Feiyu Lian ; Degang Xu ; Maixia Fu ; Hongyi Ge ; Yuying Jiang ; Yuan Zhang
http://ieeexplore.ieee.org/document/7942015/
The terahertz (THz) spectra in the 0.2–1.6 THz (6.6–52.8 cm−1) range of various strains of maize grains (MIR162, Bt-11, Mon810, and Jinboshi781) were investigated using a THz time-domain spectroscopy system. Principal component analysis (PCA) was used to extract the feature data based on the cumulative contribution rates (above 95%); the top four principal components were selected, and a support vector machine (SVM) method was then applied. Several selection kernels (linear, polynomial, and radial basis functions) were used to identify the four maize grain types. The results showed that the samples were identified with accuracy of nearly 92.08%; additionally, total positive identification was more than 91.67%, and negative identification reached 93.33%. The proposed approach was then compared with other methods, including principal component regression, partial least squares regression, and backpropagation neural networks. These comparisons showed that the PCA-SVM approach outperformed the other methods and also indicated that the proposed method that combines THz spectroscopy technology with PCA-SVM is efficient and practical for transgenic ingredient identification in maize
- a Department of Physics, Capital Normal University, Beijing Key Lab for Metamaterials and Devices, Key Lab of Terahertz Optoelectronics, Ministry of Education, and Beijing Advanced Innovation Center for Imaging Technology, Beijing 100048, China
- b College of Information Science and Engineering, Henan University of Technology, Key Laboratory of Grain Information Processing and Control, Ministry of Education, Zhengzhou, Henan 450001, China
http://www.sciencedirect.com/science/article/pii/S0030401817300603?np=y&npKey=471b13ae12faa43f83824dc4b2431c665331c62b0344b4566b15cd4bceb13752
Terahertz (THz) response of a chemical vapor deposited graphene on a quartz substrate has been investigated by using an ultrafast optical-pump THz-probe spectroscopy. Without photoexcitation, the frequency-dependence optical conductivity shows a strong carrier response owing to the intrinsically doped graphene. Upon photoexcitation, an enhancement in THz transmission is observed and the transmission increases nonlinearly with the increase of pump power, which is rooted in a reduction of intrinsic conductivity arising from the strong enhancement of carrier scattering rather than THz emission occurrence. The modulation depth of 18.8% was experimentally achieved, which is more than four times greater than that of the previous reported. The photoinduced response here highlights the variety of response possible in graphene depending on the sample quality, carrier mobility and doping level. The graphene provides promising applications in high-performance THz modulators and THz photoelectric devices.
