Laser Spectroscopy: Techniques and Applications
This work describes experimental techniques using laser spectroscopy and presents specific practical applications for this technology in many fields, including physics, engineering, chemistry, medicine and bioscience. The general spectroscopic features of molecules are delineated; transition metal and rare earth complexes are examined; and transition selection rules are explained.
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From Wikipedia, the free encyclopediaClose-up of a table-top dye laser based on Rhodamine 6G, emitting at 580 nm (yellow-orange). The emitted laser beam is visible as faint yellow lines. The orange dye solution enters the laser from the left, and is pumped by a 514 nm (blue-green) beam from an argon laser. The dye jet is in the center of the image, behind the yellow window.
A dye laser is a laser which 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. The wide bandwidth makes them particularly suitable for tunable lasers and pulsed lasers. Moreover, the dye can be replaced by another type in order to generate different wavelengths with the same laser, although this usually requires replacing other optical components in the laser as well.
Dye lasers were independently discovered by P. P. Sorokin and F. P. Schäfer (and colleagues) in 1966.
In addition to the usual liquid state, dye lasers are also available as solid state dye lasers (SSDL). SSDL use dye-doped organic matrices as gain medium.
3 Narrow linewidth dye lasers
4 Chemicals used
5 Excitation lasers
6 Ultra-short optical pulses
A dielectric mirror used in a dye laser.
A dye laser consists of an organic dye mixed with a solvent, which may be circulated through a dye cell, or streamed through open air using a dye jet. A high energy source of light is needed to 'pump' the liquid beyond its lasing threshold. A fast discharge flashlamp or an external laser is usually used for this purpose. Mirrors are also needed to oscillate the light produced by the dye’s fluorescence, which is amplified with each pass through the liquid. The output mirror is normally around 80% reflective, while all other mirrors are usually more than 99.9% reflective. The dye solution is usually circulated at high speeds, to help avoid triplet absorption and to decrease degradation of the dye. A prism or diffraction grating is usually mounted in the beam path, to allow tuning of the beam.
Because the liquid medium of a dye laser can fit any shape, there are a multitude of different configurations that can be used. A Fabry–Pérot laser cavity is usually used for flashlamp pumped lasers, which consists of two mirrors, which may be flat or curved, mounted parallel to each other with the laser medium in between. The dye cell is usually side-pumped, with one or more flashlamps running parallel to the dye cell in a reflector cavity. 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 flashlamp produces. Axial pumped lasers have a hollow, annular-shaped flashlamp 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 flash lamp, for even better transfer efficiency, but have a lower gain due to diffraction losses. Flash pumped lasers can only be used for pulsed output.
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 ring laser design is often chosen for continuous operation, although a Fabry–Pérot design is sometimes used. In a ring laser, the mirrors of the laser are positioned to allow the beam to travel in a circular path. The dye cell, or cuvette, is usually very small. Sometimes a dye jet is used to help avoid reflection losses. The dye is usually pumped with an external laser, such as a nitrogen, excimer, or frequency doubled Nd:YAG laser. The liquid is circulated at very high speeds, to prevent triplet absorption from cutting off the beam. Unlike Fabry–Pérot cavities, a ring laser does not generate standing waves which cause spatial hole burning, a phenomenon where energy
Components of Spectroscopic Instrumentation
AbsorptionBased Laser Spectroscopy
Photoluminescence IntensityBased Laser Spectroscopy
Photoluminescence LifetimeBased Laser Spectroscopy
involving long lifetimes