More than 50 large aperture optics coated by Safran Reosc have been delivered to LULI for the APOLLON laser facility. Coating designs, processes and measurements are discussed with regard to the requirements. As a part of these optics is mounted on the beam line, we present operational performances with a specific focus on LIDT. This paper also relates the challenge to give a reliable LIDT value within a specific application toward the coatings of those component that have been tested by several LIDT-testing facilities. This test results are discussed and compared with LIDT test performed with the APOLLON laser beam.
In this paper we are giving a summary of the Apollon 10 PW facility laser design together with updated laser
performance. The Apollon facility is currently under construction in France. The APOLLON laser system is a laser
designed for delivering pulses as short as 15 fs (10-15 s) with an energy exceeding 150 Joules on target. The peak power
delivered by this laser system will be 10 Petawatts (1016W). The Apollon laser system will be delivering 4 beams: one 10
PW beam (F1 beam 400 mm diameter), one 1 PW beam (F2 beam 140 mm diameter) and two additional probe beams
(F3 and F4) at a repetition rate of 1 shot per minute. The laser system is based on Ti-sapphire amplifiers pumped by
frequency doubled solid-state lasers. The repetition rate of the high energy part will be 1 shot per minute. The main beam
at the output of the last amplifier will be split and dispatched to two experimental areas. The main laser beam is
delivering 30 J before compression at a repetition rate of 1 shot per minute and we are currently increasing to get 100J.
We present preliminary simulation and experimental results obtained in the frame of QOMA project funded by the European Space Agency (ESA), involving the design and development of a diode-pumped solid state (DPSS) Nd:YAG laser. The simulation results were obtained using the LASCAD software code, while the experimental results were obtained at the Laboratoire Charles Fabry (France) and the National Technical University of Athens (NTUA).
We propose and demonstrate an architecture that achieves passive coherent combination of two fiber femtosecond
chirped-pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac interferometer. The
experiment shows that the temporal, spectral, and spatial qualities of each beam are retained, with the generation of 250
fs pulses at 35 MHz repetition rate, an uncompressed average power of 10 W, and a combining efficiency of 96%. The
behavior of this architecture in the presence of high accumulated nonlinear phase is investigated.
Cryogenic cooling is a very interesting and promising apparatus for high power lasers, especially with Yb-doped
materials. In fact, it is now well known that operating this type of laser materials at cryogenic temperatures such as 77K
(liquid nitrogen temperature) positively affects their performance, especially at high power levels, because of increased
thermal conductivities and absorption and emission cross sections. We present a high-power diode-pumped Yb:CaF2 laser operating at cryogenic temperature (77 K). A laser output power of 97 W at 1034 nm was extracted for a pump
power of 245 W. The corresponding global extraction efficiency (versus absorbed pump power) is 65%. The laser small
signal gain was found equal to 3.1. The laser wavelength could be tuned between 990 and 1052 nm with peaks which
well correspond to the structure of the gain cross section spectra registered at low temperature.
Many industrial and scientific applications need ultra-short pulses with high average power. Diode-pumped systems
based on ytterbium-doped crystals have a huge interest thanks to their good thermal and spectroscopic properties. Among
them, Yb:CALGO and Yb:CaF2, hold exceptional positions exhibiting a very atypical combination of ultrabroad
bandwidth and high thermal conductivity, therefore very promising for short pulse and high power applications.
In this paper we present an overview of the results obtained with these two crystals. First, we detail the origin of this
exceptional gathering of their broad emission bands and good thermal properties. Second, we present the results obtained
in femtosecond regime with these two crystals including a discussion on the actual limitations of Yb-doped ultrafast solid-state lasers.
Many industrial and scientific applications need ultra-short and energetic pulses. Diode-pumped systems based on
ytterbium-doped crystals have a huge interest thanks to their good thermal and spectroscopic properties. Among them,
Yb:CaF2, shows very promising results for short pulse generation, and its long fluorescence lifetime, 2.4 ms, indicates a
high energy storage capacity.
We present a diode-pumped regenerative amplifier based on an Yb:CaF2 crystal optimized to produce short pulses for
various repetition rates ranging from 100 Hz to 10 kHz. The experiment is performed with a 2.6-% Yb doped 5-mm-long
CaF2 crystal grown by using the Bridgman technique and used at Brewster angle. To optimize the injection pulse
spectrum in terms of bandwidth and maximum gain, the seed pulses are generated by a broadband Yb:CALGO oscillator
centered at 1043 nm with a FWHM bandwidth of 15 nm at a repetition rate of 27 MHz. The pulses are then stretched to
260 ps with a transmission grating. The shortest pulse duration generated is 178-fs, and the corresponding energy is
1.4 mJ before compression (620 μJ after), at a repetition rate of 500 Hz for 16 W of pump power. The bandwidth is 10
nm centered at 1040 nm. At 10 kHz repetition rate, 1.4 W of average power before compression is obtained,
corresponding to an optical-optical efficiency of 10%. We also noticed that the pulse duration tends to increase above 1
kHz, reaching 400 fs at 10 kHz.
The increase of the output power in fiber lasers and amplifiers is directly related to the scaling of the core diameter. State
of the art high power laser and amplifier setups are based on large mode area (LMA) photonic crystal fibers (PCF)
exhibiting core diameters ranging from 40 μm up to 100 μm1 (rod-type PCF). For instance, a two-stage femtosecond
chirped pulse amplification (CPA) system based on 80 μm core diameter rod-type PCF was demonstrated generating
270 fs 100 μJ pulses2. Although highly suited to reach very large mode areas, this fiber design suffers some drawbacks
such as high bend sensitivity (for core diameter equal to or larger than 40 μm3) and practical handling (cleaving, splicing,
etc.) due to presence of air holes. As an alternative we have recently proposed all-solid photonic bandgap (PBG) Bragg
fiber (BF) design4. Due to their waveguiding mechanism completely different from total internal reflection this type of
fiber offers a very flexible geometry for designing waveguide structures with demanding properties (singlemodedness in
large core configuration5, chromatic dispersion6, polarization maintaining7, low bend sensitivity8). During the last few
years our interest was mainly focused on the realization of an active BF and scaling up the core diameter. We showed
that, in principle, core diameters in excess of 50 μm can be reached9. As an example, an Yb-doped LMA BF with 20 μm
core diameter was realized and single transverse mode operation in continuous wave (cw)9 and mode-locking10
oscillation regimes was demonstrated. Moreover, operation of two dimensional all-solid PBG fibers in laser and
amplifier regimes was recently demonstrated11-13.
In this paper we report on the first demonstration of amplification of femtosecond pulses in LMA PBG BF. A single
transverse mode was obtained and the BF allowed for generating 5 μJ 260 fs pulses in a system with a moderate
stretching of 150 ps.
We report the generation of 63 fs pulses of 290 nJ energy and 4.6 MW peak power at 1050 nm based on the use of a
single polarisation maintaining ytterbium-doped fiber parabolic amplification system. We demonstrate that the operation
of the amplifier beyond the gain bandwidth limit plays a key role on the sufficient recompressibility of the pulses in a
standard grating pair compressor. This results from the accumulated asymmetric nonlinear spectral phase and the good
overall third-order dispersion compensation in the system.
Laser ablation for the formation of apodized patterns on intraocular lenses, as an alternative of the
conventional injection molding, has been proved to be a very promising new technique. For the precise lenses
ablation, the use of suitable laser wavelength and pulse duration, resulting in a small optical penetration depth
in the lens and in confinement of the energy deposition in a small volume, as well as the reduced thermal
damage to the surrounding tissue, is essential.
Mid-infrared laser wavelengths, at which the organic biological simulators absorption coefficient is large,
meet well the above conditions. Towards the complete understanding of the intraocular lens ablation
procedure and therefore the choice of the optimum laser beam characteristics for the most accurate, efficient
and safe surgical application, the comparative study of various mid-infrared laser sources is of great interest.
In this work we investigate the potential of the development of three different mid-infrared laser sources,
namely the Yb:YAG, the Cr:Tm:Ho:YAG and the Er:Tm:Ho:YLF laser, operating at 1029 nm, 2060 nm and
2080 nm respectively and their ability in forming patterns on biomaterials. Pumping was achieved with
conventional Xe flash lamps in a double elliptical pump chamber. A properly designed Pulse-Forming-
Network capable of delivering energy up to 800 J, in variable lamp illumination durations is used. Several
hundreds of mJoules were achieved from the Yb:YAG laser oscillator and several Joules from the Ho:YAG
and Ho:YLF laser oscillators. Free running and Q-switched laser operation studies and preliminary
experiments on laser and biomaterials (biopolymers and animal tissues) interactions will be reported.
The increasing use of lasers in biomedical research and clinical praxis leads to the development and application of new, non-invasive, therapeutic, surgical and diagnostic techniques. In laser surgery, the theory of ablation dictates that pulsed mid-infrared laser beams exhibit strong absorption by soft and hard tissues, restricting residual thermal damage to a minimum zone. Therefore, the development of high quality 3 μm lasers is considered to be an alternative for precise laser ablation of tissue. Among them are the high quality oscillator-two stages amplifier lasers developed, which will be described in this article. The beam quality delivered by these lasers to the biological tissue is of great importance in cutting and ablating operations.
As the precision of the ablation is increased, the cutting laser interventions could well move to the microsurgery field. Recently, the combination of a laser scalpel with an optical trapping device, under microscopy control, is becoming increasingly important. Optical manipulation of microscopic particles by focused laser beams, is now widely used as a powerful tool for 'non-contact' micromanipulation of cells and organelles. Several laser sources are employed for trapping and varying laser powers are used in a broad range of applications of optical tweezers. For most of the lasers used, the focal spot of the trapping beam is of the order of a micron. As the trapped objects can vary in size from hundreds of nanometres to hundreds of microns, the technique has recently invaded in to the nanocosomos of genes and molecules. However, the use of optical trapping for quantitative research into biophysical processes requires accurate calculation of the optical forces and torques acting within the trap.
The research and development efforts towards a mid-IR microbeam laser system, the design and realization efforts towards a visible laser trapping system and the first results obtained using a relatively new calibration method to calculate the forces experienced in the optical trap are discussed in detail in the following.
The development of a TEA HF (SF6:C3H8:He) oscillator-double amplifier laser system with one common switching element and one common power supply unit is presented. All three cavities employ the conventional charge transfer excitation circuit and the surface corona discharge preionization scheme. For each amplifier the small signal gain coefficient go and the saturation energy density Es are determined and their dependence on the charging voltage and the active gas concentrations is investigated. The performance characteristics of the laser system i.e. maximum output energy, pulse duration, spectral and beam profile evolution through all three stages of the system are given. Additionally, beam propagation measurements through a 150cm long, 250μm core diameter GeO2 mid-IR fiber are presented.
The interaction of a TEA (Transversally Excited Atmospheric pressure) corona preionized oscillator double amplifier HF (hydrogen fluoride) laser beam with dentin tissue is reported. Pulses of 39 ns in the wavelength range of 2.65-3.35 μm and output energies in the range of 10-45 mJ, in a predominantly TEM00 beam were used to interact with dentin tissue. Ablation experiments were conducted with the laser beam directly focused on the tissue. Several samples of freshly extracted human teeth were used, cut longitudinally in facets of about 1mm thick and stored in phosphate buffered saline after being cleaned from the soft tissue remains. The experimental data (ablation thresholds, ablation rates) are discussed with respect to the ablation mechanism(s). Adequate tissue removal was observed and the ablation behavior was, in the greates part of the available fluences, almost linear. From the microscopic examination of teh samples, in a scanning electron microscope (SEM), the irradiated surfaces displayed oval craters (reflecting the laser beam shape) with absence of any melting or carbonization zone. It is suggested that the specific laser removes hard tissue by a combined photothermal and plasma mediated ablation mechanism, leaving a surface free from thermal damage and with a well-shaped crater.
In this study a frustrated total internal reflection (FTIR) Q-switched and free-running Er:YAG laser, as well as a novel design transversally excited atmospheric pressure (TEA) oscillator-double amplifier corona preionised high beam quality Hydrogen-Fluoride (HF) laser system, all developed in our lab, were used in dentin ablation experiments. In the case of the Er:YAG laser, pulses of 190 ns in Q-switched operation and of 80 μs pulse width in free-running operation at 2.94 μm were used, while HF laser pulses of 39 ns in the wavelength range of 2.6-3.1 μm in a predominantly TEM00 beam were also used to interact in vitro with dentin tissue. Several samples of freshly extracted human teeth were used, cut longitudinally in facets of 0.4-1.5 mm thick. Ablation experiments were conducted with the laser beam directly focused on the tissue or after being waveguided through suitable mid-IR fiber/waveguide alternatively ended with quartz end-sealing caps. The correlation between the various laser beam parameters, as wavelength, pulse duration, repetition rate, energy and spatial distribution of the beam profile and the ablative characteristics (ablation rates, tissue surface morphology) of dentin surface were investigated.
Mid-IR lasers are already used successfully in numerous surgical operations. The Er:YAG and the HF laser, are the main laser sources emitting in the 3.0 μm range of the spectrum, and as this wavelength coincides with the peak of the water and other main soft and hard tissue components absorption curves, it is clear that these lasers would be very useful in numerous medical fields as dentistry, dermatology, angioplasty, ophthalmology etc. Recently, the development of flexible, low loss, able to deliver high power and safe to enter the human body waveguides and fibers for pulsed mid-infrared laser radiation initiated the efforts of the extension of laser surgery in the area of the minimally invasive endoscopy. The laser-induced fluorescence (LIF) is proposed for diagnosis in several pathologies, as in arterial atherosclerosis, in malignancy or for early dental caries detection. LIF is also investigated as a suitable method for monitoring the on line laser surgery interventions.
Transmission measurements of Q-switched Er:YAG laser radiation, through cyclic olefin polymer-coated silver hollow glass waveguides, were performed under straight and bent conditions and the beam quality at the output of the waveguide was studied.
The effect of the 2.94 μm Er:YAG laser radiation propagation through sapphire fibers with diameters varying from 250 μm to 550 μm, on the quality of the laser beam is investigated. A comparison was made between the fibers performance in free-running and Q-switched Er:YAG laser radiation.
In the last few years, there has been an increasing interest for the 3 m laser radiation in various medical applications, as this wavelength is strongly absorbed by the water and the other components of soft and hard tissue. An intensive development effort is going on throughout the world, in order to develop reliable lasers emitting in the 3 m wavelength range. Our laser development effort with the Q-switched Er:YAG laser is briefly described in this article. Additionally for medical applications there is a great demand for good flexible delivery systems, in the mid-IR wavelength region. In this work the radiation transmission of a Q-switched Er:YAG laser, emitting at 2.94 m, through high power (HP) oxide glass fibers of 450 ?m core diameter was studied. Attenuation measurements were obtained as a function of the laser energy input and as a function of curvature, at 90o, 180o and 360o bending angle. The output beam quality was studied using a beam profiler. Experiments with the same delivery system transmitting free-running Er:YAG laser radiation, were performed for comparison. The results are promising for the delivery of Q-switched Er:YAG laser radiation, as the fibers exhibited attenuation of 0.7 dB/m, and no damage of them was observed.
A TEA-TEA HF (SF6:C3H8:He) oscillator-amplifier laser system with one common switching element and one common power supply unit was designed. Two different preionization schemes were employed. One using a corona discharge on a glass plate and another one using semiconductor slabs. For both arrangements the improvement of the laser beam characteristics of the TEA HF laser oscillator, such as beam profile and output energy, was investigated. The beam profile is discussed and presented in detail in 2D and 3D figures with the help of a beam analyzer system and the gain measurements for the specific active gas mixture and the specific laser head geometry are given in terms of the small signal gain coefficient go and the gain value G parameters.
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