We have numerically optimized several broadband aperiodic normal-incidence multilayer mirrors based on Sb/B4C for the 85 – 125 Å spectral domain for spectroscopy applications below the silicon L-edge (λ = 125 Å). Three multilayer mirrors were then synthesized. The designed multilayer structures were optimized for a maximum uniform reflectivity in the 90 – 100, 95 – 105 and 100 – 120 Å wavebands, respectively. All the Sb/B4C multilayer mirrors were synthesized via magnetron sputtering in argon medium. The multilayers reflection spectra were evaluated with the use of a laboratory XUV spectrograph employing a laser-plasma radiation source, the mirror under study, a transmission diffraction grating and a backside-illuminated CCD matrix. The experimentally recorded spectra were compared with the theoretical ones. Numerical calculations of aperiodic Sb/B4C multilayer structures with different layer densities are presented. Effects of lower densities and small random variations of the individual layer widths on the reflection spectra are discussed.
We present the design, calculations and simulations of high-resolution concave-VLS-grating-based soft X-ray and VUV spectrographs, as well as a plane VLS grating instrument. We have designed a normal-incidence imaging VLS grating spectrograph for a 820 – 1690 Å spectral interval and a series of grazing-incidence VLS spectrographs with imaging capabilities. The experimentally recorded spectral images of laboratory laser plasmas were obtained with the aid of a VLS spectrometer based on a concave aperiodic multilayer mirror and a plane VLS grating. Two modifications of this spectrometer were implemented with two different VLS gratings. These modifications exhibit spectral resolution of 500 and 800 over the 125 – 300 Å spectral waveband. Spatial resolution corresponds to double CCD-detector pixel size.
Our intention is to develop high-resolution stigmatic spectral imaging in the XUV (2 – 40 nm). We have designed, aligned and tested a broadband stigmatic spectrometer for a range of 12–30 nm, which makes combined use of a normalincidence multilayer mirror (MM) (in particular, a broadband aperiodic MM) and a grazing-incidence plane varied linespace (VLS) reflection grating. The concave MM produces a slightly astigmatic image of the radiation source (for instance, the entrance slit), and the VLS grating produces a set of its dispersed stigmatic spectral images. The multilayer structure determines the spectral width of the operating range, which may amount to more than an octave in wavelength (e.g. 12.5–30 nm for an aperiodic Mo/Si MM), while the VLS grating controls the spectral focal curve. The stigmatism condition is satisfied simultaneously for two wavelengths, 14 and 27 nm. In this case, the condition of non-rigorous stigmatism is fulfilled for the entire wavelength range. A LiF laser plasma spectrum was recorded in one 0.5 J laser shot. A spatial resolution of 26 μm and a spectral resolution of 900 were demonstrated in the 12.5 – 25 nm range. We also report the design of a set of flat-field spectrometers of Harada type with VLS gratings. VLS gratings were made by ebeam and interference lithography. A technique (analytical + numerical) was developed for calculating optical schemes for writing plane and concave VLS gratings with predefined line density variation.
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