Topic
Absorption (electromagnetic radiation)
About: Absorption (electromagnetic radiation) is a research topic. Over the lifetime, 76674 publications have been published within this topic receiving 1381221 citations.
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TL;DR: The broadband, coherent nature of narrow-linewidth fiber frequency combs is exploited to measure the full complex spectrum of a molecular gas through multiheterodyne spectroscopy, and the measured phase spectrum agrees with the Kramers-Kronig transformation of the absorption spectrum.
Abstract: The broadband, coherent nature of narrow-linewidth fiber frequency combs is exploited to measure the full complex spectrum of a molecular gas through multiheterodyne spectroscopy. We measure the absorption and phase shift experienced by each of 155 000 individual frequency-comb lines, spaced by 100 MHz and spanning from 1495 to 1620 nm, after passing through hydrogen cyanide gas. The measured phase spectrum agrees with the Kramers-Kronig transformation of the absorption spectrum. This technique can provide a full complex spectrum rapidly, over wide bandwidths, and with hertz-level accuracy.
744 citations
TL;DR: Three two-dimensional conjugated polythiophenes with bi(thienylenevinylene) side chains with biTV-PTs, designed and synthesized for application in polymer solar cells, are shown to be promising polymer photovoltaic materials.
Abstract: Three two-dimensional (2-D) conjugated polythiophenes with bi(thienylenevinylene) side chains (biTV-PTs), P1, P2, and P3, were designed and synthesized for application in polymer solar cells. The absorption spectral, electrochemical, and photovoltaic properties of the biTV-PTs were investigated and compared with those of poly(3-hexylthiophene) (P3HT). The biTV-PTs show a broad absorption band from 350 to 650 nm; especially, the absorption spectrum of P3 displays a broad plateau and much stronger absorbance than that of P3HT in the wavelength range from 350 to 480 nm. Cyclic voltammograms reveal that the onset oxidation and reduction potentials of the biTV-PTs positively shifted by ca. 0.2 V in comparison with those of P3HT, indicating that the HOMO energy level of the biTV-PTs is ca. 0.2 eV lower than that of P3HT. Polymer solar cells (PSCs) were fabricated based on the blend of the polymers and 1-(3-methoxycarbonyl)propyl-1-phenyl-[6,6]-C-61 (PCBM) with a weight ratio of 1:1. The open circuit voltage of ...
741 citations
TL;DR: In this paper, an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial is presented, where light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths.
Abstract: We present an ultra broadband thin-film infrared absorber made of saw-toothed anisotropic metamaterial. Absorbtivity of higher than 95% at normal incidence is supported in a wide range of frequencies, where the full absorption width at half maximum is about 86%. Such property is retained well at a very wide range of incident angles too. Light of shorter wavelengths are harvested at upper parts of the sawteeth of smaller widths, while light of longer wavelengths are trapped at lower parts of larger tooth widths. This phenomenon is explained by the slowlight modes in anisotropic metamaterial waveguide. Our study can be applied in the field of designing photovoltaic devices and thermal emitters.
736 citations
TL;DR: In this article, a microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated, which is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids.
Abstract: A microwave ultra-broadband polarization-independent metamaterial absorber is demonstrated. It is composed of a periodic array of metal-dielectric multilayered quadrangular frustum pyramids. These pyramids possess resonant absorption modes at multi-frequencies, of which the overlapping leads to the total absorption of the incident wave over an ultra-wide spectral band. The experimental absorption at normal incidence is above 90% in the frequency range of 7.8–14.7 GHz, and the absorption is kept large when the incident angle is smaller than 60°. The experimental results agree well with the numerical simulation.
735 citations
TL;DR: In this article, the authors study the carrier dynamics in planar methyl ammonium lead iodide perovskite films using broadband transient absorption spectroscopy and show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9'meV.
Abstract: We study the carrier dynamics in planar methyl ammonium lead iodide perovskite films using broadband transient absorption spectroscopy. We show that the sharp optical absorption onset is due to an exciton transition that is inhomogeneously broadened with a binding energy of 9 meV. We fully characterize the transient absorption spectrum by free-carrier-induced bleaching of the exciton transition, quasi-Fermi energy, carrier temperature and bandgap renormalization constant. The photo-induced carrier temperature is extracted from the transient absorption spectra and monitored as a function of delay time for different excitation wavelengths and photon fluences. We find an efficient hot-phonon bottleneck that slows down cooling of hot carriers by three to four orders of magnitude in time above a critical injection carrier density of ∼5 × 1017 cm−3. Compared with molecular beam epitaxially grown GaAs, the critical density is an order of magnitude lower and the relaxation time is approximately three orders of magnitude longer. Hot carriers in perovskites experience slow cooling.
717 citations