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Thread: Molecular Beam Epitaxy and Effusion cells

  1. #11
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    Quote Originally Posted by kecked View Post
    Can you explain how you change the gas to krypton in a ndyag laser? Are you pumping the rod with a flashlamp? This makes no sense to me otherwise. Xenon is more commonly used. Flash lamps are really approachable but be ready for a lot of failures and a few loud bangS.
    I am going to put the rod inside the “flash lamp”, researching the metastable band gaps it appears krypton is better for pumping

  2. #12
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    ... if NdYAG, then research better in direction of 808nm-diode-pumping - here I'Ve posted some images of different 808nm-diodes opened and lasing.

    Most are meant for "end-pumping", will post images of a "side-pumping" diode too: https://photonlexicon.com/forums/sho...ng-and-marking

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  3. #13
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    Quote Originally Posted by VDX View Post
    ... if NdYAG, then research better in direction of 808nm-diode-pumping - here I'Ve posted some images of different 808nm-diodes opened and lasing.

    Most are meant for "end-pumping", will post images of a "side-pumping" diode too: https://photonlexicon.com/forums/sho...ng-and-marking

    Viktor
    So if the frequency is higher (greater energy) wouldn't that just produce a little more heat when the electron was let down and you will still see lasing of the ND YAG crystal. Would this not just require extra cooling of the gas. It just seems like the diode method of pumping is really limited in terms of power and how much voltage you can apply (without burning out the diode).



    I found a periodic table of spectra and I am trying to see if the maker will add a scale for each element as well as include the non visible spectra. This of course does not cover mixes or compounds but its a good start.

    Also don't you want to try to collect up as many frequencies as your cavity creates. If you try to create a single mode laser cavity don't you end up sacrificing A LOT of power on the output of the beam?

    Why did you choose to use dielectric mirrors? I was reading the best optics for NIR is silver or gold plated aluminum, or is the gold what you are referring to as the "dielectric"? Silicon oxide coated aluminum did not show to be as good for 1064 nm or even the surrounding frequencies. Also I can mill my own aluminum parts and sputter gold on in my garage, trying to coat Aluminum before it oxidizes in silicon oxide is a sticky issue.

  4. #14
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    ... what powers or energy densities are you aiming on?

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  5. #15
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    Quote Originally Posted by VDX View Post
    ... what powers or energy densities are you aiming on?

    Viktor
    As high as I can possibly attain, my core design which is a complex solid works model is not open source but is build like a brick shit house. All the materials are mechanically and thermally over designed to account for design changes and modifications. Cooling of optics and gas is taken into account. The internal design is set up for fine tuning of alignment prior to the final assembly. I will likely use a diode for alignment purposes.

  6. #16
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    ... a bit more detail could help - are you planing for Kilowatts, Megawatts or Gigawatts?

    The diode-modules in my linked thread are in the ranges from some Watts to 500 Watts ... Direct-Diode-Lasers are available with powers of up to 10 Kilowatts CW ... pulsed diode-pumped solid state lasers have some ten to hundred Kilowatts peak powers - some in the Megawatts too ... lasers used for fusion-research or military applications are even more hefty ...

    So give the rough range, you are aiming on ... and the amount of Kilo-, Mega- or Giga-Dollars too, you have access to ...

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  7. #17
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    Quote Originally Posted by VDX View Post
    ... a bit more detail could help - are you planing for Kilowatts, Megawatts or Gigawatts?

    The diode-modules in my linked thread are in the ranges from some Watts to 500 Watts ... Direct-Diode-Lasers are available with powers of up to 10 Kilowatts CW ... pulsed diode-pumped solid state lasers have some ten to hundred Kilowatts peak powers - some in the Megawatts too ... lasers used for fusion-research or military applications are even more hefty ...

    So give the rough range, you are aiming on ... and the amount of Kilo-, Mega- or Giga-Dollars too, you have access to ...

    Viktor
    I was hoping for 10-30 kw of power. Also if the cost is to high for these diodes that would be an issue as well. I have not decided if I want to do CW or pulsed, if I do pulsed I will have to figure out how to make a Kerr effect lense.

    The problem with diodes is they are solid state devices and then we are right back to my original OP of having to build my own MBE or ion beam implantation device due to cost issues (assuming these things get quite expensive when you increase power).

  8. #18
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    ... if it's 10 to 30 kW pulsed, then search an used 20W to 30W fiberlaser - they are new around 3000 to 5000 USD imported from China or from 8000€ up from an European vendor.

    If 10 to 30 kW CW, then multiple the prices with 10x to 30x.

    When developing them complete DIY, then count the years to decades, the actual vendors have invested in their developments ...

    Viktor
    Aufruf zum Projekt "Müll-freie Meere" - https://reprap.org/forum/list.php?426
    Call for the project "garbage-free seas" - https://reprap.org/forum/list.php?425

  9. #19
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    Quote Originally Posted by VDX View Post
    ... if it's 10 to 30 kW pulsed, then search an used 20W to 30W fiberlaser - they are new around 3000 to 5000 USD imported from China or from 8000€ up from an European vendor.

    If 10 to 30 kW CW, then multiple the prices with 10x to 30x.

    When developing them complete DIY, then count the years to decades, the actual vendors have invested in their developments ...

    Viktor
    Yep, this will be a life work not a weekend thing.

    I was looking at the spectral line data from NIST and Yb and Nd themselves dont have a spectral line at 1064 or anywhere close. In fact they dont go above 500 ish nm. Aluminum appears to be like a super material as far as spectra. So its obviously the interaction of Nd, Yb and Al that gives the nice 1064 spectra line but if you were an electonic materials designer how would you know to mix these together to get that specific spectra line?

    BTW your laser project looks cool but I am not sure why you would assume that I think I can accomplish this over the weekend or why bringing up other companies efforts is relevant?
    Last edited by akmetal; 03-02-2019 at 10:07.

  10. #20
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    Quote Originally Posted by akmetal View Post
    So if the frequency is higher (greater energy) wouldn't that just produce a little more heat when the electron was let down and you will still see lasing of the ND YAG crystal. Would this not just require extra cooling of the gas.
    In general, yes. The devil is in the details. Most materials (including ND:YAG and ND:YVO4) have a preference for absorption at certain wavelengths. You'll still get some pumping outside of these wavelengths, but it won't be nearly as efficient. Considering how awful most lasers are when it comes to efficiency to start with, you really want to stay as close to the ideal case as you can.

    And then there's the heat issue. Considering that a laserscope (flashlamp-pumped Z-fold YAG) needs water cooling on the lamp *and* the rod, you can see that "extra cooling" may not always be an option. In short, what is fine for a low power application suddenly becomes a real problem when you scale things up to the tens-of-killowatts range.

    It just seems like the diode method of pumping is really limited in terms of power and how much voltage you can apply (without burning out the diode).
    The solution is obvious - more diodes!

    I'm only half-joking though. Some high power diode-pumped YAGs actually do gang a bunch of bar diodes together in a big array and the focus that IR down to the rod. Its the brute-force approach, but it works - at least to a point. (Need to be able to keep the diodes cool and make sure you don't damage the rod during the pumping process.)

    Note that it is absolutely possible to pump a YAG rod to the point of failure with commercially-available off-the-shelf diode lasers. (Disclaimer: don't try this at home!) Believe it or not, some of the latest YAG surgical lasers actually operate right below the point of catastrophic optical damage when pumping the rod. I've read stories of people who have tried repurposing these lasers for show use, but because they can't figure out the secret sauce that the original manufacturers used to protect the lasing medium they end up frying the rod after just a few minutes of use.

    Also don't you want to try to collect up as many frequencies as your cavity creates. If you try to create a single mode laser cavity don't you end up sacrificing A LOT of power on the output of the beam?
    Depends on the difference in gain for those frequencies. Allowing a low-gain frequency to resonate in the same cavity will sap power from other frequencies that might have higher gain. And even if your total power creeps up, now you're focusing two different wavelengths. Not ideal for cutting/burning applications.

    Then too, some lasing lines might have longer dwell times at the lower metastable levels before they fall back to the ground state. True, in gas lasers you can help this by adding a quench gas, but even so this isn't always effective. And as long as those atoms in your lasing medium are stuck in that lower metastable level they won't be absorbing pump energy to get back to the high energy state, so they're not doing you any good.

    Regarding mirror choice, it's not always about what is "best", but rather what is optimal - that is, best for a given price point. Dielectric mirrors are normally very efficient, but I'm sure there are cases where other materials might have even higher efficiency. But is the extra few percent worth the cost? Dielectric mirrors are everywhere. Gold-plated aluminum mirrors not so much.

    Adam

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