Newton interferometer with phase-shifting and phase-scanning measurement modes

• Phase compensation module (PCM) and Newton interference module (NIM) are proposed for surface contour measurements.
• Two measurement modes, phase-shifting and phase-scanning, are employed for manipulating the interference pattern.
• The results confirm the feasibility and capability of the interferometer.

In this paper, a novel Newton interferometer, which consists of a phase compensation module (PCM) and a Newton interference module (NIM), is proposed to measure the surface contour such as surface flatness and surface step-height. Where the PCM separates the incident beam into two sub-beams; and the NIM further divides each of the two sub-beams into two sub–sub-beams and then exports an interference pattern, which is formed by the interference of the beams having optical path difference within the coherence length, with the phase information of the contour. Two measurement modes, phase-shifting and phase-scanning, are employed for manipulating the interference pattern and then retrieving the surface contour. The phase-shifting measurement mode, which involves a narrow-band source, is suitable for smooth surface examinations, whereas the phase-scanning measurement mode, which employs a broad-band source, can be used for smooth surface or piece-wise smooth surface measurements. This paper first introduces the measurement theory and a setup for realizing the interferometer, and then presents two experiments involving the use of the setup, one for determining the flatness of a gauge block using the phase-shifting mode and the other for measuring the step-height on a silicon substrate using the phase-scanning mode. The results of the experiments reveal the validity and feasibility of the proposed interferometer.