Information

Date: 14th Apr 2022

Members: Dan Chen, Satoru Ikeda

Place: Kamioka Hokubu-kaikan 1F meeting room

Background

The mirror substrates made for KAGRA O5 may have high internal scattering, and we are developing a simple measurement method for this purpose.
The idea is using a camera to take a picture.
At first we used a laser pointer (Green, 1mW) as a laser beam source and a sapphire sample from Mitaka to check the measurement principle.

Result

ASI camera (ASI224MC) is not suitable for this measurement because of the noise.
The reason can be the insufficient noise reduction in the camera or poor lens we used or both.

A digital camera (Canon EOS Kiss M2) successfully captured the scattered light from the sapphire sample with 61s exposure time and ISO6400.

Detail

Laser source

Model: UC-S1
Wave length: 532nm
Max power: 1mW

ASI camera

Camera: ASI 224MC
Lens: CCTV LENS 2.1mm 3MP
Application: Planetary Imager

Result: we tried several conditions for exposure time and gain, but the scattered light in the sample was not clear because of noise.

Digital camera

Camera: Canon EOS Kiss M2
Lens: EF-M15-45 F3.5-6.3 IS STM
Exposure time: 61s
ISO: 6400
Color temperature: 6000K
F: 16
Focus length: 45mm
Recorde image quality: best (about 15MB/picture)
Output image format: jpeg

Result:
With the above condition, the scattered light was observed. In order to make it clear, we took a picture with the Green laser ON and OFF, then we made a diff image using "imageJ". The diff image shows the internal scattered light clear.

What we learned:
Because the scattered light we want to measure is very faint, we need to avoid environmental light and stray/scattered light generated outside of the sapphire sample interfering with the measurement.