Abstract
The spatial-intensity profile of light reflected during the interaction of an intense laser pulse with a microstructured target is investigated experimentally and the potential to apply this as a diagnostic of the interaction physics is explored numerically. Diffraction and speckle patterns are measured in the specularly reflected light in the cases of targets with regular groove and needle-like structures, respectively, highlighting the potential to use this as a diagnostic of the evolving plasma surface. It is shown, via ray-tracing and numerical modelling, that for a laser focal spot diameter smaller than the periodicity of the target structure, the reflected light patterns can potentially be used to diagnose the degree of plasma expansion, and by extension the local plasma temperature, at the focus of the intense laser light. The reflected patterns could also be used to diagnose the size of the laser focal spot during a high-intensity interaction when using a regular structure with known spacing.
Highlights
The interaction of high-intensity laser pulses with solid targets results in the production of compact high energy ion sources[1,2,3], as well as X-ray[4], THz[5], EMP[6, 7] and high harmonic generation[8, 9]
The temperature of beams of electrons, ions or photons generated in intense laser–solid interactions is typically diagnosed by spectral measurements using spectrometers[16], stacked dosimetry film[17] or nuclear activation[18]
It remains difficult to diagnose the temperature of the plasma within the spatially localized region of the laser focus, near the critical density, and at a time limited to the laser pulse interaction time
Summary
The interaction of high-intensity laser pulses with solid targets results in the production of compact high energy ion sources[1,2,3], as well as X-ray[4], THz[5], EMP[6, 7] and high harmonic generation[8, 9]. We measure the spatial-intensity profile of light reflected during the interaction of intense laser pulses with microstructured targets (which are being investigated as a route to increase laser energy absorption[25, 26]). Patterns in both the reflected laser light at the fundamental harmonic and second harmonic light generated at the critical density surface[27] are characterized experimentally. The influence of the size of the laser focus relative to the target structures on the reflected light patterns is investigated, highlighting the potential to use this approach to diagnose the laser focus on high-intensity laser shots
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