Papers by Keyword: Interferometer

Abstract: In this study, we proposed a moved-view analysis, a method for obtaining the Soret coefficient S_T by analyzing the interference fringe change during field-of-view movement in the steady state. This analysis was designed to solve the problem that the sign of the concentration gradient could also be reversed if the plot of the concentration distribution was only slightly shifted owing to the narrow field of view. The data obtained from the experiment conducted to measure S_T at the International Space Station were analyzed using moved-view analysis. For the moved-view analysis, the linearity of the concentration distribution induced by the Soret effect is larger than that for the method without field-of-view movement, and a more reliable S_T can be obtained. The analysis error that sometimes occurred when the laser wavelength switched led to the underestimation of the phase change Δϕ, resulting in generating the data with low linearity. This unreliable data should be removed.

Abstract: Phase-shifting interferometry is widely used because it can measure phase with high accuracy. Changing optical path length with a PZT transducer and changing frequency of the optical source with a laser diode (LD) are two common methods to apply the desired phase shift between the arms in the interferometer. In any case, however, it is not easy to apply the desired shift accurately, and if not, measurement errors occur. In order to reduce the errors, the effect of the phase shift error has been analyzed numerically especially in the case with LD.

Abstract: As is well known, the phase-shifting interferometry techniques allow to reach longitudinal resolution to ~ 0.1 nm, but the value of lateral resolution remains at the level of ~ 1 mm. For providing of high lateral resolution of linear measurements in the interference microscope profilometer it was proposed to use a position detection sensor of sharp edge. Principle of sensor’s measurement is based on registration of laser spot intensity scattered by the measurement sample surface under displacement of sample in the lateral direction. The paper shows the prototype scheme of measurement system containing the Linnik interferometer used for surface nanorelief measurement and a position detection module of sharp edge. Measurement process and experimental results are presented. The combining of measurement results performed by the Linnik interferometer and a position detection sensor of sharp edge can allow us to precisely (better then diffraction limit) define the position of sharp edge on the reconstructed surface nanorelief.

Abstract: Copper beryllium (CuBe)is materials that are widely used for mechanical applications. In this paper,the use of copper beryllium for cantilever spring of a vibration sensor will beinformed. Cantilever spring plays important role in a vibration sensor, becauseit transfers vibration energy of the measured system into the sensor.Therefore, it is important to know the dynamic characteristics of thecantilever spring. An optical method, called Levitation Mass Method (LMM), isproposed to measure the dynamic characteristic of the cantilever. In themethod, the force of cantilever spring is measured as the inertial force workedon a mass. A pneumatic linear bearing is used to realize a linear motion withsufficiently small friction acting on the mass, i.e., the moving part of thelinear bearing. The inertial force acting on the mass is calculated from thevelocity of the mass, and the velocity is determined highly accurately by meansof measuring the Doppler shift frequency of the laser light beam reflecting onthe mass using an optical interferometer. It is shown that the proposed methodshows the dynamic characteristic of the vibration sensor well.

Abstract: With the improvement of precision in various fields, we present a new method for the measurement of the absolute distance of a remote target based on the laser interferometry technique. In this paper, we obtain the interference fringes change information (the distance information) with the help of laser scanning with different frequency. It does not require the target to move in the direction of measurement. We have done experiments to compare this new methods results with the results of RENISHAW interferometer. Its improved that the accuracy of distance measurement is 10^-4~10^-5 relatively.

Abstract: In recent years optical disks have been very popular and in manufacturing process error detection in optical disks becomes very important, especially for the defects whose size of a few millimeters in length and several hundred nanometers in depth. The authors have developed a new system to measure the defects of disk substrates using a Mach-Zehnder interferometer with a phase shifting method. But it was found that optical disks had undulation of the optical thickness and it disturbed the detection of defects. To solve the problem moving-average method was developed and introduced in data processing to distinguish the defect from the undulation, and with modified unwrapping program the defect was visualized by binary image processing.

Abstract: This article presented a rotary self-check phase unwrapping algorithm. The algorithm was mainly to process phase unwrapping for the phase main value got from Interferometer in accurately measuring object surface topography, and then accurately restored the object surface topography. The object surface topography measured by Interferometer generally tended to be smooth, the phase unwrapping was not difficult without noise interference. The algorithm processed phase unwrapping by the path of gradually rotational diffusion from the middle to the around in the wrapped phase map, at the same time the check for the error was carried out. It used the median filter technology to process the phase unwrapping error, and avoided the transmission of phase unwrapping error, had a greater inhibitory effect on the noises. This method did not identify the residuals, had small amount of operations, and Unwrapping velocity was several times faster than the fastest traditional branch blocking algorithm.

Abstract: A form error characterization of a reflective-type scale grating, which is used in three-degree-of-freedom (3-DOF) encoders for position measurement of a planar motion stage, is presented. The scale grating has a micro-structured surface, the pitch of which is 1 µm in both X- and Y- direction. The periodic pattern on the scale grating generates diffracted beams when a laser beam incidents to the grating surface. The ±1st order diffracted beams from the grating contain information about the stage motions of not only X- or Y- directional in-plane displacement but also Z-directional out-of-plane displacement, and are therefore able to be utilized for multi-axis position detection. Accuracies of the position detection are mainly determined by a period deviation and a Z-directional out-of-flatness of the scale grating. The form error characterization of the grating is possible by using Fizeau interferometer, although the form error of a reference mirror in the Fizeau interferometer still remains as a measurement error in the form of the measured scale grating. In this paper, a new method was proposed to evaluate the form error characterization of the scale grating for the 3-DOF encoder, while eliminating the form error of the reference mirror in the Fizeau interferometer.

Abstract: A new, common-path, in-axis concentric beam-splitting Michelson interferometer is demonstrated for optical coherence tomography (OCT), which can be used to perform high-resolution cross-sectional in vivo and in situ imaging of biological tissues. A piece of glass tube with its inner diameter smaller than the beam-width of the collimated light is used to split the light into a reference and sample beam. In order to obtain the optimal spectral interferogram of this OCT system, an infrared optical path adjustment method was introduced in this paper.

Abstract: We presented a method for measuring the topological charge of a Fractional optical vortex (FOV) by a ring-type multi-pinhole interferometer (RMPI). We retrieved the sampled phase of the FOV passing through a ring-type multi-pinhole plate from the Fourier transform of a single far-field diffraction intensity pattern, and found the phase of FOV around the center approximately be linear with the azimuthal angle, the slope of the phase to the azimuthal angle at the linear part is equal to the topological charge of the FOV. Thus we proposed a method for measuring the l state and determining orbital angular momentum (OAM) of a FOV based on the property.