Green-sensitive - Geola - lasers and holography experts

Green sensitive photomaterials for holography

VRP-M - Silver-Halide photomaterial

VRP-M may be used in embossed holography (origination), as well as in art holography (one or two steps holograms recording). Resolution: more than 3000lines/millimeter.

VRP-M photomaterials are available coated on glass plates and on triacetate film. The largest plate size available as a standard size is 406x300 mm. The standard glass thickness is 2.5 mm. The largest standard film width is 1 meter. Custom glass and film substrates sizes are available for the coating on request. Guaranteed material lifetime - 12 months.

White-light holograms made on VRP-M have a natural green reconstruction colour that can be easily changed by the technique of colour -shifting using D-Sorbitol (described below).

Characteristic curve of green sensitive VRP-M emulsions, showing spectral sensitivity versus wavelength, is shown in Fig.1. As it is seen from the curve - VRP-M works well in the green and in deep blue regions of spectrum, showing the peak at approximately 70 microJoule/cm2 (~530 nm).

Fig.2 shows the optical density after VRP-M exposure by CW radiation and after development versus energy. Grain size is shown in Fig.3. The diffraction efficiency versus exposure for reflection holograms recorded on VRP-M (using a pulsed laser) is presented in Fig.4. The maximum diffraction efficiency is seen to be >45%. Material lifetime is more than two year.

Figure 1: VRP-M spectral sensitivity curve.

Figure 2: VRP-M characteristic curve.

Figure 3: VRP-M diffraction efficiency curve.

Figure 4: VRP-M Grain size distribution curve.

Processing and handling recommendations

- Unseal and process in indirect non-actinic light with use of a dark-red light filter (transmission zone 600 nm and more).
- Temperature of processing solutions - 20±2°C.
- Storage condition: Humidity 65% and 12-15deg. Celsius.

Default Chemical set of SM-6 developer and PBU-Amidol bleach can be obtained from our web shop. Developer for the embossed holograms originating - Neofin Blau, can be obtained in any specialized photoshop.

The VRP-M emulsion may be used equally well with pulsed lasers and with CW radiation.

Recommended VRP-M processing

rocedure	Embossed holograms originating	Mastering and Copying with Pulsed Radiation	Mastering and Copying with CW Radiation
Exposure:
ORIGINATING	60-80 microJ/cm2
MASTERING		20-40 microJ/cm2	60-80 microJ/cm2
COPYING		30-60 microJ/cm2	70-90 microJ/cm2
Development	Neofin Blau	SM-6 , 2min	SM-6 , 2min
Wash	Water, 1-2min
Bleach	GP-431 until clear (~2-3 min)	PBU-Amidol until clear (~2-3 min)
Wash	Water 5 min.
Final Wash	Water with wetting agent (Agepon) 1min
Drying	Slow Air

GP- 431 Bleach (Concentrated solution)
1. Take 600ml of distilled water and dilute therein in the following order
Ferric Nitrate (8-hydrate): 150g
Potassium Bromide: 30g
2. Take 250ml of methanol and dilute therein 0.3g of Phenosafranine.
3. Add solution 2 to the solution 1.
4. Add distilled water to obtain totally 1 liter of the obtained solution. Store in dark and cool place.
Working solution: 1 part of concentrated GP-431 bleach + 4 parts of distilled wate

All material performances given above are guaranteed only for the use with the default chemistry.

For the conventional CW holography one, on own risk, may also use the standard Kodak D-19 developer (3 min.) and Sulfuric- Potassium dichromate bleach (2-3min. : 30ml sulfuric acid + 5gm potassium dichromate + 1 liter of water).

Colour control

Adjustable colour shifting is accomplished by soaking the hologram for 1 minute in an aqueous solution of D-Sorbitol (sugar substitute - C6H14O6) or usual Sugar powder, 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.

Fig. 5. VRP-M colour shifting withD-sorbitol

VRP-M latensification

Quite rarely some VRP-M batches 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 sec. and go up to around 10 sec. 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).

PFG-04 - Dichromate gelatin photomaterials

It is designed for the recording of reflection Denisyuk-type holograms using CW laser radiation (488nm, 514nm -Argon laser). PFG-04 photomaterials are available coated on glass plates only. The largest plate size available as a standard size is 406x300 mm. The standard glass thickness is 2.5 mm. Custom glass substrates sizes are available for the coating on request.

Guaranteed material lifetime - 12 months.

Processing and Handling Recommendations:

The material spectral sensitivity curve is shown in figure1. The sensitivity reaches 100mJ/cm2 in the blue spectrum range and 250mJ/cm2 in the green. Due to its grainless structure, this material has very high resolving power and a diffraction efficiency of >75% (figure2), but has the lowest sensitivity from all holography emulsions offered by Geola's distribution network.

The recommended processing technique of the exposed hologram consists of the following operations:

1). Thermal Hardening after exposure (100OC) - Depending on the layer freshness. See figure3.

2). Cooling to Room temperature.

3). Bathing in running filtered water - 3min

4). Bathing in 50% Isopropyl Alcohol solution for 2 - 3 min

5). Bathing in 75% Isopropyl Alcohol solution for 2 - 3 min

6). Bathing in 100% Isopropyl Alcohol solution for 2 - 3 min

7). Drying in a desiccator (100OC) for 60 min

8). Emulsion layer preservation using optical anhydrous adhesive and protective glass.

Note that the processing solution temperatures must not exceed 20OC for fresh layers. If holograms appear "milky" in colour then the processing solution temperature should be decreased or the thermal hardening period should be prolonged. The material shelf life is 12 months (average observed period).

Figure 1: Spectral sensitivity curves for PFG-04.

Figure 2: Diffraction efficiency curve for PFG-04.

Figure 3: Hardening time for PFG-04 versus Storage Time. The black curve refers to a storage temperature of 18 Degrees Celsius and gray curve to a storage temperature of 4 Degrees Celsius.