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Thorlabs Lab Fact: Dove Prisms Alter Polarization State and Image Orientation

We present laboratory measurements of the polarization and rotation state of a beam transmitted through Thorlabs’ PS992 and PS992M Dove Prisms. We also examine the influence of stress-induced birefringence on the final polarization state. In a polarization-dependent experiment, it is important to understand how the polarization and orientation of the input beam is altered by a Dove prism. While it is known that Dove prisms introduce changes in the polarization of the transmitted light [1], we also find that localized stress-induced birefringence can significantly alter the polarization state. Finally we compare theoretical predictions of induced polarization change to the measured polarization change for both our unmounted and mounted versions of Dove prism.

For our experiment we used the HL6320G Laser Diode (635 nm) as the light source. The laser beam was initially aligned using two crossed Glan-Taylor polarizers (GT10-A). The first polarizer set the polarization axis, and the rotation angle of the second crossed polarizer was recorded. The Dove prism was then placed in between the two polarizers, and the power of the beam was recorded after the second polarizer as a function of prism angle. Additionally, measurements were taken to determine the radii and orientation angle of the polarization ellipse. The polarization shift caused by the PS992 unmounted Dove prism and PS992M mounted Dove prism were measured. The unmounted prism was tested for polarization changes due to birefringence effects as well.

The figure to the top right summarizes the measured results for image orientation as a function of prism angle. While it is well known that Dove prisms are used to invert images, it is interesting to note that the image rotation angle is twice that of the prism rotation angle. The figure to the bottom left summarizes the results of stress-induced birefringence on polarization state, while the figure to the bottom right summarizes the effects a Dove prism has on the polarization state and compares that to the theoretical values. Data is presented for both the unmounted and mounted Dove prisms with minimal stress. While Dove prisms do rotate the image, the polarization does not rotate with the image. Rather, the polarization is transformed from linear to various degrees of elliptical. For details on the experimental setup employed and the results summarized here, please click here.

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[1] Miles J. Padgett & J. Paul Lesso, "Dove prisms and polarized light," J. Mod. Opt. 46, 175-179 (1999).