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Thread: Laser media frequencies

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    Default Laser media frequencies

    Hello All,

    Is there a book that has an exhaustive list of all materials that have been used for laser experiments and gives the primary frequency generated from said material (crystals, gases, everything)

    IF so, is there any academic material on say why CO2 produces 10,000 nm and ND YAG produces 1,100 nm. Why are crystal lasers more powerful and could gas lasers be just as powerful with the proper cooling and gas circulation?

    My specific project was a CO2 laser until I realized that CO2 will not produce the proper frequency I need at 10,000 nm. I need ~ 1,100 nm but the only laser I could find that will produce primarily in that frequency is a ND YAG laser which is a crystal laser. Does a gas laser exist that produces this frequency, I would think out of all the gasses known to man there would have to be a gas that produces ~ 1,100 nm

    Also a geologist friend of mine just indicated that YAG is a synthetic crystal which means that someone deliberately created this stone for lasers ... how did they know they would need yttrium aluminum garnet and how did they know to dope it with Neodymium?

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    I typed a very elaborate response to your question assuming you had a legit use for alternative wavelengths. . I then read your post on the other forum and pulled my response based on your massive naivete and lack of Google-Fu.


    I'm not interested in helping you foolishly try a really bad approach to shooting down drones.

    Steve
    Last edited by mixedgas; 12-11-2018 at 16:48.
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    So did the forum not let you completely delete the post?

    Whew it sent me an email copy of your post before you deleted it. Thank you so much. I am going through abe books now.

    It would still be cool to know the thought process of some one sitting there one day saying ... hey im going to create synethic yittrium aluminum garnet and dope it with neodymium.

    Also why use diode lasers to pump it, why not use a CO2 laser to pump the ND YAG laser?

    Perhaps once I have read through the material I will slowly develop the intuition to develop my own gas or crystal.
    Last edited by akmetal; 12-11-2018 at 21:19.

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    Quote Originally Posted by akmetal View Post
    So did the forum not let you completely delete the post?

    Do you really think if there was a high power gas laser with efficiency better then Co2 and not requiring Deuterium Fluoride or superheated Chlorine,Oxygen, Bromine and dense Iodine vapor moving while burning through a perfectly optically clear laminar flow at upwards of Mach 2.5, that it would not be in production?

    If there were such a way to make a cheap beast like that my former employer would gladly license it.

    f I found it he'd pay me enought to comfortably retire on the spot.

    Steve
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    Quote Originally Posted by mixedgas View Post
    Do you really think if there was a high power gas laser with efficiency better then Co2 and not requiring Deuterium Fluoride or superheated Chlorine,Oxygen, Bromine and dense Iodine vapor moving while burning through a perfectly optically clear laminar flow at upwards of Mach 2.5, that it would not be in production?

    If there were such a way to make a cheap beast like that my former employer would gladly license it.

    f I found it he'd pay me enought to comfortably retire on the spot.

    Steve
    That is a very good point. Yea i read about the bromine lasers and they seemed nasty and I dont have any desire to circulate nasty poisen through a cooling system.

    Well it looks like I have some serious reading to do and if I do create said gas or even solid state/crystal I will try to post the performance youtube video here.



    They were never told it was impossible - so they did it.
    Last edited by akmetal; 12-11-2018 at 21:35.

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    Overconfidence taken to an extreme, coupled with a desire to shoot at something he doesn't like and thinking that a laser would hide his identity while executing his fantasy. I'm guessing he also wants to make a "light sabre". Why not? All it takes is someone with enough confidence.

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    Quote Originally Posted by akmetal View Post
    Is there a book that has an exhaustive list of all materials that have been used for laser experiments and gives the primary frequency generated from said material (crystals, gases, everything)
    There are likely several books on the subject. Google is your friend. Here's a good starting point. A member here has also produced an app that had a pretty comprehensive list of lasing lines, but I can't find a link to it anymore. (Laser Line software - anyone remember this?)

    is there any academic material on say why CO2 produces 10,000 nm and ND YAG produces 1,100 nm.
    Short answer: Quantum Mechanics.

    More in-depth answer: it's a result of the difference in energy between specific electron excitation states. Different molecules have different "allowed" energy states for their bound electrons. Find a substance that has a pair of meta-stable states corresponding to the wavelength you want and you're on the path. (Note: this is *hard*.)

    Why are crystal lasers more powerful and could gas lasers be just as powerful with the proper cooling and gas circulation?
    There is no hard and fast rule about which laser type is more powerful. *Some* crystal lasers are more powerful for a given application, while in other applications gas lasers are better. Some gas lasers are incredibly powerful. (Look into gas-dynamic lasers, deuterium-fluoride lasers, and chemical oxygen iodine lasers.) Likewise, there are massively powerful crystal lasers. (Shiva/Nova comes to mind.) For a given wavelength and operation mode (continuous vs pulsed) you can say that one technology is superior to the other. Change one of the variables, however, and you'll get a different "best" answer.

    I need ~ 1,100 nm but the only laser I could find that will produce primarily in that frequency is a ND YAG laser which is a crystal laser. Does a gas laser exist that produces this frequency, I would think out of all the gasses known to man there would have to be a gas that produces ~ 1,100 nm
    There may be several gases that can be made to lase at ~ 1100 nm, but other than the COIL technology mentioned above (hideously expensive, very complicated, and toxic to boot), I'm not aware of one off the top of my head.

    More importantly though, this is something that has been researched to death already, and for that specific wavelength range the current "best solution" is YAG, unless you have the resources of a nation-state and want to experiment with the aforementioned chemical oxygen iodine laser. I should point out that this is a bit of a fools errand, however, as the US Government spent over $5 billion developing the COIL (and the modified 747 to carry and power it) before eventually deciding that the technology was a dead end. They are now focusing on YAG and direct diode solutions for output in this wavelength range.

    YAG is a synthetic crystal which means that someone deliberately created this stone for lasers ... how did they know they would need yttrium aluminum garnet and how did they know to dope it with Neodymium?
    See above answer about electron energy levels. And if you really want to get deep into it, you're looking at a *bunch* of 400-level (and up) college physics classes to understand the quantum mechanical math behind it. (For the record, I gave up long ago.) Suffice to say that in the early years of lasers (1960's-1980's) the research involved a lot of trial and error. But now with a ton of math (and computers to help), they're getting better about predicting materials that will work for a desired wavelength. And even so, they still struggle. (Look at how long it took to get direct-injection green diodes, for example.)

    Quote Originally Posted by akmetal View Post
    It would still be cool to know the thought process of some one sitting there one day saying ... hey im going to create synethic yittrium aluminum garnet and dope it with neodymium.
    Also why use diode lasers to pump it, why not use a CO2 laser to pump the ND YAG laser?
    Again, back to Quantum Mechanics and those electron energy levels. To pump (excite) the electrons to high energy levels you need to use a wavelength that is very close to the energy needed for the jump. Long wavelength = small jumps, short wavelength = larger jumps.

    If you tried to pump YAG with the output of a CO2 laser you wouldn't be able to achieve a population inversion because you wouldn't be exciting the electrons to the metastable level from which they fall to emit 1064 nm light. At best you'd just heat up the YAG rod.

    Perhaps once I have read through the material I will slowly develop the intuition to develop my own gas or crystal.
    Perhaps.

    Quote Originally Posted by mixedgas View Post
    Do you really think if there was a high power gas laser with efficiency better then Co2 and not requiring Deuterium Fluoride or superheated Chlorine,Oxygen, Bromine and dense Iodine vapor moving while burning through a perfectly optically clear laminar flow at upwards of Mach 2.5, that it would not be in production?
    HAHA! I had totally forgotten about the flow dynamics of the COIL laser, to say nothing of the H-F / D-F lasers. Excellent point Steve! You know, the more I read about the work on the YAL-1, the more in awe I am at the entire effort. You really have to give them credit for getting the damned thing to lase in the first place, let alone keeping it running inside a plane flying all over the place. Alignment alone had to be a cast-iron bitch! (Airplanes tend to be rather flexible, after all...)

    If there were such a way to make a cheap beast like that my former employer would gladly license it.
    Assuming the military didn't grab it first! They'd kill for something like that...

    Quote Originally Posted by akmetal View Post
    That is a very good point. Yea i read about the bromine lasers and they seemed nasty and I dont have any desire to circulate nasty poisen through a cooling system.
    Copper Bromide lasers are child's play compared to the lasers Steve was talking about. Seriously, do some reading about the COIL-based YAL-1. If that doesn't give you pause, nothing will.

    As for your final comment about the Wright Brothers, remember that the only ones who told them human flight was "impossible" were the uneducated. There were ample examples in nature (birds) that showed it was entirely possible, plus the world already had lighter-than-air vehicles. Most scientists knew it was only a matter of time before someone solved the heaver-than-air problem. The true challenge was *controlled* flight, and that is honestly their biggest innovation. Apart from that it was just some engineering and finding a lightweight engine that made enough power.

    In this case, while the laws of physics don't explicitly prevent what you're looking for, a great number of people have spent a lot of time looking, and the consensus is that, for near IR wavelengths, gas lasers are inferior to YAG and direct diode technologies. But even with that caveat, it's still conceivable that they missed something. Still, the Wright Brothers had it easy by comparison.

    Adam

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    Quote Originally Posted by akmetal View Post
    They were never told it was impossible - so they did it.
    Because what they were doing was NOT impossible. It's important to know the difference between impossible vs not impossible.
    Last edited by absolom7691; 12-12-2018 at 08:49.

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    COIL was tough enough to solve that the AF Lab published a detailed, low cost, technical book on it in the 1980s, they were not worrying about it being too easy to solve. My local regional library had it in the 80s.

    You can spend hours upon hours reading Marvin J. Weber's book on Gas Laser Wavelengths. Get an old one because the new editions are edited by someone who took a lot of detail out. All it does is give you a huge list of tables and then the references to go look up. Calibrated laser power meters did not exist in commercial form or were not common in the heyday of the laser researcher, so most books rank the estimated gain per meter on a unitless 1 to 5 scale. It was up to the researcher to make up that scale before publishing.

    So yes, something might have slipped through the cracks, but without testing each system and optimizing six to ten variables each time, you'd have to get extremely lucky. If you start from the book, you are effectively playing "laser spin the bottle". Lasers that were easy to make and showed incredible promise on the first few runs are ultimately the ones that went into production, with a few devices that would be very useful in the lab slipping through the cracks. Anything that was really useful got noticed and patented by DOD or Commercial Researchers. You can spend all day at DTIC dot mil looking at research reports, some amazing, some stating where they hit a wall.


    The thermodynamics just does not work out for most 3 level and 4 level gas laser systems. There are a few systems being looked at again, mostly behind the former Iron Curtain by people who made their lives dedicated to looking for a breakthrough in metal vapor lasers. One of those systems at 6.5 microns was suddenly found to be very medically useful, but not for reasons of raw power. Optically pumped metal vapor was finally made to work well with diode pumping a few years ago. The AF sponsored researcher went public with it, and the numbers are not spectacular. But it has really good uses for probing the atmosphere.

    Diode pumped solid state mediums are just so much more efficient and easier to make, so they are the new world. Gas is not dead, and CO is really starting to prove useful.

    I've been on the NKC-135A at Dayton and I got the impression that the folks riding in the cabin were my kind of Heroes.
    While well built, it seemed primed for a disaster if some plumbing let go.

    It really comes down to density and heat transfer for the high power stuff.



    Steve
    Last edited by mixedgas; 12-12-2018 at 11:59.
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    Steve,

    Do you mind if I repost your post and maybe get it added as a sticky for others wanting to research this subject?

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