X-RAY MICROSCOPY 



(A) 



(B) 



DIFFRACTION 

 ERROR 



/ = (XL)>'2x'/V(l + x) microns 



(2) 



PROJECTED SOURCE 

 DIAMETER 



MONOCHROMATIC 

 POINT SOURCE 



Fig. 3. Definingthe two major causes for image 

 unsharpness in ultrasoft x-ray microscopy due to 

 (a) finite source size and (b) Fresnel diffraction. 



the ideal image edge position, formed with- 

 out diffraction, to the position of the first 

 intensity maximum. This may be shown 

 from diffraction theory to be given by the 

 relation 



with L measured in cm and X in angstroms. 

 L is the source to image distance and x is 

 the ratio of sample-to-image distance to 

 sample-to-source distance, d/c. It is evident 

 from this relation, as plotted in Fig. 4, that 

 the diffraction error is maximum for x equal 

 to unity and primary magnification eciual 

 to 2X (71/ = 1 + x), assmning the camera 

 length, L, to be constant. As has been (2) 

 pointed out, the diffraction limit for 2X 

 magnification is actually 70% of that for 

 high magnification projection microscopy 

 for dimension c held constant, i.e., for con- 

 stant sample field. In order to reduce this 

 error one must use either unit primary mag- 

 nification (contact method) or high primary 

 magnification. For contact microradiography 

 Eq. (2) may be written as 



/ = (Xd)i/2 (3) 



and for projection microradiography (x » 1) 



CAMERA EFFICIENCY -S. AND DIFFRACTION ERROR - f 



0.50 



0.25 



0.00 



CMR* 



Fig. 4. Illustrating the very high efficiency and relative freedom from P'resnel diffraction error for 

 contact microradiography. 



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