17:15 〜 19:15
[PEM14-P06] 磁気光学フィルタを用いた昼間観測/熱圏観測のためのナトリウムライダー開発の現状
キーワード：ナトリウムライダー、磁気光学フィルタ、ファラデーフィルタ
The Sodium (Na) lidar installed at the EISCAT radar site in Tromsø, Norway (69.6º N, 19.2º E) has been observing Na density, background temperature, and wind speed in the mesopause region (80–115 km altitude) since 2010. With its highly stable output and nearly maintenance-free operation, the lidar has played a crucial role in elucidating the relationship between auroras and the dynamics of the mesosphere and lower thermosphere during winter nights.
Currently, efforts are underway to:
(1) extend the observation altitude range of nighttime measurements up to 200 km, and
(2) expand the observation period to year-round measurements, including summer, while maintaining the same altitude range for nighttime observations.
To achieve this, we are developing an ultra-narrowband filter (FWHM ~10 pm) that efficiently eliminates background light other than the laser beam. A magneto-optical filter (Faraday filter) is being developed and integrated into the lidar receiver system.
Current Development Stages:
1. A lidar receiver system has been constructed using a 50 cm telescope with an optical system designed explicitly for Faraday filter observations. Without removing the Faraday filter, an observation light beam can be blocked using a translation stage, allowing continuous 589 nm laser light to be introduced via an optical fiber. This setup enables laser frequency scanning to measure the filter’s transmission characteristics. In the summer of 2023, the receiver system and observation container were shipped and installed on-site.
2. Faraday filter transmission characteristics were measured using a prototype Faraday filter at RIKEN with a high spectral resolution of a few MHz under varying cell temperatures and a magnetic field of 170 mT. The measured transmission profiles were validated against theoretical predictions, yielding excellent results.
3. A thermal stability test of the transmission profiles has been conducted, considering long-term observations. In Faraday filter observations, transmission profiles are measured before and after each observation to verify consistency. The measured profiles are used for data analysis.
Discussions on these topics will be presented in the talk.
Currently, efforts are underway to:
(1) extend the observation altitude range of nighttime measurements up to 200 km, and
(2) expand the observation period to year-round measurements, including summer, while maintaining the same altitude range for nighttime observations.
To achieve this, we are developing an ultra-narrowband filter (FWHM ~10 pm) that efficiently eliminates background light other than the laser beam. A magneto-optical filter (Faraday filter) is being developed and integrated into the lidar receiver system.
Current Development Stages:
1. A lidar receiver system has been constructed using a 50 cm telescope with an optical system designed explicitly for Faraday filter observations. Without removing the Faraday filter, an observation light beam can be blocked using a translation stage, allowing continuous 589 nm laser light to be introduced via an optical fiber. This setup enables laser frequency scanning to measure the filter’s transmission characteristics. In the summer of 2023, the receiver system and observation container were shipped and installed on-site.
2. Faraday filter transmission characteristics were measured using a prototype Faraday filter at RIKEN with a high spectral resolution of a few MHz under varying cell temperatures and a magnetic field of 170 mT. The measured transmission profiles were validated against theoretical predictions, yielding excellent results.
3. A thermal stability test of the transmission profiles has been conducted, considering long-term observations. In Faraday filter observations, transmission profiles are measured before and after each observation to verify consistency. The measured profiles are used for data analysis.
Discussions on these topics will be presented in the talk.