A tunable laser is a laser whose wavelength of operation can be altered in a controlled manner. While all laser gain media allow small shifts in output wavelength, only a few types of lasers allow continuous tuning over a significant wavelength range.
CW dye laser based on Rhodamine 6G. The dye laser is considered to be the first broadly tunable laser.
A typical laser diode. When mounted with external optics these lasers can be tuned mainly in the red and near infrared.
A dye laser is a laser that uses an organic dye as the lasing medium, usually as a liquid solution. Compared to gases and most solid state lasing media, a dye can usually be used for a much wider range of wavelengths, often spanning 50 to 100 nanometers or more. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. The dye rhodamine 6G, for example, can be tuned from 635 nm (orangish-red) to 560 nm (greenish-yellow), and produce pulses as short as 16 femtoseconds. Moreover, the dye can be replaced by another type in order to generate an even broader range of wavelengths with the same laser, from the near-infrared to the near-ultraviolet, although this usually requires replacing other optical components in the laser as well, such as dielectric mirrors or pump lasers.
Close-up of a table-top CW dye laser based on rhodamine 6G, emitting at 580 nm (yellow). The emitted laser beam is visible as faint yellow lines between the yellow window (center) and the yellow optics (upper-right), where it reflects down across the image to an unseen mirror, and back into the dye jet from the lower left corner. The orange dye-solution enters the laser from the left and exits to the right, still glowing from triplet phosphorescence, and is pumped by a 514 nm (blue-green) beam from an argon laser. The pump laser can be seen entering the dye jet, beneath the yellow window.
The internal cavity of a linear dye-laser, showing the beam path. The pump laser (green) enters the dye cell from the left. The emitted beam exits to the right (lower yellow beam) through a cavity dumper (not shown). A diffraction grating is used as the high-reflector (upper yellow beam, left side). The two meter beam is redirected several times by mirrors and prisms, which reduce the overall length, expand or focus the beam for various parts of the cavity, and eliminate one of two counter-propagating waves produced by the dye cell. The laser is capable of continuous wave operation or ultrashort picosecond pulses (trillionth of a second, equating to a beam less than
A ring dye laser. P-pump laser beam; G-gain dye jet; A-saturable absorber dye jet; M0, M1, M2-planar mirrors; OC–output coupler; CM1 to CM4-curved mirrors.
A cuvette used in a dye laser. A thin sheet of liquid is passed between the windows at high speeds. The windows are set at Brewster's angle (air-to-glass interface) for the pump laser, and at Brewster's angle (liquid-to-glass interface) for the emitted beam.
