CHAPTER 1 

 INTRODUCTION 



SEVENTY years ago the great optician Ernst Abbe dis- 

 covered the theoretical Hmit for the resolving power of the 

 optical microscope. No objective, however perfect from the 

 point of view of geometrical optics, can resolve details finer than 

 about one half of the wavelength of light in the medium in which 

 the object is embedded. Even by using ultraviolet rays and 

 immersion the Abbe limit cannot be substantially reduced below 

 0.1 microns or 1000 Angstroms.* 



It appears that Abbe was depressed rather than elated by his 

 discovery, which meant that he could not go on endlessly per- 

 fecting the microscope to which he had devoted his life's work. 

 This can be guessed from his remark ". . . it is poor comfort 

 to hope that human ingenuity will find means and ways to over- 

 come this limit." 



Human ingenuity was indeed powerless at Abbe's time, and 

 for some time after, until new physical discoveries opened the 

 way for progress. The first hope emerged, in 1912, when the 

 wave nature of X-rays was discovered. X-rays had indeed the 

 short wavelength required for a supermicroscope, and, unlike 

 the short ultraviolet rays, they had also sufficient penetrating 

 power, but no X-ray microscope could be constructed for lack 

 of X-ray lenses. By the very reason of their short wavelength, 

 matter is not a refracting but a dispersing medium for X-rays. 

 Therefore, geometrical X-ray optics could not develop on the 

 lines of light optics, and although in the last ten years respectable 

 progress has been made in the imaging of objects with X-rays 



* 1 micron = l|x = 10^ cm; 1 Angstrom = lA = 10"^ cm 



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