Should the laser light be polarized for holography? Is the light of a laser pointer polarized? I have tested one and it was slightly polarised but not completely. Can the use of a polarization filter improve the quality of hologram??
Vidar Hegdal - Mon, May 10, 99 02:43:16 PM
It's best to use a polarized laser or pointer for holography in order to avoid internal reflections in the plate or glass. You can check if the laser is polarized by a pair of ordinary, polarized sunglasses. If the beam vary a lot in intensity when you rotate the sunglasses, the laser is polarized. The polarization should be adjusted (by rotating the laser) so that the beam intensity is at a minimum when the sunglasses are horizontal when you use a 'sideways' reference beam. Of course, the glasses should be removed after you have adjusted the polarization of your laser.
Good luck.
195.204.220.192
Timo Junker - Sat, May 15, 99 04:37:29 AM
i noticed some black rings or lines over the image of my hologramm. i think it has something to do with the polarization, but i'm not sure. i noticed the rings only if i use a sandwich (glas-film-glas, or filmplate-glas). the rings are not so strong or sometimes there aren't no rings if i use my hene-laser. i test it out if there are some rings when i use a polarization-filter with my pointer. 132.187.248.32
Ronny Andreassen - Sun, May 16, 99 03:00:24 PM
Black rings are usually caused by movement of the film (or object), especially when using the sandwich technics. I have allso got black rings when using my laserpointer and filmplates. When it appears I think it's because of the laser itself, and correct me if I'm talking rubbish, but I can bet appr.1$ that it's because of something called mode-hopping (caused by heat). My conclusion is that black rings or lines have nothing to do with polarization. Correct me if I'm wrong :-) 130.67.15.242
Binu Thomas - Mon, May 17, 99 03:33:08 PM
Polarization is not a must for taking holograms. The quality of the hologram is independent of laser light polarization. The important thing to get a good hologram is coherence length and the angle of reference and object beams. Since the outlet of most laser is a brewster angle mirror usually laser light are polarized. But laser polarization is a must for taking hologram of a ........ Wait for nexr reply 203.197.152.24
Timo Junker - Thu, May 20, 99 07:28:33 AM
hi Ronny, my black lines are not from polarization because the rings are if i use bb-glasplates and pfgo1. but the rings are only to see if my exposure time is long. my lasermodules are running all the time. i can do exposuretimes for 60sec. and no problem with batteries, but with power supply. If my exposuretimes are 90sec. i have problems with batteries and powersupply. has anyone the same or different experiences?
TimoJunker@holografie.com 132.187.3.122
Ronny Andreassen - Thu, May 20, 99 12:42:03 PM
Timo, I hope and I think that Frank DeFreitas have the answer on this one. The lines you are talking about is a usual phenomenon when using BB-plates. It can be some internal reflections in the plates itself, but since you are mentioned the battery and power-supply mystery it's caused by something else. If you listen to one of Frank's last talkshows he discussed some advantages when using batteries as capassitores ???, maybe you can couple some batteries in parallel to your power-supply to make it more ripple free??? Now I'm on realy realy thin Ice..have a nice day. 130.67.15.242
Steve Michael - Wed, Jun 16, 99 07:46:05 PM
Hi Pascal: it is always best to use a polarized laser when making holograms, especially when making split beam holograms. This insures that the electrical vectors of both beams are pointing in the same directions and you get maximium energy from your laser beam. If you're using a randomly polarized laser with split beam setups, then the electrical vectors from each beam are causing high and low and in-between energy levels and your hologram will have much less contrast and brightness. This is probably also the case when doing single beam setups because you still have two beams of light exposing the hologram and if they're vectors are not matched, then energy is lost and cancelled. 209.122.205.93
Steve Michael - Wed, Jun 16, 99 08:03:20 PM
In regards to black out zones in film (not black fringes), this is caused by very small air pocket areas between the glass plates and the film. These are destructive interference zones and the only way to insure no air is to lay the sandwiched film on a towel and press out the air with paper towels press across one surface or a soft cloth. I've ran into this problem with my 12x16 film exposures.
It's quite depressing to find a black zone when using a $20 piece of film. As for the black fringes, I don't believe this is caused by the power supply used. Frank and I have discussed this throughly. First of all, never use a polarizer in any of your beams. Some polarizers have 200 lines/inch, some 50, etc. The less amount of lines, then you get blotches (dark areas) when projected on a white screen. They're less prominient at 200 lines/inch. A polarizer is only used to check the direction of polarization of your beam, NEVER used in a beam during an exposure. If you're not using a polarizing filter in your beam(s) and you're still getting black fringe patterns, then your polarization direction is not correct relative to your reference beam's incidence on the plate or film. If your using a side reference beam to your plate holder, your polarization should be s type or vertical. If you're using an over or under beam, then your polarization should be p type, or horizontal. I've run into this problem too and if you're getting fringes, then rotate your laser 90 degrees and try again. This of course is expensive trail and error, so a polarizer filter is important. If you get polarizing sheets from Edmund, for example, you can't tell which way the sheets polarized. I have a 35mW laser that I know is polarized vertically, so I have no problem. But with a pointer, you don't know. The best polarizer filter to get is a photographic polarizer filter that has an arrow or dot on its edge that shows when you are polarizing sunlight. If the dot is in the top position and your pointer light is cut off, then the pointer is rotated to give p or horizontal polarization. If you then need vertical polarization, rotate the pointer in its holder by 90 degrees. 209.122.205.93
Steve Michael - Wed, Jun 16, 99 08:05:35 PM
Also, If you're sandwiching film in glass plates, make sure your reference angle is Brewster's angle, 56 degrees. This will guarantee no swirly patterns on your film caused by internal reflections between the glass plates. Works like a charm every time! 209.122.205.93
Kris Meerlo - Sun, Jul 18, 99 02:04:12 PM
It's not necessary to sandwiching film between glass plates.
I made a filmholder at the following way.
I made two clamps and strecht the film between two springs.
The results are less polarization problems.
192.87.194.46
nickhardy@ukonline.co.uk - Tue, Jan 25, 00 08:13:15 PM
Why not index match to a single glass? Use turps and hand held roller to squeeze the turps out. Wipe off excess with a paper towel. Works well on thicker films, thin stuff is a bit tricky (especially those 50x60cm holos!)
Let the film settle for at least 15 minutes for exposures up to 10 sec.
If the film curls up off the glass increase the room humidity by boiling a kettle. Agfa made products to work at 55% relative humidity.
50 to 70% humidity is normally OK and doesn't swell the emulsion causing colour change.
Nick
Nick 212.134.26.100
Sam - Sun, Mar 19, 00 12:28:11 PM
Will holographs capture the polarization or phase of the laser? For instance if you make an exposure of say a tank(or any other article).You make the first exposure with a polarized beam(assume the first reference beam is at 0 degrees). Then you turn the tank to a different position and use a reference beam polarized at 90 deg.ON THE SAME FILM .When developed will you get a different picture depending on what phase you light up the holographic plate with? Thanks 166.72.234.135
Steve Michael - Fri, Mar 31, 00 06:04:04 PM
Hi Sam: I'm first assuming this is a tranmission hologram and will be reconstructed with laser light. If so, you'd have to change the polarization when reconstructing to see if the different images showed up separately. This would make an excellent experiment and if it worked, might have some far reaching effects such as volume hologram optical storage. 207.172.11.147
Sam - Wed, Apr 05, 00 05:52:20 AM
Sorry it took so long to get back. Thanks steve, my thoughts were to use holograph optical elements(HOE's) that would be phase stearable. Change the the phase of the beam and get a new set of optics. I wonder what the resolution would be in terms of (intensity of the HOE ,per change in phase).I'm assuming that as you add HOE's the brightness would decline for a certain amount for each one added. At some point (where?) I believe each additional added HOE would strongly blur all the different HOE's on the plate.Thanks 166.72.234.107
Sam - Wed, Apr 05, 00 06:06:02 AM
One other thing.Whatever the HOE's per phase (bad pun)would be it would be a really large number. 166.72.234.107
Branden Miller - Thu, Jul 13, 00 01:29:51 AM
How do you test if sungalsses are actually polarized? 206.163.48.124
Sam - Fri, Sep 01, 00 10:15:54 AM
To test if sunglasses are polarized use two pair. Put one in front of the other,look through them,and rotate the glasses in opposite directions as you look through them. The intensity of light should vary according to the polarization of the lenses. When one pair of glasses is 90 degrees rotated
in respect to the other you should have the least light intensity. 32.102.245.93