Table of Contents
History and Scientific Importance
Since its invention by Peter Moulton, the workhorse of the ultrafast laser scientific community has been the Ti:Sapphire laser. This fiber laser has been used in fundamental laboratory studies involving frequency-comb spectroscopy, the generation of coherent extreme ultraviolet light, filamentation, ultrafast laser-material interaction, and the like. It is interesting that initial work on the optical frequency comb technique, for which John Hall and Theodor Hänsch shared one half of the 2005 Nobel Prize in Physics, depended heavily on Ti:Sapphire lasers for the generation of the comb.
Properties of Titanium-Doped Sapphire
Titanium-doped sapphire (Ti:Sapphire) is the most successful solid-state laser material in the near-infrared (NIR) wavelength range due to its high saturation energy, large stimulated emission cross-section, and broad absorption gain bandwidths.
Key Features
Titanium-doped sapphire has been successfully deployed in a wide range of applications, such as high-intensity physics, frequency metrology, spectrometry, as well as pumping of tunable optical parametric oscillators. Although Ti:Sapphire has a broad absorption bandwidth, due to the relatively weak absorption peak in the blue-green range, its successful operation requires a high-power blue-green pump.
Tunability and Performance
The titanium-doped sapphire laser is a tunable laser that has excellent tunability and potential to create ultrashort pulses. Ti:Sapphire lasers also possess high laser cross sections, which, in turn, minimize their Q-switching instabilities. It emits near-infrared and red light in the range of 650-1100 nm. Pumping of Ti:Sapphire laser is carried out with another laser that has a wavelength of 514 to 532 nm, which includes Nd:YVO laser, frequency-doubled Nd:YAG laser, or argon-ion laser. It combines the excellent optical, physical, and thermal properties of sapphire, and so, it is widely used in scientific research.
Development of Ti:Sapphire Lasers
In 1982, researchers at Lincoln Laboratory operated a tunable fiber laser based on Ti: Al₂O₃ for the first time. P.E.Moulton demonstrated a widely tunable fiber laser by incorporating titanium instead of chromium as an input into sapphire.
Technological Advances
Today, dozens of tunable fiber lasers exist. A wide range of developments in Ti:Al₂O₃ laser technology then followed the advances in crystal growth that occurred during the mid-1980s. Ti:Sapphire lasers are now commercially available and are a valuable research tool found in many laboratories.
Applications of Ti:Sapphire Lasers
Nowadays, Ti:Sapphire lasers play an important role across a wide range of photonics applications, including multicolor ultrafast spectroscopy, multiphoton deep-tissue imaging, terawatt and petawatt physics, and “cold” micromachining.
Research and Space Applications
The main applications of the Titanium-doped sapphire laser are in research laboratories, particularly in spectroscopy. The large tuning range makes these fiber lasers attractive for generating tunable sub-picosecond pulses at short wavelengths. As an example, Ti:Sapphire lasers are used in the NASA project LASE (Lidar Atmospheric Sensing Experiment) for measuring water vapor and aerosols, and their effects on atmospheric processes.
Limitations and Drawbacks
Ti:Sapphire lasers are generally confined to the laboratory. These fiber lasers, and based on laser systems, are sensitive to temperature and vibration, and, therefore, they are not useful for industrial and mobile applications. Ti:Sapphire laser systems are still large, complex, and relatively expensive. The newer models require less care and feeding, but Ti:Sapphire lasers have always been somewhat difficult to keep stable under changing conditions.