In order to solve the problem of coherent noise in the measurement of laser interferometer with point source, the method of suppressing coherent noise with ring source is described. The radiation intensity of the central noise point in the interference field under the illumination mode of the ring source is analyzed. In this paper, an optical system based on annular lens is used to generate ring source, and a Fizeau interferometer based on ring source illumination is built in ZEMAX Non-sequence mode. The simulation results show that the radiation intensity of the interference field noise point under the ring source illumination mode reaches 9.8357w/cm2, and the visibility of fringe is low. After adding the bulk scattering element with an average optical path of 0.2 and a scattering angle of 3°, the interference field radiation intensity becomes more uniform, and the fringe visibility was obviously improved.
The transmission sphere(TS) can only be used with a laser interferometer at a specific wavelength. This paper proposes a design method that can make the TS work at multiple wavelengths. First, use the achromatic form to design the TS so that it can be used at two wavelengths at the same time, and then adjust the interval between the TS’s lens to make it at the other two wavelengths, so that the TS can be used of 4 wavelengths in total. Using this method, a TS with a diameter of 101.6mm and F# of 3 is designed. The final TS can work at the wavelengths of 532nm, 721nm, 660nm and 570nm, and the accuracy of the transmission wavefront at each wavelength meet measurement requirements.
Testing wavefront distortions at the design wavelength is critical for optical system qualification. Existing technologies and methods for measuring transmitted wavefronts typically operate at only a few specific wavelengths. In previous research, we propose a method for estimating the wavefront distortion of an optical transmission system in a broad bandwidth. We establish the relationship between the transmitted wavefront and wavelength, using Zernike fringe coefficients to represent the wavefront. We have also experimentally tested a single lens represents the monochromatic transmission system at four wavelengths with interferometers. The results show the monotonic Zernike-wavelength curves of in 400~1000nm bandwidth can be predicted by fitted Conrady formula with three data points. In this paper, we further test a doublet achromatic lens at five wavelengths with interferometers, and we find most Zernike-wavelength curves of the doublet achromatic lens are still monotonic, which can solved by binomial Conrady formula with two data points. Using three points to fit Conrady formula for part of monotonic curves is the same as using two points to solve binomial Conrady formula. However the Z8- wavelength curve which have an inflection point must solved by Conrady formula with three data points. The experimental results of achromatic system are more representative, it shows that Zernike-wavelength curve of achromatic system can be expressed by Conrady formula. In practice testing, if the wavefronts measuring at different wavelengths are accurate, the wavefront of arbitrarily wavelength in a certain band can be estimated by solving Conrady formula. Our experiment shows that the Conrady formula can represent the dispersion characteristics of some optical systems, especially for achromatic system. And the feasibility of measuring transmitted wavefront in a certain band based on Zernike coefficient is verified. The new method will help to simplify the process of multi-wavelength interferometric measurements.