Vladimir M. Shalaev is an American physicist of Russian descent known for his work in the fields of nanophotonics, plasmonics, and optical metamaterials [1]-[4]. Vladimir (Vlad) M. Shalaev is currently the Robert and Anne Burnett Distinguished Professor of Electrical and Computer Engineering [5], Professor of Biomedical Engineering [6] and Professor of Physics [7] at Purdue University. Prof. Shalaev also serves as Scientific Director for Nanophotonics at Purdue University's Birck Nanotechnology Center [8].
Shalaev received a Master of Science Degree in physics with honors in 1979 from Krasnoyarsk State University (Russia) and a PhD Degree in physics and mathematics in 1983 from the same University. His doctoral work involved theoretical analysis of resonant interaction of laser radiation with gaseous media, in particular i) Doppler-free multi-photon processes in strong optical fields and their applications in nonlinear optics [9], spectroscopy [10] and laser physics [11], and ii) the (newly-discovered then) phenomenon of light-induced drift of gases [12] (here and thereafter in this article, only selected, representative papers by Shalaev are cited; for the complete list of his publications visit the Publications page of this website).
In 1983 Shalaev joined the Faculty of Krasnoyarsk State University, Dept. of Physics, and research staff of L.V. Kirensky Institute of Physics (Krasnoyarsk, Russia) [14] where he conducted research in the area of i) resonant nonlinear optics of gaseous media [15], ii) light-induced gas kinetics [16], and iii) linear optics and optical non-linearities of fractal objects, such as fractal clusters and rough films [17], [18]. In their collaborative work [17], Shalaev and Stockman were the first to point out that in clusters formed by conducting nano-particles, the fractal geometry underlies sharp localization of light-induced electron-density oscillation modes – surface plasmons. Inside the nanometer-sized plasmon confinement areas, colloquially known as “hot spots”, the amplitude of the (oscillatory) local electric field can exceed that of the applied external field by several orders of magnitude. This local field enhancement in turn leads to greatly amplified optical responses from impurity particles (dopants) bound to a fractal cluster resulting in i) giant Raman scattering [17] and ii) enhanced non-linear optical phenomena, including Coherent Anti-Stokes Raman Scattering (CARS) and degenerate-four-wave-mixing-based Optical Phase Conjugation [18]. Generation of higher optical harmonics was also found to be enhanced, although to a lesser extent [18].
In 1990 Shalaev was awarded a Humboldt Foundation Fellowship and, as a Humboldt Fellow, in 1990-1991 he continued his research into optics of fractal media at Heidelberg University in Germany and at Paris-Sud University in France [19]- [21]. In work [19], inherent optical non-linearities of metal fractal clusters (in contrast with that of impurity particles adsorbed on cluster's monomers [18]) were investigated theoretically and experimentally, and the conclusion was reached that degenerate four-wave mixing/optical phase-conjugation was enhanced by six orders of magnitude, as a result of aggregation of silver nano-particles into fractal clusters. The authors themselves summed up their findings as follows: "The studies of metal fractal clusters have shown them to Ье а promising nonlinear optical medium with а unique comЬination of the following properties: giant nonlinearity, rapid response, broadbandness and spatial-frequency-polarization selectivity of interaction with radiation" [19].
In 1991-1993 Shalaev carries on his studies as a Research Associate Professor at University of Toronto (Canada), Department of Chemistry [22]-[24]. During this time, with the Moskovits group, he demonstrated the highly localized optical modes - "hot spots" - for fractal systems [23]. He also predicted that nonlinear phenomena in random systems can be enhanced not only because of the high local fields in hot spots but also due to the rapid, nanoscale spatial variation of these fields in the vicinity of hot spots, which serves as a source of additional momentum and thus enables indirect electronic transitions [24].
In 1993 Shalaev joins the Faculty of New Mexico State University, Department of Physics (Las Cruses, New Mexico, USA). Research carried out in this period includes developing a theory (in collaboration with A. K. Sarychev) of giant Raman scattering from semi-continuous metal films [25], [26] and surface-enhanced optical nonlinearities of such films, in particular those responsible for the optical Kerr-effect, four-wave mixing, second and third-harmonic generation [27]. The nonlinear optical signals had been found to come from nm-sized areas corresponding to the plasmon modes of the film. It was established that near the percolation threshold of a semi-continuous metal film, Raman scattering from the molecules absorbed on the surface of the film is enhanced on average by more than six orders of magnitude. The enhancement is associated with the excitation of the localized electromagnetic eigenmodes of the film which have the geometrical form of spatially separated, sharp, large field-amplitude peaks.
In 2001, Shalaev joins the Faculty of Purdue University, where he serves now as Bob and Anne Burnett Distinguished Professor of Electrical and Computer Engineering [5].
Significant part of the research carried out by Shalaev since early 2000s until the present time involved optical metamaterials (MMs). Optical MMs are artificial, nanostructured media (often containing a metallic/plasmonic component) that display unique optical properties (so far) not observed in naturally occurring materials. One of the most spectacular features of optical MMs that can be achieved through deliberate design is negative index of refraction, and the resulting exotic optical media are referred to as negative-index metamaterials (NIMs) [28]. Prospective applications for NIMs include superlens capable of imaging objects and fine geometrical features that are much smaller in size than the wavelength of light, optical nanolithography, nanocircuits, and metacoatings that can render objects invisible [29]. Shalaev with co-workers werethe first to experimentally realize an optical NIM [29]. They achieved a negative index of refraction of -0.3 at the optical telecommunication wavelength, 1.5μm, using a double-periodic array of gold nano-rods: the value of the refractive index was inferred from experimental data on amplitudes and phases of reflected and transmitted light.
One possible approach to engineering negative index of refraction, which was taken by the authors of [30], involves strong magnetic response of the material at optical frequencies. Generally, the response of naturally occurring materials to the magnetic component of electromagnetic waves at optical frequencies is weak compared to their response to the electric component. Various metamaterial-based approaches have been employed to produce strong, resonant optical magnetism, thus extending and enhancing light-matter interactions. Shalaev with co-workers experimentally demonstrated nanostructured composites displaying strong magnetic response across the whole visible spectrum [31]. They employed metamaterials consisting of arrays of paired thin silver rods and used geometrical parameters of the nanostructure to control its resonant magnetic properties.
Electromagnetic energy dissipation in the metallic part of metamaterial nanostructure has been a major obstacle hindering technological application of metamaterials. Shalaev with co-workers were the first to experimentally demonstrate the principal possibility of compensating for energy dissipation in NIMs through incorporation into the metamaterial design of an optical gain medium [32].
Shalaev made a significant contribution to transformation optics (TO) - a new branch of electromagnetism which is based on the form-invariance of Maxwell's equations under coordinate transformations (provided the electric permittivity and magnetic permeability of the medium are appropriately transformed) [33]-[35]. TO provides the means for engineering inhomogeneous, metamaterial-based optical media where light propagates in a predefined, almost arbitrarily prescribed manner [36]. Shalaev contributed original designs of some of the most important TO devices: "invisibility cloak" - a device which guides light around itself, making the “cloak” and an object inside it invisible [37], a hyperlens magnifying nanometer-scale geometrical detail and producing a viewable far-field image, and light concentrator performing the opposite function - effectively collecting light and focusing it into nano-scale spatial domains [36].
Prof. Shalaev with co-workers, most notably - Prof. A. Boltasseva, were among the first to recognize the importance of introducing new plasmonic materials that would help bring to fruition the promise of plasmonics and metamaterials to give rise to a new generation of integrated optical and optoelectronic devices. They drew attention of researchers in the field to the opportunities afforded by alternative materials (other than conventional metals such as gold and silver traditionally employed in the field of plasmonics and metamaterials) that exhibit metallic properties and possess significant advantages over noble metals in terms of proposed device performance, design flexibility, the ease of component fabrication and system integration, and device tunability [38]. One promising class of alternative plasmonic materials comprises the so-called Transparent Conducting Oxides (TCOs), exemplified by such compounds as indium tin oxide (ITO), and doped - e.g. with gallium or aluminum - zinc oxide (ZnO) and cadmium oxide (CdO). The metal-like properties of dopant electrons in TCOs underlie their ability to sustain surface plasmons similar to those in noble metals but at lower frequencies: in the near- to mid-infrared spectral range. The advantageous distinctive features of TCOs include their compatibility with modern semiconductor technology (for example, ITO is widely used in production of solar panels and flat-panel displays), tunable optical properties (variable e.g. by changing the dopant concentration), and chemical and mechanical stability [38]-[41]. Another promising class of alternative plasmonic materials for the visible and lower-frequency spectral ranges consists of transition metal- (titanium-, zirconium-, tantalum-, etc.) nitrides. These materials are electronically conductive and the carrier concentration in these compounds can be varied, e.g. through the material composition or film deposition conditions, which allows for the tuning of their optical properties to meet the requirements of a particular device or application [38]. Another important advantage of these ceramic materials over noble metals is that they are refractory: they retain their thermal stability up to and above 2,000 Co [38], which makes them promising candidates to fulfill the demands of high-temperature plasmonic applications, e.g. electric power generation through thermophotovoltaics [42].
Shalaev made a significant contribution to the development of the field of optical metasurfaces – planar (much thinner than the wavelength of light), laterally nano-structured metamaterials with unique optical properties [43]-[45]. Planar geometry of metasurfaces allows for easier component fabrication and integration in comparison with 3D, multilayer metamaterials, making metasurfaces promising functional components for nanophotonics and optoelectronics [46]. Early work on the flat optics was conducted by Erez Hasman in Technion, Israel, Philippe Lalanne in France and Nikolay Zheludev in Southampton, UK. The Capasso group (which obtained a number of pioneering, breakthrough results in the field) first demonstrated for the mid-infrared (mid-IR) wavelength of 8μm that special nanoantenna-array metasurfaces create phase discontinuities for the electromagnetic waves passing through them and drastically change the flow of reflected and refracted light [43]. This phenomenon was then extended to the near-IR wavelength region, and it was shown that the phenomenon is robust and exists in a wide spectral range [43]. The research that followed yielded various metasurface-based, "flat" optical components, including waveplates, lenses, holograms, and ultra-thin light absorbers [47]-[49], [45].
Shalaev was among the group of researchers who were the first to experimentally demonstrate the spaser – a device analogous to laser, but generating coherent surface-plasmon field instead of light [50], [51]. In contrast to conventional lasers, the size of a spaser is not limited from below by the wavelength of light, making spaser a promising coherent optical source for nanophotonics. The spaser developed by Shalaev with co-workers used a 44 nm core-shell nanostructure with gold core as the plasmonic resonator (providing optical feedback necessary for lasing/spasing) and a dye–doped silica shell as the optical gain medium [51]. Outcoupling of surface plasmon oscillations in this system to photonic modes made it essentially a single-particle nanolaser.
Prof. Shalaev and his colleagues at Purdue University and elsewhere have recently performed studies on plasmon-enhanced heterogeneous photocatalysis [52],[53]. One of the central ideas in this field is to utilize hot electrons generated in the process of surface plasmons decay. This approach offers an opportunity to selectively enhance preferred chemical pathways while inhibiting the alternatives [52].
Prof. Shalaev received a number of awards for his research and leadership in the field of nanophotonics and metamaterials, including
V. Shalaev is a Fellow of
Prof. Shalaev co-/authored three- [61]-[63] and co-/edited four [64]-[67] books in the area of his scientific expertise. Over the course of his career, he contributed 28 invited chapters to various scientific anthologies and published a number of invited review articles, over 600 publications in total, including over 300 research papers in refereed journals [68]. He is also a co-inventor in 24 patents [68], and he made over 300 invited presentations at International Conferences and leading research centers, including a number of plenary and keynote talks [69],[70].