Multi-pulse PFIR Microscopy
One main limitation of the regular PFIR microscopy is its relatively weak signal. The peak force tapping cycle of an AFM is usually a few kHz (1kHz up to 8 kHz), which means that the tip and sample are in contact a few thousand times per second. At each tip-sample contact, a laser pulse is emitted to excite the photothermal expansion of the sample, and the cantilever responses are extracted to be used as a signal. However, for samples with low photothermal responses or IR absorption, the PFIR signals are often weak.
The implementation of the multi-pulse PFIR is to illuminate multiple laser pulses per peak force tapping cycle. So more photothermal responses are generated per unit time. The resulting method improves the signal quality of PFIR microscopy.
Left: An illustration of the multi-pulse PFIR scheme. Right: comparison of the single-pulse PFIR signal versus multi-pulse PFIR signal on spatial imaging of the phonon polaritons of h-BN.