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.
A sensitive, real-time seven core optical fiber based Mach-Zehnder interferometer (MZI) sensor for liquid refractive index detection is proposed, fabricated and characterized. A trapezoid body with an inverted wedge shape groove in the center is used to design the MZI. The two ends of the trapezoid body play the roles of micro-prisms, and the middle parts of the trapezoid body and the groove play the roles of reference and sensing arms. A series of performance tests were carried out by immersing the sensor in different kinds of solutions to verify the universal applicability of the sensor. The MZI sensor is as small as only 43 μm × 8 μm, and at the same time with sensitivity of 1616 nm/RIU. Nominally, we realized a completely integrated optical sensing system. And, this system actually could be the building block of more powerful integrated chemical sensing chip for health, security and industry application.
Pulsed terahertz reflected imaging technology has been expected to have great potential for the non-invasive analysis of artworks. In this paper, three types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by a pulsed terahertz reflected imaging system. These preset defects include a circular groove, a cross-shaped slit and a piece of “Y-type” metal plate built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. Additionally, three-dimensional analyses have been performed in order to reveal the internal structure of defects. Terahertz reflective imaging can be applied to the defect investigation of the murals.
Terahertz time-domain spectroscopy (THz-TDS) imaging technology has been proposed to be used in the non-invasive detection of murals. THz-TDS images provide structural data of the sample that cannot be obtained with other complementary techniques. In this paper, two types of defects hidden in the plaster used to simulate the cases of defects in the murals, have been investigated by the terahertz reflected time domain spectroscopy imaging system. These preset defects include a leaf slice and a slit built in the plaster. With the terahertz reflective tomography, information about defects has been determined involving the thickness from the surface of sample to the built-in defect, the profile and distribution of the defect. With this THz tomography, different defects with the changes of optical thickness and their relative refractive index have been identified. The application of reflective pulsed terahertz imaging has been extended to the defect detection of the murals.
Terahertz (THz) radiation is an under developing range in the electromagnetic spectrum. It has attracted a lot of
attentions due to its various potential applications. However, THz systems are difficult to be integrated into a smart size
due to the limitation of its long wavelength. In this presentation, we propose a new approach to design planar lenses with
a thickness of several hundred nanometers in the THz range. The fabricated lenses are characterized with a focal plane
imaging system and it is found that they can focus the THz light and image an object well. It is expected that this new
approach can pave a way for smart THz systems integration.
Although the long-focal-depth (LFD) function of cylindrical microlenses was previously realized by the phase modulation method, however, there still has no report of obtaining a uniform axial intensity distribution through the pure phase modulation mechanism. In this paper, the amplitude modulation mechanism is proposed for designing LFD cylindrical microlenses. An apodized window function of the incident light is used to suppress the axial intensity oscillations, so that a uniform axial intensity profile is achieved. Rigorous electromagnetic theory and the boundary element method are applied to analyzing focal performance of the designed cylindrical microlenses. Through replacing the incident plane wave with a two dimensional Bessel beam, numerical results demonstrate that the designed cylindrical microlens not only holds an LFD property, but also maintains a uniform axial intensity distribution as we expected. Moreover, the designed LFD cylindrical microlens has a high diffraction efficiency on the real focal plane. It is believed that the designed LFD cylindrical microlens with a uniform axial intensity profile should have wide application prospects in many micro optics systems.
Through exploiting a modified focal-length function, two-dimensional metallic cylindrical focusing micromirrors
(MCFMs) with different preset focal depths are designed. Rigorous electromagnetic theory and the boundary element
method are applied to analyzing the focal characteristics, including the actual focal depth, the relative focal depth, the
focal spot size and the diffraction efficiency. Through setting the preset focal depth to be positive or negative, numerical
results reveal that the designed MCFMs can successfully modulate the optical field distribution to achieve a long axial
focal depth or increased lateral resolution, respectively. In addition, due to the inherent achromatic aberration property of
the metallic reflective system, the common long-focal-depth region of the designed MCFM under multiwavelength
illumination is greatly enlarged, in comparison with a dielectrically cylindrical microlens. It is expected that the designed
MCFMs should have many practical applications in micro optics systems.
Vectorial diffraction methods provide accurate analysis of subwavelength diffractive optical elements, but they
usually consume a lot of computing time and computer memory. On the other hand, scalar diffraction methods
have simpler physical models and cost much less computer resources at the expense of a large numerical error.
Therefore, an approximate method is highly required, which can substantially relieve the computational burden
and possess a high accuracy. We firstly propose such an approximate vectorial method, i.e., the improved first
Rayleigh-Sommerfeld method (IRSM1), and apply it to analysis of two-dimensional (2-D) cylindrical microlenses
and metallic cylindrical focusing micromirrors. The IRSM1 is clearly proved to be much more accurate than
the scalar diffraction method. In addition, compared with the vectorial boundary element method, the IRSM1
consumes much less computing time and computer memory. Besides of the above, the IRSM1 is expected to
be used in optical designs of subwavelength diffractive optical elements by incorporating with the simulated
annealing method or the Yang-Gu algorithm.
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