Ti-sapphire laser
Ti-sapphire laser, or Titanium-sapphire lasers, emit near-infrared light, tunable in the range from 650 to 1100 nanometers. These lasers are mainly used in scientific research because of their tunability and the possibility of generating ultra-short pulses.
Titanium-sapphire refers to the lasing medium, a crystal of sapphire (Al2O3) that is doped with titanium ions. A Ti:sapphire laser is usually pumped with another laser with a wavelength of 514 to 532 nm, for which argon lasers (514.5 nm) and frequency-doubled Nd:YAG, Nd:YLF, and Nd:YVO lasers (527-532 nm) are used. Ti:sapphire lasers operate most effectively at a wavelength of 800 nm.
Common types of Ti:sapphire lasers include:
Mode-locked oscillators
These generate ultrashort pulses with a duration of 10 femtoseconds to a few picoseconds, typically with a repetition-frequency of 70 to 90 MHz. Oscillators are normally pumped with a continuous laser beam from an argon or frequency-doubled Nd:YVO laser. Typically, an oscillator has an average output of 0.5 to 1.5 watt.
Chirped-pulse amplifiers
These devices generate ultrashort, ultra-high-intensity pulses with a duration of 20 to 100 femtoseconds and pulse energies up to 5 milli-joule. This corresponds to a peak-intensity of 50 giga-watt, most often at a repetition-frequency of 1000 hertz. Usually, regenerative amplifiers are pumped with a pulsed frequency-doubled Nd:YLF laser at 527 nm and operate at 800 nm.
Regenerative amplifiers operate by amplifying single pulses from an oscillator (see above). Instead of a normal cavity with a partially reflective mirror, they contain high-speed optical switches that insert a pulse into a cavity and take the pulse out of the cavity exactly at the right moment when it has been amplified to a high intensity. The term 'chirped-pulse' refers to a special construction that is necessary to prevent the pulse from damaging the components in the laser.
In a multi-pass amplifier, there are no optical switches. Instead, mirrors guide the beam a fixed number of times (2 or more) through the Ti-sapphire crystal with slightly different directions. Usually, a multi-pass amplifier uses the output of a small regenerative amplifier as an imput.
The pulses from chirped-pulse amplifiers are most often converted to other wavelengths by means of various nonlinear optics processes.
At 5 mJ in 100 femtoseconds, the peak power of such a laser is 50 gigawatts, which is many times more than what a large electrical power plant delivers (about 1 GW). When focused by a lens, these laser pulses will destroy any material placed in the focus, including air molecules.
Tunable continuous wave lasers
These are used as a laser source with a tunable well-defined wavelength.