Using the spectral interferometry technique, we measured subpicosecond time-resolved pre-plasma scale lengths and early expansion (<12 ps) of the plasma produced by a high intensity (6 × 1018 W/cm2) pulse with high contrast (109). We measured pre-plasma scale lengths in the range of 3–20 nm, before the arrival of the peak of the femtosecond pulse. This measurement plays a crucial role in understanding the mechanism of laser coupling its energy to hot electrons and is hence important for laser-driven ion acceleration and the fast ignition approach to fusion.
Ultrahigh intensity contrast, short pulse laser-solid interactions offer an attractive platform for investigating high-energy density matter, particularly in the context of structured and ultra-thin targets that form hot, dense plasma conditions. Harmonic generation can improve the contrast of laser pulses by several orders of magnitude. In this study, we present the characterization of extreme contrast, relativistic intensity second-harmonic (SH) pulses at 400 nm, using the self-diffraction frequency-resolved optical gating (SDFROG)
technique. The 400 nm pulses were generated at various input intensities using potassium dihydrogen phosphate (KDP) and lithium triborate (LBO) crystals. Our observations reveal the presence of spectral broadening,
pulse compression, and complex structures at higher input intensities. We see that extreme contrast, a few tens of femtosecond pulses can have multiple ’prepulses’ at the 100s femtosecond scale as large as ten percent of the peak value. These can preionize a solid significantly and may influence the interaction. Simulations based on nonlinear pulse propagation equations reinforce our findings.
Ultrahigh intensity contrast, short pulse laser-solid interactions offer an attractive platform for investigating high-energy density matter, particularly in the context of structured and ultra-thin targets that form hot, dense plasma conditions. Harmonic generation can improve the contrast of laser pulses by several orders of magnitude. In this study, we present the characterization of extreme contrast, relativistic intensity second-harmonic (SH) pulses at 400 nm, using the self-diffraction frequency-resolved optical gating (SDFROG)
technique. The 400 nm pulses were generated at various input intensities using potassium dihydrogen phosphate (KDP) and lithium triborate (LBO) crystals. Our observations reveal the presence of spectral broadening,
pulse compression, and complex structures at higher input intensities. We see that extreme contrast, a few tens of femtosecond pulses can have multiple ’prepulses’ at the 100s femtosecond scale as large as ten percent of the peak value. These can preionize a solid significantly and may influence the interaction. Simulations based on nonlinear pulse propagation equations reinforce our findings.
Experimental measurements of spatially resolved ultrafast dynamics of the critical surface in ultra-intense laser–solid interactions are essential for a proper understanding of the physical mechanism of the interaction. Resolving ultrafast motion at both the relevant length scales (micrometers) and timescales (femtoseconds) simultaneously has been a challenging task. Here, we demonstrate a novel technique for mapping the spatiotemporal dynamics of hot and solid dense plasma created by high contrast (picosecond contrast ∼10−9) femtosecond relativistic intensity laser pulses. This pump–probe Doppler spectrometry technique offers hundreds of femtosecond temporal resolution, together with a few micrometer spatial resolution across the transverse profile of the plasma. We present the evolution of the plasma surface critical for the probe pulse at the target front as well as the rear. Early time measurements ([Formula: see text] 5 ps) using this technique provide very important information about shock wave generation and propagation and the state of the target rear.
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