Analysis and evaluation of thermal properties of a multilayer laser gain element using time-resolved interferometric methods

An original experimental method is developed and demonstrated that provides rapid internal measurements of thermo-optic and heat transport properties of contacted optical materials. This unique method provides a powerful tool for quantifying heat transfer in laser materials. This heat transfer is a key problem influencing the scaling of solid state lasers to high output power.; The principal experiment consists of contacting a titanium-doped sapphire (Ti:Sapphire) parallelepiped shaped sample with a similar undoped sapphire sample. A pump pulse introduces heat into the Ti:Sapphire sample. The subsequent flow of heat across the interface between the two samples affects the index of refraction via the thermo-optic effect. The index change is detected as a shift in the interference fringe pattern produced in an optical beam that simultaneously monitors both samples. A time resolved sequence of probe beam interference fringe patterns, recorded by briefly opening a camera shutter at progressively later times after the initial excitation of the sample, provides detailed information regarding heat flow across the interface between the two samples with time resolution on the order of a millisecond.; Two pairs of samples are examined. One pair exhibits a substantially greater degree of surface flatness compared to the other pair. The pair of samples having laser grade flat surfaces shows excellent heat transfer properties across the interface. The samples having good, but less flat, surfaces show poor heat transfer properties across the interface. A discussion of the thermal, mechanical, and optical properties of sapphire including thermal lensing, thermal stress-induced birefringence, and thermal shock is given.; A LabVIEW program written for this set of experiments that converts the interference fringe data into phase shift and temperature maps is described, as is a MATLAB routine for measuring the required phase shifts at the interface. A feedback circuit that stabilizes the interferometer against variations caused by mechanisms other than laser-introduced heating is discussed. The experimental method of collecting data on the samples over a range of temperatures in a cryogenic refrigerator is reported. Recommendations for future work are provided that extend the sample pair design to higher output power and multiple layer gain element configurations.