Optics (physics.optics)

Abstract: The solid-state harmonic generation (SHG) derives from photocurrent coherence. The crystal symmetry, including spatial-inversion, mirror, rotational symmetries and time-reversal symmetry, constrains the amplitude and phase of the photocurrent, thus manipulates the coherent processes in SHG. We revisit the expression of photocurrent under the electric dipole approximation and give a picture of non-equilibrium dynamical process of photoelectron on laser-dressed effective bands. We reveal the indispensable role of shift vector and transition dipole phase in the photocurrent coherence in addition to the dynamical phase. Microscopic mechanism of the selection rule, orientation dependence, polarization characteristics, time-frequency analysis and ellipticity dependence of harmonics governed by crystal symmetry is clarified analytically and numerically. The theory in this paper integrates non-equilibrium electronic dynamics of condensed matter in strong laser fields, and paves a way to explore more nonlinear optical phenomena induced by the crystal symmetry.

Abstract: We show that the systematic error unique to Brillouin optical correlation-domain reflectometry (BOCDR) can be effectively suppressed by use of low-coherence light, and demonstrate distributed strain measurement with ~3 cm spatial resolution.

Abstract: Fourier Ptychographic Microscopy (FPM) is a computational technique that achieves a large space-bandwidth product imaging. It addresses the challenge of balancing a large field of view and high resolution by fusing information from multiple images taken with varying illumination angles. Nevertheless, conventional FPM framework always suffers from long acquisition time and a heavy computational burden. In this paper, we propose a novel physical neural network that generates an adaptive illumination mode by incorporating temporally-encoded illumination modes as a distinct layer, aiming to improve the acquisition and calculation efficiency. Both simulations and experiments have been conducted to validate the feasibility and effectiveness of the proposed method. It is worth mentioning that, unlike previous works that obtain the intensity of a multiplexed illumination by post-combination of each sequentially illuminated and obtained low-resolution images, our experimental data is captured directly by turning on multiple LEDs with a coded illumination pattern. Our method has exhibited state-of-the-art performance in terms of both detail fidelity and imaging velocity when assessed through a multitude of evaluative aspects.

Abstract: Non-linearities in organic exciton-polariton microcavities represent an attractive platform for second-generation quantum devices. However, progress in this area hinges on the development of material platforms for high-performance polariton lasing, scalable and sustainable fabrication, and ultimately strategies for electrical pumping. Here, we show how introducing Schlieren textures in a liquid crystalline conjugated polymer and the associated microdomains of distinct chain orientation enable in-plane Anderson localization of polaritons. In high-Q distributed Bragg reflector microcavities, this strong localization facilitated polariton lasing at unprecedented thresholds of 136 fJ per pulse, thus providing a pathway to the study of fundamental effects at low polariton numbers. Anderson localization further permitted polariton lasing in more lossy metallic microcavities while maintaining a competitive lasing threshold. The facile fabrication of these cavities will drastically reduce the complexity of integrating polariton laser with other structures and the high conductivity of metallic mirrors provides a route to electrical pumping.

Abstract: Foundation models are large machine learning models that can tackle various downstream tasks once trained on diverse and large-scale data, leading research trends in natural language processing, computer vision, and reinforcement learning. However, no foundation model exists for optical multilayer thin film structure inverse design. Current inverse design algorithms either fail to explore the global design space or suffer from low computational efficiency. To bridge this gap, we propose the Opto Generative Pretrained Transformer (OptoGPT). OptoGPT is a decoder-only transformer that auto-regressively generates designs based on specific spectrum targets. Trained on a large dataset of 10 million designs, our model demonstrates remarkable capabilities: 1) autonomous global design exploration by determining the number of layers (up to 20) while selecting the material (up to 18 distinct types) and thickness at each layer, 2) efficient designs for structural color, absorbers, filters, distributed brag reflectors, and Fabry-Perot resonators within 0.1 seconds (comparable to simulation speeds), 3) the ability to output diverse designs, and 4) seamless integration of user-defined constraints. By overcoming design barriers regarding optical targets, material selections, and design constraints, OptoGPT can serve as a foundation model for optical multilayer thin film structure inverse design.

Abstract: Advances in chip-scale photonic-electronic integration are enabling a new generation of foundry manufacturable implantable silicon neural probes incorporating nanophotonic waveguides and microelecctrodes for optogenetic stimulation and electrophysiological recording in neuroscience research. Further extending neural probe functionalities with integrated microfluidics is a direct approach to achieve neurochemical injection and sampling capabilities. In this work, we use two-photon polymerization to integrate microfluidic channels onto photonic neural probes with 3D printing. The photonic neural probes include silicon nitride nanophotonic waveguides and grating emitters. The customizability of 3D printing enables a unique geometry of microfluidics that conforms to the shape of each neural probe, enabling integration of microfluidics with a variety of existing neural probes while avoiding the complexities of monolithic microfluidics integration. We demonstrate the photonic and fluidic functionalities of the neural probes via fluorescein injection in agarose gel and photoloysis of caged fluorescein in solution and in flxed brain tissue.