Optimization of Cr -Doped Saturable-Absorber -Switched Lasers

Abstract

Cr -doped saturable absorbers are characterized by long excited state lifetime and appreciable excited state ab- sorption. In this paper, we first solve the three coupled rate equations describing the operation of Cr -doped saturable- absorber passively -switched lasers to obtain the expressions of pulse characteristics such as output energy, peak power, and pulsewidth. We then determine the key parameters of an optimally coupled passively -switched laser as functions of two variables concerning the amplifying medium, saturable-absorber medium, and pump level, and generate several design curves. These key parameters include the optimal normalized coupling parameter and the optimal normalized saturable-absorber pa- rameter which maximize the output energy (or maximize the peak power, or minimize the pulsewidth), and the correspond- ing normalized energy, normalized peak power, and normal- ized pulsewidth. The results are valid for not only Cr -doped saturable-absorber -switched lasers but also other any lasers passively -switched by saturable absorbers with long excited state lifetime and appreciable excited state absorption. Using the expressions and design curves, with the aid of a simple hand calculator, one can predict the pulse characteristics and perform the design of an optimally coupled passively -switched laser.