A small rugged interferometer was required for measuring the depletion zones generated in a protein crystal growth experiment. The exploration for an optimum solution yielded an instrument that uses solid optical design techniques, where air is removed from the optical path and replaced with 'solid air' or glass. The interferometer is a Mach-Zehnder configuration with the reference and test arms separated as orthogonal polarization states with a polarization beam splitting cube (PBSC), then recombined by another PBSC, maintaining the orthogonality of the reference and test beam polarizations. An off-the-shelf liquid crystal variable phase plate was sufficient to produce the necessary 2(pi) phase shift. The device was built and tested and shoed excellent performance. The spatial resolution of the interferometer is limited only by the 0.011mm pixels at the 5 by 5 mm detector and the imager is operating at telecentric 1:1 conjugates. Phase resolution, using the Hariharan 5-step algorithm, is measured to be better than (lambda) /50. In this paper, calibration test results are presented and future upgrades are outlined.
Understanding the phenomena of protein crystal growth has become a critical factor in the advancement of fundamental life sciences. To characterize this process, sensitive non-intrusive monitoring systems must be utilized in a micro-gravity environment. We believe detailed optical monitoring to be the superior technique for use in micro-gravity. The proposed approach includes monitoring the nucleation event, rate and form of crystal growth, and protein density variations throughout the cell volume with four different optical metrology methods running concurrently. The system will incorporate photon correlation spectroscopy, interferometry, Zernike phase contrast imagery, and high-resolution polarization microscopy. These four systems have all been combined into a single optical module that provides crystal growth process data. The module utilizes the emerging technologies of binary optics and solid optics to shrink and stabilize the system (patent-pending).
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