N. N. Ustinovskii

Transfer of microwave radiation in sliding mode plasma waveguides

A new regime of the sliding propagation of microwave radiation in plasma waveguides in atmospheric air has been investigated experimentally and theoretically. A plasma waveguide whose radius is much larger than the radiation wavelength has been created by the photoionization of an easily ionized impurity by the ultraviolet radiation of a KrF laser. The transfer of a 35.3-GHz microwave signal to a distance of 60 m has been demonstrated. The transfer mechanism is due to the total internal reflection of the wave on the optically less dense walls of the plasma waveguide.

Microwave energy channeling in plasma waveguides created by a high-power UV laser in the atmosphere

The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼1012 cm−3 in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λmw ∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor of 6 in comparison with propagation in free space.

Direct measurement of the characteristic three-body electron attachment time in the atmospheric air in direct current electric field

We report the results of theoretical and experimental study of the characteristic time for three-body attachment of electrons produced by 100 fs UV laser pulse in the atmosphere air in the external DC electric field ranged from 0.2 to 10 kV/cm.

Experimental capabilities of the GARPUN MTW Ti : sapphire – KrF laser facility for investigating the interaction of subpicosecond UV pulses with targets*

This paper describes the first experiments carried out on the GARPUN MTW Ti : sapphire – KrF hybrid laser facility and aimed at gaining insight into the interaction of subpicosecond UV pulses with solid and structured low-density carbon nanotube targets at peak intensities of ~1016 W cm−2 in a focal spot ~70 μm in size. Using X-ray absorbers, the plasma electron temperature has been measured to be ~850 eV. In our experiments, we used an optimal configuration: direct double-pass ultrashort-pulse (USP) amplification in KrF amplifier stages, with multiple laser beam filamentation suppression in a xenon-filled cell. The highest energy on a target was 0.25 J at a USP contrast relative to amplified spontaneous emission of ~3 × 1010 for intensities and ~3 × 105 for fluences. Owing to two-photon resonance in the UV spectral region, the use of xenon, with a negative nonlinear refractive index, allowed us to make the cross-sectional fluence distribution more uniform and reduce the beam divergence to 0.14 mrad (at the 10 % intensity level). Reducing the USP duration via negatively chirped pulse amplification and filamentation suppression and reducing the focal spot size on a target by using parabolic short-focus optics are expected to ensure an increase in the intensity incident on the target by one to two orders of magnitude.

Major pathway for multiphoton air ionization at 248 nm laser wavelength

Multiphoton ionization mechanisms and ionization rates of atmospheric air and constituent gases are studied at the 248-nm KrF laser wavelength within a laser pulse intensity range of 108–1013 W/cm2 using both long 25-ns and short 160-fs pulses. We have experimentally shown that it is the photoionization of water vapor naturally contained in atmospheric air that acts as the dominant process of air ionization. (2 + 1) Resonance-Enhanced Multiphoton Ionization (REMPI) occurs through 2-photon resonant excitation of water molecules, which results in a quadratic dependence of electron density on laser intensity at lower laser intensities of 108–1010 W/cm2 in the long pulse and in a cubic dependence at higher intensities of 1010–1013 W/cm2 in the short pulse. Direct 3-photon ionization and (3 + 1) REMPI take place in pure O2 and N2, respectively, and their contributions to air ionization are in the ratio of 5:3. The total ionization rate of O2 and N2 in atmospheric air is about an order of magnitude less than th...

Kerr self-defocusing of multiple filaments in TW peak power UV laser beam

An effective suppression of multiple filamentation of the sub-TW peak power supercritical laser beam in xenon gas was demonstrated in direct amplification of subpicosecond UV pulses at Ti:sapphire/KrF laser facility GARPUN-MTW. A large negative nonlinear refractive index due to a two-photon resonance of KrF laser radiation with Xe state ensured Kerr self-defocusing of a few hundred filaments with a local peak intensity of ~0.2 TW cm−2, 200-fold higher than the average one over the beam cross section, and thus homogenized the laser beam. UV filaments in Xe produced a narrow-angle monochromatic coherent cone emission at 828 nm wavelength due to stimulated hyper-Raman scattering and amplified spontaneous emission at the transition .

Extremely effective air photoionization through water vapor at 248 nm laser wavelength

Multiphoton ionization mechanisms and ionization rates of atmospheric air and constituent gases are studied at 248 nm KrF laser wavelength. We have experimentally shown that it is photoionization of water vapor naturally contained in atmospheric air that acts as the dominant process of air ionization. Total ionization rate of O2 and N2 in atmospheric air is about an order of magnitude less than that of water vapor. Relevant ionization coefficients have been measured, and that for H2O molecule is more than 2-3 orders of magnitude larger than the others.

Electron-free UV laser pulse filamentation under coherent rotational SRS in air

Coherent stimulated rotational Raman self-scattering is proposed as the mechanism of electron-free filamentation of the ultra-short KrF laser pulse in air.

Amplification and generation of radiation at the 4{sup 2{Gamma}} {yields} 1,2{sup 2{Gamma}} transition of the Kr{sub 2}F molecule in an electron-beam-pumped wide-aperture laser

The radiation amplification and oscillation are obtained in an electron-beam-pumped Berdysh laser with an active volume of 10 L in the visible range from 430 to 470 nm at the broadband 42Γ → 1,22Γ transition in the triatomic Kr2F molecule of interest for amplification of ultrashort laser pulses. It is shown that, along with absorption of laser radiation in the active medium, the amplification dynamics is considerably determined by short-lived absorption induced in the amplifier windows by bremsstrahlung X-rays. For the specific pump power 0.6 — 0.7 MW cm-3, the gain, corrected for nonstationary absorption, was ~10-3 cm-1. A scheme of a Kr2F amplifier is proposed for amplification of ultrashort pulses up to multiterawatt peak powers in the active volume ~10 L.

Laser implantation of sodium nitrite into artificial opal pores upon exposure of artificial opal samples to pulsed radiation of the ultraviolet laser

We present experimental results on the introduction (laser implantation) of ferroelectric NaNO2 into artificial opal pores upon exposure of a thin powder layer of sodium nitrite applied on the artificial opal surface to radiation of the ultraviolet excimer laser. Reflection spectra of broadband radiation from the laser-implanted sample surface are compared with the reflection spectra of pure initial opals, artificial opals impregnated with a saturated aqueous solution of sodium nitrite and evaporated from solvent, and samples in which NaNO2 was directly introduced in the form of a melt.