A method of actuating a plurality of probes by delivering photothermal energy to the probes so that the probes are heated and deform relative to a sample. The photothermal energy is delivered to the probes by: directing an input beam into an optical device; transforming the input beam with the optical device into a plurality of actuation beamlets which are not parallel with each other; and scanning the actuation beamlets across the probes, optionally via an objective lens. A spacing between the actuation beamlets is different to a spacing between the probes so that only a subset (typically only one) of the actuation beamlets illuminates a probe at any instant. As the actuation beamlets scan across the probes the probes are illuminated in an illumination sequence. The actuation beamlets are controlled so that different amounts of photothermal energy are delivered to at least two of the probes during the illumination sequence.