Intro and spatial filter power question

finelld · Post by **finelld** » Tue May 07, 2013 3:00 pm

Greetings,

My name is David. I am a retired broadcast engineer, ham radio operator, and technology experimenter and enthusiast. I made my first successful hologram about 20 years ago using a home-brew HeNe laser and Agfa 8E75 film. Today this type of film is becoming increasingly harder to come by and prohibitively expensive. For this reason and because of the potential for better results I am wanting to get into DCG holography.

I have read on these boards that most modern inexpensive DPSS units in the 473nm range are unusable. I have one that seems to be adequately coherent but is only 10mW. I have another that was advertised as TEM00 but appears to be very multimode. It is 1W. I also have a 150mW 532nm laser that may work as well. I would like to use a spatial filter with the more powerful units to do some experimenting with but I am concerned on damaging my spatial filter with the high powers. I am using a repurposed Spectra physics 332 spatial filter that I cannot find any specifications on as far as power handling capabilities go. Does anyone have any information about power limitations of spatial filters?

I have also read on these boards a fair amount of discussion about frequency stabilizing or filtering broad bandwidth lasers. I was wondering if using a sub angstrom filtration system similar to those used in Ha or O-III solar telescopes might filter the unwanted wavelengths sufficiently to allow these less expensive powerful lasers to be useful for holography. Any thoughts?

Right now I just want to get a successful DCG image. I will concentrate on quality later.

Best Regards,

David Finell

Joe Farina · Post by **Joe Farina** » Tue May 07, 2013 5:09 pm

If you could provide some more details about the lasers, some of the people on this forum might be able to give feedback regarding their potential usefulness for holography. If the 473nm laser does have enough coherence over time (i.e., over 10 to 20 minutes), then 10mW would be quite adequate for small DCG holograms in the Denisyuk format (but I would think the laser is unlikely to have that kind of coherence). If the 1W laser is multimode, then I wouldn't bother trying to use it. The 150mW green laser may or may not work, depending on what kind of laser it is (honestly, I think relatively few 532nm laser types are suitable for holography). I assume that ordinary steel pinholes are ok for common continuous-wave (not pulsed) holography power levels (I would assume that 150mW is probably ok, but personally I haven't tried putting that much power through). I don't know about a 1W blue laser, someone with more experience with high-power lasers needs to chime in here.

A narrowband filter won't be of any use.

A suitable 532nm laser of at least 50 (preferably 100mW) will probably be the best bet for your first foray into DCG holography, unless you're lucky enough to find a suitable blue laser (these are not common, and certainly not inexpensive). There are more complicated procedures using dye-sensitized DCG for use with HeNe at 633nm, but the chemicals can be extremely difficult to obtain (primarily TMG). Without TMG, the speed can become very slow (it's slow even with TMG, i.e., 15 to 20 minute exposures with a 20mW HeNe for a 4 X 5 Denisyuk hologram). A good source for holography lasers is the "for sale" section of this forum.

Dinesh · Post by **Dinesh** » Wed May 08, 2013 7:31 am

You should have no problem with the pinhole so long as you put the entire first Airy radius through. We use 500mW at 488 and routinely keep the laser on all day.

Johnfp · Post by **Johnfp** » Thu May 09, 2013 4:51 am

High power apertures, how to calculate if you need one and where to get one.
http://wiki.lenoxlaser.com/index.php?ti ... _Apertures

I do have to agree with Dinesh, I have made a DCG hologram with a Spectra Physics laser with broadband mirrors and no prism in the laser and as such was getting around 900mW and had no problem with a standard Stainless Steel pinhole. (yes, you can make a hologram with all lines from an Argon Ion laser at the same time.)

Most DCG's are a single beam reflection hologram. So using 150 mW of 532 will work excellently with exposures of about 30 - 180 seconds. No problem for a SBR hologram if using a setup similar to this.
http://www.holograms3d.com/Illustration ... Single.jpg

If your object is such that it does not let you lay the plat right on it, then you can lay the object on a black, hard, rigid surface (a painted black paving stone is fine) and set three bolts (also painted black) on their heads so that the plate can rest on the bolt ends and holds the plate just over your object. This object to plate rigidity is all that is needed for a SBR and the long exposures would not be a problem. I have even rest the plate on part of the object (like the head in the link above) and then just two bolts down near the feet to give the tripod stabiliy.

Good luck in DCG, very challenging, fun and rewarding.

John

holowizard · Post by **holowizard** » Mon Jul 01, 2013 6:22 am

The trick to doing this safely (both for your eyes and the pinhole) is to do the initial alignment at low power, and gradually ramp it up. DPSS and ion lasers are current-dependent systems, and so can be infinitely varied from threshold to maximum output. I have put 5W of broadband Argon output through a 15 micron pinhole with a 60X objective (using a Data Optics SF). The optical mode can actually change size or position as gain increases (even if it stays TEM00), so some adjustment is likely necessary as you increase power. Multi-watt beams of any wavelength will punch a new hole in even a stainless steel pinhole disc in a second or two (power densities can reach 100s of KW/cm2, and the metal is only 12 to 25 microns thick), so mechanical stability becomes critical under those conditions.

Ed Wesly · Post by **Ed Wesly** » Mon Jul 01, 2013 9:56 am

Because of the concerns mentioned above, it is sometimes a good idea to place your shutter after the spatial filter, so that once the pinhole is tuned it can stay that way thanks to thermal equilibrium, along with the beamsplitter, etc. This might mean multiple shutters. Hopefully there is no mechanical creep to cause the devices to go out of alignment.

I keep a closed circuit TV camera trained at critical parts of the set up to monitor drift, especially when working with high energy lasers.

142laser · Post by **142laser** » Mon Jul 01, 2013 1:55 pm

Hi david,
Welcome to the forum. Information on green lasers is available on Sam's Lser FAQ (on the iInternet). We have green lasers for sale from 10 mW to 200mW+ priced from $600 to $3,000. Take a look at the for sale page...Coherent, Lasos, JDS, Adlas, Spectra Physics Excelsiors (not listed there, on e bay now under my handle of 142laser). If we can help let me know. best wishes for bright holograms, Phil