Abstract
An external modulation laser module assembly (EMLMA) is proposed to suppress nonlinear errors in an interferometry system and improve its measurement performance. The EMLMA employs both phase modulation with radio frequency signal and a specific modulation amplitude switching mode, enabling the suppression of noise introduced by spurious reflections. The amplitude modulation reduces the influence of stray and background light by transforming the signal of interest to a high-frequency bandwidth. Experimental results show that the measurement error and stability of the interferometry system are significantly improved using the proposed light source module. After modulation, the spurious reflection-induced offset is decreased, and the measurement resolution improves from 7 to 2 nm. The EMLMA can replace the light source of any interferometric measurement system without altering the optical measurement structure. The proposed method reduces the influence of nonlinear errors in homodyne interferometry and provides a basis for further improvement of the interferometry performance.
Highlights
Laser interferometry is employed to realize rapid and ultra-precision displacement measurement in the fields of ultra-precision engineering and nanotechnology [1,2]
We present an external modulation laser module assembly (EMLMA) based on hybrid phase/amplitude modulation to reduce the coherent noise arising from the spurious interference, stray light, and intensity drift
In this study, aiming at the characteristics of the additional optical path difference caused by the spurious reflection, the spurious-reflection induced coherence offset (SICO) could be eliminated by appropriately choosing the parameters of the phase modulation (PM) [32]
Summary
Laser interferometry is employed to realize rapid and ultra-precision displacement measurement in the fields of ultra-precision engineering and nanotechnology [1,2]. The development of these fields has set more stringent requirements on the measurement accuracy of laser interferometry [2,3]. Homodyne interferometry has numerous advantages, such as no limit of speed measurement, a simple optical path, and effortless integration [6,7,8]. It has obvious technical advantages and application prospects in numerous fields. Variations in the intensity of the measurement light have a large influence on the measurement results [4,6,9]; homodyne interferometry is affected by changes in the external environment
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