Simple technique for measuring the energy-transfer-upconversion parameter in solid-state laser materials

Scaling the output power from solid-state lasers to higher power levels, whilst maintaining high efficiency and good beam quality is a challenging task. The chief difficulty is heat generation and its deleterious effects on laser performance. The main origin of heat generation is often considered to be quantum defect heating. However, many solid-state laser media also suffer from the problem of energy-transfer-upconversion, which can lead to a dramatic reduction in the effective upper laser level lifetime and a large increase in the fractional heat loading unless appropriate measures are taken. Thus, an accurate knowledge of the upconversion parameter and the impact of upconversion on laser performance is very important for power scaling of solid-state lasers, particularly when operating in pulsed (Q-switched) mode. The standard method for determining upconversion parameters, based on measurements of fluorescence decay times, can be quite time consuming and requires very careful attention to detail in the experimental set-up and pumping conditions if it is to yield accurate values