Day 1 continued: Learning to See Through Walls
David Norris
These tantalizing scenarios were among many presented during today’s meeting. Though the focus remains on developing non-invasive deep imaging techniques for biological tissue, in particular using cameras and modulators placed only on the front side of a sample, the discussion also addressed more general questions on the theoretical limits of beam control and applications of scattering media to wide-field sensing.
Nearly all the strategies for achieving high-resolution imaging involve tailoring the excitation waveform to the given system’s scattering matrix, the complex amplitudes connecting input and output modes. Some techniques measure this matrix explicitly, in transmission or reflection; others use photo-acoustic interaction or phase conjugation (time-reversal) to find the right combination of input modes. One important element still being weighed is the use of digital versus analog phase conjugation, with the former providing complete control of the waveform and intensity, and the latter a higher resolution and faster response time.
A complementary approach is to extract image information from the coherence properties of light, including higher-order statistical moments. Ori Katz presented new work influenced by stellar speckle interferometry, in which a diffraction-limited image is recovered via autocorrelation and inverse Fourier transform without the need for adaptive optics. Other strategies include creating input pulses with particular statistical properties, or modulating the spatial coherence of the excitation light to probe correlation lengths in the sample. These techniques can also work at the single quantum level, opening the door to secure quantum authentication algorithms based on spatial keys.
More later as the Incubator meeting concludes, and we take a look at the outlook and next steps for this emerging field.
