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  • 1
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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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    NASA TECHNICAL REPORTS
  • 2
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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
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Robust Quantitative Measurement of Flows and Transparent or Highly Reflective Objects (1995)
    In:  CASI
    Details
    Publication Date: 2019-08-17
    Description: The liquid crystal point diffraction interferometer (LCPDI) is a new instrument that has been developed for the measurement of phase objects. The LCPDI uses 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 wave-fronts. A solid state camera provides very high data density and automated data reduction. The instrument can measure either transparent objects like fluids and lenses, or highly reflective opaque objects like mirrors. In the former case, the refractive index distribution is measured and then related to various properties like temperature, density, chemical composition, or thickness. In the latter case, the measured phase distribution is related to the object shape. The objects measured must be stationary or quasisteady state because the measurement requires the acquisition of several frames of image data during which time the object's properties must not have changed. The data acquisition time depends on the speed of the frame grabber and the required number of data frames. Typically, three to five frames taking 1 to 2 seconds are required. The potential for faster data acquisition exists.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: NASA-TM-107086 , NAS 1.15:107086 , E-9964 , Technology 2005; 24-26 1995; Chicago, IL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
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