Re: [ATM] [ ] making Foucault tester

["Bob May" <rmay@nethere.com>]

Yes, that is all true!  But why go out and buy a laser when all
you need is a LED???  You're going to be running the laser diode
in the LED mode anyway!  Not only that, but you've got to get the
laser diode out of the package that it is in and resolder it into
the  the tester the way that you want it to be.  Thge leads on
the laser diode will be small and thus it will be easy to
overheat the diode and destroy it.  Much better to start with the
right stuff to begin with and not have to worry about short leads
of the surfacce mounted laser diode.
There is circuitry in a laser diode pen to keep the laser from
getting too much current - it isn't a simple resistor like a LED
would have but some nicce feedback circuit that keeps the laser
working at a particular power output.  Go too high by a small
fraction of the power necessary and you'll pop that thing in
nothing flat!  Better for the neophyte electronics person to
leave the control of the laser diode alone and do it the simpole
way.
Lastly, I'll note that the divergencce of a laser diode is only
in one direction, that being of the direction of the planar
structure of the diode.  In the perpendicularr direction, the
divergence is not that big.  In addition, the wide divergence
direction, the beam intensity isn't flat but rather quite
gaussian in its intensity slope and you don't want that for doing
the Foucault test as it will give a false reading at the outer
zones of the mirror unless you have the beam exactly pointed at
the mirror so that the light from the laser diode is the same on
both edges of the mirror.
Why do it the hard why when the simple way works better?
Bob May

rmay at nethere.com
http: slash /nav.to slash bobmay
http: slash /bobmay dot astronomy.net


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