Volume 86, Number 3, May 2009
Article Number 38002
Number of page(s) 6
Section Interdisciplinary Physics and Related Areas of Science and Technology
Published online 13 May 2009
EPL, 86 (2009) 38002
DOI: 10.1209/0295-5075/86/38002

Quantitative assessment of non-conservative radiation forces in an optical trap

Giuseppe Pesce1, 2, Giorgio Volpe3, Anna Chiara De Luca1, 2, Giulia Rusciano1, 2 and Giovanni Volpe4, 5

1   Dipartimento di Scienze Fisiche, Università di Napoli “Federico II", Complesso Universitario Monte S. Angelo Via Cintia, 80126 Napoli, Italy, EU
2   ICFO - Institut de Ciencies Fotoniques, Mediterranean Technology Park - 08860, Castelldefels (Barcelona), Spain, EU
3   CNISM, Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Sede di Napoli Napoli, Italy, EU
4   Max-Planck-Institut für Metallforschung - Heisenbergstr. 3, 70569 Stuttgart, Germany, EU
5   2. Physikalisches Institut, Universität Stuttgart - Pfaffenwaldring 57, 70569 Stuttgart, Germany, EU

received 24 February 2009; accepted in final form 14 April 2009; published May 2009
published online 13 May 2009

The forces acting on an optically trapped particle are usually assumed to be conservative. However, the presence of a non-conservative component has recently been demonstrated. Here, we propose a technique that permits one to quantify the contribution of such a non-conservative component. This is an extension of a standard calibration technique for optical tweezers and, therefore, can easily become a standard test to verify the conservative optical force assumption. Using this technique, we have analyzed optically trapped particles of different size under different trapping conditions. We conclude that the non-conservative effects are effectively negligible and do not affect the standard calibration procedure, unless for extremely low-power trapping, far away from the trapping regimes usually used in experiments.

87.80.Cc - Biophysical techniques (research methods): Optical trapping.
82.70.Dd - Colloids.
05.40.Jc - Brownian motion.

© EPLA 2009