Page 3 of 17 FirstFirst 123456713 ... LastLast
Results 21 to 30 of 165

Thread: How to create super bright laser beams

  1. #21
    Join Date
    Feb 2008
    Location
    Northern Indiana
    Posts
    921

    Default

    I think your diagram works well if only materials ( heathink and baseplate ) are machined by extrusion on bar block Al/Cu. If is hot laminated materials, the temperature varation have an inpact on form memory material like ) or ( if heat or cold.
    Just my experience on the metal plates, and the longer it takes the more it moves.
    (Thanks google to help me for translation )
    If I understand correctly you mean the temp differential will cause movement in the metal and problems with alignment? I think alignment will be the hardest thing to overcome in a system that is based on temp differentials.

    Incidentally I looked at FBGs for stabilizing a seed laser at 1064, a few months ago. Best accuracy yet Affordable stuff was all +/- .3 nm. Good enough for our purposes, except 2 nm steps between red wavelengths are NOT a stock product.
    I have seen papers where they have used 1 diffractive element to tune all individual diode at once. Somehow the angle of incidence has an effect on the freq. the individual diodes lock to. Then the individual beams of slightly varying wavelengths are combined via a grating. I think this may be out of range for the experimenter? The elements were made via holographic methods if I recall.

    I think planters and others are on to something. Andy has shown it will work. I think its a matter of finding a practical way of doing it without the esoteric gratings.

  2. #22
    Join Date
    Feb 2011
    Location
    New Hampshire
    Posts
    3,513

    Default

    Steve,
    You are not stealing my fire. I'm blazing hot! Prism dispersion and re-convergence has been around for I would hazard, hundreds of years. The previous application of prism combining for 8 wavelengths when steep cutoff/on, long pass filters were more expensive and lower performance would have been obvious, even trivial. The development of low cost, high performance dichroics for combining the common three RGB wavelengths has made the extra effort of angle adjustment and the space required much less attractive. Now, the availability of moderate power single mode diodes @ low cost, the serendipitous large wavelength shift of the AlGaInP lasers and the popularity of WDM in telecommunications and extreme brightness fiber coupled diode arrays makes me want to revisit this approach. I have a lot of experience with cooled modules in projector applications. They are not difficult.

    I would not approach this with diffraction. These other examples use diffraction inter-cavity and so the losses are much lower. The gain is wavelength selected as it is generated and not after the fact. Refraction in a prism does not have the losses associated with the higher orders. Because the output of these diodes is polarized the use of a prism at Brewster's angle would have almost zero losses. PCB combining is done after the combining prism has co-aligned these beams.

    I would not expand this approach to other wavelengths. Dichroic combiners are really easy, stable, low loss and compact. The real bottleneck is high quality, high power red. The extra space required and adjustment needed would probably outweigh the benifits. The GaN diodes (green and blue) have much less wavelength shift with temperature and would be limited to manufacturing variability. As an aside, 445 and 462nm might be worth a look.

    Jors,

    Do you see it now? You are right. The beams do enter the prism at slightly different angles and exit the prism at the same angle because of their different wavelengths.

  3. #23
    Join Date
    May 2014
    Location
    Barcelona, Spain
    Posts
    439

    Default

    Yes, thanks Eric. This is what I thought. However, its a hi-end setup, with precise temp tuning, super-narrow angles entering prism.... damn reds!

  4. #24
    Join Date
    Feb 2008
    Location
    Northern Indiana
    Posts
    921

    Default

    So, I did a little experiment. I put put my single mode rgb through a prism. I have no clue what kind of glass its made from.

    I measured the distance to the wall the dots landed on. I then measured the distance between R and G then G and B. From this I figured out the angle the beams deviated from each other. The R to G was 2.99mrad and the G to B 2.6 mrad. Then I estimated the rgb wavelengths to be 640, 520, and 450 respectively. I then divided the angle by the difference in wavelength. R to G = 25urad per nm and G to B = 37urad per nm. This is a rough idea but the best I can do with the 3 colors available. The refractive index is not linear with freq. (obviously or a prism wouldn't disperse light like the pink floyd picture) So, using the R to G of 25urad per nm and multiply by the spread of 30nm (650-620nm what I used as hopeful spread on a 170mw SM) I get 750urad. Keep in mind the actual number will be smaller because the refraction is less towards the red.

    Next I calculate a triangle with 750urad as the apex and sides 1000mm long. The opposite side is .75mm. In theory (roughly estimated) if the width of our beams right after knife edging is .75mm or less we can place a prism 1000mm away and combine wavelengths spaced 30nm apart.

    Anyone follow this train of though? Make sense?

  5. #25
    Join Date
    Feb 2011
    Location
    New Hampshire
    Posts
    3,513

    Default

    It does make sense to me. If the dispersion is that low it is unlikely a practical, simple prism dispersion combiner can be built. Andy's combiner was able to get two beams that were 20C or approx. 5.6nm apart to co-align. So, either he is using a transmission diffraction grating,a very dispersive prism or he has some neat multi-pass prism like refractive combiner.

  6. #26
    Join Date
    Feb 2008
    Location
    Northern Indiana
    Posts
    921

    Default

    I have another prism around here that I am currently looking for. It is very heavy compared to normal glass. As soon as I find it I will repeat the test. It should help by a factor of 1.5, I am hoping. Also, I should have said the beam centers are .75mm max after knife edging not width. Helps a little.

  7. #27
    Join Date
    Feb 2011
    Location
    New Hampshire
    Posts
    3,513

    Default

    I just did some research based on a highly dispersive glass called SF-11 that is available in a dispersing prism from Thor Labs. It looks like the differential dispersion between 638nm and 630nm can be as much a 1.0 degree (17mrad) as you adjust the input angle of incidence to within a frog's hair of 50 degrees. The maximum dispersion occurs just before the angle of incidence will give total internal reflection. Only increasing the angle of incidence to 55 degrees will reduce the dispersion to 3mrad. You will need to adjust the angle of incidence much more precisely than I would have thought, but it looks like it could work well.

  8. #28
    Join Date
    Feb 2008
    Location
    Northern Indiana
    Posts
    921

    Default

    Found other prism. Big difference. Getting 10X the dispersion between red and green as before (33mrad) This is looking more feasible. The "acceptance triangle" I'll call it is now 100mm by .8mm.

  9. #29
    Join Date
    Dec 2010
    Location
    DC/VA metro area, USA
    Posts
    554

    Default

    I was amused to note that the combining optic was so unimportant it was redacted.

  10. #30
    Join Date
    Feb 2011
    Location
    New Hampshire
    Posts
    3,513

    Default

    Found other prism. Big difference. Getting 10X the dispersion between red and green as before (33mrad) This is looking more feasible.
    Do you notice that the dispersion increases as you rotate the angle of incidence and then just before the angle becomes too low that the dispersion is maximum? I will look at another glass like BK7 (calculate it) and if the dispersion is somewhat less than the SF-11 then not important, but if the calculations show that the SF-11 should be MUCH more effective then it might be worth the risk that you aren't using the best available prism and I'll pick one up. Don't forget, if this gets close we can always use two prisms in series.

    Also, at maximum dispersion, do you notice any distortion of the far field spots? There is a finite bandwidth for each beam and the prism will be stretching the spots in the same direction as the dispersion. Hopefully, this is a lot less.

    I was amused to note that the combining optic was so unimportant it was redacted.
    This occurred to me about 2 seconds after I read about logsquared's first experiment. But, for what it's worth those images have convinced me that this can be done and if it can be done...I love challenges.


    To make this more exciting, I think someone posted that the anticipated 1W Oclero is single mode.

Posting Permissions

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