I was trying to change the laser diode in one of our broken OBIS Lasers (640nm, 40mW). Thus I thought I would buy this Thorlabs HL6362MG diode.

If I connect the diode to a power supply directly at 2.6V then it works. The old diode also works (just weak) with the same pins connected to the power supply. Therefore I assume that the pin code of the diode that I bought, matches the original one.

However, when I place the diode into the laser itself, it doesn't work. The old one, however, does work (just that it emits way to weak).

Any ideas?

Thank you.

  • \$\begingroup\$ Is this for a confocal? Are you planning to replace the OBIS with the diode or replace the diode in the OBIS? If you're planning on just using the diode -- the beam coming out of the OBIS is 0.8 mm in diameter with a divergence of 1.3 mrad (0.075 deg) - but the raw laser diode has no optics and the divergence due to diffraction from the output aperture 10x 21 deg! -there is no monitoring circuitry, no cooling. You can build your own (with some effort) but the OBIS sheet says: "Simply plug in the DC source and your laser is operating." \$\endgroup\$
    – D Duck
    Commented Jun 23, 2018 at 13:37
  • \$\begingroup\$ Hi. No, the obis laser itself is only emitting at 0.8mW although it’s set to 40mW so I assume the Diode within the laser is broken. I thought it’s easy to replace it...it’s for a flow cytometer...any ideas which diode would work? \$\endgroup\$
    – Danny
    Commented Jun 23, 2018 at 19:53

1 Answer 1


Every diode has a different voltage, threshold and slope. So the OBIS would need to be recalibrated to work correctly with the new laser diode. Also with a new laser diode the fan angle and pointing is different so all the optics need to be re-optimized. And then you need to confirm polarization, azimuth and other factors. Why not send it back to Coherent for service?

  • \$\begingroup\$ we don't really need super good beam properties for flow cytometry \$\endgroup\$
    – Danny
    Commented Jun 25, 2018 at 15:36
  • \$\begingroup\$ Also it doesn't really matter wether its 40mW or 42mW or 35mW...as long as its more or less content. So I thought just replacing the diode would be fine. The new diode doesn't give any light at all however which is weird. Shouldn't it emit at least a bit? When I connect it directly to a power supply it emits over a range of voltages. Sending it back to coherent for service is simply a cost factor. She service is 50% of the new laser...so ideally if I could repair the laser myself it would be great :-). \$\endgroup\$
    – Danny
    Commented Jun 25, 2018 at 15:42

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