Ti-sapphire laser
|
|
Titanium_sapphire_osc.jpg
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 ultrashort 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 millijoules. This corresponds to a peak intensity of 50 gigawatts, 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 input.
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.