Laser-plasma source of soft x-ray and extreme ultraviolet radiation for high precision reflectometry.

Abstract

The paper presents the results of developing a laser-plasma source (LPS) for soft x-ray and extreme ultraviolet radiation intended for high-accuracy laboratory reflectometry. The design of key components of the LPS is described in detail. Plasma excitation is achieved using focused laser pulses with the following parameters: wavelength-1064 nm, pulse energy-800 mJ, duration-5 ns, frequency-10 Hz, divergence <5 mrad, impinging on a rotating solid target at an angle of 45° relative to normal incidence. To protect the optical input and monochromator optics from contamination by target debris, the vacuum chamber is equipped with magneto-gas-dynamic units. The source size measured as full width at half maximum (FWHM) was ∼56 μm, while the target surface oscillation amplitude during rotation was less than 5 μm. The operational wavelength range of the source spans 3-30 nm, within which spectral power density varies between 1 and 3 × 1013 photons/(0.1 nm × pulse × sr). The temporal stability of the signal over a 1-h observation period shows a standard deviation root-mean-square of 0.52%. The target lifetime is about one year.