This PDF file contains the front matter associated with SPIE Proceedings Volume 11441, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Infrared thermal imager is widely used as target detection, search and tracking system due to its super night vision capability. The traditional thermal imager will cause column noise and serious image degradation due to temperature change, which will affect the observation effect. Therefore, it is necessary to carry out non-uniformity correction by the baffle (or shutter). However, in the process of shutter correction, there will be a short time for the search and tracking equipment to fail to work, which is easy to cause target loss. At present, all search and tracking systems require the installation of a continuously working infrared thermal imager without shutter. In order to realize the non-uniformity correction technology of infrared thermal imaging without shutter, a fast correction method for image gradient optimization based on noise template is proposed in this paper. Due to the special manufacturing process of the detector, when the temperature of the detector changes, the output image will produce vertical stripes with regular shapes. The noise patterns obtained at different temperatures are linearly related. Therefore, there is a noise model M, which makes the noise matrix at any temperature can be expressed as the product of M and a constant k (k is related to the detector Temperature K). The fringe noise of the image is quantified by detecting the sum of the absolute values of the transverse gradients of the image, and the non-uniformity correction without shutter is realized by adjusting the parameters so that the sum of the absolute values of the transverse gradients is minimized. This method can not only compensate temperature drift, but also replace the shutter to realize one-point correction, which reduces the power consumption of the whole machine and improves the reliability. There is no need for complicated calibration work in High and low temperature test chamber. It is not even necessary to record the current detector working temperature in real time for calculation. This method is simple in structure and easy to implement. The practical application proves that the infrared thermal imaging system has clear imaging. The effect is excellent.

Ginseng drugs are reported to have multiple health benefits, which are believed to boost energy, lower blood sugar and cholesterol levels. However, ginseng products can vary in their components and medicinal properties. Panax ginseng, American ginseng and radix pseudostellariae are different medical substances. Therefore, it is of great significance to accurately and quickly identify them for the quality control and clinical medication safety of TCM (traditional Chinese medicine). However, the identification of the botanical origins of crude drugs through anatomical and chemotaxonomical studies is limited. It is noted that the effective identification of the herbal species can be interpreted by terahertz wave. The frequency range of the terahertz wave is from 100 GHz to 3 THz. Most of the vibrational and rotational energy levels of biological macromolecules are in the terahertz band. Terahertz time-domain spectroscopy (THz-TDS) is used to obtain the time-domain spectrum of ginseng drugs at room temperature. It was shown that we can discriminate different ginseng samples by the terahertz waves.

In cigarette manufacturers, the detection of cigarette quality has always been the key problem in the entire industry's production chain. The efficiency and accuracy of detection technology are directly related to product quality and furthermore, it will affect the credibility and economic benefits of the entire enterprise. For the cigarettes with blasting beads, in order to ensure the safety of smokers during smoking and to obtain a better experience, determining the presence or absence, location, and damage condition of beads in the cigarette filter is critical. Therefore, it is necessary to test the beads in the manufacturing process of the cigarette, thereby timely remove the unqualified product. In this paper, a nondestructive testing method based on reflective terahertz time-domain spectral imaging system is proposed, which can easily evaluate the presence or absence approximate position and damage condition of beads in the cigarettes filter. To lay a foundation for further accurate and effective measurement of the positional offset of beads and to evaluate the damage condition of beads, it is of great significance to improve the production efficiency and tobacco quality of the tobacco factory.

Terahertz wave generation from laser induced air plasma has a close relevance with the applied external electric field. In this paper, by applying a high-voltage DC electric filed onto the laser induced air plasma, we demonstrated that the amplitude of generated terahertz wave increases linearly with the external electric field strength, the terahertz amplitude and power are quadratic in the lower power region and the terahertz amplitude is linear with the pump light power in the high power region. Moreover, the polarization direction of the generated terahertz wave changes synchronously with the direction of applied external electric field. The results proved the effect of external electric field on the power and polarization of terahertz wave generation from laser induced air plasma.

The vortex beam has attracted much attention due to its great potential applications in communication and medicine area. To compare with the regular light, the vortex beam carrying the orbital angular momentum can greatly increase information capacity in communication. In this paper, a new method is presented to generate terahertz vortex beam based on the complementary open-rings metamaterial. The structure is composed of a metasurface-dielectric-metasurface, which top and bottom layer are both complementary open rings, and the dielectric layer is polyimide. And the vortex beam generators with topological charge of 1 and 2 have been designed according to the phase principle of Pancharatnam-Berry (P-B), which based on the different orientation of open ring unit cells. The amplitude and phase of the cross-polarized transmitted beam were manipulated by rotating the orientation of the complementary open rings, while ensure the amplitude of the transmitted beam stays unchanged, and the phase of the cross-polarized transmitted beam cover the range of 1*2π (where l is the topological charge). The vortex beam characteristics has been studied when circularly polarized light incident on the measurface of vortex beam generators with the CST MICROWAVE STUDIO.

The simulation results show that the transmitted beam are well meet the characteristic of vortex beam, which the transmittance of cross-polarized vortex beam is as high as 64% at 1.48 THz while the phase can cover the range of 1*2π. That is, the presented transmissive vortex beam generators can convert incident circularly polarized beam into a cross-polarized vortex beam carrying orbital angular momentum. The approach demonstrated in this paper which is high conversion efficiency, simple structure, quick response, and has potential applications in the field of terahertz communication.

We design a simple optical element to generate a monochromatic plate-like diffraction-free terahertz (THz) beam. By using 3D-printing technology, this element can be fabricated easily and quickly. Numerical and experimental results show that the output beam of such element has a one-dimensional (1D) invariant transverse profile, i.e. it is a plate-like THz beam in free space. In order to make this kind of beam more practical, we design a lens group system to increase the diffraction-free length from 5cm to more than 20cm. In addition, a fast numerical algorithm based on diffraction integral has been built to analyze the measured results.

Terahertz time-domain spectroscopy (THz-TDS) is a sensitive technique to characterize vibrational modes. It is widely used to monitor polymorphism of solids. This study investigated the terahertz (THz) absorption spectra of azithromycin dihydrate over a temperature range from 90 to 300 k to access more information about the structure and vibrational dynamics of hydrates. As the temperature was increased, the absorption peaks became wider and shifted towards lower frequencies. The temperature dependence of the absorption spectra was explained by the anharmonicity of the vibrational potentials. This method provides more information to characterize the temperature dependence of hydrate structures and contributes to the quality monitoring for the pharmaceutical industry.

The non-uniform response of infrared focal plane array (IRFPA) detectors has a serious impact on image quality. First, the image is not clear visually, there are serious fixed mode noise, and second, the dynamic range, which reduces the resolution of infrared image. In view of the shortcomings of the existing non-uniformity correction schemes and the actual engineering requirements, this paper proposes a scheme combining registration-based correction algorithm with micro-motion system, which calculates the relative displacement between two adjacent images by projection estimation. At this time, the scene motion is judged. When the motion is inadequate, the scene motion is controlled to make the controller operate according to a certain trajectory, so that the scene conditions can meet the requirements of the correction algorithm as far as possible, solve the practical application requirements, make the image quality achieve better results, and perform the performance of the algorithm. The test results show that the scheme can effectively correct the non-uniformity and obtain better correction effect.

Terahertz wave is generally an electromagnetic wave at the wavelength of 0.1-10 THz (30-3000 μm). The terahertz laser is a new type of radiation source with many unique advantages and has broad applications. Generally, the size of a normal laser cavity is from a few of to several hundred millimeters, and the size of a micro-cavity is mainly from a few of to several hundred micrometers in the wavelength region of ultraviolet, visible, and near-infrared. However, if the wavelength increases to the terahertz region, the wavelength is of the order of the micro-cavity size. The power distributions inside and outside the cavity of a terahertz laser are significantly different from those for a conventional laser cavity. In this paper, a theoretical model is established to study the outputted and leaked power of a micro-cavity in the terahertz band. We assume that the wavelength of an emission terahertz source is 240 μm and simulate the output features of a micro-cavity laser with the Finite-Difference Time-Domain (FDTD) algorithm. The output characteristics of a micro-cavity have been analyzed by using two types of material and different thicknesses of the sidewall. It has been found that when the thicknesses of both silver and aluminum sidewalls are reduced to around 16 μm, the power leaking from the micro-cavity begins to increase with the decrease of the sidewall thickness. In this way, the sidewall no longer restrains terahertz radiation inside the cavity. The simulation results might be referred for the design of a terahertz laser with the micro-cavity.

Infrared target detection and tracking technology has been widely used in the fields of transportation, medical, safety and military affairs, etc. However, there stills exists some challenges in infrared target detection and tracking, such as dim small target, complex background, target occlusion and appearance changes, etc. On the other hand, as the most effective bio-intelligence system, Human Visual System (HVS) has significant advantages in image processing. In this paper, several brain-inspired models (including lateral inhibition, receptive field, synchronous burst, visual attention, and cognitive memory) and Deep Neural Networks (DNNs) have been studied. Furthermore, the relevant mathematical models are established, the corresponding algorithms are proposed, and the comparison experiments are conducted. In summary, applying the brain-inspired models and DNNs to the infrared target detection and tracking is beneficial to achieve the accurate infrared target detection and robust tracking under complex conditions.

Terahertz wave has been inspired great interests for its myriad applications, such as biochemical sensing and highbandwidth communications, etc. THz sources are the key technology toward the wide applications. Therefore, THz sources are highly focused on developments, especial those with wide band, high power, room temperature operation. Vacuum electronic THz sources are important directions in THz sources. Institute of Electronics, Chinese Academy of Sciences (IECAS) with the history over 60 years has developed many kinds of vacuum electronic devices, such as klystrons, space traveling wave tube amplifier (TWTA), Gyrotron and extended interaction oscillator (EIO), etc. In this paper, we report the progresses in IECAS of Terahertz traveling wave tube. The three types of TWT are described, the first kind of TWT is the high power for the pulse SAR and ViSAR, the second kind of TWTA is for the space satellite communication, and the third kind of TWT is the TWTA module. Through the studies of small size cathode, electron optics system, low attenuation high frequency structure, and high transmission window, the 220GHz TWT is developed. The experimental results show that the output power is 5.8W at the frequency of 215GHz, and signal bandwidth is 5GHz. The second kind of TWTA is the design and the TWTA module is being developed.

This paper proposes the deconvolution image restoration algorithm, which uses the point spread function constructed by the physical characteristics of the terahertz beam to reconstruct the terahertz image and improve the image resolution[1]. At the same time, by constructing a point spread function with different penetration depths in the sample, the effect of image chromatogram on the sample can also be achieved. The integrated circuit (IC) electronic package terahertz imaging results clearly show the spatial position of the pins, internal chips and defects of the electronic packages, and analyze a variety of failure defect types, which are <1% more than the actual size.

Flexible infrared detectors with multispectral imaging capability are attracting great interest with increasing demand for sensitive, low-cost and scalable devices that can distinguish coincident spectral information and achieve wide field of view, low aberrations, and simple imaging optics at the same time. However, the widespread use of such detectors is still limited by the high cost of epitaxial semiconductors like HgCdTe, InSb, and InGaAs. In contrast, the solution-processability, mechanical flexibility and wide spectral tunability of colloidal quantum dots (CQDs) have inspired various inexpensive, high-performance optoelectronic devices covering important atmospheric windows from short-wave infrared (SWIR, 1.5 – 2.5 μm) to mid-wave infrared (MWIR 3 – 5 μm). Here, a potential route leading to flexible infrared electronic eyes with multispectral imaging capability is demonstrated by exploring HgTe CQDs photovoltaic detectors. At room temperature, the HgTe CQDs detectors demonstrate detectivity D* up to 6 × 10¹⁰ Jones in SWIR and 6.5 × 10⁸ Jones in MWIR. At cryogenic temperature, the MWIR D* becomes BLIP and increases to 1 × 10¹¹ Jones. Besides high D* , the HgTe CQDs detector shows fast response with rise time below 300 ns. By stacking CQDs with different energy gaps or coupling CQDs with tunable optical filters, dual-band and multi-band infrared detection can be achieved in wide spectral ranges. Finally, infrared images are captured with flexible HgTe CQDs detectors at varying bending curvatures, showing a practical approach to sensitive infrared electronic eyes beyond the visible range.

Natural Cordyceps usually has rarity and upstanding curative effects on the disease, but some substitutes also have been used and adulterants confused the market. Therefore, controlling the quality of Cordyceps sinensis and its products is very critical to ensure their safety and efficacy. Terahertz spectroscopy can be used to qualitatively analyze complex mixed systems, examine all components of medicinal herbs, and reflect the overall information of samples. We report experimental measurement of Hirsutella sinensis, one of the Cordyceps sinensis myceliums in the spectral range of 0.2- 2.5 THz using terahertz time-domain spectroscopy (THz-TDS). Additionally, we demonstrate that THz-TDS combining with principal component analysis (PCA) methods was proposed for the identification of Cordyceps sinensis mycelium. The results of chemometric analysis show that the method can better detect the stability of traditional Chinese medicine.

We present the technique and experimental laboratory setup for measuring and analysis of diffuse reflectance spectra obtained by tunable infrared quantum cascade laser with an average power of 15 mW. Using causality relations for real and imaginary part of reflectivity we can calculate extinction coefficient. We use the dumped harmonic oscillator model to calculate synthetic spectra and test Kramers – Kronig relations for spectra calculations. To improve the accuracy of calculated extinction spectra we apply extrapolation of experimental spectra and phase correction. Using experimental setup and numerical methods of spectra analysis we could identify the powder of 30 μg of Acetylsalicylic acid and 40 μg of L-Tyrosine.

One novel Topas-based Photonic Crystal Fiber (PCF) has been modeled and analyzed for chemical analytes detection in terahertz frequency range. The sensor was realized by filling different kinds of chemical analytes in the hollow core of the PCF, consisting of five layers air holes of hexagonal lattices in the cladding. The propagation characteristics of proposed sensor have been investigated by adopting the Full Vectorial-Finite Element Method (FV-FEM) with anisotropic perfectly matched layers (PMLs). Numerical results indicated that the hollow-core provided a high relative sensitivity as well as low transmission loss. When optimal design parameter was selected as core diameter 𝐷_core = 400 μm, the PCF sensor showed high relative sensitivity of 80.32%, 83.3%, 84.64% with negligible confinement loss of 1.01×10⁻¹⁰ cm⁻¹, 7.65×10⁻¹¹ cm⁻¹, 7.49×10⁻¹¹ cm⁻¹ at 1 THz frequency for Water, Ethanol, Benzene, respectively. Moreover, other important mode properties such as the core power fraction, Effective Material Loss and dispersion, were discussed completely in the terahertz frequency range. With the outstanding waveguiding properties, the simple sensor can be produced at a low cost and provided a new avenue for chemical sensing.

Sartans represent the most frequently prescribed antihypertensive agents, which exert their action by inhibiting the binding of angiotensin Ⅱ(AT), a blood pressure regulating agent to its AT receptor. Among them, olmesartan, irbesartan and candesartan are excellent AT receptor inhibitors, and their excellent properties are closely related to the representative molecular structures. There are five-membered nitrogen ring, carbonyl group (C=O) or carboxylic group (-COOH) in such three kinds of sartans, and different structures could be distinguished successfully with terahertz time domain spectroscopy (THz-TDS) due to the characteristics of finger-print features. In this work, the vibrational spectra of olmesartan, irbesartan and candesartan have been characterized by THz-TDS. Distinctive absorption peaks are observed at 0.52, 1.08, 1.36 THz for olmesartan, 0.65, 0.74, 1.09, 1.28 THz for irbesartan and 0.60, 1.47 THz for candesartan by THz-TDS measurement, respectively. Density functional theory (DFT) has been used to simulate three kinds of sartans. The theoretical simulation has predicted characteristic peaks of three sartans in the 0.2~1.6 THz range, and the absorption peaks have been simulated at 0.51, 0.71, 1.12, 1.30 THz for olmesartan, 1.05, 1.33 THz for irbesartan, 0.59, 1.53 THz for candesartan. In addition, the molecular structures of three kinds of sartans have also been analyzed. The simulated results were agreement with experimental results very well, and the vibrational modes of peaks were also assigned based on the simulated results of DFT calculation in this study.

The FDK algorithm has played an important role in both biomedicine and industry because of its celerity and simplicity for the reconstruction of CT images. However, artifacts and attenuation may occur in FDK reconstruction under large cone angle with circular trajectory owing to the insufficient data. In this paper, a factor k is introduced to change the projected surface, based on the idea of rebinning algorithm. In that case, the path of filtering was arbitrarily changed and a unified pre-weighting formula was presented, which consequently enable the filtering path variable FDK (v-FDK) to be smoothly converted to P- FDK and T-FDK by tuning the k factor. Numerical simulations demonstrated our proposed algorithm an effective method for improving the reconstruction accuracy especially in the case of large cone-angles. On top of that, an optimal k value was found which can be used to obtain a reconstructed image with better quality than the image obtained by P-FDK and T-FDK.

The highly hysteretic insulator-to-metal phase transition (IMT) of vanadium dioxide (VO₂) enables an effective path to actively tuning terahertz (THz) wave, which holds great promise for the next generation optical memory devices. In the THz range, existed VO₂-based memory device are driven by electric, which suffers some problems, such as slow write time at scale of several seconds, complicated circuit fabrication for electric conduction, and so on. Here, we propose an all optically-controlled THz wave memory device with inexpensive, straightforward and scalable fabrication of VO₂. We demonstrate the reconfigurable THz-wave memory device with 1 bit and 2 bits programmed by two continuous lasers and its potential write time of tens of microseconds driven by ultrafast amplifier laser. This work paves the way for robust multifunctionality in optically-controlled terahertz switching, photonic memory, and ultrafast terahertz optics. And combining our memory device with spatial light modulator, its functionality can be further extended into spatial dimension, such as being a programmable and reconfigurable spatial THz wave modulator for the cutting-edge THz ghost imaging.

The simplistic infrared target observation feature is the main reason for that the particle filter tracking algorithm are always failed. Considering the limitations of infrared target feature description, we constructed an observation model based on high frequency features and high frequency features. The template update method was also analyzed. Finally, we designed the flow of particle filter tracking algorithm combining the gray feature and the high frequency feature. The simulation results show that proposed method has the good robustness and accuracy in infrared target tracking under complex background.

In this study, terahertz non-destructive testing technology was used to insulation materials. The terahertz wave nondestructive testing was carried out to test the thickness of the layer, the air hole in the insulation layer and the defect of adiabatic structure. The refraction and absorption coefficients of terahertz wave in asbestos-filled nitrile rubber, aramid fiber-filled ethylene propylene diene monomer(EPDM) and silica-filled polyurethane rubber were studied. Two terahertz wave scanning imaging results were compared. Terahertz wave has a good penetrating ability to the insulation material and can be used to test the insulation layer thickness. At the same time, quality defects such as stratification and porosity of samples with a thickness of 2 mm can be identified. It is proved that terahertz technology can be applied to the detection of insulation materials and internal defects.