivity were determined by evaluation of three plasma paramethers:
ionization temperature using Saha-Boltzmann plot, excitation temperature using Boltzmann plot, plasma density using
Saha-Boltzmann plot and Stark broadening.
The Calibration-Free LIBS technique was applied to both coins and the analytical determination of elemental
composition was employed. In order to confirm the Edict Law elemental composition the results were corroborated by
Neutron Activation Analysis (NAA). In both cases the results determined by CF-LIBS agreed to with the Edict Law and
NAA determination. Besides the major components for the bronze alloy some other impurities were observed.
Finally, in order to determine the coin damage made by the laser, the OCT (Optical Coherence Tomography) technique
was used. After tree pulses of laser 54μg of coin material were removed reaching 120μm in depth.
Measure roughness in some sort of samples can present several problems when it is done in traditional way (with
physical contact). For instance, soft samples will present at least two kinds of problem: (a) the value presented by the
equipment not represents the sample roughness; (b) the equipment can perform serious damages to the sample. Using a
commercial type OCT (Thorlabs Inc.) with 6μm axial resolution (in air) and 6μm lateral resolution, measurements of
roughness standards with Ra nominal values of 0.8, 1.6, 3.2, 6.3, 12.5, 25.0 and 50.0 μm. A homemade software analysis
the OCT images, and automatically calculates the Ra and Rz values. This procedure was performed to validate this
methodology comparing the OCT and roughness standards values.
In this work we use the optical coherence tomography (OCT) technique to produce in vitro transversal section
images of human hair. It was possible to identify in the A-scan protocol its principal structures: cuticle, cortex and
medulla. The mean diameter of medulla was 29 ± 7 μm and hair diameter was 122 ± 16 μm in our samples of standard
Afro-ethnic hair. We also compared the OCT signal before and after chemical treatment with 18% w/w ammonium thioglycolate solution. After chemical treatment, it was not possible to identify the main structures of hair fiber, due the index matching promoted by deleterious action of chemical agent. A tridimensional image was built starting from 601 cross-sectional images (slices). Each slice was taken in steps of 6.0 μm at 8 frames per second, and the whole 3D image was built in 60 seconds.
A backscattering Lidar system has gone through an automation process for operation through a high-speed
internet gateway in a fiber-optic network interconnecting research groups for experimental demonstrations of
specific technologies or novel Internet applications. This network is essentially a large, geographically distributed
laboratory facility, available worldwide to the research community, for field trials of optical components and
equipment, for fundamental and applied research in optical transmission and networking technologies, and for
the development of advanced Internet applications. The description of the steps taken to automate this system
will be given in detail. The laser source, a meteorological mini-station, a sliding rooftop door, and a trasient
recorder for acquisition were adapted for LABVIEW controlling and to be put into a web station for control
through the internet and enhancing its operational capabilities. This upgrade in the system was lowcost and can
provide multiple applications such as long-term operation during field campaigns and/or as an educational tool
to the lidar technique and atmospheric studies.
We report here the development and construction of a two-flashlamp pumping cavity for a Cr:LiSAF rod, to be operated
as a multipass amplifier in a Chirped Pulse Amplifier system. The pumping cavity was designed to minimize the
thermal load on the gain medium by the utilization of intracavity filters, aiming operation with high gain and the highest
possible repetition rate. Operating as a laser, 30 Hz repetition rate and 20 W average power were obtained for the first
time at a maximum gain per pass of 1.5. Changing the pumping characteristics, the laser provided 16 W at 8 Hz
repetition rate, at a maximum gain of 3.6. A four-pass multipass amplifier geometry was designed for the pumping
cavity, that was integrated and synchronized to a Ti:Sapphire Chirped Pulse Amplifier system. The amplification
properties of the gain medium were determined, in one, two and four passes, along with the gain dependence on the
repetition rate. The amplifier final configuration provided amplification by a factor 150 to 20 ps stretched pulses,
resulting in final compressed pulses with 60 fs and 0.5 TW of peak power at 5 Hz repetition rate.
Fluorescence technique appears very important for the diagnosis of cancer. Fluorescence detection has
advantages over other light-based investigation methods: high sensitivity, high speed, and safety.
Renal cell carcinoma (RCC) accounts for approximately 3% of new cancer incidence and mortality in the United States.
Unfortunately many RCC masses remain asymptomatic and nonpalpable until they are advanced. Diagnosis and
localization of early carcinoma play an important role in the prevention and curative treatment of RCC. Certain drugs or
chemicals such as porphyrin derivatives accumulate substantially more in tumors than normal tissues.
The autofluorescence of blood porphyrin of healthy and tumor induced male SCID mice was analyzed using
fluorescence and excitation spectroscopy. A significant contrast between normal and tumor blood could be established.
Blood porphyrin fluorophore showed enhanced fluorescence band (around 630 nm) in function of the tumor growth. This
indicates that either the autofluorescence intensity of the blood fluorescence may provide a good parameter for the "first
approximation" characterization of the tumor stage.
The usual method to determine the ablation threshold of solid samples by ultrashort laser pulses is done by focusing the
laser beam on the samples surface by a known lens, requires the knowledge of all the geometrical parameters (lens focus,
beam propagation parameters, beam quality, sample position), and a series of measurements for different pulse energies.
We present here a simpler method for determining ultrashort laser pulses ablation threshold for solid samples. The
method uses a focusing lens, and requires only the knowledge of the pulse power, employing a diagonal translation of
the sample through the laser beam waist, resulting in a pattern etched on the sample surface. The ablation threshold value
is obtained measuring only one dimension of this pattern and a straightforward mathematical relation, There is no need
to know any other geometrical parameter of the laser beam or of the lens used. The technique was employed to
determine the ablation threshold of pure and Cr doped LiSAF samples for 20 picoseconds pulses, and a dependence with
the Cr concentration was observed.
Development of cholesterol biosensors is of great importance in clinical analysis because the concentration of
cholesterol in blood is a fundamental parameter for the prevention and diagnosis of a number of clinical disorders such
as heart disease, hypertension and arteriosclerosis. In general, determination of cholesterol is based on
spectrophotometry; but this method involves complicated procedures and the cost is high because expensive enzyme
must be used in each assay.
We report here the observation, for the first time, of the enhancement of Europium-Tetracycline complex
emission in cholesterol solutions. This enhancement was initially observed with the addition of the enzyme cholesterol
oxidase, which produces H2O2, the agent driver of the Europium tetracycline complex, to the solution. However, it was
found that the enzyme is not needed to enhance the luminescence. A calibration curve was determined, resulting in an
easy-handling immobilization method with a cheap stable material. This method shows that the complex can be used as a
sensor to determine cholesterol in biological systems with good selectivity, fast response, miniature size, and
reproducible results.
In this paper we present the spectroscopic properties of YLF:Yb:Tm:Nd system identifying the most important processes that lead to the thulium blue up conversion emission, under excitation around 792 nm. Analysis of the 475 nm emission for the samples with different concentrations of Nd3+ ions showed that energy transfer between Nd3+ and Yb3+ is the main mechanism and responsible for an enhancement in up conversion.
We report here the development, construction and characterization of a flashlamp pumped Cr:LiSAF rod pumping cavity designed to minimize the thermal load on the crystal. The cavity is a close coupled one with 2 Xe lamps and absorptive filters between the lamps and the Cr:LiSAF rod, and is refrigerated with cooled water. A compact and stable (g1×g2=0.57) resonator was designed for lasers tests and gain medium characterization, and we expected to obtain operation at 20 Hz repetition rate. Nevertheless, the thermal load minimizing design was so successful that allowed laser operation up to 30 Hz with an average power of 20 W. When operating with a 10% transmission output coupler this laser exhibited an overall laser efficiency of 0.6% under 100 J electrical pumping, and a slope efficiency of 0.8%. Under these conditions, a maximum gain per pass of 1.5 was obtained, suitable for regenerative amplifiers. To increase the gain, the intracavity filters were substituted by glass plates, resulting in a gain per pass of 3.6, adequate for multipass amplifiers. In this configuration, and operating as a laser resonator, it showed a maximum overall efficiency of 2.81% under 88 J electrical pumping with a 25% transmission output coupler, and maximum output power of 18 W at 8 Hz. A study of the thermal load on the crystal was conducted by observation of the upper laser level lifetime, and we concluded that there are no noticeable accumulated thermal effects on the Cr:LiSAF emission.
Optical Coherence Tomography was used to monitor subsurface caries evolution process in vitro. Human tooth was used and bacteria were employed to induce caries lesions. Twenty-five human third molars, were used in this study. The teeth were cut longitudinally at mesio-distal direction; the surfaces were coated with nail varnish except for two squared windows (2x4 mm); at the cement-enamel junction. Artificial lesions were induced by a S. Mutans microbiological culture. The samples (N = 50) were divided into groups according to the demineralization time: 3, 5, 7, 9 and 11 days. The culture medium, was changed each 48 hours. After the demineralization process the samples were rinsed with double-deionized water and stored in a humid environment. The OCT system was implemented with average power of 96 μW in the sample arm, providing a 23 μm of axial resolution. The images were produced with lateral scans step of 10 μm. The detection system was composed by a detector, a demodulator and a computer. With the images generated by OCT it was possible to determine the lesion depth as function of sample exposition time to microbiological culture. We observed that the depth of the lesion in the root dentine increased from 70 μm to 230 μm, depending of exposure time, and follows the bacterial population growth law. This OCT system accurately depicts hard dental tissue and it was able to detect early caries in its structure, providing a powerful contactless high resolution image of lesions.
The tetracycline-europium (Tc-Eu) complex is known to show emission at 615 nm. On addition of hydrogen peroxide (HP), a strongly fluorescent complex is formed. In this paper it is reported that the europium fluorescence intensity is increased when urea hydrogen peroxide is added to the tetracycline-europium aqueous solution. It was conceived that this enhancement could be used to determine urea hydrogen peroxide (UHP) levels. This method is simple, practical, and relatively free of interference from coexisting substances, and it can be applied successfully to assess urea peroxide in biological samples, for example, on human whole blood. The values obtained for whole blood agree with the urea concentration variation verified in 50 patients, including 25 pre-dialysis, 15 dialysis subjects and 10 controls. This method is non invasive and can help in the identification of renal and cardiac diseases.
Evaluation of molar dental restorations on enamel is performed using optical coherence tomography (OCT) with 10 µm resolution. Images of ~50 µm failure gaps in the restorations are demonstrated and the OCT images are compared with x-ray and optical microscopy pictures. The results demonstrate the potential of the technique for clinical evaluation of dental restorations.
Compared with the traditional organic fluorescent materials, the lanthanide coordination compounds have a large variety of applications, for example glucose sensing, based on the luminescence enhancement of a lanthanide-tetracycline complex due to enzymatically generated H2O2 at physiological glucose concentrations. It is known that the fluorescence is based on the energy-transfer from the ligand to the central lanthanide ion. The aim of this work was to study the optical properties of Europium, Erbium, Ytterbium, Holmium, Terbium and Neodymium tetracycline complexes. An increase in europium emission band was observed for the first time, with addition of urea peroxide in the solution. This method works at neutral pH and the luminescence was detected at visible lanthanides luminescence after a 10 min. incubation time of the samples.
In this work we report the creation of color centers in LiF and YLF crystals by high intensity, ultrashort laser pulses. We used pure and Tm3+ and Oxygen doped samples, all irradiated with a Ti:Sapphire CPA laser system and also with electron beam, at room temperature. In both kinds of irradiations the production of photochromic damages and color centers that have absorption bands in UV and visible range was observed. A comparison between the two kinds of irradiation was done and the involved processes are described in this paper. F2+ stable centers were produced by the ultrashort laser pulses irradiation in contrast to the well-known, short lived centers produced by electron beams, and a mechanism was proposed to explain the observed stability.
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