Vladimir E. Levashov

High throughput and resolution compact spectrograph for the 124–250 Å range based on MoSi2-Si sliced multilayer grating

Abstract Reflection sliced multilayer gratings with 4900 grooves/mm and number of periods N =500 have been produced by sputter-slice technique. Spectra of laser produced plasma of aluminum in the range of 124–250 A have been recorded with a spectral resolution of about 300 in the first order. Comparison with a high resolution spectrum obtained with a conventional spectrograph and theoretical calculations of the diffraction efficiency is given.

Broadband normal-incidence aperiodic multilayer mirrors for soft X-ray dispersive spectroscopy: theory and implementation

Aperiodic multilayer structures (MSs) show promise as broadband soft X-ray mirrors for stigmatic diffraction spectroscopic instruments. We have derived aperiodic MSs optimized for maximum uniform normal-incidence reflectivity throughout a prescribed wavelength range, e.g., 130 - 190 Å (R=24 %), 125 - 250 Å (16 %), etc. Each of these aperiodic MSs exhibits an unparalleled integral reflectivity which substantially exceeds that of any periodic multilayer mirror pertaining to the corresponding wavelength range. Several Mo/Si aperiodic MSs were synthesized by magnetron sputtering on concave substrates to exhibit a relatively uniform reflectivity of (15 - 11)% in the 125 - 250 Å range, close to the theoretical predictions. These multilayers served as the focusing elements of high-transmission stigmatic transmission grating spectrograph with a plate scale of 20 or 4 Å/mm. The spectrograph was employed to investigate the laser plasma - gas jet interaction and characterize the Xe gas-jet laser-plasma XUV radiation source simultaneously with spatial and spectral resolution in the wavelength range above 124 Å. We have theoretically explored into the reflection of extremely short X-ray pulses by MSs. Special-design aperiodic MSs were shown to possess the unrivaled capacity to reflect few-cycle X-ray pulses ranging into the attoseconds. Aperiodic MSs have been calculated that are capable of reflecting pulses which comprise only three wave periods of an X-ray electromagnetic wave.

Synthesis and measurement of OsSi multilayer mirrors optimized for the wavelength 380 Å

Abstract Flat and spherical OsSi multilayer mirrors were synthesized and studied. Measured normal incidence reflectivity was 20% at the wavelength λ = 380 A . The effect of impurities in silicon layers on the multilayer reflectivity in ultra soft X-ray region is discussed.

Interaction of a pulsed gas target with Nd-laser radiation and laser-produced plasma

A spectroscopic investigation was made of a debris-free soft X-ray radiation source driven by the pulses of a solid-state laser (0.4 J, 6 ns, 1.08 microns) focused in a pulsed xenon jet. Source images at a wavelength of 180 Å were obtained using a concave soft X-ray multilayer mirror. To obtain space-resolved source emission spectra above 125 Å, advantage was taken of a stigmatic high-transmission broadband diffraction spectrograph. The spectrograph comprised a large-aperture transmission diffraction grating (1000 or 5000 lines/mm) and a novel aperiodic focusing normal-incidence multilayer mirror possessing a uniform reflectivity in the 125 -250 Å range. The yield of soft X-ray radiation was determined with the aid of a fast absolute-calibrated X-ray AXUV-5 photodiode. The photoabsorption in the peripheral gas-jet regions was found to play a significant role in the soft X-ray yield. Numerical model simulations were performed to elucidate the plasma dynamics. The soft X-ray spectrograph was also employed to study the interaction of the pulsed gas jet with the incident stream of the plasma produced by laser irradiation of a ~1-cm distant solid target. The soft X-ray spectra arising from the interaction were attributed to the charge exchange of multiply charged plasma ions with gas jet atoms.

Reflectivity Measurements Of Multilayer X-Ray Mirrors At Normal Incidence

Evaporated and sputtered multilayer mirrors consisting of the layers Ti-Si, Nb-Si, Mo-Si and Ti-Be for the wavelength range λ = 30-35 nm are synthesized on flat and spherical substrates. Preliminary measurements are carried out at sliding incidence for λ = 0.154 nm (CuKa∝ ) and for the range λ = 10-21 nm. To measure the reflectivity under normal incidence for the wavelengths range λ ~30-35 nm an experimental method of studying point X-ray source image is developed. Plasma from the focused laser beam at the surface of sulphur is used as an X-ray source. This source and its image produced by multilayer spherical mirror are studied simultaneously with XUV spectrograph of spatial resolution. The comparison of the spectra of the source, which contains many lines and its image, enables one to find the spectral dependence of mirror reflectivity at nearly normal incidence (for incidence angle up to 0.1° ) . Another facility was used for flat multilayer reflectivity measurement at λ~10 - 21 nm Experimental reflectivities in this range are up to 51 %.

Thin-film optical constants and multilayer mirror reflectivity in ultrasoft x-ray range

Optical constants of Si, C, Mo, and Nb thin films as well as of fused quartz and float glass substrates have been determined experimentally in the (lambda) approximately equals 80 - 190 angstrom wavelength range. The dependence of optical constants on film thickness and film production technology is demonstrated. The factors influencing substance permittivity in the soft x-ray range are discussed. It is discovered that the main of them is the presence of impurities introduced into the film during its deposition. The chemical composition of multilayer Mo-Si x-ray mirrors is studied. It is shown that if O, N, and Ar impurities in Si films are taken into account, the available experimental data on the reflectivity and resolution of Mo-Si mirrors in the soft x-ray range can be described quantitatively.

Synthesis and measurement of Os-Si multilayer mirrors optimized for the wavelength 380 Å

Flat and spherical Os - Si multilayer mirrors were synthesized and studied. Measured normal incidence reflectivity was 20% at the wavelength lambda equals 380 angstrom. The effect of impurities in silicon layers on the multilayer reflectivity in the ultrasoft x-ray region is discussed.