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  • 1
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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
    Format: application/pdf
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  • 2
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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
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  • 3
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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
    Format: text
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  • 4
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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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  • 5
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    Liquid-Crystal Point-Diffraction Interferometer for Wave-Front Measurements (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a 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 with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results,
    Keywords: Optics
    Type: NASA-TM-112892 , NAS 1.15:112892 , Applied Optics (ISSN 0003-6935); 35; 10; 1633-1642
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  • 6
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    Quantitative Interferometry in the Severe Acoustic Environment of Resonant Supersonic Jets (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: There is renewed interest in the study of supersonic jets due to advances in high speed jet propulsion, supersonic combustion, and jet noise suppression for the next generation supersonic commercial transport. Understanding fundamental fluid dynamic and acoustic processes for these applications requires quantitative velocity, density and temperature measurements. In this paper we present data demonstrating a new, robust interferometer that can provide accurate data even in the presence of intense acoustic fields. This novel interferometer, the Liquid Crystal Point Diffraction Interferometer (LCPDI), was developed earlier for space flight experiments and is applied here to the case of a supersonic shock-containing jet. The LCPDI is briefly described, then integrated line-of-sight density data from the LCPDI for two underexpanded free jets are presented. The experimental shock spacings agree well with theory.
    Keywords: Acoustics
    Type: High Speed Jet Flows; Jun 21, 1998 - Jun 25, 1998; Washington, DC; United States
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  • 7
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    Liquid-Crystal Point-Diffraction Interferometer (1996)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Liquid-crystal point-diffraction interferometer (LCPDI) invented to combine flexible control of liquid-crystal phase-shifts with robustness of point-diffraction interferometers. Produces interferograms indicative of shapes of wavefronts of laser beams having passed through or reflected from objects of interest. Interferograms combined in computers to produce phase maps describing wavefronts.
    Keywords: PHYSICAL SCIENCES
    Type: LEW-15810 , NASA Tech Briefs (ISSN 0145-319X); 20; 6; P. 8a
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  • 8
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    Effect of Refractive Index Variation on Two-Wavelength Interferometry for Fluid Measurements (1998)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Two wavelength interferometry can in principle be used to measure changes in both temperature and concentration in a fluid, but measurement errors may be large if the fluid dispersion is small. This paper quantifies the effects of uncertainties in dn/dT and dn/dC on the measured temperature and concentration when using the simple expression dn = (dn/dT)dT + (dn/dC)dC. For the data analyzed here, ammonium chloride in water from -5 to 10(exp infinity) C over a concentration range of 2-14% and for wavelengths 514.5 and 633 nm, it is shown that the gradients must be known to within 0.015% to produce a modest 10% uncertainty in the measured temperature and concentration. These results show that real care must be taken to ensure the accuracy of refractive index gradients when using two wavelength interferometry for the simultaneous measurement of temperature and concentration.
    Keywords: Optics
    Type: NASA/TM-1998-207925 , NAS 1.15:207925 , E-11213
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  • 9
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    Quantitative Interferometry in the Severe Acoustic Environment of Resonant Supersonic Jets (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-10
    Description: Understanding fundamental fluidic dynamic and acoustic processes in high-speed jets requires quantitative velocity, density and temperature measurements. In this paper we demonstrate a new, robust Liquid Crystal Point Diffraction Interferometer (LCPDI) that includes phase stepping and can provide accurate data even in the presence of intense acoustic fields. This novel common path interferometer (LCPDI) was developed to overcome difficulties with the Mach Zehnder interferometer in vibratory environments and is applied here to the case of a supersonic shock- containing jet. The environmentally insensitive LCPDI that is easy to align and capable of measuring optical wavefronts with high accuracy is briefly described, then integrated line of sight density data from the LCPDI for two underexpanded jets are presented.
    Keywords: Acoustics
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  • 10
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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
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