Wavefronts reconstruction of transparent flats by redividing the detectable folded interference harmonics

• Published in: Optics and lasers in engineering Vol. 171; p. 107794
• Main Authors: Chang, Lin, Zhou, Yonghao, Yu, Yingjie
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2023
• Subjects: Folded frequency solution; Multi-surface interferometry; Transparent optics; Wavelength-tuning; Transparent optics; Multi-surface interferometry; Folded frequency solution; Wavelength-tuning
• ISSN: 0143-8166; 1873-0302
• DOI: 10.1016/j.optlaseng.2023.107794

•The under-sampling problem with folded frequencies in multi-surface WPI is analyzed.•Using active frequency folding undersampling, the correct frequency can be obtained as a solid basis for phase demodulation.•The spectral lines near the frequency peaks are redivided, and the frequencies can be accurately solved.•Based on the solved frequency of each harmonic, extended measurement distances can be reached, and efficient phase demodulation is achieved. The difficulty in multi-surface measurements comes from that each measured surface contributes harmonics to the fringe patterns, and the wavelength-shifting technique is an efficient technique that allows the harmonics to have different frequencies. When under-sampling in multi-surface measurements occurs, harmonic frequencies can not be detected by the spectrum directly. As a typical case in under-sampling, the problem of harmonic frequencies folded in the obtained spectrum as false frequencies are addressed in this paper. This contribution demonstrates an efficient algorithm enabling the detection of real and accurate harmonic frequencies, whereby the wavefronts can also be correctly reconstructed. Then the frequency detection accuracy is improved by redividing a smaller spectral interval of the selected frequency bands. Comparative studies based on the Zernike polynomials verify the effectiveness of the proposed method. Experiments for a transparent flat were performed, and the maximum PVQ, PV, and maximum RMS errors for repeatable measurements verified the effectiveness of the proposed algorithm in practical application.