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.
We have been working on an interferometric method for high-efficiency synthesis of cylindrical vector beams.
These are the class of laser beams that are linearly polarized in a cylindrical basis, the most common examples being beams where the polarization is purely radial or purely azimuthal.
The latest movie from this experiment is here and on our YouTube channel. In this movie you can see the characteristic 'donut' shape of the beam and the intensity transmission pattern through a polaroid which demonstrates the radial and azimuthal polarization states. These beams have many applications in, for example, high-resolution miroscopy and optical trapping.
We have been working on an experiment to demonstrate evanescent wave optical binding of microparticles.
The latest movie from this experiment is here and on our YouTube channel. In this movie you can see 1 micron diameter silica microparticles suspended in water above the surface of a glass prism. The microparticles organise into 1D chains when exposed to the evanescent field of a laser beam reflected from the surface below.
We will be publishing movies from our experiments like the one shown here of an optically trapped microbubble, together with references to the relevant papers. You can subscribe to the channel by using the button below:
