Complex spatiotemporal coupling distortion pre-compensation with double-compressors for an ultra-intense femtosecond laser

(3+1)-dimensional Pearcey-Gaussian wave packet with arbitrary velocity driven by flying focus

The group velocity (GV) modulation of space-time wave packets (STWPs) along the transverse and longitudinal directions in free space is constrained by various factors. To surmount this limitation, a technique called "flying focus" has been developed, which enables the generation of laser pulses with dynamic focal points that can propagate at arbitrary velocities independent of GV. In this Letter, we propose a (3+1)-dimensional Pearcey-Gauss wave packet based on the "flying focus" technique, which exhibits superluminal propagation, transverse focus oscillation, and longitudinal periodic autofocusing. By selecting appropriate parameters, we can flexibly manipulate the position, the size, and the number of focal points- or make the wave packet follow a desired trajectory. This work may pave the way for the advancement of space-time structured light fields.

Detrimental effects of period-chirped gratings in pulse compressors

We present a comprehensive simulative and experimental investigation of how period-chirped pulse compression gratings affect the compressed pulses. A specifically developed ray-tracing tool was used for the simulative investigations. It is shown that the chirp creates a characteristic spatio-spectral error pattern, which leads to a degradation of the beam quality and an increase of the pulse duration. The experimental investigations, for which both a narrow-bandwidth continuous-wave and a pulsed laser beam were guided through a Treacy-compressor comprised of period-chirped gratings, confirm the simulation results and present methods on how to identify the chirp's characteristic error pattern in practice.

Simulating spatiotemporal dynamics of ultra-intense ultrashort lasers through imperfect grating compressors

The upcoming 100 Petawatt (PW) laser is going to provide a possibility to experimentally study vacuum physics. Pulse compression and beam focusing, which can be affected by the spatiotemporal coupling, are two key processes of generating a 100 PW laser and then determine whether its physical objective can be achieved or not. We improved our previous model of the spatiotemporal coupling where only the grating wavefront error and the output optical field of a common compressor configuration were included, and in the improved model, the grating amplitude modulation, the spatio-spectral clipping, and the optical field inside the compressor were added. By using it, we theoretically investigated the spatiotemporal dynamics of an ultra-intense ultrashort laser passing through an imperfect grating compressor for different cases, especially the spatio-temporal/spectral coupling and the on-target intensity variation induced by the phase and amplitude modulation at different grating positions in two different compressor configurations. This study is of importance for both engineering development and physical application of the upcoming Exawatt-class laser.

Propagation of ultrashort laser fields with spatiotemporal couplings using Gabor's Gaussian complex decomposition

In ultra-intense chirped pulse amplification laser systems, pulses of ultrashort duration and high energy are generated using large spectral bandwidths and large beam diameters. Hence, the spatiotemporal couplings of the laser field can become significant and affect the field structure. The propagation of such pulses is simulated in this work using a code developed in-house, based on Gabor's decomposition of the initial complex field into Fourier transform limited Gaussian pulse beam terms. Subsequently, the analysis of the temporal, spatial, and angular chirp, as well as pulse front tilt couplings for a super-Gaussian beam of 25 fs duration allows quantification of their signatures in the near field and focus.

Survey of spatio-temporal couplings throughout high-power ultrashort lasers

The investigation of spatio-temporal couplings (STCs) of broadband light beams is becoming a key topic for the optimization as well as applications of ultrashort laser systems. This calls for accurate measurements of STCs. Yet, it is only recently that such complete spatio-temporal or spatio-spectral characterization has become possible, and it has so far mostly been implemented at the output of the laser systems, where experiments take place. In this survey, we present for the first time STC measurements at different stages of a collection of high-power ultrashort laser systems, all based on the chirped-pulse amplification (CPA) technique, but with very different output characteristics. This measurement campaign reveals spatio-temporal effects with various sources, and motivates the expanded use of STC characterization throughout CPA laser chains, as well as in a wider range of types of ultrafast laser systems. In this way knowledge will be gained not only about potential defects, but also about the fundamental dynamics and operating regimes of advanced ultrashort laser systems.

Single-shot spatiotemporal characterization of a multi-PW laser using a multispectral wavefront sensing method

The single-shot spatiotemporal characterization of an ultrahigh intensity laser pulse was performed using a multispectral wavefront sensor. For the measurement of the spatio-spectral electric field, a femtosecond laser pulse was spectrally modulated and separated by a Fabry-Perot etalon coupled with a grating pair, and its spatio-spectral electric field was measured with a wavefront sensor. The spatiotemporal electric field was reconstructed from the measured spatio-spectral electric field of a multi-PW laser pulse. We found that the spatiotemporal distortion could reduce the focused laser intensity by 15%, compared to the case of a diffraction-limited and transform-limited laser pulse.

Simulating an ultra-broadband concept for Exawatt-class lasers

The rapid development of the optical-cycle-level ultra-fast laser technologies may break through the bottleneck of the traditional ultra-intense laser [i.e., Petawatt (PW, 10¹⁵ W) laser currently] and enable the generation of even higher peak-power/intensity lasers. Herein, we simulate an ultra-broadband concept for the realization of an Exawatt-class (EW, 10¹⁸ W) high peak-power laser, where the wide-angle non-collinear optical parametric chirped-pulse amplification (WNOPCPA) is combined with the thin-plate post-compression. A frequency-chirped carrier-envelope-phase stable super-continuum laser is amplified to high-energy in WNOPCPA by pumping with two pump-beamlets and injected into the thin-plate post-compression to generate a sub-optical-cycle high-energy laser pulse. The numerical simulation shows this hybrid concept significantly enhances the gain bandwidth in the high-energy amplifier and the spectral broadening in the post-compression. By using this concept, a study of a prototype design of a 0.5 EW system is presented, and several key challenges are also examined.

In-house beam-splitting pulse compressor for high-energy petawatt lasers

One of the most significant bottlenecks in achieving kilojoule-level high-energy petawatt (PW) to hundreds-petawatt (100PW) lasers is the requirement of as large as meter-sized gratings so as to avoid the laser-induced damage in the compressor. High-quality meter-sized gratings have so far been difficult to manufacture. This paper proposes a new in-house (intra-) beam-splitting compressor based on the property that the damage threshold of gratings depends on the pulse duration. The proposed scheme will simultaneously improve the stability, save on expensive gratings, and simplify compressor size because the split beams share the first two parallel gratings. Furthermore, as the transmitted wavefront of a glass plate can be better and more precisely controlled than the diffraction wavefront of a large grating, we propose glass plates with designed transmitted wavefront to compensate for the wavefront distortion introduced by the second and third gratings, and other in-house optics, such as the beam splitter. This simple and economical method can compensate for the space-time distortion in the compressor, and thus improve focal intensity, which otherwise cannot be compensated by a deformable mirror outside the compressor. Together with a multi-beam tiled-aperture combining scheme, the proposed novel compressor provides a new scheme for achieving high-energy PW-100PW lasers or even exawatt lasers with relatively small gratings in the future.

Description of spatio-temporal couplings from heat-induced compressor grating deformation

High average power high-intensity laser systems can suffer from a heat-induced deformation of the final compressor gratings, which introduces wavefront aberrations and spatio-temporal couplings to the pulse. Here, we use a simple numerical description, that was first introduced by Li et al. (Appl. Phys. Express, 10, 102702, 2017 and Optics Express, 26, 8453, 2018), to calculate the resulting degradation of the peak intensity and the 3-dimensional deformation of the laser pulse as a function of average power, and verify the results using experimental data. For a typical 100 TW-class laser we find that non-negligible pulse distortions can occur at an average power as low as 2.7 Watts. An open source implementation of our numerical description is available for researchers to estimate the effects of spatio-temporal couplings for their specific laser configuration.