A photoelastic modulator-based birefringence imaging microscope for measuring biological specimens

John Freudenthal; Andy Leadbetter; Jacob Wolf; Baoliang Wang; Solomon Segal

doi:10.1117/12.2071271

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18 November 2014 A photoelastic modulator-based birefringence imaging microscope for measuring biological specimens

John Freudenthal, Andy Leadbetter, Jacob Wolf, Baoliang Wang, Solomon Segal

Proceedings Volume 9268, Optics in Health Care and Biomedical Optics VI; 92680C (2014) https://doi.org/10.1117/12.2071271
Event: SPIE/COS Photonics Asia, 2014, Beijing, China

Abstract

The photoelastic modulator (PEM) has been applied to a variety of polarimetric measurements. However, nearly all such applications use point-measurements where each point (spot) on the sample is measured one at a time. The main challenge for employing the PEM in a camera-based imaging instrument is that the PEM modulates too fast for typical cameras. The PEM modulates at tens of KHz. To capture the specific polarization information that is carried on the modulation frequency of the PEM, the camera needs to be at least ten times faster. However, the typical frame rates of common cameras are only in the tens or hundreds frames per second. In this paper, we report a PEM-camera birefringence imaging microscope. We use the so-called stroboscopic illumination method to overcome the incompatibility of the high frequency of the PEM to the relatively slow frame rate of a camera. We trigger the LED light source using a field-programmable gate array (FPGA) in synchrony with the modulation of the PEM. We show the measurement results of several standard birefringent samples as a part of the instrument calibration. Furthermore, we show results observed in two birefringent biological specimens, a human skin tissue that contains collagen and a slice of mouse brain that contains bundles of myelinated axonal fibers. Novel applications of this PEM-based birefringence imaging microscope to both research communities and industrial applications are being tested.

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John Freudenthal, Andy Leadbetter, Jacob Wolf, Baoliang Wang, and Solomon Segal "A photoelastic modulator-based birefringence imaging microscope for measuring biological specimens", Proc. SPIE 9268, Optics in Health Care and Biomedical Optics VI, 92680C (18 November 2014); https://doi.org/10.1117/12.2071271

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