Showing papers on "Interferometry published in 1984"
TL;DR: The high resolution surface profile of a 3-D diffuse object is obtained by measurement of the phase distribution across the image of a projected sinusoidal grating deformed by the surface, based on phase-shifting interferometric techniques.
Abstract: The high resolution surface profile of a 3-D diffuse object is obtained by measurement of the phase distribution across the image of a projected sinusoidal grating deformed by the surface. A shearing polarization interferometer is used for projection. Deformed grating images are detected by an array camera and processed by a microcomputer. Surface height resolutions of better than 10 μm have been attained, limited essentially by electronic quantization noise. In contrast to direct deformed grating analysis, this method, based on phase-shifting interferometric techniques, is capable of accurate measurement even with coarse projected gratings and low density image sensing arrays. Areas of application include industrial quality control, biostereometrics, robotics, and solid modeling for computer graphics.
990 citations
TL;DR: The second edition of Dainty's widely read book on laser and astronomical speckle as discussed by the authors is a beautiful soft-bound book identical to the first edition (sans typographical errors), except for a rewritten Chapter 7 on "Stellar Speckle Interferometry" and a new Chapter 8 on "Recent Developments" in the overall field of speckles.
Abstract: This is the second edition of a widely read book on laser and astronomical speckle. I have, through the years, extensively used the material in the first edition for teaching purposes and for “meaty” homework problems. The book is very readable, with good introductory material for helping the uninitiated “over the hurdles,” and yet, with a development in each subject to the state of the art in depth (as of 1975). The second edition is a handsome soft-bound book identical to the first edition (sans typographical errors), except for a rewritten Chapter 7 on “Stellar Speckle Interferometry” and a new Chapter 8 on “Recent Developments” in the overall field of speckle. Both are by J. C. Dainty. The other chapters are 1) “Introduction” by J . C. Dainty; 2) “Statistical Properties of Laser Speckle Patterns” by J. W .
439 citations
01 Jan 1984
TL;DR: A technique that combines ideas of phase shifting interferometry (PSI) and two-wavelength interferometer (TWLI) to extend the phase measurement range of conventional single-wa wavelength PSI is described.
Abstract: This paper describes a technique that combines ideas of phase shifting interferometry (PSI) and two-wavelength interferometry (TWLI) to extend the phase measurement range of conventional single-wavelength PSI. To verify theoretical predictions, experiments have been performed using a solid-state linear detector array to measure 1-D surface heights. Problems associated with TWLPSI and the experimental setup are discussed. To test the capability of the TWLPSI, a very fine fringe pattern was used to illuminate a 1024 element detector array. Without temporal averaging, the repeatability of measuring a surface having a sag of ~100 μm is better than 25-A (0.0025%) rms.
376 citations
TL;DR: A generalized algorithm for use with digital heterodyne or fringe- scanning interferometers was developed that removes many of the restrictions that had previously applied to the data collection scheme.
Abstract: A generalized algorithm for use with digital heterodyne or fringe- scanning interferometers was developed that removes many of the restrictions that had previously applied to the data collection scheme. The required phase steps may be chosen with unequal spacing and to extend over a range greater than 2w. The integrating-bucket and phase-step approaches produce identical results.
370 citations
TL;DR: In this article, a technique that combines ideas of phase shifting interferometry (PSI) and two-wavelength interference (TWLI) to extend the phase measurement range of conventional singlewavelength PSI is described.
Abstract: This paper describes a technique that combines ideas of phase shifting interferometry (PSI) and two-wavelength interferometry (TWLI) to extend the phase measurement range of conventional single-wavelength PSI. To verify theoretical predictions, experiments have been performed using a solid-state linear detector array to measure 1-D surface heights. Problems associated with TWLPSI and the experimental setup are discussed. To test the capability of the TWLPSI, a very fine fringe pattern was used to illuminate a 1024 element detector array. Without temporal averaging, the repeatability of measuring a surface having a sag of ~100 μm is better than 25-A (0.0025%) rms.
365 citations
TL;DR: In this paper, the performance of phase-sensing interferometers employing squeezed states and homodyne detection is analyzed and compared to a system employing direct detection, and it is shown that both detection schemes reach the standard quantum limit on position-measurement sensitivity.
Abstract: The performance of phase-sensing interferometers employing squeezed states and homodyne detection is analyzed and compared to the performance of systems employing direct detection Standard differenced direct-detection Michelson and Mach-Zehnder interferometers are shown to be suboptimal in the sense that an observation/measurement-noise coupling occurs, which can degrade performance Homodyne-detection interferometers in which the phase shift in one arm is the conjugate of that in the other arm do not suffer from the preceding drawback Overall, however, the performance of differenced direct-detection and homodyne-detection interferometers is similar in single-frequency operation In particular, both detection schemes reach the standard quantum limit on position-measurement sensitivity in single-frequency interferometric gravity-wave detectors at roughly the same average photon number This limit arises from back action in the form of radiation pressure fluctuations entering through the energy-phase uncertainty principle Multifrequency devices can circumvent this uncertainty principle, as illustrated by the conceptual design given for a two-frequency interferometer which can greatly surpass the standard quantum limit on position sensing This configuration assumes that ideal photodetectors respond to photon flux rather than energy flux
226 citations
TL;DR: In this paper, the authors proposed a method of incorporating an interpolation formula in the self-calibration solution for antenna phases to deal with the anisoplanatic case.
Abstract: 1, Introduction. An assumption implicit in the usual scheme for self-calibration of radio interferometer data is one of i»oplanaii»m: that oyer each element of the array, all wavefronts arriving from different parts of the sky to which the interferometer pairs are sensitive are subject to identical tropospheric/ionospheric path delays. Approximate validity of the isoplanatism assumption is a necessary condition for the success of selfcalibration. This memorandum is an outline of a means by which the self-calibration algorithm might be modified in order to deal with the anisoplanatic case. Anisoplanatism is a severe problem with a low-frequency array, such as the one which has been proposed by R. A. Perley and W. C. Erickson [8] for construction at the VLA site. This is because, of the extreme magnitude of ionospheric effects at long wavelengths, and the large field of view of such an instrument. An initial attempt at a scheme for self-calibration of low-frequency array data is outlined in Perley and Erickson's proposal; and the need for a generalization of the self-calibration algorithm is reiterated in [2] and [4]. In § 2 is described a method of incorporating an interpolation formula in the selfcalibration solution for antenna phases. The idea is to express the phase corruption seen by a given array element, in an arbitrary direction, as a linear combination (i.e., as an interpolation) of the phase corruptions {/r}£Li toward the centers of some small number m of \"isoplanatic patches\". Setting m — 5 to 20, or so—with the patches judiciously centered—might suffice in a typical instance. When the source model used for self-calibration is given by a set of CLEAN point source components, it is easy to modify the solution scheme so as to yield the /{. Choice of an appropriate interpolation formula is discussed in § 3. Having obtained from the ^self-calibration solution algorithm a set of n spacevariant antenna phases, one for each antenna, the next problem is finding a way to make use of this information in mapping. The usual mapping/deconvolution schemes, such as Fourier inversion combined with CLEAN or with the maximum entropy deconvolution algorithm, are not designed to cope with space-variant effects. A means of utilizing the space-variant antenna phases in a modified, mosaicing version of the usual map/CLEAN combination is outlined in § 4. A drawback of the method described in § 2 is the increase (by a factor « m) over the usual number of solution parameters, or degrees of freedom, in the self-calibration solution algorithm. Because of this increase, a better source model, higher signal-tonoise ratio (S/N), or a larger number of antenna elements, (or a combination of all three) becomes desirable. By incorporating assumptions of spatial and temporal correlation of the antenna phases^ one may try to hold this larger number of degrees of freedom in check; this idea is pursued in §5 5-6. Perley and Erickson argue that for the proposed low-frequency array, which is designed to operate at 75 and 150 MHz, simple and accurate source models often will be available (perhaps from 327 MHz observations). And their data suggest that the spatial extent and the velocities of the ionospheric irregularities responsible for the severest phase fluctuations at 75 MHz are such that the techniques of §§ 5-6 would be useful. They report that during this summer they have found the typical case in 327 MHz VLA observations to be one of
223 citations
TL;DR: In this article, an instantaneous phase measuring interferometer (PMI) was proposed to measure displacements at one point to a resolution of 0.003 um, with a measurement time aperture of less than 1 As.
Abstract: Conventional phase measuring interferometry normally requires one-half to sixty seconds acquisition time, limiting measurement to stationary phenomena such as optical element wavefronts. We have developed an instantaneous phase measuring interferometer (PMI) that measures displacements at one point to a resolution of 0.003 um. We describe this instrument and an interferometer measuring phase to X/2000 with a measurement time aperture of less than 1 As. Also described is an attached system for analyzing and displaying wavefronts at up to 10 Hz.
221 citations
TL;DR: In this article, a new type of hydrogen sensor is reported in which an optical fiber is used as the sensing element and the fiber is coated with palladium which expands on exposure to hydrogen.
Abstract: A new type of hydrogen sensor is reported in which an optical fiber is used as the sensing element. The fiber is coated with palladium which expands on exposure to hydrogen. This changes the effective optical path length of the fiber, which is detected by interferometric techniques. Preliminary experiments have demonstrated the effect and suggest a high sensitivity and a wide dynamic range for this kind of sensor. The experimental results are compared to calculated optical path length changes. Application of this kind of sensor to the detection of other chemicals appears feasible.
200 citations
TL;DR: A family of three phase measurement techniques are described that are spatial analogs of the popular temporal phase-shift methods and the need for an active element such as a piezoelectric translator or an electro-optic crystal is eliminated simply by adding tilt to the fringe pattern.
Abstract: A family of three phase measurement techniques are described that are spatial analogs of the popular temporal phase-shift methods. For these spatial techniques, the need for an active element such as a piezoelectric translator or an electro-optic crystal is eliminated simply by adding tilt to the fringe pattern. Measurements are obtained over a uniform grid with an accuracy comparable to temporal phase-shift interferometry. Advantages and disadvantages are discussed.
191 citations
TL;DR: A Fourier transform spectrometer with no mechanical moving parts is described, which may be built in a relatively small size and with moderate cost and may lead to the application to time-resolved spectroscopy.
Abstract: A Fourier transform spectrometer with no mechanical moving parts is described. The interferogram is generated spatially by a triangle common-path interferometer and is detected by a self-scanning photodiode array. The spectrum is reconstructed by fast Fourier transform in a microcomputer system. Since no moving part is used and a common-path interferometer is employed for simple, stable, and easy alignment, this spectrometer may be built in a relatively small size and with moderate cost. The self-scanning photodiode array as a multichannel detector may lead this spectrometer to the application to time-resolved spectroscopy. The optical throughput is much larger than that of a multichannel dispersion-type spectrometer, because in the system neither a slit nor an aperture is necessary. The emission spectra of a low pressure mercury lamp and a LED are shown to demonstrate the system performance.
Patent•
13 Apr 1984TL;DR: In this article, a laser interferometer system and associated method for etching endpoint detection, and for monitoring etching or growth to a selected depth is presented, which is implemented by scanning the laser beam across scribe lines on a wafer which is undergoing fabrication (growth or etching) and monitoring the resulting interference pattern.
Abstract: A laser interferometer system and associated method for etching endpoint detection, and for monitoring etching or growth to a selected depth. The process implemented by the system involves scanning the laser beam across scribe lines on a wafer which is undergoing fabrication (growth or etching) and monitoring the resulting interference pattern. Alternatively, the process implemented by this system involves moving the laser beam across the scribe line to detect the position of the scribe line; locking the laser beam on the scribe line; and monitoring the resulting interference pattern.
TL;DR: A new real-time interferometer based on diffraction phenomena is discussed, which consists of a point-diffraction interferometers fabricated on a transmission grating and achieved by simultaneously introducing a phase shift on the three separate channels of diffracted interferograms.
Abstract: A new real-time interferometer based on diffraction phenomena is discussed. It consists of a point-diffraction interferometer fabricated on a transmission grating. The real-time data-analysis capability is achieved by simultaneously introducing a phase shift (piston) on the three separate channels of diffracted interferograms. Mathematical analysis and preliminary observational results are included.
TL;DR: In this paper, an asymmetric interferometric channel waveguide modulator in Ti:LiNbO 3 at 0.83-μm wavelength was used for X-, Y-and Z -cut substrates.
Abstract: Measurements are described on asymmetric interferometric channel waveguide modulators in Ti:LiNbO 3 at 0.83-μm wavelength. Modulation voltages and device transmissions are compared for X-, Y- and Z -cut substrates. An interferometer intrinsic phase bias of \sim\pi/2 allows linear modulation and we have observed linearity over 67 dB for a 3-kHz bandwidth. This dynamic range is limited by optical damage effects, of which the photovoltaic effect is the most critical.
TL;DR: The moire fringes are generated by superimposing the Fourier image of the first grating on the second one in the interferometer to examine the deflection of light by the phase objects.
Abstract: In this paper, we describe deflection mapping of phase objects using a Talbot interferometer. To examine the deflection of light by the phase objects, the moire fringes are generated by superimposing the Fourier image of the first grating on the second one in the interferometer. The phase object is placed in front of the first grating. The light passing through the objects and impinging on the first grating produces the shifted Fourier image, and the resultant moire fringes give the deflection mapping, which depends on the distribution of the refractive index of the phase object. The experiments show deflection mapping of a piece of plastic plate and a candle flame. This technique is used for measuring the focal length of a lens.
TL;DR: In this article, the optical output of an interferometer is projected onto three (or more) polarisation states, detected and combined, and the maximum variation in signal and in signal/noise ratio is 6 dB.
Abstract: A technique is described in which polarisation fading of the output of an interferometer is eliminated. The optical output of the interferometer is projected onto three (or more) polarisation states, detected and combined. The maximum variation in signal and in signal/noise ratio is 6 dB.
12 Nov 1984
TL;DR: In this paper, the mirror position of the transmitting interferometer is reconstructed in the receiving interferometers by periodically scanning through three 'white-liciiit' fringes (laser reference, 6 mm range, 0.1 μpm resolution).
Abstract: Multimode fibers connect two Michelson interferometers, source,and detector. The mirror position of the transmitting interferometer is reconstructed in the receiving interferometer by periodically scanning through three 'white-liciiit' fringes (laser reference, 6 mm range, 0.1 μpm resolution).
TL;DR: In this article, the authors demonstrated that neutron absorption in one of the two beam paths of a neutron interferometer gives different interference patterns with static and with time-dependent absorption even when the time-averaged absorption is the same.
Patent•
16 Mar 1984
TL;DR: In this paper, a ranging beam is coupled to a ranging interferometer, which directs a portion of the ranging beam at the target, and the number of fringes resulting from the wave interference produced in the ranging interference produced by the reference interferer is calculated, together with the known length of the reference path, to determine the distance of the target from the ranging interrer.
Abstract: An apparatus and a method for measuring the distance to an arbitrary target includes a radiation source producing a beam of coherent radiation the frequency of which is continuously varied. The beam is divided into a ranging beam and a reference beam. The ranging beam is coupled to a ranging interferometer, which directs a portion of the ranging beam at the target. The ranging interferometer produces a first signal indicative of the phase difference between a portion of the ranging beam directed at and scattered by the target and another portion of the ranging beam which has traveled over a path of fixed length. The reference beam is coupled to a reference interferometer. A portion of the reference beam is directed by the reference interferometer along a reference path of a predetermined length, and the phase difference between the portion of the reference beam directed along the reference path and another portion of the reference beam which has travelled over a path of a fixed length is measured. The number of fringes resulting from the wave interference produced in the ranging interferometer and the number of fringes in the wave interference pattern produced by the reference interferometer are counted and used, together with the known length of the reference path, to determine the distance of the target from the ranging interferometer.
TL;DR: A new technique for computer-based Talbot interferometry has been presented and fast and automatic aberration measurement has been achieved with improved accuracy and sensitivity.
Abstract: A new technique for computer-based Talbot interferometry is presented. Fast and automatic aberration measurement has been achieved with improved accuracy and sensitivity. Experimental results are given that agree with the results of calculation by ray tracing.
TL;DR: A new method of instrument calibration and data analysis is presented for single-etalon interferometric measurements of winds, temperatures, and emission line intensities for the multichannel Fabry-Perot interferometer on the Dynamics Explorer spacecraft.
Abstract: A new method of instrument calibration and data analysis is presented for single-etalon interferometric measurements of winds, temperatures, and emission line intensities. The technique has been developed for the multichannel Fabry-Perot interferometer on the Dynamics Explorer spacecraft. A numerical representation of the instrumental transfer function is used based on a truncated Fourier series with empirically determined coefficients. The numerical form is compared with the conventional analytic form. The Fourier coefficients describing the instrument function are generated at the wavelength of a stable He–Ne laser and are translated to other wavelengths using an interpolation technique for both phase and power. A quasi-linear least-squares fitting process involving matrices provides for a rapid and accurate data reduction.
Patent•
17 Jul 1984TL;DR: In this article, an approach for the measurement of the absolute distance between a piano test and a piano reference surface which are in close proximity to each other is presented, using a polarization phase modulated Fizeau interferometer.
Abstract: Apparatus is disclosed for the measurement of the absolute distance between a piano test and a piano reference surface which are in close proximity to each other. The preferred way of accomplishing this is with a polarization phase modulated Fizeau interferometer in which the reference surface is a front surface polarizer. The modulated interference pattern is photosensed with an array camera, and the signals processed to provide the absolute distance between the piano test surface and the piano reference surface. A method is also disclosed, using the instant invention, for determining the flying height of a magnetic head assembly used in computer mass storage systems.
IBM1
TL;DR: This paper presents a new interferometric profile measurement technique based on using a rigid differential interferometer probing the test object which is moved by a stage that makes the profile measurement largely insensitive to flatness errors of the mechanical stage and enables extremely precise measurements.
Abstract: In scanning systems for surface profile measurement, e.g., stylus systems, the profile of a surface is generally determined by measuring the distance of the surface relative to a reference plane. This can be either a plane defined by a moving stage under a rigid stylus or a plane defined by a moving stylus if a fixed stage is used. In both cases, the measurement precision is limited by the straightness of a linear motion. This paper presents a new interferometric profile measurement technique based on using a rigid differential interferometer probing the test object which is moved by a stage. Information on the surface profile is obtained by scanning the surface with two laser spots simultaneously and measuring the optical path difference between the reflected light beams. This makes the profile measurement largely insensitive to flatness errors of the mechanical stage and enables extremely precise measurements. Data processing is done digitally using a storage scope and a microprocessor. The suitability of this method for measuring the profiles of magnetic sliders and SIMS sputter craters has been investigated. The experimental work includes long- and short-term repeatability tests and an extensive investigation of the temperature dependent behavior of the measuring instrument.
TL;DR: In this paper, the phase shift introduced by rotational motion of a two-crystal neutron interferometer has been measured and found to agree with prediction within 0.4%.
Abstract: The phase shift introduced by rotational motion of a two-crystal neutron interferometer has been measured and found to agree with prediction within 0.4%. This agreement is obtained without making the in-crystal phase corrections employed in a recent study of a linearly accelerated three-crystal interferometer.
TL;DR: In this paper, interference fringes with a tilted wavefront are spatially scanned perpendicularly to the spatial carrier by a TV camera and the interference distribution along a raster scan is sinusoidally interpolated in each carrier interval and optical phases are calculated over the whole area under test.
TL;DR: In this paper, a singlemode fiber-optic interferometer for measuring subangstrom vibrations has been designed and constructed based on the Fizeau configuration and employs peak detection schemes in the signal processing.
Abstract: A single‐mode fiber‐optic interferometer for measuring subangstrom vibrations has been designed and constructed. The interferometer is based on the Fizeau configuration and employs peak detection schemes in the signal processing. The instrument has been used to measure the displacement of a cricket’s tympanic membrane.
TL;DR: In this paper, a high-resolution microwave spectrometer was developed by converting the Owens Valley solar interferometer to frequency-agile operation using 27 m antennas equipped with phase-locked receivers which can change their observing frequency in 25 or 50 ms.
Abstract: A high-resolution microwave spectrometer has been developed by converting the Owens Valley solar interferometer to frequency-agile operation. The system uses 27 m antennas equipped with phase-locked receivers which can change their observing frequency in 25 or 50 ms. Microwave spectra between 1 and 18 GHz are obtained in a few seconds by successive observations at up to 86 discrete frequencies. At each frequency the data are equivalent to the total power from each antenna and the interferometric amplitude and phase. All data are fully calibrated with respect to cosmic sources.
TL;DR: Very long baseline interferometry (VLBI) experiments at a frequency of 89 GHz (3.4mm wavelength) using hydrogen maser frequency standards show that under good atmospheric conditions coherence can be maintained for times up to 700 s, corresponding to an Allan standard deviation of approximately 10−14 as discussed by the authors.
Abstract: Very long baseline interferometry (VLBI) experiments at a frequency of 89 GHz (3.4-mm wavelength) using hydrogen maser frequency standards show that under good atmospheric conditions coherence can be maintained for times up to 700 s, corresponding to an Allan standard deviation of approximately 10−14. The stability appears to be largely limited by the phase noise resulting from fluctuations in delay through the troposphere. Methods of estimating the interferometer fringe amplitudes and closure phases in the presence of large phase fluctuations are examined. The spectrum and the Allan standard deviation of the observed phase fluctuations are derived.
TL;DR: Simple expressions for the halfwidth and finesse of a Fabry-Perot interferometer fringe broadened by defects have good accuracy for most practical forms of defect and are applicable to mirror surface defects, parallelism errors, angular dispersion of illumination, finite spectral linewidth, and fluctuations in interferometers spacing.
Abstract: Simple expressions are given for the halfwidth and finesse of a Fabry-Perot interferometer fringe broadened by defects. The expressions are unrestricted as to defect magnitude and have good accuracy for most practical forms of defect. The results are applicable to mirror surface defects, parallelism errors, angular dispersion of illumination, finite spectral linewidth, and fluctuations in interferometer spacing as well as most combinations of two or more types of broadening defect. An experimental investigation of broadening due to parallelism errors confirms the theory.
TL;DR: A Fizeau wavelength meter optimized for use with pulsed laser sources has been developed and characterize which demonstrates a cw resolution better than 2 parts in 107 and a pulsedresolution better than 1 part in 106.
Abstract: A Fizeau wavelength meter optimized for use with pulsed laser sources has been developed and characterized which demonstrates a CW resolution better than 2 parts in 10 to the 7th and a pulsed resolution better than 1 part in 10 to the 6th. The static optical design is based on a Fizeau wedge interferometer, which together with spatial filtering and collimating optics is used to produce a pattern of parallel fringes which is imaged on a linear photodiode array and analyzed by a minicomputer. A series of CW and pulsed measurements of various narrowband laser sources are described, and particular difficulties involved in pulsed laser measurements with the wavemeter are examined.