Nitrogen Lasers

Nitrogen lasers are an excellent source of high intensity, short pulse, and ultraviolet (UV) radiation. They offer an inexpensive source of pulsed UV laser radiation at 337 nm.  Nitrogen lasers were first developed in 1963 and have been available commercially since 1972.  Nitrogen lasers find applications in research in physics, chemistry and medicine. Some typical applications include treatment of pulmonary tuberculosis, nonhealing wounds, etc. They are also excellent sources for general spectroscopy, laser-induced fluorescence and photochemistry, as well as in teaching laboratories. Because of their tunability, dye lasers may be used for a large variety of applications in the UV-visible region. For experiments in the life science laboratory, nitrogen and dye lasers can easily be fiber-optically coupled to a microscope.

The active medium in nitrogen lasers is nitrogen gas, generally pressurized from 20 torr up to 1 atmosphere.  A high vacuum is not required for this type of laser: a vacuum of 25 to 75 torr is sufficient.  The nitrogen supply can be either of a standard gas grade, supplied through a gas cylinder, or from liquid nitrogen.  Nitrogen gas offers higher purity for the application (in fact, generally a higher purity than is needed), but can be expensive.  Liquid nitrogen is less expensive, but it tends to boil off, whether in use or not, so it has to be replenished regularly.  It can also cause serious burns if it is not handled careful.  Appropriate handling procedures can be gleaned from the appropriate Material Safety Data Sheet (MSDS).

Nitrogen lasers consist of housing in which the tube resides.  The tube itself consists of a housing containing two transverse, flat electrodes parallel to the output beam. In some nitrogen lasers the gas flows in the tube, while others have a sealed tube. 

The gain provided by nitrogen lasers is extraordinarily high, (pulses from this laser last 5-10 ns.), so much so that a single pass of light down the laser tube amplifies light enough to produce a powerful output beam. No mirrors are required for these lasers.  When pumped by nitrogen lasers, dye lasers are tunable over a wide spectral range from 360 to 990 nanometers. Dye lasers equipped with frequency doublers are even tunable in the deep UV region from 235 to 345 nm.

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