[Laser] Kerry Bank's question re lamp modulation

[Charles Pooley]

There are problems replying to this forum (not others I reply to)
   
   
  Kerry Banke  wrote:
   
>As part of the experiment in communicating using fluorescent and HPS 
>lamps, I am interested in which lamps have the greatest depth of 
>modulation...
   
   
  It will be easier to understand  the issue if you classify lamps as 
to light production mechanism.
   
  Incandscent (halogen) radiates, and the power varies with 4th power 
of temperature, and the visible portion more than that because the peak 
of emission is below visible wavelengths.  Maximum bandwidth can be had 
with a ling thin straight wire filament, so the power divided by the 
mass of filament is highest.  I'd read thet the straight filament lamps 
used for movie projector sound tracks were good to 400 Hz or so.
   
  Fluorescent uses a phosphor, the fluorescence persistance being the 
dominant process limiting bandwidth.  BW can be improved by choice of 
phosphor.
   
  Arc lamp bandwidth will depend on deionizatiuon of the fill gas and 
any significant lifetime of the emitting component of the plasma.  
Probably the maximum BW would be from use of a wall cooled narrow lamp.
   
  Non-phosphor (not white) LEDs are the champ in BW.  Over 10s to 100's 
of MHz being available.  If you do use a white one, the blue part of 
the spectrum will moduate with high BW, but the phosphor will not.  A 
blue filter for the detector will fix that.
   
  Charles Pooley    KD6HKU          www(dot)microlaunchers(dot)com
   
  (this forum doesn't accept any html)  this is 4th attempt to send