Re: [CAD_CAM_EDM_DRO] re: Re: re:Re: Interferometer designs for DRO or servo control?

Elliot Burke wrote:

>Jon,
>Short coherence length of laser diodes was true for the first visible laser
>diodes I measured 5 years ago or so, the 670 nm ones.
>
>When they switched to 650 nm a few years ago (for DVD?) the design was
>changed, and now the coherence length is quite long. There are articles in
>the optics testing literature of people making measurements with several
>meters of optical path difference with these newer (but still cheap!)
>diodes.
>
>I have used them up to about 300 mm path difference with no reduction in
>fringe contrast.
>
>
>

Very interesting! Well, I guess I'm behind the times! I have used a
670 nM L.D.
in a photoplotter, but never tried any interferometer setups with them.

Jon