Simultaneous measurement of refractive index and wedge angle of optical windows using Fizeau interferometry and a cyclic path optical configuration
TL;DR: A new technique for the simultaneous measurement of refractive index and wedge angle of optical windows using Fizeau interferometry and a cyclic path optical configuration (CPOC).
Abstract: We present a new technique for the simultaneous measurement of refractive index and wedge angle of optical windows using Fizeau interferometry and a cyclic path optical configuration (CPOC). Two laterally separated beams are obtained from an expanded collimated beam using an aperture containing two rectangular openings. The test wedge plate is placed in one of the two separated beams. Using CPOC, these two beams are made to overlap and interfere, producing interference fringes in the overlapping region. The beams reflected from the front and back surfaces of the test wedge plate interfere and produce Fizeau fringes. The refractive index is related to the spacing of the above two beam fringes. The wedge angle is determined from the evaluated values of the refractive index and Fizeau fringe spacing. The results obtained for a BK-7 optical window are presented.
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TL;DR: In this paper, a quasi-monochromatic light source was used for the measurement of residual wedge angle (RWA) of transparent nearly parallel plate (PP) using phase shifting interferometry (PSI).
14 citations
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 "Simultaneous measurement of refract..."
...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 article, the authors proposed a composite wedge interference structure by combining wedges with different geometry and showed that the composite structure provides selection of a single resonance in transmission within the impact area of a large diameter monochromatic beam and enables wavelength tuning when a small diameter multi-wavelength beam is used.
Abstract: In the present paper, we propose a compact composite wedge interference structure by combining wedges with different geometry. We use interferential wedges with optical thickness from several micrometers to several hundred micrometers and apex angles of the order of tens microradians. The aim of the conducted study is to prove that such a structure exhibits improved optical properties in comparison to a conventional wedge. We have carried out simulations and experiments with a structure built from two wedges. We have shown that, instead of multiple transmission peaks observed for a single interferential wedge, the composite structure provides selection of a single resonance in transmission within the impact area of a large diameter monochromatic beam and enables wavelength tuning when a small diameter multi-wavelength beam is used. The first property ensures analysis of light beams characterized with a wide spectrum. The second feature allows for increase of the wavelegth tuning range at keeping spectrally narrow transmission peak if the structure is formed by a thin and a thick interferential wedges. Two such structures have been realized using a technique which we have developed. The experiments made with this structures show that the produced transmission peak is narrowed spatially and spectrally at the expense of lower transmission which achieves 50–60% of transmission ensured by the used interferential wedges.
10 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
11 Nov 2014
TL;DR: In this article, the application of the polarizing triangular cyclic interferometer to distinguish different types of polarizing components is investigated, and distinct output signals from polarizer and wave plates under examination can clearly be observed.
Abstract: The application of the polarizing triangular cyclic interferometer to distinguish different types of polarizing components is investigated. The distinct output signals from polarizer and wave plates under examination can clearly be observed.
2 citations
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TL;DR: In this paper, a wavelength-tuned Fizeau interferometer is applied to the problem of flatness testing of transparent plates and the resulting front surface profile exhibits less than 2 nm of residual error attributable to spurious reflections from within the plate.
Abstract: A wavelength-tuned Fizeau interferometer is applied to the problem of flatness testing of transparent plates. When the plate is positioned at a specific distance from the reference surface and an integer-math 13-frame phase-shifting algorithm is applied, the system directly filters out unwanted interference arising from backsurface reflections. The resulting front-surface profile exhibits less than 2 nm of residual error attributable to spurious reflections from within the plate.
179 citations
TL;DR: Two 19-sample algorithms that suppress multiple-interference noise up to the second order of the reflectance of the test plate are presented and Experimental results show that the variation in surface shape and optical thickness of a glass parallel plate of 250-mm diameter was measured with a resolution of 1-2 nm rms.
Abstract: Wavelength-scanning interferometry permits the simultaneous measurement of variations in surface shape and optical thickness of a nearly parallel plate. Interference signals from both surfaces of the test plate can be separated in frequency space; however, these frequencies are shifted from the expected frequency by the refractive-index dispersion of the test plate and any nonlinearity that is due to wavelength scanning. Conventional Fourier analysis is sensitive to this detuning of the signal frequency and suffers from multiple-beam interference noise. We propose new wavelength-scanning algorithms that permit a large tolerance for dispersion of the test plate and nonlinearity of scanning. Two 19-sample algorithms that suppress multiple-interference noise up to the second order of the reflectance of the test plate are presented. Experimental results show that the variation in surface shape and optical thickness of a glass parallel plate of 250-mm diameter was measured with a resolution of 1–2 nm rms.
104 citations
TL;DR: In this article, an on-axis, vibration insensitive, polarization Fizeau interferometer is realized through the use of a novel pixelated mask spatial carrier phase shifting technique in conjunction with a low coherence source and a polarization delay-line.
Abstract: An on-axis, vibration insensitive, polarization Fizeau interferometer is
realized through the use of a novel pixelated mask spatial carrier phase
shifting technique in conjunction with a low coherence source and a
polarization delay-line. In this arrangement, coherence is used to
effectively separate out the orthogonally polarized test and reference beam
components for interference. With both the test and the reference beams
on-axis, the common path cancellation advantages of the Fizeau
interferometer are maintained. The interferometer has the unique ability
to isolate and measure any surface that is substantially normal to the
optical axis of the cavity. Additionally, stray light interference is substantially reduced due to the source's short coherence. An expression
for the fringe visibility on-axis is derived and compared with that of a
standard Fizeau. Using a 15 mW source, the maximum camera shutter
speed, used when measuring a 4% reflector, was 150 usec, resulting in
very robust vibration insensitivity. We experimentally demonstrate the
measurement of both sides of a thin glass plate without the need to modify
the plate between measurements. Experimental results show the
performance of this new interferometer to be within the specifications of
commercial phase shifting interferometers.
82 citations
TL;DR: A new 19-sample wavelength-scanning algorithm is demonstrated that permits large tolerance in the air-gap distance, thus making it somewhat independent of the thickness of the test plate, and the minimum residual reflection noise with this algorithm for testing a glass plate is approximately lambda/600.
Abstract: Testing for flatness of an optical parallel plate in a Fizeau interferometer suffers from problems caused by multiple-beam interference noise. Each internal-reflection component can be separated from the signal by its modulation frequency in a wavelength-scanned interferometer; however, the frequency depends on the thickness and the refractive-index dispersion of the test plate and on the nonlinearity of the scanning source. With a new 19-sample wavelength-scanning algorithm we demonstrate the elimination of the reflection noise, the effect of the dispersion up to the second order of the reflectance of the test plate, and as the nonlinearity of the source. The algorithm permits large tolerance in the air-gap distance, thus making it somewhat independent of the thickness of the test plate. The minimum residual reflection noise with this algorithm for testing a glass plate is ∼λ/600. Experimental results show that the front surface of the test plate was measured within 1 nm rms of its true shape over a 230-mm-diameter aperture.
42 citations
TL;DR: In this article, a phase shifting Fizeau interferometry was used to measure the refractive index and wedge angle of transparent plates used as optical components in different experiments, and a near IR external cavity diode laser having spectral resolution up to 10−7 was employed to measure a test plate by introducing amplitude modulation technique.
Abstract: It is shown that Fizeau interferometry provides an accurate optical method to measure the refractive index and wedge angle of transparent plates used as optical components in different experiments. A near IR external cavity diode laser having spectral resolution up to 10−7 has been employed to measure the refractive index of the test plates by introducing amplitude modulation technique in the detection system of our phase shifting Fizeau interferometry. Detection of spatial fringes has been performed to find out the wedge angles of the plates by using a He–Ne laser along with the CCD-image sensor.
26 citations