We proposed a novel interference elimination method for CW-THz reflection imaging. Based on the study of interference mechanism in the imaging window, inverse processing was proposed to realize the interference elimination. Theoretical calculation showed that the interference phenomenon was closed related to the characteristics of imaging window. The refractive index and thickness of the window were the two main factors for the interference. Moreover, polarization was also taken into consideration for the CW-THz reflection imaging because the reflectivities of the s and p polarized waves were different from each other. This method was applied in different imaging systems for the demonstration of its feasibility. The high resistivity float-zone silicon (HRFZ-Si) plate was employed as the imaging window in the normal incidence system with a terahertz quantum cascade laser (THz-QCL) operating at 4.3THz. The oblique system employed quartz plate as the imaging window with an optical pumped THz laser operating at 2.52THz. Pork and liquid samples of water and edible oils were chosen as the imaging samples to demonstrate the interference elimination method.
In this paper, a novel strategy for diagnosis of bTBI is proposed by measuring terahertz (THz) spectroscopy of serum in a rat model. A compressed air-driven shock wave generator was used to establish bTBI model of rats. It was validated by a neurological deficit assessment method. The spectral differences of serum for different degrees of bTBI rats have been demonstrated by THz time-domain spectroscopy (THz-TDS). Moreover, based on the THz spectra of serum, the principal component analysis (PCA) and support vector machine (SVM) were performed to automatically identify the degrees of bTBI. The results indicate that THz spectroscopy could provide a sensitive, rapid and label-free diagnosis method for bTBI.
Significance: Terahertz wave is a potential tool for biological tissues due to its noninvasiveness and high sensitivity to water. Attenuated total reflection (ATR) with the characteristics of high sensitivity and nondestruction has been applied for THz imaging.
Aim: We aim to develop an imaging methodology to facilitate practical application of THz ATR imaging.
Approach: We have demonstrated a horizontally scanning THz continuous wave ATR imaging system. The effective imaging area was as large as the prism imaging surface by optimizing the ATR prism, and the influence of secondary reflection can be well avoided. By taking the image resolution and stability of this system into consideration, the incident angle α to the prism bottom was chosen to be 30 deg.
Results: The image resolution of this system can be up to 400 and 450 μm in horizontal and vertical directions, respectively. Furthermore, U87-glioma regions of mice brain tissues with different sizes and C6-glioma regions of rat brain tissues with relatively large size can be differentiated clearly from normal brain tissues by this imaging system. The volume and location of the tumor region shown in the THz images are similar to those visualized macroscopically in the corresponding visual and H&E-stained images.
Conclusion: We indicate terahertz horizontal-scanning ATR imaging technique with large effective imaging area, and high resolution could be used as an alternative method for label-free and high-sensitivity imaging of biological tissues.
Region of interest segmentation is essential for computer aided application of THz imaging. However, THz images is severely degraded by motion blur, poor resolution and noise. A robust, accurate and time-saving algorithm is in dire need for the ROI segmentation of THz images. Recently, ROI segmentation of THz-TDS images and passive THz images has been widely studied. While the ROI segmentation of THz continuous wave (CW) image is still in its infancy. In this paper, we proposed a hybrid ROI segmentation method for THz CW images. The hybrid method combines block match 3D denoising, fuzzy c-means clustering, morphology operation and canny edge detection. The hybrid method is implemented to two images acquired with a THz CW reflection imaging system. To evaluate the performance of our algorithm, we calculated the accuracy, sensitivity and specificity. As the result indicates, this hybrid ROI segmentation method performs well for THz images.
In this paper, we demonstrated that tumors in freshly excised whole brain tissue could be differentiated clearly from normal brain tissue using a homemade continuous terahertz (THz) wave attenuated total reflection (ATR) imaging system. The resolution of this system was about 400μm×450μm at 2.52THz. The terahertz images characters of fresh brains with tumor was studied using this THz-ATR imaging system. Tumor regions could be differentiated clearly from normal brain tissue by THz intensity imaging at different frequencies. The high absorption regions in THz images corresponded well to the tumor regions in the hematoxylin and eosin-stained microscopic images. Moreover, the morphological reconstruction method was applied to restore the blurred imaging results. The noise caused by power fluctuation in THz-ATR image was almost eliminated and the visibility of objects has been successfully enhanced. These promising results suggest that THz-ATR imaging could be used as a tool for label-free and real-time imaging of brain tumors, which would be great potential as an alternative method for the fast diagnosis tumor region during brain surgery.
We set up the terahertz continuous reflectometry imaging system and the spatial resolution of our system was roughly 0.6×0.6mm at 2.52 THz. We also demonstrated that the paraffin embedded traumatic brain injury (TBI) in rat model sample can be differentiated clearly. The results show that the THz reflection intensity of the TBI area was lower than that of normal area. These promising results suggest that THz reflection imaging has great potential as an alternative method for the fast diagnosis of TBI.
We investigate a photonic crystal fiber (PCF) which consists of squeezed triangle lattice and elliptical air holes. Birefringence and dispersion properties of this PCF have been numerically estimated by the supercell lattice method. Numerical results show that the birefringence is on the order of 10-2 over ultrabroad wavelength rang from1.3μm to 1.7μm and birefringence can be reached 1.71×10-2 at the operating wavelength of 1.55μm. It is also demonstrated that two near-zero dispersion of -1.75(ps/nm/km) (x-polarized mode) and-0.33(ps/nm/km) (y-polarized mode) at 1.55μm can be achieved. Morever, the fluctuations of the dispersion with fiber parameters are very small. The simulation results show that our proposed PCF are robust to fabrication imperfections.
Photonic crystal fiber (PCF) with high birefringence and low dispersion is proposed in this work. Both two different sizes of elliptic air holes in the fiber cladding and a small elliptic air hole in the fiber core are used in our proposed PCF. The high birefringence is introduced on the combined effect of elliptical air holes and the squeezed lattice. The birefringence and the dispersion of this PCF have been numerically estimated by the supercell lattice method. The simulation results show that the high birefringence with the order of 10-3and the low dispersion of both x-polarized mode and y-polarized mode at the wavelength of 1.55μm can be obtained. The dependence of both the birefringence and the dispersion on structure parameters is analyzed. The simulation results show that flat birefringence and dispersion can be obtained.
A low-flattened index-guiding photonic crystal fiber (PCF) with high birefringence and low effective mode area is proposed. Elliptical air-holes with different diameters are distributed on the squeezed lattice. With the supercell lattice method, we simulate numerically the dispersion property and the birefringence property of the fundamental modes in this PCF. Simulation results show that the proposed PCF has a total dispersion as low as 0 ±1(ps/nm/ km) over ultra-broad wavelength band from1.3μm to1.6μm . Meanwhile, the birefringence can be reached the order of 10−3 and the low effective mode area is also obtained. Moreover, the influences on the birefringence and dispersion by geometrical parameters have also been discussed in detail.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.