Abstract
A time-dependent analytical thermal model of the temperature and the corresponding induced thermal stresses on the pump face of quasi- continuous wave (qcw) end-pumped laser rods is derived. We apply the model to qcw diode-end-pumped rods and show the maximum peak pump power that can be utilized without fracturing the rod. To illustrate an application of the model, it is applied to a qcw pumped Tm:YLF rod and found to be in very good agreement with published experimental results. The results indicate new criteria to avoid fracture when operating Tm:YLF rods at low qcw pump duty cycles.
Highlights
The power scaling of diode–end–pumped solid–state lasers is a very active area of research
When the continuous wave pump power exceeds the power at which crystal fracture occurs, the pump source is often modulated in time, creating a so called quasi–continuous wave pump, with the effect of reducing the average pump power to below the fracture limit, while maintaining a high output power during the on-time of the pump pulse
In this paper an analytical thermal model that determines the transient behaviour of the temperature and the corresponding induced stresses on the pump face of an isotropic laser rod is derived from first principles
Summary
The power scaling of diode–end–pumped solid–state lasers is a very active area of research. In order to investigate the thermally induced stresses and the power limitations due to fracture, a thermal model of the laser gain medium is required. Existing analytical thermal models that describe the temperature and stresses in laser crystals are restricted to special cases and approximations, such as cw pump sources and steady–state conditions [1,2,3,4,5]. In this paper an analytical thermal model that determines the transient behaviour of the temperature and the corresponding induced stresses on the pump face of an isotropic laser rod is derived from first principles. We validate the model through finite element analysis, and apply the model to qcw pumped Tm:YLF laser rods, and find favourable agreement between the calculated fracture limits and the experimentally determined values reported in the literature. We illustrate how the model may be used to estimate the peak pump power that can safely be used to qcw pump a laser rod at a given duty cycle, opening the way to fracture–free power scaling with qcw pump sources
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