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  • 1
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    Fiber optic phase stepping system for interferometry (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A closed loop phase control system using an all-fiber optical configuration has been developed for use in phase-stepping interferometry. This system drives the relative phase of two interfering beams through a sequence of pi/2 rad increments so that the initial relative phase of these beams can be determined. This phase-stepping system uses optical fibers to provide spatially uniform phase steps from a flexible, easily aligned optical configuration. In addition, this system uses phase feedback to eliminate phase modulator errors and to compensate for phase drifts caused by environmental disturbances.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Applied Optics (ISSN 0003-6935); 30; 729-734
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    High data density temperature measurement for quasi steady-state flows (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new optical instrument, the liquid crystal point diffraction interferometer (LCPDI), is used to measure the temperature distribution across a heated chamber filled with silicone oil. Data taken using the LCPDI are compared to equivalent measurements made with a traversing thermocouple and the two data sets show excellent agreement This instrument maintains the compact, robust design of Linnik's point diffraction interferometer and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction.
    Keywords: Fluid Mechanics and Heat Transfer
    Type: NASA-TM-111695 , NAS 1.15:111695 , E-9549
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  • 3
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    Liquid crystal point diffraction interferometer (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new instrument, the liquid crystal point diffraction-interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with very high data density and with automated data reduction. This dissertation describes the theory of both the PDI and liquid crystal phase control. The design considerations for the LCPDI are presented, including manufacturing considerations. The operation and performance of the LCPDI are discussed, including sections regarding alignment, calibration, and amplitude modulation effects. The LCPDI is then demonstrated using two phase objects: defocus difference wavefront, and a temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to theoretical or independently measured results and show excellent agreement. A computer simulation of the LCPDI was performed to verify the source of observed periodic phase measurement error. The error stems from intensity variations caused by dye molecules rotating within the liquid crystal layer. Methods are discussed for reducing this error. Algorithms are presented which reduce this error; they are also useful for any phase-stepping interferometer that has unwanted intensity fluctuations, such as those caused by unregulated lasers.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-106899 , E-9547 , NAS 1.15:106899
    Format: application/pdf
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  • 4
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    Phase-stepping fiber-optic projected fringe system for surface topography measurements (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A projected fringe interferometer for measuring the topography of an object is presented. The interferometer periodically steps the phase angle between a pair of light beams emanating from a common source. The steps are pi/2 radians (90 deg) apart, and at each step a video image of the fringes is recorded and stored. Photodetectors measure either the phase and theta of the beams or 2(theta). Either of the measures can be used to control one of the light beams so that the 90 deg theta is accurately maintained. A camera, a computer, a phase controller, and a phase modulator established closed-loop control of theta. Measuring the phase map of a flat surface establishes a calibration reference.
    Keywords: OPTICS
    Format: application/pdf
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  • 5
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    A preliminary study on ice shape tracing with a laser light sheet (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Preliminary work towards the development of an automated method of measuring the shape of ice forming on an airfoil during wind tunnel tests has been completed. A thin sheet of light illuminated the front surfaces of rime, glaze, and mixed ice shapes and a solid-state camera recorded images of each. A maximum intensity algorithm extracted the profiles of the ice shapes and the results were compared to hand tracings. Very good general agreement was found in each case.
    Keywords: LASERS AND MASERS
    Type: NASA-TM-105964 , E-7375-1 , NAS 1.15:105964
    Format: application/pdf
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  • 6
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    Active phase compensation system for fiber optic holography (1988)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Fiber optic delivery systems promise to extend the application of holography to severe environments by simplifying test configurations and permitting the laser to be remotely placed in a more benign location. However, the introduction of optical fiber leads to phase stability problems. Environmental effects cause the pathlengths of the fibers to change randomly, preventing the formation of stationary interference patterns which are required for holography. An active phase control system has been designed and used with an all-fiber optical system to stabilize the phase difference between light emitted from two fibers, and to step the phase difference by 90 deg without applying any constraints on the placement of the fibers. The accuracy of the phase steps is shown to be better than 0.02 deg., and a stable phase difference can be maintained for 30 min. This system can be applied to both conventional and electro-optic holography, as well as to any system where the maintenance of an accurate phase difference between two coherent beams is required.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-101295 , E-4277 , NAS 1.15:101295
    Format: application/pdf
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  • 7
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    Laser interferometric measurement of ion electrode shape and charge exchange erosion (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A novel projected fringe profilometry system was applied to surface contour measurements of an accelerator electrode from an ion thruster. The system permitted noncontact, nondestructive evaluation of the fine and gross structure of the electrode. A 3D surface map of a dished electrode was generated without altering the electrode surface. The same system was used to examine charge exchange erosion pits near the periphery of the electrode to determine the depth, location, and volume of material lost. This electro-optical measurement system allowed rapid nondestructive digital data acquisition coupled with automated computer data-processing. In addition, variable sensitivity allowed both coarse and fine measurements of objects having various surface finishes.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 91-2121
    Format: text
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  • 8
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    Projected-Fringe Profilometer Maps Erosion Of Electrode (1995)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Report describes use of projected-fringe, phase-stepping optical profilometer to measure three-dimensional shape of surface of molybdenum electrode eroded in ion engine. Instrumentation used in these measurements similar to that described in "Projected-Fringe, Phase-Stepping Profilometer" (LEW-14996).
    Keywords: ELECTRONIC SYSTEMS
    Type: LEW-15947 , NASA Tech Briefs (ISSN 0145-319X); 19; 5; P. 99
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  • 9
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    A phase-stepped point diffraction interferometer using liquid crystals (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new instrument, the liquid crystal point diffraction interferometer (LCPDI), has been developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point diffraction interferometer (PDI) and adds to it phase stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wavefronts with high data density and with automated data reduction. The design of the LCPDI is briefly discussed. An algorithm is presented for eliminating phase measurement error caused by object beam intensity variation from frame-to-frame. The LCPDI is demonstrated by measuring the temperature distribution across a heated chamber filled with silicone oil. The measured results are compared to independently measured results and show excellent agreement with them. It is expected that this instrument will have application in the fluid sciences as a diagnostic tool, particularly in space based applications where autonomy, robustness, and compactness are desirable qualities. It should also be useful for the testing of optical elements, provided a master is available for comparison.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-106922 , E-9634 , NAS 1.15:106922 , International Symposium on Optical Science, Engineering, and Instrumentation; Jul 09, 1995 - Jul 14, 1995; San Diego, CA; United States
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  • 10
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    Defocus Measurement Using a Liquid Crystal Point Diffraction Interferometer (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A liquid crystal PDI is demonstrated by measuring the defocus change between two positions of the interferometer. Errors caused by average intensity variations are discussed.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-106687 , E-9043 , NAS 1.15:106687 , Optical Fabrication and Testing Workshop; Jun 06, 1994 - Jun 09, 1994; Rochester, NY; United States
    Format: application/pdf
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