4,221 research outputs found
Parametric amplification of optical phonons
Amplification of light through stimulated emission or nonlinear optical
interactions has had a transformative impact on modern science and technology.
The amplification of other bosonic excitations, like phonons in solids, is
likely to open up new remarkable physical phenomena. Here, we report on an
experimental demonstration of optical phonon amplification. A coherent
mid-infrared optical field is used to drive large amplitude oscillations of the
Si-C stretching mode in silicon carbide. Upon nonlinear phonon excitation, a
second probe pulse experiences parametric optical gain at all wavelengths
throughout the reststrahlen band, which reflects the amplification of
optical-phonon fluctuations. Starting from first principle calculations, we
show that the high-frequency dielectric permittivity and the phonon oscillator
strength depend quadratically on the lattice coordinate. In the experimental
conditions explored here, these oscillate then at twice the frequency of the
optical field and provide a parametric drive for lattice fluctuations.
Parametric gain in phononic four wave mixing is a generic mechanism that can be
extended to all polar modes of solids, as a new means to control the kinetics
of phase transitions, to amplify many body interactions or to control
phonon-polariton waves
Principles and promise of Fabry-Perot resonators at terahertz frequencies
Fabry–Perot resonators have tremendous potential to enhance the sensitivity of spectroscopic systems at terahertz (THz) frequencies. Increasing sensitivity will be of benefit in compensating for the relatively low power of current high resolution continuous wave THz radiation techniques, and to fully express the potential of THz spectroscopy as source power increases. Improved sensitivities, and thus scanning speeds, will allow detailed studies of the complex vibration-rotation-tunneling dynamics that large molecules show at THz wavelengths, and will be especially important in studying more elusive, transient species such as those present in planetary atmospheres and the interstellar medium. Coupling radiation into the cavity presents unique challenges at THz frequencies, however, meaning that the cavity configurations common in neighboring frequency domains cannot simply be translated. Instead, novel constructions are needed. Here we present a resonator design in which wire-grid polarizers serve as the input and output coupling mirrors. Using this configuration, Q-factors of a few times 10^5 are achieved near 0.3 THz. To aid future investigations, the parameter space that limits the quality of the cavity is explored and paths to improved performance highlighted. Lastly, the performance of polarizer cavity-based Fourier transform (FT) THz spectrometers is discussed, in particular those design optimizations that should allow for the construction of THz instrumentation that rivals and eventually surpasses the sensitivities achieved with modern FT-microwave cavity spectrometers
Antenna-coupled TES bolometer arrays for CMB polarimetry
We describe the design and performance of polarization selective
antenna-coupled TES arrays that will be used in several upcoming Cosmic
Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully
lithographic polarimeter arrays utilize planar phased-antennas for collimation
(F/4 beam) and microstrip filters for band definition (25% bandwidth). These
devices demonstrate high optical efficiency, excellent beam shapes, and
well-defined spectral bands. The dual-polarization antennas provide
well-matched beams and low cross polarization response, both important for
high-fidelity polarization measurements. These devices have so far been
developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave
atmospheric windows for CMB observations. In the near future, the flexible
microstrip-coupled architecture can provide photon noise-limited detection for
the entire frequency range of the CMBPOL mission. This paper is a summary of
the progress we have made since the 2006 SPIE meeting in Orlando, FL
Antenna-coupled TES bolometer arrays for CMB polarimetry
We describe the design and performance of polarization selective
antenna-coupled TES arrays that will be used in several upcoming Cosmic
Microwave Background (CMB) experiments: SPIDER, BICEP-2/SPUD. The fully
lithographic polarimeter arrays utilize planar phased-antennas for collimation
(F/4 beam) and microstrip filters for band definition (25% bandwidth). These
devices demonstrate high optical efficiency, excellent beam shapes, and
well-defined spectral bands. The dual-polarization antennas provide
well-matched beams and low cross polarization response, both important for
high-fidelity polarization measurements. These devices have so far been
developed for the 100 GHz and 150 GHz bands, two premier millimeter-wave
atmospheric windows for CMB observations. In the near future, the flexible
microstrip-coupled architecture can provide photon noise-limited detection for
the entire frequency range of the CMBPOL mission. This paper is a summary of
the progress we have made since the 2006 SPIE meeting in Orlando, FL
Ultracompact high-efficiency polarising beam splitter based on silicon nanobrick arrays
Since the transmission of anisotropic nano-structures is sensitive to the polarisation of an incident beam, a novel polarising beam splitter (PBS) based on silicon nanobrick arrays is proposed. With careful design of such structures, an incident beam with polarisation direction aligned with the long axis of the nanobrick is almost totally reflected (~98.5%), whilst that along the short axis is nearly totally transmitted (~94.3%). More importantly, by simply changing the width of the nanobrick we can shift the peak response wavelength from 1460 nm to 1625 nm, covering S, C and L bands of the fiber telecommunications windows. The silicon nanobrick-based PBS can find applications in many fields which require ultracompactness, high efficiency, and compatibility with semiconductor industry technologies
Dual-Band Quasi-Coherent Radiative Thermal Source
Thermal radiation from an unpatterned object is similar to that of a gray
body. The thermal emission is insensitive to polarization, shows only
Lambertian angular dependence, and is well modeled as the product of the
blackbody distribution and a scalar emissivity over large frequency bands.
Here, we design, fabricate and experimentally characterize the spectral,
polarization, angular and temperature dependence of a microstructured SiC dual
band thermal infrared source, achieving independent control of the frequency
and polarization of thermal radiation in two spectral bands. The measured
emission of the device in the Reststrahlen band (10.3-12.7 um) selectively
approaches that of a blackbody, peaking at an emissivity of 0.85 at Lx=11.75 um
and 0.81 at Ly=12.25 um. This effect arises due to the thermally excited phonon
polaritons in silicon carbide. The control of thermal emission properties
exhibited by the design is well suited for applications requiring infrared
sources, gas or temperature sensors and nanoscale heat transfer. Our work paves
the way for future silicon carbide based thermal metasurfaces.Comment: Journal of Quantitative Spectroscopy & Radiative Transfer (2018
Enhanced transmission with a graphene-dielectric microstructure at low-terahertz frequencies
Here, we report on the transmissivity of electromagnetic waves through a stack of monolayer graphene sheets separated by dielectric slabs at low-terahertz frequencies. It is observed that the multilayer structure possesses band-gap properties and supports a series of bandpass and band-stop regions, similar to the cases of stacked metallic meshes separated by dielectric slabs at microwave/THz frequencies and a metal-dielectric stack at optical frequencies. The transmission resonances in the bandpass region are identified as coupled Fabry-Pérot resonances associated with the individual cavities of dielectric slabs loaded with graphene sheets. It is also noticed that these resonances lie within a certain characteristic frequency band, independent of the number of layers in the graphene-dielectric stack. The study is carried out using a simple analytical transfer-matrix approach or, equivalently, a circuit-theory model, resulting in the exact solution for the multiple dielectric/graphene sheet surface-conductivity model. Also, an independent verification of the observed phenomena is obtained with commercial numerical simulations.Ministerio de Ciencia e Innovación TEC2010-16948Unión Europea FEDER CSD2008-00066Junta de Andalucía TIC-459
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