Papers by Keyword: Interferometry

Abstract: The work is devoted to studying the polished surface state of K8 optical glass by ellipsometry, IR spectroscopy and surface roughness measurement methods. It is shown that for chemically stable K8 glass the change of the surface state is insignificant, that is caused by its composition.

Abstract: We propose a new approach for determining the distribution of full-field refractive index based on the angle deviation method (ADM) with a surface plasmon resonance (SPR) sensor in phase detection. The inhomogeneous distribution of refractive index causes the variant deviation angles in the test light. SPR sensor is a sensitive angular sensor especially for phase detection. For the full–field phase measurement, we should use the four-step phase shift interferometry (PSI) to measure the phase shift profile of the test light after reflected from the SPR sensor. Thus the phase shift is caused by the variation of the refractive index. The approach can plot the full-field refractive index distribution in a short time and its resolution can be better than 2.2×10^-8 (RIU).

Abstract: In this paper, we firstly explain the concept of surface plasmon resonance imaging and a main key issue in the field of localized SPR imaging, which is the trade-off between resolution and sensitivity. We will then explain how V(z) scanning confocal microscope can overcome the trade-off and enable us to make a localized detection of multiple analytes in small quantities. This paper provides a brief review on a chronological development of the confocal surface plasmon embedded interferometric microscope and highlights the key idea behind each developments. Theoretical detection limit of the confocal system is within a single molecule detection regime, where 100kD molecule can be detected with 100μJ of light in the confocal system. We also discuss some key challenges in achieving the theoretical limit, such as, microphonic vibration and slow scanning speed of the system and how to get around these challenges. Lastly, we discuss some possible future developments to improve the system.

Abstract: The technique utilizing single-frequency laser interferometry has very high measurement accuracy, but it has rigorous requirements for optical design which is affected by many factors. In order to achieve single-frequency laser interferometry with large stroke and high precision, the integral layout, the polarization phase shifting technique and the common mode rejection method are adopted to design the length interferometry system. This paper analyzes factors and design requirements which affect measurement accuracy with large stroke. Based on polarization phase shifting technique, the system employs the four-beam-signal detection technique and the common mode rejection method, to make a differential processing of four mutually orthogonal signals. Thus, the influences of zero-drift of intensity and environmental change on system are reduced. Combined with a 200 phase subdivision, the system achieves the resolution with 0.8 nm. Under the VC++ environment, the displacement measurement results are compensated and corrected according to the environmental parameters. Compared with the Renishaw XL-80 laser interferometer, the system has better stability in short term. In the measuring range of 60 mm, the effectiveness of the system is verified.

Abstract: Experimental facility situated in the test section of the wind tunnel suction type was adjusted both in the total construction and in the construction of the fluttering body, the methodology of the measurement and evaluation of the flow and dynamic parameters during flutter were also changed. Preserved was the conception of the NACA0015 profile with two degrees of freedom, rotational and translational. Torque elasticity was now realized by the coil spring and changed by different length of this spring or by different diameter of the spring wire. The pitch angle of the profile was now measured by the magnetic rotary encoder. The translational position was indicated by the magnetic linear encoder and was centered by plane springs situated on both ends of the shiftable frame. With this model the testing measurement was realized by its self-excited vibration of flutter type in the range of Mach numbers M=0.20-0.215 and Reynolds numbers 263 000 – 283 000. Results obtained with M=0.21 and Re=276 000 are presented.

Abstract: Digital holography can record 3-D image of the object by using one CCD camera. Surface shape can be measured by changing angles of the object-illuminating mirror. But the measured signals are wrapped because of the periodicity of a sinusoidal function, and then phase unwrapping is needed. We have developed a new modified phase unwrapping method and applied it to surface measurement. Unwrapping errors were significantly reduced in comparison to application of the previous method.

Abstract: A сontinuous growth of the intensity of metal working processes in mechanical engineering, changes in the structure, functionality and cost of technological equipment, an increasing use of high-strength materials which, as a rule, are characterized by low machinability, determine the necessity of an integrated approach both to the studies of the working capacity of cutting tools and to the control of machining conditions in order to achieve maximum technical and economic efficiency in operating automated manufacturing equipment and numerically controlled machine tools.

Abstract: We are concerned with the problem of interferometric phase estimation using multiple baselines. Simple close-form efficient expressions for computing the Cramer-Rao lower bound (CRLB) for general phase estimation problems is derived. Performance analysis of the interferometric phase estimation is carried out based on Monte Carlo simulations and CRLB calculation. We show that by utilizing the Cramer-Rao lower bound we are able to determine the combination of baselines that will enable us to achieve the most accurate estimating performance.

Abstract: An apparatus capable of comparing displacements with picometer accuracy is currently being designed at NIST. In principle, we wish to compare one displacement in vacuum to a second, equal displacement in gas, in order to determine gas refractive index. If the gas is helium, the refractive index is expected to be amenable to high-accuracy ab initio calculations relating refractive index to gas density or to the ratio of pressure and temperature (P/T); the measured refractive index can then be used to infer (P/T) with an accuracy goal of about 1×10^-6 (relative standard uncertainty). If either the pressure or temperature is known, the refractive index measurement will allow us to determine the second quantity. Our goal is to achieve an uncertainty limited primarily by the uncertainty of the Boltzmann constant (before redefinition of SI units, which will give the Boltzmann constant a defined value). The technique is an optical analog of dielectric constant gas thermometry and can be used in a similar manner. The dimensional metrology is uniquely challenging, requiring picometer-level uncertainty in the comparison of the displacements.

Abstract: High-precision length measurements are strongly demanded for not only industry requirements and science purposes.In 2009, a femtosecond optical frequency comb (FOFC) was adopted in Japan as the national standard tool for measuring length. Recently, numerous studies have focused on FOFC-based high-precision length measurement because this approach offers the possibility of development of a ultimate green length traceability system. A single-wavelength helium–neon (He–Ne) laser was used as a length standard. An FOFC emits discrete pulse-train-shaped light. This markedly different characteristic exists between a He-Ne laser and an FOFC is the reason for the challenge. Previous attempts to challenge this problem have not been satisfactory. This has limited the development and applications of FOFC-based length measurement. In this work, we review our efforts of FOFC-based high-precision length measurement toward developing an ultimate green length traceability system.