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

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.

A study is made of the stability of the emission of a high-frequency train of pulses by a solid-state laser with periodic Q switching. Generation of a single pulse is analyzed theoretically by single-mode rate equations. The point mapping method is employed in a study of the stability of a periodic train of pulses characterized by different periods and pumping rates, and also of a periodic train consisting of a few pulses of different durations. The results are compared with the experimental data.

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 analysis is made of the operation of hybrid resonator-free optically bistable devices. An analysis is made for the delay time and the finite width of the pass band in the feedback circuit. The values of the parameters are divided into ranges corresponding to stationary, periodic, and stochastic operation.

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%.

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.%.