Occurrence of half integral diffraction orders in XUV-soft X-ray spectra using a free-standing transmission grating

Effect of distortion in free-standing gold microstructure transmission gratings resulting in appearance of half integral orders in X-ray spectra is reported. XUV-soft X-ray spectra of moderate Z plasmas produced by 2GW, 4 ns/28 ns (FWHM), Nd: glass laser pulses showed low intensity peaks corresponding to half integral orders (up to m=7/2), in addition to the normal diffraction orders. These are explained to occur due to a symmetric distortion in the part of grating structure used, which leads to a periodicity in twice the grating period. Experimentally measured intensity ratios of different diffraction orders are consistent with the theoretical values calculated for the grating structure observed under a scanning electron microscope. This distortion, however, does not affect the spectral resolution of 0.6Å (in the first order) as expected and measured for the undistorted part of the grating structure.