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The Easy Way!



DIY  HOLOGRAPHY 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 about  marks from bubbles, dust and blemishes then you may prefer to use the  proprietary 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 halide  hologram recording plates by Diffusion


 


By  Jeff  Blyth,   Institute of  Biotechnology ,  University of  Cambridge   Tennis court rd. Cambridge CB2  1QT


Tel : 01223  334152   ( 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 Journal  Vol 47  pp 87- 91   1999


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 coating  of  pure gelatin on a glass plate is treated with  silver nitrate. The coating is then immersed in a bath of bromide ion and dye. This then precipitates  extremely fine grains of silver bromide in the gelatin layer.



 


Materials 


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


2. Gelatin of  bloom strength  between 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 1N  volumetric standard solution is a useful form)


5. Potassium Bromide


6. Chromium acetate , (you can use chrome  alum instead)


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


8. Sodium hydroxide


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


 


Concentration of Solutions 


(quantities  will need to be judged by you to suit your requirements)


Silver nitrate : 6%  w/v  in (DI) water , (or  the 1N volumetric standard solution diluted by 1volume  to 2 volumes DI water.)


Stock dye solns :  for  633nm  1g. /1000 ml  Methanol,   but for  532 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 bromide  4%  w/v  in 3/2  methanol /water (3% lithium bromide gives a finer grained hologram than the equivalent concentration of potassium bromide, however 4% potassium bromide works well).


Chromium acetate  solution  1%  or  Chrome Alum   2%


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


Ascorbic acid 1% solution in water , adjusted to around  pH  5 with  any alkali.



 


Preparation of  plates  


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 solution  and 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 dry  I rub them over with a 1% solution of  3-amino-propyltriethoxysilane  in acetone on a tissue until it has evaporated, and leave them in air to interact with the silane for  at least two hours before coating. (The silane solution has to be freshly prepared for each batch of plates). 



 


Preparation of coating solution  for a 10 x 8 plate


Add  30g  gelatin to 170ml cold distilled water and  mark the liquid level on the beaker.  Place beaker in a water bath and heat while stirring constantly  until gelatin solution  is between 60 and 70o 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 the  presubbed glass plate (preheated  to around 70oC) at  an angle of about  30o  to 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 . (You  may have to accept the tendency of the coating  to not completely  cover the lower part closest to the  furthest edge. )  Lean plate against something for a few minutes while coating  gels.  Run a  knife along thick layer  at the bottom to free plate rather than risk tearing the delicate coating. (Since no hardener is involved yet  the gel  can be readily  scooped up and  recoated  if you  are not satisfied.).  Put  plate in cold solution of  chromium acetate for  1 minute. Shake off  drips 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 around  60oC for several hours).  Rinse the hardened plate in DI water  and  dry in a  warm 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 before  running a scalpel blade along the gelatin side first so that it is cut and not torn apart..


Alternatively  a  Meyer bar can be used.  About 7 turns per cm.


 


AgBr  loading  operation.


1.  For a 5 x 4 plate place approx  3 ml  6% silver nitrate soln. in the centre and at once squash it with a clean flat cover plate (preferably transparent  plastic 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 and  immediately  remove the excess  silver  solution  on its surface  by  gently  brushing over  the plate with a soft squeegee (windscreen wiper blade).


 


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


 


4. Under safelight conditions ,  add  2.5 ml of  dye solution  per 100ml  of  potassium  bromide  solution ,  add about  0.5 ml  of 1%  ascorbic acid solution (this is the same solution as is used in the final sensitizing bath ) agitate the bath  and plunge plate in while maintaining  the agitation for about  2 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  (any  AgBr only on the surface can be removed by gently rubbing  with ungloved finger.) Plates usually come out  this bath  beautifully clear under  the green safe light, without any surface deposit.


 


 7) Sensitizing  bath step


The plate can be immersed for 1 minute in 1% ascorbic acid solution adjusted to  pH 5  using a  little sodium carbonate or hydroxide . Alternatively  the  well known  triethanolamine pre-swelling technique can be used  with the  advantage  of increased  brightness  at  a shorter wavelength.  (prolonged settling period may  then be necessary  however to avoid creep  while the exposure is being made).


 After exposure the plate is then developed  as per the first part above.


 


 

Queries: Email Jeff-at-biotech.cam.ac.uk, replacing -at- with @