HeNe laser for a high-precision phase-shifting interferometer based on peak power locking and weak thermal coupling

Aiming at the problem of lacking several-milliwatt HeNe lasers with stable output in the field of precise interferometry, a light source schema based on peak power locking and weak thermal coupling is proposed in this paper. A weak thermal coupling structure driven by thermoelectric coolers (TECs) is developed based on the thermal conduction model of the laser tube, and the operating temperature of the tube is regulated through the feedback of the intensity signal of the reference light. Eventually, a two-milliwatt laser output with a wavelength drift of 0.04 pm within 24 h is achieved. The power loss, which is faced by the commercial frequency stabilization technique for HeNe lasers, is avoided by locking the operating mode at the peak gain position in the proposed method. In addition, stable single-longitudinal-mode output is achieved through this method, solving the issue of unstable interferogram contrast in spatiotemporal domain associated with the laser coherence fluctuation. Based on these characteristics, the new, to our knowledge, laser is applied for the surface shape measurement of an irregular-shape monocrystalline silicon component, resulting in the single-measurement error being reduced and the repeatability accuracy in the vibrating environment being improved.