V. V. Bukin

Plasma filament investigation by transverse optical interferometry and terahertz scattering

Transverse plasma distribution with 10(17) cm(-3) maximum electron density and 150 μm transverse size in a plasma filament formed in air by an intense femtosecond laser pulse was measured by means of optical interferometry. Two orders of magnitude decay of the electron density within 2 ns was obtained by combined use of the interferometry and newly proposed terahertz scattering techniques. Excellent agreement was obtained between the measured plasma density evolution and theoretical calculation.

Spatio-temporal dynamics of electron density in femtosecond laser microplasma of gases

The formation and evolution of femtosecond laser plasma produced in microvolumes of gases at different pressures upon their multiply ionization by high intensity pulses of fundamental and second harmonics of a Ti:sapphire laser is studied. The interferometric technique for precise ultrafast optical diagnostics of such plasma was applied. The numerical technique of interferogram processing and reconstruction of instant spatial distribution of refractive index and free electron density in laser-induced plasma applied for this proposes is described. The spatiotemporal distribution of the refractive index and free electron density were studied with a spatial resolution of ∼1 μ m and a temporal resolution of ∼70 fs.

Superluminal source of directional pulsed wideband electromagnetic radiation

A photoemission source of directional pulsed wideband electromagnetic radiation in the microwave region is developed, and the time profile of the generated pulse is investigated. The source is a vacuum photodiode of a parabolic shape in which a Cherenkov radiation pulse is formed by an electron current wave excited by an incident laser pulse and propagating along the surface of the anode mesh with a phase velocity higher than the speed of light.

Optimal polarization of a two-colored pump for terahertz generation with a phase-unstable scheme

The polarization properties of a scheme for terahertz (THz) generation by an optical breakdown of a gaseous media using a two-colored femtosecond pulse are investigated. It is found that if the scheme is not stabilized over the phase shift between the pump waves, the maximal THz signal is observed when the pump pulses are elliptically polarized. At this rate the stability of the THz signal power is also maximal. These observations are in compliance with a photocurrent model of THz generation.

Picosecond laser system with a wavelength of 193nm based on a solid-state Nd:YAG laser, parametric oscillator, and ArF amplifier

Powerful picosecond UV pulses at a wavelength of 193nm are produced using a Nd:YAG laser radiating at a wavelength of 193nm with subsequent nonlinear transformations of the radiation and amplification in an excimer gain medium to an energy of 10 mJ.

Interferometric diagnostics of femtosecond laser microplasma in gases

The laser plasma formed in gaseous media due to their optical breakdown under tightly focused femtosecond laser pulses has been experimentally investigated. Pump-probemicrointerferometry is chosen to perform spatial and temporal diagnostics of the plasma. Time dependences of the laser plasma electron density are obtained. It is shown that in breakdown of different gases (air, nitrogen, argon, and helium) at different pressures (in the range from 1 to 10 atm) the electron concentration continues to increase during ∼1 ps when the laser irradiation is over. This effect is related to the impact ionization of the plasma by the hot electrons formed in interaction of intense femtosecond laser pulses with matter. The results of theoretical simulation of the post-ionization processes are presented.

Combining Raman and laser induced breakdown spectroscopy by double pulse lasing

AbstractA new approach combining Raman spectrometry and laser induced breakdown spectrometry (LIBS) within a single laser event was suggested. A pulsed solid state Nd:YAG laser running in double pulse mode (two frequency-doubled sequential nanosecond laser pulses with dozens microseconds delay) was used to combine two spectrometry methods within a single instrument (Raman/LIBS spectrometer). First, a low-energy laser pulse (power density far below ablation threshold) was used for Raman measurements while a second powerful laser pulse created the plasma suitable for LIBS analysis. A short time delay between two successive pulses allows measuring LIBS and Raman spectra at different moments but within a single laser flash-lamp pumping. Principal advantages of the developed instrument include high quality Raman/LIBS spectra acquisition (due to optimal gating for Raman/LIBS independently) and absence of target thermal alteration during Raman measurements. A series of high quality Raman and LIBS spectra were acquired for inorganic salts (gypsum, anhydrite) as well as for pharmaceutical samples (acetylsalicylic acid). To the best of our knowledge, the quantitative analysis feasibility by combined Raman/LIBS instrument was demonstrated for the first time by calibration curves construction for acetylsalicylic acid (Raman) and copper (LIBS) in gypsum matrix. Combining ablation pulses and Raman measurements (LIBS/Raman measurements) within a single instrument makes it an efficient tool for identification of samples hidden by non-transparent covering or performing depth profiling analysis including remote sensing. Graphical abstractCombining Raman and laser induced breakdown spectroscopy by double pulse lasing

Backward Terahertz Radiation from a Two-Color Femtosecond Laser Filament

We report the first experimental observation of backward terahertz emission from the two-color laser induced plasma filament in air. The ratio of measured forward-to-backward terahertz radiation is ∼25/1. This result agrees with numerical simulations based on interferometric model assuming 0.3 mm long plasma source.

Interferometry diagnostics of plasma channel of femtosecond filament

Results of the electron density dynamics in the plasma channel of a femtosecond filament in air, nitrogen and argon from the moment of ionization up to hundreds of picoseconds after it are presented. Anisotropy of the refractive index was found, which is preceded and accompanied by ionization of the gas at the time of passage of high-intensity femtosecond laser pulse.

The dependence of terahertz signal and third harmonic amplitudes on mutual polarization of two-color pump components under optical breakdown of air

In this paper we measured the dependence of the signal of the third harmonic and terahertz radiation on the mutual polarization of the first and second harmonic to compare the mechanisms of their generation. For this purpose we used the output radiation of laser system Spitfire pro with the following parameters: pulse duration 35 fs, central wavelength 800nm, repetition rate 1kHz, energy of the first and second harmonic are 2mJ and 240mJ respectively. The radiation was focused by parabolic mirror with focal length 7,5 cm in air. The energy of terahertz and third harmonic radiation was measured by Holey cell and photomultiplier respectively.