a Dynamic Model of Optically Pumped Energy Storage Lasers.
Abstract
A dynamic, complete model of optically pumped, energy storage laser media has been developed. This model predicts stored energy density and heat deposition as a function of both time and space. The relevant physics for solid state and liquid energy storage media has been considered including non-radiative loss mechanisms such as cooperative relaxation and multiphonon relaxation, and radiation loss mechanisms such as spontaneous emission and, for one particular geometry, amplified spontaneous emission. The model was applied to two energy storage media: xenon flashlamp pumped neodymium in glass and resonantly pumped (either xeF or dye) trivalent thulium in glass. The former system requires a complete spectral and temporal knowledge of the radiance of the xenon flashlamps used. The theory presented by Tenholme and Emmett at the Ninth International Conference on High Speed Photography was used for this purpose. It is a phenomenological theory that takes the lamp bore size, arc length, fill pressure and instantaneous lamp current to predict instantaneous lamp radiance. This in turn requires a knowledge of the pulse forming network's (PFN) parameters which are utilized in an integration of the PFN's loop equation for the current. Because the Trenholme -Emmett theory has only been used in a time-integrated manner previously, it was necessary to perform time-resolved spectroscopy on the 13 mm bore lamps used in these experiments to check and modify the Trenholme-Emmett theory. The differences found included a dependence upon the time derivative of the current, a stronger dependence on current and different lines and linewidths than those found by Trenholme and Emmett. For the nonradiative losses in both Nd and Tm systems classical electromagnetic cooperative relaxation theory was used. A concentration squared dependence is predicted and a 3/2 power dependence observed. The linear dependence on concentration of an impurity having a high energy vibration predicted by multiphonon decay theory was observed for Nd in phosphate glasses. This is strong evidence for stimulated phonon emission. Measured zero -doping fluorescence lifetimes were used in the model. Comparisons of predictions with experiment are presented. Finally, the model was applied to a large aperture, active-mirror configuration Nd:glass amplifier. This necessitated including the effect of ASE on the inversion density. Because of the unique geometry of the active mirror amplifier ASE could be approximated as a parasitic oscillation which clamps the inversion at a specific level determined from small signal gain measurements. Comparisons with the measured small signal performance of several active mirrors is shown and agreement is excellent. Consequently the model has become an on-line design tool for optimization of large aperture amplifiers.
- Publication:
-
Ph.D. Thesis
- Pub Date:
- December 1980
- Bibcode:
- 1980PhDT........69K
- Keywords:
-
- Physics: Optics; Energy;
- Dynamic Models;
- Energy Storage;
- Flux Density;
- Glass Lasers;
- Optical Pumping;
- Fluorescence;
- Photons;
- Relaxation (Mechanics);
- Thulium;
- Xenon Lamps;
- Lasers and Masers