Microdroplet target synthesis for kilohertz ultrafast lasers*

The difficulty of finding suitable solid targets for high rep-rate (up to kHz) lasers has been one of the major setbacks for the applicability of solid-target laser interaction experiments. In this work, we have developed a method for producing spatially stable micron-scale liquid targets of flexible shapes at kHz repetition rate for use in air and vacuum, by perturbing 5 and 30-$\mu $m diameter streams with fs laser pulses and monitoring the temporal development of the perturbation. Using water, we have produced features such as 2.1-$\mu $m diameter droplet and 1.3-$\mu $m diameter neck with less than $\pm $0.3-$\mu $m shot-to-shot variation, with prospects for further reduction in size and variability. The use of such micron-scale targets can be expected to prevent conductive heat dissipation, thus increasing the interaction temperature by more than two orders, enhance field strength for ion acceleration and allow spatially-deterministic laser-cluster experiments.