Riccardo Sapienza

A micrometre-scale Raman silicon laser with a microwatt threshold

Nature 498, 7455 (2013). doi:10.1038/nature12237

Authors: Yasushi Takahashi, Yoshitaka Inui, Masahiro Chihara, Takashi Asano, Ryo Terawaki & Susumu Noda

The application of novel technologies to silicon electronics has been intensively studied with a view to overcoming the physical limitations of Moore’s law, that is, the observation that the number of components on integrated chips tends to double every two years. For example, silicon devices have enormous potential for photonic integrated circuits on chips compatible with complementary metal–oxide–semiconductor devices, with various key elements having been demonstrated in the past decade. In particular, a focus on the exploitation of the Raman effect has added active optical functionality to pure silicon, culminating in the realization of a continuous-wave all-silicon laser. This achievement is an important step towards silicon photonics, but the desired miniaturization to micrometre dimensions and the reduction of the threshold for laser action to microwatt powers have yet to be achieved: such lasers remain limited to centimetre-sized cavities with thresholds higher than 20 milliwatts, even with the assistance of reverse-biased p–i–n diodes. Here we demonstrate a continuous-wave Raman silicon laser using a photonic-crystal, high-quality-factor nanocavity without any p–i–n diodes, yielding a device with a cavity size of less than 10 micrometres and an unprecedentedly low lasing threshold of 1 microwatt. Our nanocavity design exploits the principle that the strength of light–matter interactions is proportional to the ratio of quality factor to the cavity volume and allows drastic enhancement of the Raman gain beyond that predicted theoretically. Such a device may make it possible to construct practical silicon lasers and amplifiers for large-scale integration in photonic circuits.

Author(s): Th. K. Mavrogordatos, S. M. Morris, S. M. Wood, H. J. Coles, and T. D. Wilkinson

In this article, we investigate the spontaneous emission properties of radiating molecules embedded in a chiral nematic liquid crystal, under the assumption that the electronic transition frequency is close to the photonic edge mode of the structure, i.e., at resonance. We take into account the tran…

[Phys. Rev. E 87, 062504] Published Mon Jun 17, 2013

Author(s): Xuele Liu and G. S. Agarwal

In light of the interest in the transport of single photons in arrays of waveguides, fiber couplers, photonic crystals, etc., we consider the quantum mechanical process of the tunneling of photons through evanescently or otherwise coupled structures. We specifically examine the issue of tunneling be…

[Phys. Rev. A 87, 063841] Published Mon Jun 24, 2013

Heat-transport mechanism mediated by near-field interactions in plasmonic nanostructures networks is shown to be analogous to a generalized random-walk process. Existence of superdiffusive regimes is demonstrated both in linear ordered chains and in three dimensional random networks by analyzing the asymptotic behavior of the corresponding probability distribution function. We show that the spread of heat in these networks is described by a type of L\'{e}vy flight. The presence of such anomalous heat transport regimes in plasmonic networks opens the way to the design of a new generation of composite materials able to transport heat faster than the normal diffusion process in solids.

A phase relation observed in ensemble measurements of photosynthetic proteins is borne out at the single-molecule level.

Authors: Richard Hildner, Daan Brinks, Jana B. Nieder, Richard J. Cogdell, Niek F. van Hulst

Author: Marc Kirschner

We present a stochastic model for amplifying, diffusive media like, for instance, random lasers. Starting from a simple random-walk model, we derive a stochastic partial differential equation for the energy field with contains a multiplicative random-advection term yielding intermittency and power-law distributions of the field itself. Dimensional analysis indicate that such features are more likely to be observed for small enough samples and in lower spatial dimensions.

Zinc Oxide thin films were grown on c-sapphire substrates using pulsed laser deposition. Pump power dependence of surface emission spectra, acquired using a quadrupled 266 nm laser, revealed room temperature stimulated emission (threshold of 900 kW/cm2). Time dependent spectral analysis plus gain measurements of single-shot, side-emission, spectra pumped with a nitrogen laser revealed random lasing indicative of the presence of self-forming laser cavities. It is suggested that random lasing in an epitaxial system rather than a 3-dimensional configuration of disordered scattering elements, was due to waveguiding in the film. Waveguiding causes light to be amplified within randomly-formed closed-loops acting as lasing cavities.

Author(s): C. Sauvan, J. P. Hugonin, I. S. Maksymov, and P. Lalanne

We provide a self-consistent electromagnetic theory of the coupling between dipole emitters and dissipative nanoresonators. The theory that relies on the concept of quasinormal modes with complex frequencies provides an accurate closed-form expression for the electromagnetic local density of states ...

[Phys. Rev. Lett. 110, 237401] Published Wed Jun 05, 2013

Announcement: Nature papers enhanced

Nature 498, 7452 (2013). doi:10.1038/498006a

As the requirements for data presentation in research papers have grown, Nature’s space limitations have remained tight, so more and more essential displayed information has been relegated inappropriately to our Supplementary Information sections. Hard on the heels of our relaxation of constraints on our

Nature Photonics 7, 454 (2013). doi:10.1038/nphoton.2013.95

Authors: Jung-Hoon Park, Chunghyun Park, HyeonSeung Yu, Jimin Park, Seungyong Han, Jonghwa Shin, Seung Hwan Ko, Ki Tae Nam, Yong-Hoon Cho & YongKeun Park

Author(s): J. R. Ott, M. Wubs, P. Lodahl, N. A. Mortensen, and R. Kaiser

We investigate cooperative fluorescence in a dilute cloud of strongly driven two-level emitters. Starting from the Heisenberg equations of motion, we compute the first-order scattering corrections to the saturation of the excited-state population and to the resonance-fluorescence spectrum, which bot...

[Phys. Rev. A 87, 061801] Published Wed Jun 05, 2013

Nature Physics 9, 357 (2013). doi:10.1038/nphys2614

Authors: Q. Baudouin, N. Mercadier, V. Guarrera, W. Guerin & R. Kaiser

In conventional lasers optical cavities are used to provide feedback to gain media. Mirrorless lasers can be built by using disordered structures to induce multiple scattering, which increases the path length in the medium, providing the necessary feedback. Interestingly, light or microwave amplification by stimulated emission also occurs naturally in stellar gases and planetary atmospheres. The possibility of additional scattering-induced feedback—random lasing—could explain the unusual properties of some space masers. Here, we report experimental evidence of random lasing in a controlled, cold atomic vapour, taking advantage of Raman gain. By tuning the gain frequency in the vicinity of a scattering resonance, we observe an enhancement of the light emission due to random lasing. The unique possibility to both control the experimental parameters and to model the microscopic response of our system provides an ideal test bench for better understanding natural lasing sources, in particular the role of resonant scattering feedback in astrophysical lasers.

Author(s): Mohammad-Ali Miri, Matthias Heinrich, Ramy El-Ganainy, and Demetrios N. Christodoulides

We show that supersymmetry can provide a versatile platform in synthesizing a new class of optical structures with desired properties and functionalities. By exploiting the intimate relationship between superpatners, one can systematically construct index potentials capable of exhibiting the same sc...

[Phys. Rev. Lett. 110, 233902] Published Thu Jun 06, 2013

Xing Ri Jin, Jie Gao
We demonstrate a quantum phase flip gate between two QDs that resonantly couple to plasmonic double-bar resonators with asymmetric coupling strengths. Large coupling strengths can be achieved due to the deep subwavelength mode volumes of the optical modes in plasmonic double-bar resonators. High ... [Opt. Lett. 38, 2110-2112 (2013)]

Author(s): Andreas Reiserer, Christian Nölleke, Stephan Ritter, and Gerhard Rempe

A single neutral atom is trapped in a three-dimensional optical lattice at the center of a high-finesse optical resonator. Using fluorescence imaging and a shiftable standing-wave trap, the atom is deterministically loaded into the maximum of the intracavity field where the atom-cavity coupling is s...

[Phys. Rev. Lett. 110, 223003] Published Thu May 30, 2013

Chemical mapping of a single molecule by plasmon-enhanced Raman scattering

Nature 498, 7452 (2013). doi:10.1038/nature12151

Authors: R. Zhang, Y. Zhang, Z. C. Dong, S. Jiang, C. Zhang, L. G. Chen, L. Zhang, Y. Liao, J. Aizpurua, Y. Luo, J. L. Yang & J. G. Hou

Visualizing individual molecules with chemical recognition is a longstanding target in catalysis, molecular nanotechnology and biotechnology. Molecular vibrations provide a valuable ‘fingerprint’ for such identification. Vibrational spectroscopy based on tip-enhanced Raman scattering allows us to access the spectral signals of molecular species very efficiently via the strong localized plasmonic fields produced at the tip apex. However, the best spatial resolution of the tip-enhanced Raman scattering imaging is still limited to 3−15 nanometres, which is not adequate for resolving a single molecule chemically. Here we demonstrate Raman spectral imaging with spatial resolution below one nanometre, resolving the inner structure and surface configuration of a single molecule. This is achieved by spectrally matching the resonance of the nanocavity plasmon to the molecular vibronic transitions, particularly the downward transition responsible for the emission of Raman photons. This matching is made possible by the extremely precise tuning capability provided by scanning tunnelling microscopy. Experimental evidence suggests that the highly confined and broadband nature of the nanocavity plasmon field in the tunnelling gap is essential for ultrahigh-resolution imaging through the generation of an efficient double-resonance enhancement for both Raman excitation and Raman emission. Our technique not only allows for chemical imaging at the single-molecule level, but also offers a new way to study the optical processes and photochemistry of a single molecule.