Characterization of an optical pulse slicer for gas-phase electric field measurements using field-induced second harmonic generation

Abstract

This work describes the characterization of an optical pulse-slicer for performing electric field measurements using the Electric Field Induced Second Harmonic generation (or E-FISH) method. This laser-based diagnostic generally favors ultrashort (sub-nanosecond) pulses, given their intrinsically higher intensities and superior measurement time resolution. However, such laser systems can often prove inaccessible due to their high costs. Our response to this problem is to develop a Pockels-cell-based pulse slicing scheme, compatible with the more affordable and ubiquitous class of nanosecond laser sources. Using such a slicer, we demonstrate the ability to slice a 35 mJ, 20 ns (FWHM), 1064 nm pulse from a conventional Nd:YAG laser down to about 3 ns (FWHM) with an energy of 2 mJ . These shorter pulses are in turn used to make electric field measurements in a pulsed electrostatic field (at 5 bar) using E-FISH . In agreement with previous studies, measurements performed with these sliced pulses not only have the expected benefit of improving the time resolution of the field measurement, but also reduce the possibility of laser-plasma interactions due to the lower laser pulse energy required. The current pulse slicer incorporates an off-optimum design Pockels cell, which limits the minimum pulse width and maximum energy that may be realized. It is anticipated that higher energies and a reduction in the pulse width to around 100 ps may be achieved with further optimization, and could present a cost-effective approach to extending the applicability of the E-FISH method.