From: jl@glen--canyon.com   
      
   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?   
      
      
   John Larkin   
   Highland Tech Glen Canyon Design Center   
   Lunatic Fringe Electronics   
      
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