image plane reference beam

rzeheb · Post by **rzeheb** » Sat Oct 24, 2009 8:30 pm

I recently upgraded my holo lab with a nice spatial filter (thanks Dave!) and a collimating mirror. The quality improvement to the first transmission master I made (today) was dramatic. So now I want to make the H2 reflection image plane and I have a question. Should my collimated and filtered reference beam be used on the H1 or on the H2? My feeling is that it should be used on the H1 however the two holography books I have seem to be split (no pun intended) on this as one book shows the collimated beam on the H1 and the other book shows the collimated beam on the H2 :doh:

Kaveh · Post by **Kaveh** » Sun Oct 25, 2009 9:29 am

Collimating on H1 is far more important than H2. Any distortions and aberrations get worse with distance of image point from recording plate. With H1, your image points are, say, 20cm from the plate. With H2, they would be 0 to 5, say. Ideally you want to collimate both, but H1 far more important.

You can check the quality of your H1 collimation by projecting the real image from it onto a card or ground glass screen. The highlights must focus to a sharp point, and you should be able to see the tiniest detail perfectly. Otherwise either you are not collimating well or there is some change in your geometry, e.g. plate is tilted.

rzeheb · Post by **rzeheb** » Sun Oct 25, 2009 11:35 am

Hi Kaveh. Thanks for confirming my suspicions. Since I only have one collimating mirror and one spatial filter it sounds like the ideal set up for making the H2 would be to use the collimated reference beam on the H1 but to move my spatial filter to the uncollimated reference beam on H2 in order to give the cleanest image. BTW, I did use an opaque screen to view the real image under collimated illumination and it certainly seemed to me that the image focused sharply and with more detail than on earlier attempts that did not use collimated light. That's the main reason I suspected collimation should stay on H1. I can see a second spatial filter in my future!

Much thanks!

dave battin · Post by **dave battin** » Sun Oct 25, 2009 1:24 pm

Hi Ron, sounds like the new spatial is working well for you. Kaveh got it correct. As long as you are not projecting your H1's image to far from the plate H2 plate this will work for you. When you were at my lab did i give you a small concave mirror? I can send you one and its a an good alternative to using a lens for H2's referance beam. i think i have your address ill send you one this week. when using this mirror dont use it to far off axis and sometimes you will need to find a "sweet spot" without any aberrations/scratches, but its amazing how well these work especially when doing longer distance (off table)one beam work !

rzeheb · Post by **rzeheb** » Sun Oct 25, 2009 11:32 pm

Hi Dave. I would love to try using a concave mirror instead of a lense for spreading my reference beam. Thank you very much for offering to send me one. So, I shot a series of H2s this evening using a collimated reference beam on the H1 and the spatial filter on the reference beam for the H2. The holos were the best I have yet made and I am quite happy with them. The images are sharp and well defined. Some reconstruct about 2 inches in front of the plate and others in the plane of the plate and behind the plate. My main complaints are: (1) the viewing angle is pretty narrow (maybe 30 or 40 degrees) and (2) I can no longer abide by these tiny 2.5 by 2.5 inch plates. The answer to complaint #2 is to move on to 4X5 film which I'm sure will create challenges of its own, but which I am ready to face. However, I am not sure what to do about complaint #1. Any suggestions on tips and tricks to extend the viewing angle on reflection image plane holograms? Also, any recommendations on the best minispotlight to use for display?