Study On The Design Of Long-Pulse Dual Wavelength Nd:YAG Medical Laser System

In 1983,American doctor Anderson and Parrish developed the theory of "selective Photothermolysis", which was regarded as the foundation of laser hair removal and treating cutaneous vascular lesions with laser. The design plan of long-pulse dual wavelength laser system has been brought forward, which consists of 1064nm and its frequency-doubled 532nm two wavelengths laser. The 1064nm infrared laser could be used to remove hair, and the 532nm visible green light was fit for treating cutaneous vascular lesions. In order to meet the actual demand of clinic, the pulse width and energy of this two laser both could be adjusted in a certain field.The current situation and treating principle of hair removal and skin vascular lesions have been introduced first, then the cause of designing long-pulse dual wavelength laser has been presented, and the pivotal and difficult technology have been analyzed. Accordingly the resolutions to the problems said above have been brought forward, which were demonstrated as follows:(1) The new switch device IGBT was used as the DC chopper of the Xenon flash lamp discharge circuit, and the traditional single long pulse was replaced by quasi-continuous long pulse bursts. Controlling the driving signal of IGBT, the pulse width and energy of long pulse burst can be adjusted easily .we selected the specific driving module M57962 as IGBT driver, and designed a circuit to eliminate the surge voltage of IGBT. We also calculated the parameters of the chopping circuit, and measured the output wave figures.(2) We selected KTP as the nonlinear frequency-doubled crystal, discussing the best length and the best azimuth angle of the crystal. The dual-pass intracavity frequency-doubled construction was developed, the main factor which induced phase mismatched was analyzed, and the resolution was also discussed to increase the efficiency of long pulse frequency-doubled as possibly as we can. (3) The fundamental theory and control method of phase-shifted of PWM full bridge converter were analyzed. The ZVS-PWM circuit was used to realize the soft switch of the switch gates. On the basis of this circuit, the main circuit of the pulse power supply was developed.(4) The whole construction of the laser system was designed, and the parameters of the cavities and resonators were well designed. Moreover, we designed and drew a fiber coupling device, which had simple configuration and high precision of adjusting and installation.