A Laser Shadowgraphy Methodfor Studying Vibrations of Incandescent Solids

Document Type : Original Article


1 Department of Physics, Faculty of Science, Cairo University, Cairo, Egypt.

2 Laser Photonics Research Center, Departmentof EngineeringPhysics, Military Technical College, Cairo, Egypt.


This paper discusses a newlaser shadowgraphymethodfor 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 setup that included a modulatedlaser to backlight the vibrating object and to generate an analogue shadowgraph,a photo-detector installed in front of the shadowgraph, isconnected to a lock-in amplifier, and synchronized by the laser modulator,to retrieve the vibration signal from the noisy optical background. The methodwasapplied successfully to detect the resonance frequency of tungsten filament atincandescencetemperature inside an automotive lamp as a proof of concept. This method can be also adapted to test the thermo-elastic characteristics of refractory alloy samples,the mechanical properties of high temperature refractory MEMS lightingsandnano-structured tungsten based advanced thermal shock-resistant lighting sources.