How to make a grating?

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Updated: 2005-03-28 by HoloM (the god)
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Peter

How to make a grating?

Post by Peter »

Hi group,

I would like to make a simple grating. As far as I know I only need
a splitted colimated beam where the number of lines/mm is controlled by
the angle of the two beams.

Does anybody know how to calculate that angle for a given number of lines/mm using a HeNe Laser?`

Thank you

Peter
Dinesh

How to make a grating?

Post by Dinesh »

The easiest geomotry is to angle a mirror next to the plate, ie put the mirror next to the plate so that the mirror can "hinge" at the plate.
If you use the standard geometry with one beam hitting the plate at right angles and the other coming in from the same side at an angle theta as measured from a line perpendicular to the plate (The 'plate normal'), then, using a wavelength lambda, the line spacing, d (mm/line), is given by
lambda = d*sin(theta)
If you measure the angle of the beam from the plate and not the plate normal, then
lambda = d*cos(theta)
If neither of the beams is coming in at right angles to the plate then if one beam comes in at theta from above plate normal and the other at phi from below it,
lambda = d*(sin(theta) - sin(phi))
Be careful that you don't calculate (sin(theta-phi))
Again, if the angles are measured from the plate and not the plate normal
lambda = d*(cos(theta)-cos(phi))
To get the spatial frequency, simply invert d. Spatial frequency (lines/mm), f, is
f = 1/d
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