Real-time frequency-encoded spatiotemporal focusing through scattering media using a programmable 2D ultrafine optical frequency comb

Abstract

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.

Towards smart optical focusing: deep learning-empowered dynamic wavefront shaping through nonstationary scattering media

“…5(a)-5(c), under circumstances without sudden disturbance, the PBR target can always be reached after fine-tuning using the adaptive recursive algorithm (gray line), while the traditional algorithm (red line) never reaches the target. In these circumstances, the adaptive recursive algorithm always shows much better GFP (17)(18)(19)(20)(21)(22)(23)(24)(25) than traditional algorithm results (8)(9)(10)(11)(12)(13)(14)(15)(16)(17). As seen from Fig.…”

“…Time reversal methods, such as time-reversed ultrasonically encoded (TRUE) method [17] and time reversal of variance encoded light (TROVE) [18], take advantage of guide stars (e.g., focused ultrasonic modulation) to encode diffused light; then, only the encoded light is time-reversed and focused inside the scattering medium. Precompensated wavefront shaping techniques modulate the phases of light incident into the scattering medium based on the measurement of the transmission matrix [8,10,11,[19][20][21] or the maximization of feedback provided by the optical [7,[22][23][24][25] or photoacoustic signal strength [2], with a goal to pre-compensate for the scattering-induced phase distortions. As for the memory effect, image information is encoded in the autocorrelation of the measured speckles as long as the imaging area is within the memory effect regime, and thus images can be reconstructed from speckles with iterative phase retrieval algorithms [1,[26][27][28][29].…”

Nonlinear field-control of terahertz waves in random media for spatiotemporal focusing

“…Recent works have shown that the intrinsic coupling between spatial and temporal dimensions in scattering media can be leveraged to manipulate the temporal properties of pulses by controlling the spatial features of the illumination 28,29 . As a result, spatial wavefront shaping can be applied to achieve spatiotemporal focusing, corresponding to a simultaneous focusing in space and pulse re-compression in time, either through iterative approaches or by measuring the frequency-dependent transmission matrix of the sample 21,[30][31][32] . These approaches have shown how to control the envelope of the transmitted waveform successfully (e.g., to adjust the centre of the transmitted pulse [32][33][34][35] ), but they remain unsuitable for manipulating the carrier-wave properties (e.g., the carrier-envelope offset of the transmitted pulse).…”

Fast holographic scattering compensation for deep tissue biological imaging

“…These methods aim at finding correction patterns from a series of test measurements. Despite usually being slower, recent developments have enabled impres-sively fast corrections on the order of a millisecond and below using acousto-optic light modulation [36,37].…”

“…However, as imaging depths increase, so does the complexity of the wavefront scrambling, and full wavefront compensation can easily overburden the possibilities of any correction technique. The demonstration that cor-recting even a small fraction of the aberration can yield a 55 single, strongly amplified speckle which acts as an imag-sively fast corrections on the order of a millisecond and below using acousto-optic light modulation [36,37].…”