Characterization of a 100 micrometer-scale cryogenically cooled gas jet for near-critical density laser-plasma experiments

In this work, we present the design and characterization of a thin, high density pulsed gas jet for use in the study of near critical laser plasma interactions with ultrashort Ti:sapphire laser pulses. The gas jet uses a range of capillary nozzles with inner diameters between 50 and 150 μm and is operated in the sonic regime. Cryogenic cooling of the gas valve body to -160°C provides the necessary density enhancement for reaching overcritical plasma densities at λ = 800 nm (Ncr ≈ 1.7 × 1021 cm-3) using hydrogen gas at jet backing pressures below 1000 psi. Under certain conditions, fast expansion of the gas from a nozzle can lead to formation of clusters; here, we use our previously demonstrated all-optical method to estimate the cluster mean size and density. For the jets studied here, we find that cluster formation only begins at distances from the nozzle exit greater than a few times the nozzle orifice diameter.