Laser Doppler Velocity Interferometer (LDVI) is extremely sensitive to the velocity, and subsequent displacement measurement, of a moving object, and in this work it is used in mechanical vibration analysis.
In the initial stage of the research, the building floor vibrations are detected by using LDVI system (modified Michelson interferometer). For the elimination of transient noise vibration, an anti-vibration system using a steel plate and a pneumatic tire tube is used. By using this LDVI, the floor vibrations are detected and the frequencies are 96.4 Hz and 11.4 Hz, further a mechanical filter system is used to eliminate 96.4 Hz vibration and the lower frequency vibration of 11.4 Hz is found to transmit the filter.
In the later part of the present research, a new laser Doppler heterodyning system is developed. It can measure very high velocities, which give the heterodyne frequency beyond the detector response time. The principle of the method is based on reduction of the Doppler frequency that a laser beam undergoes when it is reflected obliquely a moving mirror. By making the laser beams fall upon the moving mirror in angles $Θ_1$ and $Θ_2$, the heterodyne frequency to be obtained is $Δf=\frac{2vf}{c}(cosΘ_1-cosΘ_2)$, here v is mirror velocity and f is laser frequency. Thus the heterodyne frequency detected decreases by the factor of ($cosΘ_1-cosΘ_2$).
