Littrow grating prism

The linewidth of the RGH lasers can be reduced and the tunability of the RGH lasers can be realized using gratings, prisms, etalons, or some combination of these elements in the laser resonator. The lowest level of frequency selection is usually obtained with a grating used in a Littrow geometry at one end of the resonator or with one or more prisms for the tuning element. This technique provides tunability over the emission band of the RGH lasers and realizes selection of single vibrational transition in lasers such as XeF or XeCl. Narrow linewidths of 80 cm for KrF and 5 cm for ArF have been demonstrated with two prisms in the resonator. 

Because most prism materials such as glass or quartz absorb in the infrared region, it is more convenient to use a Littrow grating (Sect. 4.1) as wavelength selector in this wavelength range. Figure 5.28 illustrates the line selection in... 

As the beam leaves the prism predisperser, it is focused on the entrance slit of the grating monochromator. The slit is curved, has variable width, and opens symmetrically about the chief ray (optical center line of system). The monochromator itself is of the off-axis Littrow variety (James and Sternberg, 1969 Stewart, 1970 Jennings, 1974) and uses a double-pass system described by McCubbin (1961). The double-pass aspect of the system doubles the optical retardation of the incident wave front and theoretically doubles the resolution of the instrument. The principal collimating mirror is a 5-m-focal-length, 102-cm-diam parabola. 

Heitmann et al. [11] designed a very compact double monochromator, consisting of a 300 mm prism pre-monochromator and a 400 mm echelle grating monochromator, both in Littrow mounting, which is shown schematically in Figure 4.3. The prism monochromator selects the part of the spectrum that is of interest, and the echelle monochromator provides the high dispersion of the selected spectral interval, which is better than 2 pm per pixel at 200 nm (see Welz et al. [10]). 

Two basic designs of prism spectrometer are commonly used for spectrochemical analytical purposes, the Cornu and the Littrow types. Many of these instruments are presently in use, although grating spectrometers are gradually replacing prism instruments. 

FIGURE 22 Multiple-prism Littrow (MPL) grating solid-state dye laser oscillator. The cavity length is about 75 mm and the excitation is performed semilongitudinally at a angle relative to the optical axis [From Duarte, F. J. (1999). Appl. Opt. 38, 6347-6349.]... 

A conventional monochromator (either Ebert, Czerny-Turner, Littrow or Echelle) may be used (see AAS sections for details), but some of the more basic instrumentation uses interference filters. These are optical filters that remove large bands of radiation in a nondispersive way. A dispersion element such as a prism or a grating is therefore not required. Only a relatively narrow band of radiation is allowed to pass to the detector. The disadvantage with such devices is that they are not particularly efficient and hence much of the fluoresced light is lost. An alternative development is the multi-reflectance filter. This is shown diagramatically in Figure 3, and has the... 

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