A broadband THz metamaterial absorber was designed based on the transmission line theory, and the inductive mesh structure was selected as the meta-surface. The absorber samples were fabricated by electrohydrodynamics(EHD)-based printing technology, which is a cost-effective and high-precision technology for flexible electronic device fabrication. The absorption in (98-353) GHz exceeded 90%, and the experimental data matched well with the theoretical and simulation results. It was also proven that the absorption spectra were insensitive to the linewidth and surface resistance of the inductive mesh structure, so that the design has high tolerance to possible fabrication error.
The paper introduces the principle and structure of the PIN diode detector, and then describes the researching background and the responding characteristic of the detector. The high responsibility of photodiode response characteristic is important. The paper designs a set of testing device to measure the responsibility. The optical part can produce a laser pulse of 1.06μm with a certain frequency and energy, with the aid of white light source and CCD camera, the laser beam can focus on the surface of the photon detector of PIN diode. The signal-testing instruments can measure the responding characteristic of the photon detector, and the average noise power. The paper gives the waveforms of the laser pulse and the responding signals.
Spectral response curves of photoemission materials and spectral matching factors between detectors and reflecting spectrum of scenes are of importance in the study of detectors and imaging devices. For studying the two questions an automatic spectral recording system was developed and the schematic diagram of the system was demonstrated in this paper. A lot of experiments by use of the system were made to obtain spectral response curves and characteristic parameters of multi-alkali and GaAs:Cs-O photocathodes during activation procedure and these experimental results were given. It was found that electron affinity of Na2KSb, Na2KSb+Cs and [Na2KSb+Cs]+Sb+Cs multi-alkali photocathodes were 0.70-0.91eV, 0.35-0.41eV and 0.33eV respectively calculated from threshold wavelength of spectral response curves and quantum yield during preparation. On-line spectral response measurements of GaAs:Cs-O reflection-mode photocathodes during activation process and decay procedure were carried. The prepared GaAs:Cs-O reflection-mode photocathodes which used national p-type GaAs substrate can obtain 1025μA/lm sensitivity.
As compared with III generation intensifiers, IV generations have bigger sensitivity and much broader spectral response for low light level imaging detectors. IV generation intensifier properties are improved for NEA photo-cathode sensitivity and spectral response. In this paper, a new method is introduced to increase NEA photo-cathode sensitivity and expand infrared response. In the method, spectral response of GaAs:Cs-O NEA photo-cathode is controlled with automatic survey instrument of dynamic spectral response on photo-electronic materials. During processing NEA photo-cathode, it is observed that sensitivity rises slowly when photo-cathode is illuminated with incident ambient radiation, and infrared sensitivity begins reduction when photo-cathode is measured with automatic survey instrument. The reduction of infrared sensitivity has influenced on spectral matching factor of photo-cathode-object combination and detecting distance and has resulted in the practical use of low light level night vision instrument. During processing NEA photo-cathode with Cs-O layer, we can keep watching spectral response change with automatic survey instrument: when sensitivity rises slowly as photo-cathode is illuminated with incident ambient radiation and infrared sensitivity reaches a highest peak value, we can achieve optimum GaAs:Cs-O photo-cathode for low light level imaging detectors. We studied the thickness of a layer GaAs:Cs-O photo-cathode with take off X-Ray photo-electron spectroscopy, it is clear that the thickness of Cs-O layer is about 0.7~1.0 nm.
In this paper, a large activation and analysis system is introduced , which consists of automatic spectral response recording equipment, x-ray photoelectron spectrometer and ultrahigh vacuum chamber. Then, activation and on-line spectral response measurement are described. For the first time, on-line measured spectral response curves of GaAs:Cs-O NEA photocathodes are presented. These curves indicate the typical variation in spectral response caused by the deposition of cesium and oxygen. By the way of comparing and analyzing those curves, some valuable data obtained which are helpful in investigating the mechanism of the activation.
On-line spectral response curves of GaAs:Cs-O NEA photo- cathode of reflection model is first presented and the relation between spectral response curves and the thickness of Cs-O layer is discussed. When Cs and O is deposited on the surface of cleaning GaAs wafer, photo-cathode's spectral response rises sharply and long-wavelength threshold tends to a fixed value at the beginning of the activation. But, as Cs and O are deposited continually, spectral response rises slowly and the long-wavelength threshold tends to be shortened. When a fine thickness of Cs-O layer is reached, the optimum spectral response is obtained. As a quantity Cs-O is further increased, both the spectral response and the long-wavelength threshold decrease. The thickness of GaAs photo-cathode surface layer that consists of Cs-O layer and GaAs-O layer is researched by take-off angle XPS technology. Thickness of Cs-O layer is approximately equal to 0.7 nm, and the GaAs-O layer is approximately 0.2nm. Our experiments show when the thickness of Cs-O layer is approximately equal to 0.7nm, and the GaAs-O layer is approximately 0.2mm. Our experiments show when the thickness of Cs-O layer is 0.7nm or so and the GaAs-O layer tend to be disappeared, NEA photo-cathode with the optimum spectral response is achieved which can be used widely in low-light level imaging detectors.
Proc. SPIE. 4580, Optoelectronics, Materials, and Devices for Communications
KEYWORDS: Staring arrays, Signal to noise ratio, Infrared imaging, Diffraction, Optical transfer functions, Imaging systems, Sensors, Computing systems, Signal processing, Modulation transfer functions
The modern trend in focal plane arrays (FPAs) implementation is to include an increasing amount of analog signal processing in micro technology circuitry embedded in the FPA construction. This technology includes such function as time-delayed integration (TDI). While such integration makes the FPA and its associated signal processing more compact and faster, it introduces new complications into the testing of the FPA, since the detector outputs, by themselves, are no longer directly accessible. The CdHgTe FPAs detectors with on-chip TDI have been successfully incorporated into infrared imagers. These impose requirements on the instrumentation to establish the modulation transfer function (MTF) of the integrated FPAs. This paper details a method for measuring the MTF for such arrays within 3-5μ+m and 8-14μ+m spectral band. A description of a test facility for testing and evaluating MTF of FPA is given. We use a knife-edge target to measure MTF. The Pentium III computer system takes the charge of controlling and calculating. Some other methods of MTF measurement will be mentioned.
In this paper, on the base of explaining the importance of spectral response, the way to derive characteristic parameters of NEA photocathode from its spectral response is introduced. Then, an automatic spectral response recording system is described. The system is used to take spectral response curves during the activation procedure. For the first time, on-line measured spectral response curves of GaAs:Cs-O NEA photocathodes are presented. These curves indicate the typical variation in spectral response caused by the deposition of cesium and oxygen. By the way of comparing and analyzing these curves, many important parameters of photocathodes are obtained, and the reasons that cause the bad behavior of NEA photocathodes are discussed.
This article first describes the background of the research and manufacture of evaluation system of Negative Electron Affinity photocathode. This article designs a set of super high vacuum system for activating NEA photocathode on the base of activation theory, the process of design and debugging is given. The system is composed of three parts: super high vacuum system for GaAs material activation, multi-meter testing system, surface analysis system. The system is used for on-line evaluation of activating of NEA photocathode. The technical parameters and structure of the evaluation system of NEA photocathode are given in the paper. The system is finished and experiments are made. At last the picture of the system is given.
Spectral response is an important parameter of photocathodes. By analyzing measured spectral response curves, much information about the photocathodes can be obtained which is useful to investigation of photocathodes. The principle measuring the spectral response of photocathodes is expounded in this paper. The on-line measurement system was developed, which can measure the spectral response of optoelectronic devices within range of 400nm~1800nm. It can also measure the reflectance of monochromatic light, the monochromatic photocurrent, and integral sensitivity of photocathodes. The measurement system was used to on-line measure spectral response of multi-alkali photocathodes(Na2KSb:Cs) when they are being prepared. Combining measurement of reflectance of monochromatic light, by which the thickness of photocathodes can be timely obtained, the optimum thickness of photocathode is looked for. The measurement system also used in the investigation of GaAs:Cs-O NEA photocathodes. Surface escape probability, electron diffusion length and back-interface recombination velocity are the factors that influence the quantum yield of NEA photocathode. It is difficult to directly measure these parameters. But they can be obtained by simulation of measured spectral response. The reflective GaAs samples were activated and evaluated. The results were given and analyzed.
In this paper, several automatic system for determining spectral response of photocathodes are described. Some of them are use in on-line spectral response measurement. The technology of the on-line measurement is introduced and some experimental results are given. As a result, the technology is proved to be convenient and efficient.