Page 4 of 12 FirstFirst 12345678 ... LastLast
Results 31 to 40 of 111

Thread: 445nm diode info

  1. #31
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
    Posts
    2,124

    Default diode frequency

    I've been told that these diodes are +/- 10nm on purpose to combat speckle on the screen. So they could be 440-450nm depending on your luck. Don't forget that there are 50mw single mode 445nm diodes out there. I have one and the beam quality is really great. Nobody needs a watt in their livingroom. I have about 150mw whitelight from diodes and it is plenty bright. It would take 10 times that to double the apparent brightness. Is it worth all that? Plus the beam quality will be very low. Now add to that the danger from reflection and those who try to use this for a beam show and you have a bad situation.

  2. #32
    Join Date
    Jan 2009
    Posts
    1,622

    Default

    In my experience with these diodes so far, the beam quality isn't so bad. I'm getting 1.6mrad on the fast axis by .16 mrad on the slow axis. That's far superior to my multimode red modules.. I'm fairly satisfied with these numbers myself. Of course the beam isn't round, but for show use that's not too much of a problem for me.

  3. #33
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
    Posts
    2,124

    Default beam

    What optics do you use and can you supply an image of the beam at say 20 feet?

  4. #34
    Join Date
    Jan 2009
    Posts
    1,622

    Default

    I'm using an Aixiz AR-coated (for 405nm) three-element glass lens assembly in an Aixiz module.. I measured divergence at 30m.. I'll supply a photo of the profile at that distance this evening after work.

  5. #35
    Join Date
    May 2009
    Location
    UCSB
    Posts
    681

    Default

    I have been testing these diodes at high currents (1.5A and 2A) for the past few days, and my findings are available on my website http://www.krazerlasers.com/lasers/445nm/

    I have so far concluded that 1.5A is 'safe' (no power drop during a 50 hour period), but that 2A is NOT safe (power dropped 15% in the first 15 hours).

    In the mean time, I am really trying to find someone who has a working projector and an oscilloscope who can take scope captures of the diode in eco/non eco mode. I don't really care if you take it just voltage across the diode, voltage on a photo diode in the beam, through a current sens resistor, I just need to know the pulse length in normal/echo mode because I am unshure if my testing was done in normal/echo mode.

  6. #36
    Join Date
    Jan 2009
    Posts
    58

    Default

    According to your graph it appers COD occurred at about 1.8W

  7. #37
    Join Date
    May 2009
    Location
    UCSB
    Posts
    681

    Default

    Quite the contrary, it has been emitting coherent photons for a good 25 hours after upping the current to 2A, whatever the method is its a slow degradation. I hope to put this sample under the SEM at work and see if the facet has been damaged or if it due to defects in the gain region, I strongly suspect the latter.

    I am debating trying some pulsed tests after this test finishes to see when the COD kicks in, but I worry the results may be of little relevance since none of us are going to be running these diodes pulsed. It would be a chance to play with my shiny new LDI-928 driver

  8. #38
    Join Date
    Jul 2009
    Posts
    24

    Default

    Quote Originally Posted by RedlumX View Post
    Indeed so, it's about the longitudinal modes. I found this surprising as, I believe, this is a multi-emitter diode and why all emitters should run at the same wavelength escapes me. The diode seems to behave like any other higher power red or 405nm diode in this respect. Perhaps there is some reason behind this. But first of all, more detailed and systematic studies are needed, in particular each diode is different and I know from the red diodes that different samples of the same model can behave very differently.
    I don't think it's multi-emitter, I think it's a single emitter. You can likely tell the dimensions with a decent microscope, or stick it in an SEM for quick exact measurements. Or if someone has a dead one they're not using, I can stick it in an SEM when I have some free time.

    Quote Originally Posted by king4quarter View Post
    Good article. Crazy to think though, that he had already left Nichia when it was published, and would be in court with them the next year.

    Also extremely crazy to think how far we've come in only 10 years since then.

    And he's a nice guy, to boot.

  9. #39
    Join Date
    Jan 2006
    Location
    Switzerland
    Posts
    129

    Default

    Quote Originally Posted by pullbangdead View Post
    I don't think it's multi-emitter, I think it's a single emitter.
    The reasons why I think it is multiemitter are: the large power, the high asymmetry, the fact that at threshold once can see (when projecting on a screen) individual dots lighting up, which smear out when increasing the power.

    On the other hand I checked by scanning the beam stripe over the slit of the OSA, that if there is "single mode", then the wavelength stays constant (up to the resolution which is a few Ghz). When the power is increased, then there is a transition to multimode and the mutual balance of the various peaks changes when scanning over the stripe (then also the interference pattern of the transverse modes blurs). So it seems that the "emitters" are locked to one wavelenghth at low power and at higher gain they unlock and at even higher gain the spectrum turns into a chaotic mess. The noise in the laser output grows accordingly.

    It would be very interesting to settle this once for all. Probably this has a simple and well-known explanation by experts of diode lasers.... perhaps there are other constructions of diodes which have an extended size but are not multi-emitter in the classical sense.. I don't know.

  10. #40
    Join Date
    Jul 2009
    Posts
    24

    Default

    Quote Originally Posted by RedlumX View Post
    The reasons why I think it is multiemitter are: the large power, the high asymmetry, the fact that at threshold once can see (when projecting on a screen) individual dots lighting up, which smear out when increasing the power.

    On the other hand I checked by scanning the beam stripe over the slit of the OSA, that if there is "single mode", then the wavelength stays constant (up to the resolution which is a few Ghz). When the power is increased, then there is a transition to multimode and the mutual balance of the various peaks changes when scanning over the stripe (then also the interference pattern of the transverse modes blurs). So it seems that the "emitters" are locked to one wavelenghth at low power and at higher gain they unlock and at even higher gain the spectrum turns into a chaotic mess. The noise in the laser output grows accordingly.

    It would be very interesting to settle this once for all. Probably this has a simple and well-known explanation by experts of diode lasers.... perhaps there are other constructions of diodes which have an extended size but are not multi-emitter in the classical sense.. I don't know.
    I believe this well illustrates at least part of the solution:

    Click image for larger version. 

Name:	Multimode.PNG 
Views:	133 
Size:	20.0 KB 
ID:	17880

    That image is from Osram discussing the beam characteristic implications of using wider lateral confinement to allow for higher powers. Single-mode diodes are limited to ~2um ridge widths, the above image is for a 10um ridge width.

    As far as the power itself, Osram has also published as high as 8W from single-emitter laser diodes in the blue region (with wide lateral confinement, naturally, they published 20um-wide ridges, compared to the 10um image above).
    Last edited by pullbangdead; 06-21-2010 at 23:59.

Posting Permissions

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