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1.
Adv Mater ; : e2107950, 2022 Jan 06.
Artigo em Inglês | MEDLINE | ID: mdl-34991178

RESUMO

Surface-enhanced infrared absorption (SEIRA) spectroscopy can provide label-free, non-destructive detection and identification of analytes with high sensitivity and specificity, and therefore has been widely used for various sensing applications. SEIRA sensors usually employ resonant nanophotonic structures, which can substantially enhance electric field and hence light-matter interactions by orders of magnitude in certain nanoscale hot spots of the devices. However, as ever smaller hot spots are employed to further enhance the field, the delivery of analytes into such hot spots becomes increasingly challenging. Here, we demonstrate high-performance nanophotonic SEIRA sensors based on nano-patch antennas with a liquid gallium ground plane, which not only lead to ultra-high field confinement and enhancement, but also allow for convenient and efficient delivery of analytes into nanometric hot spots by employing a simple procedure suitable for point-of-care applications. Our sensors exhibited superior sensitivity in the mid-infrared spectral region. Around 10% molecular vibrational signals (i.e., the modulation of a sensor's reflection spectrum owing to the molecular vibrational modes of the analytes) near 2900 cm-1 were achieved from sensing monolayer 1-octadecanethiol. Our cost-effective and reliable method for realizing liquid-metal-based nanophotonic structures provides a new strategy for developing high-performance sensors and other photonics applications in the infrared region. This article is protected by copyright. All rights reserved.

2.
Light Sci Appl ; 10(1): 5, 2021 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-33402668

RESUMO

Nanophotonic resonators can confine light to deep-subwavelength volumes with highly enhanced near-field intensity and therefore are widely used for surface-enhanced infrared absorption spectroscopy in various molecular sensing applications. The enhanced signal is mainly contributed by molecules in photonic hot spots, which are regions of a nanophotonic structure with high-field intensity. Therefore, delivery of the majority of, if not all, analyte molecules to hot spots is crucial for fully utilizing the sensing capability of an optical sensor. However, for most optical sensors, simple and straightforward methods of introducing an aqueous analyte to the device, such as applying droplets or spin-coating, cannot achieve targeted delivery of analyte molecules to hot spots. Instead, analyte molecules are usually distributed across the entire device surface, so the majority of the molecules do not experience enhanced field intensity. Here, we present a nanophotonic sensor design with passive molecule trapping functionality. When an analyte solution droplet is introduced to the sensor surface and gradually evaporates, the device structure can effectively trap most precipitated analyte molecules in its hot spots, significantly enhancing the sensor spectral response and sensitivity performance. Specifically, our sensors produce a reflection change of a few percentage points in response to trace amounts of the amino-acid proline or glucose precipitate with a picogram-level mass, which is significantly less than the mass of a molecular monolayer covering the same measurement area. The demonstrated strategy for designing optical sensor structures may also be applied to sensing nano-particles such as exosomes, viruses, and quantum dots.

3.
Opt Express ; 28(9): 14169-14175, 2020 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-32403877

RESUMO

This feature issue presents recent progress in long-wavelength photonics, focusing on wavelengths that span the mid-infrared (3-50 µm), the long-wavelength infrared (30-60 µm), and the terahertz (60-300 µm) portions of the electromagnetic spectrum. The papers in this feature issue report recent progress in the generation, manipulation, detection, and use of light across this long-wave region of the "photonics spectrum," including novel sources and cutting edge advances in detectors, long-wavelength non-linear processes, optical metamaterials and metasurfaces, and molecular spectroscopy. The range of topics covered in this feature issue provide an excellent insight into the expanding interest in long-wavelength photonics, which could open new possibilities for basic research and applications in industries that span health, environmental, and security.

4.
Phys Rev Lett ; 122(10): 107402, 2019 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-30932659

RESUMO

We demonstrate amplification of longitudinal optical (LO) phonons by polar-optical interaction with an electron plasma in a GaAs structure coupled to a metallic metasurface using two-color two-dimensional spectroscopy. In a novel scheme, the metamaterial resonator enhances broadband terahertz fields, which generate coherent LO phonons and drive free electrons in the conduction band of GaAs. The time evolution of the LO phonon amplitude is monitored with midinfrared pulses via the LO-phonon-induced Kerr nonlinearity of the sample, showing an amplification of the LO phonon amplitude by up to a factor of 10, in agreement with a theoretical estimate.

5.
Nat Commun ; 8: 14626, 2017 03 07.
Artigo em Inglês | MEDLINE | ID: mdl-28266509

RESUMO

The magnetic circular dichroism and the Faraday rotation are the fundamental phenomena of great practical importance arising from the breaking of the time reversal symmetry by a magnetic field. In most materials, the strength and the sign of these effects can be only controlled by the field value and its orientation. Furthermore, the terahertz range is lacking materials having the ability to affect the polarization state of the light in a non-reciprocal manner. Here we demonstrate, using broadband terahertz magneto-electro-optical spectroscopy, that in graphene both the magnetic circular dichroism and the Faraday rotation can be modulated in intensity, tuned in frequency and, importantly, inverted using only electrostatic doping at a fixed magnetic field. In addition, we observe strong magneto-plasmonic resonances in a patterned array of graphene antidots, which potentially allows exploiting these magneto-optical phenomena in a broad THz range.

6.
Nat Commun ; 6: 8969, 2015 Nov 20.
Artigo em Inglês | MEDLINE | ID: mdl-26584781

RESUMO

Metamaterials and plasmonics are powerful tools for unconventional manipulation and harnessing of light. Metamaterials can be engineered to possess intriguing properties lacking in natural materials, such as negative refractive index. Plasmonics offers capabilities of confining light in subwavelength dimensions and enhancing light-matter interactions. Recently, the technological potential of graphene-based plasmonics has been recognized as the latter features large tunability, higher field-confinement and lower loss compared with metal-based plasmonics. Here, we introduce hybrid structures comprising graphene plasmonic resonators coupled to conventional split-ring resonators, thus demonstrating a type of highly tunable metamaterial, where the interaction between the two resonances reaches the strong-coupling regime. Such hybrid metamaterials are employed as high-speed THz modulators, exhibiting ∼60% transmission modulation and operating speed in excess of 40 MHz. This device concept also provides a platform for exploring cavity-enhanced light-matter interactions and optical processes in graphene plasmonic structures for applications including sensing, photo-detection and nonlinear frequency generation.

7.
Opt Express ; 23(3): 2713-9, 2015 Feb 09.
Artigo em Inglês | MEDLINE | ID: mdl-25836133

RESUMO

Quantum Cascade devices with an emission wavelength centered around 5 µm have been shaped into compact, yet long (8 mm and 12 mm) spiral cavities to increase mid-infrared superluminescence (SL) power. Up to ~57 mW of SL power at 250 K is obtained with a Gaussian emission spectrum with a full width at half maximum of 56 cm(-1) and a coherence length of ~107 µm.

8.
Opt Express ; 21(25): 31012-8, 2013 Dec 16.
Artigo em Inglês | MEDLINE | ID: mdl-24514675

RESUMO

We investigate the impact of Distributed Bragg Reflectors (DBR), ion-milled directly on top of Fabry-Perot type Quantum Cascade (QC) laser ridges, following fabrication and processing of the devices and observe a more than 10-fold reduction in spectral full-width-half-maximum (FWHM) and a maximum of 20dB side-mode suppression ratio (SMSR), maintained to peak optical power. As predicted by our model, and experimentally verified, there is a "sweet-spot" in terms of grating length, ~200 µm on a 3 mm long laser ridge, and a trade-off between spectral narrowing and output power, set by the grating depth, varied from 1.8 to 2.5 µm.

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