Spatial-carrier Phase-shifting Method Research Articles

A single-frame spatial carrier phase-shifting method realized by minimizing the coefficient of variation

An advanced spatial carrier phase-shifting algorithm based on minimizing the coefficient of a variation method is proposed, which realizes the phase extraction of a single-frame spatial carrier fringe pattern. In our test, compared with the existing classical algorithms, the proposed method is proved to have the dual advantages of efficiency and accuracy. In addition, the main factors that may affect the performance of the method are analysed and discussed. The results show that the method proposed is a fast and accurate single-frame phase detection method, which can provide an effective solution for real-time phase demodulation.

Carrier fringe pattern analysis: Links between methods

Introducing a carrier into a fringe pattern makes the phase retrieval problem well-posed, and has become one of the pillar techniques in optical metrology. The carrier fringe pattern analysis for high-accuracy phase retrieval is hence important, for which, many well-known methods have been developed, such as the Fourier transform method, the windowed Fourier transform based methods (the windowed Fourier filtering and the windowed Fourier ridges), the spatial carrier phase-shifting method, and the sampling moiré method. These methods were developed independently and seemingly different. The purpose of this paper is to reveal the close relationships between them, and to connect these methods into a tight-knit methodology family.

Double-exposure phase calculation method in electronic speckle pattern interferometry based on holographic object illumination

Multiple-exposure phase calculation procedures are widely used in electronic speckle pattern interferometry to calculate phase maps of displacements. We developed a double-exposure process based on holographic illumination of the object and the idea of the spatial carrier phase-shifting method to examine transient displacements. In our work, computer-generated holograms and a spatial light modulator were used to generate proper coherent illuminating masks. In this adjustment all phase-shifted states were at our disposal from one recorded speckle image for phase calculation. This technique can be used in the large scale of transient measurements. In this paper we illustrate the principle through several examples.

Noise suppression in spatial carrier phase shifting method

The spatial carrier phase shifting method (SCPSM) has advantages over both the Fourier transform and phase shifting methods. Unlike the phase shifting method, only a single fringe pattern is needed, and unlike the Fourier transform method, SCPSM is not computationally intensive. However, these advantages are at the cost of increased susceptibility to noise. In this work, a novel bandpass filter is developed and applied for noise suppression in SCPSM. As an angular carrier frequency of π/2 is widely used, the bandpass filter can be simply designed from a known low-pass filter. The developed filter is applied to a simulated fringe pattern to show its benefits.

Quantitative evaluation of digital shearing interferogram using the spatial carrier method

In this paper we describe a digital shearing interferometer system. The set-up is composed of a Mach - Zehnder interferometer which allows us to split the image of one object and to recombine the two images shifted and tilted. The tilt between the two images is chosen in order to produce a carrier frequency. The spatial carrier phase-shifting method is used for the quantitative evaluation. Two separate shearograms of an object under test are recorded using a CCD-sensor and stored in a frame grabber. The phases of the two shearograms are calculated from the complex amplitudes and the gradient is obtained from the phase difference. Experimental results are presented.

Two directional spatial-carrier phase-shifting method for analysis of crossed and closed fringe patterns

Various interferometric and fringe projection techniques may result in crossed and closed fringe patterns with the information about the phenomena tested. Recent applications require the analysis on the basis of a single fringe pattern. Here, we address two problems: simultaneous analysis of the information about two events, and analysis of fringe pattern with high phase gradients in both x and y directions. The analysis of a fringe pattern is performed by the spatial-carrier phase-shifting method used sequentially for x and y sampling directions. The error analysis of the method in reference to both problems is presented.