Evgenii N. Ragozin

Reflection of few-cycle x-ray pulses by aperiodic multilayer structures

We report on the numerical investigation of the reflection of extremely short (femto-and attosecond) x-ray pulses by multilayer structures (MSs). Periodic and aperiodic MSs are considered. We formulate the conditions whereby the reflection does not significantly change the pulse shape and length. The optimization of broadband aperiodic MSs from the viewpoint of the reflection of few-cycle pulses and the possibility of chirped-pulse compression are considered. It is shown that the power reflection coefficient can be appreciably higher than unity. Aperiodic MSs have been calculated which are capable of reflecting pulses comprising only three wave periods.

Reflection of atto-and femtosecond X-ray pulses from aperiodic multilayer mirror

The reflection of femto-and attosecond soft and hard X-ray pulses from multilayer structures (MSs) was investigated. The conditions are formulated under which the pulse shape and duration barely change upon reflection. The MSs are optimized for the reflection of extremely short pulses, and the possibility of compressing chirped pulses is considered. It is shown that the power reflection coefficient can be appreciably larger than unity. The aperiodic MSs capable of effectively reflecting pulses containing no more than three wave periods are calculated.

Soft X-ray flat-field VLS spectrographs

We have analysed the capabilities of flat-field spectrometers with concave VLS reflection gratings from the standpoint of spectral imaging in the soft X-ray range. Two types of such instruments are shown to exist: spectrographs with as flat as possible a portion of the focal surface (of Harada spectrograph type) and those with a nearly constant distance from the grating centre to the focal surface, which permits reaching a high spatial resolution with the use of a crossed focusing mirror (without a loss in spectral resolution). Three 0.25, 0.5, and long spectrographs of Harada type were calculated for operation in the ranges 90 – 250, 50 – 200, and , respectively. We show that each of the calculated instruments may be converted to an instrument of the second type for operation in the second and fourth diffraction orders without significant changes in scheme geometry. In this case, the theoretical spatial resolution is equal to throughout the optimisation range.

Imaging diffraction VLS spectrometer for a wavelength range λ > 120 Å

A broadband stigmatic (imaging) soft X-ray (λ > 120 A) spectrometer is experimentally realised. The optical configuration of the spectrometer comprises a plane grazing-incidence reflection grating with a spacing varying across its aperture according to a preassigned law [a so-called varied line-space (VLS) grating] and a broadband spherical normal-incidence mirror with an aperiodic Mo/Si multilayer structure. The average plate scale amounts to ~5.5 A mm−1. The radiation is recorded with a matrix CCD detector (2048 × 1024 pixels of size 13 μm). The line spectra of the multiply charged ions LiIII and FV–FVII excited in laser-produced plasma are recorded with a spatial resolution of ~26 μm and a spectral resolving power R ≈ 500 is experimentally demonstrated.

Interaction of laser plasmas with noble gases

The interaction of a noble gas jet (Xe, Kr, He) with a laser plasma at a distance of ∼1 cm from a solid target (Mg, (CH2)n, LiF, or CF4) was studied for the first time. The line spectra that were excited in the course of charge exchange of multicharged ions with noble gas atoms in the interaction region were recorded. A clean (debris-free) soft X-ray source excited by laser pulses focused into a xenon jet was designed and investigated.

Broadband High-Resolution Imaging Spectrometers for the Soft X-Ray Range

We develop imaging (stigmatic) XUV spectrometers with the use of plane grazing-incidence varied line-space (VLS) diffraction gratings and focusing normal-incidence multilayer mirrors (MMs), including broadband aperiodic ones. A stigmatic 12–30 nm spectrometer with a resolving power of at least 500 is demonstrated.

Normal-incidence Sb/B{sub 4}C multilayer mirrors for the 80 A < {lambda} < 120 A wavelength range

Periodic and aperiodic Sb/B4C multilayer structures have been theoretically calculated and synthesised for the first time for the application in soft X-ray optics in the 80 A < l < 120 A range. The reflection spectra of the periodic multilayer mirrors are mea- sured using synchrotron radiation and laser plasma-generated radi- ation. The experimental spectra are theoretically interpreted with the inclusion of transition layers and substrate roughness. The den- sity of antimony layers is supposedly r(Sb) = 6.0 g cm -3 , and the thickness of transition layers (if any) in the Sb/B4C multilayer structures does not exceed 10 A. A peak reflectivity of 19 % is attained at a wavelength of 85 A. An aperiodic mirror optimised for maximum uniform reflectivity in the 100 - 120 A range is tested employing the laser plasma radiation source.