Current Laboratory Projects

Polarimetry

Research is ongoing in the areas of imaging polarimetry and imaging spectropolarimetry. A rotating-retarder imaging polarimeter for the 3-5 micron region of the infrared spectrum has been built. The instrument incorporates a form-birefringent achromatic retarder. The retarder was fabricated with a retardance of approximately 132 degrees, which we have found to be optimal with respect to noise immunity. A method of calibration of the system using known inputs from a polarization state generator has been demonstrated, and continuing efforts will emphasize its full-scale implementation.

The Poincaré Sphere is used for teaching and understanding polarization.

We are also investigating methods of making the system agile, in the sense of reducing the number of raw measurements required for its operation and allowing it to be tailored at the time of the measurement for sensitivity to any prescribed target polarization. The rotating-retarder polarimeter provides a test bed for demonstrating and refining these techniques.

Spectrometry

A concurrent program of research features the design and construction of snapshot imaging spectropolarimeters. These instruments use thick (high order) retarders to encode the spectral dependence of each Stokes vector component into a single irradiance spectrum via sideband modulation. The spatially-resolved spectrum can then be captured with snapshot capability by the Computed Topography Imaging Spectrometer or CTIS. Prototype systems for the visible and infrared portions of the spectrum are underway.

3-D LADAR Imaging

The 3-D Imaging Lab is exploring techniques to combine snapshot imaging spectroscopy with 3-D Laser RADAR (LADAR). A system to incorporate a spectrometer with a LADAR system to produce contiguous spectral images is under development.

Images produced by this instrument will contain information in three spatial dimensions (x, y and z), and in wavelength dimension, (l). Full spatial image reconstruction is expected along with a 30-band spectral sampling. This work is applicable in spectral target recognition for civil, industrial, and military applications. This research is moving towards the concept of 4-D imaging, with x, y, z, and λ as dimensions as a function of time.

The image at left was taken with a laser radar camera operating at a wavelength of 857 nm.