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Thread: Measuring a Laser for SLM - Suggestions Please

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    Default Measuring a Laser for SLM - Suggestions Please

    I have this desire to be able to measure the longitudinal modes of lasers. Perhaps this comes from my long term holography hobby . As desires go, I realise that this isn't going to set the world alight, but i'm interested in learning what different methods are available for carrying out this process.

    Ideally, i'd like to point a laser at an instrument and be able to see (perhaps on a screen) whether or not it was operating in single longitudinal mode.

    I've heard that a scanning fabry perot interferometer is what is really required, but these don't appear on Ebay too often, even if they did I wouldn't have a clue as to how to spot a good one.. Are there any other methods available that are perhaps more within the hobbyist budget?

    Can anyone please explain exactly how the measurement process works so I can better understand?

    Does anyone have anything for sale that would fulfil my desires?

    Cheers

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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    For diodes the glass plate trick works well enough, for lasers with longer coherence length you need something with higher resolution, like a scanning interferometer or a long-arm Michelson interferometer.

    Tell what kind of laser you have in mind!

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    Quote Originally Posted by RedlumX View Post
    Tell what kind of laser you have in mind!
    Well, I guess that's part of the problem as I would like to try many different sorts of lasers. It would also be nice to prove my own lasers were truly SLM.

    I have a 200mW Coherent 532 Ring laser, two Coherent C315m's one at 80mW and one at 15mW, two 35mW 632.8nm HeNe's, a 10mW 632.8nm HeNe, a 20mW 488nm Coherent Sapphire and a stupid amount of JDSU 532nm MicroGreen lasers of varying powers. That's just the ones that I believe are SLM and are capable of making holograms. We then start adding the 445nm C*sio diodes the 200mW DPSS 473nm and various red diode lasers, Oh, and the HeCd and the argon and the 2W RGB laser projector...

    Hehe... I can't believe I just typed that... do I *really* have so many lasers? I must get around to selling some of them, perhaps one day

    Cheers

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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    Quote Originally Posted by Jem View Post
    ...lots of lasers...

    Hi,
    My name's Jem...
    and I'm a Laser-hollic


    I know it's tough Jem; but we can help. The next laser you buy; send over this way and I'll look after it for you.
    - There is no such word as "can't" -
    - 60% of the time it works every time -

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    Quote Originally Posted by Jem View Post
    Well, I guess that's part of the problem as I would like to try many different sorts of lasers. It would also be nice to prove my own lasers were truly SLM.

    I have a 200mW Coherent 532 Ring laser, two Coherent C315m's one at 80mW and one at 15mW, two 35mW 632.8nm HeNe's, a 10mW 632.8nm HeNe, a 20mW 488nm Coherent Sapphire and a stupid amount of JDSU 532nm MicroGreen lasers of varying powers. That's just the ones that I believe are SLM and are capable of making holograms. We then start adding the 445nm C*sio diodes the 200mW DPSS 473nm and various red diode lasers, Oh, and the HeCd and the argon and the 2W RGB laser projector...

    Hehe... I can't believe I just typed that... do I *really* have so many lasers? I must get around to selling some of them, perhaps one day

    Cheers

    Jem
    Well the Compass' don't need testing ;-) Other DPSS lasers won't run SLM unless specifically designed for it, almost not worth to even test. The high power Hene's might have short coherence length, here a scanning FPI would be needed for checking. The argon will work only if equipped with an etalon, and to adjust it you'd need a scanning or Michelson interferometer as well. The HeCd will have very short coherence length, a few mm perhaps, so not worth. The blue Nichia is better in this respect, except for beam quality. But for this and any other diode, you need to very precisely monitor the spectrum and its stability; the glass plate trick should well for these and red diodes since their mode spacing is so large.

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    Thanks for the reply.

    Interestingly the Kimmon HeCd supposedly has a coherence length of around 10cm, as do the HeNe's. When I get around to it I intend setting up a Michelson Interferometer again to test the HeCd. I'd like to test the JDSU's as i'm not certain of their SLM operation, although the one that I have tried does make nice holograms so I guess that's SLM.

    @Dan... Yep, it's taken a few years, but at least i can talk about it openly now, I know i'm amongst friends here

    Cheers

    Jem
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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    Sam's FAQ, Fabry=Perot page:

    http://repairfaq.ece.drexel.edu/sam/...a.htm#liasgsf3


    one dollar, two dollar, and five dollar versions.

    One of these days, I might have to do the "sound card interface" Fabry Perot.

    Steve

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    Thanks Steve. Can't say I understand it all, but i'll try and digest it a bit more later.

    So, I guess my dream of just buying a secondhand piece of equipment that will do these measurements is a no-goer, what a shame...

    Let me know when you get the "sound card interface" Fabry Perot off the ground
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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    IF you want to try Sam's 3$ red FP interferometer, I have the same mirrors from Ebay, about 20 of them, and would be glad to pop a pair into the mail for the cost of postage and shipping materials. &^%$ shipping materials are not cheap!

    I'd need some one to cut the code for the sound card.

    Steve

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    Thanks for the offer Steve, it's much appreciated. However, I think this project is beyond my skill level, besides it looks like it's only any use for HeNe's - correct?

    I'm sure something will eventually become available 'off the shelf'
    Quote: "There is a theory which states that if ever, for any reason, anyone discovers what exactly the Universe is for and why it is here it will instantly disappear and be replaced by something even more bizarre and inexplicable. There is another that states that this has already happened.... Douglas Adams 1952 - 2001

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