Preliminary results of development of a single-mode Q-switched Nd: YAG ring laser at 213 nm and its application for the microsurgical dissection of retinal tissue ex vivo.

The Nd: YAG laser family offers wide possibilities for surgery applications in medicine. The radiation at 213 nm provides similar tissue effects as compared to 193 nm excimer lasers, but offers considerable practical advantages in the operating room. As such, it is of considerable interest to create single-mode Q-switched fifth harmonic Nd: YAG pulsed lasers with a high coefficient of efficiency and low divergence. Parameters of the ring three-mirror anisotropic cavity TEM00-Nd: YAG laser were calculated on the basis of the analysis of Gaussian beam behavior in the three-mirror ring cavity, with one convex spherical mirror and one intracavity positive lens. On the hand of numerical calculations a prototype of a single-mode Q-switched Nd: YAG-213 nm laser with an output energy of 4 mJ and a beam divergence of 1 mrad has been developed. At a pulse repetition rate of 50 Hz, it has a generation efficiency in the Q-switched mode of 0,6%. A hollow core wave guide is used in combination with a short length of a special fused silica optical fiber to guide the laser beam. Full-depth dissection of rabbit retina ex vivo was achieved at the intensities of 0.18-0.05 J/cm2 and a repetition rate of 50 Hz, with a linear cutting rate of 6 mm/s. Although the retina was completely cut, heat necrosis of the choroid did not occur. We are currently in the process of testing the dissection of retinal tissue during retinotomy, and the formation of holes in the trabecular meshwork in glaucoma surgery.