Hi all, 

The next Optical Sciences seminar will be given by Neel Mackinnon from the Quantum Theory group at 3pm on Thursday 9th May in 222. Neel will be presenting the following: 

Title: Electromagnetic Helicity within a Chiral Medium

Abstract: The electromagnetic helicity is a locally conserved quantity of the free electromagnetic field which, in a sense, describes the “handedness” of the field. The name “helicity” can be justified by the fact that the total helicity of an electromagnetic field, integrated over all space, is proportional to the difference in the number of left- and right-handed circularly polarised photons in the field. The concept of helicity can also be made meaningful in presence of matter – in this case it is no longer conserved, but charges and currents may act as sources or sinks of helicity. The definition of helicity can then be very straightforwardly extended to apply within dielectrics. 

However, this straightforward extension runs into difficulties if the dielectric material is chiral (that is, if it can exhibit optical rotation). This talk will introduce some of the features of electromagnetic helicity, and describe a proposed modification to the definition of the helicity density within a chiral medium.

The talk will last around 20 minutes, followed by coffee and biscuits in the common room. 

Hope to see you there,

Frances 

Optical angular momentum transfer on total internal reflection

Hi all,

The next seminar will be held this Thursday 25th April, 3.30 pm, Kelvin Building lecture theatre 257, with Atirach Ritboon from the Quantum Theory group.

Abstract:

1. We study the mechanism of optical angular momentum transfer from light to a dielectric medium on total internal reflection. We employ a quantized approach and, in particular, work with a single-photon pulse. This allows us to evaluate the force and torque per photon and also, crucially, to evaluate forces and torques conditioned on transmission or reflection at an interface. The reflected electric and magnetic fields of an incident paraxial beam carrying orbital and spin angular momentum are obtained using an angular spectrum method. We calculate the expectation value of the single-photon torque exerted on the dielectric, due to total internal reflection of a single-photon pulse, using the dipole-based Lorentz force density. We apply this result to describe the angular momentum transfer from light on passing through an M-shaped Dove prism. 

Hope to see you there, and for coffee and biscuits in the common room afterwards,

Frances

Adaptive Prospective Optical Gating Allows 4D Imaging and Quantification in the Developing Zebrafish Heart

Next seminar this Thursday 11th April, 4pm, room 222 Kelvin Building, this time with Chas Nelson from the Imaging Concepts Group!

Title:

Adaptive Prospective Optical Gating Allows 4D Imaging and Quantification in the Developing Zebrafish Heart.

Abstract:

Researchers interested in the heart have long used a wide range of imaging techniques to see, understand and quantify changes throughout heart development, repair and, in certain species, regeneration. Two major challenges in imaging the heart are the contrasting problems of high-frequency heart beating and low-frequency morphological changes. I will demonstrate how using our established method of prospective optical gating, in combination with light-sheet microscopy, can allow the synchronised capture of 3D images of the in vivo beating zebrafish heart. However, prospective optical gating alone is limited to snapshots of the heart at chosen target heartbeat phases and only over the scale of tens of minutes.
We have now developed adaptive prospective optical gating technologies that we are using in combination with light-sheet microscopy to enable a range of 3D+time and 3D-timelapse imaging experiments. Our adaptive prospective optical gating technology allows us to carry out 48+ hour, in vivo, 3D-timelapse imaging of the computationally 'frozen' heart across developmental stages, e.g. heart looping, and throughout injury response and repair. Imaging across these timescales is not possible with prospective optical gating alone and phase-locked timelapse imaging is not possible using retrospective optical gating alone: only with our hybrid system are such longitudinal studies possible. Our hybrid prospective-retrospective optical gating system allows researchers to study and understand cardiac development and repair without the use of chemicals or optogenetics to stop or modify the natural heart beating.

Hope to see many of you there,
Cheers,
Chiara.

Extended-depth point localisation microscopy using Airy-beam-based point-spread functions

Hi all!

Imaging Concepts Group's turn this week at the Optical Seminar, with Zhuang taking a break from his thesis to tell us about some of his PhD work:

Title: 

Extended-depth point localisation microscopy using Airy-beam-based point-spread functions

Abstract:

The precise localisation of point sources in optical microscopy enables nm-resolution imaging of single-molecules and biological dynamics. Existing approaches for point localisation, however, suffer from the very limited depth range and thus not suitable for imaging thick samples. We utilise the lateral translation property and the diffraction-free propagation of Airy-beam-based point-spread functions to localise point emitters in 3D space with the key advantages of extended depth range, higher optical throughput and potential for imaging higher emitter densities than are possible using other techniques. The proposed techniques are demonstrated for blood-flow imaging in a live zebrafish. 

Thursday 4th of April, 4pm, room 312 Kelvin Building.

As usual, snacks and soft drinks in the common room afterwards :)

Hope to see many of your there,

Cheers,

Chiara.

Portable, real-time, methane-imaging camera

Hello everyone!

This weeks Optical Sciences Seminar will be given by myself on my work developing a gas imaging camera. I will give a short presentation on the device and then do a live demonstration!

The seminar will take place on Thursday 14th March in Kelvin 222 at 16:00.

Snacks will be provided in the common room afterwards, where discussions can take place.

In the meantime I hope these images whet your anticipation.

Cheers,
Kyle

The output of the portable, real-time, methane-imaging camera. Methane is highlighted in a green false coloured overlay. The gas cells are 10mm thick and the tube is releasing a low pressure methane cloud

The portable, real-time, methane-imaging camera without its housing

Optical Simulation of a Quantum Particle Living on a Surface of a Tetrahedron

Hello all!

The first of the Optics Group's Seminars will be by Jakub Belin who will give a talk titled "Optical Simulation of a Quantum Particle Living on a Surface of a Tetrahedron".

The talk will take place on 28th February at 16:00 in Kelvin 222.

Abstract:

We analyze propagation of waves on the surface of the simplest Platonic solid, the regular tetrahedron.  We find the time evolution of a quantum particle confined to such a surface is completely analogous to the diffraction pattern from a certain grating profile, and can therefore be investigated in a simple diffraction experiment.  The quantum particle exhibits perfect quantum state revivals, which translate into the fractional Talbot effect in the equivalent diffraction experiment.  We present the results of such an experiment and compare them with numerical simulations.

As usual, snacks will be provided afterwards in the common room. I hope to see you there!

Cheers,
Kyle

Skyrmion structure in vector beams

Hi everyone, 

The first talk of the year will be given on Thursday 17th January by Scarlett Gao from the Quantum Theory group on the following: 

Skyrmion structure in vector beams
Vector beams have both a spatially varying amplitude and polarization, for light, or spin direction for electrons.  Associated with these we find a topological feature, the skyrmion number, that it is robust against any deformation during propagation. The simplest way to map out this feature is to use the associated skyrmion field.  This is a transverse or divergenceless field and so has neither sources nor sinks.  Mapping out the skyrmion field for these beams reveals constraints on the manner in which vector beams can be manipulated.

The talk will begin at 4pm in lecture theatre 312 and will last around 20 minutes. This will be followed by refreshments in the common room. 

Hope to see you there!

Frances