Chiral metasurfaces play critical role in physics,materials science,pharmacognosy,and commu-nications.To achieve high-performance chiral responses,such as high circular dichroism(CD)and high-quality factors(Q-factors),bound-state-in continuum(BIC),BIC-based metasurfaces have been extensively studied as a promising platform.However,most realized BIC metasurfaces rely on metallic constituents whose high electromagnetic losses and absence of dynamic chirality tuning together impose a severe limit on their practical potential.This paper presents an all-dielectric chiral BIC metasurface.By illumination sym-metry breaking,the metasurface exhibits a CD value of 0.93.Additionally,dynamic tuning of CD is enabled by external optical pumping.This scheme provides a new avenue for dynamically manipulating the chiral metasurface,which can be used to achieve more complex dynamic chiral characterization and applications.

With the rapid advancement of artificial intelligence, machine learning techniques have provided fast and efficient solutions to numerous complex design challenges. This study develops and validates a Bayesian Hyperparameter Optimization-based Random Forest Model (BO-RF) to assist in the design of metamaterial absorbers. The model achieves high-precision fitting from structural parameters to absorption performance metrics. The Random Forest algorithm is employed to rank the importance of the absorber’s features, and nine regression models are compared using Root Mean Square Error (RMSE), Mean Absolute Error (MAE), and the Coefficient of Determination (R2) as evaluation metrics. The results demonstrate that the BO-RF model outperforms others, achieving an RMSE of 0.01743, a MAE of 0.01147, and an R2 of 0.99506 on the test set. Additionally, based on this model, a scalarized weighted-sum optimization framework is established to simultaneously maximize absorption rate and bandwidth. The model terminates and outputs the optimal solution upon meeting convergence criteria, with results closely matching the simulations, thereby confirming its accuracy. The developed model reduces the prediction time for a single parameter set to 10 microseconds, significantly lowering the cost of parameter prediction in metamaterial devices and providing a useful and efficient tool for related research fields.

To achieve accurate positioning of wire faults in integrated circuits (ICs) and solve the core problem of difficulty in identifying fault points in THz TDR systems in complex electromagnetic environments due to weak reflected signal amplitudes and susceptibility to noise inundation. This study builds a pulse time-domain reflection diagnostic device based on a terahertz time-domain spectroscopy system, innovatively proposes a dual signal enhancement strategy, and for the first time extends the application of this technology system to fault diagnosis of IC interconnect wires. Firstly, the pearson correlation coefficient is used for fault reflection signal feature recognition, and then the moving window integration method that matches the reference pulse length is adopted to amplify weak reflection pulses at the sub-picosecond level. To verify the effectiveness of the method, planar IC samples with dielectric constants of 2.2 (test group) and 3.0 (validation group) were prepared, and open and short circuit fault points ranging from 10 mm to 40 mm were pre-set on them. The experimental results show that in the test group, the maximum positioning error is 1.298 mm (short circuit fault, relative error 12.981 %), and the minimum positioning error is 76 mu m (relative error 0.191 %); In the verification group, the positioning error of the 40 mm short circuit fault is only 123 mu m (relative error -0.331 %), and the accuracy of fault type identification reaches 100 %. This method effectively solves the bottleneck of extracting and identifying weak reflected signals under low signal-to-noise ratio (SNR) conditions, providing a new high-precision diagnostic solution for the field of integrated circuit failure analysis.

Abstract Terahertz (THz) spectroscopy holds considerable promise for the detection of organic and biomedical molecules. However, in practical applications, the mismatch between the THz wavelength and the absorption cross-section of analytes makes it challenging to effectively measure the spectra of trace samples. This limitation necessitates the introduction of micro enhancement structures, such as waveguides, photonic crystals, and metasurfaces, to strengthen the interaction between the analyte and THz waves. A terahertz absorption enhancement structure based on a tunable defect mode in a one dimensional photonic crystal integrated inside a coaxial waveguide is proposed. By adjusting the thickness of a lossless liquid layer, a series of resonant peaks can be excited, thereby amplifying the THz absorption spectral features of trace samples. When a 0.2 µ m α -lactose film is employed as the trace analyte, an absorption enhancement factor of approximately 56.3 is achieved over the frequency range of 0.5–0.56 THz. The required sample area is reduced to about 1/1700 of that needed in a conventional free-space measurement with a 5 mm beam waist spot. This approach offers a new pathway for highly sensitive THz detection of trace analytes.

A characterization method for terahertz beam in time domain spectroscopy (TDS) systems is proposed, by employing a mask composed of an echelon and a baffle to spatially encode the beam. The beam is scanned horizontally at multiple vertical positions, each corresponding to a distinct measurement plane defined by the echelon’s stepped structure. The scanning step size is set to half the height of a single echelon step. During the scanning process, time-domain signals are acquired from specific regions of the beam. Multivariate linear equations are then constructed based on the encoded spatio-temporal data obtained from different scanning positions. Through inverse reconstruction, a spatial intensity distribution image of the terahertz beam is obtained. Compared with the basic scanning configuration, the imaging resolution is effectively doubled, thereby clearly revealing details of the spot size, shape, and intensity profile. Furthermore, the impact of potential noise on imaging quality is analyzed, demonstrating that excellent reconstruction can be achieved if the ratio of the estimated maximum single-pixel intensity to the noise fluctuation variance is below 0.8 %. In addition to being well-suited for the accurate imaging of small spots, this method eliminates the requirement of large-scale optical path adjustments, enhancing the convenience and controllability of the measurement process.

We propose and experimentally demonstrate a dual-linear-polarization multiplexed metasurface capable of independently generating point-focused and focused orbital angular momentum (OAM) terahertz beams at 140 GHz. The metasurface consists of polymer-based birefringent meta-atoms fabricated via high-resolution 3D printing, enabling full 0-2$\pi$ transmission phase control for both orthogonal polarizations through independent geometric parameter tuning. For y-polarized incidence, the device achieves a focal length of 82 mm with a high efficiency of 50.71%. For x-polarized incidence, it produces an focused OAM beam with a topological charge of $\ell$ = -2 and a focal length of 115 mm, maintaining an efficiency of 54.61%. The measured focal positions, beam profiles, and phase structures exhibit strong agreement with full-wave simulations, with only minor deviations attributed to fabrication and measurement constraints. Compared with previously reported designs, the proposed all-resin structure offers simplified fabrication, single-layer multifunctional implementation, and high phase-control accuracy. This work demonstrates a scalable and low-cost strategy for multifunctional terahertz beam shaping and multiplexing, with promising applications in terahertz imaging, communication, and sensing.

This work proposes a transmission-type all-dielectric metasurface design strategy based on polarization-space cooperative multiplexing to address the need for high channel density and high integration in terahertz (THz) multi-channel information processing. The method, implemented on a low-refractive-index photosensitive resin platform, combines the transmission and geometric phases of birefringent unit cells to enable independent phase control of orthogonal circular polarizations. Polarization and spatial degrees of freedom are further multiplexed through a spatially interleaved arrangement. Four metasurfaces are designed and fabricated using this strategy. Numerical results show that, with only a limited number of periodically arranged unit cells, the devices realize multi-focal focusing and high-purity focused optical vortex generation with a topological charge of ℓ = -2 across four polarization channels. The numerical aperture ranges from 0.414 to 0.707, and the achieved focal lengths, field distributions, and modal purities closely match the target designs. Single-layer samples fabricated by low-cost 3D printing exhibit focusing and modal characteristics at 0.14 and 0.28 THz consistent with simulations, confirming the effectiveness and scalability of the proposed approach. This strategy offers higher functional density with simpler structure and lower cost, providing a promising route for high-capacity THz communication and multidimensional information multiplexing.

A high-power mid-infrared (MIR) optical parametric oscillator (OPO) is reported, which was pumped by a diode-end-pumped, acousto-optically Q-switched Tm:YLF laser at 1908nm. Based on thermal simulations of the Tm:YLF crystal, the pump power range was rationally selected, yielding 12.88 W of 1908 nm laser output at the laser diode power of 70 W and repetition rate of 4.2 kHz, with a pulse width of 110.40 ns. Using a dual-pass doubly resonant cavity and a 50 mm-long PPMgLN crystal, the maximum MIR output power of 2.35 W was achieved at 130 °C, corresponding to the conversion efficiency of 18.25%. It is believed to be the highest average power, peak power, and single pulse energy reported to date for PPMgLN-based OPOs pumped at around 2 µm. The MIR OPO was tunable across the range of 3.58-4.10 µm. The output characteristics were systematically investigated under different output couplers, cavity geometries, and crystal lengths. The OPO exhibited good pulse stability with the MIR pulse width of 46.20 ns and a good beam profile (Mx2 = 4.87, My2 = 6.44). Additionally, analysis of parasitic nonlinear processes confirmed the presence of first-order quasi-phase-matching sum-frequency mixing, which provided a convenient approach for monitoring the MIR wavelength.

Red-edge lasers operating within the 670-780 nm wavelength range have demonstrated considerable importance in remote sensing, with particular value in vegetation monitoring, crop identification and precision agriculture. In this work, a widely tunable red-edge laser based on an optical parametric oscillator driving intra-cavity second harmonic generation is reported. Using a double pass pumping BaGa4Se7 doubly optical parametric resonant oscillator with intra-cavity KTiOPO4 second harmonic generation, a broadband tunable output was achieved covering the range of 648.12-799.42 nm. The proposed red-edge laser system delivers an output energy above 1 mJ across a tuning range exceeding 150 nm, and the spectral linewidth is measured to be less than 0.3 nm. A comparative analysis, both theoretical and experimental, has revealed that the intra-cavity configuration reduces the threshold and improve the conversion efficiency compared to the extra-cavity configuration. The development of this widely tunable laser, with its tuning range spanning the entire red-edge region, is expected to play a vital role in advancing remote sensing technologies.

Objective Laser diode (LD)-pumped all-solid-state lasers emitting pulses at 1064 nm with high repetition rate, high output power, and narrow pulse width play an important role in various fields, including LIDAR ranging and imaging, space communication, laser processing, and nonlinear optical frequency conversion. Especially, high repetition rate contributes to improving the frame rate and suppressing the background noise for near-distance ranging and imaging, whereas high pulse energy is favorable for enlarging detection distance for long-distance ranging and imaging. To satisfy the multi-functionalized detection requirements, lasers with adjustable repetition rates (above kHz) and high pulse energy have become one of the keys to LiDAR systems. In addition, as application platforms impose increasingly stringent constraints on the volume and mass of payload, the miniaturization and lightweight design of lasers have become an imperative trend. In this paper, an 885 nm LD-pumped electro-optic Q-switched Nd:YAG master oscillator power amplifier (MOPA) system is reported, which realizes a nanosecond pulsed laser with adjustable kilohertz repetition rate, high pulse energy, and high beam quality. Based on the obtained results, a miniaturized laser prototype has been successfully developed, which is expected to be used in the fields of LIDAR ranging and imaging in special platforms. Methods Figure 1 shows the schematic diagram of the 885 nm LD-pumped nanosecond Nd:YAG MOPA laser system. The MOPA laser system consisted of an LD end-pumped electro-optic (EO) Q-switched master oscillator and an amplifier. Both the master oscillator and the amplifier use LDs with an emitting wavelength of 885 nm as the pump sources to reduce the quantum loss, decrease the thermal load of the gain medium, and improve the laser conversion efficiency. A planar-convex oscillator cavity is adopted as a laser resonator to increase the laser mode volume and optimize the mode matching at different repetition rates. In the amplifier, to improve the power extraction efficiency, a concave lens is placed between the master oscillator and the amplifier to ensure mode matching between the seed light of the master oscillator and the pump light of the amplifier. Further, a multi-segment composite Nd:YAG crystal is used as the gain medium of the amplifier to mitigate the thermal loading of the laser at high pump power. Finally, a 1064 nm laser with adjustable high repetition rate, high pulse energy, and high beam quality is realized. Results and Discussions By optimizing the resonant cavity structure, cavity mode matching is achieved at repetition rates of 1 kHz and 4 kHz, obtaining pulse energies of 3.10 mJ and 1.58 mJ, respectively. Using a one-stage single-pass amplifier based on a three-segment composite Nd:YAG crystal as the gain medium, the single pulse energies are amplified to 12.40 mJ and 3.95 mJ with pulse widths of 4.2 ns and 5.1 ns, respectively. The corresponding peak powers are 2.95 MW and 0.77 MW. The quality (M2) factors at two repetition rates are not more than 1.32, and the maximum root mean square (RMS) value of power fluctuation over 10 minutes is 0.15%. Based on the above results, a miniaturized laser prototype has been successfully developed. Conclusions In this paper, an adjustable high-repetition-rate EO Q-switched 1064 nm Nd:YAG MOPA laser system with high pulse energy, narrow pulse width, high beam quality, and compact structure has been demonstrated. By optimizing the resonant cavity structure of the master oscillator, mode matching between the laser mode and pump mode is achieved at the repetition rates of 1 kHz and 4 kHz. The maximum pulse energies of 3.10 mJ and 1.58 mJ are obtained, respectively. Based on a one-stage single-pass amplifier, pulse energies are amplified to 12.40 mJ and 3.95 mJ at repetition rates of 1 kHz and 4 kHz, respectively, where optical-to-optical conversion efficiencies are 28.2 % and 27.9 %. The pulse widths are 4.2 ns and 5.1 ns, respectively, and the corresponding maximum peak powers are 2.95 MW and 0.77 MW. The M2 factors are not more than 1.32, and the RMS value of power fluctuation over 10 minutes is 0.15 %. Based on the MOPA laser system, a miniaturized laser prototype with adjustable high repetition rate, high pulse energy, narrow pulse width, high beam quality, and high stability has been successfully developed, making it an ideal laser source for laser ranging.

A novel Tethered Balloon-Borne Rayleigh Lidar (TBBRL) system is developed, with middle atmospheric observations successfully conducted. Validation results demonstrate exceptional agreement (coefficients of determination R-2 > 0.95) between simulated and measured echo photon counts, confirming the system's outstanding accuracy and stability. Compared to the ground-based lidar, the TBBRL system exhibits significant performance advantages when deployed at 2-3 km altitude, achieving an extension in maximum detection range over 10 km. Notably, the system maintains robust operational capability under reduced visibility conditions that typically incapacitate conventional ground-based systems, demonstrating superior environmental resilience and measurement reliability. Temperature profile retrievals show excellent consistency with both the NRLMSISE-00 model and TIMED/SABER data, with mean correlation coefficient (R) values exceeding 0.91 and 0.93, while the mean root mean square error (RMSE) values were below 5.4 K and 3.5 K, respectively. The TBBRL system, which combines the advantages of cost-effectiveness, operational endurance and environmental adaptability, offers an innovative and promising approach to study middle atmospheric dynamics.

With the rapid advancement of artificial intelligence, deep learning offers an efficient solution for the design of complex metamaterials. This study proposes a design framework for two-dimensional terahertz metamaterial absorbers based on deep learning-surrogate optimization. A convolutional neural network is developed to encode metamaterial structures as 6 x 6 x 1 grayscale images and predict their absorption spectra at 251 uniformly spaced frequency points within the 12-15 THz range. The model achieves high prediction accuracy, with a loss value of 0.0312 and root mean square error of 0.249 on both training and test sets. To enable inverse design, a single-objective optimization model is constructed and integrated with a surrogate optimization algorithm. The optimization is performed by categorizing structures based on the number of metal blocks, systematically exploring all possible configurations, and iteratively identifying the optimal solution. The predicted absorption performance shows strong agreement with full-wave simulation results, confirming the model's reliability. By integrating deep learning with surrogate optimization, this approach forms a closed-loop framework for both forward prediction and inverse design. It significantly reduces the computational cost of parameter tuning and enables a scalable, automated design process for terahertz metamaterials, offering a powerful strategy for advanced electromagnetic device development.

Objective In most of strategies, the metasurfaces are designed for specific application and the functionalities remain fixed once they are constructed. These metasurfaces lack of adjustability significantly hinders the practical applications. As a promising platform for developing multifunctional, ultrafast reconfigurable devices, dynamically programmed coding metasurfaces have rapidly emerged as a research frontier. Nevertheless, their transition from laboratory prototypes to terahertz-system-level implementations, particularly in addressing the critical demand for cross-band adaptive operations in next-generation 6G networks, remains hindered by fundamental challenges in spectral scalability. In this work, we propose a reconfigurable metasurface based on VO2. This study demonstrates a novel approach for multi-frequency beam manipulation, which includes beam splitting, deflection, scattering, and radar cross-section (RCS) reduction, thereby addressing the critical demand for integrated terahertz wavefront control in next-generation wireless communication systems and stealth applications. Methods To realize these objectives, a three-layer metasurface is constructed. The bottom layer consists of metal ground plane. The middle layer is polyethylamide dielectric spacer with relative permittivity of 3 and thickness of 30 & micro;m. The top layer adopts metal-VO2 circular ring and inner metal circle. The inner circle radius r is a variable and varies according to the different functions of the designed metasurface. Material behavior is characterized through VO2 phase transition model, and Drude parameters are used for this purpose. In this work, conductivity of VO2 is set as 200 S/m and 200000 S/m for the fully insulating and metallic states, respectively. Subsequently, full-wave electromagnetic simulations are conducted in CST Microwave Studio by applying periodic boundary conditions to approximate infinite array behavior. The coding unit adopts 4 & times;4 super subunit structure to ensure stable phase response of the structure. The inner circular units of the 1-bit digitally coding metasurface are designed with radii of 20 mu m and 28 mu m, corresponding to binary states 0 and 1, respectively. The phase difference between the two is 180 degrees at 1.32 THz and 1.55 THz. Stripe ("0101/0101") and checkerboard ("1010/0101") sequences are implemented. To broaden the application scope of coding metasurfaces, we further develop 2-bit coding metasurfaces through precise modulation of the geometric parameter r. For the 2-bit coding metasurface, four different units 0, 1, 2, and 3 are configured, with r values of 22 & micro;m, 20 & micro;m, 2 & micro;m, and 28 & micro;m, respectively. The phase difference between the adjacent two is 90 degrees at 1.55 THz and 1.75 THz. The "0123/0123" and "2222/0000" coding sequences and their convolution product "2301/0123" coding metasurfaces are constructed. In addition, the random sequence generated by Matlab is utilized for diffuse scattering and RCS reduction. Finally, far-field scattering and the RCS reduction results are evaluated under the vertical incidence of THz plane wave. Results and Discussions This study focuses on two specific states: the ambient temperature insulating state (before phase transition of VO 2) and the thermally stabilized metallic state (after phase transition of VO2). First, the amplitude and phase diagrams of 1-bit coding metasurface obtained by CST simulation show adjacent units with a phase difference of 180 degrees (Figs. 3 and 5), satisfying 1-bit phase condition of the coding metasurfaces. By designing reasonable 1-bit coding structure, the metasurface frequency point switches from 1.32 THz to 1.55 THz. The far-field diagram results are shown in Figs. 4 and 6. At 1.32 THz, when the THz plane waves are incident on the stripe and checkerboard coding patterns before phase transition of VO2, single perpendicular reflection is generated [Figs. 4(b) and (d)]. After phase transition of VO2, reflected terahertz beams are distributed in two or four different directions, respectively [Fig. 4(a) and (c)]. When switch to 1.55 THz, the insulating state generates dual-beam and four-beam [Figs. 6(c) and (d)], while the metallic state exhibits specular reflection [Figs. 6(a) and (b)]. Second, in order to expand the application potential of coding metasurfaces, 2-bit coding metasurface configurations are designed. The amplitude and phase diagram of 2-bit coding metasurface obtained by CST simulation shows the phase difference between adjacent elements is approximately 90 degrees (Fig. 7). The 2-bit coding structure work at 1.55 THz and 1.75 THz, where the sequences "0123/0123", "2222/0000", and "2301/0123" are simulated [Figs. 8(a) -(c)]. At 1.55 THz and 1.75 THz, different sequences of metasurfaces generate different reflection beams before phase transition of VO2. Primarily, the far-field images of the "0123/0123" coding sequence shows that the single reflected beam is deflected by an angle [Figs. 8(g) and 9(d)]. Additionally, the beams are reflected in two different directions on the x-axis when the coding metasurface arranged in "2222/0000" sequence [Figs. 8 (h) and 9(e)]. The far-field image of the "2301/0123" sequence is the combination of the "0123/0123" sequence and the "2222/0000" sequence, verifying the characteristics of convolution [Figs. 8(i) and 9(f)] . When VO2 is in the metallic state, all reflected waves exhibit specular reflection [Figs. 8(d)-(f), 9(a)-(c)]. Finally, the random sequence coding generated by Matlab is utilized, and the far-field image presents the characteristics of diffuse scattering [Figs. 10(c) and (d)] . The RCS reduction is over 10 dB for the incident angle ranging from 0 degrees to 30 degrees within the range from 1.5 THz to 1.8 THz [Fig. 10(b)] . Conclusions In this paper, the beam splitting switching and multi-frequency point response of the coding metasurface are achieved by adjusting the temperature of VO2. A 1-bit coding metasurface is designed, whose working frequency can be dynamically switched at 1.32 THz and 1.55 THz, with the bandwidth of 0.23 THz. Furthermore, a 2-bit coding metasurface is designed, demonstrates discrete dual-band operation at 1.55 THz and 1.75 THz with a bandwidth of 0.20 THz. In addition, the coding metasurface exhibits diffuse scattering characteristic and shows significant reduction in RCS after the random arrangement. The coding metasurface enables dynamic multi-frequency control of terahertz waves, providing a novel design paradigm for multifunctional terahertz metasurfaces.

For terahertz systems where reflected signals carry effective information, such as terahertz time-domain reflection systems and full-duplex communication systems, existing nonreciprocal terahertz devices often treat reflected signals as interference and suppress them during isolation. This makes them incompatible with the requirements of such systems for isolating incident signals while directionally extracting and detecting reflected signals. To address this limitation, this study innovatively proposes a terahertz isolator based on a magneto-optical selection-multi-port architecture. The device converts linearly polarized light into a specific circular polarization state through orthogonal double gratings, and by combining the magneto-optical selectivity of InSb material, a nonreciprocal transmission path is constructed. Furthermore, the magneto-optical regulation mechanism innovatively combines branch waveguides with multiple ports and the characteristic of regulating terahertz transmission paths, while achieving isolation of incident/reflected signals and directionally extracting the reflected signals. The simulations of the influences of structural dimensions and external environmental conditions on the nonreciprocal characteristics of the device indicate that when the temperature is 250 K, the magnetic field is 0.3 T, and the structural parameters are set as follows: branch length of 170 mu m, center-to-center spacings of adjacent branches of 125, 125, 120, and 120 mu m, InSb layer thickness of 5 mu m, grating layer thickness of 50 mu m, and substrate layer thickness of 20 mu m, then the device achieves a high isolation of 63.12 dB at 0.73 THz. Additionally, at 0.78 THz, the bidirectional transmission efficiency reaches 36.31%, with a 3 dB bandwidth of 0.25 THz. This device has the advantages such as high isolation, low operating magnetic field strength, and integration of dual functions. It reduces interference from incident signals on reflected signals, simplifies subsequent processing steps such as noise reduction and localization of effective reflected signals, and improves the system's detection performance for weak signals. This provides essential support for expanding terahertz applications to more fields, including non-destructive testing and communication.

Objective Lasers operating near 2 & micro;m, within an atmospheric transmission window and the eye-safe region, exhibit strong overlap with water-vapor absorption and thus offer broad potential for gas monitoring, lidar, ranging, imaging, medical therapy, communications, and electro-optical countermeasures. In addition, they can also serve as sources for generating infrared lasers in other spectral bands. Tm:YAP crystals, owing to their excellent properties, are promising gain media for high-repetition-rate, high-power, and high-energy all-solid-state lasers in the 2 & micro;m band. However, achieving a high-performance actively Q-switched Tm: YAP laser remains challenging. Electro-optic (EO) Q-switching requires high driving voltages and is difficult to operate stably at high repetition rates and average powers, while acousto-optic (AO) Q-switching is constrained by the damage threshold of Tm:YAP, strong thermal lensing, a limited extinction ratio, and the risk of damage induced by water-vapor absorption. To date, no acousto-optically Q-switched Tm:YAP laser has been reported that simultaneously delivers an average power exceeding 20 W and a peak power exceeding 100 kW, particularly near the 1.94 & micro;m water-vapor absorption peak, which restricts its applications in military, medical, sensing, and nonlinear frequency conversion fields. In this study, an all-solid-state acousto-optically Q-switched Tm:YAP laser operating at 1.94 & micro;m with high average power, high peak power, and large pulse energy at kilohertz-level repetition rates is proposed, thereby addressing the frontier application demands of 2 & micro;m lasers. Methods Under high-power pumping, absorption in the Tm:YAP crystal induces pronounced thermal lensing and a high risk of thermal fracture. As a guide for the experiment, finite-element simulations are performed on a b-cut slab crystal with dimensions of 1.7 mm >< 6 mm >< 26 mm. The temperature and stress distributions are analyzed to determine the safe operating regime, which corresponds to an upper pump power limit of approximately 120 W for a pump spot radius of 400 & micro;m. Furthermore, the evolution of the optical path difference (OPD) and the corresponding thermal focal length range are characterized under high pump power. The thermal management differences between slab and bulk crystals are compared, along with the impact of crystal orientation and pump spot size on the thermal focal length. The results indicate that the employed slab crystal maintains a thermal focal length exceeding 30 mm under 120 W pumping, demonstrating its suitability for high-power operation. To minimize the cavity length, a compact L-shaped plano-concave cavity is designed and constructed based on the simulation results. The distance between the front cavity mirror (M1) and the crystal end face is optimized to approximately 35 mm, while the output coupler (M3), a concave mirror with a curvature radius of 200 mm and a transmission of 20 degrees o, is positioned as close as possible to the AO crystal. This configuration provides a broad stability zone while maintaining stable beam sizes at both the gain medium and the AO crystal. This method effectively mitigates thermal lensing in the gain medium under high-power dual-end pumping without the need for intracavity lens compensation, thereby enabling high-power, high-efficiency laser output with good beam quality. Results and Discussions At moderate pump powers, the effects of pump spot size and output coupler transmission on the static characteristics of the Tm:YAP laser are investigated. A pump spot radius of 427 & micro;m effectively reduces the threshold and increases the slope efficiency, while an output coupler with 20 degrees o transmission enables a maximum output power of 10.19 W at 70 W pump power, with broadband emission spanning 1936 -1949 nm. The influences of repetition rate and duty cycle are further examined. Lowering the repetition rate shortens the pulse duration and increases both single-pulse energy and peak power, while also enhancing water-vapor absorption and the risk of damage. Accordingly, a pump spot radius of 427 & micro;m, 20 % output coupler transmission, 5 kHz repetition rate, and 25 % duty cycle are determined as the optimal conditions for high-power operation. Under high pump power, the output increases linearly with pump power without obvious saturation. At 120 W pump power and 5 kHz repetition rate, the laser delivers a maximum average power of 27.92 W with a slope efficiency of 35.67 degrees o, single-pulse energy of 5.58 mJ, pulse duration of 48 ns, and peak power of 116.25 kW. The pulse train and waveform are stable, the emission spectrum narrows to 1936.5-1939.4 nm with a central wavelength of 1938.18 nm, and the beam quality factors are M-x(2)=2.44 and M-y(2)=2.56. Continuous operation at 120 W pump power for 30 min yields an average output of 27.90 W with a root mean square (RMS) power instability of 0.11 degrees%, confirming excellent stability. Performance comparison demonstrates that this study achieves nanosecond laser output in the near 2 mu m band with simultaneously high average power and high peak power, providing a new technical route for laser sources toward medical, sensing, and nonlinear frequency conversion applications. Conclusions A high-power, high-energy all-solid-state acousto-optically Q-switched Tm:YAP laser operating at 1.94 mu m is demonstrated. A double-end-pumped b-cut slab Tm:YAP crystal is employed, and the pumping conditions and cavity design are optimized through thermal-effect analysis to achieve efficient thermal management and high thermal tolerance. At 120 W pump power and a repetition rate of 5 kHz, the laser delivers 27.92 W average power with a pulse duration of 48 ns, single-pulse energy of 5.58 mJ, and peak power of 116.25 kW. The output power increases linearly with pump power, while the emission spectrum covers the range of 1936.5-1939.4 nm. The beam quality factors are measured as M-x(2)=2.44 and M-y(2)=2.56, and the RMS power instability is 0.11 degrees o over 30 min. With its high performance, compactness and stability, this laser is well suited for medical, defense, sensing, and mid-to far-infrared optical parametric oscillator pumping applications.

Terahertz hollow core negative curvature fiber (HCNCF) offers high-performance waveguiding but face fabrication challenges due to complex processes. In this article, we present a simple and cost-effective new paradigm, the film-to-fiber method, utilizing commercial polyimide (PI) films to form a typical six-cladding-tube HCNCF structure. Additionally, metal microstructures can be integrated onto the PI film to enhance waveguiding properties. Three HCNCF types-without metal structures, with full metal integration, and with selective metal placement-are fabricated and characterized using terahertz time-domain spectroscopy system across 0.2-1.5 THz. Experimental results, including experimental loss, refractive index (birefringence), dispersion, and other parameters, align well with numerical simulations. This study introduces a cost-effective and flexible fabrication approach that accommodates polymer films of arbitrary thickness, providing a new paradigm for HCNCF manufacturing and advancing terahertz applications.

Nonlinear effects in the terahertz regime play a pivotal role in advancing terahertz wave generators with higher frequencies, particularly through harmonic generation processes. However, the development of efficient nonlinear terahertz materials that exhibit high conversion efficiency, compatibility with large-scale on-chip integration, and stable operation at room temperature remains a significant challenge. Graphene-assisted nonlinear metamaterials provide a promising platform for investigating nonlinear effects within the terahertz frequency regime. In this study, we present a transmission-mode nonlinear metamaterial-integrated device that synergistically combines the resonant characteristics of metamaterials with the nonlinear enhancement properties of graphene. This integrated structure enables efficient dual-frequency third harmonic generation (THG) at 9.535 THz and 10.959 THz, achieving a conversion efficiency of 0.127% under a pump intensity of MW/cm2. A comprehensive theoretical analysis is conducted to investigate both the linear and nonlinear operational characteristics of the integrated device. The enhancement mechanism of THG is systematically investigated by examining the electric field distributions and plasmonic resonance characteristics. Additionally, the influences of device structural parameters and terahertz wave incidence angle on the operational characteristics are thoroughly evaluated. The proposed graphene-based nonlinear metamaterial shows exceptional potential for broad applications in terahertz integrated systems and related photonic technologies.

Exosomal microRNAs (miRNAs) are among the most common biomarkers for tumor diagnosis. However, singlemiRNA detection lacks ideal sensitivity and specificity for diagnosing a certain tumor in clinics. In this work, we fabricated a convenient multi-miRNA detection platform for sensitive and specific detection on exosomal miRNAs in the plasma of patients using a terahertz (THz) metamaterial biosensor on the basis of strand displacement amplification (SDA) and AuNPs. The proposed multi-miRNA detection platform was highly sensitive to miRNA15, miRNA-21, miRNA-145, miRNA-155, miRNA-423, and miRNA-451, and the limit of detection (LOD) obtained were 12.54 aM, 19.66 aM, 17.50 aM, 25.40 aM, 24.11 aM and 26.59 aM, respectively. The biosensor we constructed can be used to diagnose pancreatic cancer patients effectively in complex clinical samples. The use of multiple miRNAs demonstrated strong practicality in the combined diagnosis of patients with pancreatic cancer. These studies demonstrate that the multi-RNA detection platform boasts advantages such as low cost, rapid, high sensitivity, and specificity, offering a potential tool for future clinical applications.

To meet the testing requirement of pulse-coded laser ranging systems, an FPGA-based coded laser pulse target simulator is demonstrated in this work, based on multi-phase clock method. The simulator can generate echo pulses with a programmable time delay when triggered by laser pulse sequence. A temporal resolution of 1ns (corresponding distance of 15 cm) is realized with a delay range from 74 ns to 5.24 ms (corresponding to distance from 11.1 m to 786 km).The simulator can also modulate the echo pulses' width, which is used to simulate the influence of complex environments such as atmospheric turbulence on the time-domain characteristics of laser pulses, with a broadening resolution of 1ns. Results from the experiment confirm that this approach effectively overcomes the limitations in precision, stability, and coding compatibility found in traditional solutions, providing a reliable technical support for the development and testing of pulse-coded laser ranging systems.

All-dielectric chiral metasurfaces, as an emerging micro-nano optics device, have been favored in the fields of encrypted communication and optical device integration in recent years due to the strong circular dichroism and spinning effect at tiny sizes. Here, an all-silicon monolayer metasurface capable of simultaneous polarization and phase modulation is constructed. This approach transcends conventional limitations of single meta-atom wave manipulation by employing two pairs of chiral isomers to construct functional ‘meta-molecules’. Within each meta-molecule, the rotation of individual chiral meta-atoms imparts distinct phases to the excited circularly polarized light, which recombines into linearly polarized light with varied polarization in the transmitted wave. Subsequently, geometric phase modulation is incorporated between adjacent meta-molecules to achieve precise wavefront phase control. Through spectral analysis of simulations and theoretical calculations, this metasurface maintains 92% polarization conversion efficiency while accomplishing planar wavefront shaping. This metasurface, fabricated entirely from silicon, features high refractive index, low loss, and low cost, enabling direct processing with commercial silicon wafers. It establishes a novel platform for multi-parameter metasurface operations, demonstrating significant application value in THz imaging, sensing, and wireless communications.