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Thread: Another one viasho is dying in front of my eyes

  1. #1

    Default Another one viasho is dying in front of my eyes

    Yesterday I noticed that something was wrong in my projector. Opened it up, checked the each color power - green gives ~600mW instead of 1500 and output power is very unstable. Opened the module - the pump diode is OK (~5W), baseplate temperature is OK (25,1C). This is the second viasho module, which I lost

  2. #2
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    I have a few thoughts. Is it unstable in that it flickers with rapid fluctuations or is it more like a lumia with the beam swelling,drifting and the the power rising and falling slowly? Is the power averaging @ 600mw how high and low does it go? Is there obvious mode drift with the beam passing through several different modes as you adjust the power? Can you adjust the power and in general it will increase as you increase the input current or is there little or a negative relationship?

    If the pump is stable at approximately 5W and the power is rapidly unstable ie it flickers then I suspect a loose crystal (vanadate or KTP) If the slow scenario is occurring then I suspect a photo-damaged KTP. After working with this type of laser a lot recently I am kind-of amazed that the Chinese are able to get the performance that they do from these lasers at the multi-watt level without blowing through the KTP SHG crystals. I certainly have. I have talked to the engineers at Coherent and several crystal manufactures (the good ones) and no one recommends running several watt CW green lasers with KTP any more and certainly not below 70 degrees C. I suspect they manage this by running the laser multimode with the KTP in close proximity to the vanadate to reduce the local intensity. Nevertheless, while these lasers can run for a long while, if they are near the raged edge of crystal damage and this is more likely the result of each individual laser's mode structure than an individual user's specific power setting then they may need to be considered as expendable.

    The direct diodes are looking a little less daunting as a result.

  3. #3
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    Quote Originally Posted by planters View Post
    may need to be considered as expendable.
    I believe this is the definition of "Viasho".... as found in Websters dictionary.

  4. #4

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    It more like flickering and flashing, with increasing current radiation intensity increases nonlinearly but without visible negative relationship. After starting the module power is about 200mW, after 10-20 sec increasing to 600-700mW. Also noticeable how beam modes are changing with increasing current + very large threshold current ~3A.

    Do you mean that they not fixed firmly? I tried to re-collimate KTP and pumping lens but this did not give a positive result.
    If the pump is stable at approximately 5W and the power is rapidly unstable ie it flickers then I suspect a loose crystal (vanadate or KTP) If the slow scenario is occurring then I suspect a photo-damaged KTP
    Chinese manufacturers say that this is a very special HGTR KTP capable of operating at room temperature )))
    I have talked to the engineers at Coherent and several crystal manufactures (the good ones) and no one recommends running several watt CW green lasers with KTP any more and certainly not below 70 degrees C.
    I threw the email to Frank, see what he will answer...

  5. #5
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    Chinese manufacturers say that this is a very special HGTR KTP capable of operating at room temperature )))
    Ya, right. I wonder why Coherent was unable to get some of these.

    It more like flickering and flashing, with increasing current radiation intensity increases nonlinearly but without visible negative relationship.
    Can you meter the electrical input to the diode to confirm it is indeed stable?

  6. #6

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    I checked it right now with the oscilloscope - a bit of noise (about 20-30 mV) but otherwise nothing criminal in power line. 5.8A and 1.87V on diode....
    Can you meter the electrical input to the diode to confirm it is indeed stable?
    You ask a rhetorical question, any fool can grow a magic crystal
    I wonder why Coherent was unable to get some of these
    .

  7. #7

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    If anyone is curious that viasho replied on my request - he just ignored my email. Great chinese support and service)))

  8. Default

    Quote Originally Posted by Bbe View Post
    If anyone is curious that viasho replied on my request - he just ignored my email. Great chinese support and service)))
    Hi,dear Sir

    This is Frank from Viasho.

    Sorry for the delay reply,and if you had sent email to Viasho,and I thought it might be blocked by the email server.

    Anyway, can you tell me when you had bought this laser?What is the SN?

    Frank
    http://www.viasho.com
    wzc@viasho.com
    Whatsapp: +8613911142669

  9. #9

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    Quote Originally Posted by Bbe View Post
    If anyone is curious that viasho replied on my request - he just ignored my email. Great chinese support and service)))
    Hi Bbe
    I confirm ...
    I have 4 DPSS 532nm Viasho, 2x 1W V-Fold and 2x 300mW all misaligned, of course...
    Their biggest problem is the design, they have only one TEC t so the crystals can not be stabilized at the correct operating temperatures, where the passages fluctuation and change in TEM mode.
    Driver issue, it's basic, I did not elaborate on the stability for the moment, the only practical thing is the Analog / TTL / switch ON

    As for Frank, he did not seem to know there something about lasers, so just to sell, and his answers here ... it's too old, it has no info ...
    I am not a manufacturer, just subcontractor electronic wiring, and I have all the production records, with all components, providers, plans and amendments, changing versions since 1992.

    Bbe, I am at your disposal for any discussion.

    Cheers, Christophe.

  10. #10

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    Hi Christophe,

    Another big problem of design - hugely primitive optics mounts. I was very surprised when I saw them for the first time. Many people will argue - if you need a good laser - buy jenoptik or something like that. I can agree only partially - Viasho positioned itself as a professional company, it is abnormal when a commercial product works only 100 hours of 10,000 hours, regardless of what technologies (crystals or mechanics) is used in these products. It is my opinion.
    As for temperature stabilization - I did some tests on this point. Temperature measured on a baseplate in the vicinity of the ndyvo4 crystal at various diode currents:

    0,5A...23,9C...0mW
    1,5A...24,1C...5mW
    2,5A...24,2C...70mW
    3,0A...24,5C...90mW
    3,5A...24,8C...140mW
    4,0A...24,8C...410mW
    4,5A...24,9C...400mW
    5,0A...25,0C...440mW
    5,5A...25,0C...570mW
    5,8A...24,9C...630mW

    It is obvious that the optic power does increase non-linearly, but the temperature of the baseplate is quite stable. What do you think about this?

    As you can see, Frank replied here (maybe it's a coincidence or magic power of this forum). He offers to ship the module and driver back to China, but I am inclined to send the module without driver, because I believe that it is a waste of money.

    Let's see what will happen next....

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