fringes from PLT5 520B at 36 mA

[jbeale1]

Not really an issue, just a report. Here is what I get with a lensed Osram PLT5 520B ( aliexpress.us/item/3256807281696166.html ) shining on a 1/4 inch thick of glass ( amazon.com/dp/B00ES3T4FW ) when run at 36 mA drive current with bench supply near 6 V (but I have a 22 ohm resistor in series, so that is about .036*22 = 0.79 volts drop right there, meaning laser Vf near 5.2 V). The interference rings are not exactly round, more oval in this case so I guess the glass surfaces are not precisely parallel (?) Increasing to 37 mA drive current, I see the fringes get washed out.
My UNI-T UT385 laser power meter set to 520 nm reads 3.2 mW optical power for this drive current, measured at the laser housing output face with lens removed.

[DEHiCKA]

Those LD's wavelenth typically have ten times more temperature dependancy per degree C, than current dependancy per mA.
With 1mA single mode current window you will need LD temperature to be stabilized within 0.1C range.
Probably more like within 0.05C range to make sure it will not fall out of single mode operation.

[0x23]

Thanks for the feedback. Thats something I will look out for. However the temperature drifts I observed so far without any stabilization are below 1 fringe (over the reference arm) after a short warmup periode. My experience so far is that this can easily compensated with the drive current without leaving the single mode regime.

[AdrianFleckDTecInnovation]

Is there any experience with the PLT5 520EB_P I use this one, but is it also sutable ragarding line koherence kenghts ?
what do i have to look for in hte datasheet.