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The laser-induced damage threshold (LIDT) of nematic liquid crystals is investigated in the femtosecond regime at ≃ 1030 n m . The thickness and breakdown of freely suspended thin films ( ≃ 100 n m ) of different mixtures (MLC2073, MLC2132, and E7) is monitored in real time by spectral-domain interferometry. The duration of laser pulses was varied from 180 fs to 1.8 ps for repetition rates ranging from single shot to 1 MHz. The dependence of the LIDT with pulse duration suggests a damage mechanism dominated by ionization mechanisms at low repetition rate and by linear absorption at high repetition rate. In the single-shot regime, LIDTs exceeding 1 J / c m 2 are found for the three investigated mixtures. The LIDT of polyvinyl alcohol is also investigated by the same method.

We report a novel time-resolved ultrafast transient spectroscopy setup to investigate third-order nonlinear dynamics on the femtosecond time-scale. Through measurement of the transient Kerr-induced carrier-frequency shift, the method enables to detect weak nonlinear phase-shift (below 50 mrad) without heterodyne detection. It provides temporal resolution to investigate both instantaneous and delayed nonlinear processes and polarization resolution to probe various terms of the third-order nonlinear susceptibility.

The growing development of few-cycle light sources has triggered the development of innovative pulse shaping devices, capable of handling bandwidths spanning over multiple optical octaves [1] . We propose an ultra-broadband reflective SLM, whose design is issued from our previous investigations on thick cells of thermotropic nematic liquid crystal (LC) [2] , [3] . It overcomes the typical limitations of LC-SLM, by eliminating the need for an electrode. The device, referred to as a Thermo-Optically-Addressed Spatial Light Modulator (TOA-SLM), relies on an optically-induced change of the local temperature of a liquid crystal layer ( Figure 1a ). The temperature is controlled by "recording" beam, while the "readout" beam is the modulated beam. The optical isolation between the recording and readout beams is performed by a gold layer which endorses three additional functions: partial absorption of the recording beam, local heating of the LC by diffusion, and reflection of the readout beam. TOA-SLM also includes two substrates and a layer of 50-100 μ m of the nematic mixture E7. The LC being thermotropic and birefringent, both the ordinary and extraordinary optical refractive indices are locally modulated. Arbitrary phase modulation is then achieved by spatially shaping the recording laser.

International audience; This article tries to theoretically compute the stimulated emission crdss-sections when We know the oscillator strength of a broad material class (dielectric crystals hosting metal -transition impurity atoms). We apply the present approach to Ti:sapphire and check it by computing some emission cross-section curves for both it and o polarizations. We also set a relationship between oscillator strength and radiative lifetime. Such an approach will allow future parametric studies for Ti:sapphire spectroscopic properties. (C) 2016 Elsevier B.V. All rights reserved.

We report on the status of the re-commissioning of a high energy OPCPA laser system with programmable spectrum that serves as a frontend for a 10 PW laser at ELI-Beamlines. The OPCPA chain was developed by a consortium of National Energetics and Ekspla along with scientists of ELI-Beamlines.1 The laser system, consisting of three picosecond OPCPA stages, pulse cleaner, Offner stretcher, and 5 nanosecond OPCPA stages pumped by Nd:YAG lasers with programmable pulse shape (NL944, Ekspla), allows for precise spectral shaping while achieving high nonlinear conversion efficiency. Employing a subsequent Nd:glass power amplifiers (PA), the system was demonstrated to yield>1 kJ of energy, while maintaining broad spectrum of > 13 nm (FWHM). After recommissioning the OPCPA frontend in Dolni Břežany, an output energy of 4.3 J, flat beam-profile and good far-field quality has been demonstrated. The spectral shape has been optimized to support > 15 nm bandwidth and >1.5 kJ, consistent with 10 PW operation of the fully integrated laser system after compression.

State-of-the-art physics experiments are pushing the development of lasers with ultra-high peak power pulses. 4 PW pulses have been produced with TiSa [1] and 10 PW with the same gain medium is scheduled at LULI (Apollon) and at ELI-NP. The other approach is to use Nd-doped glass as gain medium, whose interest is in its capability of delivering higher energy at the expense of a longer pulse duration. Based on this gain material combined with an OPCPA based front-end, a kJ-10 PW class laser has been designed and built. The front-end, consisting of picosecond OPCPA, temporal pulse cleaning and nanosecond OPCPA, delivers pulses with excess of 4 Joules at 5 Hz with a shaped spectrum to pre-compensate for gain distortions in Nd:glass power amplifiers. Two liquid-cooled, mixed glass power amplifiers, namely PA1 and PA2, are used for further amplification. Up to now, they have been activated demonstrating 70 J at 1 shot a minute after PA1 and 1 kJ at 1 shot every 7 minutes for PA2. The Fourier limit of the spectrum is 150 fs meaning 6 PW capability after compression. This energy level has been obtained with only 3 Joules seed energy, from the OPCPA and partial activation of PA2. Scaling of this result suggests that more than 1.7 kJ should be obtained leading to 10 PW after compression while the output spectrum will remain compatible with 150 Fs thanks to the OPCPA spectral tailoring capability.

The 10PW OPCPA/glass laser under construction for ELI-Beamlines will exhibit output pulses delivered every minute with an energy of 1.5kJ within 150fs duration. We will show results of the sub-sections as well as output performances.

Overview of progress in construction and testing of the laser systems of ELI-Beamlines, accomplished since 2015, is presented. Good progress has been achieved in construction of all four lasers based largely on the technology of diode-pumped solid state lasers (DPSSL). The first part of the L1 laser, designed to provide 200 mJ

International audience; 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. Design update and recent results of the Apollon 10 PW facility (PDF Download Available). Available from: https://www.researchgate.net/publication/316893870_Design_update_and_recent_results_of_the_Apollon_10_PW_facility [accessed Sep 12, 2017].

In order to transport multi-petawatt (PW) femtosecond laser beams with large spectral bandwidth, specific mirrors have to be designed and manufactured. We report on an experimental study of the laser-damage resistance and other optical properties of coating materials deposited in a 1-m class coating chamber. The study is conducted on single-layer coatings deposited by electron beam evaporation at 500 fs. Based on the experience of large optics for nanosecond applications, hafnia and silica are particularly investigated. However, in the case of sub-15 fs, the spectral specifications for PW beam transport mirrors cannot be reached by classical high laser-resistant quarter-wave SiO2/HfO2 stacks. Therefore, we investigate the laser resistance of different dielectrics of interest deposited with electron-beam processes: Al2O3, Y2O3, Sc2O3, HfO2, Ta2O5, TiO2. The influence of multiple pulse irradiations and environmental conditions, such as vacuum and temperature, is studied. With the investigation of multilayer stacks, we also show that there is no difference in behavior when a film is studied as a single layer or embedded in a stack. Based on these results, we were able to optimize high reflective (>99.5%), broadband (300 nm) and high laser-induced damage threshold (2.5 J/cm2) mirrors for PW applications.

A multilayer mirror for spectral filtering adapted to ultra-short and multi-PW Ti:Sa laser has been designed, manufactured and characterized. The method used to determine both the reflectivity shape and the coating design leads to global compensation of gain narrowing, saturation and spectral phase. The result is a spectral control on 200 nm range while keeping a flat spectral phase. This kind of filter will enable obtaining 15 fs pulse duration for multi-PW laser systems based on Ti:Sa.

Dielectric mirrors, hybrid metal-dielectric and a new generation of hybrid metal-dielectric gratings with high damage threshold suitable for 10 PW laser systems are presented.

The peak power handling capability of ultra-short pulse lasers is main concern for new facilities, like those for the French Apollon 10P, and European Extreme Light Infrastructure (ELI) projects. Indeed, these last generation lasers require complex, large (O1m) and resistant optical components with optimized thin-film coatings. Using on one hand the recent development of high laser resistant broadband high reflective coatings through a joint project with the Laboratoire d’Optique Appliquee and Fresnel Institute, and on the other hand its long time experience with polishing and measuring large and complex optical components, Reosc decided to demonstrate the feasibility of a O500mm aperture, 90° deviation, F/2.5 high output NA Off-Axis Parabola (OAP) dedicated to focus fs ultra-intense laser beams. The prototype of the 90° OAP has a concave surface with 20mm of aspherisation for focal length of F1250mm. The OAP is coated with a hybrid Metal/Multi-Layer-Dielectric coating. It provides a reflectivity up to 98%, an absolute Group Delay Dispersion (GDD) below 100fs² and a Laser-Induced Damage Threshold (LIDT) up to 0.5J/cm², at 15fs and under vacuum. These performances are achieved on the whole surface and on the 200nm spectral range required by the sub 20fs PW-systems. In this paper, Reosc report the developments required for the polishing, the coating and the measurements of the OAP and we will show the performances achieved on the prototype.

We present a high-contrast 10-fs Front-End for Ti:sapphire PW-lasers within the Apollon-10PW project. This injector uses OPCPA pumped at 100Hz by Yb-based CPA chain. Combination of OPCPA and XPW permits a >1012 contrast ratio.

The strategy used to develop an innovative high contrast multiterawatt femtosecond laser chain based on a hybrid (solid/gas) technology is reported. The laser system includes a Ti:sapphire oscillator generating 50 fs pulses at 950 nm, an optical parametric chirped pulse amplification stage, a second harmonic frequency converter for pulse temporal cleaning, and a final photolytical XeF(C–A) excimer amplifier for direct high peak-power amplification of ultrashort laser pulses in the blue (475 nm) spectral region. Several important issues concerning the design of the laser front-end, the energy extraction and beam phase control in the high peak-power XeF(C–A) amplifier are theoretically addressed. A detailed description of the XeF(C–A) amplifier and careful measurements of its energetic, optical and pumping characteristics are also given, together with the first pilot amplification experiments in the low density XeF(C–A) medium to assert the significance of our approach.

Dielectrics as single layers and broadband high-reflective stacks were deposited by electron beam deposition processes compatible with 1-meter class optics. After being physically and optically characterized, samples were irradiated with several ultrafast lasers (KYW:Yb 500fs, Ti:Sa 40fs and Ti:Sa 11fs) with single and multi-pulses. The setups of the test platforms, laser-induced damage threshold investigations of intrinsic materials, dielectric multilayers and hybrid metal/dielectric multilayers and electric field intensity distributions are described.

In new laser facilities, broadband ultra-short pulses need to be transported in large and energetic beams to the experiment chambers through high performance optical components. We studied laser resistance of electronbeam- deposited materials in order to design meter scale high reflective optics according to petawatt-system requirements. We report intrinsic laser resistance of several dielectric materials, spectral performances of high reflective coatings and their laser induced damage threshold at different pulse durations from 150ps to 11fs.

The spatial quality of intense femtosecond pulses from chirped pulse amplification (CPA) systems is of great importance in order to reach very high peak intensity on the target. We review various aspects of this quality, present results obtained all along a CPA chain and discuss improvement implemented or still to be implemented.

We report for the first time the use of a spatially dispersive laser cavity as a regenerative amplifier of ultrashort pulses. By spatially dispersing the beam on a Ti:sapphire crystal and amplifying independently the wavelengths, we were able to overcome gain narrowing. An energy of 1.6 mJ was obtained with a spectrum of 81 nm at full width at half-maximum (FWHM). We discuss the different advantages of this technique and also theoretically investigate the possibility for intracavity dispersion compensation.

International audience; The principal objective of Apollon-10P project is the generation of 10 PW peak power pulses of 15 fs duration at 1 shot/minute. The technological challenges and the current status of the Apollon laser system are discussed in detail.

Oxides as single layers and HR-multilayers were irradiated by single and multi laser pulses at 1030nm and 500fs. Conditioning effect and correlation between LIDT of intrinsic materials and stacks through the EFI distribution are investigated.

We describe the design and operation of a 2-stage multi-pass Ti:sapphire amplifier laser system, which is optimised for a broad transmission bandwidth and incorporates a novel reflective spherical mirror pulse-stretcher. Output energies of 180 mJ after compression, and amplified bandwidths up to 30 nm are observed.

We report on background-free intensity autocorrelation studies of sub-50 fs pulses from a Kerr lens mode-locked (KLM) Ti: sapphire laser over an intensity dynamic range of approximately 7 orders of magnitude. Results reveal the presence of a low intensity pedestal, at the 10 −5 level, which can be improved by incorporating a hard aperture in the cavity. We also present the results derived from a ray tracing code used to investigate the propagatin of pulses through a cylindrical mirror stretcher/compressor. The strong dependence of the residual pedestal level with initial pulse bandwidth and spectral clipping is discussed. The various limiting effects of both the seed oscillator and the stretcher/compressor on the final pedestal intensity level in the linear amplification regime are discussed.

The influence of the radially varying Ti:Sapphire gain on the spectral amplitude and phase of a 15 femtoseconds pulse is studied

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International audience; Transparent high optical quality and large Ti-sapphire (Ti(3+)-doped Al(2)O(3)) single crystals have been grown by the Kyropoulos technique (KT) for optical amplification. The present work shows that by the utilization of KT growth technology and the optimization of the growth conditions it is possible to grow Ti-doped Al(2)O(3), 100 mm in diameter and 5 kg in weight. We have demonstrated that large Ti(0.25 atom %)-doped Al(2)O(3) crystals show high chemical homogeneities and good optical properties and amplify the energy without any special annealing. Ti-doped sapphire crystals are for high power laser applications and particularly for the shortest pulses ever produced from a laser oscillator.

International audience; We designed a 10PW (150 J-15 fs) laser system based on the use of titanium-doped sapphire power amplifiers. The solution is to provide an overall compensating spectral gain narrowing and shifting technique for obtaining a controlled output spectrum. © 2011 Optical Society of America.

We present easy-scalable pulse recompression method based on spectral broadening due to self phase modulation in bulk medium. Our experiment demonstrates a possibility of compression of high-energy pulses above 1J from 30 to 14 fs.

Apollon-10P is a French funded 10 petawatt hybrid CPA laser system (OPCPA and titanium doped power amplifiers) that will be operating in 2013. The system will deliver pulses with energy of 150 joules in 15 fs pulse duration at 1 shot every minute. The OPCPA based front-end will deliver 30 mJ at 10 Hz with a spectrum having the availability to handle 10 – 15 fs pulses. The 1.5 ns stretched pulses will be further amplified up to 300 joules in Ti:Sa amplifiers. The choice of this hybrid solution has appeared to be the most efficient one in term of balance between ultra-short pulse duration and amplification efficiency and cost.

International audience; The characterization of a temporal filter based on cross-polarized wave generation working in the few-optical-cycle regime is presented. We show that this device dramatically improves the spectral quality of the ultrashort seed pulses, opening the way to the production of sub-10 fs pulses with high incoherent and coherent contrast. The dispersion compensation conditions for an optimized behavior of the process are experimentally and theoretically discussed.

We propose an efficient scheme for femtosecond contrast filtering based on cross-polarized wave generation with a super-Gaussian-shaped beam. We reach 50% intensity transmission with a 2.2 time pulse shortening.

International audience; We present a chirped pulse amplification (CPA) Ti:Sa laser generating sub-15 fs pulses with expected high temporal quality. Gain-narrowing in the pre-amplifier is balanced by a variable spectral reflectivity mirror and by a fine adaptation of the saturation conditions. A crossed polarized wave generation (XPW) filter is introduced to enhance the contrast, reduce the pulse duration and improve the spectral quality. The pulses are generated at 10 Hz repetition rate, with pulse energy of 110 μJ and very clean Gaussian spectrum. The temporal contrast is evaluated by a measurement before the XPW filter and calculations of the enhancement by the filter. The potential temporal incoherent contrast is 10^12 and the coherent contrast 10^10. The performances of the system make it suitable as an injector for petawatt lasers operating in the double CPA scheme.

Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved, for the first time to our knowledge, with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic. Wave-front distortions of a 100-fs laser that are due to third-order nonlinear effects have been compensated for. This technique, which permits correction in a straightforward process that requires no feedback loop, is also used on a 10-TW Ti:sapphire-Nd:phosphate glass laser in the subpicosecond regime. We also demonstrate that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity.

Summary form only given. A laser front-end delivering 10-fs pulses and exhibiting a temporal contrast higher than 1011 will be presented. The system is based on CPA in TiSa and on cross-polarized-wave generation for contrast improvement and pulse shortening.

International audience; We demonstrate the technique of cross-polarized wave (XPW) generation at 1 μm with a 310-fs optical parametric chirped-pulse amplification system at the millijoule level. We show an improvement of the temporal contrast by three orders of magnitude with an energy transmission of 22%. Additionally, we report that XPW generation preserves the beam spatial quality and shortens the pulse duration by a factor of 3^1/2, resulting in a peak power transmission of ∼35%.

In this paper, we present results of a ray tracing simulation of a stretcher-compressor arrangement for blue-green high contrast multiterawatt femtosecond laser Ti:sapphire laser chain, not only in terms of final pulse duration and contrast, but also with respect to the alignment sensitivity and the optical quality of components. The ray tracing simulation uses OSLO software and includes dispersion of the materials of the laser chain.

We study the formation of femtosecond filaments in an amplifying medium (Ti:Sa). Subthreshold onset of filamentation as well as flux amplification without fragmentation is observed, in good agreement with simulations.

International audience; Femtosecond laser filamentation is studied in a broadband amplifying medium, sapphire doped with electronically excited Ti ions. Evidence for fluence amplification of self-guided pulses, increase of filamentation length, as well as a lowering of the input laser power necessary for filamentation is reported.

Since the beginning of the 90's the generation of high-intense laser pulses has known an unprecedented evolution thanks to the conjunction of the possibility of the Chirped Pulse Technique and the availability of spectrally broad-band laser media. Lasers capable of producing petawatt pulses can now be built on few optical tables in a small laboratory. We review the generation and the amplification of ultra-short pulses by the Chirped Pulse Amplification technique.

International audience; Nonlinear elliptical polarization rotation is used to improve the contrast of femtosecond pulses by several orders of magnitude. Using nonlinear induced birefringence in air, we produced cleaned pulses with an energy of a few hundreds of microjoules. This technique presents several major advantages, such as convenience and stability of the setup. We investigated the phase profile required for obtaining high-energy pulses. No phase distortion is observed, and the spatial quality of the beam is preserved.

Summary form only given. We demonstrate a novel 10-100-Hz terawatt source where the thermal distortion is not anymore an issue while varying the repetition rate. The problem of thermal distortion has been already demonstrated for high repetition rates laser as 1-kHz. One recent example for controlling this effect is a thermal eigenmode amplifier where the thermal lens is used to transform a classic multipass amplifier to a real eigenmode cavity. This method has shown very good results in a several mJ, ultrashort Ti:sapphire amplifier laser chain. An amplifier crystal cooled to 125-K has been also demonstrated for a kHz, 0.2-TW laser system. For intermediate repetition rate (10-100 Hz) the thermal aberration is less critical due to the relative high diameter of the pump beam on the amplifier. Nevertheless, it has to be taken into account to preserve a constant high beam quality during amplification.

International audience; We present the design and characterization of a femtosecond high-intensity laser system emitting a near-diffraction-limited beam. This system was dimensioned in order to reach intensities in excess of 10^20 W/cm^2 at a high repetition rate for ultrahigh-field physics experiments. We describe the improvements that were added to a conventional chirp pulse amplification configuration in order to decrease the deleterious effects of gain narrowing, gain shifting, thermal focusing in the amplifier stages, and spatial degradation due to multipass amplification processes.

The use of a new crystal: Yb:GdCOB for the development of a regenerative amplifier is reported. This chirped pulse amplification system generates 21-mJ pulses with a bandwidth of 8 nm leading to 350-fs, 12-mJ pulses after compression.

Summary form only given. The chirped pulse amplification method reduced dramatically non-linear effects, enabling thereby higher amplification levels. But when increasing average power needed to pump the Ti:sapphire amplifier crystals, strong thermal effects appear which affect beam propagation by inducing unwanted wavefront distortions. Moreover, amplification process narrows the spectrum of a chirped pulse because of gain narrowing and gain saturation effects. Our laser chain is composed of a Kerr lens mode locked Ti:sapphire laser oscillator delivering a 80 Mhz/300 mW a pulse train with a spectrum of 65 nm FWHM centered around 810 nm. Pulses are stretched through an Offner triplet, and amplified at -10 Hz through three multipass amplifiers to reach, first the millijoule regime through a high-gain amplifier.

We have experimentally studied thermal effects in highly pumped Ti:sapphire crystals in the 140–340 K temperature range. We demonstrate that a critical temperature exists, which depends on pumping and probing conditions, below which detrimental thermal effects completely disappear. In particular, we show that in a typical high-intensity Ti:sapphire amplifier, thermal lensing and wave-front distortions can be suppressed keeping the crystal temperature lower than ∼230 K.

We report the wavefront correction of high intensity laser beam, using deformable mirror. The B-integral and the thermal lensing wave-front distortions are characterized and compensated.

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.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.