Optical Coherence In All the Right (and Wrong) Places (hosted by FIP Faculty Dr. Adam Wax)

This Optics Seminar is hosted by our FIP faculty member, Dr. Adam Wax, Theodore Kennedy Professor of Biomedical Engineering.

The spatial and temporal coherence of optical fields are basic properties that have been successfully exploited in biomedical optics. For example, the short temporal coherence of broadband light is used by optical coherence tomography (OCT) to measure distances between scatterers and interfaces in biological tissue. OCT can perform ultrasound-like, cross-sectional, micron-scale imaging, finding utility from clinical medicine to developmental biology. However, coherence properties can have their downsides. As was recognized shortly after its invention, laser light has a high degree of spatial coherence, leading to speckle in images of rough surfaces. Speckle generally degrades image quality. Thus, designing laser sources with decreased spatial coherence has the potential for speckle-free laser imaging.

In my talk I will discuss two areas of research in my lab. First, I will discuss our work using OCT to characterize the microfluidic-scale physiology of cilia-driven fluid flow. Cilia are motile cellular organelles that generate fluid flow across different surfaces. Cilia are responsible for the directional flow of respiratory mucus, and defects in cilia lead to recurrent respiratory infections. We recently used OCT to perform quantitative cilia-driven flow velocimetry in Xenopus embryos (tadpoles), an important animal model in cilia research. We also have used insights gained from OCT imaging of cilia-driven fluid flow to design new quantitative imaging methods for characterizing cilia performance. Second, I will discuss our recent work into the coherence properties of random lasers. Random lasers exploit the light-confining properties of scattering media to generate laser light at many randomly-oriented spatial modes. While the temporal coherence of random lasers are understood, their spatial coherence has been poorly characterized. Our recent work shows that random lasers can have low spatial coherence, in contrast to the high spatial coherence of traditional lasers. I will discuss this work and its implications for imaging using laser light.