Research Of Electro-optically Q-switched Er:YAG Laser

With the extensive application of 2.94μm laser in medicine, higher requirement to the laser pulse is proposed to more security medical operation. Comparing with free-running regime, Q-switched Er:YAG laser is the effective method of obtaining narrower pulse. Up to now, although some attention has been paid to Q-switched Er:YAG by abroad scholar, no literature report is at home. In this dissertation, the design of Q-switched Er:YAG laser is proposed on the basis of the comprehensive research.From the theory of energy level, the analytic expression of the photon flux density inside the laser resonator has been obtained by analysing the rate equations of Er:YAG laser crystal. Depending on the Q-switched dynamics, we may obtain peak power and the relationship between pulse width and population inversion. Furthermore, theoretical analysis and numerical computation were presented, which are about the output characteristics of laser, energy extraction efficiency and the best mirror reflectivity. Then, thermal lens formula has been gotten by analyzing the thermal lens effect of laser rod.The program, which is about Q-switched Er:YAG laser, made a detailed analysis and specific design to the discharge parameters of pump power, the selection of Q-switched crystal, crystal structure, laser resonator geometry and the compensation to thermal lens effect inside the laser resonator. According to the program, pulses of 103~110ns duration and 87mJ energy have been obtained. A free-running and Q-switched pulsed laser was used for the cavity preparation experiments of the dentine respectively. Using scanning electron microscopy, the samples showed that Q-switched laser is better.