and VRP-M emulsions have peak sensitivities to exposures
in the millisecond regime. In order to obtain optimal
sensitivity to exposures different from this regime the
technique of latensification must be used.
Latensification is usually done directly after the
holographic exposure. Before applying the process a
latensification time appropriate for your system must be
worked out. This procedure is as follows: Place a 25W
white lamp at a distance of 1m from a test holoplate or
film such that its light uniformly illuminates the
emulsion. You will need to try several exposure times.
First of all you will need to develop the unexposed
emulsion under normal safelight conditions. The plate
will darken a little. This is called the fog
level. After development wash this control plate, dry
and keep it handy. Now a series of exposures with small
test plates must be made. Start at about 2 secs and go
up to around 10 secs. After each exposure develop your
plate and match the darkening of this plate to your
control plate. If it is the same, more exposure is
needed so go back and repeat the process. Stop when a
result that is just marginally darker than the fog level
is obtained. This is then the correct latensification
exposure for your geometry.
Now that the proper latensification time has been
discovered, after every proper holoplate exposure you
must take your plate and illuminate it exactly as
described above for the time that you have worked out.
Then all processing is as normal.
Latensification stabilizes and enhances the latent image
formed by the holographic exposure. If required,
chemical processing may be done with significant delay
after latensification (~8 hours).
the VRP-M emulsion we recomend two colour shifting
techniques. One produces a fixed colour-shift towards
the red of approximately 50 nm. The other produces an
adjustable colour shift.
The fixed colour shifting is accomplished by soaking the
final hologram for 1 minute in a bath of Potassium
Iodide solution. Adjustable colour shifting is
accomplished by soaking the hologram for 1 minute in an
aqueous solution of D-Sorbitol (sugar substitute -
C6H14O6) with added wetting agent. The colour of the
final hologram depends on the solution concentration (Fig.5).
After soaking, the film must be taken out and put onto a
flat surface. Water drops must be removed using a
rubber wiper such as a windscreen wiper. Here one must
be delicate - if too much force is employed you may
obtain a somewhat different colour than that predicted
by Fig. 5. If, after drying of the
hologram, the replay colour achieved is not
satisfactory, the film or plate may be washed in warm
water and then soaked anew in another D-Sorbitol
solution of different concentration.