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Issue 2, 2013
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Twin-focus photothermal correlation spectroscopy

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We introduce a novel concept for optical correlation spectroscopy of non-fluorescent absorbing nano-particles termed twin-focus photothermal correlation spectroscopy (Twin-PhoCS). This method exhibits a unique axial sensitivity, allowing for either the measurement of very slow axial dynamics or the determination of axial heterogeneities on sub-diffraction limited length-scales. To this end, the photothermal nano-lensing mechanism [Markus Selmke, Romy Schachoff, Marco Braun, and Frank Cichos, ACS Nano, 2012, 6(3), 2741] provides two sharply separated detection-subvolumes, comprising the twin-focus. The achieved axial sensitivity is superior to single detection-volume or dual-focus based fluorescence correlation spectroscopies. We demonstrate the sensitivity by measuring radiation-pressure induced flow velocities of diffusing 14 nm gold-colloids down to 10 nm ms−1 with the help of the provided analytical correlation functions.

Graphical abstract: Twin-focus photothermal correlation spectroscopy

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Article information

05 Sep 2012
02 Nov 2012
First published
23 Nov 2012

RSC Adv., 2013,3, 394-400
Article type

Twin-focus photothermal correlation spectroscopy

M. Selmke, R. Schachoff, M. Braun and F. Cichos, RSC Adv., 2013, 3, 394
DOI: 10.1039/C2RA22061J

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