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Subject: Re: shape of witness sample
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Date: 12/26/01 at 12:22 PM
Posted by: Vladimir Tchoutko
In Reply to: shape of witness sample posted by charlie on 12/19/01 at 3:13 PM:
It is a well known problem. Of course, the spectral parameters depend on the shape of piece (actually on the angle of light incidence). But for relatively simple coatings including the general AR coatings and the pieces with not very big curvature the difference is not catastrofic. So practically always the flat witness is good enough. And besides usually in spectrophotometers we use relatively narrow paraxial beams. To compensate the possible effect of curvature you can place the same but uncoated lense in spectrophotometer reference channel , or to decrease the beam diameter. Try to place your piece ajusting its optical axes with the light beam axes to decrease error.
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