This PDF file contains the front matter associated with SPIE Proceedings Volume 12284, including the Title Page, Copyright information, Table of Contents, and Conference Committee listings.

An atmospheric plasma jet was generated by ionizing nitrogen ejected from a torch loaded with high voltage. The acquisition of transmission spectra by terahertz time-domain spectroscopy was carried out at three locations at different distances from the plasma torch nozzle. Combined with the theoretical model of terahertz pulse propagation in uniform plasma medium, the average density of plasma was calculated from the phase shift and spectral amplitude ratio measured experimentally. By comparing the measurement results of plasma density with those of Langmuir double-probe for these three different positions, the feasibility of measuring average density of atmospheric plasma with terahertz time-domain spectroscopy was corroborated.

Terahertz technology has been widely used in Chemical component recognition, high-speed communication, and security check imaging. Terahertz metrology plays an important role in all of these applications. The progress of terahertz spectrometers calibration and terahertz radiometry at the National Institute of Metrology, China, is introduced in this paper. A technique for calibration of terahertz time-domain spectrometers is introduced. The terahertz timedomain spectrometer is online calibrated with the terahertz echo pulse, and the measurement repeatability is improved. A high absorbance coating fabricated and a terahertz radiometer is developed. Broadband terahertz radiation is highly absorbed and accurate measured with this terahertz radiometer. A portable terahertz power is fabricated for measurement of terahertz sources and calibration of terahertz power meters.

A new metamaterial modulator based on a metamaterial absorber is proposed for the first time by utilizing the negative differential conductance (NDC) effect in n-GaAs. The modulator consists of gold square resonators on an n-GaAs substrate integrated with a gold film on the bottom. This device's absorption spectrum, which is in the range of terahertz (THz), can be modulated by applying high bias voltages between the resonators and the bottom gold film. The nonlinear response of this modulator operating under the ideal mode is investigated in detail by FDTD Solutions. The simulation results show that the bias voltage causes a redshift of the resonance frequency of the absorber and an increase in the resonance strength. This phenomenon can be attributed to the NDC effect resulting from the transferred-electron mechanism, which reduces the electron mobility and increases the electron effective mass under the bias voltage high enough. The absorption of modulators with square resonators of different sizes has also been investigated, and similar trends on the change of resonance frequency and resonance strength appear. This kind of device enables the dynamic control of THz waves by applying different voltages, which can be used as a terahertz modulator.

As a topological crystal insulator, tin telluride (SnTe) has unique properties that are different from those of traditional topological insulators. Due to its helical multi-surface states, strong topological protection characteristics, gapless topological surface states, narrow bulk band gap, high mobility at room temperature and other excellent properties, SnTe has a great application potential in photodetectors with minimal energy consumption, broad spectrum and ultra-fast response. However, the preparation of large area high quality SnTe nanofilms is still a big challenge. Here, we report a facile and efficient preparation method for large area SnTe nanofilm (2 cm ×2 cm) by RF magnetron sputtering method. The nanofilm having a thickness of 5.8 nm and surface roughness of 0.51 nm was obtained. Moreover, the prepared nanofilm was crystallized without annealing treatment and exhibited uniform surface. The photoconductive prototype device based on the SnTe nanofilm demonstrated a significant photoelectric response under an illumination of 365, 555 and 850 nm light source at room temperature. Furthermore, the ultraviolet, visible and near infrared photoelectric performance of the device remained stable even after six months in the atmosphere of the drying cabinet. These results indicate that the SnTe nanofilm has potential applications in broad spectrum photodetectors.

Optical constants of lactose pumped by strong terahertz (THz) waves have been investigated. The sample was measured by a THz-pump/THz-probe system, in which the electric field strength of the pump-THz waves exceeds 120 kV/cm. When the lactose sample is pumped by strong THz pulses, its probed response signal lasts about 2 ps. With different delay time, the optical constants of lactose was also measured and discussed. The experimental results show that the optical properties of lactose molecules can be changed by high-intensity THz waves, and this change is related to the applied the interaction time, which is in the order of picosecond.

We propose and demonstrate a multi-peak high-sensitivity refractive index sensor for the terahertz band. The designed sensor is composed of a flexible polyimide substrate and a metal structure array covering the top, which is easy to be processed and convenient to be used. According to different structural changes, we can adjust the resonant frequency of the designed metamaterial sensor. The simulation results show that the sensor has three resonance peaks (0.46, 1.06, and 1.29 THz respectively) in the frequency range of 0.1-1.4 THz, and among them the maximum refractive index sensing sensitivity obtained is 272 GHz/RIU. The proposed metamaterial sensor with such high sensitivity performance has potential application prospects in biomedical sensing and trace substance detection.

A cylindrical metal tapered probe with a periodic sub-wavelength groove is studied in this paper. The surface plasmon polaritons (SPPs) is supported by periodic ring grooves on the surface of the metal line. To achieve enhancement of the electric field, the tapered tip is used to focus the surface waves tightly. The affection of the sub-wavelength microstructure parameters on the transmission loss and the enhancement factor of the electric field are compared. When the frequency of the electromagnetic field is low, the loss of the periodic grooved metal line negative correlates with the groove depth and width but positive correlates with the radius and the period. As the frequency increases, the correlation between the transmission loss of the metal line and the groove depth, width, radius, and the period reverse. Similar to the loss of the metal line, the field enhancement factor of the probe tip is also vulnerable to the frequency of the electromagnetic field. The field enhancement factor of the probe tip increases as the period decreases when the electromagnetic field frequency is low. In contrast, the field enhancement factor of the probe tip declines as the period decreases as the frequency increases. However, the field enhancement factor of the tip positive correlates with the groove depth and width but negative with the radius in the whole passband. The simulation result prove the feasibility of the proposed method and pave the way for the development of low-loss, miniaturized, low background noise, and high-focus electric field enhancement factor terahertz near-field probes.

Wireless communication and sensing show more and more similarities in system design and signal processing flows. A common transmitter sharing is preferred for communication and sensing to reduce equipment cost, hardware size, and power consumption. In this paper, we propose and demonstrate a joint photonic transmitter for wireless communication and sensing at mmW-band based on heterodyne detection. The key device of the photonic transmitter is a dual-drive Mach- Zehnder modulator (DMZM) and a multichannel tunable optical filter (MTOF). The two arms of the DMZM are driven by a specially coded sine wave and a specially coded single chirped linear frequency modulation (LFM) wave, respectively. Besides, both of the two amplitude-coded waves are simultaneously modulated onto the two lasers coupled into the DMZM. By filtering out appropriate sidebands using the MTOF, an amplitude-shift-keying (ASK) signal for wireless communication and a dual-chirp LFM for sensing at mmW-band can be simultaneously generated after heterodyne detection. When the product of the two baseband signals used to code the sine and LFM waves is fixed, the envelope of the mmW LFM wave for radar sensing keeps constant. The simulation results show that a 11.5-Gbit/s ASK signal and a dual-chirp LFM signal with constant envelope are successfully generated at the same time. By properly setting the frequencies of the lasers and the sine wave, the generated ASK signal can be centered at 28GHz for 5G mmW communication, and the generated LFM wave can be distributed around 79GHz for vehicle radar sensing. Thanks to the dual chirps of the mmW LFM wave, range-Doppler decoupling is achieved.

High-speed Terahertz Time domain spectroscopy (High-speed THz-TDS) system is developed on the basis of traditional THz-TDS. It can effectively compensate for the shortcomings of traditional THz-TDS. High-speed THZ-TDS features fast spectrum scanning speed and High spectrum resolution. But it needs a stable local clock signal to lock the repetition rate of the laser in the system. In this paper, a method of taming OCXO with China's BeiDou Navigation Satellite System (BDS) is proposed to generate stable clock signals. Using this signal as the local clock for the high-speed THZ-TDS. The cost of this method is 2,600 yuan, less than one-tenth of the price of rubidium atomic clocks, without significantly reducing stability. This method provides a high stability, low cost clock signal for high-speed THZ-TDS system, and has long term stability.

Terahertz imaging has a wide range of applications in the field of nondestructive testing. In this paper, a novel thickness-testing method based on active terahertz imaging with a non-cooled focal plane array terahertz camera is proposed, which uses the poly tetra fluoroethylene (PTFE) as the object to study. Firstly, we capture the active terahertz images of PTFE wafers of different thickness using IRXCAM-THz-384 camera. Second, by using the curve fitting method, interpolation method, grey theory model, neural network and support vector machine, the relationship between the thickness of PTFE wafers and grayscale is predicted. Then the accuracy of different methods is compared. Finally, we establish the thickness-grayscale relationship model. The experimental results show that the predicted greyscale data is close to the actual data, and the error range can be controlled within 1%, which verifies the accuracy of the model and meets practical engineering application standards.

In this article, the band structures of InAs/InAsSb superlattices are calculated by sp3s* model, which is based on empirical tight-bonding method (ETBM). First, the band structures of InAs/InAsSb superlattice with varies period are calculated, the calculated bandgap results are consistent with experiment values. The conduction band edge (Ec level) for the two sets of InAs/InAsSb T2SLs are approximately independent of the cutoff wavelength (or band gap), and they are significantly lower than the conduction band edges of InAs/GaSb. The relationship between periodic structure and cutoff wavelength is obtained under the condition of strain balance. Then the holes effective mass at Γ point of mini-band along the growth direction for different structure InAs/InAsSb superlattice are derived. Finally, the composition segregation function is included in our model in order to study the impact of Sb segregation on InAs/InAsSb superlattice. These material parameters obtained from our calculated results can be used in the design of T2SL-based IR detectors.

HgCdTe films with low defect density grown by molecular beam epitaxy(MBE) has been proved to be irreplaceable materials for fabricating high performance infrared focal plane arrays(IRFPAs) such as dual band detector, high operating temperature(HOT) detector and avalanche photodiode(APD) detector. CdZnTe is the best choice of substrates for epitaxy of HgCdTe owning to the perfectly matched lattice. However, the Cd-rich or Te-rich precipitates in CdZnTe substrates are hard to completely eliminate. These precipitates in the CdZnTe substrates induced the formation of precipitate-related defects at the HgCdTe layer, resulting in detrimental device performance, especially for detectors with small pixel size and high operability. To understand the origin of the precipitate-related defects at the HgCdTe layer, we investigated the influences of Cd-rich and Te-rich precipitates in CdZnTe substrates on dislocations and macro-defects in HgCdTe gown by MBE. Gridlines were produced by photolithographic and wet etching process to locate small defects in SEM according to the location in dark field microscopy. Results indicated that Cd-rich precipitate leads to formation of a dislocation cluster in HgCdTe film. Etch pit density(EPD) in dislocation cluster area is in the range of 2×10⁶ to 6×10⁶ cm^-2, about one to two orders of magnitude larger than EPD in a normal region. EPD in the cluster varies with depth of Cd-rich precipitates, and the relationship between them accords well with 1/h dislocation fall-off law, suggesting a minimum EPD of 5×10⁵ cm^-2 in dislocation cluster. In contrast, no dislocation cluster was found in HgCdTe film on CdZnTe with Te-rich precipitates, but Te-rich precipitates can lead to macro-defects, even under the optimum growth conditions. The typical macro-defect density resulted from Te-rich precipitates of state-of-the-art HgCdTe/CdZnTe is range from 100 to 500 cm^-2, which is considered limited by Te-rich precipitates with size of 100 to 1000 nm if the high-density macro-defects caused by particles or pollution residues on CdZnTe substrates are excluded.

Herein, SnSe2 QDs have successfully been prepared by liquid-phase ultrasonic exfoliation of the group IV metal-sulfide compounds. The morphology and structure of the SnSe2 QDs were characterized by transmission electron microscopy (TEM) and high-resolution transmission microscopy (HR-TEM), and the composition of the materials was analyzed by X-ray diffraction (XRD) and Raman spectroscopy (Raman). The absorbance of the samples with different wavelengths was analyzed by UV-Vis spectrophotometer, and the fluorescence intensity at different excitation wavelengths was studied by fluorescence spectrometer (PL), and the effect of different centrifugal speeds on the particle size of QDs and the spectral red-shift caused by the size effect was investigated. The average lateral sizes of SnSe₂ QDs samples obtained at centrifugal speeds of 3500, 1500 and 500 rpm were 1.86 nm, 2.73 nm, and 3.3 nm, respectively. The SnSe₂ QDs exhibited significant absorption in the infrared band and red-shift with increasing QDs size, The results demonstrated the potential use of this new material in infrared detection.

Silicon has been widely used in the field of low-cost photodetectors. However, the use of traditional silicon material for high performance infrared detectors is hindered by its indirect band gap. Recently, black silicon has attracted the attention of researchers working on optoelectronics as it can be considered a new type of material with high absorption, and expansion of the response band can be achieved by supersaturated doping. Importantly the material is compatible with the silicon process. With the development of science and technology, the application of photodetectors can have a great impact on our lives, so the research on black silicon photodetectors is also becoming popular. Up to now, significant progress has been made in the development of black silicon photodetectors. This paper summarizes the preparation of black silicon materials and the application prospect of black silicon photodetectors.

Colloidal quantum dots (CQDs) have been widely applied in the design and development of optoelectronic devices due to their controllable size, tunable band gap and inexpensive low temperature solution processing etc. However, the preparation method of quantum dots film is a critical part of the preparation process of optoelectronic devices, which can restrict the application of CQDs in optoelectronic devices. In this paper, different preparation technologies of CQDs film are summarized. The advantages and disadvantages of different preparation technologies of CQDs film are discussed to suggest suitable options for different CQDs film based optoelectronic devices.

Ultraviolet (UV) photodetector has been widely used in astronomical observation, missile warning, optical communication, flame and environmental detections and so on. Herein, recent research progress on UV focal plane detectors is summarized, including commonly used materials in this field. Furthermore, commercially available UV focal plane detectors, and its structure and performance are also discussed. Finally, the practical problems limiting the further development and application of UV focal plane detectors are summarized and discussed in this paper.