Real-time frequency-encoded spatiotemporal focusing through scattering media using a programmable 2D ultrafine optical frequency comb
Optical wavefront shaping is a powerful tool for controlling photons in strongly scattering media. Its speed, however, has been the bottleneck for in vivo applications. Moreover, unlike spatial focusing, temporal focusing from a continuous-wave source has rarely been exploited yet is highly desired for nonlinear photonics. Here, we present a novel real-time frequency-encoded spatiotemporal (FEST) focusing technology. FEST focusing uses a novel programmable two-dimensional optical frequency comb with an ultrafine linewidth to perform single-shot wavefront measurements, with a fast single-pixel detector. This technique enables simultaneous spatial and temporal focusing at microsecond scales through thick dynamic scattering media. This technology also enabled us to discover the large-scale temporal shift, a new phenomenon that, with the conventional spatial memory effect, establishes a space-time duality. FEST focusing opens a new avenue for high-speed wavefront shaping in the field of photonics.
© 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC). Submitted 21 May 2019; Accepted 3 December 2019; Published 19 February 2. We thank HC Photonics for providing the PPLN crystal oven, H.-C. Chui for discussion on the frequency doubling, H. Mikami for insightful discussion on the AOD operation, and Y. Li for preparing the animation illustration of the principle. Funding: Funding was provided by Local Innovative and Research Teams Project of Guangdong Pearl River Talents Program No. 2017BT01X137, China, and NIH grant nos. DP1 EB016986 (NIH Director's Pioneer Award) and R01 CA186567 (NIH Director's Transformative Research Award). Author contributions: X.W. and Y.S. designed the system. X.W. built the system and conducted the experiments. Y.S. theoretically analyzed and optimized the 2D-OFC. J.C.J. programmed the control system and user interface. A.S.H. initiated the GPU processing system and the use of orthogonal AODs for frequency-encoded wavefront measurement. C.Y., S.X., and Z.Y. designed, built, and characterized the ultranarrow linewidth fiber laser system. Z.Y. and L.V.W. supervised the project. All authors wrote the manuscript and commented on it. Competing interests: X.W., Y.S., J.C.J., and L.V.W. have a provisional patent application entitled "Frequency-encoded spatiotemporal (FEST) focusing", US Provisional 62/817,415, through the California Institute of Technology, Pasadena, CA. The other authors declare that they have no competing interests. Data and materials availability: All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.
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