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Thread: Polorising/Combining cube and polorising the beam.

  1. #11
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    Yep, heres a picture of the head with the lid removed.

    Jim
    Attached Thumbnails Attached Thumbnails laser head.JPG  


  2. #12
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    Still waiting for help and advice off one of the guru's.

    Jim

  3. #13
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    Jim it could be a stripe size mismatch issue, unfortunately unless you have specs on the dead diode then you will never be sure. Im assuming that all the good stuff - vandate lbo etc is inside what you describe as 'the chamber'. There is good and bad in this.

    Good is that this will all have remained aligned - to the original 808 output but this means you may need to get very very close to that diodes position and orientation before you get anything from the output.

    Bad because vandate floureces very brightly when you pump it with 808 and I have observed this through an ir filter in the past which has helped me to see when the beam from the pump diode is close to optimally focussed. If the vandate is not visible you may not have this luxury.

    The pump beam needs to be focussed to as small a spot as possible in the vandate so you get maximum power density and therefore max effeciency in the conversion to 946nm lasing within the vandate.

    Once you have this state sorted - lets call it the z axis you will then need to very carefully adjust the x and y axes of the diode to bring it into alignment. This may take you a very long and frustrating time and may not get you lasing but it may be the best approach. You are likely to find that the diffeence between lasing and not lasing is a tiny tiny ammount of movement on the diode so any large or fast movement wont get you anywhere. Remember 946nm is a line that vandate is not that happy lasing at so you have a job from the outset.

    The parts of the cavity that are currently fixed may well need tweaking to bring the laser up to optimum but these should not be touched untill you see blue and optimise the laser diode position to get the most out. Otherwise you could easily loose the blue and never get it back. Dont touch the OC assuming it has adjustment and is not just adhered in palce as its possibley the hardest part to get back in position.

    Now this is a random thought but may be true - anyone else offer confirmation or condemnation of this is welcome. The 2nd Harmonic conversion is very sensitive to polarisation and it may well be that the diode is creating a 946 line that is not in the correct plane. The conversion effeciency may well not good enough to promote frequency doubling - though in green dpss this is important but will allow lower green outputs rather than non at all. What I'm saying is that you may need to rotate the diode around at 90 degrees in respect to the beam path to get anything or to optimise.

    Have you measured the ld output at the max current that your driver will give...what do you get? It looks likely that your diver is designed for a lower power diode but this means that if you can increase what the driver is supplying you should end up with more blue or if you can get a comparable ammount of blue to original and the new diode is running far from its max it may well outlive all of us! Also try and see if you are getting any sort of beam from the output (remove the ir filter and see if there is 946 or 808 escaping) the 808 will be less dense as it will be focuses in the vandate near to the LD. but you may get a more defined 946 beam out at least it would tell you the prob is only with the doubling of the light.

    I hope you are not put off by all this - it will not be an easy task but you know it makes blue light - you just need to convince it of that fact

    And I would stress what allthatwhichis said about being very careful. That faint red glow you see is the ir glow of 808 but as its right on the periphery of our visual sensitivity it looks pretty dim. I dont know how 808 compares but 780nm appears 0.0000150 times as bright as 555nm (our peak sensitivity) so that faint glow will be doing lots of damage that you wont realise. Even the uncolimated beam will be bad - imagine how bright a 200mW vis DVD diode with no lens would appear across a room - it would likely be tough to look at and now think you have maybe 5-10 times the power there - and thats before you run it to its capacity. Lecture over

    Good luck and keep us posted.

    Rob

    PS i use a webcam for ir viewing, its a PITA but at least if you fry it you can go get another dead cheap you cant do that with your retinas - sorry I did say lecture over

  4. #14
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    Kevin (Junktronix) saw this thread last week and has very kindly sent me a 1W pump as he also thinks that I picked the wrong one.
    Hopefully I will recieve it later this week. I will post how I get on.
    I measured the 808 around the head with my lasercheck and could only find a few stray mWs, this tallied with what I saw with my camera.

    Jim

  5. #15
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    Well a further update..........
    I have put the new 1W pump diode in and that works
    I also moved the chamber about a little bit and I have seen it lasing blue

    I'll have another play with it tomorrow and hopefully get it working and properly aligned.

    There still is the question of polarisation, how can I change it if needed?

    Jim

  6. #16
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    Well done Jim
    it looks like the 4w is not far enough into its active region or the stripe width is too big (or is not focussed tightly enough). You may get the 4W to work by tweaking the focus but to do this you will prob. need to move it fore and aft in relation to the chamber - and thats when you are certain that its output is beyond threshold.
    I know you will be happy that the 1W is working but I would not worry too much about aligning this as its no going to yeild much blue. Even if the laser had a 50mW output before then that would mean using that 1W diode an ir to 473 conversion effeciency of 5% which i doubt is very likely. As usual I stand to be corrected on this as I am just speculating based on the fact that blue DPSS is not vary easy to achieve, as I think an 808 to 532 conversion would typically be in the 10-20% region, so 5% from a 473 may be a bit too much to hope for.
    I would see if you can get the power supply to give a bit more juice to that 4W and see if you can get that to work. You are more likely to get a usable laser at the end of the day and as I said the other day if it runs below its max it will live for ages.

    Rob

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