N. G. Ivanov

Multi-terawatt femtosecond laser system of visible range based on a photochemical XeF(C-A) amplifier

AbstractThis paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titanium-sapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fsradiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifieris created in a XeF 2 /N 2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of firstexperiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented todemonstrate that a laser beam peak power of 14 TW has been attained.Keywords: Chirped pulses; Femtosecond pulses; Hybrid (solid/gas) laser system; Photochemical XeF(C-A) amplifier;Second harmonic INTRODUCTIONAt present, the development of ultra-high power laser sys-tems with a pulse duration of 10–100 fs is based mainly onnear-infrared solid-state titanium-sapphire or parametric am-plifiers and amplification of positively chirped pluses, i.e.,stretched in time (0.5–1 ns), by linear frequency modulation(Strickland & Mourou, 1985) with their subsequent com-pression to the initial duration. Stretching of a pulse is re-quired to decrease its power below a threshold at which thebeam is self-focused; in solid-state systems, pulses are nor-mally stretched about 10

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.

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.

High-power excimer laser systems

Two-high power excimer laser systems with square (25 × 25 cm) and circular (with a diameter of 40 cm) cross sections of the output laser beam are described. The first (second) system consists of four (five) excimer lasers. The experimental results on the generation of the high-quality high-power laser pulses are presented. Laser beams with a pulse duration of 1–250 ns, a divergence of 0.01 mrad, a spectral line width of 0.01 cm−1, and a pulse energy of up to 330 J are obtained.

Amplification of sub-nanosecond pulse in THL-100 laser system

The results of the formation and amplification of positive chirped 0.1 ns laser pulse at a central wavelength of 470 nm in the laser system THL-100 are presented. It is shown that a front-end allows forming a radiation pulse with a Gaussian intensity profile and the energy up to 7 mJ. At amplification in XeF(C-A) amplifier of the pulse with 2-5 mJ energy a saturated mode is realized and 3.2 J output laser beam energy is reached.

Kerr nonlinearity effect on femtosecond pulse radiation filamentation in air

The conditions for filamentation of femtosecond pulse laser radiation when focusing in air are studied experimentally and theoretically. A good agreement between experimental and calculated results is shown if neglecting the filament plasma. It is shown that the Kerr nonlinearity plays a fundamental role in the generation, existence, and cessation of a filament at a small numerical aperture (NA ≤ 2.15 × 10–3). The Kerr effect first leads to the beam self-focusing and generation of a filament, and at the final stage, to radiation defocusing and a sharp decrease in its axial intensity due to the beam wavefront distortions. In the case of aberration focusing, a spatial quasi-soliton is formed after a visible filament due to the balance between Kerr self-focusing and diffraction spreading. The quasi-soliton is a source of the directional white supercontinuum.

Influence of the input radiation pulse characteristics on the parameters of a XeF(C – A) amplifier in a THL-100 laser system

We report the results of experimental and theoretical investigations on the influence of spatial and energy parameters of input radiation with a pulse duration of on output characteristics of a XeF(C – A) amplifier in a visible-range, multi-terawatt THL-100 laser system. Dynamics of the energy density radial distribution for laser radiation passing through the amplifier is studied. Results of numerical simulation are presented for amplification of laser beams with Gaussian and super-Gaussian radial energy density distributions. It is shown that the laser energy of obtained experimentally is not the limiting value. According to calculations, the output energy of the amplifier with such mirror configuration may reach , which in the case of a pulse compressed down to corresponds to the radiation power of .

Modeling of lasing possibility in XeF(C-A) amplifier of the THL-100 laser system

Results of experimental measurements and numerical simulations of the N2 and XeF2 gas pressure effects on the gain characteristics are presented in the paper. It is experimentally and theoretically is shown that maximum total gain (5-6)×104 achieved at a pump energy E = 240 J, 0.2 Torr XeF2 and 0.5 atm N2 pressure. Increasing and decreasing of N2 pressure leads to decrease of the gain. The possibility of the XeF(C-A) amplifier operation in a generator mode is discussed and the theoretical study results of generation are presented. It is shown that an annular laser radiation with energy up to 8.5 J can be obtained. The study results of the influence on the laser energy of N2 and XeF2 pressure and reflectance coefficient of output mirror are presented.

Influence of the gas mixture composition on pumping energy dissipation in a XeF(C-A) amplifier of the hybrid femtosecond laser system THL-100

The influence of the composition of a gas mixture in a XeF(C-A) amplifier of the THL-100 hybrid femtosecond laser system on the main channels of energy loss is studied via numerical simulation. It is shown that an increase in the N2 buffer gas pressure from 100 to 760 Torr increases the fraction of absorbed energy transferred to the upper laser level XeF(C,ν = 0), while an increase in the XeF2 partial pressure increases energy loss in collision quenching of the XeF(B, C) states and reduces the energy transferred to the XeF(C,ν = 0) state.