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A Laser Shadowgraphy Method for Studying the Vibrations of Incandescent Solids
H.S. Ayoub, A.F. EL-Sherif, H.H. Hassan, S.A. Khairy and Y.H. Elbashar

This paper discusses a new laser shadowgraphy method for investigating the in-plane vibration of refractory solid objects at incandescent temperatures. The method is applied whenever the use of Doppler laser vibrometer is inefficient due to small dimensions, high luminosity and poor reflectivity of the test object. We designed an experimental arrangement that included a modulated laser to backlight the vibrating object and to generate an analogue shadowgraph, a photodetector installed in front of the shadowgraph, is connected to a lock-in amplifier, and synchronized by the laser modulator, to retrieve the vibration signal from the noisy optical background. The method was applied successfully to detect the resonance frequency of tungsten filament at incandescence temperature inside an automotive lamp as a proof of concept. This method can be also adapted to test the thermoelastic characteristics of refractory alloy samples, the mechanical properties of high temperature refractory microelectro-mechanical systems (MEMS) lighting and nanostructured tungsten-based advanced thermal shock-resistant lighting sources.

Keywords: Diode laser, laser shadowgraphy, non-Doppler vibrometry, optical engineering, optoelectronics, optical physics, laser metrology, incandescent temperatures

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