Optics Seminars OIST
Wednesday 14th April 2021: 4 - 5:30pm on Zoom
Title: Engineering light-matter interactions for optical nanotweezers and for chip-scale infrared microspectrometers
Speaker: Prof. Kenneth Crozier
Physics and Electronic Engineering, The University of Melbourne, Australia
We discuss two applications of engineering light-matter interactions at the nanoscale.
The first is for optical nanotweezers. We use (simulated annealing to design plasmonic nanoapertures that function as optical nanotweezers. The nanoapertures have irregular shapes that are chosen by our algorithm. We present electromagnetic simulations that show that these produce stronger field enhancements and extraction energies than nanoapertures comprising double nanoholes with the same gap geometry. We show that performance is further improved by etching one or more rings into the gold surrounding the nanoaperture. Lastly, we provide a direct comparison between our design and work that is representative of the state of the art in plasmonic nanotweezers at the time of writing.
The second is for chip-scale infrared microspectrometers. Miniaturized spectrometers are advantageous for many applications and can be achieved by what we term the filter-array detector-array (FADA) approach. In this method, each element of an optical filter array filters the light that is transmitted to the matching element of a photodetector array. By providing the outputs of the photodetector array and the filter transmission functions to a reconstruction algorithm, the spectrum of the light illuminating the FADA device can be estimated. Here, we experimentally demonstrate an array of 101 band-pass transmission filters that span the mid- to long-wave infrared (6.2 to 14.2 μm). Each filter comprises a sub-wavelength array of coaxial apertures in a gold film. As a proof-of-principle demonstration of the FADA approach, we use a Fourier transform infrared (FTIR) microscope to record the optical power transmitted through each filter. We provide this information, along with the transmission spectra of the filters, to a recursive least squares (RLS) algorithm that estimates the incident spectrum. We reconstruct the spectrum of the infrared light source of our FTIR and the transmission spectra of three polymer-type materials: polyethylene, cellophane and polyvinyl chloride. Reconstructed spectra are in very good agreement with those obtained via direct measurement by our FTIR system.
Tuesday 30th March 2021: 1 - 2pm: 1 - 2pm on Zoom
Title: All in a spin: rotational dynamics of trapped, levitated microparticles
Speaker: Prof. Kishan Dholakia
School of Physics & Astronomy, University of St Andrews, Scotland
Trapping microparticles in vacuum has led to the burgeoning area of levitated optomechanics. Here we will describe recent work on rotating particles in vacuum. This offers a rich playground for dynamics. In particular we describe how we can attain very high rotation rates by spin angular momentum transfer and observe optical binding of particles in vacuum. For a single particle in vacuum stochastic, thermal fluctuations combine with nonconservative optical forces to break detailed balance and produce increasingly coherent, apparently deterministic motion. In turn this leads to the highest Q value ever reported for a vacuum traded microparticle opening up new studies of sensors.
Wednesday 24th March 2021: 3 - 4pm on Zoom
Title: Ultrathin multimodal endoscopic probes
Speaker: Dr. Jiawen Li
Lecturer, Faculty of Health and Medical Sciences, The University of Adelaide, Australia
Preclinical studies and clinical diagnostics increasingly rely on techniques to visualize internal organs at high-resolution via endoscopes. Miniaturized endoscopic probes are necessary for imaging small luminal or delicate organs (e.g., small airways, blood vessels and bile ducts) without causing trauma to tissue. However, current fabrication methods limit the performance of these ultrathin endoscopic probes, resulting in 1) low resolution or depth of focus and/or 2) incapability to conduct multimodal measurements.
This talk will introduce our latest research to address the above two fundamental challenges, working towards widespread applications of endoscopic probes. To overcome the first challenge, we have utilized 3D micro-printing technology to fabricate freeform optics directly on an optical fiber to correct nonchromatic aberrations of an ultrathin endoscopic probe. To allow multimodal studies of biological processes with high spatial heterogeneity in vivo (i.e., the second challenge), we have developed a suite of ultrathin fiber probes that allow measurements of the microstructural (imaging) and physical/chemical (sensing) information deep in living organisms. This advance enables image-guide sensing, and simultaneous co-localised measurements of complex biological process.
Wednesday 10th March 2021: 4 - 5pm on Zoom
Title: Selective nanoparticle manipulation using two color techniques with a nanofiber
Speaker: Assoc. Prof. Mark Sadgrove
Physics Department, Tokyo University of Science, Japan
I will discuss some recent results regarding the use of a two-color, counter-propagating nanofiber mode technique to selectively trap or transport metal nanoparticles according to their size. Although the two color technique shares some similarities with the well established two color traps for atoms using a nanofiber, to the best of my knowledge the present method is unique in that it relies on the behavior of the modes in the fiber taper to achieve a trapping potential.
The difference in resonant wavelengths of the metal nanoparticles leads to a dichotomous regime in which one particle size can be trapped, while the other is transported - effectively a sieve where the size of the particles retained and the size of those which pass through is set by the relative mode power. The results are arxived, but still unpublished, and constructive comments and criticism are most welcome.
Wednesday 3rd March 2021: 5-6pm on Zoom
Title: Flexible Quantum Control and Simulation in a Quantum Gas Microscope
Speaker: Dr. Carrie Ann Weidner
Department of Physics and Astronomy, Aarhus University, Denmark
Abstract:The first demonstrations of quantum gas microscopes (QGMs) [1,2] in 2009-10 opened up a new avenue for research in quantum simulation in few- and many-body systems. The Rb-87 quantum gas microscope at Aarhus University allows for manipulation of the internal states of the individual atoms  and near-arbitrary control of the potential the atoms experience. The atoms may be imaged using traditional fluorescence microscopy or via spatially-selective, minimally destructive Faraday imaging [4-5]. As a result, our experiment provides a novel and flexible platform for a variety of studies in quantum control and simulation. So far, all work with QGMs has been limited to the study of dynamics in one and two dimensions, but our world exists in a three-dimensional space. Recently, we have demonstrated three-dimensional tomography of the atom distribution in our microscope by taking several fluorescence images of the same trapped atoms while varying the focal plane of the imaging system . This work represents a stepping stone towards the extension of QGM-based quantum simulation into three dimensions.
In this talk, I will describe the basic working principles of our experiment. Then I will dive into the tomography work and its implications for future explorations. Finally, I will describe the possibilities of opening our experiment up for use with the general public and research community, work that builds on our previous demonstrations of BEC optimization [7-8].
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Thursday 25th Feburary 2021: 4 - 5pm on Zoom
Speaker: Prof. Dr. Lukas Novotny
Photonics Laboratory, ETH Zurich, Switzerland
Localized optical fields exert both conservative and non-conservative forces on polarizable objects. These forces can be used to control and manipulate the motion of atoms, molecules or nanoparticles. In this presentation I discuss our experiments with optically levitated nanoparticles in ultrahigh vacuum. Using active feedback control we cool the particle’s center-of-mass motion to near strand-still and measure its quantum zero-point energy. A laser-trapped particle in high vacuum defines a harmonic oscillator with ultrahigh quality factor. I will show that its damping is dominated by photon recoil heating. A levitated nanoparticle is a model system for studying non-equilibrium processes, nonlinear interactions, and ultrasmall forces.
Tuesday 16th Feburary 2021: 4 - 5pm on Zoom
Title: Biomedical and environmental applications of plasmonic sensors
Speaker: Dr. Francesca PINCELLA
Senior Lecture, Institute for Chemical Research, Kyoto University, Japan
In this talk, I will introduce the most prominent sensing techniques that rely on plasmon resonances, namely surface plasmon resonance (SPR), localized surface plasmon resonance (LSPR) and surface-enhanced Raman scattering (SERS). The talk will start with an introduction to plasmonics, followed by an overview of the booming fields of nanoplasmonics and nanotechnology, with particular attention devoted to chemistry-based bottom-up approaches. I will then report my experience in the design, synthesis and deposition of two-dimensional plasmonic arrays for the development of versatile and cheap plasmonic sensors for the detection of various biomolecules and biopolymers, from glucose for diabetes diagnostics to lignin for wood utilization and processing. A few examples of SPR-, LSPR- and SERS-based sensors will be discussed, with emphasis on the current challenges linked to the widespread real-world applications of these technologies.
Tuesday 9th Feburary 2021: 1 - 2pm on Zoom
Title: Optical microfibers: from low-loss waveguides to miniature optical sensors
Speaker: Prof. Limin Tong
College of Optical Science and Engineering, Zhejiang University, China
Optical microfibers and nanofibers fabricated by physical drawing of glass fibers have (sub-)wavelength-scale diameter, extraordinary surface smoothness and diameter uniformity, which bestow them with low optical loss, excellent mechanical strength and flexibility. A waveguiding microfiber can offer tight optical confinement, high fractional evanescent fields and enhanced surface field intensity, making it highly sensitive to environmental changes in the optical near fields and thus favorable for optical sensing on micro- and nanoscale. In this talk, we’ll firstly give a brief introduction to microfiber optics, followed by typical results in microfiber fabrication and characterization. Then, we’ll focus on functionalization and application of microfibers for optical sensing. Finally, we’ll give a brief summary and discuss the challenges and opportunities in this field.
Wednesday 3rd Feburary 2021 : 4 - 5pm on Zoom
Title: The creation and control of structured light
Speaker: Prof. Andrew Forbes
University of the Witwatersrand, South Africa
Structured light is a term used to describe optical fields that have been tailored in their spatial intensity, phase and polarisation distributions, and may even be extended to include tailored light in the time and frequency domain too. Structured light has found many applications, including optical manipulation, atom optics, high-dimensional quantum information processing, laser materials processing, light-matter interactions and novel lasers to name a few, spanning both fundamental science and applications. In this colloquium, I will explore how to create, manipulate and detect structured light fields, and cover some example applications in classical and quantum optics. It will be a tutorial style talk that covers the basics of the field while hinting at what such control could bring in the laboratory.
Andrew has at various times in his career found himself as teacher, janitor, secretary, receptionist, web-master, systems engineer, sales rep, manager, director, and sometimes a scientist. He is presently a Distinguished Professor within the School of Physics at the U. Witwatersrand (South Africa) where in 2015 he established a new laboratory for Structured Light. Andrew is active in promoting photonics in Africa, a founding member of the Photonics Initiative of South Africa and initiator of South Africa’s Quantum Roadmap. He is a Fellow of SPIE, the OSA, the SAIP, and an elected member of the Academy of Science of South Africa. He holds an A-rating by the South African NRF, 3 honorary professorships, is editor-in-chief of the UK’s Journal of Optics and sits on the editorial board of three other international journals. Andrew has won several awards, including the NSTF national award for his contributions to photonics in South Africa, the Georg Forster prize from the Alexander von Humboldt Foundation for outstanding contributions to photonics, and the SAIP Gold Medal, the highest award for physics in South Africa, making him the youngest winner to date. Andrew spends his time having fun with the taxpayers’ money, exploring structured light in lasers as well as classical and quantum optics.
Wednesday 27th January 2021 : 4 - 5pm on Zoom
Title: Temperature in plasmonic nano-optical trapping
Speaker: Dr Jérome Wenger
CNRS research director, Institut Fresnel, France
Plasmonic nanostructures generate strong field gradients enabling efficient optical trapping of nano-objects. However, the infrared laser used for trapping is also partly absorbed into the metal. This leads to Joule heating and the generation of a local temperature gradient. Several questions then come out: how large is the temperature increase inside the plasmonic nanodevice? How to control it without changing the infrared laser power? And most importantly, what is its influence on the trap potential? In this seminar, I will present some of our current answers to these questions. Different fluorescence-based techniques will be presented to measure locally the temperature. This will lead to a discussion on the influence of the plasmonic design on the local temperature. We have also derived a different approach to experimentally measure the trap stiffness in plasmonic nanotweezers. Using this methodology, we discuss the optimization of the trap performance based on the plasmonic design. We also reveal the major role played by the surfactant added to the solution and relate this effect to the thermophoretic force.
Wednesday 20th January 2021 : 4 - 5pm on Zoom
Title: From 2D and 3D billiards for light to mesoscopic optics
Speaker: Prof. Dr. Martina Hentschel
Theoretical Physics of Complex Dynamic Systems, Technische Universität Chemnitz, Germany
The investigation of the propagation of light in mesoscopic, i.e. often micrometer-scale, systems is a rich subject providing insights ranging from quantum chaos in open systems to new schemes for realizing microlasers. The concept of quantum-classical, here wave-ray, correspondence, proves to be a useful tool in many contexts. The confinement of light in optical microresonators is due to total internal reflection, leading to billiards for light. We illustrate the consequences of a chaotic light dynamics and discuss their impact on the far-field emission characteristics of individual optical microcavities with and without internal sources, and for cavity arrays.
The propagation of electromagnetic waves in three-dimensional optical microcavities requires to pay attention to the evolution of the light's polarization as a new degree of freedom. In systems like dielectric Möbius-strips or cone-shaped microtube cavities, the polarization state of resonant whispering gallery-type modes may differ strongly from the reference case of homogeneous cylinders. Whereas we find that the polarization of the electromagnetic field follows the wall orientation in thin Möbius strips, thereby reflecting the accumulated geometric phase, we observe that the electromagnetic field ignores the Möbius topology when the strip thickness is increased. Breaking of symmetries further influences the morphology of resonances and can induce a transition from linear to elliptical polarization that is both of theoretical interest from the point of view of spin-orbit interaction of light and their interpretation in terms of Berry phases, and relevant for potential applications. Spin-orbit coupling of light can be observed in cone-like systems.
Monday 18th January 2021 : 2 - 3pm on Zoom
Title: Metaphotonics and metasurfaces
Speaker: Prof. Yuri Kivshar
Nonlinear Physics Center, Research School of Physics, Australian National University, Australia
ITMO University, St. Petersburg, Russia
Future technologies underpinning high-performance optical communications, ultrafast computations and compact biosensing will rely on densely packed reconfigurable optical circuitry based on nanophotonics. For many years, plasmonics was considered as the only available platform for subwavelength optics, but the recently emerged field of Mie resonant metaphotonics provides more practical alternatives for nanoscale optics by employing resonances in high-index dielectric nanoparticles and their structures such as metasurfaces. In this talk, I aim to discuss some recent advances in the physics of dielectric Mie-resonant nanostructures with high quality factors (Q factors) for efficient spatial and temporal control of light by employing multipolar Mie resonances and bound states in the continuum, with applications of these concepts to nonlinear optics, nanolasers, and sensing.
Yuri Kivshar received PhD degree in 1984 in Kharkov (Ukraine). From 1988 to 1993 he visited and worked at several research centers in USA and Europe, and in 1993 he moved to Australia where he established Nonlinear Physics Center. His research interests include nonlinear physics, metamaterials, and nanophotonics. He is Fellow of the Australian Academy of Science, OSA, APS, SPIE, and IOP. He received many national and international awards including Pnevmatikos Prize in Nonlinear Science (Greece), Lyle Medal (Australia), Lebedev Medal (Russia), The State Prize in Science and Technology (Ukraine), Harrie Massey Medal (UK), Humboldt Research Award (Germany), SPIE Mozi Award (USA).
Wednesday 13th January 2021: 4 - 5pm on Zoom
Title:Interfacing a single quantum emitter to fiber-guided photons
Speaker: Prof. Kali Prasanna Nayak
Center for Photonic Innovations, University of Electro-Communications, Japan
Engineering light-matter interaction at single quanta level has been a long-standing challenge for realizing optical quantum information technology. One key requirement is to isolate and confine atoms and photons to subwavelength dimensions to realize an efficient quantum interface. In this context, tapered optical fibers with subwavelength diameter waist, optical nanofibers, and nanofiber-based cavities provide a unique fiber-in-line platform for optical quantum interfaces. The key point of the technique is that the fiber-guided light can have strong transverse confinement while interacting with the surrounding medium in the evanescent region. Furthermore, the optical nanofiber-based cavities provide unique possibilities for cavity QED approach to realize an efficient quantum interface. In this seminar, I will discuss the key challenges and experimental developments towards interfacing single quantum emitters to nanofiber-guided modes.
Tuesday 22nd December 2020: 4 - 5pm on Zoom
Title: Nano-Material Optical Manipulation and Structural Order Control
Speaker: Prof. Keiji Sasaki
Research Institute for Electronic Science, Hokkaido University, Japan
Optical trapping and manipulation based on optical forces are promising tools for positioning, transporting, and aligning fine particles without mechanical contacts. We aim to realize the ultimate performance of nano-material optical manipulation. We are challenging how small particles and molecules can be trapped and selectively positioned, and how high spatial-resolution and precision can be achieved for the manipulation and motion-control of nanomaterials. For this purpose, we are trying to design optical forces exerted on nanoparticles and molecules by shaping the amplitude, phase, and polarization of the optical electric field on single-nanometer scale. Here, we present our research progresses on nano-material manipulation using optical nanofiber and plasmonic nanostructures.
1. Optical selection and sorting of nanoparticles according to quantum mechanical properties
We experimentally demonstrated selective transportation of nanodiamonds (NDs) with and without nitrogen-vacancy centers (NVCs). Quantum resonant absorption of the NVCs induces the pushing optical force, while the ND having high refractive index causes the scattering force. We prepared a tapered optical fiber with ~400-nm diameter, that has characteristics of single-mode propagation with diffraction-limited cross-section over millimeter length. Two laser beams with 532-nm (in resonance of NVC) and 1064-nm (out of resonance of NVC) wavelengths were introduced into the nanofiber from both ends, so that the absorption force can be extracted by balancing the scattering forces with the counter-propagating beams. 50-nm NDs were attracted by the gradient force of the evanescent field around the nanofiber, and moved along the fiber by the absorption and scattering forces. By adjusting the powers of two lasers, we succeeded in selective transportation of NDs, where NDs with NVCs slowly move in one direction whereas the NDs without NVC move in the opposite direction. Furthermore, we also propose a methodology for precisely determining the absolute values of absorption cross-sections for single nanoparticles by monitoring the optically driven motion, called as “optical force spectroscopy”. Optical force spectroscopy sensitively measures the interaction between light and nanoparticles separately from the scattering effects, based on the photon momentum change and not the energy change.
2. Nano-space manipulation of nanoparticles with designed plasmonic fields
Recently, we propose a novel approach to forming the single-nanometer-scale localized fields of optical vortex (Laguerre-Gaussian mode) by employing the whispering gallery mode plasmonic nano-cavities. We designed the tailored plasmonic structure consisting of metal multimer surrounding a nano-gap. This metal structure makes it possible to localize the optical vortex field into the gap space with conserving the high-order orbital and spin angular momenta (OAM and SPM). The transfer of the angular momenta from this nano-vortex fields to molecules or nanoparticles induces rotational radiation pressure, i.e., optical torque, and gradient force directed to the center, which causes nano-vortex flow of molecules/particles and may lead to chiral structuring of molecule/particle assemblies. We succeeded in rotational manipulation of a polymer nano-bead with a gold triangle trimer structure. The plasmonic nanostructure was illuminated with a circularly polarized beam of a near-infrared laser, so that the nano-sized field with the OAM and SPM is formed within the gap. The motion analysis of the nanoparticle indicated the orbital rotation with <50-nm diameter. We will explain detailed analyses of the rotational motions and their relations to the chirality of the plasmonic fields.
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Tuesday 15th December 2020: 12 - 1pm on Zoom
Title: From cold atoms to living cells with sculpted light
Speaker: Prof. Halina Rubinsztein-Dunlop
Director of Quantum Science Laboratory, School of Mathematics and Physics, The University of Queensland, Australia
The ability to sculpt light fields using spatial light modulators (SLM) or Digital Micromirror Devices (DMD) has given us tools of choice for the production of configurable and flexible confining potentials at the nano and micron-scale. We categorise the techniques used to create sculpted light to those based on time averaged methods and those utilising spatial light modulators in either Fourier plane or direct imaging plane. A rapid angular modulation of Gaussian beam with a two-axis acousto-optic modulator, AOM, can be used as highly configurable time-averaged traps. This type of modulation has found applications in holographic tweezers and ring traps for ultra-cold atoms. SLMs can be used as a way of producing extremely versatile structured light. SLMs in Fourier plane which control the phase and /or amplitude of an input Gaussian beam, with the pattern representing the spatial Fourier transform of the desired amplitude pattern. The optical system then focuses this sculpted light pattern to the plane containing the system of interests, performing a Fourier transform and recovering the desired pattern. Yet another way for production of dynamical, fast and flexible structured light fields is using digital micromirror devices (DMD), which is based on direct imaging of amplitude patterns. DMD can configure the amplitude of an input beam either in the Fourier plane or in a direct imaging configuration. Sculptured light produced using these methods promises high flexibility and an opportunity for trapping and driving systems ranging from studies of quantum thermodynamics using ultra cold atoms to trapping and manipulating nano and micron-size objects or even using these objects inside a biological cell.
Friday 11th December 2020: 2 - 3pm on Zoom
Title: Ultrafast quantum simulator with attosecond precision at ultracold temperatures
Speaker: Prof. Kenji Ohmori
Institute for Molecular Science, National Institutes of Natural Sciences (NINS), Japan
Many-body correlations govern a variety of important quantum phenomena including the emergence of superconductivity and magnetism in condensed matter as well as chemical reactions in liquids. Understanding quantum many-body systems is thus one of the central goals of modern sciences and technologies. Here we demonstrate a new pathway towards this goal by generating a strongly correlated ultracold Rydberg gas with a broadband ultrashort laser pulse. We have applied our ultrafast coherent control with attosecond precision  to a strongly correlated Rydberg gas in an optical dipole trap, and have successfully observed and controlled its ultrafast many-body electron dynamics [2-4]. This new approach is now applied to an atomic BEC, Mott insulator lattice, and arbitrary array assembled with optical tweezers to develop into a pathbreaking platform for quantum simulation of strongly correlated many-body electron dynamics on the ultrafast timescale [5-7].
This project is in progress in tight collaboration with Hamamatsu Photonics K.K.
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 UC Boulder / NIST Quantum Technology Website: CUbit Quantum Initiative "A metal-like quantum gas: A pathbreaking platform for quantum simulation".