A novel high resolution contactless technique for thermal field mapping and thermal conductivity determination: Two-Laser Raman Thermometry

We present a novel high resolution contactless technique for thermal conductivity determination and thermal field mapping based on creating a thermal distribution of phonons using a heating laser, while a second laser probes the local temperature through the spectral position of a Raman active mode. The spatial resolution can be as small as $300$ nm, whereas its temperature accuracy is $\pm 2$ K. We validate this technique investigating the thermal properties of three free-standing single crystalline Si membranes with thickness of 250, 1000, and 2000 nm. We show that for 2-dimensional materials such as free-standing membranes or thin films, and for small temperature gradients, the thermal field decays as $T(r) \propto ln(r)$ in the diffusive limit. The case of large temperature gradients within the membranes leads to an exponential decay of the thermal field, $T \propto exp[-A \cdot ln(r)]$. The results demonstrate the full potential of this new contactless method for quantitative determination of thermal properties. The range of materials to which this method is applicable reaches far beyond the here demonstrated case of Si, as the only requirement is the presence of a Raman active mode

Acoustic phonon propagation in ultra-thin Si membranes under biaxial stress field

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.We report on stress induced changes in the dispersion relations of acoustic phonons propagating in 27 nm thick single crystalline Si membranes. The static tensile stress (up to 0.3 GPa) acting on the Si membranes was achieved using an additional strain compensating silicon nitride frame. Dispersion relations of thermally activated hypersonic phonons were measured by means of Brillouin light scattering spectroscopy. The theory of Lamb wave propagation is developed for anisotropic materials subjected to an external static stress field. The dispersion relations were calculated using the elastic continuum approximation and taking into account the acousto-elastic effect. We find an excellent agreement between the theoretical and the experimental dispersion relations.The authors acknowledge financial support from the FP7 project MERGING (grant no. 309150); the Spanish MICINN projects nanoTHERM (grant no. CSD2010-0044) and TAPHOR (MAT2012-31392). JGB gratefully acknowledges support from the Spanish government through a Juan de la Cierva fellowship. MP and AS acknowledge funding from the Academy of Finland (grant no. 252598).Peer Reviewe

Engineering nanoscale hypersonic phonon transport

Controlling the vibrations in solids is crucial to tailor their mechanical properties and their interaction with light. Thermal vibrations represent a source of noise and dephasing for many physical processes at the quantum level. One strategy to avoid these vibrations is to structure a solid such that it possesses a phononic stop band, i.e., a frequency range over which there are no available mechanical modes. Here, we demonstrate the complete absence of mechanical vibrations at room temperature over a broad spectral window, with a 5.3 GHz wide band gap centered at 8.4 GHz in a patterned silicon nanostructure membrane measured using Brillouin light scattering spectroscopy. By constructing a line-defect waveguide, we directly measure GHz localized modes at room temperature. Our experimental results of thermally excited guided mechanical modes at GHz frequencies provides an eficient platform for photon-phonon integration with applications in optomechanics and signal processing transduction

Generalized nonreciprocity in an optomechanical circuit via synthetic magnetism and reservoir engineering

Synthetic magnetism has been used to control charge neutral excitations for applications ranging from classical beam steering to quantum simulation. In optomechanics, radiation-pressure-induced parametric coupling between optical (photon) and mechanical (phonon) excitations may be used to break time-reversal symmetry, providing the prerequisite for synthetic magnetism. Here we design and fabricate a silicon optomechanical circuit with both optical and mechanical connectivity between two optomechanical cavities. Driving the two cavities with phase-correlated laser light results in a synthetic magnetic flux, which in combination with dissipative coupling to the mechanical bath, leads to nonreciprocal transport of photons with 35dB of isolation. Additionally, optical pumping with blue-detuned light manifests as a particle non-conserving interaction between photons and phonons, resulting in directional optical amplification of 12dB in the isolator through direction. These results indicate the feasibility of utilizing optomechanical circuits to create a more general class of nonreciprocal optical devices, and further, to enable novel topological phases for both light and sound on a microchip.Comment: 18 pages, 8 figures, 4 appendice

Dynamical back-action at 5.5 GHz in a corrugated optomechanical beam

[EN] We report on the optomechanical properties of a breathing mechanical mode oscillating at 5.5 GHz in a 1D corrugated Si nanobeam. This mode has an experimental single-particle optomechanical coupling rate of vertical bar g(o, OM)vertical bar= 1.8 MHz (vertical bar g(o, OM)vertical bar/2 pi=0.3 MHz) and shows strong dynamical back-action effects at room temperature. The geometrical flexibility of the unit-cell would lend itself to further engineering of the cavity region to localize the mode within the full phononic band-gap present at 4 GHz while keeping high go, OM values. This would lead to longer lifetimes at cryogenic temperatures, due to the suppression of acoustic leakage.This work was supported by the EU through the FP7 project TAILPHOX (ICT-FP7-233883) and the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish projects TAPHOR (MAT2012-31392). D.N-U and J.G-B acknowledge support in the form of postdoctoral fellowships from the Catalan (Beatriu de Pinos) and the Spanish (Juan de la Cierva) governments, respectively.Navarro-Urrios, D.; Gomis-Bresco, J.; El-Jallal, S.; Oudich, M.; Pitanti, A.; Capuj, N.; Tredicucci, A.... (2014). Dynamical back-action at 5.5 GHz in a corrugated optomechanical beam. AIP Advances. 4(12). https://doi.org/10.1063/1.4902171S412Aspelmeyer, M., Kippenberg, T. J., & Marquardt, F. (Eds.). (2014). Cavity Optomechanics. doi:10.1007/978-3-642-55312-7Kippenberg, T. J., Rokhsari, H., Carmon, T., Scherer, A., & Vahala, K. J. (2005). Analysis of Radiation-Pressure Induced Mechanical Oscillation of an Optical Microcavity. Physical Review Letters, 95(3). doi:10.1103/physrevlett.95.033901Hossein-Zadeh, M., Rokhsari, H., Hajimiri, A., & Vahala, K. J. (2006). Characterization of a radiation-pressure-driven micromechanical oscillator. Physical Review A, 74(2). doi:10.1103/physreva.74.023813Eichenfield, M., Chan, J., Camacho, R. M., Vahala, K. J., & Painter, O. (2009). Optomechanical crystals. Nature, 462(7269), 78-82. doi:10.1038/nature08524Pennec, Y., Laude, V., Papanikolaou, N., Djafari-Rouhani, B., Oudich, M., El Jallal, S., … Martínez, A. (2014). Modeling light-sound interaction in nanoscale cavities and waveguides. Nanophotonics, 3(6). doi:10.1515/nanoph-2014-0004Chan, J., Alegre, T. P. M., Safavi-Naeini, A. H., Hill, J. T., Krause, A., Gröblacher, S., … Painter, O. (2011). Laser cooling of a nanomechanical oscillator into its quantum ground state. Nature, 478(7367), 89-92. doi:10.1038/nature10461Safavi-Naeini, A. H., Alegre, T. P. M., Chan, J., Eichenfield, M., Winger, M., Lin, Q., … Painter, O. (2011). Electromagnetically induced transparency and slow light with optomechanics. Nature, 472(7341), 69-73. doi:10.1038/nature09933Pennec, Y., Rouhani, B. D., Li, C., Escalante, J. M., Martinez, A., Benchabane, S., … Papanikolaou, N. (2011). Band gaps and cavity modes in dual phononic and photonic strip waveguides. AIP Advances, 1(4), 041901. doi:10.1063/1.3675799Gomis-Bresco, J., Navarro-Urrios, D., Oudich, M., El-Jallal, S., Griol, A., Puerto, D., … Torres, C. M. S. (2014). A one-dimensional optomechanical crystal with a complete phononic band gap. Nature Communications, 5(1). doi:10.1038/ncomms5452Oudich, M., El-Jallal, S., Pennec, Y., Djafari-Rouhani, B., Gomis-Bresco, J., Navarro-Urrios, D., … Makhoute, A. (2014). Optomechanic interaction in a corrugated phoxonic nanobeam cavity. Physical Review B, 89(24). doi:10.1103/physrevb.89.245122Chan, J., Safavi-Naeini, A. H., Hill, J. T., Meenehan, S., & Painter, O. (2012). Optimized optomechanical crystal cavity with acoustic radiation shield. Applied Physics Letters, 101(8), 081115. doi:10.1063/1.4747726Safavi-Naeini, A. H., Hill, J. T., Meenehan, S., Chan, J., Gröblacher, S., & Painter, O. (2014). Two-Dimensional Phononic-Photonic Band Gap Optomechanical Crystal Cavity. Physical Review Letters, 112(15). doi:10.1103/physrevlett.112.153603Johnson, S. G., Ibanescu, M., Skorobogatiy, M. A., Weisberg, O., Joannopoulos, J. D., & Fink, Y. (2002). Perturbation theory for Maxwell’s equations with shifting material boundaries. Physical Review E, 65(6). doi:10.1103/physreve.65.066611Navarro-Urrios, D., Gomis-Bresco, J., Capuj, N. E., Alzina, F., Griol, A., Puerto, D., … Sotomayor-Torres, C. M. (2014). Optical and mechanical mode tuning in an optomechanical crystal with light-induced thermal effects. Journal of Applied Physics, 116(9), 093506. doi:10.1063/1.4894623Barclay, P. E., Srinivasan, K., & Painter, O. (2005). Nonlinear response of silicon photonic crystal micresonators excited via an integrated waveguide and fiber taper. Optics Express, 13(3), 801. doi:10.1364/opex.13.000801J. Chan, Ph.D. thesis, California Institute of Technology, Los Angeles, 2014.Gorodetsky, M. L., Schliesser, A., Anetsberger, G., Deleglise, S., & Kippenberg, T. J. (2010). Determination of the vacuum optomechanical coupling rate using frequency noise calibration. Optics Express, 18(22), 23236. doi:10.1364/oe.18.02323

A self-stabilized coherent phonon source driven by optical forces

[EN] We report a novel injection scheme that allows for phonon lasing in a one-dimensional optomechanical photonic crystal, in a sideband unresolved regime and with cooperativity values as low as 10-2. It extracts energy from a cw infrared laser source and is based on the triggering of a thermooptical/free-carrier-dispersion self-pulsing limit-cycle, which anharmonically modulates the radiation pressure force. The large amplitude of the coherent mechanical motion acts as a feedback that stabilizes and entrains the self-pulsing oscillations to simple fractions of the mechanical frequency. A manifold of frequency-entrained regions with two different mechanical modes (at 54 and 122 MHz) are observed as a result of the wide tuneability of the natural frequency of the self-pulsing. The system operates at ambient conditions of pressure and temperature in a silicon platform, which enables its exploitation in sensing, intra-chip metrology or time-keeping applications.This work was supported by the European Comission project TAILPHOX (ICT-FP7-233883), the ERC Advanced Grant SOULMAN (ERC-FP7-321122) and the Spanish MINECO project TAPHOR (MAT2012-31392). The authors sincerely thank B. Djafari-Rouhani, Y. Pennec and M. Oudich for the design of the OM photonic crystal, A. Trifonova, S. Valenzuela and E. Weig for a critical reading of the manuscript and A. Tredicucci for fruitful discussions. A. M and A. G thank L. Bellieres and N. Sanchez-Losilla for their contributions in the OM photonic crystal etching processes. DNU and JGB gratefully acknowledge the support of a Beatriu de Pinos and a Juan de la Cierva postdoctoral fellowship, respectively.Navarro Urríos, D.; Capuj, NE.; Gomis-Bresco, J.; Alzina, F.; Pitanti, A.; Griol Barres, A.; Martínez Abietar, AJ.... (2015). 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Phonons in Slow Motion: Dispersion Relations in Ultra-Thin Si Membranes

We report the changes in dispersion relations of hypersonic acoustic phonons in free-standing silicon membranes as thin as \sim 8 nm. We observe a reduction of the phase and group velocities of the fundamental flexural mode by more than one order of magnitude compared to bulk values. The modification of the dispersion relation in nanostructures has important consequences for noise control in nano and micro-electromechanical systems (MEMS/NEMS) as well as opto-mechanical devices.Comment: 5 page