Using an autocollimator to align 4f systems

Johnstone, Graeme and Patton, Brian (2022) Using an autocollimator to align 4f systems. FocalPlane (29 Jun). (

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Modern microscope systems comprise many optical elements with precise alignment tolerances. As such, as the complexity of the system increases, the challenge to align them rapidly becomes a major hurdle to implementing home-built designs. One recurring problem is the ability to chain active elements (deformable mirrors, scanning devices, spatial light modulators) in such a way that they are all imaged at conjugate planes. A misalignment of one element can propagate through the system, adding significant aberrations to the overall image. An autocollimator is a very useful tool for a number of applications in an optics laboratory. We use a home built autocollimator that was designed outside our group, by the people behind the openRAMAN project. This instrument is built from standard optical components and the referenced pages give some further examples of typical applications. While the discussion of autocollimator usage often highlights the ability to measure small angle deviations in an optical path, the ability to measure the focal length of a lens in situ is particularly useful when building and aligning 4f systems in microscopes and other complex imaging experiments. The autocollimator used in the examples and is very similar to the design specified in the aforementioned links. In the Supplemental Note , we present a list of the Thorlabs parts that are used in our autocollimator. We have found it to be such a useful and easy to use apparatus that we keep it permanently constructed, aligned and ready to use.