Enhanced diagnostics of radiating relativistic singularities and BISER by nonlinear post-compression of optical probe pulse

Abstract

The enhancement of the resolution of pump-probe optical diagnostics for ultrafast processes by compressing the probe pulse duration using the CafCA approach [1] is considered on an example of the BISER soft-X-ray generation [2] with the J-KAREN-P laser [3].

In-vacuum post-compression of optical probe pulse for relativistic plasma diagnostics

“…Dependence of the probe duration (FWHM) on the estimated probe energy is displayed on Figures 5(b) and 5(c). There was a strong correlation observed at low pulse energies, where the compression was nearly perfect (compare with the ideal compression estimated using [33,34] , open circles). At higher energies, there was a complex dependence due to interplay of probe energy fluctuation and imperfect compression.…”

“…Nevertheless, the shortest probe pulses were compressed down to τ F W HM = 18 fs and τ Ef f = 30 fs, Figure 4(b). For this pulse shape with relatively few low-intensity satellite pulses, the main parameter determining resolution is the Full Width at Half Maximum [19,34] ; thus, the temporal blur with this probe pulse was reduced ∼ 2.6 times compared to the original best 46 fs probe duration.…”

“…If there were distortions, we would have seen them as an intensity pattern on the plasma-free Schlieren image. The spatial resolution estimated from the 11b) of [33] (c) Probe pulse duration dependence on the estimated probe energy for all studied laser modes (solid circles), and estimated [33,34] smallest self-emission spots was 1.4 × 1.7 µm.…”

“…After propagating through the two lenses, the laser pulse achieved a fluence of ∼ 100 − 1000 mJ/cm 2 (depending on the pulse energy), which was sufficient to drive the nonlinear processes required to achieve spectral broadening within a few mm of fused silica (FS) [34] . The laser pulse propagated through a sequence of 1, 2, 3, and 5 mm thick, plane-parallel FS plates set at the Brewster's angle (angle of incidence 55.6 • ), which created a 14 mm long beam path inside the FS material.…”

“…thin glass, crystal or plastic plates [27][28][29][30] ) proposed originally as Thin Film Compression by Prof. G. Mourou [31] in 2014. The method implementing a solid nonlinear medium for SPM after the main laser compressor is called Compression after Compressor Approach (CafCA) [32][33][34] . Gases have very small nonlinearity coefficients, thus requiring intense focused pulses propagating through long (tens of cm or even meters) fibers to achieve significant SPM-induced spectral broadening.…”