INFRA-RED AND ULTRA-VIOLET MICROSCOPY 



237 



There are "solid" frequency transformers which might possibly be 

 used in microscopy. They consist of the photoconductor D and the 

 electro-luminescent layer E, sandwiched between the two thin trans- 

 parent conducting layers Q and Co (Fig. 9.13). Both layers Q and Co 

 are deposited on the inner faces of the two glass plates A and B. 

 A heavy alternating current is fed through D and E by means of C^ 

 and Co. As the photons reach D the resistance of the layer drops 

 locally thereby giving rise to the increased potential difference to which 



Fig. 9.13. Diagrammatic solid image converter. 



the layer E is locally subjected. The layer E radiates visible light 

 opposite the area of the layer D affected by the infra-red radiation. 

 In order to convert an infra-red image into a visible one, television 

 scanning tubes are also suitable. W. Heimann has evolved a tube 

 of this type sensitive up to 35 /^. 



In the ultra-violet field, photography is in general use as standard 

 emulsions remain sensitive to wave-lengths up to 023//. Figure 914 

 shows the diagram of Burch's microscope for photomicrography in 

 visible and ultra-violet light. The ultra-violet source is at S^ (mercury 

 arc without continous spectrum). The lens Lx images Si on the slit F^ 

 of the monochromator which consists of the objective L3, the prism P 

 and the auto-coUimator mirror M^. Directing suitably the latter, 

 and after reflection on the mirror Mg, a spectrum is obtained from 

 which a monochromatic portion is isolated by means of the slit F... 

 By means of the lens L5 (field lens) and reflection on the mirror M3, 

 the sHt F2 is imaged in the condenser C which is a mirror objective. 

 The condenser C is adjusted so as to image L5 on the specimen at A 

 (Kohler illumination), the lens L4 imaging Lg on Z.5. Uniform illumi- 

 nation in monochromatic light of the specimen is thus obtained. 



