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We employ multiple sinusoid modulated optical tweezers to measure thefrequency dependent rheological parameters of a linear viscoelastic fluid overfive decades of frequency in a single shot, hitherto not achieved using activemicrorheology alone. Thus, we spatially modulate a trapped probe particleembedded in a fluid medium with a combination of a square wave - which is bydefinition a superposition of odd sinusoidal harmonics - and a linearsuperposition of multiple sinusoids at a wideband frequency range, withcomplete control over the amplitude, frequency and relative phase of themodulating signals. For the latter, we selectively excite the particle bylarger amplitudes at high frequencies where the particle response is low,thereby enabling wideband active microrheology with large signal-to-noise. Thismitigates the principal issue associated with conventional active microrheology- which is low bandwidth - and also renders our method better in terms ofsignal to noise, and faster compared to passive microrheology. We determine thecomplex viscoelastic parameters of the fluid by extracting the phase response(relative to input excitation) of the probe from the experimentally recordedtime series data of the probe displacement, and employing well-knowntheoretical correlations thereafter. We test the efficacy of our method bystudying a linear viscoelastic media (polyacrylamide-water solution) atdifferent concentrations, and find good agreement of the measured fluidparameters with known literature values.

Single-shot wideband active mircorheology using multiple-sinusoid modulated Optical Tweezers