In this Letter, we present a low-cost, high-resolution spectrometer design for ultra-high resolution optical coherence tomography (UHR-OCT), in which multiple standard achromatic lenses are combined to replace the expensive F-theta lens to achieve a comparable performance. For UHR-OCT, the spectrometer plays an important role in high-quality 3D image reconstruction. Typically, an F-theta lens is used in spectrometers as the Fourier lens to focus the dispersed light on the sensor array, and this F-theta lens is one of the most expensive components in spectrometers. The advantage of F-theta lens over the most widely used achromatic lens is that the aberrations (mainly spherical aberration, SA) are corrected, so the foci of the dispersed optical beams (at different wavelengths) with different incident angles could be placed on the sensor array simultaneously. For the achromatic lens, the foci of the center part of the spectrum are farther than those on the side in the longitudinal direction, causing degradations of the spectral resolution. Furthermore, in comparison with the achromatic lens with the same focal length, those with smaller diameters have stronger SA, but small lenses are what we need for making spectrometers compact and stable. In this work, we propose a simple method of using multiple long-focal-length achromatic lenses together to replace the F-theta lens, which is >8-fold cheaper based on the price of optical components from Thorlabs, US. Both simulations and in vivo experiments were implemented to demonstrate the performance of the proposed method.

In this study, we propose an underwater ghost-imaging scheme using a modulation pattern combining offset-position pseudo-Bessel-ring (OPBR) and random binary (RB) speckle pattern illumination. We design the experiments based on modulation rules to order the OPBR speckle patterns. We retrieve ghost images by OPBR beam with different modulation speckle sizes. The obtained ghost images have a better contrast-to-noise rate compared to RB beam ghost imaging under the same conditions. We verify the results both in the experiment and simulation. In addition, we also check the image quality at different turbidities. Furthermore, we demonstrate that the OPBR speckle pattern also provides better image quality in other objects. The proposed method promises wide applications in highly scattering media, atmosphere, turbid water, etc.

Hadamard single-pixel imaging is an appealing imaging technique due to its features of low hardware complexity and industrial cost. To improve imaging efficiency, many studies have focused on sorting Hadamard patterns to obtain reliable reconstructed images with very few samples. In this study, we propose an efficient Hadamard basis sampling strategy that employs an exponential probability function to sample Hadamard patterns in a direction with high energy concentration of the Hadamard spectrum. We used the compressed-sensing algorithm for image reconstruction. The simulation and experimental results show that this sampling strategy can reconstruct object reliably and preserves the edge and details of images.

Photoelectron spectroscopy is a powerful tool in characterizing the electronic structure of materials. To investigate the specific region of interest with high probing efficiency, in this work we propose a compact in situ microscope to assist photoelectron spectroscopy. The configuration of long objective distance of 200 mm with two-mirror reflection has been introduced. Large magnification of 5× to 100×, lateral resolution of 4.08 µm, and longitudinal resolution of 4.49 µm have been achieved. Meanwhile, the testing result shows larger focal depth of this in situ optical microscope. Similar configurations could also be applied to other electronic microscopes to improve their probing capability.

Non-line-of-sight (NLOS) imaging is an emerging technique for detecting objects behind obstacles or around corners. Recent studies on passive NLOS mainly focus on steady-state measurement and reconstruction methods, which show limitations in recognition of moving targets. To the best of our knowledge, we propose a novel event-based passive NLOS imaging method. We acquire asynchronous event-based data of the diffusion spot on the relay surface, which contains detailed dynamic information of the NLOS target, and efficiently ease the degradation caused by target movement. In addition, we demonstrate the event-based cues based on the derivation of an event-NLOS forward model. Furthermore, we propose the first event-based NLOS imaging data set, EM-NLOS, and the movement feature is extracted by time-surface representation. We compare the reconstructions through event-based data with frame-based data. The event-based method performs well on peak signal-to-noise ratio and learned perceptual image patch similarity, which is 20% and 10% better than the frame-based method.

We simulate the measurements of an active bifocal terahertz imaging system to reproduce the ability of the system to detect the internal structure of foams having embedded defects. Angular spectrum theory and geometric optics tracing are used to calculate the incident and received electric fields of the system and the scattered light distribution of the measured object. The finite-element method is also used to calculate the scattering light distribution of the measured object for comparison with the geometric optics model. The simulations are consistent with the measurements at the central axis of the horizontal stripe defects.

Polarized hyperspectral imaging, which has been widely studied worldwide, can obtain four-dimensional data including polarization, spectral, and spatial domains. To simplify data acquisition, compressive sensing theory is utilized in each domain. The polarization information represented by the four Stokes parameters currently requires at least two compressions. This work achieves full-Stokes single compression by introducing deep learning reconstruction. The four Stokes parameters are modulated by a quarter-wave plate (QWP) and a liquid crystal tunable filter (LCTF) and then compressed into a single light intensity detected by a complementary metal oxide semiconductor (CMOS). Data processing involves model training and polarization reconstruction. The reconstruction model is trained by feeding the known Stokes parameters and their single compressions into a deep learning framework. Unknown Stokes parameters can be reconstructed from a single compression using the trained model. Benefiting from the acquisition simplicity and reconstruction efficiency, this work well facilitates the development and application of polarized hyperspectral imaging.

Multi-channel detection is an effective way to improve data throughput of spectral-domain optical coherence tomography (SDOCT). However, current multi-channel OCT requires multiple detectors, which increases the complexity and cost of the system. We propose a novel multi-channel detection design based on a single spectrometer. Each camera pixel receives interferometric spectral signals from all the channels but with a spectral shift between two channels. This design effectively broadens the spectral bandwidth of each pixel, which reduces relative intensity noise (RIN) by √M times with M being the number of channels. We theoretically analyzed the noise of the proposed design under two cases: shot-noise limited and electrical noise or RIN limited. We show both theoretically and experimentally that this design can effectively improve the sensitivity, especially for electrical noise or RIN-dominated systems.

For speckle-correlation-based scattering imaging, an iris is generally used next to the diffuser to magnify the speckle size and enhance the speckle contrast, which limits the light flux and makes the setup cooperative. Here, we experimentally demonstrate a non-iris speckle-correlation imaging method associated with an image resizing process. The experimental results demonstrate that, by estimating an appropriate resizing factor, our method can achieve high-fidelity noncooperative speckle-correlation imaging by digital resizing of the raw captions or on-chip pixel binning without iris. The method opens a new door for noncooperative high-frame-rate speckle-correlation imaging and benefits scattering imaging for dynamic objects hidden behind opaque barriers.

To date, fluorescence imaging systems have all relied on at least one beam splitter (BS) to ensure the separation of excitation light and fluorescence. Here, we reported SiO2/TiO2 multi-layer long pass filter integrated GaN LED. It is considered as the potential source for imaging systems. Experimental results indicate that the GaN LED shows blue emission peaked at 470.3 nm and can be used to excite dye materials. Integrating with a long pass filter (550 nm), the light source can be used to establish a real-time fluorescence detection for dyes that emit light above 550 nm. More interestingly, with this source, a real-time imaging system with signature words written with the dyes, such as ‘N J U P T’, can be converted into CCD images. This work may lead to a new strategy for integrating light sources and BS mirrors to build mini and smart fluorescence imaging systems.