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Temperature-dependent transient processes initiated by a direct photogeneration of singlet oxygen in suspensions of human erythrocytes and solutions of serum albumin are studied. The processes appear as anomalous jumps in the temperature dependences of the deformability coefficient of erythrocytes and the refractive index of the extracellular medium and protein solution. In the temperature regions of anomalous jumps, cells and proteins transfer to a metastable state of a lower activity, but they can be isothermally photoreactivated. Simultaneously, a reversible rearrangement of the aqueous phase occurs near the cell and protein surfaces, accompanied by the formation of an extended corona (hydrogel). The transient processes are interpreted as phase transitions in the membrane of erythrocytes and conformation transitions in proteins. The interaction between erythrocytes and albumin via hydrogel is discovered (hydro-conformational interaction). A qualitative physical model of the early stages of the light-oxygen effect is proposed, in which collective magnetic interactions between the electron spins of oxygen molecules and the nuclear magnetic moments of protons in H{sub 2}O molecules play a dominant role. (special issue devoted to the 80th anniversary of academician n g basov's birth)

Highly UV excited KI : In+ and KI : Sn2+ crystals exhibit at low temperatures pronounced emission bands peaking near 3.3 eV along with the activator luminescence. The spectra and the lifetimes of the 3.3 eV emission are close to the well-known radiative characteristics of the triplet self-trapped excitons in pure crystals of KI. The observation of exciton luminescence in doped crystals of KI confirms that excitons are involved in the process of F-center formation caused by intense optical excitation of the impurities in alkali halides.

A quantitative study of the up-conversion process ( 4 I 13 2 → 4 I 15 2 ) + ( 4 I 13 2 → 4 I 9 2 → 4 I case11 2 ) , essential in the 3 μm emission of Er3+ in YAG, over a large concentration range (0.1 to 100 at% Er3+) and pumping energy has been performed. The concentration and sample dependence of the “intrinsic” lifetime of 4I 13 2 and 4I 13 2 laser levels is tentatively explained by energy transfer to aleatory impurities. The quadratic concentration dependence of the up-conversion parameter, obtained experimentally, and the possibility to describe the up-conversion process by rate equations are explained by large migration effects and effective interactions between nearest neighbours.

The results of the luminescence-quenching measurements of the $^{4}$${\mathit{S}}_{3/2}$ level of ${\mathrm{Er}}^{3+}$ in yttrium aluminum garnet are reported. Decay data in a large temperature (10--300 K) and concentration range (0.1--100 at.%) are analyzed. The quenching process depends strongly on concentration and temperature. At low ${\mathrm{Er}}^{3+}$ content (\ensuremath{\le}3 at.%) the quenching is dominated by two-ion dipole-dipole cross-relaxation processes. It is shown that the previous proposed mechanisms can only explain the high-temperature data, and a possible active mechanism at low temperatures is proposed. At higher concentrations the quenching process depends strongly on temperature, the migration on donors playing an essential role, especially at low temperatures, where the supermigration regime is observed. The quadratic concentration dependence of the transfer parameters at high ${\mathrm{Er}}^{3+}$ content is connected with the three-ion cross-relaxation processes. The temperature dependences of the supermigration rates are consistent with two types of three-ion processes, i.e., one phonon-assisted process at low temperatures (T100 K) and another very efficient resonant one [${(}^{4}$${\mathit{S}}_{3/2}$${,}^{2}$${\mathit{H}}_{11/2}$)${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{15/2}$${]}_{\mathit{D}}$+[${(}^{4}$${\mathit{I}}_{15}$ $_{/2}\ensuremath{\rightarrow}^{4}$${\mathit{I}}_{13/2}$${)}_{\mathit{A}1}$+${(}^{4}$${\mathit{I}}_{15/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{9/2}$${)}_{\mathit{A}}$ at high temperatures (Tg150 K). It is shown that at 300 K for Cg10 at.% ${\mathrm{Er}}^{3+}$ the transfer is of direct donor-acceptor type, due to the above cross relaxation. Thus, at 300 K, the energy from the pumping $^{4}$${\mathit{S}}_{3/2}$ level is transferred to the 3-\ensuremath{\mu}m laser levels ${(}^{4}$${\mathit{I}}_{11/2}$ and $^{4}$${\mathit{I}}_{13/2}$) by a three-ion cross relaxation. This study has emphasized the possibility of very efficient three-ion processes in the luminescence quenching of rare earth elements at large activator concentrations.

An analysis was made of the concentration dependence of the up-conversion energy transfer parameter ?2. This dependence was quadratic at low excitation densities.

A pulse laser on a phosphate glass activated by Cr3+-Yb3+-Er3+ ions (λ = 1.54 μm) was used to pump Y2Al5O12:Er3+ (YAG:Er) crystals to the lower laser level of a 3-μm transition (4I11/2 → 4I13/2) in Er3+ ions (λ = 2.94 μm). For a pumping pulse energy of Eexc = 200 mJ, the efficiency of 3-μm lasing was 20%. A differential efficiency of the YAG:Er laser in the case of a resonance pumping into the lower laser level amounted to 26%.

Stornatologic service is most popular of all kinds of medical aid, since up to 90% of people suffer from caries, parodontosis holds the second place after such a widespread disease as cardiovascular pathology. The treatment of the tooth hard tissue, intervention into pulp and parodontium using conventional methods are accompanied with painfulness and unpleasant sensation. A lack of efficient methods of anesthesia and pulp devitalization, a high percentage of complica tions after pulpitis treatment made it necessary to search for new methods of treatment which exclude these negative aspects. Application of laser radiation may be one of the ways in resolving this problem. Such attempts have been made repeatedly with the development of laser technology.'3 However, not all of them turned out to be successful. The greatest difficulties occurred on surgical intervention into hard tooth tissue. The best results have been so far attained when using pulsed CO2 laser operated at the wavelength A =1O.61um. For instance, at pulse width 1O1us and frequency 10-20 Hz, the tooth channel drilling was efficient at energy density in pulse P . 10 JIcm2. 4'5 The electron-microscopic investigations have proved the tooth microstructure to be preserved for this laser operation mode. The traces of graphitization were observed only in the vicinity of the lateral walls of the channel.

Excitation of Y2.94Tm0.06Al5O12 crystals with ruby laser radiation resulted in generation of stimulated radiation due to the 3F4–3H5 transition. The duration of the output pulses was approximately five times the duration of the pump pulses. This was attributed to the accumulation of excitation at 1D2 and 3H4 levels.

The luminescence kinetics study of the 4S 3 2 level of Er3+ in YAG in the concentration range up to 100 at.% Er, stresses the importance of migration of energy among donors in the energy transfer process. At 77 K the supermigration regime is installed under 10 at.% Er. For low Er concentrations the mechanism of transfer is dipolar; at high Er doping an unusual nonlinear dependence of the transfer rate on concentration is observed, regardless the origin of the investigated sample and the method of crystal growth. Possible processes inside the Er3+ ion system, leading to the observed behaviour, are discussed.

An investigation was made of the lasing properties of Q-switched YAG:Er/sup 3 +/ crystals (/sup 4/I/sub 11/2/--/sup 4/I/sub 13/2/). An energy of 100 mJ was obtained in the TEM/sub 00/ mode and the pulse duration was 65 nsec. Under free-lasing conditions, the efficiency was 1.25% and the output radiation energy 5 J. The radiation parameters were strongly influenced by the Stark splitting of the /sup 4/I/sub 11/2/ and /sup 4/I/sub 13/2/ active levels.

An investigation was made of the contribution of radiative and nonradiative transitions to the deactivation of the upper laser levels 4S3/2, 4I11/2 and 4I13/2 of the Er3+ ion in mixed yttrium-erbium aluminum garnets. The optimal activator concentrations, ensuring minimum concentration quenching of the luminescence, were determined. A comparison of the Einstein coefficients, deduced from the corresponding integrated absorption coefficients, with the experimentally determined room-temperature lifetimes of the levels 4I11/2 and 4I13/2 established that the quantum efficiency of the 4I13/2 level was unity (to within the experimental error) and that of the 4I11/2 level did not exceed 0.017. However, the possibility of using high activator concentrations made the laser utilizing the 4I11/2–4I13/2 transition sufficiently efficient.

A comparison of theoretical and experimental results shows that a suitable selection of the spectroscopic parameters of YAG:Er3+ crystals can ensure a qualitative agreement between calculations and experiments (within the limits of the relevant errors). Calculations demonstrate a considerable contribution of direct pumping of the upper active level by flashlamp excitation. The maximum theoretical value of the differential efficiency for the best laser head is 2.7%.

Impurity clouds in dislocation-free silicon crystals are investigated by CO2-laser radiation scattering. Experiments on crystals which, are grown at rates between 4 to 45 cm/h support earlier results on the generation of impurity clouds. The source of the clouds are microinclusions of impurities (O and C) in the solid crystals. At temperatures below the melting point of silicon and above 900 °C the clouds expand in dependence on the crystal growth rate (i.e. cooling rate) and their size is determined by the diffusion coefficient of the impurity.

Local inhomogeneities in semiconductors (i.e. structural defects and regions of enhanced impurity concentration) can influence crystal properties and device parameters. The influence of structural defects is probably caused by their action as impurity s egregation sites 1,2. Thus the impurity inhomogeneities are the most interesting object of investigation. Most methods such as electron-probe microanalysis, transmission electron microscopy (TEM), etc. detect only regions of high impurity concentration, i.e. inclusions (particles captured during crystal growth), precipitates and their colonies. On the other hand, probe resistivity measurement reveals only regions of large size. However the inhomogeneities of small size (say 10 μm) and of relatively low concentration can have a crucial effect on crystal properties.For instance they control the quality of germanium detectors 3,4. Such impurity inhomogeneities can be detected and studied by low angle scattering of IR laser beams 5,6.

An investigation was made of the kinetics of the luminescence due to 4I11/2 → 4I15/2 and 4I13/2 → 4I15/2 transitions in the Er3+ ion in yttrium erbium aluminum garnet crystals subjected to strong resonant excitation argon laser radiation (λ = 4880 nm). The efficiency of the cooperative process resulting in nonlinear quenching of the luminescence from the 4I13/2 level and sensitization of the 4I11/2 level was estimated. The influence of this process on the kinetics of lasing as a result of the 4I11/2 → 4I13/2 transition (λ = 2.94 μ) was analyzed.

An electrooptic filter was used for broad-band tuning (720–900 nm) of a flashlamp-pumped Al2O3:Ti3+ crystal laser. Some characteristics of the use of electrooptic filters in tunable laser resonators are analyzed. It is shown that the observed deviation of the Al2O3:Ti3+ laser tuning characteristics from a linear dependence on the voltage across the filter is due to a combination of two factors: the wavelength dependence of the active medium gain and the width of the filter transmission band.

Studies of the spectra of stimulated emission from Y3AI5O12:Er3+ crystals (4I11/2–4I13/2) containing 20 wt.% activator ions, showed that, as the temperature decreased from 300 to 77°K, a change was observed in the emission wavelength (at T = 300°K it was found that λ1 = 2.9364 μλ2 = 2.8310μ and at T = 77°K it was found that λ1 = 2.6930 μ, λ2 = 2.8970 μ). This could not be attributed to a thermal redistribution of the populations of the Stark components of the 4I11/2 and 4I13/2 upper and lower active levels. An analysis of the results showed that the temperature shift of the stimulated emission spectrum was due to changes in the processes of relaxation of excitation from the upper levels of the Er3+ ion which caused substantial changes in the populations of the 4I11/2 and 4I13/2 multiplets.

An experimental investigation was made of nonradiative relaxation of the excitation from the 4S3/2 level of the Er3+ ion in Y3Al5O12. It was found that quenching of the excitation from the 4S3/2 level cannot be described using a single microparameter at all stages of the excitation decay process.

A method is proposed for determining the photoionization cross section of an excited state from the change in the relative quantum efficiency of intracenter luminescence. Measurements are reported of the cross sections of photoionization by intense radiation from an XeCl excimer laser of mercury-like Tl+, In+, and Sn2+ ions in alkali halide crystals.

Measurements were made of the rate constants of transfer of the excitation energy by the interaction between Er3+ ions excited to 4I11/2,13/2 states in Y3Al5O12 crystals. The constants were used to determine the influence of the cooperative processes on lasing of an Y3Al5O12:Er3+ crystal as a result of the 4I11/2–4I13/2 transition.

A study was made of the possibility of using thermal sensitization of a silver halide photographic emulsion for recording YAG:Er3+ laser radiation (λ = 2.94 μm). Using an FT-101 photographic film it was possible to record the radiation down to energy densities of ~ 1 mJ/cm2 in a dynamic range of ~ 100 with a resolution of at least 50 lines/mm when the laser pulse duration was ~ 150 μsec. This method was employed to determine for the first time the spectral width of a line emitted by a YAG:Er3+ laser operating in the free-running regime.

An analysis was made of a new configuration of a laser utilizing the 4I11/2–4I11/2 transition in the Er3+ ions in YAG with a high activator concentration (~5×1021cm−3). It is shown that at a certain excitation rate the cross-relaxation processes increase considerably the lasing efficiency and make it possible to achieve cw emission as a result of transitions from a long-lived lower level.

Measurements were made of the ratio of the luminescence energies represented by the 4I11/2–4I13/2 and 4I11/2–4I15/2 transitions in Er3+ ions in (Y1–xErx)3Al5O12 crystals. The Einstein coefficients of these transitions were also determined. The cross section of the 4I11/2–4I13/2 (X2–Y6) stimulated emission transition was measured. The concentration dependences of the absolute quantum efficiencies of the luminescence from the 4I11/2 and 4I13/2 levels were obtained.

The development of a pulsed Y3Al5O12:Er3+ laser (4I11/2–4I13/2 transition, λ = 2.94 μ) with activator concentrations of 30 wt.% (T = 300 °K) is reported. A pulse repetition frequency of f = 20 Hz was obtained under free-oscillation and Q-switched conditions. Stimulated emission due to this transition at T = 300 °K was obtained over the whole concentration series of the Y3Al5O12–Er3Al5O12 system with Er3+ concentrations of between 10 and 100 wt.%.

An electrooptic LiNbO3 filter is used for tuning free running oscillation (720-900 nm) and giant pulses (760-820 nm) of a flash lamp pumped Ti:A12O3 laser. The tuning laser characteristics and the peculiarities of electrooptic filters application in tunable laser resonators are analyzed.

The advent of effective solid-state pulse lasers operating in the 3-pm range [1, 2] that became available during the last ten years sets forth the problem of designing methods of registration and visualization of laser radiation within this range. Today, a researcher may choose from a good number of IR radiation visualization techniques resting upon the effect of a change of properties in various materials under the influence of heat [3]. In terms of such indicators as sensitivity, dynamic range, resolution, as well as a number of operational characteristics, the "thermal sensitization" technique applied to silver-halide photoemulsions [4] is far superior to any other available technique for visualization of IR radiation pulsed laser fields. This technique has been originally applied to photoregistration of pulsed gas laser radiation in the range of 5 and 10 pm. This paper presents the results of the experimental study of the potential of the method for registration of a YAG:Er3+ laser radiation at λ = 2.94 μm. The following parameters were determined: sensitivity, 2 mJ/cm2; dynamic range, 100; resolution with the generation pulse duration of 200 μs, not worse than 50 lines/mm.© (1989) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A model of the last parts of the bacteriorhodopsin (bR) photocycle is proposed on the basis of experimental data for the kinetic behavior of the 'O' intermediate during a temperature pulse in distilled water suspension. The model includes the previously proposed (but not well characterized) intermediate 'N' between the 'M' and 'O' states of bR. This intermediate exists in fast temperature-dependent quasi-stationary equilibrium with the red-shifted intermediate 'O' and has a maximum of absorption close to the bR spectrum.

The optical inhomogeneities with character size α~5–13μ and deviation of dielectric permittivity ⧍e~10−3 — 10−4 were observed in the experiments on the CO2-laser small angle acattering by semi-insulating GaAs. The temperature- influence experiments show that these inhomogeneities are the clusters of free carriers. These carriers appear in the regions of high concentration of ionized at room temperature centers. High temperature annealing experiments show that these centers are complexes of impurities with high and low diffusion coefficients. The concentration ~1016 cm−3 of free carriers in each inhomogeneity is estimated. The total number of carriers located in all impurity clusters is ~ 1012cm−3, while they occupy only 0.1% of the crystal volume.

Stimulated emission due to the 4I11/2–4I13/2 transition (λ = 2.936 μ) in yttrium aluminum garnet (Y3Al5O12) doped with Er3+ ions (30 wt%) was observed for the first time at 300°K. The output energy from crystals of 50×3 mm dimensions was 0.3 J under free-oscillation conditions and 0.05 J in the case of Q switching. The lifetime of the 4I11/2 level was determined for crystals with 3–30 wt% Er3+. The energy from the higher Er3+ levels relaxed in a cascade manner through 4I11/2 to 4I13/2.

The method of adiabatic pulsed laser calorimetry is considered. It is shown that this method of determination of the volume absorption coefficient of optical materials heated by laser pulses of different duration makes it possible to find the dimensions of submicron defects and to analyze the nature of nonlinear absorption without damage to the optical material.

Lasing was induced in Y1.5Er1.5Al5O12 (λ = 2.94 μm) crystals by selective pumping of the electronic–vibrational wing of the 4I15/2–4I13/2 transition. A population inversion was established in this YAG:Er3+ laser by a strong interaction between the excited Er3+ ions at the 4I13/2 level and the transfer of energy from the lower active level to the upper one in accordance with the 4I13/2–4I9/2, 4I13/2–4I15/2 scheme.

Pulsed photothermal radiometry of biological objects is described. The absorption coefficients of YAG:Er3+ and CO2 laser radiation and thermal diffusivities in various biological tissues were determined experimentally.

An investigation was made of electrooptic modulation of the Q factor of a resonator of a titanium-activated corundum laser. One electrooptic switch was used to achieve continuous tuning (in the range 760–820 nm) of the wavelength of the giant pulses generated in the Al2O3:Ti laser. The energy of the giant pulses was 10–30 mJ and their duration was 50–70 ns.

Experimental and theoretical studies demonstrated that steady-state emission was possible from an YAG:Er3+ laser utilizing the self-terminating 4I11/2–4I13/2 transition with a cross-relaxing lower level (4I13/2)

These crystals produce 30 nsec pulses of peak power 1.4 MW in the single-pulse mode, or 40 nsec and 1 MW in the repetition mode (500 Hz repetition frequency). The beam produces a bright plasma when focused on the surface of a metal.