From: cd@notformail.com   
      
   On Sat, 13 Dec 2025 07:23:39 -0800, john larkin    
   wrote:   
      
   >On Sat, 13 Dec 2025 14:10:55 -0000 (UTC), Phil Hobbs   
   > wrote:   
   >   
   >>Cursitor Doom  wrote:   
   >>> On Sat, 13 Dec 2025 11:09:08 -0000 (UTC), Phil Hobbs   
   >>>  wrote:   
   >>>   
   >>>> Gerhard Hoffmann  wrote:   
   >>>>> Am 13.12.25 um 05:47 schrieb Bill Sloman:   
   >>>>>   
   >>>>>> One thing to keep in mid with your constant current source is that the   
   >>>>>> lasing region is very compact, and even a very brief over-current can   
   >>>>>> burn it out.   
   >>>>>>   
   >>>>>   
   >>>>> Yes, it is usually the frequency-selective optical reflector grid   
   >>>>> that dies in ms. Faster than we are used from semiconductors.   
   >>>>>   
   >>>>> Gerhard   
   >>>>>   
   >>>>>   
   >>>>   
   >>>> A nice juicy carpet shock can blow the front facet off much faster than   
   >>>> that (although the fragments will still be moving for awhile afterwards.   
   >>>>   
   >>>> Cheers   
   >>>>   
   >>>> Phil Hobbs   
   >>>   
   >>> No one seems to have come up with a viable solution, so I've been   
   >>> giving it some extra thought. I considered the use of a semi-silvered   
   >>> mirror at 45 degrees to the plane of the beam and sampling the light   
   >>> level off that reflection, but then realized the loss through the   
   >>> mirror would be unacceptable. The only other idea I can think of is to   
   >>> use a mirror just off the plane of the beam which can swivel around   
   >>> for a split second every few seconds to deflect the beam into the path   
   >>> of the diode. That seems cumbersome and clunky but it's the only thing   
   >>> I can come up with, not being a designer of any description.   
   >>>   
   >>   
   >>You’re very likely to blow up more lasers trying to do constant power.   
   >>Start with constant current, then wrap a constant power loop around it.   
   >>   
   >>Cheers   
   >>   
   >>Phil Hobbs   
   >   
   >I'm thinking that one would get a bettter optical output tempco by   
   >driving a laser diode from a negative resistance source. Or, at least,   
   >some proper impedance. It wouldn't take long to measure things.   
   >   
   >(Measuring IS a bit more difficult than talking)   
   >   
   >Or a current source twiddeled by a temp sensor.   
   >   
   >But why does the OP need extremely stable optical output?   
      
   I could probably live without it, to be honest. I tend to over-think   
   things massively. I could probably run those diodes fine at 10mA below   
   their maximum constant current provided the current was reasonably   
   stable. Hell, I've got dozens of the things; I'll blow a few up and   
   find out empirically like everyone else does if they're honest. :)   
      
   --- SoupGate-Win32 v1.05   
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