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Table 2 Optical parameters for the 1500-m laser strainmeter

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