Biomedical applications of nonlinear microscopy

Nonlinear microscopy is an expanding field and is finding new applications in the biomedical sciences. There is an ongoing technological development which provides answers to questions in the biomedical and biophysical sciences, which are difficult to answer without this technique.

Label-free and three dimensional imaging are important advantages of nonlinear microscopy compared to standard optical investigation techniques. An overview over various nonlinear interactions which are utilized in the biophysical sciences will be presented along with current applications from our own group.

Lysozyme crystals in optical tweezers

Momentum transfer from light to small particles can be used to overcome Brownian motion, trapping them with a tightly focused beam.  If the particle is anisotropic, in either its shape or optical properties, the orientation of the particle can also be controlled.  Lysozyme crystals are birefringent and have a highly reproducible morphology, with an aspect ratio that can be varied as a function of growth conditions. They thus represent an opportunity for a detailed study of the relative importance of the shape and optical anisotropy.

Growth of high quality protein crystals is important for structural biology studies, and we have explored the use of tweezers for growth of lysozyme from seeds.  Optical trapping has been reported for polymer molecules on the order of the size of some globular proteins, which suggests that it may be possible to nucleate a crystal in a chosen location, away from the walls of the container.  Preliminary experiments in this direction will be described.

Norse Celestal Mythology - Norse Constellations

Most people have some knowledge of the Greek mythology and that most of the western constellations originate from them. But there are a number of different star myths, as a Scandinavian it is natural to think about the Norse mythology and constellations. We know that the Vikings were skillful sailors and must have been able to navigate, something that indicate a deeper knowledge of astronomy and quite possible constellations based on norse mythology. This is an attempt to shed some light on the Norse constellations and star names.

The Stormy Sun - how does it affect our technology based society and climate?

Our Sun appears to be a quiet, boring yellow sphere gliding over the sky each day. But the Sun is a stormy beast - affecting the Earth in many ways. Solar storms interact with our magnetosphere and create northern lights and space weather. It is well known that it affects our technology based society by interrupting radio-communication, navigation and power distribution as well as posing harm to humans in Space. Today, new satellites are monitoring the Sun 24 hours every day. They provide space weather forecasts and warn about solar storms that may hit the Earth just like the weather forecasts we see on TV every day about the weather.

Numerous attempts have been made over the years to link various aspects of solar variability to changes in the Earth's climate. In recent years there has been a growing concern about the possible anthropogenic forcing of climate change through the increasing atmospheric content of greenhouse gases. As a result the connection between solar variability and global climate change is sometimes considered a very controversial area of research. Does the Sun contribute to climate change? A brief discussion about solar forcing and natural climate climate change will be given.

Quantum optics with microwave photons in superconducting circuits; dynamical Casimir effect and artificial atoms

We have been able to observe the Dynamical Casimir Effect (DCE) in a superconducting circuit consisting of a coplanar transmission line with a tunable electrical length [1]. The rate of change of the electrical length can be made very fast (a substantial fraction of the speed of light) by modulating the inductance of a superconducting quantum interference device at high frequencies (~10 GHz). In addition to observing the creation of real photons, we detect two-mode squeezing in the emitted radiation, which is a signature of the quantum character of the generation process. This phenomenon was predicted 40 years ago and has not been observed until now.

We also study an artificial 3 level atom in the form of a transmon qubit coupled to superconducting 1D transmission line [2]. Strong interaction between the artificial atom and photons is revealed in the reflection of propagating microwaves and substantial extinction (99.6%) of the transmission has been observed. A strong control pulse, at the frequency corresponding to the transition between the two upper states, is used to route a weak probe tone at lower transition frequency. The maximum on-off ratio is 99% with a rise and fall time on the order of 10 ns. This fast controllable router provides a fundamental building block for quantum optics on chip.

1. C.M. Wilson et al. Nature, 479, 376 (2011).
2. I.-C. Hoi et al. Physical Review Letters, 107, 073601 (2011)

Recent Results from the ATLAS experiment on Searches for the Standard Model Higgs Boson

The so-called Higgs mechanism, which gives masses to otherwise massless fundamental particles, has been an integral theoretical part of the Standard Model (SM) of elementary particles and the forces that act between them since the 1960's. Although the SM has a number of shortcomings, it has been highly successful at incorporating and predicting a wide variety of experimental phenomena for nearly half a century.

However, it has not yet passed one "acid test" - the prediction of the existence (but not the mass) of the elusive Higgs boson. During 2011 the ATLAS and CMS experiments each collected data from about 5 inverse femtobarns of proton-proton collisions at the Large Hadron Collider (LHC) at CERN, which gave the experiments sensitivity to detect Higgs boson production over an unprecedented wide range of  mass.

The tantalizing results very recently published by the ATLAS collaboration on their searches for the SM Higgs boson in the 2011 data will be presented. The corresponding results of the CMS experiment will be summarized. Since the LHC results are by no means conclusive, the prospects for the potentially decisive 2012 run of the LHC will be briefly discussed.

Upper solar atmosphere and solar wind

A brief overview of the sun and sun-earth-space environment will be given. The upper solar atmosphere and wind are then described in more detail.

The solar wind is a flow of supersonic particles originating at the sun and filling the space between the sun and interstellar medium. The interest for the solar wind is mainly due to two reasons:

1. The solar atmosphere/wind is an example for the atmospheres of other stars which are much harder to observe.
2. It can have a large impact on the earth space environment which has become increasingly important due to the large number of artificial satellites.

The talk will focus on the basic physics of the upper solar atmosphere/wind and show how the energy loss mechanisms available to the solar atmosphere (radiation and heat conduction) determine the properties of the atmosphere/wind.

Shaping the Future of Manipulation

Advanced photonics using novel holographic beam shaping to alter the phase, amplitude and polarisation of light has come to the fore in recent years. Light may exert forces for trapping and separately be used for exquisite cell nanosurgery and controlled transfection. With regard to traps, elaborate two and three dimensional light patterns (beam shaping) can create an optical landscape. Particle and cellular motion on such a landscape will enhancing our ability to move and sort particles and perform microrheology [1-3]. In terms of nanosurgery shaped light may assist cell transfection of various therapeutic agents [4]. The use of 'non-diffracting' shaped light fields such as Bessel and Airy modes have continued to play a key role in both of these fields. Such shaping now even opens up prospects for trapping, nanosurgery and imaging through turbid media (disordered materials) [5].

1. K. Dholakia and T. Cizmar, Nature Photonics 5, 335-342 (2011).
2. M. Ploschner, M. Mazilu, T. Cizmár, and K. Dholakia, Opt. Express 19, 13922-13933 (2011).
3. Y. Arita, A. W. McKinley, M. Mazilu, H. Rubinsztein-Dunlop, and K. Dholakia, Anal. Chem. 83, 8855 (2011).
4. D. J. Stevenson, F. J. Gunn-Moore, P. Campbell, and K. Dholakia, Journal Of The Royal Society Interface 7, 863--871 (2010).
5. T. Cizmar, M. Mazilu, and K. Dholakia, Nature Photonics 4, 388--394 (2010).

Domain imaging and exchange coupling in heteromagnetic thin films and nanostructures

Since the early days of information technology, magnetic recording has fueled   research on magnetoelectronic devices; a milestone of this endeavor being the discovery of spin-selective electron scattering in magnetic multi-layers and the giant magnetoresistance (GMR) in 1988, which rapidly led to magnetic storage of digital information at unprecedented densities. The operation of spintronic devices, such as GMR spin valves and magnetic tunnel junctions, relies on an effect known as exchange bias (EB) at the interface between a ferromagnic (FM) and an antiferromagnetic (AFM) layer, which serves to pin the magnetization of a FM reference layer in these devices. Several models describing EB recognize the formation of domains in the antiferromagnet as important to the strength of this interface exchange coupling. The recent development of novel tools for magnetic microscopy, combined with the continued scaling of magnetic storage and spintronic devices, have stimulated research on the domain structure in magnetic nanostructures.

While the formation of domains in FM micro- and nanostructures is well understood and has been extensively studied over the past decades, this is not so for antiferromagnets, where probing the magnetic order is made difficult by the absence of a net magnetization. In this seminar, recent experiments which address the impact of shape and crystalline orientation on the AFM and FM domain patterns of embedded nanostructures defined in epitaxial perovskite (LaFeO₃) thin films and (LaFeO₃/La_0.3Sr_0.7MnO₃) bilayers will be discussed. Synchrotron radiation soft x-ray spectromicroscopy was used to image the AFM and FM domain contrast with a lateral resolution of less than 50 nm, relying on linear and circular magnetic dichroism in the L-edge absorption spectra of the respective magnetic ions. The impact of shape and crystalline orientation on the domain formation, as well as the interface exchange coupling between the ferromagnet and the antiferromagnet in the bilayer nanomagnets will be discussed.

Transition metal doped II-VI materials: physics and applications

The talk discusses material, spectroscopic, laser and nonlinear optical properties of wide-band Cr²⁺-doped II-VI semiconductors - a rather new class of active and passive photonic materials, developed in the last decade – and highlights the most recent break-throughs in their applications for lasers and laser technology based applications.

In contrast to conventional dielectric laser materials the Cr²⁺-doped II-VI compounds combine properties of semiconductors with that of the traditionally used dielectric active media. The semiconductor nature determines strong nonlinear optical response of these materials, giving rise to charge transport and photorefractive-like phenomena, harmonic generation and parametric processes, but also self-focusing effects. The latter phenomenon is the basis for the Kerr-Lens mode-locking – the way to generate ultimately short pulses of only single optical cycle of the electric field.

The talk discusses principles and basic physics of vibronic laser materials, which are distinguished by their ability to support the shortest, down to single optical cycle pulse durations and the ultimately broad among existing lasers tuning ranges and gain. In particular, the issues are being discussed, which are specific to infrared lasers: wavelength scaling rules, material issues and nonlinear-optical properties. Further, recent developments in such lasers as Cr.ZnSe, Cr:ZnS as well as recently proposed mixed Cr:ZnS_xSe_1-x  and Cr:CdS are being reviewed.

The strong revival of research interest in these materials in the last few years is explained by the announcement of the extremely efficient (up to >70 % slope efficiency) laser operation at room-temperature. The latest most remarkable break-through developments with this laser in our group were: 1) the broadest continuous tuning of any laser, extending from 1.97 to over 3.33 microns, 2) the first truly Kerr-lens mode-locked operation, both from Cr²⁺-ZnSe as well as in recently developed in our group few cycle Cr²⁺-ZnS – a viable competitor to Cr²⁺-ZnSe in terms of achievable power and pulse duration, 3) simultaneous generation of the fundamental and frequency doubled pulses from the mode-locked ceramic Cr:ZnSe laser, 4) soliton propagation as well as supercontinuum generation in novel infrared specialty fibers.

Summarizing, in the mid-IR wavelength range above 2 microns the Cr²⁺-doped lasers proved to be viable competitors to the conventional semiconductor lasers or more complex laser systems, based on nonlinear optical frequency conversion in such applications as medicine, trace gas monitoring, remote sensing, spectroscopy, metrology, laser radars, optical communications, and all-optical switching. Combined with Er- and Tm-fiber lasers they hold promise to be the first mid-IR fiber lasers.

Superconductivity and electrical power engineering: What is the key to industrial applications?

Superconductivity is a phenomenon where materials can carry electrical current completely without resistive losses when cooled down to very low temperatures. For electrical power engineers this is a very attractive property, and ever since its discovery more than 100 years ago many have predicted that superconductors will revolutionize the way we are generating, transmitting and using electrical energy. This has not happened yet, even though the discovery of the so-called "high-temperature" superconductors in 1986 facilitates simpler cooling schemes.

The talk will – from an electrical engineer's perspective – try to explain why, but also give examples of commercial products where superconductor technology is being used and provides obvious benefits.
 

Magne Eystein Runde, Department of Electric Power Engineering, NTNU
Magne E Runde, SINTEF Energy Research