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From: email@example.com (Bill Sloman)
Subject: Re: current source for array of infrared leds
Date: 5 Dec 2002 19:44:26 -0800
References: <firstname.lastname@example.org> <4PMG9.email@example.com> <firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org> <email@example.com>
NNTP-Posting-Date: 6 Dec 2002 03:44:26 GMT
Tony Williams wrote in message news:<firstname.lastname@example.org>...
> In article ,
> Winfield Hill wrote:
> > Tony Williams wrote...
> > > Wavelength drift can be pure hell if the IR is going
> > > through water, because water has a series of deep
> > > (steep-sided) attenuation notches.... smack bang in
> > > the 850nm to 950nm region. Been there. :-(((((
> > Tony, kindly point us to some detailed plots, if you can.
> I last saw the graph in 1982 Win, after weeks of
> struggling to find out why my water turbidity
> meter was so unstable. But yes, it was a graph
> of optical transmission through water, versus
> frquency, over the range of about 800-1200nm,
> showing a series of attenuation notches.
> I have posted something about this before, and
> Bill Sloman muttered something about the effect
> being caused by hydroxyl ions (or something).
> I'll cc this post to Bill to see if he can come
> up with an authoritive reference.
Whne I was seriously into the infra-red absorbtion spectra of
inorganic compounds - back in 1964-5 - the authoratitive reference was
Nakamoto. Amazon seems to have a much later edition - at vast expense
Infrared and Raman Spectra of Inorganic and Coordination Compounds (2
Volume Set) by Kazuo Nakamoto. John Wiley & Sons; ISBN: 0471194069;
5th Rev up edition (August 1997.
In any good university library nearby - MIT and Harvard should qualify
The wavelengths in question are hydrogen-oxygen stretches, but I
wouldn't have expected to see any fine structure in liquid water. The
fine structure I was taught about was due to the coupling between the
rotational modes of the water molecule (at microwave frequencies) and
the stretching modes you are looking at at around a micron, and I'd
have expectd that to be smeared out in a condensed phase.
Bill Sloman (Nijmegen - but I won't be back there until Sunday)
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