Study On Transient Thermal Effect In Pulsed Laser Diode End Pumped TM³⁺ Doped Laser

The emission of pulsed laser diode end pumped thulium doped laser lies in2μm which is in the eye-safe spectral region. Thulium doped laser plays an important role in laser radar, laser ranging and laser medical treatment. However, thulium doped crystal has a small stimulated-emission cross section and the output wavelength2μm covers the absorption peak of H2O and CO2. These properties lead to severe thermal effect, then the beam quality, output power, repetition frequency are seriously restricted.By studying the theory of heat conduction, we establish the transient heat conduction equation in pulsed LD end pumped thulium doped laser, and simulate the transient thermal effect. And the effects of crystal parameters and the laser operation mode on the transient thermal effect in thulium doped laser are simulated. We can grasp the change laws of transient thermal effect in pulsed LD end pumped thulium doped crystal. The main research contents are as follows:(1) Based on the actual working environment of pulsed LD end pumped Tm:YAG crystal, time-dependent temperature field analytical expression and the time-varying thermal focal length are deduced by the integral transform method and the method of separation of variables.(2) Transient temperature distribution and time-varying thermal focal length of pulsed LD end pumped Tm:YAG rod are simulated and analyzed.(3) The effects of crystal parameters and the laser operation mode on pulsed laser diode end pumped Tm:YAG rod transient temperature distribution and the time-varying thermal focal length are quantitatively analyzed.(4) Pulsed LD end pumped composite Tm:YAG rod thermal lens focal length is measured in the experiments. Compared with theoretical simulation, the theoretical results are verified.