Two anamorphic prism pairs for 445nm diode

Joe Farina · Post by **Joe Farina** » Tue Aug 24, 2010 12:56 pm

This morning there was a post on the Photon Lexicon thread about using two prism pairs to shape the output from the 445nm diode. The photos look impressive, he's saying the spot size is 8mm at 6.5 meters, and perfectly round (the photo of the spot does look perfectly round):

http://www.photonlexicon.com/forums/sho ... isms/page2

JohnFP · Post by **JohnFP** » Tue Aug 24, 2010 1:11 pm

That's good info. But I need to be a member to see the photo's. Could you, not copy, but post some type of illustration of the configuration of the prisms?

DJ Mathson · Post by **DJ Mathson** » Tue Aug 24, 2010 1:19 pm

John,

Why don´t you just become a member of the PL forum instead? It is very easy.

JohnFP · Post by **JohnFP** » Tue Aug 24, 2010 1:23 pm

I guess I could. Thanks. Another logon and password. :think: :wall:

dave battin · Post by **dave battin** » Wed Aug 25, 2010 9:46 am

The beam looks nice and round, but i'm not sure about using two prism sets (heavy light loss)? This would indicate a higher power/index would be needed to do the correcting in one set of prisims only. His setup also has an asphere lens in the housing........

Joe Farina · Post by **Joe Farina** » Wed Aug 25, 2010 10:17 am

dave battin wrote:The beam looks nice and round, but i'm not sure about using two prism sets (heavy light loss)? This would indicate a higher power/index would be needed to do the correcting in one set of prisims only. His setup also has an asphere lens in the housing........

Thanks Dave, you may be right about the losses, and I didn't notice the asphere. Good coatings on the prisms would get expensive, and they might be necessary if 4 are used.

Actually the "raw" profile of the 445nm diode might be good for many uses, since it would encourage using knife-edge mirrors for beamsplitting. For really excellent-quality reflection holograms, at least 3 beams are needed; the reference, the main object light, and a fill light on the opposite side to lessen the harshness of the shadows. In some cases it would be better to use 4 beams, and have one beam come directly from behind the scene (through ground glass or another diffusion screen) so that the background doesn't look "black."

So if the output of the diode is divided into 3 beams, the center portion could be used for the reference, and two knife-edge mirrors could be used on the left and right sides of the beam. The vast majority of light would need to go to the object beams, which don't need to be round. The center portion of the diode output (for the reference beam) might be reasonably "square," I suppose. I'm still getting my heat sink together, so I haven't been able to do any testing yet.

dave battin · Post by **dave battin** » Wed Aug 25, 2010 10:52 am

When you get the diode running you will see it's raw beam is like a flashlight/stripe combination, very raw and expanding rapidly...............

do you have a focusing optics Joe?

Joe Farina · Post by **Joe Farina** » Wed Aug 25, 2010 11:02 am

I don't have any specific focusing optics, but I have a lot of lenses that could be tried, and I'm also planning on experimenting with the two-cylindrical lens device that I showed in the gallery section.

dave battin · Post by **dave battin** » Wed Aug 25, 2010 11:13 am

The trick with using this laser is the focusing ability, a lens need to be placed very close to the output, otherwise the beam's exit diameter will be very large,
there is a possibility of using a totally raw beam for holography, it will need to be very well thought thru :think:

PS i just checked the thread and they seem to agree that two prism sets wont work either ..................

wler · Post by **wler** » Wed Aug 25, 2010 12:17 pm

Since we don't use the diodes for projectors, beam divergence is of no importance and what the guys at PL write is not much of a significance for us.

What would matter for some of us is a more circular beam profile, in order to get well through a spatial filter, and this can easily be accomplished by a single pair of prisms. Appropriately coated ones have little losses (I measured 3%) and are available for about $30 per pair (incl shipping and taxes, without rather like $15).

The standard Aixiz collimator for blue works fine and is cheap; with some high quality aspheric lens one can get a narrower beam with like 20% more power, at the expense of higher divergence and cost.

So there is nothing to worry about, except for the transvere "multimode" structure of those diodes.