[Laser] Re:: heliograph vs. laser indeed!

[Charles Pooley]

Tim Toast <toasty256 at yahoo.com> wrote:
   
  ... IF the laser can
be collimated to 20 microradians (3.8 meter spot). But, it
would require a collimator lens or mirror diameter more
than 1 meter...
  ---------------------------------------------------------
  Diode lasers can (and do in CD drives) produce diffraction limited spots.  So to first approximation, the beamwidth attaniable with a beam expanding telescope would be wavelength/aperture in radians.  At 650 nm, 6.5 cm dia optics will give about 10e-5, or 10 microradians, or about 2 arcsec.
   
  A peculiarity of most diode lasers is the need for a cylindrical element in the optics because the effective point of origin within the chip is different in one plane from that of the other.  Most if not all CD drives have them.
   
  Another way is to use the VESCEL (vertical cavity) lasers, except they are not made in visible wavelength, I think.
   
  In my "microlaunchers(dot)com" site there is an article illustrating a small optical space data link using 7 cm transmitter optics and a 30 mw 650 nm laser.
   
  Charles Pooley       KD6HKU