Latensification

PFG-01 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).

Colour control

For 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.