High Efficiency and Low Threshold Laser Source Using Ti:sapphire Crystal Fiber
Date Issued
2015
Date
2015
Author(s)
Hsu, Chun-Yang
Abstract
Titanium-Sapphire, as the most common broadband fluorescence material, is known for a wide variety of applications such as tunable laser and mode-locked laser. The central wavelength of Ti:sapphire, 760 nm, lies within a region where there are low tissue scattering loss and low water absorption. Thus, it is commonly applied to a multitude of bio-measurement systems. Ti3+:Al2O3 single-cladding crystal fiber was grown by the laser-heated pedestal growth method. It was fabricated with a 20-μm core diameter and 320-μm outer cladding diameter. Annealing methods were used for recovering the Ti3+ ion concentration, and a 1600 °C annealing temperature for 18 hours showed the best crystal quality. The measured figure of merit is 257, and the proportion of crystal defects is estimated to be 0.09%. The temperature of crystal fiber inner cavity can be figured out by measuring the fluorescence life time. The fluorescence life time is 3.05 μs with low pumping power, dropping a little to 2.95 μs with high pumping power, and its temperature slightly rises from 34 °C to 40 °C. The propagation loss of crystal fiber for signal was measured as 0.075 dB/cm. The external cavity Ti:sapphire crystal fiber laser was pumped by a 532-nm laser with different transmittance output couplers, and the experiment results were then fitted by simulation. The following conclusions can be drawn through simulation: the absorption cross section is 5.2x10-20 cm2, and emission cross section is 2.4x10-19 cm2 for our homemade Ti:sapphire crystal fiber; for 532-nm laser pump system, the optimum laser performance is reached when the fiber length is between 15 and 20 mm and the transmittance of output coupler is between 20% and 25%; for 520-nm laser pump system, the condition for optimum laser performance is the same as 532-nm laser pump system. The laser cavity was set up by coating the optical thin film on the surface of Ti:sapphire crystal fiber, and using a 532-nm frequency-doubled solid state green laser and a 520-nm green diode laser to pump it. With 532-nm laser pumping, the slope efficiency can reach 22.6%, and the threshold is 157.7 mW, while the slope efficiency is 25.9%, and the threshold is 171.7 mW with 520-nm laser pump.
Subjects
Ti:sapphire
crystal fiber
laser-heated pedestal growth method
high efficiency
low threshold
Type
thesis
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