Yasui, Aso

We replaced the steering mirrors (STM1 and STM2) in front of the IFI from PYD-20 to better ones.

The motivation is to improve the reflectivity (>99% to >99.9%) and add an AR coating on the back.

Both mirrors were successfully replaced.

Note that the POMs are not yet replaced. I'd like to do that when the reflected beam from the interferometer is available.