Degradation of femtosecond petawatt laser beams: Spatio-temporal/spectral coupling induced by wavefront errors of compression gratings

Abstract

Recently, several petawatt (PW, 1015 W) lasers with pulse duration of ∼20–30 fs have been introduced throughout the world, pushing the upper limit on laser peak power. However, besides well-known spatio-temporal coupling effects, such as residual spatial/angular chirps and pulsefront tilt/curvature, the spatio-temporal/spectral coupling in compressors induced by wavefront errors of gratings, which could dramatically distort ultra-intense pulses, has been neglected. In this work, for the first time we analyzed this phenomenon and the peak power/intensity degradation induced by it. Our results suggest that the actual performance of femtosecond PW lasers may be worse than previously estimated.

Spatio-temporal structure of a petawatt femtosecond laser beam

“…These measurements provide very fine information on the beam properties and the laser system operation. In particular, we have observed small spatio-spectral modulations that have recently been predicted [21] to result from defects of optics within the grating compressor, as well as effects resulting from the temporal dynamics of the gain during the amplification of the chirped laser pulses. As ultrahigh intensity laser-plasma interaction experiments put more and more stringent requirements on the control of the laser parameters, such information could be used in the future for extremely fine optimization of high-power laser systems.…”

“…A simple interpretation of this feature has been recently analyzed in detail in [21]. In between the first and the last gratings of the compressor the laser beam is laterally chirped, i.e.…”

Wavefront degradation of a 200 TW laser from heat-induced deformation of in-vacuum compressor gratings

“…We could observe a broadening of the second harmonic trace as the deformation of the grating surface increased. In principle, spatio-temporal couplings from the deformed gratings could cause a change in the compressed laser pulse length [8]. However, due to the complexity of the measured signal, we cannot conclude that this observed broadening is solely related to an increase of the pulse duration.…”

“…Thus, the reflected laser wavefront will be deformed. Moreover, as the beam is spatially dispersed between the gratings, the changes of the wavefront can couple into the temporal properties of the pulse and be detrimental to the overall compression [8]. Eventually, the heat can lead to catastrophic damage of the optic, e.g.…”

Characterizing extreme laser intensities by ponderomotive acceleration of protons from rarified gas

“…Typically, intensity characterization is based on separately measured spatial (focal spot) and temporal (pulse duration) characteristics at low pulse energy, then extrapolating these results to full laser power. However, the laser intensity given by this approach may significantly differ from the actual value achieved in experiment because of wavefront and spectral phase distortions in the laser stretcher-amplifier-compressor chain which can degrade the focal spot and temporal pulse shape mainly due to chromatic aberrations and frequency chirp [25][26][27]. The other indirect approach, which measures a part of the beam that 'leaking-through' a mirror in the interaction chamber, will not account for the final focusing optic, which is the main source of aberrations, particularly for short-focal length parabolic mirrors.…”