From: Design and operation of a 1500-m laser strainmeter installed at an underground site in Kamioka, Japan
Item
Value
Laser (wavelength)
Frequency-doubled Nd:YAG (532 nm)
Estimated frequency stability
3 × 10−13 (Allan variance estimation)
Beam diameter
Front
45 mm
End
32 mm
Retroreflector
Aperture diameter
380 mm
Flatness
0.2 μm
Parallelism
2 μrad