1,866 research outputs found
Out-of-equilibrium collective oscillation as phonon condensation in a model protein
In the first part of the present paper (theoretical), the activation of
out-of-equilibrium collective oscillations of a macromolecule is described as a
classical phonon condensation phenomenon. If a macromolecule is modeled as an
open system, that is, it is subjected to an external energy supply and is in
contact with a thermal bath to dissipate the excess energy, the internal
nonlinear couplings among the normal modes make the system undergo a
non-equilibrium phase transition when the energy input rate exceeds a threshold
value. This transition takes place between a state where the energy is
incoherently distributed among the normal modes, to a state where the input
energy is channeled into the lowest frequency mode entailing a coherent
oscillation of the entire molecule. The model put forward in the present work
is derived as the classical counterpart of a quantum model proposed long time
ago by H. Fr\"ohlich in the attempt to explain the huge speed of enzymatic
reactions. In the second part of the present paper (experimental), we show that
such a phenomenon is actually possible. Two different and complementary THz
near-field spectroscopic techniques, a plasmonic rectenna, and a micro-wire
near-field probe, have been used in two different labs to get rid of artefacts.
By considering a aqueous solution of a model protein, the BSA (Bovine Serum
Albumin), we found that this protein displays a remarkable absorption feature
around 0.314 THz, when driven in a stationary out-of-thermal equilibrium state
by means of optical pumping. The experimental outcomes are in very good
qualitative agreement with the theory developed in the first part, and in
excellent quantitative agreement with a theoretical result allowing to identify
the observed spectral feature with a collective oscillation of the entire
molecule.Comment: 49 pages, 10 figures; Physical Review X, (2018) in pres
Thermoreflectance techniques and Raman thermometry for thermal property characterization of nanostructures
This AIP article is published under license by AIP: https://publishing.aip.org/wp-content/uploads/2019/10/AIPP-Author-License.pdfPublishing.https://pubs.acs.org/page/policy/authorchoice_termsofuse.htmlAltres ajuts: ICN2 is supported by the CERCA Programme/Generalitat de Catalunya.The widespread use of nanostructures and nanomaterials has opened up a whole new realm of challenges in thermal management, but also leads to possibilities for energy conversion, storage, and generation, in addition to numerous other technological applications. At the microscale and below, standard thermal measurement techniques reach their limits, and several novel methods have been developed to overcome these limitations. Among the most recent, contactless photothermal methods have been widely used and have proved their advantages in terms of versatility, temporal and spatial resolution, and even sensitivity in some situations. Among them, thermoreflectance and Raman thermometry have been used to measure the thermal properties from bulk materials to thin films, multilayers, suspended structures, and nanomaterials. This Tutorial presents the principles of these two techniques and some of their most common implementations. It expands to more advanced systems for spatial mapping and for probing of non-Fourier thermal transport. Finally, this paper concludes with discussing the limitations and perspectives of these techniques and future directions in nanoscale thermometry
Contactless characterization of the elastic properties of glass microspheres
Glass microspheres are of great interest for numerous industrial, biomedical, or standalone applications, but it remains challenging to evaluate their elastic and optical properties in a non-destructive way. In this work, we address this issue by using two complementary contactless techniques to obtain elastic and optical constants of glass microspheres with diameters ranging from 10 to 60 µm. The first technique we employ is Brillouin Light Scattering, which yields scattering with longitudinal acoustic phonons, the frequency of which is found to be 5% lower than that measured in the bulk material. The second technique involves exciting the optical whispering gallery modes of the microspheres, which allows us to transduce some of their vibrational modes. The combined data allow for extracting the refractive index and the elastic constants of the material. Our findings indicate that the values of those properties are reduced with respect to their bulk material counterpart due to an effective decrease of the density, resulting from the fabrication process. We propose the use of this combined method to extract elastic and optical parameters of glass materials in microsphere geometries and compare them with the values of the pristine material from which they are formed
Injection locking in an optomechanical coherent phonon source
[EN] Spontaneous locking of the phase of a coherent phonon source to an external reference is demonstrated in a deeply sideband-unresolved optomechanical system. The high-amplitude mechanical oscillations are driven by the anharmonic modulation of the radiation pressure force that result from an absorption-mediated free-carrier/temperature limit cycle, i.e., self-pulsing. Synchronization is observed when the pump laser driving the mechanical oscillator to a self-sustained state is modulated by a radiofrequency tone. We employ a pump-probe phonon detection scheme based on an independent optical cavity to observe only the mechanical oscillator dynamics. The lock range of the oscillation frequency, i.e., the Arnold tongue, is experimentally determined over a range of external reference strengths, evidencing the possibility to tune the oscillator frequency for a range up to 350 kHz. The stability of the coherent phonon source is evaluated via its phase noise, with a maximum achieved suppression of 44 dBc/Hz at 1 kHz offset for a 100 MHz mechanical resonator. Introducing a weak modulation in the excitation laser reveals as a further knob to trigger, control and stabilize the dynamical solutions of self-pulsing based optomechanical oscillators, thus enhancing their potential as acoustic wave sources in a single-layer silicon platform.This research was funded by EU FET Open project PHENOMEN (GA: 713450). ICN2 is supported by the Severo Ochoa program from the Spanish Research Agency (AEI, grant no. SEV-2017-0706) and by the CERCA Programme/Generalitat de Catalunya. G. A. and C. M. S.-T. acknowledge the support from the Spanish MICINN project SIP (PGC2018-101743-B-I00). D. N. U., G. A. and M. F. C. gratefully acknowledge the support of a Ramon y Cajal postdoctoral fellowship (RYC-2014-15392), a BIST studentship, and a Severo Ochoa studentship, respectively. D. N. U. acknowledges the funding through the Ministry of Science, Innovation and Universities (PGC2018-094490-B-C22).Arregui, G.; Colombano, MF.; Maire, J.; Pitanti, A.; Capuj, NE.; Griol Barres, A.; Martínez, A.... (2021). Injection locking in an optomechanical coherent phonon source. Nanophotonics. 10(4):1319-1327. https://doi.org/10.1515/nanoph-2020-05921319132710
Operation of GaN planar nanodiodes as THz detectors and mixers
In this paper, we perform, by means of Monte Carlo
simulations and experimental measurements, a geometry optimization
of GaN-based nano-diodes for broadband Terahertz
direct detection (in terms of responsivity) and mixing (in terms
of output power). The capabilities of the so-called self-switching
diode (SSD) are analyzed for different dimensions of the channel at
room temperature. Signal detection up to the 690 GHz limit of the
experimental set-up has been achieved at zero bias. The reduction
of the channel width increases the detection responsivity, while
the reduction in length reduces the responsivity but increases the
cut-off frequency. In the case of heterodyne detection an intrinsic
bandwidth of at least 100 GHz has been found. The intermediate
frequency (IF) power increases for short SSDs, while the optimization
in terms of the channel width is a trade-off between a higher
non-linearity (obtained for narrow SSDs) and a large current level
(obtained for wide SSDs). Moreover, the RF performance can be
improved by biasing, with optimum performances reached, as
expected, when the DC non-linearity is maximum
Analysis of sodium copper chlorophyllin and sodium magnesium chlorophyllin by time-domain THz spectroscopy
The terahertz absorption spectra of sodium magnesium chlorophyllin (Chl-Mg-Na) and sodium copper chlorophyllin (Cu-Chl), two major members of the chlorophyll derivative family, have been measured in the range 0.2-2.5 THz, at room temperature. The capability of terahertz spectroscopy for quantitative characterization of Chl-Mg-Na intermolecular vibrations was investigated and the sensitivity of transitions with degree of hydration by changes in the molecular environment was examined. For the Cu-Chl derivative, a broad feature was observed around 1.8 THz which currently hinders clear Cu-Chl identification and quantification
Investigating the low-frequency vibrations of chlorophyll derivatives using terahertz spectroscopy
The terahertz absorption spectra of sodium magnesium chlorophyllin (Chl-Mg-Na) and sodium copper chlorophyllin (Cu-Chl), two major members of the chlorophyll derivative family, have been measured in the range 0.2-3.0 THz (6.6-100 cm-1), at room temperature. Additionally, surface-enhanced Raman scattering spectroscopy was used to supplement data in the higher frequency range. The capability of terahertz spectroscopy for quantitative characterization of Chl-Mg-Na intermolecular vibrations was investigated and the sensitivity of the 1.82-THz feature with degree of hydration by changes in the molecular environment was examined. For Cu-Chl derivative, a broad feature was observed around 1.8 THz which currently hinders clear Cu-Chl identification and quantification
Temperature-dependent low-frequency vibrational spectra of sodium magnesium chlorophyllin
Terahertz time-domain spectroscopy has been used to investigate the vibrational spectra of polycrystalline sodium magnesium chlorophyllin - one of the natural derivatives of chlorophyll - over the temperature range 88 K–298 K. A number of well-resolved absorption peaks were observed in the frequency range 0.2–2.5 THz, which are interpreted as originating from mixed character of intramolecular and intermolecular vibration modes. As the temperature is increased, the observed absorption features resolve into broader peaks. The peak centered at 1.83 THz shifts towards higher frequencies, indicating that for this feature, significant intermolecular anharmonicity exist
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
Synchronization of Optomechanical Nanobeams by Mechanical Interaction
The synchronization of coupled oscillators is a phenomenon found throughout nature. Mechanical oscillators are paradigmatic examples, but synchronizing their nanoscaled versions is challenging. We report synchronization of the mechanical dynamics of a pair of optomechanical crystal cavities that, in contrast to previous works performed in similar objects, are intercoupled with a mechanical link and support independent optical modes. In this regime they oscillate in antiphase, which is in agreement with the predictions of our numerical model that considers reactive coupling. We also show how to temporarily disable synchronization of the coupled system by actuating one of the cavities with a heating laser, so that both cavities oscillate independently. Our results can be upscaled to more than two cavities and pave the way towards realizing integrated networks of synchronized mechanical oscillators
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