Using frugal innovation to focus only on the mandatory features given by a particular application, we have developed a femtosecond laser that provides 900 fs, 12 µJ pulses at 1030 nm at the end of a 3 m long perfectly single-mode glass fiber. This system is battery powered and the output beam is easily movable in any direction and position within a 6 m diameter sphere. Our system relies on an innovative monolithic compressor including a CVBG. The compressor is 20 x 20 mm and weight a few grams. We will present the design and performances of the monolithic pulse compressor as well as the source attached to it. This device is presently used in a handheld laser instrument developed and sold by Ilasis Laser for cataract surgery.
In this paper, we investigate the potential of various large mode area fibers under thermal load, that is the state-of-the-art air-silica large pitch fibers, as well as the recently devised symmetry-reduced photonic crystal fiber and aperiodic all-solid by carefully considering the degrees of freedom offered all along the fiber fabrication. This work aims to discuss the mode filtering ability of these structures in regard to the power scaling and to confirm their potential for robust singlemode operation at high power level. Structural principles contributing to improve their performances such as the impact of air holes / solid inclusions size will be presented. We also intend to establish that the range of average absorbed/output power for which a robust singlemode operation is available can be shifted to fulfill user requests in term of power range.
Large mode area double-cladding Photonic Crystal Fibers (PCFs) with reduced cladding symmetry can provide effective suppression of high-order modes even under a significant heat load. In this work the single mode properties of different PCFs with reduced cladding symmetry are numerically compared by means of a full-vector modal solver based on the finite-element method, capable of taking into account the effects of the fiber heating. The maximum coupled pump power allowing single-mode propagation has been evaluated for each design, providing useful guidelines for further development of this kind of fibers.
We report in this communication on the investigation of novel triple-clad Very-Large-Mode-Area (VLMA) largepitch- fibers demonstrating numerically a strengthening of the fiber singlemodeness. The practical feasibility of the proposed fiber designs is ensured by taking into account the specifications of the resorted manufacturing technique. After a brief discussion about the mechanism of modal filtering into state-of-the-art air-silica leaky structures, we will present a novel kind of VLMA fibers. Here, the standard 6-fold symmetry as well as the periodic photonic crystal cladding are removed in profit to a totally aperiodic inner cladding microstructuration. This aperiodicity enables to exacerbate the singlemode robustness by maximizing the high-order-modes (HOMs) leakage out of the gain region in favour of the Gaussian fundamental mode. The behaviour of two different aperiodic LPFs is reported in regard to the refractive index of the inclusions, the doped core diameter and the operating wavelength. Thus, the scalability of these novel structures is evidenced. Finally, the manufacturability challenge is estimated by taking into account small index-mismatch between the active core and the background material.
A gain switched pulsed laser based on ytterbium doped rod PCF type fiber is presented. The high performance pump
system was based on 976 nm laser diodes incorporating high speed and high current laser diode drivers with active
feedback loop based control that enable high pulse to pulse stability. Furthermore the temperature control ensure the
adequate output spectrum of the pump laser diodes in order to match maximum of the absorption peak of Yb doped
active medium. The pulses duration in range between 48 ns to 75 ns were achieved with peak powers up to 3.6 kW.
Further, the change of the laser output spectrum in regard to the pump pulse power is observed.
We propose an in-depth investigation of all-solid microstructured optical fibers for the development of very large mode area (VLMA) fiber lasers. The inner cladding microstructure of these VLMA fibers is carefully optimized in order to get a robust single-mode laser operation in the high power regime. We describe the numerical approach used to devise a novel kind of fiber structures, the core of which should be larger than 50 μm while showing an improved single-mode emission compared to that of the state-of-the-art large pitch fibers. With the aim of overpassing the limitations of chemical vapor deposition techniques, we opted for a manufacturing process called Repusil, based on the sintering and vitrification of doped powders. Then, our opto-geometrical considerations result from the optical properties offered by this method and the use of the stack and draw. Finally, we present our very first fabrication for the proposed all-solid microstructured fibers in which a laser emission of 52 W in a continuous wave regime was obtained.
We demonstrate the amplification of a 1064nm pulse-programmable fiber laser with Large Pitch Rod-Type Fibers of various Mode field diameters from 50 to 70 μm. We have developed a high power fiber amplifier at 1064nm delivering up to 100W/1mJ at 15ns pulses and 30W/300μJ at 2ns with linearly polarized and diffraction limited output beam (M²<1.2). The specific seeder from ESI – Pyrophotonics Lasers used in the experiment allowed us to obtain tailored-pulse programmable on demand at the output from 2ns to 600ns for various repetition rates from 10 to 500 kHz. We could demonstrate square pulses or any other shapes (also multi-pulses) whatever the repetition rate or the pulse duration. We also performed frequency conversion with LBO crystals leading to 50W at 532nm and 25W at 355nm with a diffraction limited output. Similar experiments performed at 1032nm are also reported.
Many industrial applications such as glass cutting, ceramic micro-machining or photovoltaic processes require high average and high peak power Picosecond pulses. The main limitation for the expansion of the picosecond market is the cost of high power picosecond laser sources, which is due to the complexity of the architecture used for picosecond pulse amplification, and the difficulty to keep an excellent beam quality at high average power. Amplification with fibers is a good technology to achieve high power in picosecond regime but, because of its tight confinement over long distances, light undergoes dramatic non linearities while propagating in fibers. One way to avoid strong non linearities is to increase fiber’s mode area. Nineteen missing holes fibers offering core diameter larger than 80μm have been used over the past few years [1-3] but it has been shown that mode instabilities occur at approximately 100W average output power in these fibers [4]. Recently a new fiber design has been introduced, in which HOMs are delocalized from the core to the clad, preventing from HOMs amplification [5]. In these so-called Large Pitch Fibers, threshold for mode instabilities is increased to 294W offering robust single-mode operation below this power level [6]. We have demonstrated a high power-high efficiency industrial picosecond source using single-mode Large Pitch rod-type fibers doped with Ytterbium. Large Pitch Rod type fibers can offer a unique combination of single-mode output with a very large mode area from 40 μm up to 100μm and very high gain. This enables to directly amplify a low power-low energy Mode Locked Fiber laser with a simple amplification architecture, achieving very high power together with singlemode output independent of power level or repetition rate.
We present here some of the last results of the EUROPEAN project ALPINE. We present both the development of an
adjustable fibre laser pulse source and scribing results on CdTe and CIGS solar cells. The scribing tests were performed
at three different pulse durations: 400 fs, 8 ps and 250 ps. The results obtained with 250 ps are already very promising
for P3 steps in both CdTe and CIGS solar cells. In both cases the results were validated electrically.
In the case of P3 scribing for CIGS solar cells, shunt resistances as high as 125 kΩ.cm were obtained. Isolation
resistances were higher than 1 MΩ.cm. The processing speed was 2 m/s.
We developed a high power picosecond laser system at 80 MHz for third harmonic generation. We obtained 291 W at
1030 nm under 580 W of pump power at 976 nm from an all fiber master oscillator power amplifier based on rod-type
fibers. By frequency tripling, we obtained 63 W at 343 nm with excellent beam quality (M2<1.2).
We present the realization of an actively mode-locked laser based on a 30 μm core diameter single-mode double clad
photonic crystal fiber. For 19 W of pump power at 976 nm, it yields an average power of 10 W at 40 MHz. The delivered
pulses, centered at 1030 nm, have a duration of 15 ps. This corresponds to an energy of 250 nJ per pulse and a peak
power of 17 kW.
We have developed several high power picosecond sources using rod-type fiber systems. We will show that a
very simple architecture can produce average power over 90 W @ 1030 nm, 57 W @ 515 nm and 20 W @ 343
nm, with pulse repetition rates ranging from 200 kHz to 80 MHz. Particular emphasis will be given on the
control of non-linear effects in the fiber without relying on CPA.
We report on the demonstration of over 140W at 1030 nm with pulse duration down to 10 ns and M2<1.3 from a very
simple Q-switched architecture based on rod type fiber laser. These very high peak and average power lead to over 53W
at 515 nm and 19W at 343 nm. We have also obtained diffraction limited beams with an output power exceeding 240W
at 1030 nm and 120W at 515 nm in a very simple MOPA configuration. Due to the very high gain in these fibers, we can
keep pulse durations below 20 ns up to 500 kHz in a purely Q-switched system.
We derive an expression describing pre-compensation of pulse-distortion due to saturation effects in short pulse laseramplifiers.
The analytical solution determines the optimum input pulse required to obtain any arbitrary target pulse at the output of the saturated laser-amplifier. The relation is experimentally verified using an all-fiber amplifier chain that is seeded by a directly modulated laser-diode.
In this contribution, we report on an 80-μm core diameter Yb-doped rod type photonic crystal fiber laser emitting up to 94W in CW regime when operating at 977nm, which is to our knowledge the highest output power ever achieved from a single-mode solid-state laser operating at this wavelength. Key parameters of ytterbium doped 3-level laser, such as transparency pump intensity, pump absorption saturation, and gain competition between three and four level laser operation are then discussed in the particular context of high power fiber laser operating at 977nm. Possible applications of the demonstrated source are then discussed.
High peak power femtosecond oscillators exhibit great potential for many applications such as micro- and nanomachining and structuring, waveguide writing in glass, nonlinear frequency conversion or seeding of ultrafast fiber and bulk amplifiers. Ultrashort pulse durations below 50 fs are routinely produced by Ti:sapphire lasers. However, due to the need for a green pump laser, Ti:Sapphire lasers suffer from a greater complexity. Diode-pumped Ytterbium femtosecond lasers on the other hand are compact and reliable lasers, but, because of the limited amplification bandwidth, typically exhibit pulse duration greater than 60 fs. We present a directly diode-pumped 40-fs laser source with pulse energies higher than 120 nJ, more than 2 MW peak power, and a pulse repetition rate of 9 MHz. The laser setup is compact and fits in a 60 x 40 cm footprint. The laser source consists of a passively mode-locked femtosecond oscillator and fiber-based post-compression module. The oscillator operates at 9 MHz pulse repetition rate and produces pulse energies up to 300 nJ at 370 fs pulse duration. The oscillator is then focused into a standard single mode fiber in order to broaden the pulse spectrum to about 60 nm bandwidth. Owing to the high initial pulse energy the used fiber is
as short as 15 mm. After collimation it was sufficient to reflect the beam 8 times on 2 parallel chirped mirrors having 250 fs2 each. The overall transmission of this pulse compression module was about 80% resulting in 120 nJ transmitted pulse energy in 40-fs pulses.
We report on the latest development within active photonic crystal fibers for high power lasers and amplifiers with special focus on how the fibers can be improved with both polarization-maintaining and polarizing properties. We describe rod-type fibers for which a record-high power extraction of 250W/m is achieved. Moreover, we describe how active characterization is used to optimize fibers for laser and amplifier sub-assemblies with respect to beam quality, efficiency and robustness. Finally, we illustrate how the fibers can be integrated with high NA tapers and passive air-clad fibers containing Bragg grating to form an all-fiber, alignment-free, high-power fiber laser subassembly.
The fiber based generation of nearly transform-limited 10-ps pulses with 200 kW peak power (97 W average power) based on SPM-induced spectral compression is reported. Efficient second harmonic generation applying this source is also discussed.
We have applied a new, 1030 nm wavelength, infrared diode-pumped femtosecond laser source to multiphoton
microscopy, and present comparative results on the efficiency of fluorescence generation versus wavelength for several
fluorophores. It is shown that an emission wavelength of 1030 nm is optimal both for GFP and DsRed excitation.
We present the characterization of an ultrafast x-ray streak camera based on a new bilamellar x-ray tube. This camera, named FX1, has been tested in static (imaging) and dynamic (sweep) mode with several continuous and pulsed sub-picosecond UV and X-ray sources. The FX1 camera was designed to overcome some limitations observed with the PX1 camera which has been used previously at INRS to achieve high resolution sub-picosecond time resolved spectroscopy of ultrafast laser produced plasmas. Line Spread Function measurements indicated a strong improvement of the static image contribution to the temporal resolution compared to the PX1 camera performances [Rev. Sci. Instr. 71, 3627, 2000]. Furthermore a much higher dc extraction field can now be sustained at the photocathode-acceleration slit region. The FX1 camera has been successfully operated in various experimental conditions. An upper limit of the temporal response of the FX1 has been measured in the keV x-ray range in single shot mode with a laser-based x-ray source (2keV) having a duration (FWHM) of 1.4 ps. The FX1 camera has also been coupled to photoconductive switches and testesd in accumulation mode [Rev. Sci. Instr. 73, 1617, 2002] with VUV light produced with the 1 kHz Ti:sapphire laser of the CELIA. A newly assembled test-bench is now currently used at INRS for the characterisation of streak cameras in both single-shot and accumulation mode with the 10Hz Ti:sapphire laser of INRS.
We report on a novel laser source, emitting high energy (20 nanoJoule) femtosecond pulses, in a broad spectrum (250 nanometers). This source is easily tuned from 950 to 1200 nanometers, without any laser adjustment, and delivers sub-300 femtosecond pulses with a 10 nanometers spectral width.
We report on a novel laser source, emitting high energy (20 nanoJoule) femtosecond pulses, in a broad spectrum (250 nanometers). This source is easily tuned from 950 to 1200 nanometers, without any laser adjustment, and delivers sub-300 femtosecond pulses with a 10 nanometers spectral width.
Within the research project FEMTO, supported by the European Commission, a compact diode-pumped titanium:sapphire laser has been developed which matches the requirements of industrial systems, like compact dimensions and stable laser operation. To achieve this, the laser has been specially designed to be integrated directly into the machining system. For best process speed combined with optimal cutting quality, focus has been laid upon high repetition rates at moderate pulse energies. Typical average output powers are around 1.5W and repetition rates of up to 5 kHz. Accompanying to the laser development, a micro-machining system has been designed to meet the requirements of femtosecond laser micro-machining. In parallel to the machine development, machining processes have been investigated and optimized for different applications. The machining of delicate medical implants has been demonstrated as well as the machining system for general micro-machining of sensitive and delicate materials has been proven. Therefore, the developed machine offers the potential to boost the use of femtosecond lasers in industrial operation.
Tatiana Pikuz, Anatoly Faenov, A. Magunov, Igor Skobelev, F. Blasco, C. Stenz, Francois Salin, P. Monot, T. Auguste, Sandrine Dobosz, P. D' Oliveira, S. Hulin, Michel Bougeard
Results of fs laser-produced plasma diagnostics, which were provided using Focusing Spectrometer with Spatial Resolution having as an x-ray detector Princeton x-ray CD or Hamamatsu x-ray MCP, are presented. A portable, high-luminosity spherically bent crystal spectrometers were designed for the purposes of measuring very low emissivity x-ray spectra of different targets, heated by fs laser radiation, with simultaneously high spectral and space resolution. Large open aperture mica spherically bent crystals are used as dispersive elements of spectrometers. High tunability allowed to receive high-resolved spectra of clusters, heated by 35 fs Ti:Sa laser pulses with energy only 15 mJ in spectral ranges: 15-17 angstrom - for H- and He-like ions of Oxygen, 5-5.7 angstrom for Ne-like ions spectra of Kr, 3.0- 3.4 and 3.7-4.4 angstrom for H- and He-like spectra of Ar without any realignment of x-ray CCD spectrometer using one set up. Using another alignment ste up of spectrometer with x-ray MCP has been received spectra of solid targets, heated by 60 fs Ti:Sa laser pulses in spectral ranges: 15.2-17.5 angstrom near resonance lines of He-like ion of fluorine, 7.6-8.75 angstrom for spectra between He(alpha ) and K(alpha ) lines of Al and near Rydberg lines of Ne-like Cu, 3.04 - 3.5 angstrom for spectra around K(alpha ) lines of Ca, 1.38-1.59 angstrom for spectra around K(alpha ) lines of Cu. Some results of plasma diagnostics for both cases of clusters and solid targets, heated by fs laser radiation are presented and discussed.
Review of systematic investigations of x-ray radiation properties of different clusters heated by short-pulse high- intensive TI:Sa laser radiation is presented. The cluster targets were formed by the adiabatic expansion in vacuum of an Ar or CO2 gas puff produced by a pulsed valve with a Laval or conical nozzles. The gas jet pressure is varied form 15 up to 100 bar. Detailed theoretical modeling of cluster parameters have been done and compared with experimental measurements. High spectrally and spatially resolved x-ray spectra near resonance lines of H- and He- like ions of oxygen and Ar have been obtained and detailed spectroscopic analysis was consistent with a theoretical two-temperature collisional-radiative model of irradiated atomic clusters incorporating with an effects of highly energetic electronics. The role of laser prepulse for x-ray intensity emission and its spatial distribution were investigated in details. X-ray spectra radiation from plasma with electron density more than 1022 cm-3 was at first time observed. Big effect of fast electrons influence on the x-ray emission of He-like Ar spectra was demonstrated. Comparison with data under various experimental conditions clearly demonstrated that for increasing x-ray output form plasma the most essential to increase size of clusters and has reasonable value of ps prepulse.
We demonstrate a femtosecond laser chain that generates 20 TW at 10 Hz in less than 50 fs with focused intensities higher than 3 X 1019 W/cm2. This system is optimized for a broad transmission bandwidth and includes an aberration-free stretcher compressor.
It is now well established that Kerr lensing is most efficient at creating short pulses when the cavity is operated near the edges of the geometrical stability zones. In this paper, we describe the effects of the thermal aberration due to laser pumping on the beam shape and on the initiation of the self-mode-locked regime. A simple 1-D analysis of the thermal aberration shows that the phase delay is parabolic near the center of the beam while it is linear in the wings. We show that such an aberration produces the break up of the beam profile when the laser is operated near the edges of the geometrical stability zones. Kerr lensing present in the self-mode-locked regime tends to reduce the beam size in such a way that the non-parabolic contribution of the thermal aberration is not seen by the beam; hence, self-mode locking effectively suppresses beam break up.
We analyze the high power operation of self-mode-locked solid-state lasers. Excessive Kerr lensing is shown to bring the laser cavity out of the limits of geometrical stability; this situation results in temporal fluctuations, and pulse-break-up into many pulses. Kerr lensing can also reduce the size of the beam to such a point where higher-order transverse modes start to oscillate. Sudden changes in beam size are also examined. Experimental results obtained with a Ti:sapphire laser indicates that two-pulse emission can be more stable than one-pulse emission.
We present a detailed study of the spatial properties of spectral continuum generation in glasses. We show that the conical emission which accompanies filamentation in the glasses is a Cerenkov-based effect resulting from self-focusing. A theoretical analysis of the angular dependence of the emission based on a moving focal point is in good agreement with the experimental data.
In this paper we report the generation of femtosecond pulses in the near infrared by passive
mode locking of a Rhodamine 700 dye laser.Two saturable absorbers were used to produced pulses
from 775 to 800 nm. In a short cavity to avoid a multiple pulses regime, pulses shorter than 50 fsec
have been obtained.
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