  We report a demonstration of the measurement of the ratio between an optical
modulation side band component and the non-shifted light component by
time-averaged heterodyne holography in off-axis and frequency-shifting
configuration, through coherent frequency-division multiplexing with a dual
optical local oscillator. Experimental results of sinusoidal vibration sensing
are reported. This technique enables absolute measurements of sub-nanometric
out-of-plane vibration amplitudes.
