Compensation of the Air Turbulence by Two-Color Method for Straightness Measurement

Abstract

Air turbulence affects the propagating direction of a laser beam, and causes serious errors in laser straightness measurement. The effect is compensated by a two-color method utilizing the wavelength property of the turbulence. The two-color lasers are input to the same optical fiber, and then are collimated by an achromatic lens. In this case, two laser beams are modulated by a chopper at a frequency of 200 Hz and are detected by the same 4-divided position-sensing photodiode. After compensation, the air turbulence error is decreased by approximately 87%, and the direction stability of 1.3 × 10^-6 rad is achieved at a distance of 20 m.