This paper presents a practical and inexpensive method to achieve nanometer stability in laser interferometric displacement measurements in an actual environment, for example, in a machine shop. The system employed here consists of a vacuum chamber, which maintains mechanical connection between an inside measurement mirror and an outside target, a 6 atm air supply, three air pressure regulators, an air ejector and a 100 litre surge tank. Use of this system reduced the displacement measurement fluctuation from 35 nm peak-to-valley/70 s in a 146.4 mm long dead path in an ordinary environment to 1.2 nm peak-to-valley/70 s (8.2*10-9). The influences of air turbulence and floor vibration were also investigated. The total cost of this system is less than $4000.
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