"Sliced Bread" holograms

On: Fri, Dec 07, 01 08:54:44 PM

John Klayer wrote:

What is the problem when making a simple one beam reflection holograms with this diode laser? It looks like the image was sliced up like a loaf of bread parallel to the plane of the plate. I've made many other holograms like this before with HeNe and cheap laser pointers and they all looked good. I set up a Michelson interferometer with this laser and it was rock steady. Wouldn't I see a mode hop in the interferometer pattern over time? Thank you for any help.


Tom B. - Fri, Dec 07, 01 10:08:54 PM

My guess is that the laser is operating in multimode - instead of producing a single wavelength, that it is producing multiple closely spaced lines in its spectrum. The practical effect of this is that the coherence varies periodically with distance as the wavelengths get in and out of step. In your interferometer setup, you should see the fringes going away and coming back repeatedly as you vary the distance. I saw the same thing with a 30 mW laser module from Midwest Laser Products. Beautiful fringes at zero path difference, but sliced bread holograms. Pity, because it was otherwise a very nice module. If you can adjust the drive current for lower power, it might start running in single mode - I haven't tried this yet. Anyway, that's MY theory.

John Klayer - Fri, Dec 07, 01 11:32:42 PM

Thanks Tom B. for you reply, I did try the same laser diode with a different driver circuit and got the same "sliced bread" hologram. So - the laser diode may be the culprit. The LD is a Mitsubishi ML1016R, As far as I know other people have had good results with it - (Frank's D&S design). If it is the LD that is causing the problem, maybe I just got a bad diode, and should try another one - luck of the draw. Maybe better I should try the new Panasonic LNCQ05PS, 660 nm/ 50 mW diode, as I've read that the longer the wavlength, the more less likely to mode hop. Thanks again for any response.

Tom B. - Sat, Dec 08, 01 04:46:21 AM

My results with a 1016R were a bit disappointing - I found that fringe contrast and coherence length were not very good above 15 mW output. It was much better below 15 mW, but still not quite as good as my keychain laser pointer. I would be interested in your results with the LNCQ05PS. It's too bad that laser diode manufacturers don't bother to document things like linewidth and mode purity versus power. As for the wavelength/mode hop relationship, it sounds like the sort of thing that might be true, but I have only seen one second or third-hand report with no data presented to support it.

Colin Kaminski - Sat, Dec 08, 01 06:03:44 PM

This is a copy of an e-mail sent to me about a first-hand account. I try to post it once in awile because it is some of the oly diode information I have been able to find from an athoritive source. Note: I am not a Dr. and I never figured out why I was addressed that way. I am vey happy with the laser he recomended but I could not afford the peltier upgrade. Colin Hello Dr. Kominski, Our recommendations for a holographic grade diode laser would take the following form: 1. The MDL 660-35 is the best available diode source for this application. We find that the higher power diodes tend to run single mode and this diode laser has about two meters coherence length. We have found that a short wavelength diode laser such as a 635nm-15 mW tends to be broader in line width as the current density is higher and will allow other spectral lines to compete. The price on this unit is $290 and we have several choice units in stock. 2. Any diode laser will mode hop and we have found that the diode must be on for about 10 minutes to stabilize. Use an external shutter for timed exposure, do not just switch the diode on and off as an electronic shutter. We would recommend that the laser be thermally stabilized to prevent mode hops. The laser would be set up in the BTC-2000, a compact peltier based temperature controller here at the factory and the temperature adjusted until the peak spectral line of the diode is in-between mode hops. This is a technique used in our own DMI laser interferometer product and with most telecom diode lasers. The price on this unit is $1590 and units are in stock 3. The last consideration is that the diode laser beam is elliptical and is one is seeking an illumination source to expose a holographic emulsion, you must overfill the area to be exposed or attempt to shape the beam. You can use cylindrical optics and prisms for beam shaping or we can set up a circularizer at the time of laser manufacture. The laser power will be reduced by about 40% with this option. This option is known as LS-90 for $395 and units are in stock. Please contact Kathleen Fox or myself if you have any further questions. Best Regards, Will Houde-Walter

Tom B. - Sun, Dec 09, 01 02:58:16 AM

This would have been from LaserMax: http://www.oemlasers.com/index.html So how was the MDL-660? Some of their fiber-coupled visible lasers look quite interesting, too - wonder if they are affordable. regards, tom

Colin - Sun, Dec 09, 01 03:19:29 AM

I am very happy with this laser. It is the one I use most. I added some cylindrical optics from Edmund and now I have a round beam with lots of power. It mode hops for a while but after warm up I only see about one mode hop every half hour. I am working on peltier cooling for my D&S and will try it on the Laser Max as well. The fringes are very stable.

Josť Lunazzi - Thu, Dec 13, 01 09:08:32 PM

I am dissapointed with this laser. I tried four elements, only one had power close to 35 mW = 20 mW Others had only 8 mW or less, all holograms were "sliced". Maybe is the power supply, I do not know, but we suceeded in making good power suplies for the pen lasers. After some time, blue drops appeared on the surface of the glass window destroying the uniformity of the beam. Maybe due to overheat of some antireflecting coating. We employed the laser holders by Optima, although we needed to adapt the diameter with an aluminum ring because the web catalog was confusing and they delivered the wrong elements (and the wrong quantity) to us. The plastic collimating lenses seems to be very bad in quality of the beam. "slicing" is known as "contouring", a technique employed for measuring the object. The distance between fringes is proportional to the distance in wavelength between modes. But I can not say how useful this contouring would be for measurements. In specifications I read about visible diode lasers, it is indicated that the possibility of one single mode subsist increases with power output. I am delighted to share my experience with you here. If you go through my pages http://geocities.com/lunazzi (mainly that of teaching) you can see some results, but most of them are in portughese, you must choose these language. "ensino de holografia" = teaching holography".

Dooley - Thu, Dec 20, 01 01:13:03 PM

I am just curious if I am having the same problems that you are having. Do these slices look like someone did a realy horrable job squeging a window. The hologram behind looks very beautiful but it looks like someone didn't do a good job squeging the glass. Sort of like black lines that drip down. If someone could tell me if this is the same sliced bread problem or something else I would realy appreciate it. I used the mitsubishi 30 mW and the panasonic 50 mW. Both holograms looked good except for the lines. Thanks

Dooley - Fri, Dec 21, 01 12:11:31 PM

I think I solved my own problem. A simple mistake actualy. I think it was just light getting in the side of the glass plate and bouncing down the picture plain creating the evenly spaced lines.

Jonathan - Fri, Dec 21, 01 01:20:20 PM

Dooley, were those reflection or transmission holograms that you're referring to above? Are the lines straight or curved?

Dooley - Fri, Dec 21, 01 06:06:32 PM

They were one beam reflection holograms and the lines were evenly spaced and realy straight nearest the laser and had a very slight curve on the other side. It looked like someone did a bad squegee job on a piece of glass. I am gonna try a new one with the edge blacked out and see if I get better results. I'll post if I do.

Colin - Fri, Dec 21, 01 08:43:40 PM

When I have an edge exposed I use electrical tape to cover the edge.

Dooley - Sat, Dec 22, 01 02:54:33 PM

I actualy used a powerful black marker. It worked wonders and I got a beautiful hologram. No problems at all with the mitsubishi diode paired with pfg-03m. Hopefully I keep having good luck, as well as everyone else using this diode.

Colin - Sat, Dec 22, 01 08:49:04 PM

What brand of black marker? I am looking for an easy way to blacken the edges of some lenses.

Dooley - Sun, Dec 23, 01 10:08:37 PM

The marker is Pilot Super Color Marker SC-6600 It nearly blocks all of the light but does let some through because of streaks in the coverage. Two coats is usualy good enough. The problem of blocking light on the holograms is that when developing it starts to flake off which isn't a problem untill you are using the developer for more than one hologram. Then the flakes could become a problem in that they could get stuck in the emulsion. Other than that the marker is great and it will write on just about anything including glass.

Colin - Fri, Jan 04, 02 01:39:54 AM

Thank you!

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