arXiv subjects

Delong Feng

Publications and source records attributed to Delong Feng.

5 recordsLinked to original sources

arXiv2025

Photothermal Fourier-plane Phase Synchronization for Interferometric Scattering Microscopy

We introduce and experimentally implement Fourier-plane phase synchronization for optical microscopy, and demonstrate its performance with interferometric scattering microscopy. By combining a photothermal phase plate and laser beam scanning, we realize a synchronized phase for all scattering components on the Fourier plane of high numerical-aperture microscopes, where the evanescent waves and optical aberration normally produce highly inhomogeneous phase distributions. We achieve an almost perfect point spread function, exhibiting a tighter focus with 50\% enhancement of the signal and ideal circular symmetry. Particularly, by synchronizing the phase to $\pi/2$, we demonstrate the background speckles exhibit an anti-symmetric dependence on axial defocus, enabling the effective suppression of the speckles via defocus integration and thus the detection of 10 nm particles immobilized on the substrate. The concept and technique of seamless dynamic phase control on the Fourier plane constitute a key asset for modern optical microscopy.

physics.optics↗

arXiv2024

Defocus-integration Interferometric Scattering Microscopy for Speckle Suppression and Enhancing Nanoparticle Detection on Substrate

Direct optical detection and imaging of single nanoparticles on substrate in wide field underpin vast applications across different research fields. However, the speckles originating from the unavoidable random surface undulations of the substrate ultimately limit the size of the decipherable nanoparticles by the current optical techniques, including the ultrasensitive interferometric scattering microscopy (iSCAT). Here we report a defocus-integration iSCAT to suppress the speckle noise and to enhance the detection and imaging of single nanoparticles on ultra-flat glass substrate and silicon wafer. In particular, we discover distinct symmetry properties of the scattering phase between the nanoparticle and the surface undulations that cause the speckles. Consequently, we develop the defocus-integration technique to suppress the speckles.We experimentally achieve an enhancement of the signal to noise ratio by 6.9 dB for the nanoparticle detection. We demonstrate that the technique is generally applicable for nanoparticles of various materials and for both low and high refractive-index substrates.

physics.optics↗

arXiv2023

Tunable all-optical logic gates based on nonreciprocal topologically protected edge modes

All-optical logic gates have been studied intensively for their potential to enable broadband, low-loss, and high-speed communication. However, poor tunability has remained a key challenge in this field. In this paper, we propose a Y-shaped structure composed of Yttrium Iron Garnet (YIG) layers that can serve as tunable all-optical logic gates, including, but not limited to, OR, AND, and NOT gates, by applying external magnetic fields to magnetize the YIG layers. Our findings demonstrate that these logic gates are based on topologically protected one-way edge modes, ensuring exceptional robustness against imperfections and nonlocal effects while maintaining extremely high precision. Furthermore, the operating band of the logic gates is shown to be tunable. In addition, we introduce a straightforward and practical method for controlling and switching the logic gates between "work", "skip", and "stop" modes. These findings have important implications for the design of high-performance and precise all-optical integrated circuits.

physics.optics↗

arXiv2022

Optical Fingerprint of Flat Substrate Surface and Marker-free Lateral Displacement Detection with Angstrom-level Precision

We report that flat substrates such as glass coverslips with surface roughness well below 0.5 nm feature notable speckle patterns when observed with high-sensitivity interference microscopy. We uncover that these speckle patterns unambiguously originate from the subnanometer surface undulations, and develop an intuitive model to illustrate how subnanometer non-resonant dielectric features could generate pronounced interference contrast in the far field. We introduce the concept of optical fingerprint for the deterministic speckle pattern associated with a particular substrate surface area and intentionally enhance the speckle amplitudes for potential applications. We demonstrate such optical fingerprints can be leveraged for reproducible position identification and marker-free lateral displacement detection with an experimental precision of 0.22 nm. The reproducible position identification allows us to detect new nanoscopic features developed during laborious processes performed outside of the microscope. The demonstrated capability for ultrasensitive displacement detection may find applications in the semiconductor industry and super-resolution optical microscopy.

physics.optics↗

arXiv2021

Slow wave and truly rainbow trapping in one-way terahertz waveguide

Slow or even stop electromagnetic (EM) waves attract researchers' attentions for its potential applications in energy storage, optical buffer and nonlinearity enhancement. However, in most cases of the EM waves trapping, the EM waves are not truly trapped due to the existence of reflection. In this paper, a novel metal-semiconductor-semiconductor-metal (MSSM) structure, and a novel truly rainbow trapping in a tapered MSSM model at terahertz frequencies are demonstrated by theoretical analysis and numerical simulations. More importantly, functional devices such as optical buffer, optical switch and optical filter are achieved in our designed MSSM structure based on truly rainbow trapping theory. Owing to the property of one-way propagation, these new types of optical devices can be high-performance and are expected to be used in integrated optical circuits.

physics.optics↗