Abstract

In addition to one photon absorption and fluorescence in rare earth and transition metal ion doped crystals and glasses, a number of other processes can occur such as two-step excitation and energy transfer which may affect laser operation. For example, concentration quenching in Nd³⁺ doped materials is an energy transfer phenomenon, and energy transfer or two-step excitation can convert infrared photons to visible fluorescence¹ or visible lasers². It has also been shown that energy transfer upconversion (ETU), also known as Auger recombination, can increase laser threshold and change laser dynamics³. Both sequential two-step excitation (STEP) and energy transfer upconversion (ETU) have been identified in Nd³⁺ doped materials. These two processes are shown in Fig. 1. STEP involves absorption of one photon to put an ion in an excited-state, then excited-state absorption (ESA) of a second photon to an even higher lying level. In ETU, two ions which are in excited-states interact causing one ion to relax while the other is simultaneously excited to a higher state.

© 1986 Optical Society of America