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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