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Thread: Dillemma

  1. #1
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    Default Dillemma

    I just dropped $200 for a pair of AOMs, so I can use gas lasers and/or not worry about shitty Chinese DPSS blanking. This may not have been the best way to go, but hey... they came up cheap on eBay.

    That leaves about $500 in the laser budget.

    Given that I want to do lots of beam effects and some graphics effects, I want power power power!

    I already have an 80mW DVD burner red diode that needs a driver. The AOM means I can use any constant-current driver, so my life's a little easier.

    Should I:

    a) Go with the most powerful Aixiz cheap POS I can afford (150mW, $325);
    b) Go with the most powerful better-quality Chinese unit I can afford, from Laserglow (80mW, $480);
    c) Go with the most powerful Lambdapro I can afford (???); or
    c) Wait until I have some more money, then shell out for 200mW or more.

  2. #2
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    Default TTL vs AOM's

    Eric;

    I don't understand... You say you bought the AOM so you could use an ion laser, yet the lasers you said you are considering purchasing are all solid state. Since nearly all solid state lasers support TTL blanking, why bother with the AOM? (Or, more to the point, what do you have against TTL blanking?)

    I think TTL is the way to go vs an AOM simply because AOM's are such a pain to set up. I have 3 Isomet 1205-C1 AOMs here, complete with these *huge* driver boards. Supposedly everything works, but I've been pulling my hair out just trying to build a power supply for them. (+28 volts, +5 volts, -5.2 volts, all at less than 0.25% tolerance and, at least for the lower voltages, several amps of current draw.) I'm building a pass-bank right now for the -5.2 volt side.

    When I bought my 3 AOM's, my plan was to build a white light projector with one AOM on a large HeNe, one AOM on one of my single line 488 nm argons, and the last AOM on either a green argon or a green dpss. (I've alrady got a nice trichro to combine the three beams.)

    But when I finally bought a 100 mw dpss greenie (Lasever unit), I discovered that it supported TTL blanking. Now, I know that TTL won't give you the same color mixing that an analog AOM will, but like I said - it's easier to set up. So that meant that one of the AOM's wouldn't be needed...

    Then I started looking into sources of red... HeNe's max out at around 50 mw, and Krypton lasers are beyond my price range, so it looks like I'll be getting my red photons from a solid state source. Thus, another AOM will be replaced with an electronic blanking signal. So, I really only need one AOM for the single line blue from an argon, which sounds a lot like your situation.

    Whe I first read your post about wanting to use the AOM's, I'd figured that you'd be looking for an Argon. And at $500, you ought to be able to find something fairly nice. (Not a multi-watt death ray, but something like an ALC 60X or NEC 532, or even one of the Spectra-Physics 160 series single line blue Argons...)

    This assumes that you're trying to build a white light projector... If all you want is some green to mix with your 90 mw red diode, then you've already got more than enough money saved up. Given that the eye is 5X more sensitive to green vs red, you only need about 20 mw of green right now.

    Heck, if I were you I'd pick up a 100 mw DPSS green with both TTL blanking and analog intensity control. That way you can dial the sucker down to around 20-25 mw for good color balance with your red diode, and when you want to do pure beam shows you can crank it up wide open. $500 ought to buy you a really nice 100 mw dpss greenie. (For comparison, I only paid $400 for my Lasever unit, and that was over a year ago.)

    Then too, at some point you'll no doubt want to go full-color, and with 100 mw of green you're going to need about 240 mw of blue and close to 500 mw of red to get the right color balance. 240 mw of blue is going to be a little pricey, even if you stick with an argon, and 500 mw of red isn't cheap either! So if you double the amount of green you get now, that just means you'll have to double the amount of red and blue to go with it, and that's going to be *VERY* expensive indeed. (Ever price a 1 watt red diode?)

    As to which green dpss laser to buy, well - that's a matter of personal choice. I've heard good things about the Lambda Pro units, but I've never owned one. I haven't had any problems with my Lasever unit thus far, and I've owned it over a year. (not a lot of use on it though.) The laserglow and Axis units seem to be quite popular lately, but again, I have no experience with them.

    If I were you, I'd be sure to speak with Specwhore (Robert - the guy running this forum) as he sells several different DPSS units. Not sure which brand(s) they are, but I'll wager that he'll give you better customer support that your average e-bay seller...

    Adam

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    If I remember correctly, the cheaper Chinese lasers don't recover quickly from blanking -- if you blank them TTL with a 50% duty cycle, you'll get 30% or less average power when you were expecting 50%! (this from a post on alt.lasers testing the Aixiz 100mW $265 unit)

    Hence the AOM, which doesn't have that bug. I would go with gas, but I don't want to deal with the size, current, and cooling requirements. A friend of mine has a blue-line Omnichrome 532 (ALC60x) that I've been thinking of getting running at all lines, but that project is on the back burner.

    I don't think I'll be able to afford >200mW red any time soon, so I'd like to strech my budget where I can and get the greatest possible versatility right now. Yeah, I will eventually want white light, but if anything I'll want it at high enough power to do beam shows outdoors with minimal fog. (Boston winds, you know) Therefore, if there's any way I avoid needing to buy another green laser (even if it means I won't have anything approaching color balance), I'll be happy

    On the other hand, it's quite possible that my criteria of "outdoors with minimal fog" will demand a watt or five of green in any case, and so shooting for high power right now is pointless.

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    Speaking of which, what exactly are the advantages of a more expensive laser? Why would I want to pay $500 or $700 for 100mW when I could get the same for $270?

    Sure, it makes sense in holography, where beam quality and coherence length are paramount. But laser shows?

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    Outdoor shows without fog is going to require *real* power. Several watts minimum - more like several 10's of watts.

    Oh sure, if everything in your backyard is just right, you may be able to get away with a 1 watt DPSS unit, but that assumes that it's a dusty night, or it's naturally foggy, or all the street lamps were shot out with a BB gun before you started. er, um, yeah - something like that!

    Seriously though - forget about outdoor shows for the moment. That just takes too much power.

    I was not aware of the TTL blanking power problem you mentioned. I must have missed the post on alt.lasers. However, if they are talking about using blanking simply as an intensity control (IE: pulse-width modulation to emulate analog color control) then that should be easy enough to compensate for. Just re-calibrate your color control so that 30% green = 50 % duty cycle. So long as the blanking works for what it's really needed for (to switch the laser off while the galvo's move somewhere else), you should be fine with TTL...

    My controller doesn't even support analog color, so even when I finally get my whitelight projector built, I'll only have 7 colors. (well, 8 - if you count black!) Still, I've seen some color pics from other people that use this same controller, and they've gotten some stunning results with just 7 colors!

    I understand your desire for more power now, but you need to think about two things: When will you be ready to buy a larger red and/or blue laser, and how much will you realistically be able to spend then? If you're talking several years from now before you upgrade, then it makes sense to buy more power now so you'll have some more to play with in the interim. (even if color balance goes out the window.)

    Likewise, if you will have a lot more money next time (say, double to triple what you have now) then it also makes sense to buy more power now, since you'll be able to match the power when you upgrade your red.

    But if you're not going to spend much more than you do this time around, or if you'll probably be adding more lasers later this year, then I'd stick with the 100 mw green simply because it will fit the lasers that you'll soon be adding, and will get you to balanced white light rather quickly.

    As to the difference between a $400 laser and an $800 one, I'd have to say that beyond the basics of divergence, initial beam diameter, and power stability, the extra cost is wasted on a display show laser. We don't need long coherence length, because we're not doing holography. We don't need hyper accurate power stability either; plus or minus 5-10% is acceptable! Single mode vs multi-mode is a matter of preference, but at the power levels we're talking about they should all be TEMM00 anyway. We do need good cooling, however. And it's nice to be able to match (as close as is reasonable) the initial beam diameter and beam divergence of all three of your lasers in a white light projector. (Makes beam alignment at the trichro easier!)

    As for ion lasers being a pain in the rear end, I agree. But for blue your only other choice is DPSS at 473 nm, and that is going to be STUPIDLY expensive for anything over 50 mw.

    Adam

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    Adam,
    Well, I'm either going to drop $5k in upgrades sometime or get some high power lab lasers. (This is MIT...)

    The problem is a little more difficult to compensate for than you suspect. The 30% figure arises because the laser doesn't come back to 100% power immediately when you un-blank it; it takes some time. Therefore, instead of getting 100/0/100, you might get 100/0/10...20...30...

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    Another question!

    Do the expensive ones last noticeably longer or perform more reliably?

  8. #8

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    Should I:

    a) Go with the most powerful Aixiz cheap POS I can afford (150mW, $325);
    b) Go with the most powerful better-quality Chinese unit I can afford, from Laserglow (80mW, $480);
    c) Go with the most powerful Lambdapro I can afford (???); or
    d) Wait until I have some more money, then shell out for 200mW or more.
    E) wheel and deal.

    Aixiz is a joke, laserglow is overpriced CNI, lambda is only marginally better than aixiz and D) is impossible as it looks like youve been bit by the laser bug.

    If I remember correctly, the cheaper Chinese lasers don't recover quickly from blanking -- if you blank them TTL with a 50% duty cycle, you'll get 30% or less average power when you were expecting 50%! (this from a post on alt.lasers testing the Aixiz 100mW $265 unit)

    Hence the AOM, which doesn't have that bug. I would go with gas, but I don't want to deal with the size, current, and cooling requirements. A friend of mine has a blue-line Omnichrome 532 (ALC60x) that I've been thinking of getting running at all lines, but that project is on the back burner.
    The blanking recovery problem is primarially a falut with the power supply and temperature control system. However: most software mangles color code, so your at a disadvantage on both fronts.

    Some loss is expected momentarially when the laser "heats back up" but it should be damn near nothing. The duty cycle of the TTL is where it gets interesting, like you said: 50% on ttl is no where near 50% on analog, but its like comparing chocolate cake and mustard.

    With analog, since your not extinguishing the beam or dropping it below threshold very often, you are able to ramp up and down very quickly. TTL is just inherently slower as you go from full on to full off EVERY time you blank the thing.

    Technicalities aside: its really no big deal. Were talking miliseconds here when comparing the switching time. Another example: think of this as a visual representation of a logic gate complete with rise and fall times.

    AOM's have another bug: massive parasitic losses and extreme difficulty in setting up the unit in relation to the beam. Very very tight tolerances... brag mounts... weird angles on both axis'

    As buffo stated earlier: The power supply is a nightmare consisting of what would happen if analog and digital circuitry had a bastard love-child. Furthermore: they are german, so they are quite demanding.

    The losses with even a good AOM are going to be a constant 30% or more. the optics and rock eat/bounce all that. Most is bounced off the entry face and you can collect that using optics and run a lumia system off the "Waste" but thats another can of worms entirely and I dont believe the effort to collect the waste warrants the use of it for <500mW. Just my 2 cents.

    I don't think I'll be able to afford >200mW red any time soon, so I'd like to strech my budget where I can and get the greatest possible versatility right now. Yeah, I will eventually want white light, but if anything I'll want it at high enough power to do beam shows outdoors with minimal fog.
    Marconis got some wonderful reds. Shoot him a PM and see what hes up to. I prefer his units.

    As far as outdoors go: 40W. Minimum. There really is no way to make outdoor beam shows with only trace amounts of dust in the air. Some even say that 40W looks cheesy. If i was going outdoors with anything id want a couple copper vapor lasers. Wonderfully bright gold/green lines are produced by those things.

    Speaking of which, what exactly are the advantages of a more expensive laser? Why would I want to pay $500 or $700 for 100mW when I could get the same for $270?

    Sure, it makes sense in holography, where beam quality and coherence length are paramount. But laser shows?
    There are very few advantages, if any for laser shows. For all practical purposes nothing matters other than beam size/divergence and the number of photons a given unit can produce. Maybe polarization if you start getting to where you want to combine 2 same frequency lasers but thats a little past the scope of this doc.

    Holography is a different game entirely and I dont know of a single Chinese manufacturer that can come close to a Coherent c315m laser head. Those things are 100mW and surplus they go for $1500 without heatsinks/wiring/power supplies. To boot they dont blank either

    Different needs for different people.

    Another question!

    Do the expensive ones last noticeably longer or perform more reliably?
    And the answer is a big "maybe". From my experience most chinese lasers are close to exact clones.

    One place finds a system that works and 2 months later everyone else has "discovered" the same tech.

    I guess the best way to explain the development cycle in china is "He already invented the wheel, lets make it prettier! And while were at it we can save x cents by changing the power supply around a bit... Bob said something about X not working right... lets shave x more cents off the power supply and work around what bob said."

    Im not trying to discourage you from getting into the hobby or fallowing your dreams... just realize that there is a huge difference from marketing language and real product advancements.

  9. #9
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    Quote Originally Posted by Spec
    Aixiz is a joke, laserglow is overpriced CNI, lambda is only marginally better than aixiz and D) is impossible as it looks like youve been bit by the laser bug.
    What exactly do you mean when you say 'Aixiz is a joke'?

    AOM's have another bug: massive parasitic losses and extreme difficulty in setting up the unit in relation to the beam. Very very tight tolerances... brag mounts... weird angles on both axis'

    As buffo stated earlier: The power supply is a nightmare consisting of what would happen if analog and digital circuitry had a bastard love-child. Furthermore: they are german, so they are quite demanding.
    Dunno, the Isomet 232A-1 drivers I have on the way only want 28V.
    http://cgi.ebay.com/Isomet-AOM-Drive...QQcmdZViewItem
    The losses with even a good AOM are going to be a constant 30% or more. the optics and rock eat/bounce all that. Most is bounced off the entry face and you can collect that using optics and run a lumia system off the "Waste" but thats another can of worms entirely and I dont believe the effort to collect the waste warrants the use of it for <500mW. Just my 2 cents.
    D'oh!
    As far as outdoors go: 40W. Minimum. There really is no way to make outdoor beam shows with only trace amounts of dust in the air. Some even say that 40W looks cheesy. If i was going outdoors with anything id want a couple copper vapor lasers. Wonderfully bright gold/green lines are produced by those things.
    I'm not looking to do stadiums here
    Audience within a 50-100' radius, at the most.

  10. #10
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    Eric;

    Well, if you plan on having the cash later on, then go for the 200 mw green unit right now. With 200 mw of green, 500 mw of blue, and 1000 mw of red, you'd have a nice whitelight projector that would look GREAT indoors, and would be passable for *graphics only* at an outdoor show with limited throw. (50 feet or so.) Just understand that 1000 mw of red is going to cost over a grand, and the same thing goes for the half watt of blue.

    About your plans for outdoor beam shows: If you plan on purchasing a large frame Argon later on, you need to think about how you're going to power it. Do you have access to 3 phase power? If not, then you'd better set aside another $1000 to be able to build a phase converter. On the other hand, if you go with a high power DPSS unit, then you should be OK, but they're more expensive than big argons are - at least on the surplus market.

    As to the AOM power supply: My unit needs 28 volts at about 350 ma, and -5.2 and +5 volts at many amps. Not sure yet exactly how many, but it's way more than 2! (My existing power supply is based on an LM317 / LM337 pair, and they are good for 2 amps. With them hooked up the voltage pulls down below 1 volt as soon as power is applied, and the only thing that saves them is the internal current limit....) Oh yeah, and Spec wasn't kidding about German hardware being demanding. The voltage spec is + or - one quarter of a percent! At 28 volts, that means less than 7 hundredth's of a volt of ripple! Give me a break!

    On the auction you linked to, I agree that there seems to be just the one input voltage for +28 volts. But what is the "video" connection for? Is that where your blanking signal gets applied?

    I don't know - that driver doesn't look anything at all like the one I have. But who knows; maybe they improved it. But that still doesn't solve the problems of alignment and power loss that you get with an AOM.

    Believe me, if it wasn't for the fact that I already own 3 argon lasers, I'd go for DPSS blue at 473 nm in a heartbeat! For lower powered projectors they are ideal since they're so darn simple to set up. (Argons are better when you get up into higher powers, but I can't afford that sort of kit right now!)

    In a perfect world, I'd sell these three argons, along with every last one of these AOM's, and then buy the brightest 473 nm dpss I could afford. (Probably something like 80 ~ 100 mw.) But I've got too much money invested in ion lasers now to turn back. (Money that I'l never get back out of them, mind you.)

    You, on the other hand, are still able to make the choice. Think about it - do you really want to deal with the power, cooling, and alignment issues of a big ion laser? Once you've purchased an ion laser it's probably going to be cheaper to keep it. It's your call though.

    Then again, if you've got the cash, you could always go with a big honkin' mixed gas laser and a PCAOM. Then you'd be all set. But you're talking over a grand for the PCAOM itself, and some SERIOUS coin for a multi-watt Kr/Ar laser. (Not to mention the cooling and power problems...)

    Adam

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