Publications by Andreas Tittl | EPFL Graph Search

Metasurface-Enhanced Infrared Spectroscopy: An Abundance of Materials and Functionalities

Hatice Altug, Aurélian Michel John-Herpin, Felix Ulrich Richter, Andreas Tittl

Infrared spectroscopy provides unique information on the composition and dynamics of biochemical systems by resolving the characteristic absorption fingerprints of their constituent molecules. Based on this inherent chemical specificity and the capability for label-free, noninvasive, and real-time detection, infrared spectroscopy approaches have unlocked a plethora of breakthrough applications for fields ranging from environmental monitoring and defense to chemical analysis and medical diagnostics. Nanophotonics has played a crucial role for pushing the sensitivity limits of traditional far-field spectroscopy by using resonant nanostructures to focus the incident light into nanoscale hot-spots of the electromagnetic field, greatly enhancing light-matter interaction. Metasurfaces composed of regular arrangements of such resonators further increase the design space for tailoring this nanoscale light control both spectrally and spatially, which has established them as an invaluable toolkit for surface-enhanced spectroscopy. Starting from the fundamental concepts of metasurface-enhanced infrared spectroscopy, a broad palette of resonator geometries, materials, and arrangements for realizing highly sensitive metadevices is showcased, with a special focus on emerging systems such as phononic and 2D van der Waals materials, and integration with waveguides for lab-on-a-chip devices. Furthermore, advanced sensor functionalities of metasurface-based infrared spectroscopy, including multiresonance, tunability, dielectrophoresis, live cell sensing, and machine-learning-aided analysis are highlighted.

WILEY-V C H VERLAG GMBH2022

Comparison and Verification of Simulation Results of DeST Based on ASHRAE-140 Standard

Hatice Altug, Aleksandrs Leitis, Andreas Tittl

Based on the ASHRAE Standard 140-2014, this study takes the simulation results of DeST and other simulation software to comprehensively test the accuracy and validity of DeST in calculating building thermal loads and space cooling and heating equipment performance. Special cases were also designed to find out the influencing factors that led to results' differences. It was found that the solar lost through the window, the setting of shading geometry and the mode of inputting surface coefficients can make a big difference to the simulation results. The calculation deviations in most ASHRAE-140 cases are within 10%, which indicate the accuracy of DeST in building energy simulation.

IEEE2021

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IEEE2021

All-Dielectric Programmable Huygens' Metasurfaces

Hatice Altug, Aleksandrs Leitis, Andreas Tittl

Low-loss nanostructured dielectric metasurfaces have emerged as a breakthrough platform for ultrathin optics and cutting-edge photonic applications, including beam shaping, focusing, and holography. However, the static nature of their constituent materials has traditionally limited them to fixed functionalities. Tunable all-dielectric infrared Huygens' metasurfaces consisting of multi-layer Ge disk meta-units with strategically incorporated non-volatile phase change material Ge3Sb2Te6 are introduced. Switching the phase-change material between its amorphous and crystalline structural state enables nearly full dynamic light phase control with high transmittance in the mid-IR spectrum. The metasurface is realized experimentally, showing post-fabrication tuning of the light phase within a range of 81% of the full 2 pi phase shift. Additionally, the versatility of the tunable Huygen's metasurfaces is demonstrated by optically programming the spatial light phase distribution of the metasurface with single meta-unit precision and retrieving high-resolution phase-encoded images using hyperspectral measurements. The programmable metasurface concept overcomes the static limitations of previous dielectric metasurfaces, paving the way for "universal" metasurfaces and highly efficient, ultracompact active optical elements like tunable lenses, dynamic holograms, and spatial light modulators.

WILEY-V C H VERLAG GMBH2020

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Detection and differentiation of enantiomers in small quantities are crucially important in many scientific fields, including biology, chemistry, and pharmacy. Chiral molecules manifest their handedness in their interaction with the chiral state of light (e.g., circularly polarized light), which is commonly leveraged in circular dichroism (CD) spectroscopy. However, compared to the linear refractive index molecular chirality is extremely weak, resulting in low detection efficiencies. Recently, it has been shown that these weak chiroptical signals can be enhanced by increasing the optical chirality of the electromagnetic fields interacting with chiral samples. Here, we show numerically and analytically that dielectric structures can provide an optimum chiral sensing platform by offering uniform superchiral near-fields. To illustrate this, we first study a simple dielectric dimer and show that circularly polarized light can induce parallel and out of phase electric and magnetic fields, which are spectrally and spatially overlapped, and therefore produce superchiral fields at the midpoint of the dimer. This behavior is in contrast to, for example, a plasmonic dimer, where the optical chirality is limited by the electric dipolar field, which is not completely out of phase with the incident magnetic field. With the insights gained from this analysis, next we develop an approach for overlapping electric and magnetic fields in a single particle, based on Kerker effect. In particular, we introduce a Kerker-inspired metasurface consisting of holey dielectric disks, which offers uniform and accessible superchiral near-fields with CD signal enhancements of nearly 24 times.

AMER CHEMICAL SOC2019

All-dielectric Metasurfaces for Infrared Absorption Spectroscopy Applications

Hatice Altug, Aleksandrs Leitis, Mingkai Liu, Andreas Tittl, Filiz Yesilköy

We present a nanophotonic method capable of detecting mid-infrared molecular fingerprints without the need for spectrometry, frequency scanning, or moving mechanical parts. We leverage dielectric metasurfaces featuring ultra-sharp resonances each tuned to discrete frequencies, enabling us to sample molecular absorption signatures over the mid-IR spectral range. (c) 2019 The Author(s)

IEEE2019

Angle-multiplexed all-dielectric metasurfaces for broadband molecular fingerprint retrieval

Hatice Altug, Bang Hyun Lee, Aleksandrs Leitis, Mingkai Liu, Andreas Tittl

Infrared spectroscopy resolves the structure of molecules by detecting their characteristic vibrational fingerprints. Subwavelength light confinement and nanophotonic enhancement have extended the scope of this technique for monolayer studies. However, current approaches still require complex spectroscopic equipment or tunable light sources. Here, we introduce a novel metasurface-based method for detecting molecular absorption fingerprints over a broad spectrum, which combines the device-level simplicity of state-of-the-art angle-scanning refractometric sensors with the chemical specificity of infrared spectroscopy. Specifically, we develop germanium-based high-Q metasurfaces capable of delivering a multitude of spectrally selective and surface-sensitive resonances between 1100 and 1800 cm−1. We use this approach to detect distinct absorption signatures of different interacting analytes including proteins, aptamers, and polylysine. In combination with broadband incoherent illumination and detection, our method correlates the total reflectance signal at each incidence angle with the strength of the molecular absorption, enabling spectrometer-less operation in a compact angle-scanning configuration ideally suited for field-deployable applications.

2019

Enhanced Circular Dichroism and Chiral Sensing with Bound States in the Continuum

Hatice Altug, Yasaman Jahani, Andreas Tittl

We reveal that optical chirality at the nanoscale can be boosted dramatically by bound states in the continuum (BIC). We predict the enhancement of chiroptical signals from nanostructures supporting quasi-BICs in mid-IR with a record-high efficiency. (C) 2019 The Author(s)

IEEE2019

Metasurface-Based Molecular Biosensing Aided by Artificial Intelligence

Hatice Altug, Aurélian Michel John-Herpin, Aleksandrs Leitis, Eduardo Romero Arvelo, Andreas Tittl

Molecular spectroscopy provides unique information on the internal structure of biological materials by detecting the characteristic vibrational signatures of their constituent chemical bonds at infrared frequencies. Nanophotonic antennas and metasurfaces have driven this concept towards few-molecule sensitivity by confining incident light into intense hot spots of the electromagnetic fields, providing strongly enhanced light-matter interaction. In this Minireview, recently developed molecular biosensing approaches based on the combination of dielectric metasurfaces and imaging detection are highlighted in comparison to traditional plasmonic geometries, and the unique potential of artificial intelligence techniques for nanophotonic sensor design and data analysis is emphasized. Because of their spectrometer-less operation principle, such imaging-based approaches hold great promise for miniaturized biosensors in practical point-of-care or field-deployable applications.

WILEY-V C H VERLAG GMBH2019

Metasurface‐based molecular biosensing aided by artificial intelligence

Hatice Altug, Aurélian Michel John-Herpin, Aleksandrs Leitis, Eduardo Romero Arvelo, Andreas Tittl

Molecular spectroscopy provides unique information on the internal structure of biological materials by detecting the characteristic vibrational signatures of their constituent chemical bonds at infrared frequencies. Nanophotonic antennas and metasurfaces have driven this concept towards few‐molecule sensitivities by confining incident light into intense hot spots of the electromagnetic fields, providing strongly enhanced light‐matter interaction. In this Minireview, recently developed molecular biosensing approaches based on the combination of dielectric metasurfaces and imaging detection are highlighted in comparison to traditional plasmonic geometries, and the unique potential of artificial intelligence techniques for nanophotonic sensor design and data analysis is emphasized. Because of their spectrometer‐less operation principle, such imaging‐based approaches hold great promise for miniaturized biosensors in practical point‐of‐care or field‐deployable applications.

2019