In this work, we have demonstrated a stimulated emission (SE) based pump-probe microscopy with subharmonic modulation and synchronization on the pump and the probe lasers. Critically, a high frequency divider circuit divides the repetition frequency (76 MHz) of the probe laser (Ti:sapphire) to the half repetition frequency (38 MHz), which in turn drives the pump laser (pulsed gain-switched diode laser) synchronously and provides the reference signal for lock-in detection. In this way, the highest possible modulation frequency can be achieved for lock-in detection with shot noise limited sensitivity. The greatly shortened time constant (< 0.1 ms) further improved imaging speed. Over an order of magnitude improvement in signal-to-noise ratio is achieved, when compared with conventional lock-in detection implement.
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