Holographic gratings

Danny Bee · Post by **Danny Bee** » Tue Jul 15, 2008 11:34 pm

Holographic gratings made with my 405nm diode on dcg

Colin Kaminski · Post by **Colin Kaminski** » Tue Jul 15, 2008 11:58 pm

Danny, do a single beam reflection and I can tell you exactly what is happening but it looks to me like a mode hop.

Danny Bee · Post by **Danny Bee** » Wed Jul 16, 2008 12:03 am

ok i will make coat more plates and run test, thanks Colins, if i run current to the diode on the low side wount i get less chance of mode hopping?

Colin Kaminski · Post by **Colin Kaminski** » Wed Jul 16, 2008 8:03 am

With some of the medium powered red diodes that was true.

Ed Wesly · Post by **Ed Wesly** » Wed Jul 16, 2008 12:36 pm

What is the geometry of the set up? Can't rule out extremely short coherence yet, nor movement of the plate.

Danny Bee · Post by **Danny Bee** » Wed Jul 16, 2008 3:01 pm

The photos show setup one, on setup 2 they are the same except the gaps or bands are closer together, and the color bands are larger

Ed Wesly · Post by **Ed Wesly** » Fri Jul 18, 2008 3:59 pm

The banding might be from lack of coherence. Notice the reflected beam path is definitely longer than the staight through. Sometimes short coherence lengths repeat themselves, so that there is interference, then none, then back again. And this would sort of make sense in your two configurations, with the path length differences being smaller in the lower figure than the bottom.

Try putting the laser on a Michelson Interferometer and see what you get, and/or trying a geometry where path lengths can be easily equalized.

Danny Bee · Post by **Danny Bee** » Fri Jul 18, 2008 5:35 pm

Ed Wesly wrote:The banding might be from lack of coherence. Notice the reflected beam path is definitely longer than the staight through. Sometimes short coherence lengths repeat themselves, so that there is interference, then none, then back again. And this would sort of make sense in your two configurations, with the path length differences being smaller in the lower figure than the bottom.

Try putting the laser on a Michelson Interferometer and see what you get, and/or trying a geometry where path lengths can be easily equalized.

yes i will do that, and get back to you Ed

thanks Ed good info, hope my spelling and grammar is getting better and easy to read and understand.

Danny Bee · Post by **Danny Bee** » Fri Jul 18, 2008 5:52 pm

Ed Wesly wrote:The banding might be from lack of coherence. Notice the reflected beam path is definitely longer than the staight through. Sometimes short coherence lengths repeat themselves, so that there is interference, then none, then back again. And this would sort of make sense in your two configurations, with the path length differences being smaller in the lower figure than the bottom.

Try putting the laser on a Michelson Interferometer and see what you get, and/or trying a geometry where path lengths can be easily equalized.

ED if it is a very short coherence length couldnt i use it for contact copies ?

Colin Kaminski · Post by **Colin Kaminski** » Fri Jul 18, 2008 9:20 pm

Even with most mode hops a laser can be used for contact copies. It really takes a pretty wide line to erase a contact copy.