Compensation of high-order misalignment aberrations in cylindrical interferometry

Interferometry with a null corrector can be used to test cylindrical surfaces. The requirement for accurate measurement is a null fringe pattern. When the tested cylindrical surface is not perfect or seriously misaligned, a nonzero fringe pattern might be obtained. As a result, high-order misalignment aberrations (e.g., coma and spherical aberration) are introduced into the measurement. The sources and types of high-order misalignment aberrations are analyzed by orthogonal Legendre polynomials. Based on the analysis, a mathematical model was proposed to estimate the high-order misalignment aberrations. Then a wavefront difference method was proposed to calibrate the coefficients of this model. With the calibrated coefficients, the high-order misalignment aberrations can be determined and separated from the measurement results. Several experiments were conducted to demonstrate the validity of the proposed method. Compared with the lower-order misalignment aberrations removal method, the proposed method can reduce the high-order misalignment aberrations by at least half, and highly accurate results can be achieved by the proposed method.