Aleksandr K. Dmitriev

Determination of biotissue type in the course of CO2 laser ablation using backscattered radiation

The correlation between Doppler spectra due the emission of tissue destruction products at laser ablation and tissue types was established. The possibility of biotissue type relative determination at the passage of CO2 laser beam through various sequences of tissue layers is demonstrated.

Stabilisation of a femtosecond frequency standard using a Michelson interferometer

We propose an optical frequency standard based on a femtosecond laser, in which the shift of the frequency comb is controlled using a Michelson interferometer.

Perforation of biomodels and biotissues by powerful laser pulses

In vitro perforation of gelatin-based biomodels and myocardium tissue by powerful CO2 and YAG:Er laser pulses is considered. Features of the thermal and shock-wave effects on the walls of the laser channel are investigated. Patterns of laser channeling in gelatin by a single YAG:Er laser pulse were studied.

Monitoring of laser ablation of biotissues on backscattered radiation

The monitoring system for laser vaporization of biotissues based on autodyne detection method of backscattered radiation with the help of high-frequency pumping CO2 laser was developed. It was shown that this method gives the possibility to determine the instant of laser beam passage through tissue layers boundary in real-time. The magnitudes of integrated intensity of power spectrum (UPS) and weighted mean frequency of Doppler signal spectrum (v) were used for the characterization of Doppler signal in time of laser pulse. As an example the dependencies of IIPS(t) and v(t) for different sets of tissue layers are presented. The stick-slip change of these magnitudes near tissue layers boundary is the base of feed-back for irradiation stopping and change of laser radiation parameters

Destruction products after-burning in the course of laser ablation of biotissues

After-burning/evaporation of destruction products in the course of laser ablation of biotissues was studied. The size distribution of ejected particles was measured and analyzed for different intensities of laser radiation. Evaporation was experimentally modelled by water aerosol flow subjected to intense 10.6 μm radiation of CO2 laser. Numerical simulation was made for laser-induced changes of sizes and optical parameters of water and soot aerosols.

Diagnostics of CO2 laser ablation of biotissues by autodyne detection method of backscattered radiation

CO2 laser-tissue interaction was investigated by the autodyne detection method of backscattered radiation. Doppler spectra obtained in the course of pulse ablation of various pig tissues in vitro are presented. The interrelation between these spectra and some properties of biotissues was established. The possibility of the instants of time determination of the laser radiation passage through the demarcation line of biotissues is demonstrated.

Link between diffraction losses and light beam cross section in laser with telescopic resonator

The light beam cross section change in a laser and its link with the diffraction losses during the telescopic converter defocusing is discussed. In addition, the measurements of the resonator astigmatism compensation by the Brewster window are carried out. It is demonstrated that in the resonator stability region, the light beam cross section is well described by the expression using the transmission matrix elements, the simplified model for the diffraction qualitatively correlates with the test data, and the mirror astigmatism due to the inclined light beam incidence is compensated for by Brewsters window.

Resonances in the spectral density of the frequency distribution of radiation emitted from a laser with nonlinear absorption

A description is given of a method for obtaining narrow resonances of the spectral density of the radiation emitted from a gas laser with nonlinear absorption. The main properties of these resonances are discussed from the point of view of their use in very-high-resolution spectroscopy of low-pressure gases and in laser frequency stabilization. Resonances in the spectrum of the radiation emitted from a He–Ne laser with a methane absorber are reported. A resonance of this kind is used to stabilize the emission frequency of this laser.