DIYHOLOGRAPHY RECORDING MATERIAL

This is a remarkably simple way of making a holographic recording material. This is the way that we make a lot of holograms in our lab, and we find it to be by far the easiest method for making holographic plates.

In essence, we treat a glass surface to make it chemically 'sticky', we coat that with gelatin, and harden the gelatin with chromium or formaldehyde. Once we have the gelatin film we then soak into it a silver salt, and subsequently soak in potassium or lithium bromide to precipitate an ultra-fine grain precipitate of silver bromide. The bromide solution also incorporates a dye to make the plate photo-sensitive in the required wavelength range, and with addition of a little sensitiser we can produce by this method a holographic plate of quite high standard.

A worksheet (dated Nov 2000) is given below. It gives results which have good diffraction efficiency and photosensitivity compared to ultrafine grain proprietary material. But this is for the fun of doing it all yourself and getting bright results. If you are particularly concerned aboutmarks from bubbles, dust and blemishes then you may prefer to use theproprietary material.

The material on this page is based on the following article, with some changes that we have made to our protocols since publication, and any differences between the original article and the text below are solely due to those differences.

A simple way to make silver halidehologram recording plates by Diffusion

ByJeffBlyth,Institute ofBiotechnology ,University ofCambridgeTennis court rd. Cambridge CB21QT

Tel : 01223334152( fax: 334162 )email : jeff@biotech.cam.ac.uk

What follows is in the form of a worksheet based on the paper published in :

The Imaging Science JournalVol 47pp 87- 911999

A text only version of the paper can be found on the internet on the websites:-

http://www.holoworld.com/holo/paper.html

or at:-

http://www.holografie.com/paper.html

The Basic principle

A coatingofpure gelatin on a glass plate is treated withsilver nitrate. The coating is then immersed in a bath of bromide ion and dye. This then precipitatesextremely fine grains of silver bromide in the gelatin layer.

Materials

1. Presubbed glass plates . (You can use old holographic plates with the gelatin removedwith the aid of household bleach.)

2. Gelatin ofbloom strengthbetween 250 and 300 (eg. 300bloom from Aldrich cat no. 27,162-4) , (You can use culinary gelatin without any sugar or flavourings.)

3. ascorbic acid or Vitamin C,

4. Silver-nitrate ,(A 1Nvolumetric standard solution is a useful form)

5. Potassium Bromide

6. Chromium acetate , (you can use chromealum instead)

7. dye(s):Pinacyanol Chloride(forHeNe 633nm exposure)or 1,1 -diethyl -2,2 cyanine iodideforexposure at 532nm .

8. Sodium hydroxide

9. (for new glass plates)3-amino-propyltriethoxysilane

Concentration of Solutions

(quantitieswill need to be judged by you to suit your requirements)

Silver nitrate : 6%w/vin (DI) water , (orthe 1N volumetric standard solution diluted by 1volumeto 2 volumes DI water.)

Stock dye solns :for633nm1g. /1000 mlMethanol,but for532 nm dye,1g.per 500 ml methanol .

(In practice you would probably only need a hundreth of a gram to make up a few ml of these somewhat expensive dyes.)

Potassium bromide4%w/vin 3/2methanol /water (3% lithium bromide gives a finer grained hologram than the equivalent concentration of potassium bromide, however 4% potassium bromide works well).

Chromium acetatesolution1%or Chrome Alum2%

Gelatin solution. 15%:(see 2paragraphs down)

Ascorbic acid 1% solution in water , adjusted to aroundpH5 withany alkali.

Preparation ofplates

Glass plates usually need a pre-treatment step or the gelatin coating will peal off. You can use old holographic plates by simply giving them a 10 min. soak in neat domestic bleach solutionand then rub off the old gelatin layer under tap water. After a final rinse in distilled water,no further subbing step may be required.

However with new glass plates, I leave them soaking overnight in a 100% bleach(Domestos or Parazone). After the plates are dryI rub them over with a 1% solution of3-amino-propyltriethoxysilanein acetone on a tissue until it has evaporated, and leave them in air to interact with the silane forat least two hours before coating. (The silane solution has to be freshly prepared for each batch of plates).

Preparation of coating solutionfor a 10 x 8 plate

Add30ggelatin to 170ml cold distilled water andmark the liquid level on the beaker.Place beaker in a water bath and heat while stirring constantlyuntil gelatin solutionis between 60 and 70^o C.

Stir until all granules have cleared. Top up level to the mark .To remove skin and surface foam, pour through a fine mesh (nylon stocking works fine) into a preheated beaker.Then immediately proceed to next step:

Coating (by the old Victorian curtain method)

Hold the beaker in your right hand and with you left incline thepresubbed glass plate (preheatedto around 70^oC) atan angle of about30^oto the vertical with its bottom edge in a clean tray. Pour the gelatin in a line about 1 cm from the top of the plate. The pouring rate must be continuous until the furthest edge of the plate is reached . (Youmay have to accept the tendency of the coatingto not completelycover the lower part closest to thefurthest edge. )Lean plate against something for a few minutes while coatinggels.Run aknife along thick layerat the bottom to free plate rather than risk tearing the delicate coating. (Since no hardener is involved yetthe gelcan be readilyscooped up andrecoatedif youare not satisfied.).Putplate in cold solution ofchromium acetate for1 minute. Shake offdrips and then (without washing away that salt ) blow plate with cold air until dry. Once the layer is dry leave the plate to complete the chrome hardening effect overnight in a warmer. (Preferably at around60^oC for several hours).Rinse the hardened plate in DI wateranddry in awarm air flow.If you want to cut plate up for the next step then after scoring the glass on the back and cracking it, it is best not to pull sections apart beforerunning a scalpel blade along the gelatin side first so that it is cut and not torn apart..

Alternatively aMeyer bar can be used.About 7 turns per cm.

AgBrloadingoperation.

1.For a 5 x 4 plate place approx3 ml6% silver nitrate soln. in the centre and at once squash it with a clean flat cover plate (preferably transparentplastic so that you can see the air bubbles are squeezed out).Leave for 3 minutes.Safelighting is not strictly necessary here but white lighting should be subdued.

2.Remove cover plate andimmediatelyremove the excesssilversolutionon its surfacebygentlybrushing overthe plate with a soft squeegee (windscreen wiper blade).

3. Blow dry plate with coolair. Once dried, the plates can be stored for a short while in a cool, dry, dark location until needed.

4.Under safelight conditions ,add2.5 ml ofdye solutionper 100mlofpotassiumbromidesolution ,add about0.5 mlof 1%ascorbic acid solution (this is the same solution as is used in the final sensitizing bath ) agitate the bathand plunge plate in while maintainingthe agitation for about2 minutes (although with softer gelatin this could be reduced to 60 seconds, otherwise unacceptable grain growth can occur. Expect to spend a little time optimising this step for your own application).This solution can be re-used a number of times, until such a point as the dye starts to come out of solution or the brightness of the resultant holograms seems to be diminished; the dye used for 532nm exposures (see above) is far more re-useable.

5. Rinse well under running tap water(anyAgBr only on the surface can be removed by gently rubbingwith ungloved finger.) Plates usually come outthis bathbeautifully clear underthe green safe light, without any surface deposit.

7) Sensitizingbath step

The plate can be immersed for 1 minute in 1% ascorbic acid solution adjusted topH 5using alittle sodium carbonate or hydroxide . Alternativelythewell knowntriethanolamine pre-swelling technique can be usedwith theadvantageof increasedbrightnessata shorter wavelength.(prolonged settling period maythen be necessaryhowever to avoid creepwhile the exposure is being made).

After exposure the plate is then developedas per the first part above.