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Issue 23, 2014
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Optical trapping and Raman spectroscopy of solid particles

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The heterogeneous interactions of gas molecules on solid particles are crucial in many areas of science, engineering and technology. Such interactions play a critical role in atmospheric chemistry and in heterogeneous catalysis, a key technology in the energy and chemical industries. Investigating heterogeneous interactions upon single levitated particles can provide significant insight into these important processes. Various methodologies exist for levitating micron sized particles including: optical, electrical and acoustic techniques. Prior to this study, the optical levitation of solid micron scale particles has proved difficult to achieve over timescales relevant to the above applications. In this work, a new vertically configured counter propagating dual beam optical trap was optimized to levitate a range of solid particles in air. Silica (SiO2), α-alumina (Al2O3), titania (TiO2) and polystyrene were stably trapped with a high trapping efficiency (Q = 0.42). The longest stable trapping experiment was conducted continuously for 24 hours, and there are no obvious constraints on trapping time beyond this period. Therefore, the methodology described in this paper should be of major benefit to various research communities. The strength of the new technique is demonstrated by the simultaneous levitation and spectroscopic interrogation of silica particles by Raman spectroscopy. In particular, the adsorption of water upon silica was investigated under controlled relative humidity environments. Furthermore, the collision and coagulation behaviour of silica particles with microdroplets of sulphuric acid was followed using both optical imaging and Raman spectroscopy.

Graphical abstract: Optical trapping and Raman spectroscopy of solid particles

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Article information

07 Mar 2014
29 Apr 2014
First published
29 Apr 2014

Phys. Chem. Chem. Phys., 2014,16, 11426-11434
Article type
Author version available

Optical trapping and Raman spectroscopy of solid particles

L. Rkiouak, M. J. Tang, J. C. J. Camp, J. McGregor, I. M. Watson, R. A. Cox, M. Kalberer, A. D. Ward and F. D. Pope, Phys. Chem. Chem. Phys., 2014, 16, 11426
DOI: 10.1039/C4CP00994K

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