A sinusoidal phase-modulating （SPM） laser diode （LD） interferometer for real-time surface profile measurement is proposed and its principle is analyzed. The phase signal of the surface profile is detected from the sinusoidal phase-modulating interference signal using a real-time phase detection circuit. For 60 × 60 measurement points of the surface profile, the measuring time is 10 ms. A root mean square （RMS） measurement repeatability of 3.93 nm is realized, and the measurement resolution reaches 0.19 nm.
A method for rapid measuring retardation of a quarter-wave plate based on simultaneous phase shifting technique is presented. The simultaneous phase shifting function is realized by an orthogonal grating, a diaphragm, an analyzer array, and a 4-quadrant detector. The intensities of the light beams from the four analyzers with different azimuths are measured simultaneously. The retardation of the quarter-wave plate is obtained through the four light intensity values. In this method, the major axis position of the quarter-wave plate need not intensity fluctuation of light be determined in advance source. The feasibility of the In addition, the measured result is free of the method is verified by the experiments.
