OUTPUT CHARACTERISTICS
المؤلف:
Mark Csele
المصدر:
FUNDAMENTALS OF LIGHT SOURCES AND LASERS
الجزء والصفحة:
p269
24-3-2016
2073
OUTPUT CHARACTERISTICS
Beam quality is poor in a nitrogen laser. Being a super radiant laser with enormous gain, the output really consists of highly amplified spontaneous emission. In a lower-gain laser, photons traverse the cavity many times, stimulating the emission of many more photons of exactly the same wavelength. In a nitrogen laser, photons often make only one pass through the amplifier before exiting. Collimation is hence poor and divergence is quite large compared to other types of lasers. Coherence length is also poor, since the spectral width of the laser output is quite wide. Molecular nitrogen lases at 61 known wavelengths between 336.4903 and 337.9898 nm, an extraordinarily wide range for a laser, but the vast majority of lines are clustered around 337.1 nm, so the FWHM of the combined output from these lines is about 0.1 nm. Since gain is high, wavelength selectors are ineffective in allowing single line operation.
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