The aurora is a beautiful night sky optical phenomenon that is readily seen at high-latitude locations, but with more effort can also be seen and enjoyed at mid-latitude locations. Guidelines for when and where to look are presented, along with a rich array of photographic examples of mid-latitude auroras exhibiting all the usual range of green, red, and purple colors.
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Atmospheric river changes shaped mid-latitude hydroclimate since the mid-Holocene
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Abstract Dual-comb spectroscopy has been proven beneficial in molecular characterization but remains challenging in the mid-infrared region due to difficulties in sources and efficient photodetection. Here we introduce cross-comb spectroscopy, in which a mid-infrared comb is upconverted via sum-frequency generation with a near-infrared comb of a shifted repetition rate and then interfered with a spectral extension of the near-infrared comb. We measure CO2absorption around 4.25 µm with a 1-µm photodetector, exhibiting a 233-cm−1instantaneous bandwidth, 28000 comb lines, a single-shot signal-to-noise ratio of 167 and a figure of merit of 2.4 × 106Hz1/2. We show that cross-comb spectroscopy can have superior signal-to-noise ratio, sensitivity, dynamic range, and detection efficiency compared to other dual-comb-based methods and mitigate the limits of the excitation background and detector saturation. This approach offers an adaptable and powerful spectroscopic method outside the well-developed near-IR region and opens new avenues to high-performance frequency-comb-based sensing with wavelength flexibility.
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There are a range of fundamental challenges associated with scaling optoelectronic devices down to the nano-scale, and the past decades have seen significant research dedicated to the development of sub-diffraction-limit optical devices, often relying on the plasmonic response of metal structures. At the longer wavelengths associated with the mid-infrared, dramatic changes in the optical response of traditional nanophotonic materials, reduced efficiency optoelectronic active regions, and a host of deleterious and/or parasitic effects makes nano-scale optoelectronics at micro-scale wavelengths particularly challenging. In this Perspective, we describe recent work leveraging a class of infrared plasmonic materials, highly doped semiconductors, which not only support sub-diffraction-limit plasmonic modes at long wavelengths, but which can also be integrated into a range of optoelectronic device architectures. We discuss how the wavelength-dependent optical response of these materials can serve a number of different photonic device designs, including dielectric waveguides, epsilon-near-zero dynamic optical devices, cavity-based optoelectronics, and plasmonic device architectures. We present recent results demonstrating that the highly doped semiconductor class of materials offers the opportunity for monolithic, all-epitaxial, device architectures out-performing current state of the art commercial devices, and discuss the perspectives and promise of these materials for infrared nanophotonic optoelectronics.
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Abstract High-quality optical ring resonators can confine light in a small volume and store it for millions of roundtrips. They have enabled the dramatic size reduction from laboratory scale to chip level of optical filters, modulators, frequency converters, and frequency comb generators in the visible and the near-infrared. The mid-infrared spectral region (3−12 μm), as important as it is for molecular gas sensing and spectroscopy, lags behind in development of integrated photonic components. Here we demonstrate the integration of mid-infrared ring resonators and directional couplers, incorporating a quantum cascade active region in the waveguide core. It enables electrical control of the resonant frequency, its quality factor, the coupling regime and the coupling coefficient. We show that one device, depending on its operating point, can act as a tunable filter, a nonlinear frequency converter, or a frequency comb generator. These concepts extend to the integration of multiple active resonators and waveguides in arbitrary configurations, thus allowing the implementation of purpose-specific mid-infrared active photonic integrated circuits for spectroscopy, communication, and microwave generation.
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Nanophotonic structures have shown promising routes to controlling and enhancing nonlinear optical processes at the nanoscale. However, most nonlinear nanostructures require a handling substrate, reducing their application scope. Due to the underwhelming heat dissipation, it has been a challenge to evaluate the nonlinear optical properties of free-standing nanostructures. Here, we overcome this challenge by performing shot-controlled fifth harmonic generation (FHG) measurements on a SiC meta-membrane – a free-standing transmission metasurface with pronounced optical resonances in the mid-infrared (λres≈ 4,000 nm). Back focal plane imaging of the FHG diffraction orders and rigorous finite-difference time-domain simulations reveal at least two orders of magnitude enhancement of the FHG from the meta-membrane, compared to the unstructured SiC film of the same thickness. Single-shot measurements of the meta-membrane with varying resonance positions reveal an unusual spectral behavior that we explain with Kerr-driven intensity-dependent resonance dynamics. This work paves the way for novel substrate-less nanophotonic architectures.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1016/j.epsl.2020.116293
