Nonlinear absorption in directgap crystals
Abstract
A critical review of the Keldysh, Braunstein, and Basov formulations of the nonlinear absorption process in direct gap crystalline solids is presented. The two photon absorption coefficients in several alkali halides and semiconductors are calculated by means of the above three models and compared with available experimental data. It is concluded that the Keldysh formula offers a sufficiently accurate description of the multiphoton absorption process, even when the photon multiplicity is small. This is in contrast to the frequently expressed view that the Keldysh formula is incorrect for small photon multiplicities. It is found that the Keldysh formula is closely related to Braunstein's formula for allowedallowed transitions, while Basov's formula corresponds to the allowedforbidden case. It is also shown that the predictive accuracy of the Braunstein formulas can be increased by the use of nonparabolic energy bands and excitonic intermediate states. Finally, the Basov formula, which until now was considered to be the most accurate description of the two photon absorption process, is shown to contain several errors.
 Publication:

Laser Induced Damage in Optical Materials
 Pub Date:
 July 1980
 Bibcode:
 1980nlid.rept..445V
 Keywords:

 Absorptivity;
 Alkali Halides;
 Electromagnetic Absorption;
 Laser Damage;
 Semiconductors (Materials);
 Crystals;
 Energy Bands;
 Mathematical Models;
 Prediction Analysis Techniques;
 Solid State;
 Transition Probabilities;
 Lasers and Masers