Broadband x-ray optical elements based on aperiodic multilayer structures

Abstract

Collision-induced infrared spectroscopy has been used to measure the initial rate of the chemical exchange of equimolar D2 and T2 in liquid and solid forms from 9 to 23 K over 23 to 45 h. If first-order kinetics are assumed, the time constant is 100-140 h for thermal equilibrium and 16C-180 h for a hot-atom equilibrium. The latter is favoured, but cannot be confirmed. Approximately three DT molecules are formed per ion pair (using the gas-phase value of 36.6 eV/ion pair). A likely mechanism is reaction of the T2+ to the TT ion, followed by exchange. The slowness of the exchange suggests that molecular DT can be isolated and handled for fusion applications.

Research and creation of broadband X-ray mirrors with a spectral transmission band coinciding with emission lines and the possibility of filtering

“…Next, the norm of the difference between the reflection coefficient and F g f is introduced-the estimated functional F, calculated in the domain of F g f definition and representing a function of N variables (in this case, the thickness of the layers of the structure were used as fitting parameters). Then the optimal structure of the layers is found by minimizing the functional [6,7].…”

“…Thus, the use of aperiodic structures makes it possible to satisfy other conditions necessary as part of a specific task. For example, expanding the angular [4,5] or spectral [6,7] operating range, increasing the integral reflection coefficient [8], working as a polarizer, filter [9,10] or controlling pulses of electromagnetic radiation of subfemtosecond duration [11,12]. In each of the specific cases, it is necessary to impose additional conditions when optimizing the structure of such mirrors.…”

Aperiodic multilayer structures in soft X-ray radiation optics

“…To find the extremum of the F functional, advantage was taken, in particular, of a genetic algorithm and the method of steepest descent. To decrease the power of the dependence of the computation time on N, an analytical formula was derived for the partial derivatives of the amplitude reflection coefficient with respect to layer thicknesses [3].…”

“…As pointed out in Ref. [3], aperiodic MSs can serve as broadband specular polarisers for a fixed angle of radiation incidence. Aperiodic MSs were optimised for maximum uniform reflectivity in the ranges 8.8 - 12.4 nm (a Rh/B 4 C structure, optimal angle of incidence q = 42.5°), 13 - 19 nm (Mo/Si, q = 41°), and 19 - 30 nm (MoSi 2 /Si, q = 41.5°), which were practically nonreflective for p-polarised radiation in these ranges.…”

“…Along with periodic multilayer structures, also of interest are aperiodic structures which are capable of satisfying other criteria than the attainment of a high reflection coefficient in a relatively narrow wavelength interval. In the class of aperiodic multilayer structures (MSs) it is possible to solve a number of optimisation problems which are of practical significance in X-ray optics, including the optics of the soft X-ray (SXR) range [3]. Among these problems are, for instance, calculation and fabrication of MSs which provide: (i) the highest possible uniform reflectivity throughout a given interval of wavelengths or angles of incidence; (ii) a high polarisance over a broad wavelength range for a fixed angle of radiation incidence; (iii) the highest possible reflection coefficient at one or several wavelengths; (iv) the highest possible integral reflectivity of a single mirror or the highest possible integral transmission coefficient for a system consisting of several sequentially arranged MMs, filters, etc.…”