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From: jwl@ernie.Berkeley.EDU (James Wilbur Lewis)
Newsgroups: comp.graphics
Subject: Re: Ray tracing refraction
Message-ID: <27839@ucbvax.BERKELEY.EDU>
Date: 31 Jan 89 08:50:01 GMT
References: <0XryqWy00Uo1875Ud-@andrew.cmu.edu> <101880003@hpcvlx.HP.COM>
Sender: usenet@ucbvax.BERKELEY.EDU
Reply-To: jwl@ernie.Berkeley.EDU.UUCP (James Wilbur Lewis)
Organization: University of California, Berkeley
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In article <101880003@hpcvlx.HP.COM> tomg@hpcvlx.HP.COM (Thomas J. Gilg) writes:
>Question : is the index of refraction linear with repect to the
>wavelength ?  I started writting a ray tracer and took liberty in
>assuming linear response.  Any experts out there ?

No, it's not linear.  There's a table in Fundamentals of Physics 
(Halliday and Resnick) giving the index of refraction of fused quartz
at various wavelengths.  Between 300 and 800 nm  the index varies
somewhat like 1/(lambda - some constant), with an index of 1.48 at around 
350 nm dropping off to about 1.452 at 800 nm.  The curve probably doesn't 
extrapolate; I would expect a strong dependence on the crystalline structure 
of the medium, discontinuities corresponding to bandgap boundaries, and other
nasty stuff.  

A linear approximation over the visible range probably wouldn't be
too bad, though.

-- Jim Lewis
   U.C. Berkeley