A phase shifter is useful for digital interferometers. The phase shifter was designed and fabricated in this work by using liquid crystal(LC) which has merits of lower working voltage and lower power consumption than any other phase shifter such as PZT. Aberrated optical wavefront was reconstructed by computer analyses in digital Twyman-Green interferometry through the use of LC phase shifter made in this experiment. The LC phase shifter was made with nematic liquid crystal ZLI-2244-100(Merck) and BK-7 glass substrate which was coated with transparent electrode (ITO). Skyrol film (SKC : 12 μm) was used as a spacer. Threshold voltage for Freedericksz transition was measured to be 3.27 vots which was peak amplitude voltage at 2kHz square wave and from this value the splay constant, $K_1$, could be obtained to be $2.7\times10^{-7}dyne$. Voltages for phase shifting 0, π/2, π, 3π/2, and 2π were selected as 4.047, 4.433, 4.932, 5.601, and 6.459 volts respectively. In digital Twyman-Green interferometry the optical path difference between the two interfering wavefronts was changed by controlling the voltage to LC phase shifter. The wavefronts of the reference and the test mirrors were obtained from the 5 digitized interferograms at each phase shifting steps. 3 dimensional reconstruction of wavefronts were reconstructed by Zernike polynomial fittings and removing tilt components.
