Arkadi G. Yastremsky

EFFICIENT HIGH-HOMOGENEOUS WIDE-APERTURE EXCIMER DISCHARGE USING A STABILIZING LOW-CURRENT PREDISCHARGE

A technique of initiation of a self‐sustained electrical discharge for pumping excimer lasers, based on the use of a stabilizing predischarge with an electron density Ne∼1012–1013 cm−3, has been developed. It has been demonstrated that such an auxiliary discharge is stable for random disturbances of the plasma parameters. An efficient, stable, and highly homogeneous pumping discharge of duration up to 800 ns with an aperture of 6×12 cm2 and current density of ∼300 A/cm2 has been realized in Ne(He,Ar)/Xe(Kr)/HCl mixtures. The proposed technique can be used in developing wide‐aperture excimer lasers and shows promise for creating high‐repetition‐rate systems of kilowatt average power.

Development of a hybrid (solid state/gas) femtosecond laser system of multiterawatt peak power

Terawatt hybrid laser (THL-100) system on the basis of Ti:sapphire starting complex and final amplifier with gaseous optically driven active media on XeF(C-A) molecules is presented. Laser system is built at Institute of High Current Electronics SB RAS, Tomsk, Russia. It consists of Ti:sapphire starting complex and photochemical XeF(C-A) amplifier. The active media of amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length. The results of numerical modeling of the output parameters and first experimental results are presented in this paper.

Development of a 100-terawatt hybrid femtosecond laser system

Terawatt hybrid (solid state/gas) laser (THL-100) system on the basis of Ti:sapphire starting complex (50 fs, 5 mJ) and photochemical XeF(C-A) amplifier with the aperture of 24 cm is presented. Laser system is built at Institute of High Current Electronics SD RAS, Tomsk, Russia. The design and peculiarities of optical pumping of XeF(C-A) amplifier, methods of pump power measuring, gain distribution across the active volume are discussed. The results of numerical modeling of the output parameters simulation are presented and one compared with first experimental results.

A 10‐J electric‐discharge‐pumped phototriggered XeCl laser

An electric‐discharge‐pumped XeCl laser using phototriggering by x rays is reported. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a ∼3‐l active volume with an efficiency ≳2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A stability analysis of the discharge pumping has been made for the XeCl laser in terms of the current‐voltage characteristic model. The method for parametric optimization of such systems is described.

Two-dimensional simulation of initiation and evolution of a plasma channel in the XeCl laser pumping discharge

We present two-dimensional simulation results of the formation and evolution of a diffuse plasma channel in the XeCl pumping discharge. Channel formation was initiated by metallic convexity at the cathode surface with a characteristic dimension of ∼0.1 cm. Two pumping regimes were considered. Initial voltage in the second regime was increased 1.6 times and impedance was decreased 2 times in contrast with the first regime. Evolutions and spatial distributions are presented for electron density, electric field, and frequencies of the main process. In the first regime, the diffuse plasma channel forms. The main processes causing development of the plasma channel are inhomogeneous distribution of the electric field, increase of the stepwise ionization frequency at n e ∼ 10 15 cm −3 , and depletion of HCl. Increasing of the initial voltage and decreasing of the impedance in the second regime results in a quick rise of the discharge current and electron density in the discharge gap, and uniform discharge takes place during the current pulse.

Formation of pumping discharge of XeCl laser by means of semiconductor opening switch

Results of experimental and theoretical investigations of XeCl with discharge formation by means of inductive energy storage and semiconductor opening switch have been presented. Main pumping of active medium has been performed by capacitive energy storage. Measured laser output energy is 0.8 J Laser efficiency calculated from energy stored in capacitive energy storage is 2.3%. Simulations predict that the optimization of pumping conditions may increase these parameters in two times.

Two-dimensional model of inhomogeneity evolution in XeCl laser discharge

The pumping discharge of XeCl laser was modeled, taking into account the main kinetic processes. The inhomogeneity was set on the cathode, both as local enhanced density of the initial electrons, and as a metal hemisphere. It is shown, that the plasma channel with high conductivity is formed from the initial inhomogeneity in the discharge.

Development of hybrid (solid/gas state) ultra-high power femtosecond laser system on the basis of XeF(C-A) amplifier

A terawatt hybrid laser(THL-100) system on the basis of a starting complex and a final amplifier with gaseous optically driven active media on XeF(C-A) molecules is presented.The starting complex manufactured consists of a Ti: sapphire master oscillator pumped by femtosecond pulses from a continuous laser pumped by(Verdy-8) at a wavelength of 532 nm,a femtosecond pulse stretcher,regenerative and multipass amplifiers pumped by a pulsed laser at a wavelength of 532 nm,a diffraction grating compressor and a second harmonic generator(KDP).The complex has the following output parameters of the laser beam: pulse duration is 50 fs,the energy of radiation at the second harmonic(475 nm) is 5 mJ.The complex can operate in a single pulse mode and a frequency of 10 Hz. The XeF(C-A) amplifier consists of a two high-voltage pulsed generator(linear transformer),a vacuum diode with six cold explosive-emission cathodes,a electron beam injection system,a Xe filled gas chamber-converter and a laser cell.The high-voltage generator consists of 12 transformer stages,and each of them involves eight capacitors(one is C=40 nF) and spark gaps.The capacitors can be charged up to voltage of 100 kV.E-beam in vacuum diode has the parameters in total current of 300 kA,peak voltage of 550 kV,pulse duration of e-beam power about 150 ns(FWHM).The total energies of the six 100 cm ×12 cm e-beams which pass through the foil into the Xe converter are 6-7 kJ in the 150-160 ns pulse(FWHM).Pump energy cascade processes lead rapidly to the formation of Xe*2,which radiates a fraction of the deposited energy in the continuum at(172 ± 5) nm.This VUV radiation is transmitted through CaF2 windows into the laser cell containing the mixture of XeF2 vapour and N2 buffer gas.VUV radiation makes photolysis of XeF2 molecules form XeF* excimer molecules.The active medium of the amplifier pumped by VUV radiation has 24 cm aperture and 110 cm length.The results of numerical modeling of the output parameters and first experimental results are presented in this paper.According to the modeling of the XeF(C-A) amplifier parameters and the first measurement of gain,it is shown that the maxmum output energy is 2-3 J,which means that the peak power has been up to 40-60 TW in a 50 fs pulse.Furthermore,It is very important that this laser system can provide a high temporal contrast up to 109-1010.

Research of short pulse discharge XeCl laser

Results of experimental and theoretical investigations of pump discharge and generation of XeCl laser with 0.21 J laser energy, 2.7% electric efficiency nad 20 ns (FWHM) pulse duration are presented. The influence of step ionization, dissociative attachment and recombination processes on an active volume spatial uniformity and radiation parameters is shown.

Wide aperture efficient excimer laser with a stable photo triggering discharge pumping

An electric-discharge-pumped XeCl laser using phototriggering by x rays is described. A consistent input of the stored energy into the pumping discharge plasma has been realized. An output pulsed energy of about 10 J has been achieved in a 4-l active volume with an efficiency of about 2%. High spatial uniformity of the laser radiation and a stable space discharge were observed. A uniformity analysis of the discharge pumping has been made for the XeCl laser.