Vibronic Lasers

Definition: lasers based on gain media with a large gain bandwidth, caused by a strong interaction of electronic transitions with phonons

In some laser gain media, particularly in those doped with transition metal ions, there is a strong interaction of the electronic states with lattice vibrations, i.e. with phonons. This vibrational–electronic (in short: vibronic) interaction leads to a strong homogeneous broadening and thus to a large gain bandwidth. In the early years of laser technology, vibronic lasers were sometimes called phonon-terminated lasers.

Vibronic solid-state lasers, i.e. lasers based on vibronic solid-state gain media, allow for wavelength tuning over large ranges, and also the generation of ultrashort pulses. The most important types of vibronic lasers are

• titanium–sapphire lasers for wavelengths between 0.65 and 1.1 μm, also allowing the shortest pulse duration with passive mode locking
• Cr³⁺:LiSAF and Cr³⁺:LiCAF lasers, rivaling Ti:sapphire lasers, with a potential for diode pumping, although with a lower gain bandwidth
• alexandrite lasers (Cr³⁺:BeAl₂O₃) for 0.7–0.8 μm, an early type of tunable solid-state lasers
• chromium forsterite lasers (Cr⁴⁺:Mg₂SiO₄) for 1.17–1.34 μm, a wavelength region difficult to access with other lasers
• Cr²⁺:ZnSe and Cr²⁺:ZnS lasers for very broad emission in the mid-infrared region at 2–3.5 μm

The first laser demonstrated was a ruby (Cr³⁺:Al₂O₃) laser, which is also a vibronic laser.

A relatively new vibronic gain medium is Fe²⁺:ZnSe for mid-infrared emission with 3.7–5.1 μm.

The term vibronic lasers is also used in the context of molecular gas lasers, if the laser transition occurs between vibrational levels of different electronic states. Such gas lasers are usually ultraviolet lasers.

Bibliography

See also: transition-metal-doped gain media, chromium-doped gain media, titanium–sapphire lasers, phonons, gain bandwidth, gas lasers, mid-infrared laser sources

Categories: lasers, materials