Single-shot in situ pulse-duration measurement using plasma grating

Abstract

Accurate measurement of the pulse duration of ultrashort, ultra-intense laser pulses at focus is essential for strong-field science. Most existing diagnostics, however, cannot allow direct in situ measurement in the focal region because of damage-threshold limits and unavoidable spatial averaging. We present a direct single-shot far-field diagnostic based on a plasma grating. In this method, the pulse duration is encoded in the axial length of an interference-written plasma grating and retrieved from the corresponding Bragg-diffraction signal. Comparison with near-field (pre-focus) autocorrelator measurements and far-field (at-focus) scanning measurements confirms single-shot pulse-duration retrieval in the focal region over 35-130 fs, and the method remains effective at a peak intensity of $\sim 10^{16}{\rm W/cm^2}$. In principle, the measurable range can be extended to 15-300 fs and to higher peak intensities. The method is insensitive to the laser central wavelength and offers a practical approach to far-field diagnostics in high-power laser systems.

Figures (6)

• Figure 1: (a) Schematic diagram of the principle for measuring far-field laser pulse duration using holographic plasma grating. (b) Schematic of experimental setup.
• Figure 2: Calibration curves between the pulse duration of the signal pump and the resulting plasma-grating length; different colors and symbols correspond to different pulse energies. 'Chirp' indicates that the pulse duration is varied by adding dispersion, whereas 'no chirp' indicates that the Fourier-transform-limited pulse duration is varied.
• Figure 3: (a) Measured pulse duration as a function of compressor grating displacement. (b1)--(d1) Diffraction patterns recorded at compressor grating positions of $-0.04$mm, 0mm, and 0.04mm, respectively. (b2)--(d2) Corresponding temporal waveforms obtained from near-field autocorrelator measurements (blue curves) and plasma-grating diffraction analysis (orange curves) at the same three positions.
• Figure 4: Comparison of far-field temporal profiles obtained by scanning reconstruction and single-shot measurement for: (a) 50 mm-aperture incident laser beam. (b) 20 mm-aperture incident laser beam. (c)--(d) Simulated $x/t$ distributions after beam reduction with 50 mm and 20 mm apertures, respectively. (e) Simulated far-field temporal traces at $x=0$ for the two aperture sizes.
• Figure 5: (a) Pulse-duration calibration curves calculated at multiple pulse energies. (b) Experimental results obtained by varying the pulse energy at a fixed compressor setting, showing the retrieved far-field temporal profiles.