Re: green laser question

[Herbert H Gottlieb <herbgottlieb@JUNO.COM>]

On Thu, 13 Apr 2000 11:36:17 -0600 Larry Smith <Larry.Smith@SNOW.EDU>
writes:
> Can Helium-Neon be made to lase at other than the usual wavelength?
>
> Thanks,
> Larry

If you look at a neon sign through a diffraction grating or spectroscope
you will
notice bright lines of red, yellow, green, and blue. (Neon also has a
bright infra-red
line but our eyes are insensitive to infra-red).  To produce a green
laser beam
from HeNe gas, the thin-film mirrors at the ends of the laser tube are
coated with
a very thin layer of titanium oxide that is one-quarter the wavelength of
the
green light coming from the neon gas. The mirrors are also coated with
thin films that are half the wavelength of infra-red, red, yellow, and
the blue light from the neon.

At the present time off-the-shelf helium-noen lasers that produce red,
yellow, blue, or green
beams are available.   Those that produce red beams are much cheaper than
the others because the end mirrors are much less complicated to coat with
thin films.

Herb Gottlieb from New York City
(Where tourists with diffraction gratings admire the colors from the neon
lights on Broadway)