For space-borne gravitational wave detection, existing suppression strategies for clock noise and laser phase noise predominantly rely on optical frequency comb or sideband measurement techniques. The optical frequency comb method establishes a link between the clock and the laser, and this noise is then suppressed by applying corrections to the time-delay interferometry combinations. Sideband measurement techniques perform the cancellation by constructing clock noise through sideband modulation. In this work, we adopt the linear combination principle of time-delay interferometry. By using optical frequency comb technology, the clock noise and laser phase noise in the measurement are directly correlated through phase coherence. Linear combination is then applied to the measurement data stream processed by the optical frequency comb, thereby achieving the joint suppression of laser phase noise and clock noise. This work provides a feasible candidate scheme for noise suppression in space-borne gravitational wave detection.

Cooperative emission is a collective quantum optical process that requires macroscopic phase coherence among coupled emitters. Recent observations of cooperative emission in QD superlattices have renewed interest in how such coherence emerges in nanostructured solids. Meanwhile, theoretical studies have long discussed the relationship between electronic delocalization and coherence, particularly whether delocalized states necessarily give rise to cooperative emission. This study addresses this question through power-dependent steady-state PL and time-resolved PL decay measurements. The findings indicate that, although the quantum resonance peak exhibits delocalized excitonic characteristics, it shows no signatures of cooperative radiation. In particular, neither superlinear intensity scaling nor power-dependent emission delay was observed, indicating the absence of cooperative-radiation signatures. This can be understood from two disorder-related aspects. Temperature-dependent spectroscopy reveals pronounced inhomogeneous broadening and low-temperature dark-exciton participation, pointing to intra-domain static disorder and exciton-state mixing. These effects collectively hinder the establishment of macroscopic coherence. The temperature dependence of the quantum resonance peak decay lifetime is consistent with two-dimensional exciton dynamics. This work provides direct experimental evidence that electronic delocalization can be decoupled from cooperative coherence in CdSe quantum dot superlattices.

Continuous-wave terahertz (CW-THz) imaging provided a powerful tool for industrial inspection. Here, a reflective line-scanning CW-THz imaging system was built using a linear array detector by properly designing the optical configuration. By using two measurement modes in reflectometry, structural details of samples could be quickly and completely determined. To correct imaging distortions in measurements and improve the image quality, a standard U-Net convolutional neural network (CNN) was applied. Extensive experiments also demonstrated the system’s capability in imaging concealed samples. This work presented a potential tool for advancing the application values of CW-THz technology.

The rapid advancement of information age has created an urgent need for integrated physical-layer security solutions. We propose a dual-functional terahertz (THz) encryption metasurface that enables independent information retrieval in both the near field and the far field within a single device. By precisely tailoring the complex amplitude of orthogonal linear polarization components, the metasurface forms two spatially separated far-field channels for left- and right-handed circular polarizations, which can be accessed simultaneously under linearly polarized illumination and are theoretically free from interchannel crosstalk. In the near field, polarization-selective amplitude modulation reveals textual patterns, whereas in the far field, phase engineering encodes multiple digital data in focal-spot arrays under linear, left-handed, and right-handed circular polarization states. This compact metasurface provides a scalable route toward THz security tags and robust physical-layer protection for identification, anticounterfeiting, and high-capacity wireless communications.

Reconfigurable intelligent surfaces (RISs) transcend the passive response limitations of conventional meta-surface resonators by integrating active materials into metasurface elements, enabling a more flexible control of electromagnetic wave properties. However, RISs devices operating in the terahertz (THz) regime continue to face significant challenges in structural design and multifunctional implementation, particularly regarding optically-addressed THz RISs devices with independent pixel-level encoding, which remain experimentally underexplored. Here, we propose a compact and relatively efficient transmissive programmable metasurface device functioning as a phase-type spatial THz modulator, which enables separate encoding of each pixel within a 50 & times;50 resolution array, thereby achieving dynamic generation and reconfiguration of THz wavefronts. The spatial modulation of the pump pulse intensity locally activates the vanadium dioxide integrated meta-atoms across the metasurface and, thus, defines the specifically designed phase modulation of the cross-polarized transmission. Dynamic wavefront manipulation is then realized by switching the spatial intensity distribution of the pump pulse. Proof-of-concept experiments demonstrate that the same programmable metasurface can perform three distinct functionalities -zoom lens, tunable vortex beam generator, and dynamic hologram. The amplitude conversion efficiency of the device was experimentally measured to be 27%. The programmable scheme demonstrated here paves the way toward miniaturized, integrated, and multifunctional THz optical devices.

Terahertz (THz) technology has been paid intensive attentions in biological testing due to unique properties of THz radiation. Utilizing the enhancement effect of a metamaterial chip to a localized THz field, the sensitivity of current THz systems to biological tissues could be greatly improved. In this work, a metamaterial chip with a rectangular aperture array was introduced into a THz focal-plane imaging system to achieve the measurement of biological samples. The function of the metamaterial chip was theoretically simulated and experimentally characterized. By measuring two types of plant leaves, the imaging results with and without the metamaterial chip were compared and analyzed. The enhancement effect of the chip to the imaging contrast was verified. The technique was expected to further broaden applications of THz imaging in biological sensing.

A switchable chiral metasurface (CM) with high polarization conversion ratio (PCR) and absorptivity based on vanadium dioxide (VO2) is proposed and numerically demonstrated in the terahertz (THz) regime. The proposed design consists of VO2–Au‐mixed resonant pattern layer, Si dielectric layer, and Au ground plate, which can achieve tunable bifunctional linear polarization conversion (LPC) and absorption (ABS) by varying the conductivity of VO2 (). For = 10 S m−1, the designed CM possesses a function of broadband LPC. More than 90% PCR is obtained in 1.79–2.46 THz, and the corresponding relative bandwidth (RBW) is 31.28%. For = 2 × 105 S m−1, the designed CM can efficiently absorb incident electromagnetic (EM) waves in 1.54–2.76 THz with the absorptivity exceeding 90% (RBW = 56.47%). The mechanisms of LPC and ABS are analyzed. The effects of geometric and EM parameters, incident angle, and polarization angle on its bifunctional characteristics are also studied. The LPC and ABS performances are maintained within a certain range of incident angles. Furthermore, the proposed CM exhibits polarization insensitivity. The developed switchable bifunctional CM has great potential application value in advanced THz research and smart device.

Electronically controlled modulation devices with highly tunable intensities operating in the terahertz (THz) band must be developed and improved for the integration and miniaturization of THz-based systems. Notably, electronic THz modulation devices suffer from a trade-off between low insertion loss and high modulation depth, which cannot be simultaneously achieved. In this work, a THz intensity modulation mechanism based on dual Fabry-P & eacute;rot cavity resonant coupling is proposed, modeled, and described. The electrically tunable intensity modulator is composed of quartz/PEDOT:PSS:DMSO/EMIM-TFSI/gold/quartz. The reflectivity of the PEDOT:PSS:DMSO layer can be tuned using an electrical gate, thus adjusting the coupling between the two cavities. In this way, near-perfect intensity modulation (modulation depth of 94.5%) is achieved at 0.64 THz. A controllable THz amplitude grating, which can switch between three modes through electronic control, is also designed to modulate the angle distribution of the reflected wave. Additionally, a 3 x 5 intensity modulation array with individually controlled pixels is built, and 10 Arabic numerals are displayed to demonstrate the validity of the device. This research not only supports the development of innovative THz modulators but also provides an opportunity for exploring the topological dynamics of multicavity resonance.

With the rapid growth of data volumes in modern society, efficient and secure methods for information transmission, storage, and encryption have become essential. Benefiting from high-density storage and fast access to 2D data, optical encryption shows significant promise for data protection. Metasurfaces, as a type of 2D artificial metamaterials capable of precisely controlling electromagnetic waves, have greatly advanced the development of multi-channel optical encryption. However, many existing metasurface-based optical encryption devices are limited by static operation and stringent requirements on materials or light sources. Here, a 46-channel image encryption device is proposed, integrated with optically controlled metasurfaces to achieve dynamically tunable and high-capacity optical encryption. An efficient binary amplitude-phase inverse-design method is developed that enables high performance optical encryption by incorporating binary amplitude distributions into an isotropic phase metasurface. This approach imposes minimal additional requirements on the light source or the metasurface. Experimental demonstrations using an infrared-pump/terahertz-probe imaging system confirm the effectiveness and robustness of the encryption device, highlighting its potential for advanced and flexible optical encryption applications.

Terahertz (THz) near-field imaging technology is always a main research branch in the THz field, because it retains the properties of THz radiation and realizes a sub-wavelength spatial resolution. In this work, a new THz near-field technique was developed. THz near-field signals were modulated and measured by two mutually perpendicular air-plasma dynamic apertures above a sample surface. A THz near-field image was successfully obtained and the sample surface was not approached by any THz detectors or sources. The performances of the imaging technique were checked and analyzed. Its advantages were expected to accelerate the advancement of THz microscopy.

An optical pump terahertz probe measurement was performed on monolayer WS2 and h-BN/WS2/h-BN vertical van der Waals heterostructure to investigate the effect of h-BN layer on the ultrafast dynamical process of photo excited charge carriers and the complex conductivity. Based on our measurement, we find that the initial fast carrier relaxation process which is dominated by the formation of charge neutral excitons is similar in the monolayer WS2 and h-BN/WS2/h-BN heterostructure. This result indicates the effect of h-BN layer on the exciton formation process can be simply omitted. Compared to initial relaxation process, the following relaxation process, which is dominated by the Auger process and impurity or defect center assisted non-radiative process, of h-BN/WS2/h-BN heterostructure is around three times longer than that of monolayer WS2. We attribute the longer lifetime of h-BN/WS2/h-BN heterostructure to the protection of h-BN layer, which inhibits the formation of oxygen impurity and S-vacancy defect center in the WS2 layer. We further derive the complex conductivity of both monolayer WS2 and h-BN/WS2/h-BN heterostructure from our terahertz spectroscopy measurement and analyze our results using the classical Drude-Smith model.

A switchable multifunctional metasurface based on vanadium dioxide (VO2) and photoconductive silicon (PSi) is proposed in the terahertz band, which possesses the functions of absorption (ABS), linear-to-linear (LTL) and linear-to-circular (LTC) polarization conversion by utilizing the phase change property of VO2. The absorptivity, polarization conversion ratio (PCR) and ellipticity (χ) are dynamically tunable by varying the conductivity of PSi. When VO2 and PSi are in the metallic phase, the metasurface is treated as a broadband absorber with more than 90

Terahertz (THz) microscopy has become an important far-infrared inspection method because it possesses a high spatial resolution and retains THz spectral information. For further exploiting applications of THz microscopy, we propose an air-plasma dynamic aperture-based THz near-field technique to achieve sub-wavelength THz imaging without approaching a sample surface. In this work, the measurement mode of the technique was improved and a corresponding data processing method was applied to upgrade the system performances. By utilizing the proposed method, the measurement time was reduced about 4 times and the signal-to-noise ratio of the system was enhanced more than 6 times compared to the previous one. Utilizing the superiorities of the system, three unique application functions were demonstrated, including imaging of isolated objects, identifying semifluid chemicals, and characterizing a semifluid surface. The work effectively promoted the maturation of the imaging technique and greatly broadened the applications of THz microscopy in fundamental research and industrial inspection.

Strontium ferrite has been widely used in magnetic sealing, ferrofluids, and magnetic resonance imaging. To investigate the optical properties of strontium ferrite composite materials in the terahertz (THz) frequency range, we measured the refractive index, extinction coefficient, and other optical constants using a THz time-domain spectroscopy (THz-TDS) system. By analyzing the response signals of THz waves with various polarization states, we compared the changes in polarization resulting from magnetization in the strontium ferrite composites. Additionally, we examined the effect of THz field strength on the optical rotation of the samples. Our findings indicate that both the strontium ferrite composite and its magnetized counterpart exhibit optical rotation under both weak and strong THz field conditions. Notably, the optical rotation effect is more pronounced in the magnetized composite when exposed to a strong THz field. These results provide significant theoretical and experimental insights into the application of strontium ferrite materials in the THz frequency range.

The optical response characteristics of poly (vinylidene fluoride) (PVDF) are important for its wide applications in sensing and energy harvesting. A Terahertz Time-Domain Spectroscopy (THz-TDS) system was utilized to measure the optical constants of two types of PVDF piezoelectric materials in the terahertz frequency range. The optical characteristics of PVDF were determined under the experimental conditions of weak and strong terahertz field. The optical response characteristics of samples fabricated through the hot-pressing and melt-extrusion methods were analyzed. The results indicate that samples produced by the hot-pressing method exhibits stronger optical response signals, while those fabricated by the method of melt-extrusion displays weaker ones, which can be attributed to the thicker domain walls. To elucidate the underlying physical mechanisms responsible for these observed differences in optical response characteristics, the samples were measured by X-ray diffraction (XRD) technique. This analysis reveals that the variations in crystal structures among the samples lead to differences in polarity. These structural differences significantly impact the optical properties under strong terahertz fields. The findings provide valuable theoretical and experimental insights for the practical application of PVDF-based materials.

We perform time-domain terahertz (THz) spectroscopy measurement to study the complex conductivity of layered FeOCl with and without surface noble metal adsorption. A weak THz transmission intensity is obtained in pristine layered FeOCl and the transmission coefficient comparable increases with the introduction of surface noble metal nanoparticle adsorption. The frequency-resolved complex conductivity of FeOCl samples with and without noble metal nanoparticle adsorption is further obtained from measured THz transmission intensity. Using the classical Drude-Smith model, we find significant increase of carrier density and decrease of carrier-carrier scattering time with surface noble metal nanoparticle adsorption. These results provide a possible way to improve the conductivity of layered FeOCl material for its potential applications in the field of two-dimensional electronics.

A fast object classification scheme in terahertz (THz) domain is proposed. This scheme combines machine learning and THz single-pixel imaging (SPI) technologies but skips the image reconstruction in SPI. It can directly perform the linear pattern recognition task based on a few single-pixel values. This approach has advantages of low experimental complexity, simple optimization algorithms, and all-optical processing. It is verified in simulation and experiment with a classification accuracy of 90%. Our proposed scheme paves an avenue for fast classification of THz images in practical applications.

Metalens, consisting of planar micro/nanostructure arrays, has shown great potentials in beam steering, subwavelength focusing and high-resolution imaging. Taking the advantages of ultrathin thickness and compact design, it can be integrated with a photonic chip to improve the collection efficiency of optoelectronic systems. However, it remains challenging to realize the multidimensional control of terahertz (THz) waves by using a metalens, although the convergence properties have been widely studied. Here, we design and experimentally demonstrate a multifunctional cylindrical metalens by using a tri-layer metallic metasurface. By modulating the amplitude, phase and polarization states of terahertz waves independently, the cylindrical metalens can generate two focal lines at different positions for transmitted x- and y- polarized terahertz waves with varying amplitude distribution. Importantly, up to 64.7% focusing efficiency has been obtained at the frequency of 0.34 THz with a numerical aperture (NA) of 0.75. Our study offers a novel method for implementing multifunctional cylindrical metalens which lays the foundation of advanced integration with arrayed terahertz detection chips.