Stability of liquid-nitrogen-jet laser-plasma targets

Abstract

Microscopic jets of cryogenic substances such as liquid nitrogen are important regenerative high-density targets for high-repetition rate, high-brightness laser-plasma soft x-ray sources. When operated in vacuum such liquid jets exhibit several non-classical instabilities that negatively influence the x-ray source's spatial and temporal stability, yield, and brightness, parameters that all are important for applications such as water-window microscopy. In the present paper, we investigate liquid-nitrogen jets with a flash-illumination imaging system that allows for a quantitative stability analysis with high spatial and temporal resolution. Direct and indirect consequences of evaporation are identified as the key reasons for the observed instabilities. Operating the jets in an approximately 100 mbar ambient atmosphere counteracts the effects of evaporation and produces highly stable liquid nitrogen jets. For operation in vacuum, which is necessary for the laser plasmas, we improve the stability by introducing an external radiative heating element. The method significantly extends the distance from the nozzle that can be used for liquid-jet laser plasmas, which is of importance for high-average-power applications. Finally, we show that laser-plasma operation with the heating-element-stabilized jet shows improved short-term and long-term temporal stability in its water-window x-ray emission.

Laboratory cryo x-ray microscopy for 3D cell imaging

“…Here we have integrated the radiation heating stabilization of ref. 20 in the microscope as well as a flash-imaging system allowing the continuous monitoring of the jet with ~5 µm spatial resolution and 4 ns temporal resolution. With these means the laser-plasma can be moved further away from the nozzle orifice and thereby create less disturbance to the jet and a more stable source emission.…”

“…The nitrogen pinch discharge typically operates at average line brightness of 4 × 10 9 ph/(s × mm 2 × mrad 2 × line) at the λ = 2.88 nm line 18 , while the laser plasmas have demonstrated reliable operation at 4 × 10 10 ph/(s × mm 2 × mrad 2 × line) at the λ = 2.48 nm using liquid-nitrogen-jet target 19 . Martz et al 17 demonstrated that this source could produce > 1.5 × 10 12 ph/(s × mm 2 × mrad 2 × line) and we have recently stabilized the liquid jet to allow for long-term operation at these brightness levels 20 . The fabrication of normal-incidence condenser optics has reached a new level of perfection the last few years, typically increasing the average reflectivity from 0.6% to over 4.5%.…”

“…f. Lasertechnik, FHG Aachen) typically operated at 80–100 W onto a 30 µm diameter 40–60 m/s liquid nitrogen jet 17 , 19 . The stability of the jet is recently improved by a radiative heating arrangement 20 . In parallel, the jet position is continuously camera-monitored with an integrated flash-illumination system consisting of a fluorescent dye excited by a 4 ns, λ = 532 nm, 4 W, 20 Hz Nd:YAG laser providing ~5 µm spatial resolution.…”

Quantitative conversion of biomass in giant DNA virus infection

“…All X-ray imaging was performed using the Stockholm laboratory X-ray microscope, previously described in Refs. 32 , 33 , which operates in the water window. Recent improvements to the microscope have resulted in increased X-ray flux and more stable and reliable operation 32 , thus allowing longer and more complex studies of biological samples.…”

Biological Laboratory X-ray Microscopy

“…The system now allows, for the first time, extensive studies of relevant biological samples, including 3D cryo-tomography [1]. In brief, the major upgrades to the setup consist of an improved liquid jet stability by introducing a radiative heating element that counteracts initial freezing as the jet is ejected into vacuum [2], and a new condenser mirror with a factor >7 higher reflectivity at 2.48 nm.…”