Influence of energy-transfer-upconversion on threshold pump power in quasi-three-level solid-state lasers

Abstract

A simple analytical expression for threshold pump power in an end-pumped quasi-three-level solid-state laser, which takes into account the influence of energy-transfer-upconversion (ETU), is derived. This expression indicates that threshold pump power can be increased dramatically by ETU, especially in low gain lasers and lasers with pronounced three-level character due to the need for high excitation densities in the upper manifold to reach threshold. The analysis has been applied to an Er:YAG laser operating at 1645 nm in-band pumped by an Er,Yb fiber laser at 1532 nm. Predicted values for threshold pump power as a function of erbium doping concentration are in very good agreement with measured values. The results indicate that very low erbium doping levels (approximately 0.25 at.% or less) are required to avoid degradation in performance due to ETU even under continuous-wave lasing conditions in Er:YAG.

Resonantly diode-pumped continuous-wave and Q-switched Er:YAG laser at 1645 nm

“…Reduced upper state lifetimes for Q-switched Er:YAG lasers pumped by EDFLs have been reported by a number of authors [10,11,14]. Several mechanisms have been proposed to explain this reduction, including upconversion [11,14] and ASE [10]. Such mechanisms would result in an upper state lifetime reduction that is dependent on the population of the upper state, which is consistent with the result shown in Fig.…”

“…Another loss mechanism must therefore be decreasing the lifetime of the upper lasing state. Reduced upper state lifetimes for Q-switched Er:YAG lasers pumped by EDFLs have been reported by a number of authors [10,11,14]. Several mechanisms have been proposed to explain this reduction, including upconversion [11,14] and ASE [10].…”

Numerical Analysis of Laser Diode Longitudinally Pumped Solid‐state Laser Generation Dynamics Using Traveling Wave Model

“…The nonlinear terms with coefficients β ase and β up could be caused by amplified spontaneous emission (ASE) or by upconversion [22]. Energy-transfer-upconversion (ETU) is an energy-transfer process between two neighbouring ions in the upper laser level (Fig.…”

Efficient 1645 nm continuous-wave and Q‑switched Er:YAG laser pumped by 1532 nm narrow-band laser diode

“…The optical-optical and slope efficiencies are much lower than the quantum efficiency (~90%). The strong thermal effect in Er:YAG crystals is explained as a result of ETU [3,5,6,15], which is quadratic in the upper laser level population. Therefore, Er:YAG crystals with low Er 3+ doping concentration are required.…”

“…Due to good modal matching, ETU can be solved with 0.5% doped Er:YAG crystals in hybrid fiber-bulk erbium lasers. Further decreases in the Er 3+ doping concentration show slight improvements in efficiency [15,16]. LD-pumped 0.5% doped Er:YAG lasers, however, suffer from poorer modal matching, as the result of the much larger pump light divergence.…”