I. A. Makarov

Enhanced laser induced K X-rays generation during microchannel formation inside the object positioned in air

The increasing of yield of X-rays more than two times from femtosecond laser plasma produced in the target microchannel positioned in air compared to the case from fresh target’s surface was registered and the angular dependence of output of X-rays was firstly observed.

Self-channeling of femtosecond laser radiation in transparent two-component condensed medium

We have observed self-guiding of a single femtosecond visible laser pulse in the bulk of transparent nonlinear media (SiO2, KDP) and in the water. The dependence of filament length on laser pulse energy was measured. Continuous open-ended channels and frozen modifications of the matter were observed in transparent two-component condensed medium (thin glass plate placed in water).

Microspectral analysis of dentine with femtosecond laser induced plasma

Microspectral analysis of dentine plasma produced by femtosecond laser radiation with intensities of I ∼ 1013−1015 W/cm2 in ambient atmosphere has been measured. C, O, Ca, Zn, Na, and Cu spectral lines were identified. The X-ray radiation with energies E > 30 keV has been observed upon laser beam intensities of I ∼ 5 × 1015 W/cm2.

Enhancement of hard X-ray yield under the interaction of Cr: Forsterite femtosecond laser radiation with Xe clusters

Experiments on the interaction of femtosecond laser radiation (1240 nm, 140 fs,1016W/cm2) with a Xe cluster beam in a Xe-Ne binary mixture are carried out. The formation of Xe clusters in the presence of light carrier gas (Ne) is found to narrow the Xe cluster beam and enhance the x-ray yield (at about 4 keV). X-ray generation efficiency is about 10−8.

Hot plasma diagnostics during femtosecond laser ablation in a cavity

On-line diagnostics of hot plasma induced by superintense femtosecond laser pulses in a cavity during the deep hole drilling of solid target has been developed. Such a plasma is characterized by higher values of hard X-ray yield and hot electron temperature in comparison with the same parameters measured for flat nearsurface plasma. Dynamics of X-rays yield in the cavity during the deep hole drilling demonstrates several repetitive stages. The yield and energy of X-rays from plasma ignited in a cavity depend on the beam waist position respect to the target surface plane, i.e. focusing regime. We have detected strong second harmonic signal that correlated with hard X-Ray yield in the time of cavity formation. Depth resolved elemental analysis of compound targets, based on this diagnostics technique, has been proposed.

Tracking of buried layers during plasma-assisted femtosecond laser drilling of compound targets

It was shown that drilling of multi-layered target placed in the air by tightly focused femtosecond laser radiation with high fluence (up to 1000 J/cm2) can be monitored online using plasma-induced X-ray emission and second harmonic of incident laser radiation. The technique based on X-rays registration is appeared to be more flexible than the method based on detection of second harmonic since its accuracy depends crucially on the target type. We demonstrated that the X-ray signal clearly indicates the transition from one layer to another during the microdrilling of targets consisting of 2–4 layers of titanium foil when a laser beam is focused beneath the target surface at a depth comparable to the layer thickness. The diagnostics of microchannel production in the chicken eggshell was performed for the first time. It was found that the presence of albumen beneath the shell accounts for longtime generation of X-ray pulses.

Femtosecond laser plasma in CaF2 crystal microchannel and effective generation of characteristic X-ray radiation

The dependence of the characteristic X-ray radiation yield from CaF2 crystal on the formed microchannel depth under highly intensive (I ∼ 3 × 1015 W/cm2) laser pulses with different contrast was obtained. The maximum of the characteristic X-ray radiation yield at these experimental conditions corresponded to the microchannel depth of 30–50 μm. The efficiency of the laser radiation conversion to the characteristic X-ray radiation increased from 6 × 10−8 for the surface up to 10−7 in the microchannel. The dependence of the characteristic X-ray radiation yield on the viewing angle showed that the source of X-ray radiation was located near the surface inside the microchannel.

Enhanced x-ray emission from hot plasma produced by double-pulse laser irradiation of solid target at atmospheric conditions

We present the results of our experiments directed to the suppression of atmospheric gases influence on delivering of superintense femtosecond laser radiation to solid target at atmospheric conditions.The suppression of atmospheric gases effects is attained by expositing the target to a double-pulse radiation and caused by reducing gas density near the target surface). In our scheme the first pulse (nanosecond UV pulse from XeCl excimer laser) acts as a vacuum pump. The second laser pulse (tightly focused femtosecond pulse) delaying up to several microseconds respect to the first laser pulse delivers the basic energy necessary for switching a hot plasma on the target surface. We have observed the maximum X-ray yield increasing up to 17 times under double pulses exposure compare with the single femtosecond pulse regime.

Plasma channel formation and micromodification of KDP crystal by tightly focused Cr:forsterite femtosecond laser radiation

Experiments on single pulse plasma channel formation in non-linear KDP crystal by tightly focused (NA = 0.47) fundamental and doubled Cr:forsterite laser radiation with energy of 0.1 ÷ 10 μJ and 100 fs pulse duration were carried out. We propose the simple model of non-linear absorption of femtosecond laser radiation in plasma channel. This model allows estimate laser intensity in the channel and plasma parameters.

Plasma channels characteristics dependence on tightly focused femtosecond laser radiation parameters

Tight focusing of femtosecond laser radiation with microjoule pulse energy in non-linear crystal volume (intensity of the order of 10 W/cm2) causes self-focusing, multiphoton ionization of the matter, plasma channel formation, electrons heating, and subsequent micromodification of the structure. The processes threshold, behavior and efficiency strongly depend on such laser pulse parameters as pulse duration, energy and radiation wavelength