The Key Laboratory on Night Vision Technology

Fengcheng, China

The Key Laboratory on Night Vision Technology

Fengcheng, China
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Li X.-F.,North Night Vision Technology Co. | Li X.-F.,The Key Laboratory on Night Vision Technology | Zhao X.-F.,North Night Vision Technology Co. | Chen Q.-J.,North Night Vision Technology Co. | Wang Z.-H.,North Night Vision Technology Co.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2014

The making process of K2Te(Cs) solar blind ultraviolet cathode was described and samples of K2Te(Cs) solar blind ultraviolet cathode were made. The spectral response, spectral reflectance and fluorescence spectra under the excitation condition of 250 nm wavelength about K2Te(Cs) and Cs2Te solar blind ultraviolet cathodes were measured. The measuring results showed that under the existing technological condition, the spectral response of K2Te(Cs) solar blind ultraviolet cathode is higher, the peak wavelength of spectral response is shorter than that of Cs2Te solar blind ultraviolet cathode. However, their long wavelength thresholds of both cathodes were basically same. The peak wavelength of spectral response of K2Te(Cs) cathode is about 250 nm, long wavelength threshold is about 336 nm. In addition, K2Te(Cs) solar blind ultraviolet cathode has better solar blind property; the spectral sensitivity at 633 nm is ranked at the order of magnitude of 10-4 mA/W, one order of magnitudes lower than that of Cs2Te solar blind ultraviolet cathode. As for the spectral reflectance, the measuring results showed that the spectral reflectance of K2Te(Cs) solar blind ultraviolet cathode is higher than that of Cs2Te solar blind ultraviolet cathode within the scope of 200~437 nm wavelength, however is basically same as that of Cs2Te solar blind ultraviolet cathode within the scope of 437~600 nm wavelength, the refractive index and extinction coefficient of K2Te(Cs) solar blind ultraviolet cathode are less than that of Cs2Te solar blind ultraviolet cathodeThe measuring results on fluorescence spectra indicated that under the same condition and within the scope of 250~350 nm wavelength, the fluorescence of K2Te(Cs) ultraviolet cathode is stronger than that of Cs2Te ultraviolet cathode, the more strongly the fluorescence, the more transition electrons and the higher spectral response of cathode. The properties of K2Te(Cs) solar blind ultraviolet cathode are better than that of Cs2Te solar blind ultraviolet cathode, and thus can be applied to image device for solar blind ultraviolet detection as well.


Li X.,The Key Laboratory on Night Vision Technology | Li X.,North Night Vision Science and Technology Group Co. | Lu Q.,North Night Vision Science and Technology Group Co. | Zhang Y.,North Night Vision Science and Technology Group Co.
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2012

We addressed the characteristics of the Na2KSb(Cs) multi-alkali photocathode and its photoluminescence. Four different types of antimony-alkali compounds films, Na3Sb, K3Sb, Na>2K<1Sb, and Na2KSb, were deposited by alternative, thermal chemical vapor deposition (CVD) of Na, K and Sb, respectively, on glass substrates in the ambient environment. The impacts of the deposition conditions, including the deposition rate, layer thickness, substrate temperature, and stoichiometric ratio (Na, K, and Sb), on the photoluminescence and fluorescence were evaluated. The film growth was well controlled by on-line monitoring the photoelectron current and the leakage current. The fluorescence of the films was characterized at a laser wavelength of 785 nm. The results show that the stoichiometric ratio strongly affects the fluorescence intensity. For example, when it comes to fluorescence intensity, the Na2KSb films outperform the other 3 types of films. The highest intensity was observed with the Na2KSb grown at a ratio of 2:1:1; and as the ratio deviated from 2:1:1, its intensity decreased, accompanied with ablue-shift. We suggest that the stoichiometric ratio of the Na2KSb films be controlled by means of its fluorescence intensity.


Li X.,North Night Vision Technology Co. | Li X.,The Key Laboratory on Night Vision Technology | Feng L.,The Key Laboratory on Night Vision Technology | Shi F.,The Key Laboratory on Night Vision Technology | Zhang Y.,North Night Vision Technology Co.
Hongwai yu Jiguang Gongcheng/Infrared and Laser Engineering | Year: 2014

The characteristics of multi-alkali cathode, making process as well as the application in the second generational image intensifier was introduced, the sealing process between cathodes and envelops was explained, and cathode was fed to pre chamber of XPS analysis instrument. The percentage of atoms of each element in the thickness of different layer of multi alkali cathode was obtained by XPS analysis. First wide spectrum scan on the top surface of multi alkali cathode was made, and then the narrow spectrum scan was made on every element, following by argon ion etching. Etching after a certain time, wide spectrum and narrow spectrum scan on the multi alkali cathode were made; an argon ion etching was carried out until to the interface of glass window. Argon ion etching combined with XPS spectra analysis, atomic percentage of Na elements, K elements and Sb elements was obtained within the multi-alkali cathode film thickness. The results show that the multi-alkali cathode structure is a two-layer structure, i.e. Na2KSb base layer and adsorbed Cs atoms layer. In two film layer, Na2KSb layer is thicker, while the Cs atomic layer is thin, only 2.7% for the entire cathode film thickness. In addition, the number percentage of Na atoms, K atom, Sb atoms does not follow 2:1:1 stoichiometric ratio, and in the entire cathode layer thickness range, the percentage of atoms of the three elements does not remain constant, and does not appear in the ideal state of the atomic percentage of the three elements at a position reached 2:1:1. Theory and practice has proved it is possible to obtain high sensitivity only with strict stoichiometric ratio Na2KSb film. Thus by molecular beam epitaxy, multi-alkali cathode with higher composition control accuracy stoichiometric ratio 2:1:1 could be produced, the higher cathode sensitivity will be obtained.


Li X.-F.,North Night Vision Technology Co. | Li X.-F.,The Key Laboratory on Night Vision Technology | Feng L.,The Key Laboratory on Night Vision Technology | Lu Q.,North Night Vision Technology Co.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2013

The spectral reflectivities of Na2KSb film both with and without the activation layer of Cs-Sb were measured. The measurement results show that the spectral reflectivity of these two films within the wavelength range of 200~700 nm are substantially the same. So it can be inferred that the refractive index of both films are also substantially the same, and both films are substantially no change in its internal constituent. Because the spectral reflectivity is not changed, and the optical path difference of the two films are substantially the same, it can be inferred that the Cs-Sb layer was coated on the surface of Na2KSb, so the activation process of Na2KSb surface is a surface effect. In addition, Na2KSb (Cs) multi-alkali cathode film was analysis by XPS, the results showed that three elements was existed mainly in addition to Na, K, and Sb, but also the presence of CO2 and a small amount of Cs elements. The reason of the presence of C and O on the surface of Na2KSb (Cs) is oxidation in the unsealed process of sample. After 10 second time of argon ion etching, Na2KSb (Cs) multi-alkali cathode film was analyzed by XPS, the results show that the energy spectrum of Cs atoms has disappeared. When continued for 600 seconds time of the argon ion etching, on Na2KSb (Cs) multi-alkali cathode film surface, the spectrum of the Si atoms in XPS spectroscopy was appeared. This showed that argon ion has already etched to the glass window surface. According to the etching time analysis, the thickness of the multi-alkali cathode film surface Na2KSb (Cs) of Cs atomic layers approximately 3nm, and the Cs atomic layer exists only in the surface of the multi-alkali cathode layer, No deep into the multi-alkali cathode film inside. The fluorescence spectrum of multi-alkali cathode with the Cs-Sb activation and without Cs-Sb activation has been measured. The measurement results showed that the peak wavelength of fluorescence spectrum of sample with Cs activation has shifted toward to short directions, while peak intensity of samples with the Cs-Sb has reduced compared with sample without Cs activation. This phenomenon lustrated that not only quantity of transition electron of Na2KSb multi-alkali cathode with Cs activation has increased, but also the energy level of transition electron has increased. This phenomenon can be defined as "volume effect" during the activation process. So during activation process of Na2KSb multi-alkali cathode, the reason of sensitivity increasing is a kind of surface effect and a kind of "volume effect". Yet this "volume effect" refers to the structure change inside the multi-alkali cathode layer material, rather than surface Cs atoms diffused inside film.


Li X.-F.,The Key Laboratory on Night Vision Technology | Li X.-F.,North Night Vision Technology Co. | Lu Q.,North Night Vision Technology Co. | Guo Q.,North Night Vision Technology Co.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2013

The characteristics of photoluminescence and the measuring principle of photoluminescence of LLL image intensifier were discussed, and the fluorescence spectrum of multi-alkali photocathode of FOP (optical fiber panel) input window was measured. The test results suggest that the fluorescence spectrum of multi-alkali photocathode of FOP window is not a smooth Gauss curve, but a curve with some small interference peaks being added to a Gauss curve, for there are two special light beams in the fluorescence transmitted by FOP window. One light beam is collimated light and the other is the folded light beam at the very moment when the incidence angle is equivalent to critical angle of total reflection. Both light beams have fixed phase difference or optical path. When the difference between the phase differences of the two light beams lives up to the integral multiple of λ, they will interfere to produce constructive interference peak; when the difference between the phase differences of the two light beams lives up to the odd multiple of 1/2λ, they will interfere to produce destructive interference peak. If constructive interference peak is produced exactly at the peak wavelength of fluorescence spectrum, then the measured peak fluorescence intensity is higher than its inherent peak fluorescence intensity; on the contrary, if destructive interference is produced exactly at the peak wavelength of fluorescence spectrum, then the measured fluorescence intensity is lower than its inherent fluorescence intensity. Furthermore, due to the impact of interference, the half peak width of fluorescent curve can not be accurately determined. Hence, the impact of interference factors should be taken into consideration when analyzing the fluorescence spectrum of photocathode of FOP window.


Li X.-F.,The Key Laboratory on Night Vision Technology | Li X.-F.,North Night Vision Technology Co. | Lu S.-L.,North Night Vision Technology Co. | Yang W.-B.,North Night Vision Technology Co. | Zhao X.-F.,North Night Vision Technology Co.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2012

The measurement principle of fluorescence spectrum on Na 2KSb film of multi-alkali photocathode was described and three samples were measured in the position of different radius. The data result shows that the peak wavelength of fluorescence spectrum on Na 2KSb film from center to edge of the cathode surface gradually increases, and the peak fluorescence intensity gradually increased as well. The reason is that the antimony atom density of cathode surface from the center to the edge gradually reduces. When the antimony in Na 2KSb film exceeds stoichiometry required, the fluorescence peak wavelength shifts towards the short-wave direction, while the fluorescence intensity decreased at the same time. When the antimony in Na 2KSb film achieves stoichiometry required, the fluorescence peak wavelength reaches the maximum value, while the fluorescence intensity reaches the strongest at the same time. By fluorescence test one can judge whether the stoichiometry of Na 2KSb film reaches to the ratio 2:1:1 or not, in another words whether antimony in Na 2KSb film is overdose or not. In addition by measuring the fluorescence spectra at different positions of the cathode surface, we can measure component uniformity in the Na 2KSb cathode film. The more uniform antimony atom density is in the cathode surface, the more accurate the monitor method of film growth by measuring changes of the cathode photocurrent is, thus component uniform can be better, Na 2KSb film thickness can be thicker, long-wave absorption of visible light is more, the sensitivity of the cathode is higher. Therefore, during the manufacturing process of multi-alkali cathode of image intensifier, one has to make the uniform antimony atoms density on cathode window surface in order to achieve higher sensitivity.


Li X.-F.,The Key Laboratory on Night Vision Technology | Li X.-F.,North Night Vision Technology Co. | Yang W.-B.,North Night Vision Technology Co. | Wang J.,North Night Vision Technology Co. | Qiu Y.-S.,North Night Vision Technology Co.
Guangzi Xuebao/Acta Photonica Sinica | Year: 2012

The characteristics of multi-alkali photocathode and its application in low light level image intensifier are introduced, the principle of light induced fluorescence is described, the method to study electron transition probability of Na2KSb cathode film by use of light induced fluorescence is explored, and the fluorescence spectrum of two different cathodes in the states of work and non work are measured respectively. The test results show that, the fluorescence intensity of cathode is proportional to both its electronic transition probability and sensitivity, at the same time fluorescence intensity in work states declines compared to that in non work states. The reason is that part of the transition electrons escape from cathode surface and produce photoelectric emission. These transition electrons do not return to the ground state, therefore they do not emit fluorescence no longer. In this paper the fluorescence spectrum of cathode is also measured excited at different wavelengths of incident light. The results show that, compared with short waves excitation, long waves excitation can obtain higher intensity, which shows long waves excitation can get higher transition electron probability as well; at the same time wavelength shifts between fluorescence peak wavelength and excitation light wavelength is smaller; therefore, the energy loss is small, the photoelectric emission is more favorable. Compared the fluorescence spectrum with multi-alkali photocathode quantum efficiency, it can be concluded that transition electron energy level plays more important role in the process of photoelectric emission between transition electron number and the energy level. As to the multi-alkali cathode, due to electron transition probability of short wave excitation is relatively small, and energy loss of the transition electron diffusion process is bigger, therefore the short-wave quantum efficiency decreases as wavelength decreases. Practice has proved that the photoluminescence is an effective study way of cathode photoemission process, through the study of cathode fluorescence spectrum the cathode photoelectric emission mechanism is further revealed. This provides important reference value for further improving the process and raising the cathode sensitivity.


Li X.,The Key Laboratory on Night Vision Technology | Li X.,North Night Vision Technology Co. | Zhao X.,North Night Vision Technology Co. | Chu Z.,North Night Vision Technology Co. | Wang Z.,North Night Vision Technology Co.
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2014

The Rb2Te solar blind ultraviolet(UV)cathode was fabricated and its optical characteristics, including but not limited to the spectral response, reflectance, absorptance, and fluorescence spectra excited at a wavelength of 250 nm, were evaluated and compared with those of the Cs2Te cathode. The Rb2Te solar blind UV cathode outperforms the Cs2Te cathode in many ways. For example, the Rb2Te cathode has higher spectral response, shorter peak wavelength, and longer threshold wavelength than those of the Cs2Te cathode, respectively. In addition, its spectral sensitivity at 633 nm, around 10-5 mA/W, is one order of magnitude lower than that of the Cs2Te cathode, and depending on the wavelength, a blue-shift was observed in its total reflectance spectrum. Excited at a 250 nm, the fluorescence intensity of the Rb2Te cathode, in 200~450 nm range, is stronger than that of the Cs2Te cathode, possiblly because of its higher absorptance. We suggest that the Rb2Te cathode be a good image device for solar blind ultraviolet detection.


Li X.,The Key Laboratory on Night Vision Technology | Li X.,North Night Vision Technology Co. | Zhao X.,North Night Vision Technology Co. | Guo Q.,North Night Vision Technology Co. | Zhang Y.,North Night Vision Technology Co.
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2013

The spectral response of the Na2KSb (Cs) and Na2KSb (Cs-Sb) films, deposited by vacuum evaporation, respectively, on different sectors of glass window of the multi-alkali cathode of the second generation image intensifier, were evaluated. The work functions and the long wave threshold of the Na2KSb (Cs) and Na2KSb (Cs-Sb) films were found to be 1.35 eV and 915 nm, respectively. The results show that the Cs and Cs-Sb activation mainly reduced the electron affinity, but the Cs-Sb activation generated a higher spectral response. The slightly blue-shifted fluorescence peak of the Cs-Sb activated Na2KSb is higher than that of the Cs-activated Na2KSb, possibly because the transition involves more electrons and higher energy levels. Moreover, the Cs-Sb activation of Na2KSb not only reduced the work function, but also deformed the surface energy band because of the stress-induced lattice distortion at the interface of the Cs-Sb layer and Na2KSb films.


Li X.,The Key Laboratory on Night Vision Technology | Li X.,North Night Vision Technology Co. | Guo Q.,North Night Vision Technology Co.
Zhenkong Kexue yu Jishu Xuebao/Journal of Vacuum Science and Technology | Year: 2013

Here, we addressed the fabrication and quantum efficiency of the transmission-type and reflection-type multi alkali photocathode of the super second generation image intensifier. The influence of the absorption of the photocathode and the optical reflectance at the input of the micro channel plate (MCP) on the quantum yield was analyzed. The results show that the transmission-type and reflection-type photo-cathodes have the identical cut-off wavelength in the long wave length range, because the measurement involved the work function of the same cathode, but different cutoff wavelengths in the short wavelength range. The key parameters, including the reflectance at the MCP input, quantum yield, reflectance of the two types of photocathode, were measured. We suggest that the preliminary results may be of much basic and technological interest.

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