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 x 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 fl'om 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 be determined in advance.In addition,the measured result is free of the intensity fluctuation of light source.The feasibility of the method is verified by the experiments.
