Lateral Shearing Interferometry

A Simple Interferometric MTF Instrument

  • James C. Wyant
  • Optics Communications , Vol. 19, page 120, October 1976
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A simple law interferometric technique for measuring the modulation transfer function of an optical system is described.

High efficiency grating lateral shear interferometer

  • D. A. Thomas and J. C. Wyant
  • Optical Engineering , Vol. 15, page 477, September-October 1976
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The use of dichromated gelatin for holographically recording the component single frequency gratings of a high efficiency lateral shear interferometer is described. Interferograms obtained using a grating lateral shear interferometer simultaneously having a diffraction efficiency of 30% in each of two shearing interferograms are presented.

Use of an ac heterodyne lateral shear interferometer with real-time wavefront correction systems

An analysis is performed to determine the accuracy with which an ac heterodyne lateral shear interferometer can measure wavefront aberrations if a white light extended source is used with the interferometer, and shot noise is the predominate noise source. The analysis shows that for uniform circular or square sources larger than a derived minimum size, the wavefront measurement accuracy depends only upon the radiance of the source and not upon the angular subtense of the source. For a 1-msec integration time, a 25-cm2 collecting area, and a source radiance of 10 W/m2-sr the rms wavefront error is approximately 1/30 wave, assuming the signal is shot noise limited. It is shown that for both uniform circular and square sources an optimum shear distance is approximately 1/2 the aperture diameter required to resolve the light source. Comments are made on the optimum shear for nonuniform radiance distributions.

Interferometer for measuring power distribution of ophthalmic lenses

The use of a lateral shear interferometer in measuring the power variation of ophthalmic lenses is described and demonstrated. It is shown that an appropriate lateral shear interferometer directly measures the power variation of an ophthalmic lens. If the ophthalmic lens has a toric surface, the power for each axis can be measured separately. Individual surfaces can be tested, as well as the whole lens or the different segments of a multifocal lens. The sensitivity of the test can be selected by varying the amount of lateral shear. Because of the demonstrated simple relationship between fringe spacing and dioptric power, qualitative examination of the fringes has proved a useful adjunct to conventional quality control methods.

OTF measurements with a white light source: an interferometric technique

The use of lateral shear interferometers for measuring the optical transfer function of an optical system for a white light source is investigated. It is shown that grating lateral shear interferometers fulfill the requirements necessary to perform measurements of both the optical transfer function and the optical coherence function for a white light source. Several possible grating lateral shear interferometers are described.

Evaluation of Large Aberrations Using a Lateral-Shear Interferometer Having Variable Shear

A variable shear lateral shearing interferometer consisting of two holographically produced crossed diffraction gratings is used to test nonrotationally symmetric wavefronts having aberrations greater than 100 wavelengths and slope variations of more than 400 wavelengths/diameter. Comparisons are made with results of Twyman-Green interferometric tests for wavefront aberrations of up to thirty wavelengths. The results indicate that small wavefront aberrations can be measured as accurately with the lateral-shear interferometer as with the Twyman-Green interferometer and that aberrations that cannot be measured at all with a Twyman-Green interferometer can be measured to about 1% accuracy or better.

Double Grating Interferometer with Variable Lateral Shear

  • P. Hariharan, W.H. Steel, and J. C. Wyant
  • Optics Communications, Vol. 11, page 317, July 1974
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A modified Ronchi interferometer using two identical gratings is described. This instrument is very suitable for the measurement of small, zonal aberrations, since the shear can be changed continuously by rotating one grating with respect to the other, while the direction and magnitude of the tilt between the sheared wavefronts can be varied by adjusting the distances of the two gratings from the center of the Gaussian sphere.

Collimated Light Acoustooptic Lateral Shearing Interferometer

  • J. F. Ebersole and J. C. Wyant
  • APPLIED OPTICS, Vol. 13, page 1004, May 1974
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White Light Extended Source Shearing Interferometer

A grating lateral shear interferometer is described that can be used with a white light source. The use of the interferometer with certain types of extended sources is also demonstrated.

Double Frequency Grating Lateral Shear Interferometer

A simple grating lateral shear interferometer is described that can be made to give simultaneously two interferograms having shear in two orthogonal directions. The shear for the two orthogonal directions is produced in one plane by one double frequency crossed diffraction grating that can easily be produced holographically. Translating the grating sideways causes the irradiance of the interferogram to vary sinusoidally with time enabling the interferometer to be used with real-time heterodyne phase detection.

 

 

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