Long-trace profiler with cyclic optical configuration
TL;DR: The results of the development of a much simpler optical configuration for the long-trace profiler (LTP) are presented, which employs a cyclic optical configuration to achieve zero optical path difference for the closely spaced, laterally separated laser beams.
Abstract: The results of the development of a much simpler optical configuration for the long-trace profiler (LTP) are presented. The current technique employs a cyclic optical configuration to achieve zero optical path difference for the closely spaced, laterally separated laser beams. The accuracy of measurement is found to remain as good as that in the case of the widely used LTP, although the geometrical alignment problem is simplified significantly.
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TL;DR: The polarization phase shifting technique is used to generate four phase-shifted interferograms, which are utilized to evaluate the phase profile of the phase sample.
Abstract: A polarization phase shifting interferometer using a cyclic path configuration for measurement of phase nonuniformities in transparent samples is presented. A cube beam splitter masked by two linear polarizers is used to split the source wavefront into two counter propagating linearly polarized beams that pass through the sample. At the output of the interferometer, the two orthogonally polarized beams are rendered circularly polarized in the opposite sense through the use of a quarter wave plate. Finally, phase shifting is achieved by rotating a linear polarizer before the recording plane. In a rectangular path interferometer, although the two counter propagating wavefronts are laterally folded with respect to each other in the interferometer arms, the beams finally emerge mutually unfolded at the output of the interferometer. This phenomenon is utilized to create a reference if the sample is introduced in one lateral half of the beam in any one of the interferometer arms. The polarization phase shifting technique is used to generate four phase-shifted interferograms, which are utilized to evaluate the phase profile of the phase sample. Experimental results presented validate the proposed technique.
12 citations
Cites methods from "Long-trace profiler with cyclic opt..."
...Cyclic optical configurations have been widely applied in optical testing of convergent wavefronts [9], in long trace profilometry [10], and for measurement of the refractive index and wedge angle of optical windows [11]....
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TL;DR: In this paper, a double shearing interferometric method was proposed for profiling large-scale quasi-planar surfaces, such as semiconductor wafers, optical flats and x-ray mirrors.
Abstract: A novel interferometric method, called double shearing interferometry, is presented for profiling large-scale quasi-planar surfaces, such as semiconductor wafers, optical flats and x-ray mirrors. The surface profile is measured even if there is an inclination in the scanning stage. By adopting the common-path optical configuration and heterodyne detection, the proposed method achieves excellent resolution at the subnanometre scale and allows a robust measurement in the presence of unwanted disturbances in the measurement environment. A height resolution of 0.1 nm was achieved experimentally. The standard deviation of the analytical surface profiles was found to be 1.3 nm, even when using a conventional screw-lead scanning stage. The measured results show that the surface profile and stage inclination are determined separately. We confirmed that the resultant profile was quite consistent with that measured with a Fizeau interferometer.
9 citations
TL;DR: In this article, phase shifts between the laterally sheared emergent beam components of a cyclic path optical configuration are introduced by applying a small change in the angle of incidence of the incident beam due to the small angular rotation of the setup.
Abstract: We present a new (to our knowledge) technique for introducing phase shifts between the laterally sheared emergent beam components of a cyclic path optical configuration (CPOC). The phase shifts are introduced by applying a small change in the angle of incidence of the incident beam due to the small angular rotation of the CPOC setup. Phase-shifting interferometry has been applied along with this phase-shifting technique for a CPOC with lateral shear to find the surface slope/profile of curved optical surfaces. Results for a spherical optical surface have been discussed. An optical setup for measurement of the surface profile of toroidal beam line mirrors of synchrotron radiation sources is proposed.
7 citations
TL;DR: A new (to the authors' knowledge) technique for the generation of white light Young's type fringes using a cyclic path optical configuration is presented and the effect of the size of an incoherent broadband light source on the fringe visibility is discussed.
Abstract: A new (to our knowledge) technique for the generation of white light Young's type fringes using a cyclic path optical configuration is presented. The effect of the size of an incoherent broadband light source on the fringe visibility is discussed. Applications and advantages of the technique are described.
7 citations
TL;DR: In this article, a new technique of wedge angle measurement of a transparent nearly parallel plate (PP) is presented, where the single pass angular deviation suffered by a pair of mutually parallel, laterally separated pencil beams is enhanced by using a multipass cavity formed with two right-angle prisms.
Abstract: A new technique of wedge angle measurement of a transparent nearly parallel plate (PP) is presented. In this technique, the single-pass angular deviation suffered by a pair of mutually parallel, laterally separated pencil beams is enhanced by using a multipass cavity formed with two right-angle prisms. The resultant angular deflection is converted to linear deviation by means of a Fourier transform lens (FTL), which focuses the pencil beams on to its focal plane. A two-dimensional CCD detector array placed at the focal plane of the FTL measures the linear shift of the intensity centroid (IC) of the resulting Young's fringes formed due to the superposition of the laterally separated pencil beams. The wedge angle is determined from the measured value of the linear shift of the IC due to the PP.
2 citations
References
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20 Apr 1987
TL;DR: In this paper, a long trace surface profiler for the non-contact measurement of surface profile, slope error and curvature on cylindrical synchrotron radiation (SR) mirror is pre-sented.
Abstract: The design of a long-trace surface profiler for the non-contact measurement of surface profile, slope error and curvature on cylindrical synchrotron radiation (SR) mirror is pre-sented here. The optical system is based upon the concept of a pencil-beam interferometer with an inherent large depth-of-field. The key feature of the optical system is the zero-path-difference beam splitter, which separates the laser beam into two colinear, variable-separation probe beams. A linear array detector is used to record the interference fringe in the image, and analysis of the fringe location as a function of scan position allows one to reconstruct the surface profile. The optical head is mounted on an air bearing slide with the capability to measure 38" long aspheric optics, typical of those encountered in SR applications. A novel feature of the optical system is the use of a transverse "outrigger" beam which provides information on the relative alignment of the scan axis to the cylinder optic symmetry axis.
151 citations
TL;DR: In this paper, the authors investigated a number of error sources in a commercial figure measurement instrument, the Long Trace-Profiler II, and demonstrated that, with some simple modifications, they can significantly reduce the effect of errors and improve the accuracy and reliability of the measurement.
Abstract: Metrology requirements for optical components for third‐generation synchrotron sources are taxing the state of the art in manufacturing technology. We have investigated a number of error sources in a commercial figure measurement instrument, the Long‐Trace‐Profiler II, and have demonstrated that, with some simple modifications, we can significantly reduce the effect of error sources and improve the accuracy and reliability of the measurement. By keeping the optical head stationary and moving a penta prism along the translation stage, as in the original pencil‐beam interferometer design of von Bieren, the stability of the optical system is greatly improved, and the remaining error signals can be corrected by a simple reference beam subtraction. We illustrate the performance of the modified system by investigating the distortion produced by gravity on a typical synchrotron mirror and demonstrate the repeatability of the instrument despite relaxed tolerances on the translation stage.
112 citations
29 Jan 1989
TL;DR: A long-trace optical profiling instrument is now in operation at Brookhaven National Laboratory measuring surface figure and macro-roughness on large optical components, principally long cylindrical mirrors for use in synchrotron radiation beam lines as discussed by the authors.
Abstract: A new long-trace optical profiling instrument is now in operation at Brookhaven National Laboratory measuring surface figure and macro-roughness on large optical components, principally long cylindrical mirrors for use in synchrotron radiation beam lines. The non-contact measurement technique is based upon a pencil-beam interferometer system. The optical head is mounted on a linear air bearing slide and has a free travel range of nearly one meter. We are able to sample surface spatial periods between 1 mm (the laser beam diameter) and 1 m. The input slope data is converted to surface height by a Fourier filtering technique which distributes the random noise error contributions evenly over the entire trace length. A number of optical components have been measured with the instrument. Results are presented for fused silica cylinders 900 mm and 600 mm in length and for a fused silica toroid and several electroless nickel-plated paraboloids. 9 refs., 8 figs.
85 citations
TL;DR: Modifications of the long trace profiler at the Advanced Photon Source at Argonne National Laboratory have significantly improved its accuracy and repeatability for measuring the figure of large flat and long-radius mirrors.
Abstract: Modifications of the long trace profiler at the Advanced Photon
Source at Argonne National Laboratory have significantly improved its
accuracy and repeatability for measuring the figure of large flat and
long-radius mirrors. Use of a Dove prism in the reference beam path
corrects phasing problems between mechanical errors and thermally
induced system errors. A single reference correction now completely
removes both of these error signals from the measured surface
profile. The addition of a precision air conditioner keeps the
temperature in the metrology enclosure constant to within ±0.1 °C
over a 24-h period and has significantly improved the stability and the
repeatability of the measurements. Long-radius surface curvatures
can now be measured absolutely with a high degree of
confidence. These improved capabilities are illustrated with a
series of measurements of a 500-mm-long mirror with a 5-km radius of
curvature. The standard deviation in the average of ten slope
profile scans is 0.3 µrad, and the corresponding standard
deviation in the height error is 4.6 nm.
73 citations