Source region ultraviolet discharge lamps

Until the advent of lasers the most intense monochromatic sources available were atomic emission sources from which an intense, discrete line in the visible or near-ultraviolet region was isolated by optical filtering if necessary. The most often used source of this kind was the mercury discharge lamp operating at the vapour pressure of mercury. Three of the most intense lines are at 253.7 nm (near-ultraviolet), 404.7 nm and 435.7 nm (both in the visible region). Although the line width is typically small the narrowest has a width of about 0.2 cm, which places a limit on the resolution which can be achieved. 

Sources that emit a few discrete lines find wide use in atomic absorption spectroscopy, atomic and molecular fluorescence spectroscopy, artd Raman spectroscopy (refractomeiry and polarimciry also u.se line sources). The familiar mercury and sodium vapor lamps provide a relatively few sharp lines in the ultraviolet and visible regions and are used in several spectroscopic instruments. I loilow-cathodc lamps and clectrodelcss discharge lamps are the most important line sourcc.s for atomic absorption and fluorescence methods. Discussion of such sources is deferred to Section 9H- . 

In vacuum ultraviolet photoelectron spectroscopy (UPS), the sample atom or molecule is exposed to radiation in the vacuum ultraviolet region of the electromagnetic spectrum. A readily available source of radiation is the helium discharge lamp, whieh produces a sharp Hel line at 21.2 eV. Since the energy required for photoionization of sets of valence electrons is in the vicinity of 6 eV to this energy, we obtain a polyenergetic emission of electrons described by the Einstein relation... 

The deuterium halogen lamp is a low pressure gas discharge light source often used in spectroscopy when a full spectrum source of illumination in the ultraviolet region is needed. The origin of the continuum ultraviolet radiation extends from around 160 nm to 400 nm. 

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