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Thread: what is the Cheapest way to get into pulsed lasers

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    Default what is the Cheapest way to get into pulsed lasers

    Hello, Im new to this forum but have always had a interest in electronics and lasers and wanted to try taking on a project. I wanted to ask what is the cheapest way to get into pulsed lasers like the one in this video. https://www.youtube.com/watch?v=JLti...sExnl1B-w&t=0s. Another question I have is I have seen some laser designs with mechanical q-switching how is it possible to get a pulsed laser out of a diode pumped laser? just turning the diode off and on? what is the speed limit on switching the diode (is it limited by the diode or the amount of energy needed for lazing)?

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    ... the cheapest way is finding an old/outsourced NdYAG- or fiber-laser.

    Modulation of high power diodes can be done with up to 1 MHz (or even faster) with the correct drivers ...

    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

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    Forgive me as I am a bit of a noob, but modulating a laser diode on its own wont generate a pulse bigger than the cw. The diode would have to be pumping Ruby or YAG and then that would emit the pulse right? Does the diamter or length or the laser medium matter given that you are able to pump all of it and not leave any parts out? Lastly so Im not wasting everyone's time with basic questions, where could I find detailed information on YAG laser construction some of the math behind it?

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    ... here you can find a lot of helpful informations - http://www.k3pgp.org/Notebook/Lasersam/laserfaq.htm

    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

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    Quote Originally Posted by fiberguy View Post
    modulating a laser diode on its own wont generate a pulse bigger than the cw.
    Modulating is not the same as q-switching. Modulating only turns the laser on and off, and yes, when it's on the beam power is the same as it would be if you never modulated it.

    Q-switching is a method for storing up a much larger amount of energy than would ordinarily be produced by a laser cavity of a given size by artificially expanding the resonator. When the Q-switch is then activated, the "quality" of the original cavity is restored. (Thus, "Q-switch".) Due to the much larger intra-cavity flux that was built up the resulting output pulse is *much* bigger than it would normally be. (Sometimes big enough to damage the output optic!)

    The diode would have to be pumping Ruby or YAG and then that would emit the pulse right?
    For a Q-switched laser, yes, that's more or less how it works. (There are also non-Q-switched versions that are still pulsed lasers, but they don't produce the extremely high peak pulse power of the Q-switched versions.) Viktor suggested an ND-Yag laser for exactly this reason, as it is a commonly-available pulsed laser that uses a Q-switch to get high peak pulse power.

    However, he also suggested that if you merely need a pulsed laser (and are not interested in how powerful each pulse is), then you could simply use a diode laser with a good driver, since laser diodes can be modulated reliably at frequencies up to 1 Mhz (or higher). And a modulated diode laser is far less complicated than a flashlamp-pumped ruby or YAG, even one without a Q-switch.

    So it's really down to what is important to you: Do you need short laser pulses, or do you need short, abnormally powerful laser pulses? The first case can be achieved with a standard diode laser and a good modulating driver. The second case is probably best accomplished with a Q-switched laser.

    You linked to an engraver video but you didn't say that was what you wanted to build. And even if you are building an engraver, the sort of materials you want to engrave matter a lot with regard to the type of laser you need. (Some materials don't work well with the short wavelength IR from a YAG, which is why many engravers use a dual-laser system that also incorporates a CO2 laser for long-wavelength IR output.) Also, using a Q-switched laser for engraving is rather uncommon. Unless you're certain you need it, it's probably better to use a DPSS (Vanadate) source for your near IR laser.

    Does the diameter or length or the laser medium matter given that you are able to pump all of it and not leave any parts out?
    What do you mean, "does it matter"? The shape of the lasing medium affects several aspects of the laser's performance. Which characteristic in particular were you interested in?

    As a general rule, the longer the gain medium, the more power you can get. (Note: "Can", not will.) However, increasing the diameter of the medium (especially in optically-pumped rod lasers like a ruby laser) can also increase the power output. Longer cavities have other considerations as well - the beam quality (divergence) is often better with long cavities, and it can also help to reduce heating (more surface area for heat dissipation). But thermal lensing is usually worse with a long rod, and it's also more difficult to get very short pulses from a longer rod. Lots of engineering goes into this.

    Finally, even if you are able to pump "all" the medium, there's no guarantee that it will all participate in the lasing activity. The specific optics and the layout of the resonator play a big role here. Example: Most ruby lasers with external mirrors use confocal or plano-confocal optics, so the beam forms either a cone or a bow-tie shape as it passes through the rod. Many ion lasers use a similar arrangement. In these cases there is a portion of the gain medium that plays no role in creating the output beam.

    where could I find detailed information on YAG laser construction some of the math behind it?
    Sam's Laser FAQ is a good starting point for basic information. Check the solid state laser section. Don't know how much math you're going to find though.

    Information on turn-key home-made YAG systems is going to be difficult to find, and information on how to build a Q-switched YAG from scratch is going to be nearly impossible to find.

    It's almost certainly going to be cheaper (far cheaper) to purchase a used YAG laser vs trying to engineer and build your own system completely from scratch (especially with regard to a Q-switched YAG). There are hundreds of tiny problems that have already been engineered to death in a commercial unit. You might only find documentation on a handful of the biggest show-stoppers, however, leaving the rest of the design and development work to you. (Google Q-switch first pulse suppression for an idea as to how serious some of these problems can be!)

    Basically the point is, why re-invent the wheel if you don't have to? Old-school medical laserscope units can be found on the secondary market for just a few hundred bucks, and when functioning properly even the ancient 500 series units could produce 15-20 watts (average power) of green, with peak pulse powers of several 10's of KW of IR to the KTP doubling crystal. Remove the KTP and you'd have more than enough optical power to do some engraving, if that's your goal. Note that tailoring the output to your exact needs is still going to require some work on your part (mostly optics), but nearly all of the difficult engineering is already done for you. If you just want to use it for engraving you can probably get optical advice from others who are currently using DPSS (Vanadate) lasers. (Be aware of the additional stress that the Q-switched beam can place on your optics!)

    Now, if you have some special use case where you *need* to build your own laser, that's fine. However, in that case you would probably already have a pretty good idea of what you wanted/needed. So I'm guessing that instead this is more of a home project for you. And if you want to pursue that goal, that's cool, but just realize that you're undertaking a *huge* challenge if you want to build your own Q-switched YAG from the ground up. And it goes without saying that such a project presents some grave safety risks.

    Adam

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    Thank you so much for all of this useful information! So my end goal honestly is to more learn than anything however, I wanted to explore Laser ablation as what originally peaked my interested was fiber lasers. How ever I started looking away from fiber lasers due to the extra hardware I would need to have to deal it. I might look into it in the future if I can get access to my universities optical lab because they have tools like a spicing machine along with many other things. Also I thought most fiber markers used either Q-switching or MOPA.

    Would it still be a crazy idea to buy an off the shelf laser like below and making a mechanical shudder q-switch? I have also seen people make them with acoustic-optic modulators (pretty sure that was the set up in the video). Although I would prefer to avoid needed to buy one. YIKES! Looking at the laser modules available I might just plan on getting that and just making a basic laser with it, at least would be a good starting point. Where do you normally source mirrors and lenses without loosing an arm and a leg for it. Many of the websites I see have the bad sign of "inquire about the price".

    What risks do I run with messing with q switches? Is it just breaking mirrors and lenses or do I also have to worry about the YAG too?


    https://www.alibaba.com/product-deta...39f91958DIzYow

    Thanks again!
    Last edited by fiberguy; 11-19-2018 at 17:36.

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    ... better search for outsourced NdYAG-lasers - I've got two pretty big/heavy flashlamp-pumped complete with Galvoscanner and 120 or 150 Watts averaged power (3kW flash-lamps) -- one for 300 Euros, the other for free!

    But didn't activate them yet - have enough fiber-lasers (CW types with 50, 85 and 130 Watts, pulsed types with averaged 16 and 20 Watts) and fibercoupled IR-laserdiodes (output powers of 5, 9, 25 and 30 Watts @975nm) to "play" with

    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

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    Quote Originally Posted by fiberguy View Post
    Would it still be a crazy idea to buy an off the shelf laser like below and making a mechanical shudder q-switch?
    I don't think you'll be able to build a mechanical Q-switch that will be fast enough. By the time the optic has settled into position you will have lost a great deal of the extra energy that was stored in the longer cavity. This is why Q-switches use AOMs - they can switch *very* fast.

    The laser you linked to is an unknown quantity. You might be able to get it to lase. Beyond that though, anything is just a guess. There aren't enough specs provided to say what you might ultimately be able to build with it. For sure if you ever wanted to use it as a foundation for a Q-switched design you would need to remove all optics from that module. (Google "Z-Fold Resonator" and "L-Fold Resonator" to see what a typical optical path looks like for a Q-switched YAG, and pay particular attention to where the external optics are mounted in relation to the YAG rod.

    I might just plan on getting that and just making a basic laser with it, at least would be a good starting point.
    Agreed. Walk before you run, and all that.

    Where do you normally source mirrors and lenses without loosing an arm and a leg for it. Many of the websites I see have the bad sign of "inquire about the price".
    Laser lenses are expensive, especially when you are talking about high power units. Optics than can withstand the punishment of a Q-switched beam are even more expensive. I don't know of any substitute though. It's a limited market, and the optical suppliers know this and price their stuff accordingly.

    What risks do I run with messing with q switches? Is it just breaking mirrors and lenses or do I also have to worry about the YAG too?
    Everything inside the laser cavity is at risk. As well as things outside the cavity, like lab equipment and other people! Q-switched lasers are among the most dangerous because of the high peak pulse power. These are lasers that do not forgive. The first time you make a mistake, either someone gets hurt or something gets damaged. There is some information regarding the risks of Q-switched lasers in Sam's Laser FAQ, so I would suggest you start there. But before you undertake a project in the lab you really should discuss it in detail with some of the folks at your college to be sure everyone is OK with the danger involved. This isn't just a blindness risk - these lasers will burn human tissue. (They were often used for laser surgery.)

    Adam

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    [QUOTE=buffo;347027

    The laser you linked to is an unknown quantity. You might be able to get it to lase. Beyond that though, anything is just a guess. There aren't enough specs provided to say what you might ultimately be able to build with it. For sure if you ever wanted to use it as a foundation for a Q-switched design you would need to remove all optics from that module.

    [/QUOTE]

    Those modules usually (as far as I've seen) come without optics, they're just a pump/rod/chamber from what I've seen. Would be worth checking with the seller of course.

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    ... yes, you'll need the resonator mirrors, flashlamp-driver and AOM to get it pulsing ...

    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

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