Parallel Plate Interferometry Studies

The metrology of parallel plates in the optical fabrication and test is very important. While using the traditional Phase Shifting Interferometry, it causes large errors because of the superposition of three interferograms generated from three isolated surfaces in the measurement process. Thus the subject of this article is with great importance to the measurement of optical element like parallel plate. This article studies the principle of wavelength tuning phase-shifting interferometry, and also studies the method of calculate the flatness of parallel plate's surfaces, parallel degree and other parameters through both the time and spatial Fourier Transform. Wavelength tuning interferometey test system of the parallel plates has been established, and several interferograms have been collected using the phase shift of wavelength tuning. Both the time and spatial Fourier Transform have been used upon the obtained interferograms. Finally, several parameters of parallel plate have been figured out. The result is also compared with the normal test method which has to suppress the reflection of parallel plate's back surface. The comparison result shows the calculation algorithm used in this article can be applied in the metrology of parallel plate.