An opto-acoustic metrology device is configured to measure or inspect structures in a sample using both vertical and lateral transient perturbations. Multiple probe beams that have different locations of incidence may detect both the vertical and lateral transient perturbations produced by a pump beam, or a single probe beam may detect both the vertical and lateral transient perturbations produced by multiple pump beams that have different locations of incidence. The multiple probe beams or multiple pump beams are modulated with orthogonal waveforms, which allow the measurement of the different locations without interference from one another. The received signals are demodulated based on the orthogonal waveforms to recover the contributions to the received signals associated with each of the multiple probe beams or each of the multiple pump beams.