Spectral analysis of solid and gas target laser-produced plasma water-window sources

Laser-produced plasma (LPP) is being considered as a compact x-ray microscopy light source in the water-window (WW) region (2.3 -- 4.4nm). Nitrogen emits strongly in the WW with distinct emission lines Ly-alpha (2.48nm) and He-alpha (2.88nm). In order to realize nitrogen LPP as a WW source for microscopy it must be optimized by target and laser parameters for efficiency and low debris production.;We investigated the spectral features of laser-produced plasma from BN and nitrogen gas-jet target in the WW region. Boron-nitride (BN) plasma is formed by focusing Q-switched Nd:YAG laser pulses operating at the fundamental wavelength (1064nm), second harmonic (532nm), and third harmonic (266nm). The plasma emission in the WW is analyzed using a grazing-incidence spectrograph and filtered photodiodes. It has been found that laser wavelength as well as laser intensity has a strong effect on emission line intensity, with 1064nm producing stronger emission at a given laser intensity.;We developed a nitrogen gas-jet for use as a debris-free LPP target and details are presented. Nomarski interferometry is used to characterize the jet for different backing pressures and at different times in the jet evolution. It is found that steady state flow is reached at ∼2.0ms, allowing for short duration gas puffs to be used for LPP targets. Emission spectra for LPP formed in different positions in the gas-jet are analyzed. Spectral intensity decreases as the LPP is formed further from the nozzle exit. Gas-jet targets generate higher spectral purity compared to BN target LPP. Details of WW emission features at various locations of gas jet are also presented.