Highly sensitive and broadband ultrasound detection is important for photoacoustic imaging, biomedical ultrasound, and ultrasonic nondestructive testing.

Highly sensitive and broadband ultrasound detection is important for photoacoustic imaging, biomedical ultrasound, and ultrasonic nondestructive testing. The elasto-optical refractive index modulation induced by ultrasound arouses a transient phase shift of a probe beam. Highly sensitive phase detection with a high Q factor resonator is desirable to visualize the ultraweak transient ultrasonic field. However, current phase-sensitive ultrasonic detectors suffer from limited bandwidth, mutual interference between intensity and phase, and significant phase noise, which become key to limiting further improvement of detection performance. We report a phase-sensitive detector with a bandwidth of up to 100 MHz based on dual-comb multiheterodyne interferometry (DCMHI). By sensing the phase shift induced by the ultrasound without any resonators in the medium, the DCMHI boosted the phase sensitivity by coherent accumulation without any magnitude averaging and extra radio frequency amplification. DCMHI offers high sensitivity and broad bandwidth as the noise-equivalent pressure reaches 31 mPa / √Hz under 70 MHz acoustic responses. With a large repetition rate difference of up to 200 MHz of dual comb, DCMHI can achieve broadband acoustic responses up to 100 MHz and a maximum possible imaging acquisition rate of 200 MHz. It is expected that DCMHI can offer a new perspective on the new generation of optical ultrasound detectors.show less

In light-sheet fluorescence microscopy, the axial resolution and field of view are mutually constrained. Axially swept light-sheet microscopy (ASLM) can d

In light-sheet fluorescence microscopy, the axial resolution and field of view are mutually constrained. Axially swept light-sheet microscopy (ASLM) can decouple the trade-off, but the confocal detection scheme using a rolling shutter also rejects fluorescence signals from the specimen in the field of interest, which sacrifices the photon efficiency. Here, we report a laterally swept light-sheet microscopy (LSLM) scheme in which the focused beam is first scanned along the axial direction and subsequently laterally swept with the rolling shutter. We show that LSLM can obtain a higher photon efficiency when similar axial resolution and field of view can be achieved. Moreover, based on the principle of image scanning microscopy, applying the pixel reassignment to the LSLM images, hereby named iLSLM, improves the optical sectioning. Both simulation and experimental results demonstrate the higher photon efficiency with similar axial resolution and optical sectioning. Our proposed scheme is suitable for volumetric imaging of specimens that are susceptible to photobleaching or phototoxicity.show less

Since the discovery of topological insulators, topological phases have generated considerable attention across the physics community. The superlattices in

Since the discovery of topological insulators, topological phases have generated considerable attention across the physics community. The superlattices in particular offer a rich system with several degrees of freedom to explore a variety of topological characteristics and control the localization of states. Albeit their importance, characterizing topological invariants in superlattices consisting of a multi-band structure is challenging beyond the basic case of two-bands as in the Su–Schreifer–Heeger model. Here, we experimentally demonstrate the direct measurement of the topological character of chiral superlattices with broken inversion symmetry. Using a CMOS-compatible nanophotonic chip, we probe the state evolving in the system along the propagation direction using novel nanoscattering structures. We employ a two-waveguide bulk excitation scheme to the superlattice, enabling the identification of topological zero-energy modes through measuring the beam displacement. Our measurements reveal quantized beam displacement corresponding to 0.088 and -0.245, in the cases of trivial and nontrivial photonic superlattices, respectively, showing good agreement with the theoretical values of 0 and -0.25. Our results provide direct identification of the quantized topological numbers in superlattices using a single-shot approach, paving the way for direct measurements of topological invariants in complex photonic structures using tailored excitations with Wannier functions.show less

An ultrathin angle-insensitive color filter enabling high color saturation and a wide color gamut is proposed by relying on a magnesium hydride-hydrogenat

An ultrathin angle-insensitive color filter enabling high color saturation and a wide color gamut is proposed by relying on a magnesium hydride-hydrogenated amorphous silicon (MgH₂-a-Si:H) lossy dielectric layer. Based on effective medium theory, the MgH₂-a-Si:H layer with an ultrathin thickness can be equivalent to a quasi-homogeneous dielectric layer with an effective complex refractive index, which can be tuned by altering the thickness of MgH₂ to obtain the targeted value of the imaginary part, corresponding to the realization of high color saturation. It is verified that the proposed color filter offers highly enhanced color saturation in conjunction with a wide color gamut by introducing a few-nanometer thick MgH₂ layer. As the MgH₂-a-Si:H layer retains the advantages of high refractive index and tiny thickness, the proposed color filter exhibits large angular tolerance up to ±60°. In addition, MgH₂ with an unstable property can interconvert with Mg under a dehydrogenation/hydrogenation reaction, which empowers the proposed color filter with dynamically tunable output color. The proposed scheme shows great promise in color printing and ultracompact display devices with high color saturation, wide gamut, large angular tolerance, and dynamic tunability.show less