I am making a polar moke setup and need a non-polarising beam splitter which splits the reflected light but not the incoming one. I would be grateful for any suggestion regarding model number/ type of the component. Thank you.
Why do you want to avoid a splitting of the incoming beam? Is it because of laser intensity?
In general I would use a D-Shaped pickoff mirror instead of a beam splitter to separate the incoming from the reflected light under a small angle or spatial displacement. That way you also can avoid losing degree of polarisation in the reflected light.
Dear Biswajit Sahoo
The reference publication on colour measurement, CIE publication 15:2004, resolves this problem. In order to separate the illuminating and reflecting radiation they recommend integrating sphere 0/8 degree geometry. That is to say by using 0 degree (i.e. normal to the surface) collimated illumination and collimated specular reflectance that is set to return the beam at 8 degrees to one side.
The sample to be measured is presented to a port in the surface of a spherical cavity with an inner surface that is white coated to integrate the reflected light into a uniform colour. This is measured through a separate port. By setting the sample to reflect at 8 degrees to the normal, the specular component of the reflected light exits the sphere via a third (8 degree) port and is thus excluded from the measurement.
The best way to split the beams is to use some kind of mirror and small incidence angles to separate all incoming and outgoing beams., like Paul Seifert and David Oulton have mentioned.
If you can't use small angles for some reason you have to live with the reduced ingoing intensity and possible change in polarisation by the beam-splitter.
Classical optics components will always split all beams, ingoing or outgoing, the same way, if they have the same wavelength and polarisation. What you were looking for is a non-reciprocal optic, like an optical isolator, but I am not aware of any who would work in your case.
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