FIG. 3.

Pump-probe schematic. An intensity-modulated pump and non-modulated probe are combined and passed through a laser scanning microscope. The collected light is filtered before detection by one of two schemes. (a) For transient absorption/gain processes that imprint an amplitude modulation on the probe, the filter only needs to reject the pump before detection. (b) For phase modulation processes that shift the probe optical spectrum, a filter that cuts off part of the probe spectrum converts the spectral shift into an amplitude modulation (XPMSS).