Osa twoframe phaseshifting interferometry for testing. The phase shifting technique can quantitatively determine the phase within each fringe on the interferogram. National institute of standards and technology, manufacturing engineering. In many situations the measurement accuracy is limited by the environment and sometimes the environment is. A combination of digital phase shifting interferometry and twowavelength holographic techniques for testing a phase object is presented. Pointdiffraction interferometry without null optics or phase shifters ryeojin park, 1, 3, dae wook kim, 1 and harrison h. Laser diodes, radius of curvature metrology concepts. Principles and methods, akademie verlag, berlin 1996. In pdi systems, the test and reference beams travel the same or almost the same path. There are numerous methods for measuring and interpreting the results, so that testing the same optic on several different interferometer systems can result in different wavefront numbers.
Spatial temporal phase shifting interferometry suppressing phase errors in. Here, we propose the application of a simple twoframe psi for the testing of a range of optical surfaces, including flats, spheres, and aspheres. Primarily applied to transmitted wavefront testing, we also offer other metrology solutions including interferometric as well as shackhartmann type wavefront systems. Barrett1,2,3 1college of optical sciences, university of arizona, tucson, arizona 85721, usa 2department of medical imaging, university of arizona, tucson, arizona 85721, usa 3center for gammaray imaging, university of arizona. Perhaps this is a way to quickly find out if one possesses a gem of a scope or a dud. Faster and more accurate optical aspheric testing methods are required in many technical fields. Phase shifting interferometry psi is a useful technique in optical metrology for measuring the modulating phase of interferograms 1.
Phase fizeautwymangreen interferometer from trioptics. It is the only commercial interferometer system that can measure multiple surfaces with a. Configuration for singleshot parallel phase shifting fizeau interferometry, be, beam expander. Optical wavefront measurement using a novel phaseshifting. Interferometry homogeneity testing precision optical inc. Page 1 of 3 interferometry testing posted in refractors. By capturing several frames of intensity data as the spacing between the reference and test elements is modulated, phaseshifting interferometers psis calculate the phase at each point on the surface, allowing more accurate data analysis and higher measurement resolution. These increments are fractions of the source wavelength, or tens to hundreds of nanometers. Unlike an amplitudesplitting interferometer, such as a michelson interferometer, which separates out an unaberrated beam and interferes this with the test beam, a commonpath interferometer generates its own reference beam.
With an easytoposition, fibercoupled measurement head and motorized controls, the phasecam 6000 is ideal for measuring large, focal optical systems such as concave telescope mirrors and lens systems, as well as smallaperture, afocal components such as. Phase shifting interferometry optical shop testing. Interferometry in unstable environments phase shifting laser fizeau interferometry provides the highestperformance, lowestuncertainty measurement available for optical testing. Spherical parts requiring radius of curvature are performed using the verifireatz interferometer paired with the zmi distance measuring interferometer. A toolbox for designing and analyzing phaseshifting. Phase shifting interferometry how is phase shifting.
Phase shifting interferometry is a wellestablished technique for areal surface characterisation that relies on digitisation of interference data acquired during a controlled phase shift, most often introduced by controlled mechanical oscillation of an interference objective. Phase shifting interferometry is a wellestablished technique for areal. Zygo mark ii phase shifting interferometer with vision32 software and 100mm aperture esdi intellium z100 with 100mm aperture precision optical utilizes a variety of interferometers and interferometric techniques in order to meet the demands of the optics industry. Phaseshifting interferometry for rf phase measurement. These experiments spurred the development of the superior phase shifting pointdiffraction interferometer pspdi, which has been implemented for the testing of an allreflective lithographicquality euv optical system.
Topics covered include basic interferometers for optical testing, and concepts of phase shifting interferometry including. Phaseshifting interferometry based on principal component. Extreme ultraviolet interferometry thesisdissertation. Phaseshifting interferometry records multiple interferograms with different values of f. Phase shifting interferometry addresses several issues associated with the classical analysis of static interferograms. Psi has existed in its basic form for less than 3 decades, and may be regarded as temporal. May 29, 2019 this short course introduces the field of interferometric optical testing. Chapter 14 phase shifting interferometry engineering360. In temporal phase shifting interferometry, three or more fringe patterns acquired at a known phase offset produce a precise contour map of the surface. This can be achieved, for example, by mounting the reference optic on a linear transducer, such as a piezoelectric crystal.
Phase shifting interferometry is an increasingly powerful and useful tool in optical surface measurements. Introduction phase shifting interferometry is an increasingly powerful and useful tool in optical surface measurements. Deck zygo corporation, laurel brook road, middlefield, ct. Vibration stabilization of a phase shifting interferometer. Additionally the sign of the surface form deviation is automatically determined. In standard psi, a sequence of n interferograms isobtained having known phase shifts between them so the acquisition is synchronous. This search algorithm is used for maximumlikelihood ml estimation of a wavefront that is described by a finite set of zernike fringe polynomials. Livephase acquisition provides realtime phase with optional fringe overlay and zernike aberration feedback to actively monitor toleranced or targeted adjustments while bringing an optical system into specification. Measurements using fourier transform phase shifting interferometry leslie l. The mphase xl is a compact phase shifting twymangreen interferometer available at a variety of operating wavelengths. These include moving a mirror or the figure 4 interference fringes for coherent and incoherent sources as observed at point x. Zygo atz verifire phase shifting interferometer with metropro 9 and mx, dual 150mm and 450mm apertures 1k x 1k zygo atz verifire phase shifting interferometer with metropro 9 and mx, with dmi radius slide and 100mm aperture 1k x 1k. Phase shifting interferometry is a widely used optical metrology technique to demodulate the phase from a set of phase shifted interferograms 1 2 34567.
Combine phase interferometry and amplitude comparison for two antenna solution move realtime processing to fpga enhance tracking algorithm to reduce probability of false ambiguity selection testing test three channel operation with live data verify operation with antennas connected. Phase comparison monopulse also called phase interferometry describes a technique that can be used in radar and direction finding applications to accurately estimate the direction of arrival of a signal from the phase difference of the signal measured on two or more separated antennas. Usually a minimum of three phase shifted interferograms are need. Surface measurement 101 noncontact 3d optical metrology dr. Phase shifting interferometry psi used for testing smooth objects with very high precision vertical resolution 0. Proceedings of spie june 26 2017 direct phase measurement of aspheric surface contours. Computers have made enormous improvements in interferometric. Our pdi design has several important advantages over other pdi configurations.
It allows for high accuracy, computer control and high spatial resolution. Measurements using fourier transform phase shifting. Traditionally, interferograms were measured by locating the center of a fringe and then tracing along the fringe. The concept behind phaseshifting interferometry is to apply a timevarying phase shift between the reference and test wavefronts. Phaseshifting interferometry overcomes these limitations. A good instrument can show a 10x improvement in vibration immunity see fig. Shape software, extensive measurement analyses can be performed. Traditional psi acquires data over a series of camera frames. Fringe tracing technique in the process of optical testing, physical and.
This fullyintegrated turnkey system features a motorized zaxis stage with 1 meter of encoded travel, which simplifies part positioning and. Fivestep phaseshifting algorithms with unknown values of phase shift. First, phaseshifting interferometry does not rely on. Standard phaseshifting interferometry psi generally requires collecting at least three phase shifted interferograms to extract the physical quantity being measured. It is the only commercial interferometer system that can measure multiple surfaces with a single measurement. Classically, one measures the positions of the fringe centers. Is there an amateur in the us who tests a telescope with an interferometer like rohr is doing in germany. Several phaseshifting algorithms with an arbitrary but constant phaseshift between. Ades opticode software did the data acquisition and durango provided the analysis.
Optical system testing and alignment benefits from the unique capabilities of the dynafiz interferometer and its ability to capture and display live data. Interferometry and optical testing phase stepping and phase shifting basic concept phase shifters algorithms phase unwrapping phase shifter calibration errors spatial synchronous and fourier methods solving vibration problems multiple wavelength and vertical scanning coherence probe techniques advantages of. Its wavelengthshifting capability enables measurements that standard phaseshifting interferometers cannot perform. However, if those fringes are unstable due to environmental factors, the uncontrolled motions induce errors in the phase calculation and result in an inaccurate representation of the part under. Popular interferometric measurement techniques include phase shifting interferometry psi, and vertical scanning interferometryvsi, also known as scanning white light interferometry swli or by the iso term coherence scanning interferometry csi, csi exploits coherence to extend the range of capabilities for interference microscopy. An innovative iterative search method called the synthetic phaseshifting sps algorithm is proposed. Second, measurements can be taken at every element in the photodetector array directly yielding optical pathlength differences on a regularly spaced grid. We have demonstrated the proof of principle of the device, testing it on a wavefront emerging from a tilted spherical lens. The sensor is modular and can be configured with various measurement diameters and stands. Phaseshifting microwave interferometry for nondestructive.
Surface measurement 101 noncontact 3d optical metrology. The twowavelength method can produce interferograms with a wide range of sensitivities. Testing at another wavelength almost always results in a lower wavelength rating. The sensor is modular and can be configured with various measurement diameters and stands for specific measurement tasks. There are many ways to introduce a phase modulation or shift. In recent years, interferometer technology has advanced past traditional phase shifting interferometry with robust phase acquisition techniques that are less sensitive to vibration without compromising performance. Introduction fundamental concepts advantages of psi methods of phase shifting detecting the wavefront phase data collection psi algorithms phase shift.
Osa phasetilting interferometry for optical testing. Interferometry and its applications in surface metrology. A point diffraction interferometer pdi is a type of commonpath interferometer. Ams uses the newview interferometer to test samples, most often for roughness, waviness, and other smallscale qualities. With an easytoposition, fibercoupled measurement head and motorized controls, the phasecam 6000 is ideal for measuring large, focal optical systems such as concave telescope mirrors and lens systems, as well as smallaperture, afocal components such as flat. Most optical testing interferometers now use phase shifting techniques not only because of high resolution but also because phase shifting is a high accuracy rapid way of getting the interferogram information into the. Phase shifting interferometry with multiple accumulation justia. In a phaseshifting fizeau interferometer, the reference is moved in precise increments relative to the test surface. The maximum resonant frequency measurable is determined by the camera exposure time for synchronous measurements and camera frame rate for asynchronous excitation.
In addition, the newview is capable of testing overall form on samples which cannot be tested using large aperture. An integrated computercontrol and dataacquisition unit automates the datacollection process, and allows a detailed picture of microstructure dynamics to be built up in. Pointdiffraction interferometry without null optics or phase shifters ryeojin park,1,3, dae wook kim,1 and harrison h. Phase shifting interferometry for rf phase measurement karl 2will 1, tobias 3 meyer, abbas omar chair of microwave and communication engineering, ottovonguericke university of magdeburg, p. Phase shifting interferometry avoids the need to track. Phaseshifting interferometry for determining optical surface quality.
Advanced singleframe phase shifting interferometers can be used for data acquisition to produce high spatial resolution measurements and phase movies of the vibrating surface. Standard phaseshifting interferometry psi generally requires collecting at least three phaseshifted interferograms to extract the physical quantity being measured. The device connects to a laptop or desktop computer via usb 3. Goniometer interferometer optical testing instruments. Phaseshifting interferometry university of arizona. Phase object test using twowavelength digital phase shifting. In this paper, we estimate the coefficient, or parameter, values of the wavefront using a single interferogram obtained from a pointdiffraction. Due to physical properties of microwaves, the method can be used for various applications in nondestructive testing.
Barrett 1, 2, 3 1 college of optical sciences, university of arizona, tucson, arizona 85721, usa. All interferograms are automatically overlayed using computer software. The precision and accuracy of optical phase shifting technique is critical and affects the accuracy of optical measurements undertaken using phase shifting interferometers. In conclusion, we have described a new phase shifting pointdiffraction interferometer design based on a ln crystal pinhole. Phase tilting interferometry for optical testing is proposed to retrieve the phase from interferograms with random phase tilts. Phaseshifting interferometry for determining optical. Noise attached in the interference fringes can have catastrophic effects on. Intomatik software overview open fringes phase shifting iso. Sphericity noncontact testing using phase shifting interferometry ming chang, chingpiao hu and paul p.
Both rigid and slightly pliable materials can be tested. The phasecam 6000 is an extremely compact and lightweight dynamic laser interferometer for measurement of optics and optical systems. Both systems rely on pinhole diffraction to produce spherical reference wavefronts in a commonpath geometry. Direct phase measurement interferometry and optical testing. Phaseshifting interferometry for determining optical surface. In many situations the measurement accuracy is limited by the environment and sometimes the environment is sufficiently bad that the measurement cannot be performed. Phase sensor is the basis for interferometry measurements at trioptics. Fizeau phase shifting with a bicycle pump and needle valve when testing a flat against another flat or a convex surface against a testplate and the airgap is at least1mm or so, then varying the air pressure in the cavity using simple means becomes a practic. The twoframe psi extracts modulated phase from two randomly phase shifted. Phase interferometers are very compact, small and lightweight digital devices that can be used in almost any work environment. The largest limitation of phase shifting interferometry for optical testing is the sensitivity to the environment, both vibration and air turbulence.
The verifire vts interferometer system is a standalone upwardlooking interferometer workstation designed for stable and robust surface form and radius of curvature metrology of spherical optics. Jan 10, 2020 all interferograms are automatically overlayed using computer software. Minifiz systems that include our durango interferometry software were sold by ade phase shift from 2004 until late 2008. Due to the phase shifting algorithm the intomatikn offers higher accuracy and a larger measuring. The largest limitation of phaseshifting interferometry for optical testing is the sensitivity to the environment, both vibration and air turbulence. The radon transform is used to extract the tilted phase plane, and the phase distribution is retrieved by the least squares method. In phase shifting interferometry psi, intentional phase shifts are introduced between the reference and test arms of the interferometer. An innovative iterative search method called the synthetic phase shifting sps algorithm is proposed.
With digital phase shifting technique, only one shot of interferogram is required, so the system structure is simpler with lower sensitivity to the environmental vibration. Mar 01, 2007 phaseshifting interferometry based on such wavelength tuning is described in, for example, u. The proposed method has been applied to simulated and experimental interferograms, obtaining satisfactory results. Many of diffraction internationals customers are using minifiz interferometers. The intensities at these discrete phase values are used with simple algorithms to calculate the surface topography. The verifire mst multiple surface test laser interferometer system provides high precision measurements of surface form and transmitted wavefront of optical components and lens systems. The instrument acquires a frame of data after each incremental move. The concept behind phase shifting interferometry is to apply a timevarying phase shift between the reference and test wavefronts. Two ronchi phase gratings, g 1 and g 2, are located on the paths of the object and the reference waves. Phase shifting interferometry, in optical shop testing, d. L1l2, achromatic lenses with focal lengths f1 300 mm, f2 150 mm. Most optical testing interferometers now use phaseshifting techniques not only because of high resolution but also because phaseshifting is a high accuracy rapid way of getting the interferogram information into the computer.
Due to the phase shifting algorithm the software intomatikn offers higher accuracy and a larger measuring range with respect to surface form deviations in comparison to the intomatiks. Interferometer system dynafiz laser interferometer with. Phaseshifting interferometry for determining optical surface quality determining the surface quality of a critical component, the deviation from the intended shape whether. Phase shifting interferometry is a wellestablished technique for areal surface characterisation that relies on digitisation of interference data acquired during a controlled phase shift, most. Maxqs features portable design, autofocus and resolution of 1. Lin department of mechanical engineering chung yuan christian university chung li, taiwan abstract this paper presents an optical technique for sphericity measurement of a ball by means of phase shift interferometry. The proposed evaluation method is an analogy to phase shifting interferometry in optical testing, but it uses microwaves instead of optical wavelengths. Interferometry has been a timehonored technique for surface topography measurement. Phase shifting interferometry listed as psi phase shifting interferometry how is phase shifting interferometry abbreviated. Interferometric measurements of surface shape are relative measurement techniques in which the shape of a known surface is compared with that of an unknown surface, and the difference is displayed as a series of interference fringes. The accuracy of optical phase shifters is limited by the inherent characteristics of the piezoactuators or pzt such as nonlinearities, hysteresis, creep and thermal drift. These systems offer additional capabilities based on multiple surface testing, such as the simultaneous measurement of physical thickness profile and material homogeneity. The variable optical zoom has three different magnifications for viewing most fiber diameters and a wide range of holders and accessories can be used to easily mount testing samples. Derivation of algorithms for phaseshifting interferometry.
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