Q-switched Nd:YAG laser induced photodisruption in an eye model

Abstract

This study attempts to characterize the photodisruption in simulated eye model induced by Nd:YAG laser. To simulate the eye environment, saline solution was chosen as vitreous filled pyrex cuvette which acted like eye ball. Polymethylmethacrylate (PMMA) plate later on was placed in the pyrex cuvette to be as an intraocular lens. The laser beam was focused into saline solution using two techniques. The first technique uses single camera lens and the second technique uses combination of negative and positive lenses. Activities at the focal region were visualized by means of CCD video camera and interfaced with image processing system via Matrox Inspector sofware. The pressure wave induced at the focal region was detected using hydrophone and the plasma temperature was measured and estimated using Langmuir probe. The damage induced after exposure of laser on PMMA was observed using optical microscope. By focusing light pulses lasting in nanoseconds to a spot size, this laser can create an optical breakdown associated with plasma formation. Multiple breakdowns were observed when the laser was focused using single lens. A single ellipsoidal plasma configuration was generated with a combination of lenses. A series of acoustic-shockwave signals representing the pressure waves produced at the focal region had also been recorded. From the measurement, a maximum pressure of 0.0254 bar was obtained. The temperature raised at the plasma region was estimated to be 12,064 K or 1.04 eV. The damage threshold was obtained at a fluence of 6.86 x 102 Jcm-2 on the PMMA with various damage formations. Severe damage was observed as the number of laser pulses increases. In short, all the mechanisms involved have been successfully characterized. These information can be very useful in recognizing the opportunities and limitations of the Nd:YAG laser in medical applications.