The optical tweezers toolbox can be used to calculate optical forces and torques of particles using the T-matrix formalism in a vector spherical wave basis. The toolbox includes codes for calculating T-matrices, beams described by vector spherical wave functions, functions for calculating forces and torques, and examples.

To use the toolbox, download or clone the GitHub repository. The toolbox consists of a directory, ott-toolbox, which contains a collection of functions for calculating T-matricies, beam coefficients, force and torques. To use the functions in your code, the easiest way is to add the ott-toolbox directory to your matlab path,

addpath('<download-path>/ott/ott-toolbox');

if you regularly use the toolbox you might want to add the command to your startup.m file. You might also want to add the examples to your path

addpath('<download-path>/ott/examples');

1. To get started using the toolbox you should first take a look at the users guide for version 1.2 and the optical tweezers computational toolbox paper (pre-print). Both are available on our website.

2. Copy the examples to your working directory, and play with them. Start with example_gaussian.m.

3. It's best to use length units of the wavelength in the trapping medium, usually free-space wavelength/1.33.

4. The examples calculate the force and torque efficiencies. These are the force and torque per photon, in photon units. To convert to SI units: force_SI = force_Q * n * P/c torque_SI = torque_Q * P/w where n is the refractive index of the surrounding medium, P is the beam power in watts, c is the speed of light in free space, w is the angular optical frequency, in radians/s.

• Version 2 of the toolbox, an object orientated implementation with a focus on simulating particles in optical traps rather than just focussing on calculating optical forces/torques. (in progress)

• Automatic choice of Nmax

• Graphical user interface (in progress)

• T-Matrix routines for arbitrary particles

The package and its components may be used free-of-charge for research, teaching, or personal use. If results obtained using the package are published, the package should be appropriately referenced. For full details see LICENSE.md. For use outside the conditions of the license, please contact us.

The package can be refereced by citing the paper describing version 1 of the toolbox

T. A. Nieminen, V. L. Y. Loke, A. B. Stilgoe, G. Knöner, A. M. Branczyk, N. R. Heckenberg, and H. Rubinsztein-Dunlop, "Optical tweezers computational toolbox", Journal of Optics A 9, S196-S203 (2007)

or by directly citing the toolbox

T. A. Nieminen, V. L. Y. Loke, A. B. Stilgoe, Y. Hu, G. Knoener, A. M. Branczyk, "Optical tweezers toolbox", https://github.com/ilent2/ott

The best person to contact for inquiries about the toolbox or lincensing is Timo Nieminen

Papers describing the toolbox

• T. A. Nieminen, V. L. Y. Loke, A. B. Stilgoe, G. Knoener, A. M. Branczyk, N. R. Heckenberg, H. Rubinsztein-Dunlop, "Optical tweezers computational toolbox", Journal of Optics A 9, S196-S203 (2007)

• T. A. Nieminen, V. L. Y. Loke, G. Knoener, A. M. Branczyk, "Toolbox for calculation of optical forces and torques", PIERS Online 3(3), 338-342 (2007)

More about computational modelling of optical tweezers:

• T. A. Nieminen, N. R. Heckenberg, H. Rubinsztein-Dunlop, "Computational modelling of optical tweezers", Proc. SPIE 5514, 514-523 (2004)

More about our beam multipole expansion algorithm:

• T. A. Nieminen, H. Rubinsztein-Dunlop, N. R. Heckenberg, "Multipole expansion of strongly focussed laser beams", Journal of Quantitative Spectroscopy and Radiative Transfer 79-80, 1005-1017 (2003)

More about our T-matrix algorithm:

• T. A. Nieminen, H. Rubinsztein-Dunlop, N. R. Heckenberg, "Calculation of the T-matrix: general considerations and application of the point-matching method", Journal of Quantitative Spectroscopy and Radiative Transfer 79-80, 1019-1029 (2003)

The multipole rotation matrix algorithm we used:

• C. H. Choi, J. Ivanic, M. S. Gordon, K. Ruedenberg, "Rapid and stable determination of rotation matrices between spherical harmonics by direct recursion" Journal of Chemical Physics 111, 8825-8831 (1999)

The multipole translation algorithm we used:

• G. Videen, "Light scattering from a sphere near a plane interface", pp 81-96 in: F. Moreno and F. Gonzalez (eds), Light Scattering from Microstructures, LNP 534, Springer-Verlag, Berlin, 2000

More on optical trapping landscapes:

• A. B. Stilgoe, T. A. Nieminen, G. Knoener, N. R. Heckenberg, H. Rubinsztein-Dunlop, "The effect of Mie resonances on trapping in optical tweezers", Optics Express, 15039-15051 (2008)

Multi-layer sphere algorithm:

• W. Yang, "Improved recursive algorithm for light scattering by a multilayered sphere", Applied Optics 42(9), (2003)