Investigation of novel devices used for pulsed laser system

Abstract

With my main MPhil research focus being on the development of novel materials and devices that can potentially be integrated into the laser photonic system, I have started my research work on developing electrically tunable liquid lensed fiber that can be potentially used within the microfluidic biomedical sensors, or as optical switcher inserted within the laser cavity to serve as active laser Q-switcher. The novel functional microfluidic device investigated is a liquid lensed optical fiber with controllable focusing power. By filling water into a hollow Teflon-AF optical fiber and applying electrical field on the fiber tip, we can vary the shape and radius of curvature of the liquid lens on the fiber tip. By controlling the electric field across it, the shape, radius of curvature and focusing power of the formed liquid lens on the fiber tip can be varied. The experiment has successfully demonstrated a variation of focal length from 0.628mm to 0.111mm responding to the change of applied voltage from 0V to 3 kV (L = 2mm) for the Teflon AF fiber. Furthermore, by applying voltage higher than 2.6kV, parabolic shape of the liquid lens has been created, which can be a simple and practical method to produce micron sized parabolic lensed fiber compared to traditional mechanical polishing technique. Passive mode-locked laser is typically achieved by the Semiconductor Saturable absorber Mirror, SESAM, which is produced by expensive and complicated metal organic chemical vapor deposition method. Therefore, I have investigated the fabrication technology of saturable absorber for mode locking laser application during my MPhil study. Carbon based single wall carbon nanotube (SWCNT), saturable absorber, a promising material with the capability of producing stable passive mode-locking in the high power laser cavity over a wide operational wavelength range. This study has successfully demonstrated the high-power mode locking laser system operating at 1 micron by using SWCNT-based absorbers fabricated by dip coating method. The proposed materials and fabrication method is practical, simple and cost effective for fabricating SWCNT saturable absorber. Different from traditional spray or spin-coating deposition method, relatively uniform and large surface area SWCNT thin film (greater than 1cm{194}) is successfully coated on quartz plate to form a transmission type saturable absorber. By adjusting the dip coating parameters involving the concentration of the dip coating suspension, withdrawn speed and environment conditions (Temperature or relatively humidity), the initial transmission ratio of the fabricated absorber sample can be changed by 12%. The demonstrated high power Nd:YVO{210} mode-locked laser operating at 1064nm have maximum output power up to 2.7W, with the 167 MHz repetition rate and 3.1 ps pulse duration, respectively. The calculated output pulse energy and peak power are 16.1 nJ and 5.2 kW, respectively.