11:15 AM - 11:30 AM
[PCG20-08] Development of photon counting technique for a detector composed of MCP and CMOS image sensor.
Keywords:Photon counting, Ultraviolet, Micro channel plate
The Life-environmentology , Astronomy , and PlanetarY Ultraviolet Telescope Assembly (LAPYUTA) aims to understand the life-supporting environments of the planets and satellites in the solar system and exoplanets.
To achieve one of the goals, "discovery of terrestrial-like planets and elucidation of planetary evolution processes through the observation of upper atmospheres," it is necessary to detect exospheric atmospheres of exoplanets and their compositions by performing transit spectroscopic observations. However, the amount of light in the far ultraviolet region is low, so a detector with photon-counting capability is required.
The detector used in the LAPYUTA project is different from those used in Japanese planetary exploration and space telescopes and is composed of a micro-channel plate (MCP) and a CMOS image sensor. The CMOS image sensor is suitable for photon counting because of its high frame rate. In this detector unit, the incident light is converted to photoelectrons at the photocathode, multiplied by the MCP, and then converted to visible light at the phosphor. The photons are then detected by the CMOS image sensor. Here, the multiplication factor of the MCP is not constant, and the amount of light detected by the CMOS image sensor differs greatly even when photons with the same energy enter the photocathode. If the light is too weak, the signal will be sometimes too small against the noise of the CMOS image sensor, making detection difficult.
We have tried to solve this problem by image processing. To discriminate between incident light and noise, we focused on the intensity distribution on the CMOS image sensor and used a Gaussian filter to remove the noise. We also checked many image data and optimized the threshold value to discriminate between noise and optical signals. As a result, we confirmed that the counting results obtained by image processing were consistent with those obtained by visual counting and that there was no miscounting.
In this presentation, we will report on the photon counting method and experimental results.
To achieve one of the goals, "discovery of terrestrial-like planets and elucidation of planetary evolution processes through the observation of upper atmospheres," it is necessary to detect exospheric atmospheres of exoplanets and their compositions by performing transit spectroscopic observations. However, the amount of light in the far ultraviolet region is low, so a detector with photon-counting capability is required.
The detector used in the LAPYUTA project is different from those used in Japanese planetary exploration and space telescopes and is composed of a micro-channel plate (MCP) and a CMOS image sensor. The CMOS image sensor is suitable for photon counting because of its high frame rate. In this detector unit, the incident light is converted to photoelectrons at the photocathode, multiplied by the MCP, and then converted to visible light at the phosphor. The photons are then detected by the CMOS image sensor. Here, the multiplication factor of the MCP is not constant, and the amount of light detected by the CMOS image sensor differs greatly even when photons with the same energy enter the photocathode. If the light is too weak, the signal will be sometimes too small against the noise of the CMOS image sensor, making detection difficult.
We have tried to solve this problem by image processing. To discriminate between incident light and noise, we focused on the intensity distribution on the CMOS image sensor and used a Gaussian filter to remove the noise. We also checked many image data and optimized the threshold value to discriminate between noise and optical signals. As a result, we confirmed that the counting results obtained by image processing were consistent with those obtained by visual counting and that there was no miscounting.
In this presentation, we will report on the photon counting method and experimental results.