🚀 go-pugleaf

From earlier art, ques. re polarization of HeNe lasers can be clarified as
follows:
1--lasers usually run on several longitudinal modes--that is, if 2x cavity
   length is N wavelengths of light at the center of the lasing linewidth,
    there will be output at several adjascent modes at N+1, N-1, N+2, N-2,
     etc, and, unless constrained, adjascent longitudinal modes are
      polarized at right angles to each other (ie, if the even modes are
      vertical, the odd modes will be horizontal).

2--to force all the modes to have a common polarization plane which does
    not wander (see #3--), a polarity sensitive loss device is inserted
     intra-cavity, so lasing will occur at the polarization having the
     least loss.  This is usually done by having a glass plane tilted at
      the Brewster angle inside the cavity.  This reflects away some light
      at some polarization and none at the 'favorable' polarization.

3--without the Brewster element discussed above, the output is a set of
    crossed-polarized outputs which wander in polarization, as the cavity
    length changes with temperature as the laser warms up, etc.  It is
    said to be 'randomly polarized'.
-- 
Charles Pooley                  ckp@netcom.com    GEnie  c.pooley
EE consultant, Los Angeles, CA