Page 1 of 8 12345 ... LastLast
Results 1 to 10 of 75

Thread: PCAOM With DPSS Lasers....

  1. #1
    Join Date
    Jun 2007
    Location
    Lake Geneva, WI.
    Posts
    2,704
    Blog Entries
    1

    Default PCAOM With DPSS Lasers....

    Is their any advantage in using PCAOM with mixed beam DPSS lasers? Obviously the need for PCAOM came from the use of combined gas lasers such as argon and He-Ne or mixed gas krypton lasers. Now with fast reacting TTL and analog on a DPSS head, this may no longer be necessary especially with analog control. what are your thoughts?
    Thanks!
    Adam

  2. #2
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,218

    Default

    PCAOM's require a polarized beam. They also induce significant power losses. (Figure 15%) Granted, they're lighting fast, but they're also difficult to align and expensive.

    I think if you've got the option to get analog blanking for the three lasers in your projector, then that's the way to go. In the long run it will be cheaper and more convenient. Only real drawback is that you need to watch the manufacturer's specs with regard to analog blanking. Some of them don't really blank as fast as they claim.

    I've never heard of anyone using a PCAOM in a DPSS-based projector. Not saying that you can't, but apart from some special-use case where you absolutely need the speed of a PCAOM I can't see how you'd justify using one.

    Adam

  3. #3
    Join Date
    Jun 2007
    Location
    Lake Geneva, WI.
    Posts
    2,704
    Blog Entries
    1

    Default

    Thanks, that's what I figured. As long as you don't need ultra fast modulation, there is no need for PCAOM on an analog driven DPSS white light system.
    Thanks!
    Adam

  4. #4
    Join Date
    Apr 2007
    Location
    Toronto Canada
    Posts
    1,120

    Default

    My first laser was 300mw green with PCAOM. 300 was a lab laser without any modulation. Only problem I experienced is that you need to convert all your graphics to green. And use only one channel. Other channels have to be waaaaay off green frequency range to avoid flickering. And yes about 10-15% will go to waste....literately. There is a term used with PCAOMs called waste.

  5. #5
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,488,218

    Cool

    To clarify what Dr. Laser said, the wasted power through the crystal (optical loss) is an intrinsic property of the crystal. It is not the same as the term "waste beam", which is also associated with PCAOMs. The optical loss is there all the time, even when the PCAOM is trying to pass all wavelengths at max power.

    On the other hand, when you want to blank a wavelength (or several wavelengths), those frequencies are diffracted to a separate exit aperature on the crystal, creating a second "waste beam" that is normally not sent to the galvos. (The waste beam suffers the same 15 % power loss as the main output beam.)

    The waste beam from a PCAOM is really only relevent when you're working with a whitelight beam. In that case, the waste beam contains the wavelengths that are NOT selected for output. So if you've got a Kr/Ar laser and a 4 channel PCAOM, When you select the 647 nm Krypton red line, all the other lines from the laser will be present in the waste beam. (Your green and blue lines in this example.)

    Some projectors are designed to use this waste beam, either by sending it to a separate set of galvos or to diffraction gratings and lumina effects wheels. But more commonly the waste beam is sent to a beam dump (block of carbon).

    Adam
    Last edited by buffo; 07-01-2007 at 15:37.

  6. #6
    Join Date
    Feb 2005
    Location
    Switzerland
    Posts
    1,370

    Default

    I wonder if the beam waste of a PCAOM can be less important than the analog modulation loss on the laser?
    With the PCAOM, the laser is always ON at full power, so it can reach stability and max power and keep it all the time.
    When modulating, the laser will not have the time to stabilize itself when jumping for example to 0mW to full power (for a short time) to 0mW again...

    We can say that at least when the modulation / temperature stabilisation isn't perfectly managed by the laser driver, which is the case for a lot of "cheap" DPSS lasers.

    However, the direct disadvantage of this is that the laser is at full power all the time, so lifetime can suffer

  7. #7
    Join Date
    Jan 2007
    Location
    Sheepsville, Wales, UK
    Posts
    3,372

    Default

    Though not a common practice I agree there is an advantage if the lasers do not balnk in a linear or predictable fashion. Using a PCAOM would eliminate the unevenness so often seen in DPSS even when TTL blanked straight on and off. I also agree its an internal temp stabilisation issue so is less of a problem if you have a good laser with good internal thermal management.
    You don't have to run the lasers at full power - you could run them at some level that is below full that gives you the desired output power & colour balance and benfits from longer diode life. Plus it may well be better for a laser in the lognterm to be just on rather than being cycled by the modulation.

    Adam I have to dissagree with the point about alignment of a PCAOM. if you have a good stable adjustable height Bragg mount you can go from 0 to aligned in about 20 seconds - its a piece off piss to do - Far far easier than aligning multiple beams for example. Though no harder to do its more time consuming to tune the PCAOM driver to max out each wavelength than to actually set the crystal - though you should only need to do this once.

    Overall its a very expensive solution so I would say only worth while if absolutely critical that the beams are 100% stable - but then if you are gonna spend that sort of money you could just buy better Laser sources.

    Rob

    Oh and one more thing for anyone not familair with PCAOM - the waste (unused) beam is separated into its individaul lines. Therefore to be of any use as a white beam the lines would need recombining. I beleive NEOS do sell a reasonably expensive optic that does recombine the lines.
    Last edited by stanwax; 07-02-2007 at 01:13.

  8. #8
    Join Date
    Nov 2005
    Location
    Melbourne, Australia
    Posts
    3,677

    Default

    I was under the impression Laser Animation Sollinger did this with their Blitz lasers - used a AOM to provide super high mod speed..
    KVANT Australian projector sales
    https://www.facebook.com/kvantaus/

    Lasershowparts- Laser Parts at great prices
    https://www.facebook.com/lasershowparts/

  9. #9
    Join Date
    Apr 2007
    Location
    Toronto Canada
    Posts
    1,120

    Default

    Quote Originally Posted by dave View Post
    I was under the impression Laser Animation Sollinger did this with their Blitz lasers - used a AOM to provide super high mod speed..
    Not anymore. LAS is an old school company but still they dropped AOMs in favor of analog modulation.

    AOMs are not that easy to setup and need once in the while adjustment therapy. They waste a lot of power....about 20% in total. But they have extremely fast blanking and super smooth color changes. But they are only good for gas lasers those days.

  10. #10
    Join Date
    Apr 2008
    Location
    Poland
    Posts
    319

    Default

    One have to keep in mind that not every PCAOM driver is capable of providing intensity control to DPSS RGB laser. It is necessary to tune the crystal driver frequencies to each DPSS laser wavelength. This is common that NEOS driver come preset with gas laser wavelength table, so tuning to other wavelength laser lines would be impossible, making simultaneous intensity control impossible (with still combined output path). Worst case PCAOM crystal can modulate single wavelength, like 514nm channel for a 532nm DPSS.
    AA crystals come with nc.mod driver which is fully digital and can be tuned to other, non gas wavelengths. I have a NEOS driver that has programmable divider accessible so I can tune each channel frequency in full driver bandwidth.

    Piotr.K

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •