Pedagogically fast model to evaluate and optimize passively Q-switched Nd-doped solid-state lasers

Abstract

The coupled rate equations with the spatial overlap effect for four-level passively Q-switched lasers are fully considered. A transcendental equation is derived for the residual fraction of the inversion density after the finish of the Q-switched pulse. Comprehensive calculations for the transcendental equation were executed to attain an analytical function for precisely fitting the residual fraction of the inversion density. With the fitting function, a pedagogical model with the correction for high output coupling is developed to straightforwardly analyze the output pulse energy and peak power. Detailed experiments are carried out to validate the model.

Modeling for Spatial Overlap Effect of End-Pumped Passively Q-Switched Nd:YVO4/Cr4+:YAG Laser and Its Experimental Verification

“…The transmittance of output coupler can be well approximated to be ln(1/R oc ) for high reflectivity. However, for those reflectivity lower than e −1 , it is more general and appropriate to use (1 − R oc ) term for a wide range of reflectivity [18]. So far, we have completed the derivation of the output energy equation, and the term A e f f and S in the Equation ( 22) show the significance of considering the spatial effect.…”

“…In the condition of no gain saturation, the larger value of the η E means the more efficient population depleted in the saturable absorber, since η E cannot be directly solved as a function of ξ and α. A powerful expression derived from numerical fitting [18] for the energy utilization efficiency η E is given by…”

Sub-Nanosecond Passively Q-Switched Yellow and Orange Raman Lasers

“…Since passively Q-switched lasers eliminate a potential hazard of failure in highvoltage switching electronics of actively Q-switched lasers, the NASA space systems employed passive Q-switching technology instead of active Q-switching to increase reliability. Recently, we developed a pedagogically fast model for accurately analyzing PQS lasers in a full scope of output coupling [30]. We considered the spatial overlap effect in deriving the characteristic equation for the photon density from the coupled rate equations for the four-level PQS laser.…”

“…The developed model and equations were systematically validated with experimental explorations. The rate equations were used to analyze the operation of a four-level passively Q-switched laser [30]. From the analyzed result, the output efficiency can be characterized by the transcendental equation…”

“…Previously, we used a near-concentric cavity to realize an efficient passively Q-switched Nd:YVO 4 Raman laser at 589 nm with a KGW as an intracavity Raman gain medium at the shift of 901 cm −1 [23]. For achieving a passive Q-switching efficiency [30], we employed a near-concentric resonator to generate a large value of α via the beam focusing on the saturable absorber. The parameter α can be given by α = Aσ gs /(γA s σ), where A and A s are the mode areas for the fundamental wave in the gain medium and saturable absorber, respectively; σ gs and σ are the cross sections for the ground-state absorption of the saturable absorber and the stimulated emission of the gain medium, respectively; and γ is the inversion reduction factor.…”