Acta Photonica Sinica, Volume. 52, Issue 8, 0812001(2023)
Effect of Incident Light Scattering at AlGaAs Window Layer Interface on Resolution of Transmission-mode GaAs Photocathode
Negative Electron Affinity (NEA) GaAs photocathode, as the most promising Ⅲ-Ⅴ semiconductor photocathode for low-light image intensifier, has wide applications in underwater target detection, range gated imaging, and night vision. According to the photoemission theory of transmission‐mode GaAs photocathode, the incident light needs to pass through AlGaAs window layer before it can be absorbed and converted into photogenerated carriers by GaAs emission layer. The performance of image resolution on GaAs photocathode could result from the resolution of optoelectronic image and optical image. The resolution of optoelectronic image is determined by the longitudinal diffusion of photoelectrons in the emission layer. The resolution of optical image is mainly affected by the scattering of incident photons on the rough surface of the window layer. Most research on GaAs photocathode has focused on obtaining a higher optoelectronic image resolution, but there is rare research concentrated on improving the optical image resolution. However, the resolution of transmission-mode GaAs photocathode is hard to improve due to the ignorance of the optical image resolution. In order to study the image resolution of the transmission-mode GaAs photocathode under different wavelengths of incident light, a theoretical model based on the Scattering Transfer Function (STF) for the analysis of interfacial scattering from the AlGaAs window layer is proposed. A transmission-mode GaAs photocathode was fabricated, and the degradation of the incident optical image caused by the interfacial scattering of the AlGaAs window layer was quantitatively analyzed based on the signal-to-noise ratio fitting with reference peaks by using the variation of the STF and the Point Spread Function (PSF). The STF of the AlGaAs window layer rough surface under different incident light wavelengths was calculated and the incident light wavelength was set as 530 nm, 700 nm, and 830 nm respectively. The obvious characteristic is that the value of STF is improved when the incident light wavelength increases. Therefore, When the wavelength of incident light is reduced from 830 nm to 530 nm, the reduction of STF means that the area or integral value enclosed by the surface transfer function is smaller, resulting in the smaller the capacity of optical image information and the more blurred the imaging. The PSF of the AlGaAs window layer rough surface can be obtained by Fourier quasi-transform based on the STF. The results show that the central value of the PSF increases with the increase of the incident wavelength, which means the central energy of the optical image plane becomes more concentrated. In order to analyze the imaging quality of the third generation low light level image intensifier due to the scattering of incident light with different wavelengths on the rough surface of AlGaAs window layer, the PSF is convoluted with the original image of the given standard resolution target to simulate image degradation. When the incident light wavelength increases from 530 nm to 830 nm, the peak signal-to-noise ratio
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Xin GUO, Feng SHI, Tiantian JIA, Ruoyu ZHANG, Hongchang CHENG, Yijun ZHANG. Effect of Incident Light Scattering at AlGaAs Window Layer Interface on Resolution of Transmission-mode GaAs Photocathode[J]. Acta Photonica Sinica, 2023, 52(8): 0812001
Category: Instrumentation, Measurement and Metrology
Received: Dec. 5, 2022
Accepted: Jan. 16, 2023
Published Online: Sep. 26, 2023
The Author Email: SHI Feng (shfys@126.com)