A Convenient Way to Determine the Optimum Angle of Incidence of Fizeau Interferometer

In a Fizeau interferometer, off-axis illumination will lead to fringe optimization. Primarily due to the unique structure of our interferometer, we first analyze the influence of the optical properties of the parallel plate as a part of the interferometer on the optimal incident angle. Generally, the incident angle determination is mainly based on the graphing method proposed by Langenbeck and the estimation formula proposed by Kajava. However, Langenbeck’s method is cumbersome, and the error of Kajava’s estimation formula is large. Based on the predecessors, this paper proposes a modified method of determining the optimal angle of incidence and further derives more accurate optimal angle expressions than Kajava’s. By simply substituting the wedge angle of the wedge cavity and the reflectivity of the cavity, the optimum incidence angle can be obtained immediately. Thus, it eliminates the tedious and complex process of finding the optimum incident angle by graphing method and makes the formula method the simplest method to find the optimum incident angle. Finally, the comparison of the interference intensity at the optimum incidence angle calculated by the improved method and normal incidence is given. It is found that the beam has a good suppression effect on the sub-peak when it is incident at the optimum incident angle calculated by the method in this paper.

NOA61-Polymer Fiber Fizeau Interferometer with a Flexible NOA65-Polymer Taper for Simultaneous Measurement of Tilt Angle and Temperature

This study proposes and experimentally demonstrates a NOA61-polymer fiber Fizeau interferometer (PFFI) connected to a flexible NOA65-polymer taper (PT) for simultaneous measurement of tilt angle and temperature (T). The PT/PFFI fiber sensor consists of a taper-shaped flexible NOA65 polymer and single-mode fiber with an endface that is attached to a NOA61-polymer. The NOA61-polymer of PFFI is highly sensitive to variations of T with high repeatability and enables the simultaneous measurement of tilt angle by connecting with the highly flexible NOA65-PT. the interference fringe visibility of optical spectra in the PFFI can be highly controlled by the tilt angle of the PT and is thus capable of measuring tilt angles with high sensitivity. On the other hand, wavelength shifts of the spectra in the PFFI only occur when T varies. The proposed PT/PFFI can simultaneously detect the tilt state and the variation of surrounding T by measuring the optical spectral responses and eliminating cross sensitivity. Experimental results demonstrate the PT/PFFI can simultaneously measure tilt angles and T with good sensitivities and obtain averages of 0.4 dB/° and 0.17 nm/°C, respectively.

Computational program to evaluate local defects type Chalmers Test on a reflective optical surface

A computational tool is developed to measure the local deformations in optical surfaces from the interference patterns obtained by the Chalmers test principle and from the analysis of a reflective optical surface using a commercial Fizeau interferometer of the ZYGO. The tests were made on a concave spherical mirror with a radius of curvature of 60 cm and a diameter of 13 cm. To obtain the measurements of local deformations, a computational tool proposed for the localization of dark fringes is used by evaluating the maximum and minimum of the image obtained in the interference patterns. The results obtained show that the computational tool allows locating fringes within an interference pattern, allowing faster inter-fringe measurements and assigning an error on the surface in terms of wavelength.