Variable Wavelength Interferometry Research Articles

Alternative approach to variable wavelength interferometry

The paper presents an alternative technique of calculation the retardance of quartz waveplates. The technique utilizes continuously tuned wavelength, which identifies the zero-order fringe and simultaneously facilitates high repeatability of the optical path difference across the entire visible spectrum. Unlike in classical method, precise monitoring of the current increase or decrease of the interference order is not required. The discussion includes comparison of the standard deviation between the classical and novel approaches. Full Text: PDF ReferencesM. Pluta, Advanced Light Microscopy (Vol. 3, PWN, Elsevier, Warszawa-Amsterdam-London-New York-Tokyo, 1993). DirectLinkM. Pluta, "Object-adapted variable-wavelength interferometry. I. Theoretical basis", Journal of Opt. Soc. Am., A4(11), 2107 (1987). CrossRef M. Pluta, "Variable wavelength microinterferometry of textile fibres", J. Microscopy, 149(2), 97 (1988). CrossRef M. Pluta, "On double‐refracting microinterferometers which suffer from a variable interfringe spacing across the image plane", Journal of Microscopy, 145(2), 191 (1987). CrossRef M. Pluta, "Variable wavelength interferometry of birefringent retarders", Opt. Laser Technology, 19(3), 131 (1987). CrossRef D. Litwin, A. M. Sadik, "Computer-aided variable wavelength Fourier transform polarizing microscopy of birefringent fibers", Optica Applicata 28(2), 139 (1998). DirectLink A. Sadik, W. A. Ramadan, D. Litwin, "Variable incidence angle method combined with Pluta polarizing interference microscope for refractive index and thickness measurement of single-medium fibres", Measurement Science and Technology, IOP Publishing 14(10), 1753 (2003). CrossRef J. Galas, S. Sitarek; D. Litwin; M. Daszkiewicz, "Fringe image analysis for variable wavelength interferometry", Proc. SPIE 10445, 1044504 (2017). CrossRef D. Litwin, J. Galas, N. Błocki, "Automated variable wavelength interferometry in reflected light mode", Proc.SPIE 6188, 61880F (2006). CrossRef J. Galas, D. Litwin, M. Daszkiewicz, "New approach for identifying the zero-order fringe in variable wavelength interferometry", Proc. SPIE 10142, 101421R (2016). CrossRef D. Litwin, J. Galas, M. Daszkiewicz, T. Kryszczyński, A. Czyżewski, K. Radziak, "Dedicated optical systems of the Institute of Applied Optics", Phot. Lett. Pol., vol. 11, no. 2, pp. 29-31, (2019). CrossRef D. Litwin, K. Radziak, J. Galas "A fast variable wavelength interferometer", Proc. SPIE 11581, 115810O, (2020). CrossRef

Dedicated optical systems of the Institute of Applied Optics

The paper presents a collection of selected optical systems recently developed in the Institute of Applied Optics-INOS. The collection includes the family of techniques where the continuously modified wavelength facilitates high accuracy measurements of optical and geometrical features of the object in question i.e. the variable wavelength interferometry and confocal chromatic sensors. In addition, the paper refers to the construction of a new type of a spectrometer with rotating plasma and an illumination system supporting the road safety. Full Text: PDF ReferencesM. Pluta, Advanced Light Microscopy (Vol. 3, PWN, Elsevier, Warszawa-Amsterdam-London-New York-Tokyo, 1993). DirectLink M. Pluta, "Object-adapted variable-wavelength interferometry. I. Theoretical basis", Journal of Opt. Soc. Am., A4(11), 2107 (1987). CrossRef M. Pluta, "Variable wavelength microinterferometry of textile fibres", J. Microscopy, 149(2), 97 (1988). CrossRef M. Pluta, "On double‐refracting microinterferometers which suffer from a variable interfringe spacing across the image plane", Journal of Microscopy, 145(2), 191 (1987). CrossRef K. A. El-Farahaty, A. M. Sadik, A. M. Hezma, "Study of Optical and Structure Properties of Polyester (PET) and Copolyester (PETG) Fibers by Interferometry", International Journal of Polymeric Materials 56(7),715 (2007). CrossRef J. Galas, D. Litwin, M. Daszkiewicz, "New approach for identifying the zero-order fringe in variable wavelength interferometry", Proc. SPIE 10142, 101421R (2016). CrossRef A. Sadik, W. A. Ramadan, D. Litwin, "Variable incidence angle method combined with Pluta polarizing interference microscope for refractive index and thickness measurement of single-medium fibres", Measurement Science and Technology, IOP Publishing 14(10), 1753 (2003). CrossRef J. Galas, S. Sitarek; D. Litwin; M. Daszkiewicz, "Fringe image analysis for variable wavelength interferometry", Proc. SPIE 10445, 1044504 (2017). CrossRef D. Litwin, A. M. Sadik, "Computer-aided variable wavelength Fourier transform polarizing microscopy of birefringent fibers.", Optica Applicata 28(2), 139 (1998). DirectLink D. Litwin, J. Galas, N. Błocki, "Automated variable wavelength interferometry in reflected light mode", Proc.SPIE 6188, 61880F (2006). CrossRef M. Pluta, "Variable wavelength interferometry of birefringent retarders", Opt. Laser Technology, 19(3), 131 (1987). CrossRef K. Fladischer et al. "An ellipsoidal mirror for focusing neutral atomic and molecular beams", New journal of Physics, 12(3) 033018 (2010). CrossRef K. Fladischer et al. "An optical profilometer for characterizing complex surfaces under high vacuum conditions", Precision engineering Elsevier 32(3), 182 (2008). CrossRef A.E. Weeks et al. "Accurate surface profilometry of ultrathin wafers", Semiconductor Science and Technology", IOP Publishing, 22(9), 997 (2007). CrossRef D. Litwin et al. "Overview of the measuring systems where a continuously altered light source plays a key role: Part I", Proc. SPIE 10808, 10 8080B (2018). CrossRef D. Litwin et al. "Noise reduction in an optical emission spectrometer with rotating diffraction grating", Proc. SPIE 10142 101421Q (2016). CrossRef D. Litwin et al. "Photonics approach to traffic signs", Proc SPIE 10142 1014214, (2016). CrossRef

Investigating the optical properties and molecular structure of PEEK fiber

The automatic variable wavelength interferometry, VAWI, technique is used to determine the optical properties of Poly(ether ether ketone), PEEK, highly oriented fiber. The main part of this technique is the Pluta polarizing interference microscope attached with the automatic moving interference filter via stepper motor. The VAWI technique depends on measuring the optical path length differences at certain positions in microinterferogram. These positions are the coincidence and anti-coincidence of the fiber fringe with the free medium fringes. The measured refractive indices and birefringence values are utilized to calculate some optical constants of PEEK fiber using Cauchy and Sellmeier's equations. Also using some structure relationship, some molecular structure and orientation parameters of PEEK fiber as a function of the wavelength of the incident light are calculated. The method allows us to determine any molecular structure parameters of PEEK fiber at any wavelength in the visible spectrum. Microinterfrograms are given for illustration.

A proposed method to reconstruct the three-dimensional dispersion profile of polymeric fibres based on variable wavelength interferometry.

In this paper, we suggest a modification to the conventional variable wavelength interferometry. This modification allowed us to calculate the dispersion curve of each point inside polymeric fibres instead of calculating the mean dispersion of these fibres. This modified mathematical treatment was used to calculate the three-dimensional dispersion profile of isotactic polypropylene fibres suffering from necking deformation. The different steps of calculating the three-dimensional dispersion profile of the fibre were demonstrated. The application of this modified method revealed the variation of the fibre material dispersion before, inside and after the necking region. In addition, the birefringence profile of the necked isotactic polypropylene was determined using the proposed mathematical treatment. This allowed us to diagnose the interaction of the incident waves with necked polypropylene fibres, which gives extensive information on the orientation of the molecular chains during the formation of the necking phenomenon.

Beyond the variable wavelength interferometry—Monitoring the interaction between the ultrashort high power laser pulses and light propagating medium

This paper presents the Variable Wavelength Interferometry (VAWI) technique, its applications and expected research potential of this system equipped with a femtosecond laser. The system is configured for observation and measurement of local optical parameters modified by a high power laser pulse. The VAWI measurement technique has a unique feature that can visualize and enables investigation of the immediate matter response to a single high power laser pulse just in the pulse area, which can locally modify dielectric and optical parameters of matter along the propagation path. It affects the dielectric tensor, refractive indices and it may induce birefringence. The high power laser pulse is responsible for the nonlinear effects in the optical materials like crystals, photonic crystals, optical fibers etc. The VAWI provides the ability to measure very accurately the above optical parameters along the laser pulse propagation path and neighboring regions in the VIS-NIR spectral ranges.

Interferometric determination of the birefringence of thermo‐tropic polyester fibers and its copolymers of structure (PCPT‐co‐CPO)

AbstractThe aim of this study is to determine the optical anisotropy of three different samples of thermo‐tropic polyester fibers of structure Poly(chloro‐1,4‐phenylene terephthalate‐co‐4,4′‐oxybisbenzoate) and its copolymers (PCPT‐co‐CPO). The molar fraction of disruptor units ([CPO]) ranging from 0.40 to 0.60. The variable wavelength interferometry, VAWI technique, was used to determine the birefringence and spectral dispersion properties of such of these fibers. The Cauchy's dispersion formula and its related constants were determined using the spectral dispersion curves of the birefringence. A mathematical formula was derived for direct measurement of the birefringence profile of highly birefringent polymer fibers using VAWI technique. The effect of varying copolymer molar fractions of the three samples of thermo‐tropic polyester fibers was investigated throughout the spectral dispersion curves, the Cauchy's formula constants and the birefringence profiles. Microinterferograms are given for illustration. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Investigation of Weakly Oriented Polymeric Objects by Extended Fringe Field Interference Method

An extended interferometric method is suggested to increase the measuring accuracy of the spectral dispersion curves of weakly oriented polymeric objects. This extended method is based on the variable-wavelength interferometry fringe field interference (VAWIFFI). Using this method, the calculation of the initial interference order is more accurate, and it can be determined over a small range of the visible spectrum. The advantage of the extended VAWIFFI method is that it is not necessary to take a certain reference like the zero order fringe and/or the initial coincident configuration. In comparison to the single- and multi-fringe VAWIOFT and Pluta methods, the measurement accuracy of the extended VAWIFFI method is discussed.

Characterization of Highly Oriented Polymeric Fibers Using Modified Optical Fourier Transform Technique

This article demonstrates a modified variable wavelength interferometry optical Fourier transform technique applied to highly oriented polymeric fibers. It enables a simultaneous determination of the directional refractive indices and birefringence of fiber, which is a significant progress in comparison to the early discovery of the exit pupil pattern. This technique is based on the analysis of the diffraction pattern in the back focal plane of the polarizing microscope objective. A comparison between this modified technique and another conventional one (variable wavelength interferometry fringe field technique) has been performed.

Multi-Wavelength Interferometry for Length Measurements Using Diode Lasers

This paper describes the principle of precise length measurements using multi-wavelength interferometry. Three different examples are given in order to demonstrate PTB’s ability in this field: 1) Measurements of absolute distances up to 10 m performed by combination of the variable wavelength interferometry with fixed wavelength interferometry using two wavelengths simultaneously, 2) a three-wavelength diode laser interferometer for precision measurements of surface profiles (< 100 µm) and 3) PTB’s Precision Interferometer for length measurements of prismatic bodies, e.g. gauge blocks, using three wavelengths. The setup and principle of measurements and some results are presented and discussed in each case.

Measurement of the spectral dispersion curves of low birefringence polymer fibres

A method is suggested to overcome the difficulties of measuring the spectral dispersion of low birefringence fibres, that produce small optical path difference, δ<3 λ, where δ is the optical path difference and λ is the wavelength of light used. This method depends on variable wavelength interferometry (VAWI). The suggested method is used to measure the spectral dispersion of birefringence of polypropylene fibre with a draw ratio 4 (low birefringence fibre). This method is also used to measure the spectral dispersion of birefringence of a polyester staple from ICI (high birefringence fibre). Also, the conventional VAWI method is used to measure the spectral dispersion of this fibre to confirm the results obtained by the suggested method. Microinterferograms are given for illustration.

Determination of the Spectral Dispersion Curves of Highly Oriented Fibers Using Multiple-Beam Microinterferometry

ABSTRACT A method is suggested with its mathematical analysis to determine the spectral dispersion curves of highly oriented fibers using multiple-beam Fizeau fringes in transmission. This method depends on the use of the well-known Caushy's dispersion formula for determining the initial interference order of the deviated fringes inside the fibers. The suggested method overcomes the difficulties of measuring large optical path length differences that are produced by highly oriented fibers. The spectral dispersion curves obtained using this method are in good agreement with those obtained using conventional variable wavelength interferometry (VAWI) technique. Microinterferograms are given for illustration.

Optical microscopy study on poly(p‐phenylene terephthalamide) fibers

AbstractTwo highly oriented poly(p‐phenylene terephthalamide) (PPT) fibers of different grades, commercially known as Kevlar and Twaron, were examined at high magnification under a transmission optical polarizing microscope in the extinction position between crossed polars. An image with regions of regular fine bands is produced for both classes of fibers, which is interpreted to be due to the passage of depolarized scattered light from a material with regularly spaced discontinuities. These bands reflect the periodic pleat structure of the fibers. The fibers were chemically etched, coated with gold, and investigated under a Nomarski differential interference contrast microscope in the extinction position between crossed polars. The observation for Kevlar fibers shows a clear periodicity of transverse bands perpendicular to the fiber axis, but this is much less evident for Twaron fibers. The etchant gives smooth, nearly flat sections through the Kevlar fibers, whereas it is not very effective for the Twaron fibers. The variable wavelength interferometry (VAWI) technique, which is valuable for studying highly oriented polymeric fibers, is used to measure the mean refractive indices and birefringence of a fiber as a function of light wavelength. The results show that these fibers absorb the surrounding liquid, which may change their optical properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 360–369, 2003

Determination of optical properties, dispersion, and structural parameters of poly(ethylene terephthalate) fibers using automatic variable wavelength interferometry technique

Automatic variable wavelength interferometry (VAWI) is used in combination with a Pluta double refracting polarizing interference microscope for measuring the spectral dispersion parameters of the refractive indices of poly(ethylene terephthalate) (PET) highly oriented yarn fibers (1000 denier/250 filaments). The resulting data are utilized to calculate the spectral dispersion and structural parameters such as Cauchy's constants, the dispersion energy, the oscillation energy, the density, the mean polarizability of the monomer unit, the number of monomer units per unit volume, the dielectric constant, the electric susceptibility, the optical orientation function, and the electric polarizability constant. Microinterferograms are given for illustration. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1737–1742, 2003

Measuring large step heights by variable synthetic wavelength interferometry

Many mechanical and optical components contain step features whose surfaceheight changes far exceed the optical wavelength. Therefore, this work presents aninterferometer based on variable synthetic wavelength interferometry (VSWI) anddifferential heterodyne configuration to measure large step heights directly andunambiguously. This largely common-path configuration can substantially reducethe influence of environmental disturbances, which are the main sources of error inthe VSWI. Only one external cavity diode laser (ECDL) is employed to synthesizea series of synthetic wavelengths in descending order. The wavelengthsare combinations of the varied wavelengths and the initial wavelengthof the ECDL. In contrast to wavelength scanning interferometry, thismethod does not require the laser wavelength to be continuously tuned.The step height is sequentially measured at these synthetic wavelengthsand a lock-in amplifier resolves the corresponding synthetic fractionalfringes. The step height is determined following a succession of opticalpath difference calculations, in terms of the synthetic wavelengths andmeasured synthetic fractional fringes. Three known step heights, verifiedby a gauge block interferometer, were used to confirm the performanceof the proposed system. The results reveal that the uncertainty in themeasurement is approximately 80 nm when the measured height is up to 25 mm.

Spectral dispersion curves of polymeric birefringent textile fibers

Optical Fourier transform (OFT) polarizing microscopy combined with variable-wavelength interferometry (VAWI) was used for the determination of the spectral dispersion curves of birefringent textile fibers. We observed that the maximally bright circular fringe from the OFT technique corresponded to the anticoincidence case of the fiber fringe with the empty fringe from the VAWI technique and that the maximally dark fringe from the OFT technique corresponded to the coincidence case. With this combination of the two techniques, we identified the positions of the anticoincidence and coincidence when the VAWI technique was applied to overcome the difficulties of manually determining these positions. The intensity of the OFT patterns at the center was grabbed with a charge couple device camera and analyzed with a photodiode electrical circuit. The new observation was used for the determination of the spectral dispersion curves of the birefringence of polyethylene and aramide fibers. Microinterferograms are provided as illustrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2481–2488, 2002

Spectral dispersion curves of polymeric birefringent textile fibers

AbstractOptical Fourier transform (OFT) polarizing microscopy combined with variable‐wavelength interferometry (VAWI) was used for the determination of the spectral dispersion curves of birefringent textile fibers. We observed that the maximally bright circular fringe from the OFT technique corresponded to the anticoincidence case of the fiber fringe with the empty fringe from the VAWI technique and that the maximally dark fringe from the OFT technique corresponded to the coincidence case. With this combination of the two techniques, we identified the positions of the anticoincidence and coincidence when the VAWI technique was applied to overcome the difficulties of manually determining these positions. The intensity of the OFT patterns at the center was grabbed with a charge couple device camera and analyzed with a photodiode electrical circuit. The new observation was used for the determination of the spectral dispersion curves of the birefringence of polyethylene and aramide fibers. Microinterferograms are provided as illustrations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2481–2488, 2002

An extrapolation method based on the variable-wavelength interferometry optical Fourier transform technique for fibre birefringence measurement

The optical Fourier transform patterns of the fibres observed in the exit pupil of the polarizing microscope objective are analysed. A new extrapolation method based on the variable-wavelength interferometry optical Fourier transform technique is used to increase the accuracy of measurement of the spectral dispersion of the fibre birefringence over the whole visible spectrum. This method is used to overcome the problem of the noisy image at the interference pattern centre.

Spectral dispersion of refractive index of drawn nylon 66 fibres

The variable-wavelength interferometry technique is used for measuring the spectral dispersion of refractive indices of seven samples of nylon 66 fibres with different draw ratios (DRs). The resulting data are utilized to calculate the spectral dispersion of birefringence. Relationships between the optical parameters and the DRs are given for these fibres. In addition, refractive indices of these fibres are measured at a wavelength of 546 nm using the normal method. The results obtained for refractive indices and birefringence at this wavelength are compared with the corresponding values obtained from the spectral dispersion of refractive indices and birefringence and they are found to be in good agreement. Microinterferograms and curves are given for illustration.

Quasi-object-adapted variable-wavelength double-refracting microscope interferometry

A specific interterometric method has been developed. The method uses monochromatic light of continuously variable wavelength through the visible spectrum, and thus is referred to as variable-wavelength interferometry (VAWl). In some special circumstances, the VAWI method takes a specific form, referred to as object-adapted (or adaptive) variable-wavelength interferometry (AVAWI), which enables the optical path difference or phase retardation and derived quantities to be measured very precisely by relatively simple means. In practice, however, the most frequent interlerometric situations at the microscopic level can be qualified as the quasi-object-adapted ones. Therefore, a modified approach to quasi-object-adapted variable-wavelength interferometry (QAVAWI), its features, and performance is presented. In general, the VAWI method is much more accurate than conventional visual two-beam interferometry techniques. In particular, the AVAWI version enables the measuring accuracy of the optical path difference to be improved by two orders of magnitude, while the QAVAWI procedure offers better accuracy by at least one order of magnitude.

Adaptive variable wavelength interferometry of birefringent retarders

A variable wavelength interferometric (VAWI) method was previously proposed for testing birefringent retarders using a double-refracting interferometer. If the spectral dispersion of double refraction of the interferometer is identical with, or similar to, that of the birefringence of the retarder under study, then the VAWI method takes a specific form, referred to as object-adapted (or adaptive) variable wavelength interferometry (AVAWI), which enables the phase retardation (δ) and/or the thickness ( t) of the birefringent retarders to be measured very precisely by using relatively simple means. This new approach is quite simple in its mode of operation and gives results (δ and/or t) with the relative error as low as 0.01%.