Beam irregularities in the reference beam will be maintained 
but have only a slight effect on the picture quality. 
Experiments with holoportraits taken this way have proven that 
excellent sharpness can be achieved. 
8) .SAFETY CONSIDERATIONS. 
  
It is obvious that one should look for safety when high power 
lasers are aimed at human beings. Several publications are 
‘available on the subject (ref.10,11,12); here we refer to the 
maximal allowable retinal energy of 0,07 Jem"? (ref.13). 
a. Normal incidence. We consider first laser light falling 
directly in the eyes. The energy of the laser is spread over 
an area in the field of the cornea 
A = n(a tg a723? 
where a is the distance from laser to cornea, and a the 
divergence angle of the beam. 
The corresponding corneal energy E rz $/m(a tg ar212 
wherein ® is the output energy of thé laser. 
We assume that this energy is concentrated onto the retina 
and is uniformly spread over an area with diameter 
d: = 1,22 )\ t/d 
wherein d represents the pupil diameter and f focal distance 
of the eye. 
The concentration factor of the eye lens C s (d/d')7 and 
hence the retinal energy e - E sort” 
For actual parameters 9-2J, a-200cm, a-20?, 12x10. cm, 
f=1;5cm and d=0,/7cm, E +77488 Jcm^2. If the true phase 
distribution on the retina is considered 
E EE / (A t/187)7, with R = pupil radius. "(ref.13) 
ret gor -2 
In this case a value of 8878 Jom is-found.. So that the 
first formula, that is simpler, may safely be used. 
It becomes clear that direct viewing of the laser beam or 
even the reference beam can and probably will be very 
harmful to at least a region of the retina if safety goggles 
are not worn. 
B. Side illumination. Let us consider Fig.1]. The subject now 
looks towards a diffusing screen D, located a distance S 
ahead. This screen has a scatter angle Y and a reflection 
factor po. In practice, the illumination of any object other 
than that under study must be avoided, so that the following 
approach can be considered as unwanted reflection. 
The energy reaching point P 
E ®sin (a/2)/[a ig(a/2) 1^ 
wherein sin(a/2) is related to the attenuation caused by 
oblique illumination. 
The energy reflected from P will be : E,-E p 
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