l-)0 



KADIATIOX IU()L()(;Y 



barKor and Cartwright, 1939; Cart\vri<>;lit , 1939). Minor optics may also 

 be employed to solve the problem of achromatization. 



Multiple prism cascades may be used etTectively io obtain greater 

 prism l)nse and hence greater resohing power. Double monochromators, 

 employing essentially two single monociiromators in tandem, may be used 

 tor greater purity of radiation and freedom from scattered radiation at the 



COLLIMATING AND 

 TELESCOPE LENS 



REFLECTING 

 PRISM 



FOCAL 

 PLANE 



REFLECTING SURFACE 



Fig. 4-11. Littrow moiiiiiiiig for prism iiistnunciit. {Reproduction from Practical 

 Spectroscopy, by G. Harrison, li. Lord, and J. li. Loofbourow, Prentice-Hall, Inc., 1948.) 



(a) 



Fig. 4-12. Constant dovialion prism instrum('nt.s usiii^: (a) Pcllin-Broca prism; (h) 

 \\ adsworth mounting for prism. {Reproduction from Practical^ Spectroscopy, by 

 G. Harrison, R. Lord, and J . R. Loofbourow, Prentice- Hall, Inc., 1948.) 



expense of energy transmission (Sawyer, 1951; Harrison ef al., 1948). 

 Cascaded Pellin-Broca prisms may also be employed in such a way as to 

 minimize stray radiation (Benford, 1936). 



By reflecting the radiation back through the prism, as in the Littrow 

 moimting (Fig. 4-11), twice the dispersion and resolving power may be 

 obtained. The collimating lens then may serve also as telescope lens. 

 With this arrangement the exit slit is spatially near to the entrance slit, 

 and scattered radiation may be a problem. 



Constant deviation monochromators may be made with the Pellin- 

 Broca prism (Fig. 4-12a), with the Wadsworth mounting for the ordinary 



