Achievements and prospects of PPTR-method for monitoring/control of laser treatment in surgery purposes are presented. Connection of output laser parameters and ones of irradiated zone in tissue with parameters of measured thermal emission from irradiated tissue are analyzed. There are presented the results of investigations of the high power laser-tissue interaction and of the processes of tissue destruction stimulated by middle-infrared-range pulsed lasers radiation in different sorts of tissues carried out by PPTR-technique. PPTR and Laser Mass-Spectrometry are united in study of evolution of tissue destruction under action of power CO2 laser. The evolution of thermal signal and, correspondingly, temperature in tissue under single laser pulse treatment with rise of energy density are obtained. Method of the temperature stroboscopy which allows to see very fast tissue heating stimulated by pulsed laser treatment more elaborate are presented.
The results of the investigation of two-dimensional electron gas (2DEG) using millimeter spectroscopy technique are presented. The measurements in the millimeter region allow us to register cyclotron resonance (CR) and Shubnikov-de-Haas (SdH) oscillations of electron gas in the same time. This spectral region is optimal to study the electron heating effects also. The main attention is focused on the investigations of the magnetospectra of photocurrent, photoconductivity, transmission and differential transmission of the electron system in 2DEG of GaAs/GaAlAs heterostructures using cyclotron resonance (CR) technique. The investigations of GaAs/AlGaAs heterostructures by photoconductivity technique have shown that the magnetospectra have the complex structure (even with the change of the photocurrent polarity). The magnetospectra depend on frequency and polarization of the incident radiation. The radical changes of the CR-line and the SdH oscillations at the reversion of the magnetic field direction are discovered. The discovered effects are very promising for the development of heterostructures diagnostics methods. These effects reveal a possibility to elaborate solid state detectors to analyze the parameters of millimeter and submillimeter waves. In the study of GaAs/AlGaAs heterostructures with high mobility in pulsed electric field up to 100 V/cm we have discovered an increase of transmission in the center of the CR line. The connection of this phenomenon with collective effects such as the hot electron resonant bunching in the momentum space at non-elastic scattering by optical phonons is discussed.
The experimental investigations of solid state structures in strong electric and magnetic fields, when the strongly anisotropic distribution of hot carriers are realized due to strong interaction of charge carriers with optical phonons in the momentum space are presented. The study was stimulated by the theoretically based possibility to realize the electron resonant dynamic bunching in the momentum space under appropriate conditions and also by the creation of the submillimeter p-Ge lasers. These investigations are directed to the development of solid state analogues of vacuum electronics devices. The effect of electrons redistribution between valleys and the essential nonequidistance of Landau levels have been observed in n-Ge crystals in the electric field above 1kV/cm. This has shown the prospects of laser effect in n-Ge, n-Si, diamond. The efficiency of laser effect in these materials has to be significantly greater than in p-Ge. The emergence of collective effects like the hot electron resonant bunching effect in the momentum space at a ballistic transport of electrons up to optical phonons energy in GaAs/AlGaAs heterostructures is discussed. In GaAs/AlGaAs heterostructures the complex structure of photovoltaic response dependent on frequency and polarization of the incident radiation has been observed. This effect reveals a possibliity to elaborate solid state detectors to analyse the parameters of millimeter and submillimeter waves.
The processes of tissue damage up to destruction under laser radiation action which are characterized by definite dynamics of temperature in the region of laser heating are studied using pulsed photothermal radiometry of tissue (PPTR). The thresholds of the water evaporation from tissue and the tissue destruction for different tissues and wavelengths of incident laser radiation are considered. The difference in dentine temperatures when the tissue destruction starts for CO2 and Er lasers is discussed. The features of the destruction processes and the difference of the temperatures corresponding to the tissue destruction thresholds under CO2 laser action for hard and soft tissues are discussed.
Pulsed photothermal radiometry (PPTR) method based on analysis of experimentally measured kinetics of non-equilibrium infrared blackbody (thermal) emission from a specimen subjected to pulsed laser irradiation has been used to investigate optical properties of tissues. Detailed investigations of thermal emission kinetics and the relationship caused by pulsed YAG:Er and YAG:Ho laser irradiation of tissues with different pulse duration and over a broad energy range up to the evaporation threshold have been performed. The spectrum of dentine in the IR region is presented.
Pulsed photothermal radiometry (PPTR) of tissue based on the analysis of thermal radiation kinetics measured from tissue at laser heating is an effective method of laser-tissue interaction investigation. The processes of destruction under laser radiation action (coagulation, fusion and welding), which are characterized by definite dynamics of temperature in the region of laser heating, have been studied. The amplitude and kinetics of the thermal signal registered by PPTR technique depend on space and temporal temperature changes in the zone of heating, which is conditioned by the regime of laser action and internal processes in tissue. In the present study the investigation of thermal tissue destruction under action of high-power pulsed CO2 and YAG:Er-laser radiation has been carried out using PPTR. Soft and hard tissues have been examined. The nonlinear dependencies of thermal emission kinetics, the thermal signal amplitude, and the integral absorption on laser energy density are presented and discussed. We represent PPTR as a technique which can be used for the definition of the destruction threshold and for the regulation of laser action on tissue. PPTR method has been applied in clinics with the aim of more accurate definition of CO2 pulsed medical laser radiation dose for treatment of patients with different dermatological diseases.
The pulsed photothermal radiometry of biological objects is used for controlling and investigation of tissue damage by YAG:Er ((lambda) equals 2,94 mkm), YAG:Nd ((lambda) equals 1,06 mkm), CO2 ((lambda) equals 10,6 mkm) laser radiation thermal action, study of optical and thermophysical properties of tissue (tooth) in vivo.