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# Diffraction Refractometer

IP.com Disclosure Number: IPCOM000072237D
Original Publication Date: 1970-Jun-01
Included in the Prior Art Database: 2005-Feb-22
Document File: 2 page(s) / 22K

IBM

## Related People

Nafarrate, AB: AUTHOR

## Abstract

When a transmission diffraction grating is placed in a medium that is the same on both of its sides and a beam of light makes normal incidence onto one side, the diffracted angle for the first order is sin theta = lambda/d where d is the granting constant. If the grating is the wall of a cell filled with a medium of different refractive index, the diffracted angle is different and given by combining the above formula with Snell's Law n sin theta = n sin theta,.

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Diffraction Refractometer

When a transmission diffraction grating is placed in a medium that is the same on both of its sides and a beam of light makes normal incidence onto one side, the diffracted angle for the first order is sin theta = lambda/d where d is the granting constant.

If the grating is the wall of a cell filled with a medium of different refractive index, the diffracted angle is different and given by combining the above formula with Snell's Law n sin theta = n sin theta,.

In the drawing, a cell is filled with a medium of index n', where n' is the refraction index desired to be measured and given by n' = (x/x') (square root 1 + (x')/2/) / (square root 1 + x/2/). If l is normalized and the x's are fractions of l, n is the refraction index of vacuum n = 1, or very approximately air.

In the example, medium n' can be a gas or a liquid or a solid sample of length
l. The collimated light beam can be from a laser, but collimated light from any other source can also be used. Lenses can be used to focus the beams over the ground glass screen. The use of white light quickly displays the dispersion properties of the sample. Thus, a grating is used to measure the index of refraction.

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