Browsing by Author "Hsu, C. W."

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Open Access
Customizing the angular memory effect for scattering media
(American Physical Society, 2021-07-15) Yılmaz, Hasan; Kühmayer, M.; Hsu, C. W.; Rotter, S.; Cao, H.
The memory effect in disordered systems is a key physical phenomenon that has been employed for optical imaging, metrology, and communication through opaque media. Under the conventional memory effect, when the incident beam is tilted slightly, the transmitted pattern tilts in the same direction. However, the “memory” is limited in its angular range and tilt direction. Here, we present a general approach to customize the memory effect by introducing an angular memory operator. Its eigenstates possess perfect correlation for tilt angles and directions that can be arbitrarily chosen separately for the incident and transmitted waves, and can be readily realized with wave front shaping. This work reveals the power of wave front shaping in creating any desired memory for applications of classical and quantum waves in complex systems.
Open Access
Delivering broadband light deep into diffusive media
(IEEE - Institute of Electrical and Electronics Engineers, 2023-09-04) McIntosh, R.; Bender, N.; Yamilov, A.; Goetschy, A.; Hsu, C. W.; Yılmaz, Hasan; Cao, H.
Waves propagate diffusively through disordered media, such as biological tissue, clouds, and paint, due to random scattering. Recent advances in optical wavefront shaping techniques have enabled controlling coherent light propagation in multiple-scattering samples. We overcome wave diffusion to deliver optical energy into a target region of arbitrary size and shape anywhere inside a strong-scattering system. This is particularly important for applications such as photoacoustic microscopy and optogenetics, where light needs to be deposited deep into biological tissue. For monochromatic light, we previously introduced the deposition matrix (DM) Z(ω) , which maps its input wavefront to the field distribution in the target region. The eigenchannel with the largest eigenvalue provides the wavefront for maximal energy delivery. Since the enhancement is achieved via constructive interference of scattered waves, the optimal wavefront will vary with input wavelength.
Open Access
Depth-targeted energy delivery deep inside scattering media
(Nature Research, 2022-01-27) Bender, N.; Yamilov, A.; Goetschy, A.; Yılmaz, Hasan; Hsu, C. W.; Cao, H.
Diffusion makes it difficult to predict and control wave transport through a medium. Overcoming wave diffusion to deliver energy into a target region deep inside a diffusive system is an important challenge for applications, but also represents an interesting fundamental question. It is known that coherently controlling the incident wavefront allows diffraction-limited focusing inside a diffusive system, but in many applications, the targets are significantly larger than a focus and the maximum deliverable energy remains unknown. Here we introduce the ‘deposition matrix’, which maps an input wavefront to the internal field distribution, and we theoretically predict the ultimate limit on energy enhancement at any depth. Additionally, we find that the maximum obtainable energy enhancement occurs at three-fourths the thickness of the diffusive system, regardless of its scattering strength. We experimentally verify our predictions by measuring the deposition matrix in two-dimensional diffusive waveguides. The experiment gives direct access to the internal field distribution from the third dimension, and we can excite the eigenstates to enhance or suppress the energy within an extended target region. Our analysis reveals that such enhancement or suppression results from both selective transmission-eigenchannel excitation and constructive or destructive interference among these channels.