Laser interferometers provide an easy path for traceable measurements as most commercial instruments are inherently accurate to better than 10-7. The main problem with using these interferometers over an extended path can be the alignment requirements which can only be met with a precision rail system. Tape benches are typically 50 m (or more) long and are easily affected by building movement, requiring frequent re-alignment. An interferometer with an expanded measurement beam has significantly reduced alignment requirements and one with a beam diameter of 45 mm was used by the author to measure survey pillars. This had an alignment tolerance of +/- 10 mm allowing the use of a simple stretched wire rail system. This paper describes a simple adaptation that can be made to a commercial interferometer to expand the measurement beam without interfering with its normal operation.
Nicholas Brown, Nicholas Brown,
"Traceable measurements for tape benches made easy", Proc. SPIE 4401, Recent Developments in Traceable Dimensional Measurements, (22 October 2001); doi: 10.1117/12.445610; https://doi.org/10.1117/12.445610