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Re: combining laser beams



Note: In the old days of HeNe LASERs the cavity was external to the
discharge tube. Simply by removing the tube from the cavity it is then an
amplifier instead of an oscillator.

Adjusting such an oscillator (aligning the mirrors parallel and
perpendicular to the tube's axis) is a "bear". Not so with a ruby
cylinder. I once was puzzled why the trace of the decay of the output
disappeared from the 'scope. It was lasing!; the photo tube's window was
acting as one end of the cavity.

bc who built the piezo electric driven FTIR prism for the first LASER
ranger (under the direction of its inventor, ca.1962)



John Gastineau wrote:


herbgottlieb@JUNO.COM 12/12/02 08:09AM >>>
On Wed, 11 Dec 2002 21:25:39 -0500 Ludwik Kowalski
<kowalskil@MAIL.MONTCLAIR.EDU> writes:
I forgot to add the obvious, the "amplifier" must received
energy to populate excited levels. I suppose this can
be done with visible non-coherent light.

Please explain a possible mechanism by which non-coherent
light can provide the energy to to populate ther excited levels
Has it ever been done already? If so, where can I find out
more about it?



A ruby laser uses flashlamps to create the population inversion, so
this has been done long ago.

Note that a laser amplifier is relatively easy to make--it is just the
optical medium with a population inversion and no optical cavity. You
pass a low power beam through the medium, and stimulated emission takes
place. In a very crude sense, you're cloning the photons of the original
beam, so the beam quality at the output is similar to that of the input.

There are advantages to using a low-power laser (called the oscillator)
and a stage or three of amplification, instead of a strongly-pumped
laser consisting of only the oscillator (optical medium with inversion
surrounded by an optical cavity, a.k.a., the mirrors).

J Gastineau