О механизме поглощения и восстановления пропускания излучения в канале мелкомасштабной самофокусировки короткого лазерного импульса в неодимовом стекле

In the study of small-scale self-focusing (SSF) of a 0.5 ns Nd-laser pulse with 3-5 GW/cm2 intensity in Nd-glass samples, in addition to the characteristic filamentary damage, spectral broadening and laser radiation scattering, a jump in absorption in glasses at the wavelengths 1.06 µm and 0.66 µm was registered also. The coefficient of the induced absorption (IA) in the samples reached 0.15 cm– 1. Restoration of the transmission in the media after the end of the laser pulse had occurred over the time of 15-35ns for phosphate and 5-10 ns for silicate glasses. The physical picture of the IA effect detected as far back as the 1980-s, however, had not been clarified. Current analysis of the experimental data has shown that the absorption jump could be caused by the rapid populating of the 4I11/2 lower laser level of Nd3+ ions in glasses due to the nonlinear processes in the SSF channel: Raman scattering and spectral broadening of the laser radiation. The rates of the 4I11/2 level depopulation and recovery of the transmission were determined by dimensions of the regions with excited Nd3+ ions arising in the glass samples at the interference of laser and scattered radiation as well as by thermal properties of glasses.

Resonance line reabsorption in a laser-produced plasma showing specific deviations from axial symmetry

To predict the gain in a lasing transition in ions of a laser-produced plasma, it is essential to calculate the amount of the reabsorption of radiation emitted in the transition from the lower laser level to the ground state. An important quantity influencing the reabsorption is the plasma geometry as resulting from the design of the laser and target system. Modeling a nonaxially symmetrical geometry of the plasma arising from a target irradiated by line-focused laser beams, we consider the plasma in the form of a longitudinally cut-out circular cylinder, with central angle ø, and the length of the plasma much larger than its transversal extension. Accounting for the effect of resonance line trapping via the escape probability approach, and taking the absorption profile in the line center approximation, an explicit formula for the photon escape probability depending on the radial and angular coordinates of an interior point in the plasma is derived. This function is averaged over the angular variable to obtain an only radially varying mean escape probability.

Ultimate efficiency of nuclear-pumped gas lasers

We suggest several cascade lasing schemes: (1) cascade of laser transitions between atom (ion) excited levels when the lower laser level of one laser transition is simultaneously the upper laser level of another transition located below; (2) successive lasing, first, on ion transitions, then after ion recombination on atom transitions; (3) while using multicomponent mixtures, successive lasing on atoms (ions) of separate components. These possibilities are discussed in terms of specific lasers, some of which have been studied experimentally.

Optical Absorption and Emission in Rare Earth Heavy Metal Fluoride Glasses

Trivalent thulium is a 4-level laser system which operates in the 1.47μm spectral region. A tunable amplifier at this wavelength is of great interest since it falls in one of the telecommunication windows. For lasing action to occur the relatively long lived 3F4 lower laser level must be quenched to eliminate the self-terminating behavior of thulium. Rosenblatt et al. co-doped Tm and Th into a ZBLAN host to quench the 3F4 lower laser level.[1] Co-doping with Ho offers the possibility of more efficient laser operation, but it must be established whether Ho can effectively quench the lower level of Tm. This preliminary study indicated appreciable energy transfer occurred from the 3F4 level of Tm to the 5I7 level of Ho which decreased the lower laser level lifetime by as much as two orders of magnitude. The subsequent decay of the Ho ions is an issue requiring further investigation.