L. D. Mikheev

Amplification of ultrashort laser pulses in the photolytically driven XeF(C–A) active medium

Amplification of ultrashort laser pulses is demonstrated in a gas medium of the photolytical XeF(C–A) laser. A gas mixture of XeF2:N2:Ar was excited by vacuum-ultraviolet radiation produced by a high-current multichannel sliding discharge, which was initiated along one side of dielectric laser cavity. A small-signal gain of 1.6×10−3 cm−1 is observed for a seed pulse at 488 nm with ∼150 fs duration. The use of a second optical source together with the device optimization promise a multiple increase in the gain and the obtaining of high-contrast TW femtosecond pulses as a result of direct amplification, without application of a stretching/compression technique.

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

Direct amplification of frequency-doubled femtosecond pulses from Ti:Sa laser in photochemically driven XeF(C-A) active media

A new concept of the direct amplification of femtosecond optical pulses in photochemically driven active media, such as Xe2Cl, XeF(C–A) and Kr2F, is discussed with the main emphasis on the XeF(C–A) active medium as one of the most widely studied system. The main advantage of these systems is that they are characterized by a broad gain bandwidths (60–100 nm) which allow to support 10 fsec pulses and are centered in the blue-green region (490, 480 and 420 nm, respectively) spectrally matching to the second harmonic of a Ti:Sa laser. The last circumstance is important from the viewpoint of considerable increasing temporal contrast ratio of ultrahigh peak-power fsec systems.

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.

Amplification of femtosecond optical pulses in a photolytically driven XeF(C-A) laser amplifier

Amplification of blue-green (470-490 nm) femtosecond pulses in a gaseous active medium of a photolytically driven XeF(C-A) laser amplifier is studied experimentally. The active medium is optically pumped by the vacuum-ultraviolet radiation from two large-area multichannel surface discharges initiated along opposite planes of the amplifier cavity. The amplification factors exceeding 100 are obtained in a multipass optical scheme in the regime of homogeneous gain distribution over a beam cross-section of up to 3 cm in diameter. A small-signal gain of 0.002 cm-1 is observed at 488 nm for the continuous radiation of Ar-ion laser and for the 150 fs seed pulses as well. The registered spectra insure a good conservation of the temporal characteristics of amplified ultrashort pulses.

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.

Dynamic photolytical actinometry of the vacuum-ultraviolet radiation produced by multichannel surface discharges of submicrosecond duration

Absolute measurements of the vacuum-ultraviolet (VUV) radiation power produced by a planar broadband optical source of submicrosecond light pulse duration are carried out in the transient regime of formation of a photodissociation (bleaching) wave in a photodecomposing absorptive medium. The source is based on a multichannel surface discharge initiated in ArN(2) gas mixtures on the area of approximately 0.1 m(2). The energetic characteristics of the produced VUV radiation are determined on the basis of spatially and temporally resolved observations of the pulsed photolysis of XeF(2) vapors. It is shown that the photon flux intensity produced by the source within the spectral range of 120-200 nm reaches 1.1 x 10(23) photonscm(2) s corresponding to the effective brightness temperature of discharge plasma of 20 kK and to the intrinsic efficiency of the discharge VUV emission of 3.2%. Numerical simulations of the photolysis process show a rather weak sensitivity of the results to the fraction of discharge radiation emitted into the line spectrum, as well as to the angular distribution of emitted radiation. The spectral band of measurements can be selected according to the choice of parent photodecomposing particles.

Prospects for ultrashort hybrid solid-gas high-contrast multiterawatt laser in the blue-green region

A low density medium like a gas is attractive for laser amplification due to its high breakdown threshold and scalability to very large volumes. Moreover, the non-linear index of refraction of a gas is of three orders of magnitude lower than for a solid medium that is particularly suitable for direct amplification, without pulse stretching, of high-power ultrashort pulses. Among all gas laser media, application of the photolytical XeF(C-A) laser for high energy amplification is very attractive for the development of ultra-high power laser systems up to the petawatt power level due to the XeF(C-A) broad amplification bandwidth (80 nm FWHM centered near 475 nm) and a rather high saturation fluence (~0.05 J.cm-2), as well as a very low level of Amplified Spontaneous Emission. The paper presents the strategy of the LP3 laboratory to develop a high-contrast multiterawatt femtosecond laser chain based on a hybrid (solid/gas) technology, including a Ti:Sapphire oscillator generating 50 fs pulses at 950 nm, an Optical Parametric Chirped Pulse Amplification stage, a frequency converter, and a final high-energy amplification in the photolytical XeF(C-A) amplifier. Our approach is supported by first pilot experiments of femtosecond pulse amplification in a compact photolytical XeF(C-A) amplifier.

Initiation techniques and the vacuum-ultraviolet-radiation efficiency of a stabilized multichannel surface discharge

Multichannel surface discharges possess a number of advantageous characteristics for the optical pumping of photochemically driven lasers. This work reports on a type of large-area low-inductance sources of intense UV-VUV (vacuum-ultraviolet) radiation based on spatially stabilized multichannel discharges in gases. The discharges consist of several dozens of closely located parallel plasma channels initiated synchronously along a dielectric surface on the area of several hundred square centimeters. In comparison with a large-area diffuse surface discharge, the plasma confinement within relatively thin channels greatly improves the efficiency of the discharge emission in the VUV spectral range. Several techniques are introduced, which allow a synchronous formation and homogeneous development of multiple spatially stabilized discharge channels. Technical efficiency of the discharge radiation within the spectral range of 120–200nm reaches 5% and an effective brightness temperature of the radiating plasma exc...

Transport of broadband arbitrary radiation through a bleaching medium

A novel analytical treatment of the transport of broadband radiation arbitrarily directed through a bleaching medium is presented. The emphasis is on the principle features of photodecomposition (bleaching) wave formation. Considering radiation from a uniform planar source with stable radiative characteristics and media with a uniform initial distribution of the absorptive component, we show that this problem has an asymptotic stationary solution for a wave propagating through a medium characterized by a photodecomposition spectrum without any portion in which the absorption cross section continually runs down to zero.