In this paper, GaAlAs/GaAs vacuum photodiodes are used to test the spectral response of different external electric fields, and the influence of external electric field on NEA GaAlAs/GaAs photocathode is analyzed. Based on the spectral response curves under different bias voltages, the external voltage increases and the corresponding spectral response sensitivity increases. As the bias voltage increases, the sensitivity of the spectral response increases slowly and gradually becomes saturated. This is mainly due to the fact that under the action of a strong field, the photoelectron obtains a sufficiently high energy to escape into the vacuum, resulting in a spectral response sensitivity tending to saturation.
For the purpose of coloring the night-vision images captured by low-light image intensifiers or infrared thermal imagers, color transfer algorithms were used to transfer natural colors to these gray images. Most of the color transfer algorithms can be divided into two classes: global color transfer and point color transfer. In global color transfer algorithms, the means and variances of the initial false color image were adjusted according to those of the reference color image. In point color transfer algorithms, the matching points were determined between the grayscale image and the reference color image. These two kinds of algorithms are always carried out in two common color spaces: YUV color space and Lab color space. The color space influences the performance of the color transfer algorithms. In this paper, several typical color transfer algorithms, including basic ones and multi-resolution ones, were carried out in different color spaces. The results show that global color transfer algorithms perform better in the YUV color space and the Lab space is more suitable for point color transfer algorithms. The biggest difference between these two color spaces is that the correlation between the channels of Lab space is much lower than that of YUV space. The global color transfer algorithms adjust the color components of the initial false color image with a uniform conversion, linear or non-linear ways. This process can benefit form the correlation between the channels, which is much higher in YUV space. However, the coloring process of the point color transfer algorithms is independent from the points matching process based on grayscale. This is the reason why the point color transfer algorithms should be implemented in the Lab space.
UV(ultraviolet) image intensifier is a vacuum image device with Cs2Te (Cesium Tellurium) photocathode. It converts the incident ultraviolet(UV) light from the optical lens into electronic signal, then the electronic signal is converted into responding visible image on the phosphor screen. Defects of different sizes can be seen on the screen when it works. A system is build to inspect the distribution of the defects, then the sources and category of the defects of the view field are analyzed, including photocathode, microchannel plate and phosphor screen, some improving technique is brought to decrease the defects.
A novel concept for solar cell technology, photon-enhanced thermionic emission (PETE), was proposed for harvesting photonic and thermionic energy simultaneously. Researches show that the conversion efficiency of PETE is pretty high, calculated efficiencies for idealized devices can be above 50%, which is exceed the theoretical limits of single-junction photovoltaic cells. To explore whether the vacuum device can exhibit good performance under the conditions that combines illumination and heating, a multi-alkali vacuum photodiode is used as a quantum and thermal energy converter. The band gap of multi-alkali cathode is 1.1eV and the multi-alkali photocathode is employed at temperature below 350K.The current-voltage characteristic curve is measured under two different temperature conditions, so is the power-voltage curve. And the conversion efficiency of the multi-alkali vacuum photodiode is also calculated on the basis of experiment data. The experiment results show that the power converted by a heated and illuminated condition is greater than that obtained under illumination at room temperature or heating without illumination. The conversion efficiency of the multi-alkali vacuum photodiode is higher than that not be heated. This paper shows that the multi-alkali vacuum device presents better performance under the combined conditions. Although the power production and conversion efficiency are not very high in this research, the experiment demonstrates how the two forms of quantum and thermal of solar energy can be simultaneously utilized.