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Proceedings Paper

Separating higher-order nonlinearities in transient absorption microscopy
Author(s): Jesse W. Wilson; Miguel Anderson; Jong Kang Park; Martin C. Fischer; Warren S. Warren
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Paper Abstract

The transient absorption response of melanin is a promising optically-accessible biomarker for distinguishing malignant melanoma from benign pigmented lesions, as demonstrated by earlier experiments on thin sections from biopsied tissue. The technique has also been demonstrated in vivo, but the higher optical intensity required for detecting these signals from backscattered light introduces higher-order nonlinearities in the transient response of melanin. These components that are higher than linear with respect to the pump or the probe introduce intensity-dependent changes to the overall response that complicate data analysis. However, our data also suggest these nonlinearities might be advantageous to in vivo imaging, in that different types of melanins have different nonlinear responses. Therefore, methods to separate linear from nonlinear components in transient absorption measurements might provide additional information to aid in the diagnosis of melanoma.

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.

Paper Details

Date Published: 26 August 2015
PDF: 12 pages
Proc. SPIE 9584, Ultrafast Nonlinear Imaging and Spectroscopy III, 95840B (26 August 2015); doi: 10.1117/12.2187133
Show Author Affiliations
Jesse W. Wilson, Duke Univ. (United States)
Miguel Anderson, Duke Univ. (United States)
Jong Kang Park, Duke Univ. (United States)
Martin C. Fischer, Duke Univ. (United States)
Warren S. Warren, Duke Univ. (United States)


Published in SPIE Proceedings Vol. 9584:
Ultrafast Nonlinear Imaging and Spectroscopy III
Zhiwen Liu, Editor(s)

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