Nuffield Bursary Update (3)

Throughout the course of her Nuffield Foundation project this summer Ewa Karczewska will be making updates of her progress on our blog.  Her final instalment is below.

Ewa writes: During the 8-week project with the UCL Optical Tweezers Group I have learnt a great deal about the laboratory work as well as the current experiments run in it, which focus on the evanescent field and the micro- and nano- structures trapping. I have also gain knowledge about the evanescent wave and the different optical fibre modes.
My research was focused on the thin fibre fabrication using the “heating and pulling”method. The light (λ = 1064nm) was coupled to the tapered fibre so that the evanescent field near the taper region was created. That field was then tested with the micro-sized spheres. When the field was strong enough and the surface of the fibre was smooth enough, the spheres were observed to move along the fibre along the direction of the light propagation.
Overall, I have managed to obtain an efficient method of obtaining thin (about 1.5μm in diameter) optical fibres using the “heating and pulling” method and observe the spheres of 2μm to move along the fibre once the laser light was coupled through it. When the laser light was coupled from both sides of the fibre I could move the spheres in two directions and also balanced the two beams so that the spheres stayed in place.
I have also investigated the behaviour of the micron-sized spheres when the polarisation of the trapping light of an optical tweezers was changed from linear to circular polarisation as well as from radial to azimuthal polarisation.
That project gave me a valuable experience and a great insight into the research work, which will be very useful in my future study for PhD.

From September Ewa will be studying for the third year of her degree as a year abroad in Toronto University.

Nuffield Bursary Update (2)

Throughout the course of her Nuffield Foundation project this summer Ewa Karczewska will be making updates of her progress on our blog.  Her first instalment is below.

Ewa writes: For the past two weeks, I have been investigating and making improvements to the flame brushing method, which then allowed me to obtain the fibres of less than 2µm in diameter. Therefore, after the study on how to make a good coupling between two optical fibres using the splices, the laser beam was coupled into the fibre and the nearby spheres of 2µm in diameter have been observed to move along the fibre in the direction of the light propagation. The spheres were observed to accelerate in the thinnest part of the fibre. When the laser beam was split into two and coupled to each end of the fibre, it was possible to move the spheres in both directions by changing the intensity of the light coupled to each end.  Also it has been observed that if the fibre breaks in the thin part and the laser beam is coupled into it, the spheres accelerate and shoot off from the broken end.

Above you can see a movie of 2µm diameter polystyreen microspheres propelled along a tapered optical fibre in the evanescent field of the guided laser beam.  More movie can be found on our YouTube Channel.

Nuffield Bursary Update

Throughout the course of her Nuffield Foundation project this summer' Ewa Karczewska will be making updates of her progress on our blog.  Her first instalment is below.



Tapered glass optical fibre
with 2 micron polystyrene spheres 

 Ewa writes:  I have started this Nuffield Bursary project by studying the mechanical effect of evanescent optical fields on microscopic particles.  I have learned how to set up simple optical path using optical mirrors and lenses, and most importantly I have understood the basic ideas behind the use of the laser light for optical trapping.  Having been familiarised with the equipment in the laboratory and having been shown the experiment of array formation and optical binding in evanescent waves carried out by Marios Sergides, I have been using the heating and pulling method for making tapered optical fibres.  With this method I have produced several optical fibres of less than 2μm in diameter.  Using these fibres I will be trying to trap micron-sized spheres in the evanescent field, but first the efficiency of coupling and light transmission into the fibre must be improved.  To do this I have learned how to polish and connectorize optical fibres and measured the transmission efficiency.

New group members

Ewa Karczewska is joining the UCL Optical Tweezers Group today for an eight week research project funded by the Nuffield Foundation.  The foundation provides research bursaries for undergraduate students considering a career in research to gain experience in a research lab over the summer vacation.  The Optical Twezeers Group has peviously hosted three Nuffield bursary students: Muddassar Rashid (2008), Alex Dunning (2009) and Radhika Patel (2010).

Ewa is a second year undergraduate student at UCL, studying for an MSci degree in Physics.  She will be contributing to a number of different projects presently running in the group, and making regular updates of her progress on this blog.

Nuffield Bursary Award

Ewa Karczewska has been awarded a Nuffield Foundation Undergraduate Research Bursary to work in the UCL Optical Tweezers Group this summer. 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 three previous Nuffield Foundation Bursary students: Muddassar Rashid (2008) who worked on synthesis and properties of polarisation vortex beams, Alex Dunning (2009) who performed calculations on the properties of optical nanofibres and is now studying for a PhD at Southampton University, and Radhika Patel (2010) who worked on photonic force microscopy experiments and is taking her final exams this year.

Nuffield Bursary Update (3)

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

Radhika writes: We wanted to improve the optical tweezers setup I have been working on so this week we partly dismantled the microscope was in order to get a better look at what was inside. Having made some adjustments, Susan and I have returned to aligning the beams, trapping particles and calibrating the trap again. In addition to this, we have started the process of integrating some optical fibres into the setup. Part of the last week was spent learning how to cut and prepare the fibres for use in the setup and actually connectorising some of the fibres.

Phil, Marios and I attended Richard Berry's lecture on Single-molecule observations of turnover, co-operativity and mechanochemistry in a macromolecular complex. As this was the first talk I had attended related to optical tweezing, it was interesting to hear about some of its applications.

Nuffield Bursary Update (2)

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

Radhika writes: Since working on the optical tweezers setup with Susan Skelton, I have helped install and refine a “particle tracking system” which tracks the particle’s Brownian motion in the trap using the backscattered light from a 'probe' laser beam. We can use this method to measure the spring constant of the optical trap, and calibrate the detector sensitivity so that we can make measurements of the particle’s displacement and the absolute force applied.

We have been visited by Maria Grazia Donato from IPCF-CNR (Messina) and Gianluca Memoli from NPL this week also. Having worked with optics for many years, they have helped improve the experiment as well as my understanding of ray optics and optical tweezers.

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.