Narrowband Thermal Emission Research Articles

Critical coupling to Tamm plasmons

The conditions of critical coupling of light to Tamm plasmons are investigated with comprehensive numerical simulations, highlighting the parameters that maximize absorption of incident light in the metal layer. The asymmetric response in reflection and absorption with respect to the direction of incidence is discussed, the two cases yielding different optimal coupling conditions. These findings are relevant for the design of optimized Tamm structures, particularly in applications such as narrow-band thermal emitters, field-enhanced spectroscopy and refractive-index sensing.

Realization of narrowband thermal emission with optical nanostructures

The control of thermal emission spectra using optical resonances has been attracting increased attention both with respect to fundamental science and for various applications, including infrared sensing, thermal imaging, and thermophotovoltaics. In this mini-review, we describe the recent experimental demonstrations of narrowband thermal emission with optical nanostructures, including metallic cavities, metamaterials, and all-dielectric photonic crystals. The spectral features of the controlled thermal emission (e.g., wavelength, linewidth, peak emissivity, and angular characteristics) are strongly dependent on the choice of both materials and structures of the emitters. Through the appropriate design of optical nanostructures, arbitrary shaping of thermal emission spectra, from single-peak ultra-narrowband (Q>100) emission for midinfrared sensing to a stepwise emissivity spectrum for thermophotovoltaics, has been successfully realized.

Graphene optical-to-thermal converter

Infrared plasmons in doped graphene nanostructures produce large optical absorption that can be used for narrow-band thermal light emission at tunable frequencies that strongly depend on the doping charge. By virtue of Kirchhoff's law, thermal light emission is proportional to the absorption, thus resulting in narrow emission lines associated with the electrically controlled plasmons of heated graphene. Here, we show that realistic designs of graphene plasmonic structures can release over 90% of the emission through individual infrared lines with 1% bandwidth. We examine anisotropic graphene structures in which efficient heating can be produced upon optical pumping tuned to a plasmonic absorption resonance situated in the blue region relative to the thermal emission. An incoherent thermal light converter is thus achieved. Our results open a radically different approach for designing tunable nanoscale infrared light sources.

Ultranarrow band absorbers based on surface lattice resonances in nanostructured metal surfaces.

Nanostructured metals have received a significant amount of attention in recent years due to their exciting plasmonic and photonic properties enabling strong field localization, light concentration, and strong absorption and scattering at their resonance frequencies. Resonant plasmonic and metamaterial absorbers are of particular interest for applications in a wide variety of technologies including photothermal therapy, thermophotovoltaics, heat-assisted magnetic recording, hot-electron collection, and biosensing. However, it is rather challenging to realize ultranarrow absorption bands using plasmonic materials due to large optical losses in metals that decrease the quality factor of optical resonators. Here, we theoretically and experimentally demonstrate an ultranarrow band absorber based on the surface lattice resonances (SLRs) in periodic nanowire and nanoring arrays on optically thick, reflecting metallic films. In experiments, we observed ultranarrow band resonant absorption peaks with a bandwidth of 12 nm and absorption amplitude exceeding 90% at visible frequencies. We demonstrate that the resonance absorption wavelength, amplitude of the absorption peak, and the bandwidth can be controlled by tuning the periodicity and the thickness of nanoring and nanowire arrays. Unlike conventional plasmonic absorbers utilizing common metal–insulator–metal stacks, our narrow band absorber consists solely of metals, facilitating stronger optical interaction between the SLR of periodic nanostructures and the highly reflective film. Moreover, by introducing asymmetry to the nanoring/nanowire hybrid system, we observe the spectral evolution of resonance splitting enabled by strong coupling between two individual SLRs arising from nanoring and nanowire arrays. Designing such all-metallic nanostructure arrays is a promising route for achieving ultranarrow band absorbers which can be used as absorption filters, narrow band thermal emitters in thermophotovoltaics, and plasmonic biosensors.

Spectrally selective chiral silicon metasurfaces based on infrared Fano resonances.

Metamaterials and metasurfaces represent a remarkably versatile platform for light manipulation, biological and chemical sensing, and nonlinear optics. Many of these applications rely on the resonant nature of metamaterials, which is the basis for extreme spectrally selective concentration of optical energy in the near field. In addition, metamaterial-based optical devices lend themselves to considerable miniaturization because of their subwavelength features. This additional advantage sets metamaterials apart from their predecessors, photonic crystals, which achieve spectral selectivity through their long-range periodicity. Unfortunately, spectral selectivity of the overwhelming majority of metamaterials that are made of metals is severely limited by high plasmonic losses. Here we propose and demonstrate Fano-resonant all-dielectric metasurfaces supporting optical resonances with quality factors Q>100 that are based on CMOS-compatible materials: silicon and its oxide. We also demonstrate that these infrared metasurfaces exhibit extreme planar chirality, opening exciting possibilities for efficient ultrathin circular polarizers and narrow-band thermal emitters of circularly polarized radiation.

Spectral Features of an Omnidirectional Narrowband Emitter

A microscale-structured surface consisting of heavily doped silicon rectangle grating and slotted silver layer is studied for omnidirectional narrowband emitter. Numerical simulation is implemented to obtain spectral emittance in mid-infrared region (6–16 μm) for the transverse magnetic incidence by using the rigorous coupled-wave analysis (RCWA) method. The effects of structural parameters and incident angle on its spectral emittance are investigated. In virtue of the microcavity effect, an omnidirectional narrowband emitter is proposed. By selecting a group of structural parameters, its peak emittance reaches as high as 0.998, and the peak width Δλ/λ of the emittance peak is as narrow as 0.03 at the specified wavelength. The results reveal that our proposed structured surface has the nice spectral features of angular uniformity and wavelength-selective characteristic, which can be applied to design novel narrowband thermal emitters and detectors in the infrared region.

Radiation efficiency of narrowband coherent thermal emitters

The far field radiation efficiency achievable in narrowband thermal emitters is investigated, taking into account the full spatial and spectral variation of the emissivity. A coupled Fabry-Perot cavity model is used to develop an insight into the efficiency variation with cavity coherence and device temperature. It is found that the spatial variation of emissivity has to be explicitly included in the radiation power calculations to accurately estimate the achievable power efficiencies. The calculated radiation efficiencies of an ideal coherent cavity coupled emitter were found to vary from 0.1% to 9%, with a corresponding increase in the emission linewidth from 6.3 nm to 930 nm, and were much lower than that estimated without accounting for effects of spatial coherence. The analysis presented here can be used to determine the optimal operating temperature of a coherent thermal emitter once its emission characteristics and conduction losses are known and it is demonstrated that this optimum temperature is different from the temperature of peak blackbody emission at the resonant absorption wavelength.

Conversion of broadband to narrowband thermal emission through energy recycling

Converting from a broadband to a narrowband thermal emission spectrum with minimal loss of energy is important in the creation of efficient environmental sensors and biosensors1,2 as well as thermo-photovoltaic power generation systems3,4. Here, we demonstrate such thermal emission control by manipulating photonic modes with photonic crystals as well as material absorption with quantum-well intersubband transitions. We show that the emission peak intensity for our device can be more than four times greater than that of a blackbody sample under the same input power and thermal management conditions due to an increase in the temperature compared to the blackbody reference, and the emission bandwidth and angular spread are narrowed by a factor of 30 and 8, respectively. These results indicate that the energy saved by thermal emission control can be recycled and concentrated to enhance the narrow peak emission intensity. By constructing a thermal emission control device based on a multiple-quantum-well layer embedded in a two-dimensional photonic crystal, researchers demonstrate that they can convert a broadband thermal emission spectrum into a narrowband spectrum with minimal loss of energy.

Angle and polarization independent narrow-band thermal emitter made of metallic disk on SiO2

It is shown that the metallic disk structure can be used as an efficient narrow-band thermal emitter in the IR region. The absorption spectra of such structure are investigated both theoretically and experimentally. Calculations of thermal radiation properties of the metallic disk show that the metallic disk is a perfect emitter at a specific wavelength, which can be tuned by varying the diameter of the disk. The metallic disk exhibits only one significant localized surface plasmon polariton (LSPP) mode for both TM and TE polarizations simultaneously. The LSPP mode can be tuned by either varying the disk diameter or the spacer (made of SiO2).

NARROWBAND INFRARED EMITTER BASED ON ONE-DIMENSIONAL PHOTONIC CRYSTALS USED FOR GAS SENSING

Based on one-dimensional photonic crystals,a narrowband quasi-coherent infrared thermal emitter with the central wavelength corresponding to the infrared Absorption peak of CO2 was designed.Its central wavelength,emissivity and full width at half maximum(FWHM) are 4.23 μm,99% and 49.9nm,respectively.Transfer matrix method(TMM) and finite difference time domain method(FDTD) were used to analyze and simulate this infrared thermal emitter respectively.The results obtained by theory calculations and simulated spectral property are consistent.So the feasibility of this kind of narrowband thermal emitter is verified.

T-shaped plasmonic array as a narrow-band thermal emitter or biosensor

A T-shaped plasmonic array is proposed for application as an effective thermal emitter or biosensor. The reflection and thermal radiation properties of a T-shaped array are investigated theoretically. The angular dependent reflectance spectrum shows a clear resonant dip at 0.36 eV for full polar angles. No other significant localized resonant mode is found in the investigated spectral range from 0.12 eV to 0.64 eV. According to the Kirchhoff's law, the thermal radiation of the proposed structure can lead to a sharp peak at 3.5 microm with low sideband emission. We have also found that the T-shaped structure filled with organic material such as PMMA with different thicknesses (10 nm -50 nm) can lead to significant shift of the resonance wavelength. Thus, the T-shaped structure can also be used as a good sensor for organic materials.

Plasmonic thermal IR emitters based on nanoamorphous carbon

The development of plasmonic narrow-band thermal mid-IR emitters made from a conducting amorphous carbon composite is shown. These IR emitters have greatly improved thermal and mechanical stability compared to metallic emitters as they can be operated at 600 °C in air without any degradation in performance. The emitted thermal radiation has a bandwidth of 0.5 μm and can be set to the desired wavelength from 3 to 15 μm by changing the surface periodicity. The periodically patterned devices have in-band emissivities significantly exceeding that of the non-patterned devices, constituting simple yet efficient radiation sources at this important wavelength range.

Photonic Crystals: Shaping the Flow of Thermal Radiation

AbstractIn this paper we explore theory, design, and fabrication of photonic crystal (PhC) based selective thermal emitters. In particular, we focus on tailoring spectral and spatial properties by means of resonant enhancement in PhC's. Firstly, we explore narrow-band resonant thermal emission in photonic crystals exhibiting strong spectral and directional selectivity. We demonstrate two interesting designs based on resonant Q-matching: a vertical cavity enhanced resonant thermal emitter and 2D silicon PhC slab Fano-resonance based thermal emitter. Secondly, we examine the design of 2D tungsten PhC as a broad-band selective emitter. Indeed, based on the resonant cavity coupled resonant modes we demonstrate a highly selective, highly-spectrally efficient thermal emitter. We show that an emitter with a photonic cut-off anywhere from 1.8 μm to 2.5 μm can be designed.

Single-defect Bragg stacks for high-power narrow-band thermal emission

The radiative properties of single-defect Bragg stacks are investigated in the midinfrared region with the transfer-matrix theory. For a sufficiently small number of layers we find a regime where the structure emits radiation within a narrow range of wavelengths (δλ∕λ⩽0.01) and with an emissivity close to 1 in all directions. A description of the electric-field distribution inside the structure allows us to interpret this behavior in terms of coupling between the localized defect states and surface waves. This result should find broad applications in infrared spectroscopy, chemical sensing, and thermophotovoltaic conversion.