From: "Sir Charles W. Shults III"
Subject: Re: Laser Question ? HeNe vs Diode
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
Date: Tue, 10 Dec 2002 23:55:42 GMT
NNTP-Posting-Date: Tue, 10 Dec 2002 18:55:42 EST
Organization: RoadRunner - Central Florida
Well, HeNe lasers have many advantages in certain applications. For
instance, there are some semiconductor lasers that are not well polarized or
have strange artifacts in the beam. One artifact is the result of the die
making process, which leaves the output of a solid state laser as a dash line
instead of a dot. This is often not easily seen until you pay close attention
to it, but gas lasers tend to have nice round dots.
The polarization of a gas laser also tends to be much better, since most
have Brewster windows inside the tube. Some semiconductor lasers, in particular
the green types, are not so kind. This is because many of them use an IR laser
diode which is then pumped through a crystal to change the wavelength. This is
indeed true laser light, but the polarization is almost always completely
randomized in the crystal.
Also, the divergence of the beam is not so good for semiconductor lasers.
Gas lasers have a long, narrow bore and can make nicely coherent beams. It all
depends on the technology used, of course, but this is a general rule.
In the end, it will all depend on the application of the laser. Sometimes
you need strongly polarized light, sometimes you need a truly round dot of
light, sometimes you need a tightly collimated beam.
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