S. Montant

Piston measurement by quadriwave lateral shearing interferometry

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.

Nondestructive method for characterization of the second-order nonlinear profile and charge distribution in thermally poled fused silica.

Noncollinear frequency conversion of two femtosecond pulses is used to characterize the nonlinear profile induced in thermally poled fused silica. This technique permits one to deduce the nonlinear profile and the charge distribution induced by the poling treatment. These data and the current that passes through the sample during the poling are consistent with the occurrence of a built-in electric field associated with the diffusion of two ionic species.

Multi-petawatt high-energy laser project on the LIL facility in Aquitaine

A Multi-Petawatt High-Engergy laser coupled to the LIL (MPWHE-LIL) is under construction in the Aquitaine Region in France. This facility will be open to academic community. Nd:glass laser chain and Chirped Pulse Amplification (CPA)technique makes possible to deliver high energy. Optical Parametric Chirped Pulse Amplification (OPCPA) for pre-amplification and new compression scheme will be implemented. The MPWHE-LIL will deliver output energy of 3.6 kJ in 500 fs on target corresponding to more than 7 PW. The PW laser facility linked to UV-60kJ-ns beam from LIL, will give new scientific research opportunities.

Picosecond pulses of variable duration from a high-power passively mode-locked Nd:YVO 4 laser free of spatial hole burning

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.

Light-controlled erasure of induced χ(2) in thermally poled glasses

We demonstrate that the induced second order nonlinearity χ(2) generated in thermal poled doped borosilicate glasses can be erased by a prolonged exposure to near IR laser radiation. The evolution of the second harmonic signal with respect to laser time exposure, intensity and wavelength is reported. The IR laser radiation induced relaxation of the χ(2) is mainly related to two-photon absorption of the glass. The nonexponential time dependence of the second harmonic signal agrees with a simple model involving diffusion of photoexcited carriers. The reversible erasure process is also observed when the sample is exposed to near ultraviolet laser radiation.

Tunable 1.6–2 μm near infrared few-cycle pulse generation by filamentation

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.

Laser-induced quasi-phase matching in thermally poled glasses

Quasi phase matching was induced within a few minutes by optical means in a thermally poled glass sample. The spatial modulation of chi((2)) that was induced by two-photon absorption of the sample subjected to an intense sinusoidal pump intensity pattern resulted in a chi((2)) grating. The second-harmonic generation produced by a probe beam was diffracted in specific directions by this chi((2)) grating, thus providing a way to monitor its inscription inside the glass. This chi((2)) grating is extremely stable at room temperature and in ambient laboratory conditions. During the process of inscription, a linear index grating was also induced. It was not stable, and it relaxed rapidly.

Measurement of non-instantaneous contribution to the χ(3) in different liquids using femtosecond chirped pulses

Abstract In the Born–Oppenheimer approximation and considering a Debye nuclear motion, a theoretical computation of pump–probe two-beam coupling in liquids using femtosecond chirped pulses is proposed. This technique makes it possible to specifically evidence the non-instantaneous contribution to the third-order susceptibility χ (3) . Our model, which is an extension at the femtosecond scale of the one proposed by Dogariu et al., describes the temporal evolution of the probe signal as a function of different parameters such as the linear laser chirp, the ratio between the pulse duration and the nuclear response time. Experimentally, this method is applied to characterize the non-instantaneous χ (3) contribution in transparent liquids such as CS 2 , benzene and toluene. Time resolved pump–probe coupling data using parallel and perpendicular linear polarizations fit well with the model developed. The experimental ratio R between both fast and slow non-instantaneous χ (3) XXXX and χ (3) XYYX elements of the tensor is equal to 1.33±0.01 in all the liquids studied, and is in good agreement with the expected liquid nuclear symmetry.

3D numerical model for a focal plane view in case of mosaic grating compressor for high energy CPA chain

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.

Spatial and temporal coherence characterization of a smoothed laser beam

We present a new method for measuring coherence characteristics of the speckles obtained with a smoothed laser. This technique allows us to measure both spatial transverse and temporal characteristics, of hot spots by spatial autocorrelation.