HOLOGRAPHY MATERIALS

Slavich is a factory of approximately 1000 employees with over thirty years of experience in the field of holography emulsion production. The company was originally formed in 1931 to cater for the extensive Russian photographic emulsion market - a sector where the company retains its world leadership. In more recent times Slavich has diversified into the microelectronics sector where it is now also the largest supplier in the CIS. Slavich has highly modern imported clean-room and ultra-clean-room facilities. The factory is well on the way to international standardisation with ISO9001 certification expected in 1999.

Slavich currently produces both Silver Halide and Dichromated Gelatin emulsions for holography applications. Table 1 summarises all the materials presently available. The green-sensitive VRP-M emulsions are very close analogues to the old Agfa 8E56 products for both Pulsed and CW laser recording. Likewise, the PFG-01 material gives equivalent performance to the Agfa 8E75 product for CW recording. Unfortunately no analogue exists for 8E75 when used with pulsed Ruby radiation.

The PFG-03M emulsion is a super fine grain red sensitive emulsion for superior quality imaging. The PFG-03C material is a panchromatic equivalent to the PFG-03M.

Finally PFG-04 is a long-life Dichromated Gelatin emulsion for blue and green laser recording.

The VRP-M and PFG-01 Materials

Characteristic curves for these emulsions, showing spectral sensitivity versus wavelength, are shown in figure 1. The VRP-M light sensitivity (CW radiation) is seen to peak at aproximately 75 microJoules/cm² and that of PFG-01 (CW radiation) at aproximately 100 microJoules/cm2. Figure 2 shows the optical density after exposure by CW radiation and development versus energy. Grain size characteristics for the VRP-M and PFG-01 emulsions are presented in Figure 3. The diffraction efficiency versus exposure for reflection holograms recorded on PFG-01 (using a CW laser) and on VRP-M (using a pulsed laser) is presented in figure 4. The maximum diffraction efficiency is seen to be >40% for both emulsions. Material life is more than two years.

Figure 3: Grain size distribution curve for VRP-M and PFG-01

The VRP-M emulsion may be used equally well with frequency - doubled pulsed Neodymium lasers as with green CW radiation. The PFG-01 emulsion, however, is not sensitive to pulsed radiation from the Ruby laser and as such should be only used with CW sources. Emulsions used with pulsed radiation, should be post-sensitized with the technique of latensification (see section below).

 

 

The PFG-01 emulsion can be processed with virtually any chemistry previously applied to the Agfa 8E75 emulsion with the single addition -if necessary- of a post-exposure latensification step before chemical processing. We recommend, in particular, the SM-6 and CW-C2 developers defined in table 4 for both transmission and reflection holograms. Colour control is possible with all the normal methods used with the Agfa emulsion including TEA

 

 RecommendedChemistryforVRP-M
Table 2 shows a summary of various recommended processing schemes for use with Pulsed Neodymium lasers (526.5nm, 532nm). All these processing recipes work equally with CW Argon for both transmission and reflection holograms; however in this case latensification is usually not necessary and exposure is a little longer. In addition, for CW, you may obtain better results using the CW-C2 developer depending on your colour requirements. Uniform heating in a special oven provides easy colour control across the spectrum for pulsed lasers.

Unlike Agfa emulsions the Slavich PFG-01 and VRP-M emulsions have peak sensitivities to exposures in the millisecond regime. In order to obtain optimal sensitivity to exposures either much longer or much shorter than this timeframe the simple technique of latensification can be used. Practically speaking this means that some CW laser users and all pulsed laser users will use latensification.

Latensification is usually done directly after the holographic exposure. However before you can apply the process you must work out a latensification time appropriate for your system. This procedure is as follows: Place a 25W lamp with a dark filter (green for VRP-M and red for PFG-01 although white light also works) 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 ranging from 0 to around 4 mins and then look at how the emulsion develops. So start with zero exposure time and then under your normal safelight conditions develop the plate. The plate will darken a little. This is called the fog level. After development put this control plate into a STOP bath, wash it and keep it handy.

Now you must start to make a series of test exposures with small test plates. Start at about 0.5 mins and go up to around 4mins. After each exposure develop your plate and match the darkening of this plate to your control plate. If it is the same you need more exposure so go back again and repeat the process. Stop when you get a result that is just marginally darker than the fog level. This is then the correct latensification exposure for your geometry.

Now that you have discovered the proper latensification time all you must do is 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.

 

This material is designed for reflection hologram recording using CW radiation in the red spectral range (633nm - HeNe laser and 647nm - Krypton laser). The spectral sensitivity curve of the material is shown in figure 5. Peak emulsion sensitivity is around 1.5-2mJ/cm2. Density versus energy is shown in figure 6 and the grain size distribution curve is shown in Figure 7.

Despite a lower sensitivity than VRP-M and PFG-01, the PFG-03M material has a higher diffraction efficiency and a very high signal to noise ratio. Holograms recorded on this material have a very clear and powerful object reconstruction and excellent layer transparency. Usually a physical solution development that acts to create colloidal silver is the preferred processing method. PFG-03M does not need bleaching.

 
 Figure 6: Characteristic curve for PFG03M.

 

 

 

Table 6: Recommended processing for PFG-03C (Reflection Holograms).

This material is designed for the recording of reflection Denisyuk-type holograms using CW laser radiation (488nm, 514nm -Argon laser). The material spectral sensitivity curve is shown in figure 10. 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% (figure 11).

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

1). Thermal Hardening after exposure (100C) - Depending on the layer freshness. See figure 12.

2). Cooling to Room temperature.

3). Bathing in running filtered water - 3mins.

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

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

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

7). Drying in a desiccator. (100C) for 60 mins.

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

Note that the processing solution temperatures must not exceed 20C 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 11: Diffraction efficiency curve for PFG-04

Nina Bazunova
Tel/fax: (48535) 6-90-82
E-mail: dfet@slavich.ru