HISTORY OF ELECTRON OPTICS 



REFERENCES 



Archard, G. a., "Proc. Internat. Conference on 

 Electron Microscopy," London (1954). Pub- 

 lished by the Royal Microscopical Society 

 (1954). 



Bloomer, R. N., Brit. J. Appl. Phys., 8, 83 (1957). 



Glaser, W., Z. Physik, 117, 285 (1941). 



Haine, M. E., "Proc. Internat. Conference on 

 Electron Microscopy," London (1954). Pub- 

 lished by the Royal Microscopical Society 

 (1954). 



Haine, M. E., "The Electron Microscope" 

 (E. and F. N. Spon Ltd., London). 



Haine, M. E. and Einstein, P. A., Brit. J. Appl. 

 Phys., 3, 40 (1952). 



Haine, M. E., Einstein, P. A., and Borcherds, 

 P. H., Brit. J. Appl. Phijs., 9, 482 (1958). 



Haine, M. E. and Mulvey, T., /. Sci. Instr., 31, 

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Langmuir, D. B., Proc. I.R.E., 25, 977 (1937). 



Levt, F., Z. Angew. Phys., 2, 448 (1950). 



Liebmann, G. and Grad, M. E., Proc. Phys. Soc 

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M. E. Haine 



FIBERS (TEXTILES). See GENERAL MICRO- 

 SCOPY, p. 343. 



HISTORY OF ELECTRON OPTICS 



The history of electron optics starts more 

 or less with the discovery of cathode rays. 

 The earliest experiment of Pliicker in 1859 

 already showed a rectilinear propagation of 

 these rays. Ten years later, Hittorff dis- 

 covered that cathode rays can be deflected 

 by a magnetic field, and that an axially sym- 

 metrical magnetic field will concentrate such 

 rays. Another ten years elapsed before 

 Crookes demonstrated a better proof of rec- 

 tilinear propagation. The first attempt to 

 calculate the trajectory of charged particles 

 in fields of forces originated with Riecke in 

 1881. These were rather incomplete, and the 

 first quantitative theoretical and experi- 

 mental studies on the deflection of an elec- 

 tron beam had to wait until 1897 when J. J. 

 Thomson determined the ratio of the charge 

 to mass of the elementary particles carrying 



the elementary quantity of electricity and 

 confirmed, in a manner of speech, the beauti- 

 ful calculations performed earlier the same 

 year by H. A. Lorentz. 



The first intentional use of a solenoid for 

 concentration of cathode rays was done by 

 Wiechert in 1899. He used a relatively long 

 solenoid; a short coil for concentration was not 

 used until 1903 by H. A. Ryan. In the same 

 year, the first electrostatic concentration of 

 an electron beam was performed by Weh- 

 nelt. Very extensive calculations of trajec- 

 tories of charged particles in field.s of forces 

 were carried out in 1907 by C. Stoermer. The 

 basic equations of electron optics are im- 

 plicitly contained in the work of Stoermer, 

 although this had not been recognized for 

 many years. 



The haphazard use of electron optical ele- 

 ments and of calculations was followed by a 

 more deliberate one in the middle twenties 

 of this century. De Broglie's thesis in 1924 on 

 the wave nature of the electron became the 

 foundation of physical electron optics. The 

 formal foundation of geometrical electron 

 optics was set down in 1926 by Busch. Busch 

 actually considered a magnetic coil as an 

 optical lens, and derived the lens equation 

 for it, although he failed to use the coil as an 

 imaging element. 



The combination of these two discoveries 

 stimulated thinking in two directions. His- 

 torically, the first was the development of ap- 

 plied physical electron optics in the form of 

 electron diffraction. The momentous dis- 

 covery of diffracted electron beams by Davis- 

 son and Germer m 1926-27 was soon fol- 

 lowed by the similar experiment of G. P. 

 Thomson. On the other hand, geometrical 

 electron optical methods were first applied 

 around 1929, when cathode ray oscillographs 

 were built on the basis of electron optical 

 elements. These attempts were pursued 

 simultaneously by Briiche iri Germany and 

 by Zworykin in the United States. 



The next step in the development of geo- 

 metrical electron optics was the study of ax- 

 ially symmetrical fields as lens elements. 



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