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25 holography lessons

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18. Hologram recording

So everything is ready for recording a hologram. The laser was tested, the optical scheme was adjusted, the object was set in the shooting cabin. Recording the hologram is executed by a nonactinic illumination to which the photographic plates arenít sensitive. For the photographic plates VRP (FPR) which are sensitive to green light the red light is nonactinic.

At first we take a photographic plate from the box and check were the emulsion layer is located (see lesson 8). Then we set the photographic plate into the frame, see fig., so that the emulsion side is directed to the object. The plate is inserted by the lower face into the frame slot and the upper face is closed by the black rubber tape so that the reference beam doesnít get into it. By setting the photographic plate you should be very careful in order not to scratch occasionally the emulsion layer and not to displace the object. If a portrait is shot the customer has a possibility to look at himself in a weak reflection from the photographic plate and to sleek the hair or to correct position of the head. Then we rise the pump voltage in the supply unit of the laser up to the nominal value. The starting button is connected to the supply unit through the long cord therefore itís possible to come to the cabin before shooting and to control of the object position till the latest moment. Itís especially important by shooting domestic animals, which can involuntarily move aside and so you should simply catch the moment of the happiest position. If a complex composition with a non-standard illumination is shot at first a test hologram of small sizes, e.g. 9x12 cm, should be recorded. During shooting the plate can be simply held in the hand with the upper face closed by a strip of paper or by the plastic clamp. If everything is all right we press the starting button and the laser emits a short and powerful pulse of light. The hologram has been recorded! By shooting portraits customers often ask a question - is dangerous the laser radiation for eyes or not. It's a serious question but it is solved for a long time and the answer to it is given in many recommendations and descriptions of methods written for specialists working with laser radiation. Safe levels of illumination of the eye retina for the continuous and pulse laser radiation have been determined and the methods of calculation of the illumination levels for different conditions have been developed. For our setup with the laser energy of 1 Joule and with a two-beam diffuse illumination of the object and taking into account bright illumination of the cabin by red lanterns (see fig.), the illumination level of eyes is less than the set safe level approximately by a factor of ten. Red nonactinic light plays the important role here - the pupil of the eye converges and the level of illumination of the eye retina by the laser radiation is considerably reduced. -->