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Thread: Frequency doubling into the yellow

  1. #61
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    ... here two samples with 405nm LED through ruby or dyed glass - at max power it's not "white", but intense red or yellow-green (camera is over-saturated) ...

    Viktor
    Attached Thumbnails Attached Thumbnails 405nm-LED_Rubin_Alle.jpg  

    6-405nm@10_100_500_1000mA.jpg  

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    Short Ruby rods will lase at room temperature with a few Watts of 514.5 or 532 nm CW LASER pump when placed in a proper cavity with the correct optics. However 694 nm is not of too much use for the laser show community and it will hit thermal saturation at a few mW to 20 or so mW. The preferred method involves liquid nitrogen cooling. As for the other materials, just because you have fluorescence does NOT mean the material can sustain a population inversion and thus lase.

    Steve
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    ... what's with the find, that a 445nm laserbeam, blocked by an "orange" acrylic window, will totally block the 445nm, but there's a faint "orange" spot visible behind the window?

    Viktor
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  4. #64
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    Quote Originally Posted by VDX View Post
    ... what's with the find, that a 445nm laserbeam, blocked by an "orange" acrylic window, will totally block the 445nm, but there's a faint "orange" spot visible behind the window?

    Viktor
    In my case I found that 445 and 488 nm Diodes emitted a weak orange to green non lasing, incoherent, band spectrum. AKA like an LED....

    Probably have to start here (in Jest) http://britneyspears.ac/lasers.htm and read up on "bandgap" and "spontaneous Emission" and "Background Radiation" in semis...

    With very few exceptions lasers are three or four level systems, that extra energy from various atomic transitions has to come out somewhere, as Energy is Conserved.

    Steve
    Last edited by mixedgas; 07-24-2020 at 18:31.
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    ... OK - thanks! -- was thinking, the LD's emit only around their specified wavelength ...

    Viktor
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    Quote Originally Posted by VDX View Post
    ... OK - thanks! -- was thinking, the LD's emit only around their specified wavelength ...

    Viktor

    I wish! Thatís why gas lasers are still around. Even dpss and other solid state sources can be very dirty.

    Gas is too. I found this out when trying to use a hene for Raman with no cleanup filter. An interesting experiment is to use a steep 632 filter on the output of a hene. You will see a ton of other crap.

    i kind of think of a laser diode compared to an led like this. Itís like turning up the q in an audio filter and peaking a resonance. At some point it osc and you get a tone and in some cases side tones.

    Steve that make physical sense? Just a picture I made in my head. Below threshold the ld is acting like an led. Iím not an expert in this stuff and the more I read the more I see how little I do know. Itís however very interesting.

  7. #67
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    You got it right... Some of our beloved text book teaching tool examples of how lasers work come apart quickly when you actually have to use a laser. They die at warp speed when you set down with CAD, Modeling, a scientific calculator, a pen, and paper to actually design a laser for production.

    I'm looking at a book on designing a 0.5 mW 633 nm hene tube bore and optics right now. It has 20 pages on sizing the plasma, and 16 pages on the mirror math. It comes with a warning that the math falls apart for multimode tubes... That just gets you to the point where you can order materials and mirrors for a prototype. . The mechanical design and tube processing are a few hundred pages across multiple books to make a production laser.

    I assure you the fellow who did the Sci-Am hene design read most of it, or received help from some one who did.

    The text the US Air Force had published on a 5 Watt Argon comparative study on how to build a production laser using five possible tube designs covers three huge volumes. DTIC really wanted to know why I wanted that much microfilm printed. Worked out to like 170$ for the prints in 1990s Dollars. At the time I needed it for work. The design for the final airborne Argon is yet another volume.

    It does include enough prints that you could build one.. Turns out the first laser they tested stopped working at high altitudes, the change in the index of refraction as you fly higher detunes the cavity.
    Flipping the Brewster windows from a "Two Down" to a "One Up, One Down" fixed the refraction effects.
    The exercise of why is left to the reader and some serious Trig. A long YAG rod with Brewster angled ends would do the same thing.

    The Germans (MBB GMBH ) built a wingtip mounted lamp pumped Yag for some unsporting jetting reason. A friend has a few of the MBB medical / surgical spin-off versions as he serviced them. Sure enough, when I popped the cover on one of those, "One Up, One Down" and all sorts of compensation mechanisms.

    I think you could guess which very tough lab laser was probably the basis of the supposed 100 mW airborne HENE... Either that, or one of the designers owned shares in a Invar Producer. I'm not sure on that, but I wouldn't bet either way...

    Que ? Answer: Interesting Airborne Mapping and Ranging at really, really high resolutions in real time. The details and images of which have never really been published.. Instantaneous focus and a deep depth of field might be why... New methods of Thermal Imaging and intensified cameras came out soon afterwards and airborne imaging laser went away... Supposedly..

    The only pictures I have ever seen show a B-25 that looks like Fred Flintstone did plastic surgery on the nose.
    Last edited by mixedgas; 08-03-2020 at 16:27.
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    Ps. I have your SELEM shirt from last year. Yea been that long.....

  9. #69
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    Quote Originally Posted by kecked View Post
    Ps. I have your SELEM shirt from last year. Yea been that long.....
    Work is Hell with the re-org and downsize. Building Remodeling Hell, Designated Priority Worker Hell, and Parent Care Hell... This weekend was a nice evening with the Paramedics and their friends when Mom had a problem. She's back to normal..

    Today was my first day of vacation since I don't know when... Mostly kept an eye on Mom. I honestly wonder if I will ever see any of my friends who are more then 10 minutes away.. Ever...

    Care to guess who just got a recall order... Come fixxxx this.... For the record I am grateful to have a job.

    Steve
    Last edited by mixedgas; 08-03-2020 at 16:30.
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