3-D LOCATION & MEASUREMENT BY COHERENT OPTICAL METHODS 
the recording and measurement of the dis- 
placement or deformation of a body, together 
with the subsequent measurement. The in- 
terference patterns thus obtained correspond 
to the displacements shown. 
PHOTOFABRICATED OPTICAL ELEMENTS FOR 
MEASUREMENT PURPOSES 
Holographic techniques, and the experi- 
ence obtained in using holography, now are 
being applied for the purpose of making 
structures with the capability of exerting just 
the kind of phase modulation of incident 
coherent light beams needed to provide op- 
timum location of points determined by the 
positioning of the structure. The simplest 
example of this kind of structure is the zone 
plate, which may be made of high optical 
performance? and provides a wavefront ca- 
pable of a setting precision to a small fraction of 
a micrometre. 
As a demonstration, rather a different ele- 
ment was made on photographic material by a 
holographic process some time ago, and may 
serve to illustrate a slightly more elaborate 
form of reconstruction. Figure 7 shows how 
the element, simply illuminated with a di- 
vergent coherent wave from a laser, produces 
a series of real reconstructions in space in 
exactly predetermined positions. All of the 
reconstructions are independent of each 
other and consist of the numerals 0, 1, 2, 3, 4 
arranged in line along the axis of the optical 
system and spaced apart by 50 mm. 
FuTURE APPLICATIONS IN PHOTOGRAMMETRY 
As the need develops, holographic record- 
ing of wavefronts determining the spatial re- 
lation of points on bodies will undoubtedly 
evolve to match the problems. At present, the 
time distribution and coherence of laser 
sources in relation to the size and movement 
of the object recorded set limits to the use of 
holography!°, and it is to be expected that the 
most rapid progress will occur in short-range 
applications such as those mentioned in this 
paper. 
Longer-range photogrammetry may ben- 
efit by the use of holographic intermediate 
stages!! and, more directly, by the incorpora- 
tion of incoherent-to-coherent converters to 
synthesize holographic records of three- 
dimensional relations. 
Our own program at present continues with 
a number of studies in short-range measure- 
ment, and with the provision of fabricated 
elements for the extension of rapid and accu- 
rate measurement from one dimension into 
three dimensions. 
1353 
  
  
  
       
AS AMO CUN 
: So 
is P ^ - 
i 4 
% 
4 i # 
4 5 
| M | | 
7 o à 
7 a 
Fic. 7. Simple holographically-formed ele- 
ment producing five independent reconstruc- 
tions. 
ACKNOWLEDGMENT 
My colleagues, R.G.N. Hall and R.F. Ste- 
vens, have collaborated in realizing the ex- 
perimental part of the examples quoted in 
this paper, and acknowledgment is made for 
quoting some of their work which is not yet 
published. 
Acknowledgment is also due to J. M. Burch 
and S. J. Bennett for past discussion and col- 
laboration. 
REFERENCES 
l. Born M. and Wolf E., Principles of Optics 
(Fourth Edition), pp. 395-398, Pergamon (Ox- 
ford) 1970. 
2. Ibid., pp. 414-418. 
3. Kogelnik H., Imaging of Optical Modes, Bell 
System Technical Journal, 44, No. 3, pp. 455- 
494, (1965). 
4. Bennett S. J. and Gates J.W.C., The design of 
detector arrays for laser alignment systems, J. 
Phys E.: Sci. Instrum., 3, pp. 65-68, (1970).