Re: The cost to make a laser

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From: Tucker Hiatt (hiattu00@usfca.edu)
Date: Mon Apr 22 2002 - 21:02:22 PDT 

Message-Id: <a05100308b8ea3048e2f0@[12.236.121.220]>
Date: Mon, 22 Apr 2002 21:02:22 -0700
From: Tucker Hiatt <hiattu00@usfca.edu>
Subject: Re: The cost to make a laser

I'll venture some hypotheses regarding why the SkyPointer beam is
visible in the night sky:

1) Unless a laser beam shines directly in your eye, you see only the
light that scatters off particles in the beam path; that's what
makes the beam visible. We know that air molecules (diatomic
nitrogen, in particular?) preferentially scatter high frequency light
-- that's why the sky is blue. Perhaps the SkyPointer's green beam
has high enough frequency to scatter better off the nitrogen
molecules than does the low frequency red light of other laser
pointers.

2) The SkyPointer is a bit more intrinsically powerful than most
hand-held lasers. Its seller, Howie Glatter, says: "The laser power
output is guaranteed between 3 and 5 milliwatts, typically 4mW."
Most laser pointers that I know of advertise a power of 3 mW. [By
the way, that's 4 millijoules per second, which is relevant for my
next point...]

3) Mr. Glatter also says, "When the SkyPointer is on, the beam
pulses on and off at about 1000 Hz, at about a 75% duty cycle." A
75% duty cycle means that those 4 millijoules are actually spread
over 0.75 seconds, not one full second. That boosts the true,
visible power by 33% to 5.3 mW, I believe.

4) The human eye is (slightly?) more sensitive to green light than
to any other color.

Perhaps all these facts conspire together to make the SkyPointer so
nicely visible in the night sky. But I'd sure like to know if others
agree with these hypotheses. I wonder, too, which factor is most
important. My money is on #1.

- Tucker

At 12:20 AM -0700 4/22/02, Pinhole wrote:
>
>Subject: Re: pinhole Re: The cost to make a laser
>From: "Algis Sodonis" <asodonis@urbanschool.org>
>Date: Sun, 21 Apr 2002 21:46:01 -0700
>
>Can anyone try to explain the physics of the skypointer? How should
>it be able to have a more visilbe beam than any other laser?
>
>Algis Sodonis 

-- 
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Tucker Hiatt, Director
Wonderfest
P.O. Box 887
(39 Fernhill Avenue)
Ross, CA  94957
hiattu00@usfca.edu
415-577-1126 (voice)
415-454-2535 (fax)
http://www.wonderfest.org

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