Prism spectrograph

Adam Hilger, Ltd., of London has an RU raies ultimes) powder mixture of 50 elements. The concentrations are adjusted so only the persistent spectral lines (raies ultimes) will appear when the sample is excited in a dc arc. The base material for the RU powder is a mixture of zinc, magnesium, and calcium oxides. A spectral plate of RU powder with the iron spectrum included is shown in Figure 7-5. The plate was obtained using a prism spectrograph, so the dispersion is not linear. 

When master plates taken with the spectrograph being used are not available it is possible to identify spectral lines by comparison with spectral charts. If charts are used, it is often necessary to make proper allowance for differences in dispersion and for differences in changes in dispersion with wavelength if the charts have been prepared using a prism spectrograph. 

Adam Hilger, Ltd., has such charts prepared for its RU powder standard. The charts were made with a prism spectrograph and thus the dispersion is nonlinear. Six separate enlargements, each 10 in. long, cover the spectral region from 2440 to 6717 A. Each chart includes an iron spectrum, RU powder spectrum, and a spectrum of the base material. All persistent lines of the 50 elements in the RU powder are identified and frequent identification of wavelength is included. The spectra were obtained using dc arc excitation. 

The product U = Af2 h often named etendue. For the prism spectrograph the maximum solid angle of acceptance, Q = F/ ff, is limited by the effec-... 

In the infrared region, several materials (for example, CaF2, NaCl, and KBr crystals) are transparent up to 30 jim (Fig. 4.6). However, because of the high reflectivity of metallic coated mirrors and gratings in the infrared region, grating spectrometers with mirrors are preferred over prism spectrographs. 

Names such as spectrometer, spectroscope, spectrograph or monochromator are used for basically the same types of instruments, which are, however, applied in different ways. The principle of a prism spectrograph is illustrated in Fig.6.17. The resolving power is determined by the dispersion, dn/dA, and the length of the prism base b... 

Fig.6.19. Diagram showing the slit width required to achieve a constant band pass of 1 nm from a prism spectrograph [6.67]...

The spectral transmittance T(A) of the instrument, which is limited by the transparency of the lenses and prism in the prism spectrograph or by the reflectivity R(a) of the mirrors and grating in grating spectrographs. 

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