Research On New Optical Medical Devices For Skin Treatment

The medical applications of laser can be classified into two categories: the application of high power laser surgery and the application of low energy laser therpy. The application of high power laser requires that the laser can be controlled much precisely with less injury to surrounding tissue and shorter recovery time. The application of low energy laser therpy requires that light can be safely and simply operated with deeper penetration depth. This dissertation will show the deeply research of fractional Q-swithced Er³⁺: YAG laser for skin surgery and single LED light acupuncture for low energy laser therpy.The laser radiation of Er³⁺:YAG wavelength of 2.94μm corresponds to the electromag -netic spectrum, where water and various molecules with hydroxy have strong rovibrational absorption lines , and co- rresponds to a strong absorption peak in soft and hard biological tissues , which contains a significant amount of water or molecules with hydroxy. The laser radiation wavelength of 2.94um is of great interest for medical and biological applications. In this paper, some theoretical calculation of rate equations related to Q-switched Er³⁺:YAG laser will be performed, the Q-switched Er³⁺:YAG fractional laser will be designed and the interaction between Q-switched Er³⁺:YAG fractional laser and skin soft tissue will be analyzed deeply.Non-contact,non-invasive light acupuncture is an important development direction for china tranditional acupuncture and of the application for low energy laser, however, the laser for laser acupuncture have some defects, such as non-medical designed, unsafe for eye, which in some degree limit its development and the research. Lots of trials indicate that LED can achieve the same medical and biological effect of low laser. In this dissertation LED (wavelength 830nm,output power 500mw) is used for light acupuncture and used to treat the periarthritis of shoulder with good effect.The main works of this dissertation are as follows:(1) The lethal peculiarity of laser transition wavelength 2.94um in Er³⁺: YAG is the self saturation : the life time of the terminal laser level is longer than the lifetime of the initial one, the mode based on energy transfer either to impurities or as a cooperative upconversion inside the Erenergy system. Rate equations of Er³⁺: YAG, wavelength 2.94um, was build according to energy level theo ry of Er³⁺: YAG. The requirement of discharge time and discharge rate of Q-switched Er³⁺: YAG, the length of the resonant cavity, and the feature of laser crystal can be determ ineed according to the rate equations. The quantum efficiency and translation efficiency of Q- switched regime and stationary regime were calculated according to the rate equations, the calculated results shows that the quantum efficiency can be great-than-unity.(2) The charge and discharge circuit of pump source was dedigned to meet the need of the requirements calculate from the rate equations. The LiNbO₃ crystal with two brewst angle cut faces was chosed as the Q-switched crystal, this kind Q-switch crystal leave out a piece of polarizer ,which reduce the insert loss and the length of the cavity of resonance. The translation of the laser pass this Q-switch was calculated by Jones matrix translated of vertical horizontal linerarly polarized radication. The Q-switched Er³⁺: YAG laser system was formed and the fractional laser treatment handle based on microlens array was designed.(3) The numerical model of the photo-thermolysis interaction between fractional Er³⁺:YAG laser and the microscopic soft tissue was built. The temperature change and the pressure change are simulated according to the model. The computing results are consistent with the experiment results reported abroad.(4) The effect of laser acunpuncture has nothing to do with the coherence, which district the laser and other light, accoding to theories about laser acupuncture. Thus the LED can be an alternatives of laser for light acupuncture. The mechanism of LED light acupuncture was numerical ananlyzed from the acupuncture and moxibustion effect respectly. The computed result of the moxibustion effect indicates that the high power LED light acupuncture can get the same temperature of low energy laseracupuncture with shorter irradiation time.(5) The controlled and power supply circuit based on single chip computer, the LED acupuncture handle was designed and manufactured. The trial treatment using LED acupuncture for periarthritis of shoulder was performed with excellent effect.