Because, as discussed in the article on twobeam interferometry, the limit of measurement of level differences utilizing that technique is about 25 nanometers, the limit of measurement in multiple beam interferometry is therefore on the order of 0. Phase shifting interferometry psi is one of the best methods for both single and multiple wavelength interferometers for performing optical measurements with improved precision 42. Measure the wavelength of the hg green line by setting up the circular. A realtime wavelength scanning distance interferometry is proposed. It is therefore of a great interest for shape measurement. Wyant this paper describes a technique that combines ideas of phase shifting interferometry psi and two wave length interferometry twli to extend the phase measurement range of conventional singlewavelength psi. Laser interferometry tools for precision measurement excel precision. Us5907404a multiple wavelength image plane interferometry. All such techniques determine the length of a path by measuring the transit time an electromaq netic signal between the two endpoints. Absolute distance measurements were performed up to 200 mm with a resolution of better than. Distance measurements to noncooperative targets, using a custom designed lockin ccd and appropriate signal processing, was also demonstrated. We present a novel system that can measure absolute distances of up to 300 mm with an uncertainty of the order of one micrometer, within a timeframe of 40 seconds. Twowavelength phase shifting interferometry yeouyen cheng and james c.
Wyant this paper describes a technique that combines ideas of phase shifting interferometry psi and two wave length interferometry twli to extend the phase measurement range of conventional single wavelength psi. Step height measurement using two wavelength phaseshifting interferometry katherine creath two wavelength phaseshifting interferometry is applied to an interference phasemeasuring microscope enabling the measurement of step features. Distance measuring laser interferometer system components. Extended range twowavelength interferometry university of. Introduction he basic principle of length measurement by interferometry is the comparison of a mechanical length or a distance in space against a known wavelength of light.
The principle of this method has been described in this paper. For more information on this source, please visit zygo. Absolute distance measurements using fiberoptic multiple. Interferometry is a family of techniques in which waves, usually electromagnetic waves, are superimposed, causing the phenomenon of interference, which is used to extract information.
The displacement of the grating is determined by the grating interferometry theorem with the measured phase variation. A larger nar can be achieved by using multiple fixed andor tunable wavelengths. A multiwavelength interferometer utilizing the frequency comb. Methods for absolute distance measurements using multi wavelength interferometry or wavelength scanning interferometry have been. However, to realize large measurement range, a number of synthetic wavelengths. The principle of length measurement by interferometry is straightforward it is the comparison of a mechanical length or a distance in space against a known wavelength of light. However, the nonambiguity range nar is limited by half wavelength. Mar 12, 2018 multiple wavelength interferometry can be used to realize absolute distance measurement avoiding fringe counting 3. Accuracy is mainly dependent on the capability to measure the synthetic wavelength, using a fabryperot interferometer fp to count.
Osa displacement measurement using a wavelengthphase. Two wavelength phase shifting interferometry yeouyen cheng and james c. Measurement principle the admi is based on a two wavelength interferometer. The measurement goal of absolute distance interferometry is the extension of the range of nonambiguity from the optical wavelength scale of a few hundred nanometres to macroscopically accessible dimensions. Experiment 8 michelson interferometer 1 introduction. Page 4 of 9 experiments i to calibrate the micrometer screw of the interferometer place a na light source at l and a crosswire between l and g. In mwli, this is achieved by the joint analysis of a simultaneous interferometric measurement with multiple wavelengths i i 2, 3. The accuracy depends on the properties of the source.
However, the nonambiguity range nar is limited by halfwavelength. The principle of synthetic wave creation is used in a novel way in that the system employs an initial low. Radio frequency controlled synthetic wavelength sweep for absolute distance measurement by optical interferometry. Multiwavelength interferometry for length measurements using. Pdf multiwavelength interferometric distance sensors. Distance measuring interferometry the art of fringe counting.
The proposed system uses a michelson interferometer, a tunable laser, a wavelength meter and a computer for analysis. Multiple wavelength interferometry is, like classical interferometry, a coherent method, but it offers great flexibility in sensitivity by an appropriate choice of the different wavelengths and it can be operated on rough surfaces. Sorry, we are unable to provide the full text but you may find it at the following locations. Moderesolved frequency comb interferometry for high.
Precision length measurements by multiwavelength interferometry. Experiment 8 michelson interferometer 1 introduction the michelson interferometer uses light interference to measure distances in units of the wavelength of light from a particular source. Mar 20, 2018 lewis, a j 1993 absolute length measurement using multiple wavelength phasestepping interferometry. Absolute distance interferometry with a variable synthetic wavelength. The surface is effectively tested at a synthesized equivalent. Coherent absolute distance interferometry is one of the most interesting techniques for length metrology. The use of multiple wavelengths for interferometry leads to an unambiguity range of several millimeters with an accuracy of 2 106 of the object distance, but min. Frequency scanning interferometry a versatile high. It was developed by albert michelson and used, in 1893, to measure the standard meter in units of the wavelength of the red line in the cadmium spectrum. Experimental results reveal that the proposed method can detect a displacement up to a large distance of 1 mm and displacement variation down to the nanometer range. Motionx distance measuring laser interferometer configurations motionx, inc. The accuracy of this method depends essentially on the signal processing and on the properties of the source.
Highaccuracy distance measurements with multiplewavelength. This interferometer is called the npl national primary length bar interferometer, or primary length bar interferometer plbi for short. As a result of the development of laser light sources in the 1960s of the last century, absolute distance interferometry saw considerable development in the 1970s 9. Shape measurement by multiplewavelength interferometry. Retroreflector or plane mirror in 18 different configurations. Scanning interferometry a dissertation submitted to the. Step height measurement using two wavelength phaseshifting interferometry katherine creath two wavelength phaseshifting interferometry is applied to an interference phase measuring microscope enabling the measurement of step features. Absolute distance is measured with the accuracy of a conventional dmi by determining the interferometric order of the measurement wavelength with a variable synthetic wavelength. Therefore synthetical wavelengths are produced, using several semiconductor lasers. Absolute length measurement using multiplewavelength. Since the absolute distance interferometry with a variable synthetic wavelength uses a frequency stabilised laser 1 and a second frequency swept laser 2, it seems straightforward to expand this setup for a measurement with a fixed synthetic wavelength. Highaccuracy absolute distance measurement by twowavelength. Moreover, this technique is also applicable to rough surfaces. Absolute distance measurements using fiberoptic multiple wavelength interferometer.
Optical interferometers are the instruments that rely on interference of two or more superimposed re. Absolute distance metrology for long distances with dual frequency sweeping interferometry alexandre cabral 1. The displacement is not only measured with the frequency comb, but also with a conventional counting laser. Multiple wavelength interferometry enables an increase in the range of nonambiguity and a reduction in the sensitivity of classical interferometry. Whitelight interferometry is most convenient for short distances. Assemble and align michelson and fabryperot interferometers, calibrate them using a laser of known wavelength, and then use them characterize the bright yellow emission line in sodium. Multiple wavelength interferometry is, like classical interferometry, a coherent method, but it offers great flexibility in sensitivity by an appropriate choice of the different wavelengths and it. Distance measuring, singleaxis laser interferometers have four major elements 1. With the advent of the femtosecond frequency comb 3 a new tool for distance measurement has become available. Multiple wavelength electromagnetic distance measurement. The system uses multiple wavelength interferometry to provide range information for an object. The instrument was designed and built at the national physical laboratory npl, teddington.
Absolute distance measurements using fiberoptic multiplewavelengthinterferometer. A larger nar can be achieved by using multiple fixed andor tunable wavelengths at the cost of increased number of. A 900 fold can be added to the optical path in the interferometer module. Laser interferometry tools for precision measurement. Interferometry is an important investigative technique in the fields of astronomy, fiber optics, engineering metrology, optical metrology, oceanography. Massively parallel interferometry for the distance measurement we have constructed a michelsoninterferometer with a measurement arm that can be changed over a distance of 50 m by moving a carriage along a straight linear guidance. Sitraceable highaccuracy edm based on multiwavelength. Measuring with light long applied to optical shop testing, interferometry is now used to measure many different types of parts in a variety of applications, such as optical system performance, surface roughness, surface form, and displacement of moving surfaces. Sinusoidal phase modulating absolute distance measurement. They demonstrate the high precision achievable by this technique on multiple scales, from absolute geodetic distances up to 10 m, over prismatic bodies, e.
The existence of multiple wavelength lasers with increasing levels of stability has enhanced absolute distance. Interferometers are widely used for distance measurements, and for the majority of applications conventional so called fringe counting interferometers are completely appropriate but many applications for distance metrology require absolute distance informations. Absolute positioning by multiwavelength interferometry referenced. Multiple wavelength interferometry can be used to realize absolute distance measurement avoiding fringe counting 3. A huge advantage of frequency comb interferometry compared to conventional interferometry with a single wavelength is that the range of nonambiguity is determined by the pulsetopulse distance.
In frequency sweeping interferometry fsi, measurements are made without ambiguity, by using a synthetic wavelengths resulting from a frequency sweep. Multiple wavelength interferometry offers great f lexibility in working distance and sensitivity by permitting an appropriate choice of the different wavelengths used, and it can be operated on. Multiplewavelength and whitelight interferometry springerlink. Long range, high accuracy absolute distance measurement. Wyant this paper describes a method to enhance the capability of two wavelength phaseshifting interferometry. Step height measurement using twowavelength phaseshifting. In a single wavelength interferometric measurement the phase of the interference pattern, repeats itself at distance intervals equal to the wavelength. Multiplewavelength interferometry for absolute distance measurement. This approach of combreferenced wavelength generation offers excellent frequency stability and uncertainty, allowing for implementation of advanced techniques such as absolute distance measurement by multi wavelength interferometry,14,15,16,17,18 and realtime compensation of the refractive index of air by twocolour interferometry 19,20. Thesis, department of physics, applied optics group, university of london. Absolute distance measurement based on multiple selfmixing.
Multiplewavelength interferometry for absolute distance. Synthetic wavelength interferometry of an optical frequency. Additional improvements in precision may be provided by using a wavelength calibration device such as an etalon, a wavemeter, or a reference cell having relatively narrow transmission peaks, to improve the accuracy in determining the laser wavelengths. Frequency scanning interferometry a versatile, high precision, multiple distance measurement technique p a coe, a mitra, s m gibson, d f howell and r b nickerson physics dept, university of oxford, dw building, keble rd, oxford, ox1 3rh, uk abstract frequency scanning interferometry fsi has been developed for high precision. This symposium, considering the possibilities that have been demonstrated for the furtherance of measurement techniques using lasers, notably by interferometry, pulsed or modulated beams, recognizing the application to the precise measurement of short distances and variations of distance, measurement of medium distances, as well as measurement.
Multiwavelength interferometry for length measurements. Hi can measure absolute distance with precision in the order of nanometers. Highprecision absolute distance and vibration measurement. Multiplewavelength interferometry is, like classical interferometry, a coherent method, but it offers great flexibility in sensitivity by an appropriate choice of the different wavelengths and it. Metrological properties of the device such as resolution, measuring range, repeatability and accuracy are characterized. Multiple wavelength phaseshifting interferometry yeouyen cheng and james c. Highly accurate distance measurement with a frequency comb laser. Pdf highaccuracy distance measurement with multiple. In order to generate an interference pattern with high precision distinct fringes, it is very important to have a single highly stable wavelength source, which is achieved using the xl80 laser there are different interferometer set ups based on michelsons principle, however, the linear set up is the simplest type to explain.
Long range, high accuracy absolute distance measurement by. The frequency comb can be considered as a multiwavelength source. The measurements may include those of certain characteristics of the waves themselves and the materials that the waves interact with. Multiple wavelength interferometry enables to increase the range of unambiguity and to reduce the sensitivity of the measurement. Whether your application is on a production line, a laboratory, or in the field, excel precision can help with your precision measurement requirements.
Excel precision provides applications engineering support to. Distance measurement by multiplewavelength interferometry. Wavelength scanning distance interferometry using inflection. Optoelectronic distance displacement measurements and applications, year. Lewis, a j 1993 absolute length measurement using multiple wavelength phasestepping interferometry. Introduction electromagnetic distance measuring techniques are an essential part of horizontal control networks. The fabryperot interferometer consists of two parallel surfaces with highly re.
In general, multiple lasers are necessary for the multi wavelength technique whose beams. Multiple wavelength electromagnetic distance measurement j. Several drawbacks make the fsi not suitable for the calibration of ldms. Multiple wavelength interferometry is a wellknown technique which enables to increase the range of nonambiguity for interferometry and to reduce the sensitivity of the measurement. Multiplewavelength phaseshifting interferometry yeouyen cheng and james c. Lewis, a j 1993 absolute length measurement using multiplewavelength phasestepping interferometry. The basics interferometry is a measurement method using the phenomenon of interference of waves usually light, radio or sound waves. A sinusoidal phase modulating absolute distance measurement adm interferometer combining frequencysweeping interferometry fsi and multi wavelength interferometry mwi is proposed in this paper. Singleaxis laser interferometers distance measuring, singleaxis laser interferometers have four major elements 1.
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