Dye laser

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.

Mirrors are also needed to oscillate the light produced by the dye's fluorescence, which is amplified with each pass through the liquid.

The dye cell is often a thin tube approximately equal in length to the flashtube, with both windows and an inlet/outlet for the liquid on each end.

The reflector cavity is often water cooled, to prevent thermal shock in the dye caused by the large amounts of near-infrared radiation which the flashtube produces.

Axial pumped lasers have a hollow, annular-shaped flashtube that surrounds the dye cell, which has lower inductance for a shorter flash, and improved transfer efficiency.

Coaxial pumped lasers have an annular dye cell that surrounds the flashtube, for even better transfer efficiency, but have a lower gain due to diffraction losses.

Most dyes have a very short time between the absorption and emission of light, referred to as the fluorescence lifetime, which is often on the order of a few nanoseconds.

Under standard laser-pumping conditions, the molecules emit their energy before a population inversion can properly build up, so dyes require rather specialized means of pumping.

In the triplet state, light is emitted via phosphorescence, and the molecules absorb the lasing wavelength, making the dye partially opaque.

Flashlamp-pumped lasers need a flash with an extremely short duration, to deliver the large amounts of energy necessary to bring the dye past threshold before triplet absorption overcomes singlet emission.

With a dye jet, one avoids reflection losses from the glass surfaces and contamination of the walls of the cuvette.

The beam needs to make only a few passes through the liquid to reach full design power, and hence, the high transmittance of the output coupler.

As a result, most dyes exhibit very small Stokes shifts and consequently allow for lower energy losses than many other laser types due to this phenomenon.

CW dye-lasers can have a linear or a ring cavity, and provided the foundation for the development of femtosecond lasers.

[14] The first narrow linewidth dye laser, introduced by Hänsch, used a Galilean telescope as beam expander to illuminate the diffraction grating.

Rhodamine 6G, for example, has its highest output around 590 nm, and the conversion efficiency lowers as the laser is tuned to either side of this wavelength.

Cycloheptatriene and cyclooctatetraene (COT) can be added as triplet quenchers for rhodamine G, increasing the laser output power.

In addition to their recognized wavelength agility these lasers can offer very large pulsed energies or very high average powers.

Their tunability, (from the near-infrared to the near-ultraviolet), narrow bandwidth, and high intensity allows a much greater diversity than other light sources.

[34] Tunable lasers are used in swept-frequency metrology to enable measurement of absolute distances with very high accuracy.

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 ⁠ 1 / 3 ⁠ of a millimeter in length).
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.
Multiple prisms expand the beam in one direction, providing better illumination of a diffraction grating . Depending on the angle unwanted wavelengths are dispersed, so are used to tune the output of a dye laser, often to a linewidth of a fraction of an angstrom .
Rhodamine 6G Chloride powder; mixed with methanol; emitting yellow light under the influence of a green laser
An atomic vapor laser isotope separation experiment at LLNL. Green light is from a copper vapor pump laser used to pump a highly tuned dye laser which is producing the orange light.