5:15 PM - 7:15 PM
[PCG20-P09] Evaluation of the Quantum Efficiency of Funnel-Type Microchannel Plates for Ultraviolet Spectroscopic Observations of Exoplanetary Atmospheres
More than 5,800 exoplanets have been discovered through various observational methods. Among them, some terrestrial planets are located within the habitable zone. One of the objectives of the LAPYUTA project is to identify exoplanets that could retain liquid water on their surface,by conducting transit spectroscopic observations targeting M-type stars, which emit strong XUV radiation. Due to XUV radiation from the host star, upper atmospheres rich in hydrogen and oxygen atoms would escape. Thus, the absorption of oxygen and hydrogen emission lines increases in transit. By performing spectroscopic observations in the ultraviolet range and evaluating the transmittance, it is possible to estimate the abundance of oxygen and hydrogen atoms in the atmosphere.
For ultraviolet spectroscopic observations of exoplanet atmospheres, the ultraviolet spectroscopic instrument UVSPEX is currently under development. Since ultraviolet radiation from stars is weaker than visible or infrared light, UVSPEX adopts an image intensifier that is solar-blind. The image intensifier incorporates a microchannel plate (MCP), which is designed to improve quantum efficiency by depositing cesium iodide and shaping the entrance pores into a funnel. CsI is highly effective to enhance the photoelectric effect. The funnel shape increases the open area of each channel to approximately 90%, thereby enhancing the incident efficiency.
In this study, an MCP divided into four quadrants is used : 1)A region with no modifications at the entrance pores, 2)A region where the entrance pores are shaped into a funnel, 3)A region where CsI is deposited at the entrance pores, 4)A region where the entrance pores are funnel-shaped and CsI is deposited. The quantum efficiency of this MCP is measured to evaluate the improvement in quantum efficiency due to the funnel shape and CsI deposition.
In a previous study, the quantum efficiency of MCP was measured by using light from a deuterium lamp. The number of light spots generated on a phosphor screen by electrons amplified in the MCP was compared with the output of a photodiode with a known quantum efficiency. A CCD camera, which could fit the dynamic range of both detectors, was used for the comparison. Since the CCD camera cannot operate in a vacuum, measurements were conducted in a nitrogen environment.However, when replacing the detector and refilling the experimental setup with nitrogen, the lamp intensity fluctuated depending on the replacement time, so it impossible to compare the detector outputs under the same lamp intensity. To address this issue, the experimental setup was modified to use a beam splitter with calibrated transmission and reflection rates, allowing for the simultaneous comparison of outputs from two detectors with the constant lamp intensity. Quantum efficiency measurements for ultraviolet radiation were then conducted using this setup.
In this presentation, we will discuss the measured quantum efficiency of the MCP, the improvement rates due to the funnel shape and CsI deposition, and comparisons with previous studies.
For ultraviolet spectroscopic observations of exoplanet atmospheres, the ultraviolet spectroscopic instrument UVSPEX is currently under development. Since ultraviolet radiation from stars is weaker than visible or infrared light, UVSPEX adopts an image intensifier that is solar-blind. The image intensifier incorporates a microchannel plate (MCP), which is designed to improve quantum efficiency by depositing cesium iodide and shaping the entrance pores into a funnel. CsI is highly effective to enhance the photoelectric effect. The funnel shape increases the open area of each channel to approximately 90%, thereby enhancing the incident efficiency.
In this study, an MCP divided into four quadrants is used : 1)A region with no modifications at the entrance pores, 2)A region where the entrance pores are shaped into a funnel, 3)A region where CsI is deposited at the entrance pores, 4)A region where the entrance pores are funnel-shaped and CsI is deposited. The quantum efficiency of this MCP is measured to evaluate the improvement in quantum efficiency due to the funnel shape and CsI deposition.
In a previous study, the quantum efficiency of MCP was measured by using light from a deuterium lamp. The number of light spots generated on a phosphor screen by electrons amplified in the MCP was compared with the output of a photodiode with a known quantum efficiency. A CCD camera, which could fit the dynamic range of both detectors, was used for the comparison. Since the CCD camera cannot operate in a vacuum, measurements were conducted in a nitrogen environment.However, when replacing the detector and refilling the experimental setup with nitrogen, the lamp intensity fluctuated depending on the replacement time, so it impossible to compare the detector outputs under the same lamp intensity. To address this issue, the experimental setup was modified to use a beam splitter with calibrated transmission and reflection rates, allowing for the simultaneous comparison of outputs from two detectors with the constant lamp intensity. Quantum efficiency measurements for ultraviolet radiation were then conducted using this setup.
In this presentation, we will discuss the measured quantum efficiency of the MCP, the improvement rates due to the funnel shape and CsI deposition, and comparisons with previous studies.