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Ti:Sapphire Femtosecond Solid-State Lasers in Ultrafast Science
Femtosecond solid-state lasers, based on the Ti:sapphire gain medium, have revolutionized the field of ultrafast science in the past decade. Titanium-doped sapphire is a widely used transition-metal-doped gain medium for tunable lasers and femtosecond solid-state lasers. This type of fiber laser has several advantages, such as simplicity, excellent thermal conductivity, and stability. Nevertheless, researchers continue to investigate approaches to improving the performance of mode-locked solid-state lasers.
Key Properties and Applications of Ti:Sapphire Lasers
Titanium-doped sapphire (Ti:sapphire) is the most successful solid-state laser material in the near-infrared wavelength range due to its high saturation energy, large stimulated emission cross-section, and broad absorption gain bandwidths. It has been extensively developed for continuous-wave (CW) operation, ultra-short pulse generation, and high-power amplification. Moreover, Ti:sapphire technology has been successfully implemented in a wide range of applications, for example, high-intensity physics, frequency metrology, spectroscopy, as well as pumping of tunable optical parametric oscillators.
Pumping Challenges and System Complexity
Ti:sapphire has a broad absorption bandwidth, due to the relatively weak absorption peak in the blue-green wavelength range. Its successful operation requires high-power blue-green pump sources. As such, Ti:sapphire lasers have been pumped with multi-watt argon-ion, copper-vapor, and most notably frequency-doubled all-solid-state green lasers, resulting in fairly bulky, complicated, and expensive setups. For further advances in Ti:sapphire laser technology, it would be desirable to devise more simplified pump laser designs to reduce system complexity and cost, while maintaining or enhancing device performance concerning all important operating parameters. СW Ti:sapphire laser pumped directly by a GaN diode laser in the blue was reported, but the limited pump powers available from diode lasers in good spatial beam quality restrict the effectiveness of this approach only to low-power CW operation. On the other hand, optically-pumped-semiconductor lasers in the green can, in principle be used to pump CW Ti:sapphire laser, but limited progress has been achieved in this area so far, leaving open the need for the development of powerful alternative green sources with high spatial quality and in simple, practical all-solid-state design to pump high-power CW or mode-locked Ti:sapphire lasers.