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Applied Physics Letters

Stimulated emission and optical gain in HgI2

Ida Maria Catalano, Aldo Cingolani, Michele Ferrara, M. Lugarà, Antonio Minafra

Published Jan 1, 1978• 6 citations
Publisher

Abstract

Stimulated emission in HgI2 at 80 °K due to an exciton-electron collision cooperative process is reported. The line shape of the stimulated emission band depends on the excitation wavelength. High optical gain has been measured. These effects are observed both with one- and two-photon pumping.
DOI
10.1063/1.89824

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We have investigated the fluorescent and stimulated emission properties of PrCl3 as a function of the pump laser wavelength, pump power, and temperature. The previously reported laser emission at 645.2 nm has been studied at 295°K and at lower temperatures. At low temperatures we have observed stimulated emission at three new wavelengths, 616.8, 529.8, and 489.2 nm. The linewidths and lifetimes of various optical transitions have been measured and related to the observed optical gain at the above wavelengths. We have also observed stimulated output in 1% Pr in LaCl3.
Abstract In CuCl at 1.7 K optical gain/absorption spectra are recorded in the spectral range of bound exciton and biexciton emission. Energy, effective temperature, and oscillator strength of biexcitons are determined. The observed kinetics indicates that the total pair density in the exciton‐biexciton system is pinned at about 1.6 × 1016 cm−3 for all excitation densities above 10 kW/cm2. At intense excitation, a Fano‐interference is observed between a discrete impurity absorption line and a continuum absorption tail. The latter is followed by a band of positive gain towards lower photon energies.
The dynamics of the pulse shape and spectra of superfluorescence, stimulated superradiance, and coherent amplification of ultrashort light pulses is studied for a system of four-level atoms under incoherent cw pumping taking into account homogeneous and inhomogeneous broadening of the luminescence lines. It is found that incoherent pumping at a high level of excitation may significantly change the shape of the emission pulse in cooperative coherent processes. Also, it is found that, depending on the ratio of parameters of the pump, nonradiative transitions, and relaxation, different regimes of superfluorescence and stimulated superradiance may be realized.
The stimulated emission signal from a tunable cavity with Rydberg matter as the lasing medium is studied. The Rydberg matter is excited by heating through a non-radiative process. The emission bands are resolved by diffraction up to the fifth order using several different gratings in the cavity. The signal variation with wavelength is strong, especially in the wavelength range <2000 nm. The wavelength variation of the signal over the range 800–14 000 nm is compared with Rydberg matter theory giving good agreement. The transitions observed are from down to 6–21. There are no bands in the visible range, which is explained from the possible excitation levels in Rydberg matter. Reflecting some light out of the cavity gives lower gain (higher loss) and sharper bands, demonstrating that the device is indeed a working laser.
An analysis of a three-level system using time-dependent perturbation theory shows that two distinct photon-emission processes take place within such a system when stimulated optical emission occurs: one-and two-photon transitions. The two-photon transition consists of the emission of a stimulated photon followed by the absorption of a coherent pump photon. In three-level systems which possess a narrow pump level, two-photon transitions are dominant at high pump powers while the maser line is split into two lines due to the modulation of the wave function at an angular frequency determined by the rate of pumping. This might lead to the possibility of frequency-modulating the maser line. These results are extended qualitatively to include optical masers which possess broad pump-bands.
An analysis of a three-level system using time-dependent perturbation theory shows that two distinct photon-emission processes take place within such a system when stimulated optical emission occurs: one-and two-photon transitions. The two-photon transition consists of the emission of a stimulated photon followed by the absorption of a coherent pump photon.In three-level systems which possess a narrow pump level, two-photon transitions are dominant at high pump powers while the maser line is split into two lines due to the modulation of the wave function at an angular frequency determined by the rate of pumping. This might lead to the possibility of frequency-modulating the maser line. These results are extended qualitatively to include optical masers which possess broad pump-bands.