Terahertz(THz) wave modulator technology, due to its important value of imaging and detecting research. In the paper, we discuss the Polyethylene lens based the terahertz wave front modulation, which is benefit the terahertz wave image technology. Simulation results show that the optical system can extent the depth of imaging field of test objects based on continuous terahertz source. The way to get the image has significant meaning for detection and large image quality.
In this paper we demonstrated a coherent raster-scan imaging system that can acquire phase information based on continuous terahertz imaging. It mixes the terahertz with a Fs-laser by a electro-optic crystal of ZnTe to make a hybrid modulation on the crystal to achieve continuous terahertz detection. In this way, it can not only propagate for a long distance but also achieve phase detection for continuous terahertz imaging. The surface images of objects that are under test can be obtained by the Backward-Wave Oscillator, which the output power is 10mW at 205.994GHz. With the repetition frequency of 80MHz, the output power of the MaiTai is 1.65W and 100fs pulse light at 800nm. The images can achieve diffraction-limited resolution approximately. And the simulated results show that the system can obtain phase imaging of test objects based on continuous terahertz source. The way to get the phase of the signal has significant meaning for coherent detection of continuous terahertz source.
In this paper we proposed a method of phase extraction for continuous terahertz wave. Firstly, we study the mathematical relationship of phase between the electro-optic sampling signal and terahertz wave in the theory, and then build the platform of continuous terahertz wave, using BWO as the source of terahertz radiation and Fs-laser as the detection of pulse. After using differential circuit and the principle of electro-optic sampling, we detect the polarization properties of optical signal and transform it into electric signal. With the filter amplifying circuit for signal processing, we obtain the phase of continuous THz wave at 0.2 THz. This method of phase extraction provides a potential way to the continuous THz wave coherent imaging, which is of great significance to the further study on continuous THz wave coherent imaging.
One of the most crucial techniques of laser warning system is to acquire the direction information from the
laser threat. According to the low resolution of laser warning system with imaging mode, a new method for measuring
laser incident direction which possessed higher resolution was proposed. This novel method was based on cylindrical
lens group and linear IRFPA, and the laser incident direction was achieved by offset of line spot. It not only deduced the
direction formulas, but also analyzed the resolution of measuring laser incident direction in detail. The simulation result
shows that the FOV of this new kind of laser warning system could achieve ±16°; the azimuth resolution is up to 0.52°
and pitch resolution is up to 0.017°; the resolution increases with incident angle. In addition, an experiment with visible
light, single cylindrical lens, linear array CCD was done to verify this method and its advantage on resolution. The
analysis of laser incident orientation resolution is significant to select suitable parameter of detector and demonstrate
orientation resolution of system.
This paper describes a high performance of opto-mechanically scanned millimeter-wave imager for airport security.
It employs a crank-rocker mechanism to generate a high speed line scanning, which produces a horizontal FOV
(field of view) of 30°. Accompanied by a frame scanning mirror of ±18° in the vertical direction, it brings about a
two-dimensional scan of the scene of 146cm×75cm which is 1 meter away from the system. By this scanning
mechanism, we use a single channel of a 94GHz receiver to collect the radiation from a convex lens which acts as
the focusing element. Then the output of the receiver is passed to an A/D converter and is displayed on a
conventional PC. The new scanning arrangement meets these requirements and has been being developed into a high
performance, low-cost, and compact prototype system which hopefully will meet the present and future needs for
millimeter-wave and terahertz imaging.
This paper describes a novel multi sensors image fusion technology which is presented for concealed weapon detection
(CWD). It is known to all, because of the good transparency of the clothes at millimeter wave band, a millimeter wave
radiometer can be used to image and distinguish concealed contraband beneath clothes, for example guns, knives,
detonator and so on. As a result, we adopt the passive millimeter wave (PMMW) imaging technology for airport
security. However, in consideration of the wavelength of millimeter wave and the single channel mechanical scanning,
the millimeter wave image has law optical resolution, which can't meet the need of practical application. Therefore,
visible image (VI), which has higher resolution, is proposed for the image fusion with the millimeter wave image to
enhance the readability. Before the image fusion, a novel image pre-processing which specifics to the fusion of
millimeter wave imaging and visible image is adopted. And in the process of image fusion, multi resolution analysis
(MRA) based on Wavelet Transform (WT) is adopted. In this way, the experiment result shows that this method has
advantages in concealed weapon detection and has practical significance.