Galina Kalinchenko

Wideband All-Dielectric Diffraction Grating on Chirped Mirror

A method of integral equations (IE) is applied to a simulation of diffraction efficiency (DE) of metal-dielectric and all-dielectric diffraction gratings (DG). Two factors narrowing the spectral band of laser pulse reflection into minus first space harmonics (MFSH) are analyzed. It is found that by using a chirped mirror instead of a multilayer all-dielectric one it is possible to make diffracted spectrum 20-30 nm wider.

Seidel aberrations in grating pulse stretchers

We derived a formula for calculation of the spectral phase of ultrashort pulses propagating through aberrated stretchers. Our approach is based on Seidel aberration theory. The dependence of spectral phase dispersion terms and residual angular dispersion on the individual Seidel aberration coefficients is found. As an example, the spectral phase deviation and the residual angular dispersion of an ultrashort pulse for the Martinez/Banks stretcher using spherical optics is calculated.

All-dielectric diffraction grating for multi-petawatt laser systems

All-dielectric grating with more than 98% efficiency over the reflective band of 40 nm with the central wavelength at 1053 nm is simulated for the angle of incidence 72 degrees. For the grating design we used the fact that chirped mirrors give wider reflective band than usual quarter-wavelength dielectric mirrors. Grating grooves and the very first layer under the grooves in our model is made of fused silica; underneath of the top layer we placed a chirped stack of 13 HfO2/SiO2 layers. Tolerances for groove depth and angle of incidence are estimated, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show excellent agreement.

Mathematical simulation of impedance diffraction gratings

In this paper the eigenwaves of a periodic impedance diffraction grating (DG), and the reflection and transmittance on a finite DG are under investigation. The approximate boundary conditions (ABC) were used for simulations. The refined expression for impedance dielectric strips is obtained. Singular part of the approximate integral equations (IE) is extracted and analytically transformed. As a result an IE of second type with a smooth kernel has been derived and solved with the collocation method and the Galerkin method.

Processes in hollow cathode discharge excited by steady-state and pulse currents

A semi-analytical method to simulate the local and integral pumping rates of spectral lines in multi-component hollow cathode discharge plasma has been proposed. The contribution of different mechanisms into pumping rate of upper level of laser line 441.6 nm CdII in He-Cd mixture is discovered for CW regime. The excitation of discharge by current pulses has been analyzed. The results of theoretical calculations are in good agreement with experimental measurements.

OPTIMUM CONDITIONS FOR PUMPING LASER TRANSITIONS OF CADMIUM IONS BY VARIOUS PROCESSES IN A HOLLOW-CATHODE DISCHARGE

The interaction of electrons of various energies with helium and cadmium atoms in a hollow-cathode discharge is analyzed. On the basis of the results of this analysis the conclusion is made that helium is ionized predominantly by electrons moving from the cathode wall to the cavity axis and having energies 70<ε<300 eV, whereas helium and cadmium are ionized predominantly by electrons with energies 9<ε<70 eV which move chaotically. For each of these energy ranges, the kinetic equation is solved and the electron energy distribution function (EDF) is determined, which is used for calculating pumping rates for laser transitions of cadmium ions. The conclusion is made that the rate of population of laser transitions through charge transfer is determined by electrons having a predominant direction of motion and an anisotropic EDF. The population rate associated with electron impact and the Penning ionization is determined by electrons moving chaotically and having an isotropic EDF. The analysis of the EDF made it possible to explain differences in discharge conditions (helium and cadmium pressures) providing optimum lasing for lines pumped by different processes. Radial profiles of pump rates obtained from the analysis made it possible to calculate and explain the dependence of the laser output power on the cathode diameter.

High reflective diffraction grating for ultrafast pulse compression

A diffraction grating based on all-dielectric multi-layer structure is designed for compression of ultrafast pulses with spectrum centered at 900 nm. The grating at Littrow angle with an out-of-plane configuration shows more than 96% efficiency over the reflective band of 100 nm for the angle of incidence 41 degrees. We suggest grating grooves and the very first layer under the grooves to be made of fused silica. Reflective mirror under corrugated layer is designed as a stock of three types of dielectric nanolayers. Tolerances for groove depth and angle of incidence are estimated and, optimal duty-cycle parameter is found out. Electric field distribution inside of the grating is also numerically studied. The model is simulated by two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. The results obtained by both methods show an excellent agreement.

Positioning of Littrow mounted gratings in pulse compressors

The development of chirped pulse amplification lasers toward multi-PetaWatt power imposes more demands on laser system elements. To make the spectral band of pulse compressors wider, laser designers began to consider Littrow mounted grating setups. In this study we investigate two Littrow type configurations. The first one is roll - a grating is rotated in the grating plane by a small angle. The second configuration is pitch - a grating is rotated by small angle about an axis perpendicular to the grating grooves. In this paper we experimentally measured diffraction efficiency of rolled and pitched dielectric grating, and simulated it with two methods: numerical Fourier Modal Method in LightTrans Virtual Lab and semi-analytical Volume Integral Equation Method. Here we claim that roll is more preferable for dielectric diffraction gratings with high groove density. It is shown that the energy of laser pulse compressed by a Littrow-roll configured compressor is 2 to 5% higher than Littrow-pitch configured one.

Phase synchronism possibility in optical fibers

Optical fiber with Bragg grating inserted in fiber cladding is analyzed by means of volume integral equation method (VIE). Complex dispersion curves with two branches corresponding to positive and negative dispersion are simulated. The fiber parameters matched to phase synchronism conditions for weak Pockels-like nonlinearity are found.

Electromagnetic wave diffraction and propagation in a multilayer dielectric structure containing a diffraction grating

We develop a numerical code for simulating the EH/sub 01/ mode propagating in a structure composed of a dielectric grating placed on a multi-layer substrate. The dispersion characteristics, the spatial field distribution and the dependence of the transmission and reflection coefficients upon the frequency are calculated for different geometrical dimensions of the structure. The method of volume integral equations is applied. The analytical transformation of the integral equations makes it possible to avoid singularities and to reduce the problem of integrating to standard numerical quadratures. Due to good convergence of series and integrals it is enough to take 15-20 terms in the series and numerical quadratures to get an accuracy not worse than 0.1%. We find the frequency band where the structure can behave as a frequency-selective one. The geometrical grating parameters for the structure to be absolutely reflecting, or, alternatively, completely transparent, are found. The results of this work can form a basis for further investigations of hybrid wave propagation in complex dielectric structures.