It is difficult for Fizeau interferometer to take its common optical path characteristics and anti-vibration measurement requirements into account. In this paper, a dynamic Fizeau interferometer (DFI) is proposed for anti-vibration optical measurement, and the advantages of common optical path and high accuracy of Fizeau interferometer are retained. DFI is divided into conventional Fizeau interferometer and vibration measurement part. An assistant mirror is added to the vibration measurement part to separate the information of the reference wavefront and the test wavefront with the shortcoherence laser. The vibration information of the Fizeau cavity is obtained by measuring the vibration of each surface separately. The vibration coefficients of the reference wavefront and the test wavefront are extracted by the algorithm, and then combined with the interferograms of the Fizeau interference part. The phase to be measured is finally recovered. DFI provides a solution for anti-vibration measurement of Fizeau interferometry, which has high application value in optical measurement.
A two-step iterative algorithm (TSIA) immune to tilt shifts is proposed for phase extraction in phase-shifting interferometry (PSI). The TSIA constructs a model of the least-squares iteration of the phase distribution and the tilt shifts based on parametric decoupling. Finally, the phase distribution is extracted via the least-squares method. The experimental results show that the PTI has high accuracy and fast iterative convergence speed for the conditions of the large amplitude of tilt shifts, closed fringes, nonuniform background and modulation.
In this paper, a Fizeau interferometer with double interference cavity is proposed to solve the influence of the environmental factors in high precision phase measurement. The proposed method adds a reference mirror, combined with a low-coherence source, to construct two interference cavities, which have the synchronous phase change. One of them has an adjustable spatial carrier frequency, which is used to calculate the relative deformation phase during the test, while the other has the same null fringe with the standard Fizeau interferometer. The measured phase can be retrieved by using the least square method with the calculated deformation phase and null fringe patterns. In addition, the visibility of the fringe of the two interference cavities are analyzed. Simulation and experiment demonstrate that the proposed method can realize the dynamic measurement of the mirror under the influence of the time-varying environment, and has reliable measurement accuracy.
Fourier Transform Imaging Spectrometer(FTIS) is an instrument cable of acquiring two-dimensional spatial information and one-dimensional spectral information. The FTIS has attracted much attention and is widely applied in the fields like military reconnaissance, remote sensing, biomedicine, environmental monitoring, etc. The FTIS acquires the spectral intensity in different wavelengths by performing Fourier transform on the white light interference signal of the target generated by the FTIS. The spectral curve obtained directly by Fourier transform reflects the relationship between the wavenumber order and the spectral intensity. So wavelength calibration is required to convert the above relationship into the relationship between the wavelength and the spectral intensity, which makes it more intuitive. Therefore, wavelength calibration is a necessary step for FTIS to recovery spectrum. The traditional wavelength calibration method can only get the wavenumber order in the range of integer because of the picket fence effect in Fourier transform. It will definitely ignore the fractional part which results in the inaccurate wavenumber order, which will directly affect the precision of the wavelength calibration result. In order to solve this problem, a high-precision wavelength calibration method based on Fourier transform imaging spectrometer is proposed according to the principle of FTIS and Fourier transform. This method can calculate the wavenumber order with the precision of percentile, which will reduce the error of wavelength calibration effectively. As a result, the precision of spectral calibration can be increased eventually. This method realizes high-precision wavelength calibration by the way of adding zero to the interference fringe in the spatial domain. The core of the method is getting a more precise wavenumber order. The brief process of obtaining wavenumber order is as follows: First, the FTIS acquires the interference fringe of a monochromatic laser. Second, the original interference fringe is extrapolated with zero. Third, the subtle spectrum can be obtained by performing Fourier transform on the extrapolated interference fringe. Finally, the precise wavenumber order is calculated by dividing the abscissa of the peak value by the extrapolation multiple. The principle of this method is investigated and related simulations are then carried out. The simulation results indicate that the wavenumber order calculated by the method have the same precision with the preset parameters, which illustrates that the method can calculate the wavenumber order more accurately. Therefore, the method can improve the precision of the spectral calibration. Besides, related experiments are also performed. The laser interference fringes of different wavelengths generated by the actual FTIS all apply the method to get the wavenumber orders in the frequency domain. Then a curve which is the wavelength calibration function is fitted using the discrete relation between the wavelengths and the wavenumber orders. A laser whose wavelength is known is measured by the FTIS with the wavelength calibration function got by the proposed method. The error of the wavelength measurement result is one-fifth of the traditional method. The simulations and the experiment results indicate that the proposed method can improve the precision of the wavelength calibration, which provides the theory and technology support for spectral measurement using FTIS. It also provides a possibility for the development of FTIS towards the super resolution direction.
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