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High-energy petawatt lasers using the chirped-pulse amplification technique require meter-sized gratings to limit the beam fluence on the surface of the grating. An alternative, studied by many groups, is a mosaic grating consisting of smaller, coherently added gratings. We propose what we believe to be a new compression scheme consisting of beam phasing instead of grating mosaic phasing. This synthetic aperture compression scheme allows us to control the beam thanks to a unique segmented mirror equipped with three degrees of freedom. With this configuration, the beam is divided into small subapertures adapted to the classical grating size. After compression, these subapertures are coherently added before the focusing stage. Therefore the alignment processes are simplified. OCIS codes: 320.5520, 140.7090, 050.5080.

We present results on tunable few-cycle laser pulses generated in the near infrared region obtained by filamentation in a krypton cell combined with group velocity dispersion compensation in fused silica. We obtain a spectral broadening of a factor ∼2-3 over the entire spectral domain studied. The central wavelength is tuned from 1.6 μm to 2 μm via an optical parametric amplification source. In optimum experimental conditions, where the input central wavelength is set to 1.7 μm, 1.8 μm, and 1.9 μm, the incident power to the gas cell exceeded the critical power of Krypton by a factor of ∼4 and the achieved spectral broadening covered ∼300 nm. Using group velocity compensation in bulk fused silica, we obtain near infrared output pulses as short as 2-3 optical cycles with 200 μJ energy per pulse. This near infrared filamentation tunable few-cycle pulse source is an important achievement for strong field physics applications such as attoscience, where wavelength scaling has an important effect. [ABSTRACT FROM AUTHOR]

Abstract: Using, a time resolved optical heterodyne Kerr effect experiment along with a Raman light diffusion experiment, we have measured the nuclear (non-instantaneous) and electronic (instantaneous) contributions to the nonlinear index of refraction in tellurite niobium-doped and silicate lead-doped glasses. The experimental set-up and the procedure used to measure the nuclear and electronic contribution are detailed. Our experimental results clearly indicate that the ratio between the instantaneous and the non-instantaneous contribution remain constant while the doping concentration or the temperature of the sample vary. These ratios are ∼5 and ∼10 in tellurite niobium-doped and silicate lead glasses, respectively. [Copyright &y& Elsevier]

A high-power semiconductor saturable absorber mirror (SESAM)-passively modelocked TEM00 Nd:YAG oscillator based on a diode-side-pumped single laser head is reported. This laser provides 21.4 W of average power at a repetition-rate of 82 MHz with 18 ps pulse duration. This laser could be an essential part in future high flux monochromatic compact X-ray source systems. [ABSTRACT FROM AUTHOR]

Second-order susceptibility thermally induced in poled glass samples was erased in doped borophosphate, lead silica, and fused silica glasses using an optical method. A simple law describes the temporal evolution and the spatial profile of the erased nonlinear region versus the intensity and profile of the erasure laser beam. A comparison is made between one and two photon absorption induced spatial profiles. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Demonstrates the erasure of induced second order linearity generated in thermal poled doped borosilicate glasses using prolonged exposure to laser radiation. Evolution of the second harmonic signal with respect to laser time exposure; Relation of the induced relaxation with absorption of the glass.

The second-order nonlinear optical (SONLO) response of a series of the highly chemically and thermally stable polychlorotriphenylmethyl monoradicals 1–8 has been studied by Hyper-Rayleigh Scattering. These radicals exhibit relatively high nonlinear optical (NLO) responses with β values ranging from 118×10−30 to 755×10−30 esu, which may result from an enhancement of the SONLO activities according to their open-shell electronic state. Hyperpolarizability data for radicals 1–8 have also been correlated with their redox potentials, correlation that has turned out to be linearly proportional either with the oxidation or the reduction potentials. These data have been justified in terms of molecular orbital energies. Finally we have successfully explored the capacity of radicals 1–8 to participate in a molecular switching array involving two main steps, an acid/base reaction and a redox process. The presence of open-shell character for this family of compounds makes them attractive candidates to design new multifunctional materials that would simultaneously possess magnetism and NLO. [Copyright &y& Elsevier]

We propose an experimental method for the determination of the transfer function linewidth of a laser amplifier. This technique is based on a transfer function scan using frequency modulation to amplitude modulation (FM-to-AM) temporal modulation measurement as a function of wavelength. Using this method, we show that the output spectrum of a laser amplifier in Q-switch mode is not representative of the transfer function of the amplifier.

In order to smooth the focal spot of high-power energetic lasers, pulses are phase-modulated. However, due to propagation impairments, phase modulation is partly converted into power modulation. This is called frequency modulation to amplitude modulation (FM-to-AM conversion). This effect may increase laser damage and thus increase operating costs. For the first time, to the best of our knowledge, we have studied the impact of the Kerr effect in this process. We have shown that when the Kerr effect is followed by a dispersive transfer function, a dramatic increase of FM-to-AM conversion may occur for a particular kind of FM-to-AM conversion that we have named "anomalous." Hence, we should remove or compensate for one of the items of the sequence: phase modulation, anomalous FM-to-AM conversion, Kerr effect, or the dispersive function. We have assessed all these solutions, and we have found an efficient inspection method to avoid anomalous FM-to-AM conversion.

High-power nanosecond laser pulses are usually spectrally broadened via temporal phase modulations to tackle the issue of stimulated Brillouin scattering and to achieve optical smoothing of the focal spot. While propagating along the beamline, such pulses can undergo frequency modulation to amplitude modulation (FM-to-AM) conversion. This phenomenon induces modulations of the optical power that can have a strong impact on laser performance. Interference filters are specific FM-to-AM conversion contributors that lead to high-frequency modulations that cannot be measured using conventional means. We propose an indirect method to investigate for such FM-to-AM contributors using spectral measurements. Further analysis of the collected data makes the quantification of the defining parameters of interference filters possible. In turn, we show that it is possible to estimate the range of power modulations induced by interference filters.

We performed simulations and experiments of wavefront distortions induced by propagating through diode-pumped square-section amplifying laser rods of Nd-doped phosphate glass and 0.5 % N d :5 % L u : C a F 2 . We observed that depending on the material, wavefront distortions' profile can vary from a circular lens-like distortion to a complex astigmatic distortion. We showed that this difference comes from the relative sign of piezo-optic tensor coefficients.

We report an effect potentially harmful occurring in regenerative amplifiers due to stimulated Brillouin scattering (SBS). Most high energy laser facilities use phase-modulated pulses to prevent the transverse SBS effect in large optical components and to smooth the focal spot on target. However, this kind of pulse format may undergo a detrimental effect known as frequency modulation to amplitude modulation (FM-AM) conversion in the presence of spectral distortions. In the present letter, we show experimentally and numerically, that SBS can also potentially be created in the regenerative amplifier located in the front-end. In this scenario, some of the side bands of the pulse reflected by regen end-cavity mirror may act as a seed for SBS in an optical component, if the pulse spectrum contains frequency components exactly separated by the Brillouin frequency shift. This self-seeded SBS induces amplitude modulation with a nonlinear dependence that may be detrimental during down-stream propagation. However, we show that a careful choice of the modulation frequencies can mitigate this effect.

We report on a high-power passively mode-locked TEM(00)Nd:YVO(4) oscillator, 888 nm diode-pumped, with pulse durations adjustable between 46 ps and 12 ps. The duration tunability was obtained by varying the output coupler (OC) transmission while avoiding resorting to spatial hole burning (SHB) for pulse shortening. At a repetition rate of 91 MHz and for an output power ranging from 15 Wto45 W, we produced SHB-free 12-ps-to32-ps-long pulses. Within this range of power, these are the shortest pulse durations obtained directly from Nd:YVO(4) oscillators.

An important issue, mosaic grating compressor, is studied to recompress pulses for multiPetawatt, high energy laser systems. Alignment of the mosaic elements is crucial to control the focal spot and thus the intensity on target. No theoretical approach analyses the influence of compressor misalignment on spatial and temporal profiles in the focal plane. We describe a simple 3D numerical model giving access to the focal plane view after a compressor. This model is computationally inexpensive since it needs only 1D Fourier transforms to access to the temporal profile. We present simulations of monolithic and mosaic grating compressors.

We present what is to our knowledge a new method for measuring the relative piston between two independent beams separated by a physical gap, typical of petawatt facilities. The feasibility of this measurement, based on quadriwave lateral shearing interferometry, has been demonstrated experimentally: piston has been measured with accuracy and sensitivity better than 50 nm.

We report on a novel approach of ultra-broad bandwidth parametric amplification around degeneracy. A bandwidth of up to 400 nm centered around 800 nm is amplified in a BBO crystal by using chirped pump pulses with a bandwitdth as broad as 10 nm. A supercontinuum signal is generated in a microstructured fiber, having to first order a quadratic chirp, which is necessary to ensure temporal overlap of the interacting waves over this broad bandwidth. Furthermore, we discuss the potential of this approach for an octave-spanning parametric amplification.