Re: [ATM] Star test with pin hole

[Jarvis Krumbein <jkoptic@juno.com>]

A laser diode when used in a non-lasing mode (supply voltage less than
required for lasing) will appear as a very narrow slit and makes a good
source for a Focault test.  For the "Star"test you are trying to do with
a light source at a great distance from the mirror a bright stellar
appearing source must be used.  A good rule of thumb is to seperate the
mirror and the source about 100 X the focal length of the mirror apart. 
At the Bellingham Optics Workshop a couple of years ago, a convex mirror
was mounted on a wall at about 1000' distance.  This was then illuminated
with a fairly powerful laser and was used as a source for comparison
tests on several mirrors.  On occassion, I've used a very bright mercury
vapor lamp on a house several miles away across the Case Inlet on Puget
sound.  This is OK for null testing with a knife edge or Ronchi grating. 
A conventional LED (non-lasing type) does not produce a compact light
source.

Jarvis Krumbein

On Sat, 24 Jul 2004 19:05:21 -0500 "Ray@J-Engineering.com"
<Ray@J-Engineering.com> writes:
> Vladimir,
> I have used a non lasing laser diode before but have not removed the 
> 
> lens. See http://www.j-engineering.com/ATM for bench testing a 
> sphericalish mirror.  I should try it in this application with lens 
> removed.  Are you suggesting the source should or must appear 
> stellar?
> 
> Vladimir Galogaza wrote:
> 
> >It was said that laser diode is extremely small light source
> >when lens is removed. If I remember well it is in micron order  of 
> size
> >(light emitting region). Archives should have it.
> >
> >Vladimir.
> >
> >
> >
> >_______________________________________________
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> >
> >
> >  
> >
> 
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