We used an IQ - demodulator with a 50 MHz bandwidth ( Model AD8333 , Analog Devices ) for fast , memory - efficient optoacoustic signal detection in the FD . The IQ demodulator enables homodyne detection of baseband signals that consist of an in - phase component I t ð Þ ¼ A cos φ t ð Þ ½ and a quadrature component Q t ð Þ ¼ A sin φ t ð Þ ½ . Signals with amplitude A and phase φ were extracted from acquired I and Q data using the following equations :