Plasma Transmission Gratings for Compression of High-Intensity Laser Pulses

The peak power of a femtosecond laser is limited by the size and damage threshold of its solid-state optical components, with the final grating of a chirped pulse amplification compressor posing a challenging bottleneck on the path to higher-power systems. Practical hundred-petawatt to exawatt lasers will require optics that draw on the higher damage tolerance of plasma to manipulate high-intensity light, but plasma is a difficult medium to control and sets stringent limits on optical performance. Here we describe the design of a compact high-power laser system that uses plasma transmission gratings—with currently achievable parameters—for chirped pulse amplification. A double compression architecture compensates for the low angular dispersion of the plasma gratings. We explore the design constraints set by available plasma parameters and use particle-in-cell simulations to examine performance at high light intensity. These simulations suggest that the meter-scale final grating for a 10-PW laser could be replaced with a 1.5-mm-diameter plasma grating, allowing compression to, for example, 22 fs with 90% efficiency and providing a path towards compact multipetawatt laser systems.

Figure 1

Schematic of a plasma-grating-based laser system using a double-CPA architecture. The final grating is formed in a plasma by two short-pulse beams. An input femtosecond pulse from an oscillator is stretched, amplified, and compressed to 1–10 ps by the first stage (solid state) compressor. Compression from 1–10 ps to 10–50 fs occurs in the second stage, where only the plasma grating sees a pulse duration shorter than 1 ps and the concomitant high intensity.

Figure 2

Design space of a plasma-transmission-grating-based compressor, showing the required distance between gratings ($b$) for the pulse bandwidth ($\mathrm{\Delta }\lambda /{\lambda }_0$) and grating Bragg angle (${\theta }_B$). The color scale indicates the distance $b$ required for every picosecond of stretched pulse duration ($\mathrm{\Delta }\tau$), and the red lines indicate the upper bound of the design envelope for an available value of $n_1$.

Figure 3

Paraxial propagation calculations of light travelling through a plasma grating. (a) An 800-nm probe (blue) propagates from left to right through a plasma grating formed by two pumps in a thin ($D=80\mu \mathrm{m}$) gas sheet (gray region). The colormap shows normalized intensity. (b) Transverse profile of the diffracted beam. (c) Variation of efficiency and first-order diffraction angle with probe wavelength, showing that numerically calculated solutions closely follow the analytic theory (lines). (d) Initial and compressed pulse durations of a pulse after propagation through 100 mm of free space and the plasma grating.

Figure 4

Paraxial propagation solver calculations of grating efficiency in the presence of deviations from the ideal grating shape. (a) First-order diffraction efficiency ($\eta$) as a function of grating strength for (1) rectangular grating profiles with constant $D=100{\lambda }_0$ and varied $n_1$ (red circles); (2) rectangular profiles with constant $n_1=0.005$ and varied $D$ (blue squares); and (3) trapezoidal profiles with varied $n_1$ (green triangles), as illustrated in (c). (b) Grating efficiency for the varied functional form of the pump intensity to index modulation map: $\delta n\propto I^p$ with $\mathrm{\Phi }$ calculated based on the component $n_1$. (c) Rectangular and trapezoidal grating profiles. (d) Transverse index modulations of different orders, corresponding to data in (b).

Figure 5

PIC simulations of a probe laser crossing a plasma volume transmission grating. (a)–(d) The magnetic field amplitude (blue) and plasma density (gray) of a probe laser crossing an ion-ponderomotive grating formed by two pump lasers in a fully ionized hydrogen plasma, with (d) the probe shown at three different times. The red boxes mark the locations of the enlarged images of the probe phase fronts (a) before, (b) during, and (c) after the propagation of the probe through the grating. (f),(e) The intensity envelopes of the separated (e) diffracted and (f) zeroth-order probes after the grating. (h) The intensity envelope in time of the diffracted probe. (g) Diffraction efficiency for an infinitely wide 30-fs probe as a function of intensity.