by MilanKarakas » Wed Oct 03, 2012 6:55 am
msxc wrote:Beauty of DIY- every problem can be solved in infinite number of ways:)
Yes, and it take infinite time too.
Today tried to find some DIY polarizer (or anything I already have here), and found one diffraction grating in perfect condition. After some time, it fell to floor - twice, and two corners cracked. And that is not all... surface is now contaminated. Not fun. Someone gifted me that many years ago, and I saved it until now, and screwed up this part in few minutes. I am so unhappy.
Since it can't make 'exclusion' of unwanted part of the bad polarization, decided to see something else. One thing become strange: instead one spot - got two spots. My first thought is that this grating is bad one, but it is not. My laser has two frequencies, closely spaced (later discovered third one, pretty weak, but it is there). All that additional frequencies come to play when module temperature reaches 27C or more. Later tried freeze ceramic tile, and make small fridge around laser. Temperature was 15C, and no stray frequencies up to 26C or more.
Only bad thing is that at low temperature KTP crystal has low efficiency. Moved module from heatsink little bit, and got frequency stability and good doubling efficiency.
Then tried BGO crystal. I have few intended for scintillator for detecting gamma rays. Eight is enough to cover one PMT and I have 10, so two are spare crystals. Both surfaces are pretty good polished, and I need only one.
Found one very useful page with online calculator for various materials:
http://refractiveindex.info/?group=CRYS ... =Bi12GeO20
(not sure mine is this type or lighter one)
If I have heavier one, then refractive index is better than that of diamond (BGO: 2.61657 @ 532 nm). At Brewster angle, reflecting 'good' polarization up to 55.5%, while the rest is lost inside crystal (too long crystal, only two faces polished). Tried to put glass plate on diverged beam after this crystal serving as a polarizer, and unwanted reflected fringes are just barely observable, while illuminating power is estimated to be about 50% of ~40 mW from my DPSS module (I wish to have real polarizing beamsplitter cube, but.. eh...). Now, it look like real stuff, except end power may be very low (after addition of spatial filter/pinhole, stirring mirrors,...) maybe 15 mW or so will remain.
I wish I have money and buy decent 532 nm laser, ranging from 50 - 100 mW. Seems that making DIY laser diode laser is easier than messing with DPSS module.
But, at least I learned something about Nd:YVO4 and KTP crystals. It will be good to have separate mirrors, crystals and made setup with good polarizer intracavity - that way nothing will be lost, clean beam will be amplified and 'exported' out through OC mirror/IR filter.
My last finding about laserpointers without glued IR filters make me wonder whether it is possible to place some 1064 nm mirror in front of the laser and by placing polarizing element there, maybe will get some feedback and made it more stable + better polarization ratio.... Don't know (maybe will sacrifice one pointer).
It would be nice to see more of DIY holographers made solutions in this forum
I hope so. At least new people.
msxc
Best--
m--
[quote="msxc"]Beauty of DIY- every problem can be solved in infinite number of ways:) :D [/quote]
Yes, and it take infinite time too. :(
Today tried to find some DIY polarizer (or anything I already have here), and found one diffraction grating in perfect condition. After some time, it fell to floor - twice, and two corners cracked. And that is not all... surface is now contaminated. Not fun. Someone gifted me that many years ago, and I saved it until now, and screwed up this part in few minutes. I am so unhappy.
Since it can't make 'exclusion' of unwanted part of the bad polarization, decided to see something else. One thing become strange: instead one spot - got two spots. My first thought is that this grating is bad one, but it is not. My laser has two frequencies, closely spaced (later discovered third one, pretty weak, but it is there). All that additional frequencies come to play when module temperature reaches 27C or more. Later tried freeze ceramic tile, and make small fridge around laser. Temperature was 15C, and no stray frequencies up to 26C or more.
Only bad thing is that at low temperature KTP crystal has low efficiency. Moved module from heatsink little bit, and got frequency stability and good doubling efficiency.
Then tried BGO crystal. I have few intended for scintillator for detecting gamma rays. Eight is enough to cover one PMT and I have 10, so two are spare crystals. Both surfaces are pretty good polished, and I need only one.
Found one very useful page with online calculator for various materials:
http://refractiveindex.info/?group=CRYSTALS&material=Bi12GeO20
(not sure mine is this type or lighter one)
If I have heavier one, then refractive index is better than that of diamond (BGO: 2.61657 @ 532 nm). At Brewster angle, reflecting 'good' polarization up to 55.5%, while the rest is lost inside crystal (too long crystal, only two faces polished). Tried to put glass plate on diverged beam after this crystal serving as a polarizer, and unwanted reflected fringes are just barely observable, while illuminating power is estimated to be about 50% of ~40 mW from my DPSS module (I wish to have real polarizing beamsplitter cube, but.. eh...). Now, it look like real stuff, except end power may be very low (after addition of spatial filter/pinhole, stirring mirrors,...) maybe 15 mW or so will remain.
I wish I have money and buy decent 532 nm laser, ranging from 50 - 100 mW. Seems that making DIY laser diode laser is easier than messing with DPSS module.
But, at least I learned something about Nd:YVO4 and KTP crystals. It will be good to have separate mirrors, crystals and made setup with good polarizer intracavity - that way nothing will be lost, clean beam will be amplified and 'exported' out through OC mirror/IR filter.
My last finding about laserpointers without glued IR filters make me wonder whether it is possible to place some 1064 nm mirror in front of the laser and by placing polarizing element there, maybe will get some feedback and made it more stable + better polarization ratio.... Don't know (maybe will sacrifice one pointer). :D
[quote]It would be nice to see more of DIY holographers made solutions in this forum[/quote]
I hope so. At least new people.
[quote]msxc[/quote]
Best--
m--