We will discuss numerical methods for analyzing the various nonlinear contributions to pump-probe signals, with the ultimate objective of real time analysis using digital signal processing techniques. To that end, we have replaced the lock-in amplifier in our pump-probe microscope with a high-speed data acquisition board, and reprogrammed the coprocessor field-programmable gate array (FPGA) to perform lock-in detection. The FPGA lock-in offers better performance than the commercial instrument, in terms of both signal to noise ratio and speed. In addition, the flexibility of the digital signal processing approach enables demodulation of more complicated waveforms, such as spread-spectrum sequences, which has the potential to accelerate microscopy methods that rely on slow relaxation phenomena, such as photo-thermal and phosphorescence lifetime imaging.
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Jesse W. Wilson, Miguel Anderson, Jong Kang Park, Martin C. Fischer, Warren S. Warren, "Separating higher-order nonlinearities in transient absorption microscopy," Proc. SPIE 9584, Ultrafast Nonlinear Imaging and Spectroscopy III, 95840B (26 August 2015);