6 September 2013 Surface profile measurement of a diffraction grating by a laser beam scanning interferometer using sinusoidal phase modulation
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Abstract
It is difficult in interferometric metrology to maintain high spatial resolution over a large measurement region. In this paper this characteristic is achieved by scanning two focused laser beams of about 6 microns diameter over an object surface and a reference mirror surface, respectively, with a rotating mirror, a lens, and a polarization beam splitter. An electric-optic phase modulator generates the phase difference of a sinusoidal waveform of 10 MHz between the two focused beams to calculate the phase of the interference signal. Because the beam focused onto a diffraction grating of 50 microns period is not diffracted strongly, a surface profile of the grating can be exactly measured by this interferometer over the measurement region of 16 mm with the spatial resolution of 2 microns.
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Osami Sasaki, Takuya Kubota, Samuel Choi, Takamasa Suzuki, "Surface profile measurement of a diffraction grating by a laser beam scanning interferometer using sinusoidal phase modulation", Proc. SPIE 8839, Dimensional Optical Metrology and Inspection for Practical Applications II, 883906 (6 September 2013); doi: 10.1117/12.2025328; https://doi.org/10.1117/12.2025328
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