We numerically investigate the thermal effects in a cornea illuminated by terahertz radiation. By modifying the bioheat and Arrhenius equations, we studied the heat-transfer and temperature distributions in the corneal tissue, and evaluated the potential thermal damage. The influence of the beam radius and power density are discussed. We also estimated the effective cornea-collagen shrinkage region, and evaluated the degree of thermal damage in the cornea. We expect this work to open up a novel effective and safe thermal-treatment approach based on THz radiation for cornea reshaping in the field of ophthalmology.

Waveguides made of hyperbolic metamaterials have unique properties such as extremely high field enhancement. Here we show that hyperbolic slot waveguides, i.e., nanoscale plasmonic slot waveguides cladded by hyperbolic metamaterials can have greatly enhanced Kerr nonlinear effects at even shorter device lengths and lower pump power compared with the conventional metallic slot waveguides. This result points to novel nanoscale waveguide designs for achieving low-driving-power and compact nonlinear nanophotonic devices that are used in diverse applications at both classical and quantum levels.

To improve the phase reconstruction accuracy of two-step phase-shifting interferometry measurement method, a phase blind demodulation algorithm based on zoned background estimation is proposed. In the algorithm, a sequence of zero value points in interferograms are picked out as seeds. A Voronoi figure surrounding these seeds is created, and the Voronoi figure segments each interferogram into several zones. The background of all points in these zones is set as the seed background, and a whole background is obtained when we combine these seed backgrounds. Numerical simulation and experimental analysis are conducted. Numerical simulation results show that the root-mean-square error (RMSE) of demodulation phase of the proposed algorithm is close to that of the method with real background. Experimental results show that the demodulation phase RMSE is reduced by 16％ compared with the traditional low-pass filtering method.

Spectroscopic measurements and terahertz imaging of the cornea are carried out by using a rapid scanning terahertz time domain spectroscopy (THz-TDS) system. A voice coil motor stage based optical delay line (VCM-ODL) is developed to provide a rather simple and robust structure with both the high scanning speed and the large delay length. The developed system is used for THz spectroscopic measurements and imaging of the corneal tissue with different amounts of water content, and the measurement results show the consistence with the reported results, in which the measurement time using VCM-ODL is a factor of 360 shorter than the traditional motorized optical delay line (MDL). With reducing the water content a monotonic decrease of the complex permittivity of the cornea is observed. The two-term Debye relaxation model is employed to explain our experimental results, revealing that the fast relaxation time of a dehydrated cornea is much larger than that of a hydrated cornea and its dielectric behavior can be affected by the presence of the biological macromolecules. These results demonstrate that our THz spectrometer may be a promising candidate for tissue hydration sensing and practical application of THz technology.

Terahertz time domain spectroscopy has been widely used in both spectral analysis and imaging applications. Existing terahertz time domain spectroscopy imaging systems usually suffered the low scanning speed and huge data storage. To solve this problem, an efficient terahertz imaging method based on the compressed sensing theory was presented in this paper. By controlling the scanning motor to perform a non-equal interval sampling of the target, a group of under-sampled terahertz signal can be obtained. Based on the under-sampled signal, the compressed sensing algorithm is applied to reconstruct the complete terahertz image. The results show that, when the compression ratio is 0.5, the correlation coefficient between the reconstructed terahertz signal and the fully sampled THz signal can reach 99.95%. By analyzing the reconstructed terahertz image, the image areas with smooth intensity changing or low frequency component in frequency domain can be well recovered. The proposed method provides a practical means for efficient terahertz imaging applications.

A phase shift extraction algorithm based on the special points in two-step generalized phase-shifting interferometry is proposed.This algorithm searches the special points that meet specific requirements and calculates the phase shift via the latter's relationship with these special points.It is divided into two modes according to whether the intensity distributions of the two interference beams are recorded or not.Theoretical analysis,computer simulation and experimental verification are carried out.Experimental results show that this algorithm reaches the same level of other algorithms in speed and accuracy.Moreover,when the interferogram's fringe number is less than one,a better phase shift extraction accuracy can be obtained.

We present a study aimed at developing a terahertz time domain spectroscopy (THz-TDS) system for detection of the optical properties of ex vivo rabbit corneal tissues with different water content at terahertz frequencies (0.1–0.3THz). The refractive index decreased with frequency while the absorption coefficient increased with frequency. Our experimental results matched the theoretical calculation very well revealing that both the absorption coefficient and the refractive index of a hydrated cornea were much larger than that of a dehydrated cornea and the terahertz properties depended on the hydrate conditions of the biosamples.

太赫兹时域光谱(THz-TDS)技术从实验室走向实际应用亟需信号获取速度的进一步提高.利用音圈电机平台实现了快速光学延迟线,在此基础上建立了快速扫描太赫兹时域光谱系统.经测试,快速延迟线的扫描频率目前可达70 Hz,时间窗口可达100 ps以上.与传统的步进扫描方法相比,系统利用快速扫描方法(扫描频率为1 Hz)能够获得同等品质的信号,而测量时间却缩短为前者的1/360,极大地提高了太赫兹信号的采集速度.这种利用音圈电机平台实现太赫兹时域光谱快速扫描的方法对于太赫兹快速光谱成像技术的研究具有参考意义.

针对国内工业内窥镜只限于观察,无法满足工件三维尺寸测量的现状,设计了一种探头外径为6mm并且可以向任意方向弯曲的三维测量工业内窥镜,并介绍了该内窥镜的双目光学系统及镜体内部结构的设计。首先,基于双目立体成像的原理,提出了一种具有双物镜、单图像传感器的新型双目光学系统。其次,根据光学系统的技术要求,设计了内窥镜的头部结构。考虑到一些工件内部结构比较复杂,分别设计了内窥镜的可弯曲结构以及后部操控机构以方便一些精密工件的检测。最后,通过三维图像处理软件对待测物表面两个特征点进行长度测量试验,得到了两个特征点的间距。实验结果表明:待测物表面两个特征点的长度测量误差在±0.2mm内。该系统基本实现了工业内窥镜的三维测量功能。