1. A method of performing photothermal imaging, the method comprising: generating an excitation chirped waveform comprising a chirped sequence of pulses; controlling a laser according to the excitation chirped waveform, such that the laser emits a chirped sequence of laser pulses; directing the chirped sequence of laser pulses onto a sample; detecting, with an infrared camera, photothermal radiation emitted from the sample, thereby obtaining time-dependent photothermal signal data for each image pixel of the infrared camera; generating a truncated chirped waveform comprising a chirped sequence of truncated pulses, wherein each truncated pulse has a pulsewidth less than that of the pulses of the excitation chirped waveform, and wherein each truncated pulse is delayed by a pre-selected time delay relative to a corresponding pulse of the chirped sequence of pulses; cross-correlating the time-dependent photothermal signal data with the truncated chirped waveform, thereby obtaining, for each pixel of the infrared camera, time-dependent cross-correlation data; and generating image data based on the time-dependent cross-correlation data.