Re: interference question

[John Denker <jsd@MONMOUTH.COM>]

At 06:20 AM 9/12/99 -0400, Robert A Cohen wrote:
>  Perhaps you can extend this discussion to why light from two
> separate lasers does not produce an interference pattern, even though both
> sources are independently coherent.

Good question.  I was wondering if anybody would pick up on that.

> correct?

Actually, depending on details, it may not be correct to assume that.

I once helped build a widget that locked a dye laser to an absolute
frequency plus or minus a megahertz (out of 600 terahertz). Two independent
lasers locked like that produce an interference pattern that changes "only"
a million times per second, which can easily be observed using simple
detectors.  I would have to reword the part of my previous post that talks
about using human eyes as the front-end detectors, but otherwise it's true:
 you can have interference between independent sources.

My previous post spoke of a phase difference;  here I am speaking of a
frequency difference, which is just a phase proportional to time.

OK?