Optics


Much of our student-centered research involves optical polarization. Polarization describes the vector nature of light—the direction in which a light wave vibrates. It adds a tremendous amount of information about light-matter interactions that is not provided by the more common measurements of wavelength and intensity. Most light is at least partially polarized, and this polarization usually changes when light undergoes scattering, reflection, or transmission. Polarimeters are used to quantify these changes. We have several commercial polarimeters along with a number of custom ones built by undergraduate students. We use polarized light in applications that are relevant to fundamental physics, biology, medicine, chemistry, geology, environmental sensing, and engineering.

In addition to polarimetry, we use optical tweezers to manipulate and quantify the motion of micron-sized objects. Students in the Optics class (PHYS 347) build their own optical tweezers from scratch to trap polystyrene microspheres, measure the laser trap strength in piconewtons, and use circularly polarized light to cause calcite microcrystals to spin via angular momentum transfer. These classroom experiments train students for subsequent research projects with professional-grade optical tweezers, often involving biological and biomedical applications.

Some of our recent and upcoming research includes

  • using optical tweezers to measure the mechano-biological activity of leukemia cells
  • polarimetric and spectral analysis of butterfly wings and scarab beetle exocuticles
  • polarimetric analysis of ferrofluids in static and dynamic magnetic fields
  • Stokes vector imaging of nebulae and the solar corona
  • sensitive detection of chiral molecules such as glucose in microliter samples using polarimetry and refractometry
  • polarimetric detection of targets immersed in turbid media
  • image enhancement of simulated skin lesions with polarized light
  • analysis of evanescent waves and the polarization-dependent Goos-Hänchen shift
  • studies of optical depolarization and polarization entropy
  • Mueller matrix characterization of common and novel optical elements and instruments
  • construction of simple, inexpensive versions of optical instruments to make them more accessible to small physics departments (e.g., photoelastic modulators, Stokes and Mueller-matrix polarimeters, optical tweezers)

At the core of our research are several professional-quality polarimeters and optical tweezers, many of which are highlighted in the pages of this pdf:

Primary Optical Instruments Used by the UST Physics Department

If you need assistance with a polarimetry application, we might be able to help.  Please email Adam Green at asgreen@stthomas.edu.

We gratefully acknowledge the National Science Foundation, the 3M Company, the Imation Corporation, Axometrics, Inc., the University of Minnesota, and the University of St. Thomas for funding, equipment donations, generous educational discounts in purchasing, and professional collaborations and consultations.