11 fs, 1.5 PW laser with nonlinear pulse compression

Beam smoothing by introducing spatial dispersion for high-peak-power laser pulse compression

Post-compression can effectively further improve the peak power of laser pulses by shortening the pulse duration. Which has been investigated in various ranges of energy and central wavelength. However, the spatial intensity profile of high-peak-power laser pulses is generally inhomogeneous due to pump lasers, imperfect optical components, and dust in the optical layout. In post-compression, the B-integral is proportional to intensity, and wavefront distortions are induced in the spectral broadening stage, leading to a decrease in focusing intensity. Moreover, the beam intensity may be strongly modulated and beam inhomogeneity will be intensified in this process, causing damage to optical components and limiting the achievement of high peak power enhancement. In this study, to address these challenges, the laser pulse is first smoothed by introducing spatial dispersion using prism pairs or asymmetric four-grating compressors, and then the smoothed pulse is used for post-compression. The simulation results indicate that this method can effectively remove hot spots from laser pulses and maintain high peak power enhancement in post-compression.

Pulse fluence noise dynamics at free-space propagation

The dynamics of fluence noise of an optical pulse at free-space (e.g., vacuum) propagation has been studied. It has been shown that the fluence noise with high spatial frequency is effectively cleaned out from the primary smooth pulse either by spatial walk-off or by temporal delay at a relatively small propagation distance. This effect can be referred to as spatial and temporal self-filtering and is of major interest in ultra-high-power and ultra-short-pulse applications. The study comprises a rigorous theory and a few relevant numerical simulation examples.

Upgrading the front end of the petawatt-class PEARL laser facility

A new front-end laser system with optical synchronization of chirped femtosecond and pump pulses for the petawatt laser complex PEtawatt pARametric Laser (PEARL) has been developed. The new front-end system provides a broader femtosecond pulse spectrum, temporal shaping of the pump pulse, and a significant increase in the stability of the parametric amplification stages of the PEARL.

Small-scale fluctuations of laser beam fluence at the large B-integral in ultra-high intensity lasers

Analytical expressions for the spatial spectrum of fluence fluctuations of a laser pulse propagating in a medium with Kerr nonlinearity have been obtained. It is shown that inhomogeneities with a spatial scale much larger than the critical scale of self-focusing grow insignificantly even at large values of the B-integral. Experiments using BK7 glass and a KDP crystal as a nonlinear medium confirm the obtained theoretical results. This may be interesting for pulse post-compression, frequency doubling, and other experiments using transmission optical elements in ultra-high intensity lasers.

Laser pulse cutoff at nonlinear reflection due to Raman backscattering in plasma

A method for generating subrelativistic laser pulses with a sharp leading edge is proposed, which is based on Raman backscattering of an intense short pump pulse by a counter-propagating long low-frequency pulse propagating in a thin plasma layer. A thin plasma layer serves both to attenuate parasitic effects and to effectively reflect the central part of the pump pulse when the field amplitude exceeds the threshold value. A prepulse with a lower field amplitude passes through the plasma almost without scattering. This method works for subrelativistic laser pulses with durations up to 100 fs. The contrast of the leading edge of the laser pulse is determined by the seed pulse amplitude.

Wavefront-corrected post-compression of a 100-TW Ti:sapphire laser

We analyzed and corrected the wavefront distortion induced during the post-compression of a 100-TW Ti:Sapphire laser and achieved the intensity enhancement. In the post-compression, the spectral broadening of the laser was obtained by propagating through three 0.5 mm-thick fused silica plates and the laser pulse duration was post-compressed from 24 fs to 11 fs using a set of chirped mirrors. We measured the wavefront aberrations due to the intensity-dependent nonlinear process during the post-compression of femtosecond high-power laser pulses. By compensating for the wavefront aberrations with an adaptive optics system, the Strehl ratio of the post-compressed beam was improved from 0.37 to 0.52 and the focused intensity of the post-compressed beam could be enhanced by a factor of 1.5, while the enhancement without the wavefront correction was only a factor of 1.1 in spite of the peak-power enhancement by a factor of 1.8.

Temporal compression of high-power IR laser pulses in a KDP crystal

It is shown that a KDP crystal can be used for temporal compression of powerful pulses of the near-IR range. A method of searching for laser beam and crystal parameters suitable for compression is proposed. Temporal compression of laser pulses at a central wavelength of 1034 nm from 266 fs to 94 fs during propagation along the optical axis in a 21 cm thick KDP crystal is demonstrated experimentally.

Laser wakefield acceleration based x ray source using 225-TW and 13-fs laser pulses produced by thin film compression

We show that 13-fs laser pulses associated with 225 TW of peak power can be used to produce laser wakefield acceleration (LWFA) and generate synchrotron radiation. To achieve this, 130-TW high-power laser pulses (3.2 J, 24 fs) are efficiently compressed down to 13 fs with the thin film compression (TFC) technique using large chirped mirrors after propagation and spectral broadening through a 1-mm-thick fused silica plate. We show that the compressed 13-fs laser pulse can be properly focused even if it induces a 10% degradation of the Strehl ratio. We demonstrate the usability of such a laser beam. We observe both an increase of the electron energy and of the betatron radiation critical energy when the pulse duration is reduced to 13 fs compared with the 24-fs case.

Multiscale study of high energy attosecond pulse interaction with matter and application to proton-Boron fusion

For several decades, the interest of the scientific community in aneutronic fusion reactions such as proton-Boron fusion has grown because of potential applications in different fields. Recently, many scientific teams in the world have worked experimentally on the possibility to trigger proton-Boron fusion using intense lasers demonstrating an important renewal of interest of this field. It is now possible to generate ultra-short high intensity laser pulses at high repetition rate. These pulses also have unique properties that can be leveraged to produce proton-Boron fusion reactions. In this article, we investigate the interaction of a high energy attosecond pulse with a solid proton-Boron target and the associated ion acceleration supported by numerical simulations. We demonstrate the efficiency of single-cycle attosecond pulses in comparison to multi-cycle attosecond pulses in ion acceleration and magnetic field generation. Using these results we also propose a path to proton-Boron fusion using high energy attosecond pulses.

Sub-10 fs pulse generation by post-compression for peak-power enhancement of a 100-TW Ti:Sapphire laser

We demonstrated sub-10 fs pulse generation by the post-compression of a 100 TW Ti:Sapphire laser to enhance the peak-power. In the post-compression, the laser spectrum was widely broadened by self-phase modulation in thin fused silica plate(s), and the induced spectral phase was compensated with a set of chirped mirrors. A spatial filter stage, consisting of two cylindrical lenses and a spherical lens, was employed to reduce the intensity modulation existing in the laser beam, which effectively suppressed intensity spikes induced by self-focusing. The laser beam was post-compressed from 23 fs to 9.7 fs after propagating through a 1.5 mm fused silica plate, resulting in the peak-power enhancement by a factor of 2.1.

Enhancing the temporal contrast and peak power of femtosecond laser pulses

It is shown that a nonlinear polarization interferometer and a chirped mirror enable enhancement of the contrast of high-power laser pulses with a duration of tens and hundreds of femtoseconds by several orders of magnitude and simultaneously a several-fold reduction of their duration. Different variants of interferometers based on cubic nonlinearity in KDP and DKDP crystals are considered. The interferometer and chirped mirror parameters are optimized aimed at enhancing the peak power of the compressed pulse.