From: bill.sloman@ieee.org   
      
   On 14/12/2025 2:23 am, 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?   
      
   The OP is Cursitor Doom. He doesn't seem to want to keep the output   
   power particularly stable - it's more just a matter of monitoring it to   
   keep in a more or less sensible range.   
      
   --   
   Bill Sloman, Sydney   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)