Dual Interferometer System for Measuring Index of Refraction

Goodwin, Eric P.

doi:10.1364/oft.2006.oftuc2

Cited by 4 publications

(3 citation statements)

References 29 publications

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“…57 Another system measured the index of refraction of the hydrogel materials. 58 The most recent system was designed to measure the surface profile of both sides of the contact lens. 59 The combination of measurements from these three systems allows for a complete characterization of the optical properties of the contact lens.…”

Section: Research Background and Historymentioning

confidence: 99%

Dual interferometer for dynamic measurement of corneal topography

Micali

Greivenkamp

2016

J. Biomed. Opt

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Abstract. The cornea is the anterior most surface of the eye and plays a critical role in vision. A thin fluid layer, the tear film, coats the outer surface of the cornea and serves to protect, nourish, and lubricate the cornea. At the same time, the tear film is responsible for creating a smooth continuous surface, where the majority of refraction takes place in the eye. A significant component of vision quality is determined by the shape of the cornea and stability of the tear film. A dual interferometer system for measuring the dynamic corneal topography is designed, built, verified, and qualified by testing on human subjects. The system consists of two coaligned simultaneous phase-shifting polarization-splitting Twyman-Green interferometers. The primary interferometer measures the surface of the tear film while the secondary interferometer tracks the absolute position of the cornea, which provides enough information to reconstruct the absolute shape of the cornea. The results are high-resolution and high-accuracy surface topography measurements of the in vivo tear film and cornea that are captured at standard camera frame rates.

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Section: Research Background and Historymentioning

confidence: 99%

Dual interferometer for dynamic measurement of corneal topography

Micali

Greivenkamp

2016

J. Biomed. Opt

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“…The index match between the solution and the contact lens material results in a reduced Fresnel reflectance. Based on measurements of the lens material 10,11 and saline, 9 the power reflectivity of either contact lens surface is only 0.06% at the wavelength of the source. Each air-lens interface in the transmission sphere has nearly four times the reflectivity, even with 0.25% antireflection coatings.…”

Section: Interferometer Designmentioning

confidence: 99%

“…The index of refraction of the contact lens material was determined by a dual interferometer system. 10,11 It uses a low-coherence TwymanGreen interferometer along with a Mach-Zehnder interferometer in transmission to measure the phase and group indices of refraction to an accuracy of 0.0001. The thickness is also required for a full description of a contact lens and has been characterized in several ways, 12,13 but it will also be determined by the interferometer described in this paper.…”

Section: Introductionmentioning

confidence: 99%

Low-coherence interferometer for contact lens surface metrology

Heideman

Greivenkamp

2016

Opt. Eng

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Abstract. Contact lens performance depends on a number of lens properties. Many metrology systems have been developed to measure different aspects of a contact lens, but none test the surface figure in reflection to subwavelength accuracy. Interferometric surface metrology of immersed contact lenses is complicated by the close proximity of the surfaces, low surface reflectivity, and instability of the lens. An interferometer to address these issues was developed and is described here. The accuracy of the system is verified by comparison of glass reference sample measurements against a calibrated commercial interferometer. The described interferometer can accurately reconstruct large surface departures from spherical with reverse raytracing. The system is shown to have residual errors better than 0.05% of the measured surface departure for high slope regions. Measurements made near null are accurate to λ∕20. Spherical, toric, and bifocal soft contact lenses have been measured by this system and show characteristics of contact lenses not seen in transmission testing. The measurements were used to simulate a transmission map that matches an actual transmission test of the contact lens to λ∕18.

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Robust, motion-free optical characterization of samples using actively-tunable Twyman–Green interferometry

Imeri

Reza

2023

Sci Rep

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Optical interferometry-based techniques are ubiquitous in various measurement, imaging, calibration, metrological, and astronomical applications. Repeatability, simplicity, and reliability of measurements have ensured that interferometry in its various forms remains popular—and in fact continues to grow—in almost every branch of measurement science. In this paper, we propose a novel actively-controlled optical interferometer in the Twyman–Green configuration. The active beam control within the interferometer is a result of using an actively-controlled tunable focus lens in the sample arm of the interferometer. This innovation allows us to characterize transparent samples cut in the cubical geometry without the need for bulk mechanical motion within the interferometer. Unlike thickness/refractive index measurements with conventional Twyman–Green interferometers, the actively-tunable interferometer enables bulk-motion free thickness or refractive index sample measurements. With experimental demonstrations, we show excellent results for various samples that we characterized. The elimination of bulk motion from the measurement process promises to enable miniaturization of actively-tunable Twyman–Green interferometers for various applications.

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Dual Interferometer System for Measuring Index of Refraction

Cited by 4 publications

References 29 publications

Dual interferometer for dynamic measurement of corneal topography

Dual interferometer for dynamic measurement of corneal topography

Low-coherence interferometer for contact lens surface metrology

Robust, motion-free optical characterization of samples using actively-tunable Twyman–Green interferometry

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