From: cd@notformail.com   
      
   On Sat, 13 Dec 2025 10:25:44 -0800, john larkin    
   wrote:   
      
   >On Sat, 13 Dec 2025 17:00:34 +0000, Cursitor Doom    
   >wrote:   
   >   
   >>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. :)   
   >   
   >It would be interesting to take a few measurements, like required   
   >current to get constant optical output at a few temperatures, noting   
   >laser voltage.   
      
   Yes, I'm sure that will suffice in this instance.   
      
   >   
   >You'd need a photodiode or something.   
      
   Thanks to a previous thread and Phil's input there, I have several of   
   those too.   
      
   >Spritz some freeze spray on a laser diode or an LED. It's dramatic.   
   >   
      
   Is it cool? ;-)   
      
   >John Larkin   
   >Highland Tech Glen Canyon Design Center   
   >Lunatic Fringe Electronics   
      
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