Fluoride Fiber Lasers

Abstract

Compared to other laser platforms, fiber lasers have the advantages of outstanding heat dissipating capability, high power scalability, excellent beam quality, inherent simplicity and compactness, robust manufacturing and maintenance, and hermetically guided laser beams. Fiber lasers have seen significant progress in various aspects of laser performance, including high power/energy, short pulse duration, narrow spectral linewidths, and improved efficiency during the past sixty years. It is worth noting that most of these achievements were accomplished with silica fibers. Different from silica fibers usually producing lasers only at the 1 um, 1.55 um, and 2 um wavelength regions, fluoride fibers are of great interest for generating lasers from ultraviolet to mid-infrared due to their low phonon energy and the ultra-wide transparency window of fluoride glass. In this dissertation, dysprosium (Dy3+) doped fluoride fiber lasers at 3 um and holmium (Ho3+) doped fluoride fiber lasers at 1.2 um were investigated.To date, research activity on 3 um fiber lasers has been focused on erbium (Er3+), Ho3+ and Dy3+ doped fluoride fiber lasers. Compared to Er3+ and Ho3+ doped fluoride fiber lasers that generally produce lasers below 3 um, Dy3+-doped fluoride fiber lasers have attracted significant attention recently because Dy3+ has a much broader emission spectral bandwidth in the 3 um wavelength region and is able to produce laser radiation up to 3.4 um. However, most Dy3+-doped fiber lasers have been pumped with fiber lasers or solid-state lasers at the absorption peaks of Dy3+ at 1.1 um, 1.3 um, 1.7 um, and 2.8 um, where commercial high-power laser diodes are unavailable. We proposed to solve this problem by using Er3+ synthesized Dy3+-doped fluoride fibers, which allow us to develop compact 3.4 um fiber lasers pumped with low-cost high-efficiency diodes at 980 nm. In my Ph.D research, spectroscopic studies on Er3+-, Dy3+-, and Dy3+/ Er3+ -doped fluoride glasses was first conducted to confirm efficient energy transfer from Er3+ to Dy3+ in the Er3+/Dy3+ co-doped system when pumped at 980 nm. Then a custom Dy3+/Er3+-doped fluoride fiber was designed and fabricated and Dy3+/Er3+-doped fluoride fiber lasers beyond 3 um were demonstrated with low-cost high efficiency diode laser pumps at 980 nm. Moreover, a diode-pumped wavelength tunable fiber laser with a tuning range from 2.71 to 3.37 um was demonstrated. In addition to 2 and 3 um fiber lasers, Ho3+-doped fluoride fibers have been demonstrated as high efficiency gain media for 1.2 µm lasers. In this dissertation, a diode-pumped mode-locked Ho3+-doped fluoride fiber laser at 1.2 μm was demonstrated with a ring-cavity laser incorporated with a carbon-nanotube saturable absorber. Stable mode-locked pulses with an average power of 1 mW at a repetition rate of 18.47 MHz were obtained at a pump power of 348 mW. The pulse energy and peak power of this mode-locked laser oscillator were estimated to be about 54 pJ and 12.6 W. The pulse duration was measured to be 4.3 ps by an autocorrelator.