Paper published in Nano Letters

Our paper on the dynamics of silison nanowires in optical tweezers has been published as A. Irrera et al, 'Photonic torque microscopy of the non-conservative force field for optically trapped silicon nanowires', Nano Letters 16, 4181-4188 (2016).

From the abstract: We measure, by photonic torque microscopy, the nonconservative rotational motion arising from the transverse components of the radiation pressure on optically trapped, ultrathin silicon nanowires. Unlike spherical particles, we find that nonconservative effects have a significant influence on the nanowire dynamics in the trap. We show that the extreme shape of the trapped nanowires yields a transverse component of the radiation pressure that results in an orbital rotation of the nanowire about the trap axis. We study the resulting motion as a function of optical power and nanowire length, discussing its size-scaling behavior. These shape-dependent nonconservative effects have implications for optical force calibration and optomechanics with levitated nonspherical particles.

Review paper in Nature Nanotechnology

Our paper 'Optical trapping and manipulation of nanostructures' has been published in Nature Nanotechnology 8 807-819 (2013).

From the abstract:  Optical trapping and manipulation of micrometre-sized particles was first reported in 1970. Since then, it has been successfully implemented in two size ranges: the subnanometre scale, where light–matter mechanical coupling enables cooling of atoms, ions and molecules, and the micrometre scale, where the momentum transfer resulting from light scattering allows manipulation of microscopic objects such as cells. But it has been difficult to apply these techniques to the intermediate — nanoscale — range that includes structures such as quantum dots, nanowires, nanotubes, graphene and two-dimensional crystals, all of crucial importance for nanomaterials-based applications. Recently, however, several new approaches have been developed and demonstrated for trapping plasmonic nanoparticles, semiconductor nanowires and carbon nanostructures. Here we review the state-of-the-art in optical trapping at the nanoscale, with an emphasis on some of the most promising advances, such as controlled manipulation and assembly of individual and multiple nanostructures, force measurement with femtonewton resolution, and biosensors.

Paper published in Optics Letters

Our paper 'Optical trapping of single walled carbon nanotubes with cylindrical vector beams has been published as M. G. Donato et al, Opt. Lett. 37 3381-3383 (2012).  

From the abstract: We use laser beams with radial and azimuthal polarization to optically trap carbon nanotubes. We measure force constants and trap parameters as a function of power showing improved axial trapping efficiency with respect to linearly polarized beams. The analysis of the thermal fluctuations highlights a significant change in the optical trapping potential when using cylindrical vector beams. This enables the use of polarization states to shape optical traps according to the particle geometry, as well as paving the way to nanoprobe-based photonic force microscopy with increased performance compared to a standard linearly polarized configuration.

This paper has also been selected for inclusion in the Virtual Journal of Biomedical Optics 7 (2012)

Visit by Onofrio Marago

Onofrio Marago from the NanoSoft Lab, IPCF-CNR (Messina) is visiting our group at UCL from 26-31 January.  Our groups have a long-running collaboration, and exchange visits are funded by the Royal Society as part of our International Joint Project on Photonic Force Microscopy.

Visit by Onofrio Marago and Maria Grazia Donato

This week (21-26 November) Onofrio Marago and Maria Grazia Donato from the NanoSoft Lab, IPCF-CNR (Messina) are visiting our group at UCL.  Our groups have a long-running collaboration, and exchange visits are funded by the Royal Society as part of our International Joint Project on Photonic Force Microscopy.

Visit to NanoSoft Lab, IPCF-CNR (Messina)

Phil is spending the week of 07-11 November visiting Onofrio Marago and colleagues at the NanoSoft Lab, IPCF-CNR (Messina).  Our groups have a long-running collaboration, and exchange visits are funded by the Royal Society as part of our International Joint Project on Photonic Force Microscopy.

Visit to NanoSoft Lab, IPCF-CNR (Messina)

Phil spent the week of 13-18 September visiting Onofrio Marago and colleagues at the NanoSoft Lab, IPCF-CNR (Messina).  The visit was part of our International Joint Project on Photonic Force Microscopy funded by the Royal Society.  Among the highlights of the week was a half-day meeting on graphene with talks by Onofrio, Giuseppe Angilella (Catania) and Prof Norman March (former holder of the Coulson Chair in Theoretical Chemisty, Oxford).

Photonic Force Microscopy Book Chapter

Our book chapter on 'Photonic Force Microscopy: from femtonewton force sensing to ultra-sensitive spectroscopy' in the volume 'Scanning Probe Microscopy in Nanoscience and Nanotechnology' is published by Springer, and can be viewed on Google Books

Nuffield Bursary Update

Throughout the course of her Nuffield Foundation project this summer Radhika Patel will be making updates of her progress on our blog.  The first instalment is below.

Radhika writes:  Having joined the UCL Optical Tweezers Group at the end of June, I have been trapping micron sized particles using a diode laser and measuring the spring constant of the optical trap.  The objective was to familiarise myself with the apparatus and theory of optical trapping, and learn about different methods for calibration. Alongside this I have been learning about the experiment that Susan Skelton (PhD student) is working on which is an inverted optical tweezers.  We have been calibrating the optical tweezers for use in Photonic Force Microscopy (PFM) which is the project put forward to the Nuffield Foundation for the Undergraduate Research Bursary I was granted this summer.

Nuffield Foundation Research Bursary

Radhika Patel is joining the UCL Optical Tweezers Group this summer with a Nuffield Foundation Undergraduate Research Bursary. This scheme allows UK undergraduates to gain research experience by providing funding for up to eight weeks to complete a research project during the summer vacation. We have hosted two previous Nuffield Foundation students: Muddassar Rashid (2008) who contributed to two publications on the properties of polarisation vortex beams as a result of his project, and Alex Dunning (2009) who performed calculations on the properties of optical nanofibres and will be starting a PhD at Southampton University in October.

Radhika was a pupil at Haberdashers' Aske's School for Girls in Elstree and has just completed the third year of an MSci degree in Physics at UCL. She will be working on a project titled 'Photonic Force Microscopy' which aims to use optically trapped particles for sensitive force measurements and imaging.  We will be reporting on her progress on this blog.