@article{21080, abstract = {Tight binding was observed between the C‐terminal cross section of aromatic oligoamide helices in aqueous solution, leading to the formation of discrete head‐to‐head dimers in slow exchange on the NMR timescale with the corresponding monomers. The nature and structure of the dimers was evidenced by 2D NOESY and DOSY spectroscopy, mass spectrometry and X‐ray crystallography. The binding interface involves a large hydrophobic aromatic surface and hydrogen bonding. Dimerization requires that helices have the same handedness and the presence of a C‐terminal carboxy function. The protonation state of the carboxy group plays a crucial role, resulting in pH dependence of the association. Dimerization is also influenced by neighboring side chains and can be programmed to selectively produce heteromeric aggregates.}, author = {Bindl, Daniel and Mandal, Pradeep K and Allmendinger, Lars and Huc, Ivan}, issn = {1521-3773}, journal = {Angewandte Chemie International Edition}, number = {11}, publisher = {Wiley}, title = {{Discrete stacked dimers of aromatic oligoamide helices}}, doi = {10.1002/anie.202116509}, volume = {61}, year = {2022}, } @article{21527, abstract = {Optical metasurfaces have been heralded as the platform to integrate multiple functionalities in a compact form-factor, with the potential to replace bulky optical components. A central stepping stone toward realizing this promise is the demonstration of multifunctionality under several constraints (e.g., at multiple incident wavelengths and/or angles) in a single device, an achievement being hampered by design limitations inherent to single-layer planar geometries. Here, we propose a framework for the inverse design of multilayer metaoptics via topology optimization, showing that even few-wavelength thick devices can achieve high-efficiency multifunctionality, such as multiangle light concentration and plan-achromaticity. We embody our framework in multiple closely spaced patterned layers of a low-index polymer, with fabrication constraints specific to this platform enforced in the optimization process. We experimentally demonstrate our approach with an inverse-designed 3D-printed light concentrator working at five different nonparaxial angles of incidence. Our framework paves the way toward realizing multifunctional ultracompact 3D nanophotonic devices.}, author = {Roques-Carmes, Charles and Lin, Zin and Christiansen, Rasmus E. and Salamin, Yannick and Kooi, Steven E. and Joannopoulos, John D. and Johnson, Steven G. and Soljačić, Marin}, issn = {2330-4022}, journal = {ACS Photonics}, keywords = {metasurfaces, inverse design, multilayered metaoptics, 3D printing, topology optimization}, number = {1}, pages = {43--51}, publisher = {American Chemical Society}, title = {{Toward 3D-printed inverse-designed metaoptics}}, doi = {10.1021/acsphotonics.1c01442}, volume = {9}, year = {2022}, } @article{21584, abstract = {Bombardment of materials by high-energy particles often leads to light emission in a process known as scintillation. Scintillation has widespread applications in medical imaging, x-ray nondestructive inspection, electron microscopy, and high-energy particle detectors. Most research focuses on finding materials with brighter, faster, and more controlled scintillation. We developed a unified theory of nanophotonic scintillators that accounts for the key aspects of scintillation: energy loss by high-energy particles, and light emission by non-equilibrium electrons in nanostructured optical systems. We then devised an approach based on integrating nanophotonic structures into scintillators to enhance their emission, obtaining nearly an order-of-magnitude enhancement in both electron-induced and x-ray–induced scintillation. Our framework should enable the development of a new class of brighter, faster, and higher-resolution scintillators with tailored and optimized performance.}, author = {Roques-Carmes, Charles and Rivera, Nicholas and Ghorashi, Ali and Kooi, Steven E. and Yang, Yi and Lin, Zin and Beroz, Justin and Massuda, Aviram and Sloan, Jamison and Romeo, Nicolas and Yu, Yang and Joannopoulos, John D. and Kaminer, Ido and Johnson, Steven G. and Soljačić, Marin}, issn = {1095-9203}, journal = {Science}, number = {6583}, publisher = {American Association for the Advancement of Science}, title = {{A framework for scintillation in nanophotonics}}, doi = {10.1126/science.abm9293}, volume = {375}, year = {2022}, } @inproceedings{21590, abstract = {We introduce end-to-end inverse design in which a nanophotonics frontend is optimized in conjunction with a computational-imaging backend to minimize reconstruction errors. We present several nanophotonics designs for depth, spectral and polarization imaging.}, author = {Lin, Zin and Arya, Gaurav and Li, William F. and Roques-Carmes, Charles and Pestourie, Raphaël and Li, Zhaoyi and Capasso, Federico and Soljačić, Marin and Johnson, Steven G.}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{End-to-end nanophotonics inverse design for computational imaging}}, doi = {10.1364/cleo_at.2022.jw5q.1}, year = {2022}, } @inproceedings{21591, abstract = {We present a method for angle and wavelength sensing for underdetermined imaging systems by performing end-to-end nanophotonic inverse design with a compressed sensing backend.}, author = {Li, William F. and Arya, Gaurav and Roques-Carmes, Charles and Lin, Zin and Johnson, Steven G. and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Angular and spectral sparse sensing with end-to-end optimized nanophotonics}}, doi = {10.1364/cleo_at.2022.jw5q.2}, year = {2022}, } @inproceedings{21624, abstract = {We show in both theory and experiment that flatband photonic resonances can control and boost free-electron radiation, as validated by enhancement, band, and polarization-shaping measurements.}, author = {Yang, Yi and Roques-Carmes, Charles and Kooi, Steven E. and Tang, Haoning and Beroz, Justin and Mazur, Eric and Kaminer, Ido and Joannopoulos, John D. and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Enhanced Smith–Purcell radiation from photonic flatband resonances}}, doi = {10.1364/cleo_qels.2022.ff2c.7}, year = {2022}, } @inproceedings{21625, abstract = {We demonstrate how Implosion Fabrication, a new three-dimensional nanofabrication technique, enables the realization of three-dimensional photonic devices at optical wavelengths. We realize two- and three-dimensional optical crystals of hydrogel-embedded silver meta-atoms.}, author = {Salamin, Yannick and Mills, Brian and Yang, Gaojie and Yang, Quansan and Swain, Corban and Oran, Daniel and Sloan, Jamison and Roques-Carmes, Charles and Beroz, Justin and Kooi, Steven E. and Boyden, Edward S. and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{Three-dimensional optical crystals nanoprinted in a hydrogel}}, doi = {10.1364/cleo_qels.2022.ff2d.1}, year = {2022}, } @inproceedings{21628, abstract = {We develop a general framework to enhance and control X-ray scintillation by embedding nanophotonic structures into scintillators. We demonstrate 10-fold scintillation enhancement in a conventional scintillator, showing the potential of our technique for X-ray imaging.}, author = {Roques-Carmes, Charles and Rivera, Nicholas and Kooi, Steven E. and Yu, Yang and Joannopoulos, John D. and Kaminer, Ido and Soljačić, Marin}, booktitle = {Conference on Lasers and Electro-Optics}, location = {San Jose, CA, United States}, publisher = {Optica Publishing Group}, title = {{X-ray imaging with nanophotonic scintillators}}, doi = {10.1364/cleo_si.2022.sm3k.1}, year = {2022}, } @article{21638, abstract = {We introduce end-to-end inverse design for multi-channel imaging, in which a nanophotonic frontend is optimized in conjunction with an image-processing backend to extract depth, spectral and polarization channels from a single monochrome image. Unlike diffractive optics, we show that subwavelength-scale “metasurface” designs can easily distinguish similar wavelength and polarization inputs. The proposed technique integrates a single-layer metasurface frontend with an efficient Tikhonov reconstruction backend, without any additional optics except a grayscale sensor. Our method yields multi-channel imaging by spontaneous demultiplexing: the metaoptics front-end separates different channels into distinct spatial domains whose locations on the sensor are optimally discovered by the inverse-design algorithm. We present large-area metasurface designs, compatible with standard lithography, for multi-spectral imaging, depth-spectral imaging, and “all-in-one” spectro-polarimetric-depth imaging with robust reconstruction performance (≲ 10% error with 1% detector noise). In contrast to neural networks, our framework is physically interpretable and does not require large training sets. It can be used to reconstruct arbitrary three-dimensional scenes with full multi-wavelength spectra and polarization textures.}, author = {Lin, Zin and Pestourie, Raphaël and Roques-Carmes, Charles and Li, Zhaoyi and Capasso, Federico and Soljačić, Marin and Johnson, Steven G.}, issn = {1094-4087}, journal = {Optics Express}, number = {16}, pages = {28358--28370}, publisher = {Optica Publishing Group}, title = {{End-to-end metasurface inverse design for single-shot multi-channel imaging}}, doi = {10.1364/oe.449985}, volume = {30}, year = {2022}, } @unpublished{21673, abstract = {When impinging on optical structures or passing in their vicinity, free electrons can spontaneously emit electromagnetic radiation, a phenomenon generally known as cathodoluminescence. Free-electron radiation comes in many guises: Cherenkov, transition, and Smith-Purcell radiation, but also electron scintillation, commonly referred to as incoherent cathodoluminescence. While those effects have been at the heart of many fundamental discoveries and technological developments in high-energy physics in the past century, their recent demonstration in photonic and nanophotonic systems has attracted a lot of attention. Those developments arose from predictions that exploit nanophotonics for novel radiation regimes, now becoming accessible thanks to advances in nanofabrication. In general, the proper design of nanophotonic structures can enable shaping, control, and enhancement of free-electron radiation, for any of the above-mentioned effects. Free-electron radiation in nanophotonics opens the way to promising applications, such as widely-tunable integrated light sources from x-ray to THz frequencies, miniaturized particle accelerators, and highly sensitive high-energy particle detectors. Here, we review the emerging field of free-electron radiation in nanophotonics. We first present a general, unified framework to describe free-electron light-matter interaction in arbitrary nanophotonic systems. We then show how this framework sheds light on the physical underpinnings of many methods in the field used to control and enhance free-electron radiation. Namely, the framework points to the central role played by the photonic eigenmodes in controlling the output properties of free-electron radiation (e.g., frequency, directionality, and polarization). [... see full abstract in paper]}, author = {Roques-Carmes, Charles and Kooi, Steven E. and Yang, Yi and Rivera, Nicholas and Keathley, Phillip D. and Joannopoulos, John D. and Johnson, Steven G. and Kaminer, Ido and Berggren, Karl K. and Soljačić, Marin}, booktitle = {arXiv}, title = {{Free-electron-light interactions in nanophotonics}}, doi = {10.48550/arXiv.2208.02368}, year = {2022}, } @article{21809, abstract = {Controlling the multistage photoresponsivity remains a challenge, in part, due to the spontaneous tautomerization between isomers. Herein, we present a strategy to access three independent states (linear, cyclic keto, and cyclic enolate) of crown ether (CE)-substituted donor–acceptor Stenhouse adducts (DASAs) by limiting the tautomerization of the closed isomers. The linear–cyclic keto isomerization is reversibly triggered by treatment with metal ions (Na+ or K+) and CE, while the linear–cyclic enolate isomerization is induced by green light and heat. Density functional theory and molecular dynamics calculation results suggest that the steric effect and supramolecular interaction between the electron-donating and electron-withdrawing moieties play an important role in hindering the tautomerization between cyclic keto and cyclic enolate DASA-CE. The strategy to influence key steps in the photoswitching process inspires well-controlled multistage isomerization of photoresponsive molecules.}, author = {Duan, Yongli and Zhao, Haiquan and Xue, Guodong and Sun, Fanxi and Stricker, Friedrich J and Wang, Zhen and Mao, Lijun and He, Chao and de Alaniz, Javier Read and Zheng, Yonghao and Wang, Dongsheng}, issn = {1520-5207}, journal = {The Journal of Physical Chemistry B}, number = {17}, pages = {3347--3354}, publisher = {American Chemical Society}, title = {{Controlling the isomerization of photoresponsive molecules through a limiting tautomerization strategy}}, doi = {10.1021/acs.jpcb.2c02005}, volume = {126}, year = {2022}, } @article{21819, abstract = {The ability of molecular photoswitches to convert on/off responses into large macroscale property change is fundamental to light-responsive materials. However, moving beyond simple binary responses necessitates the introduction of new elements that control the chemistry of the photoswitching process at the molecular scale. To achieve this goal, we designed, synthesized and developed a single photochrome, based on a modified donor–acceptor Stenhouse adduct (DASA), capable of independently addressing multiple molecular states. The multi-stage photoswitch enables complex switching phenomena. To demonstrate this, we show spatial control of the transformation of a three-stage photoswitch by tuning the population of intermediates along the multi-step reaction pathway of the DASAs without interfering with either the first or final stage. This allows for a photonic three-stage logic gate where the secondary wavelength solely negates the input of the primary wavelength. These results provide a new strategy to move beyond traditional on/off binary photochromic systems and enable the design of future molecular logic systems.}, author = {Stricker, Friedrich J and Sanchez, David M. and Raucci, Umberto and Dolinski, Neil D. and Zayas, Manuel S. and Meisner, Jan and Hawker, Craig. J. and Martínez, Todd. J. and Read de Alaniz, Javier}, issn = {1755-4349}, journal = {Nature Chemistry}, pages = {942--948}, publisher = {Springer Nature}, title = {{A multi-stage single photochrome system for controlled photoswitching responses}}, doi = {10.1038/s41557-022-00947-8}, volume = {14}, year = {2022}, } @article{21823, abstract = {DFT calculations were used to find an optimal substitution site on the triene backbone of a donor–acceptor Stenhouse adduct photoswitch to tune the equillibrium and switching kinetics of DASA without modifying the donor and acceptor groups. Using this approach we demonstrate a new means to tuning DASA based photoswitches by increasing the energy of the closed form relative to the open form. To highlight the potential of this approach a new DASA derivative bearing a methyl substituent on the 5-position of the triene was synthesized and the effect of this substitution was studied using 1H NMR spectroscopy, time-dependent UV-Vis and solvatochromic analysis. The new DASA derivative shows a higher dark equillibrium, favoring the open form, and drastically faster thermal recovery than the unsubstituted derivative with the same donor and acceptor.}, author = {Peterson, Julie A. and Stricker, Friedrich J and Read de Alaniz, Javier}, issn = {1364-548X}, journal = {Chemical Communications}, number = {14}, pages = {2303--2306}, publisher = {Royal Society of Chemistry}, title = {{Improving the kinetics and dark equilibrium of donor-acceptor Stenhouse adduct by triene backbone design}}, doi = {10.1039/d1cc06235b}, volume = {58}, year = {2022}, } @article{21824, abstract = {We investigate the influence of the host matrix on the photothermally driven actuation performance of negatively photochromic, donor−acceptor Stenhouse adduct (DASA)-based polymers. Using a modular Diels−Alder “click” platform, we designed polymeric materials with varying DASA incorporation and investigated the relationships between the material composition and the resulting physical, mechanical, and photoswitching properties. We demonstrate that increasing the DASA concentration in polymer conjugates has a dramatic effect on the material’s physical and mechanical properties, such as the glass transition temperature (Tg) and elastic modulus, as well as the photoswitching properties, which are found to be highly dependent on Tg. We establish using a simple photoresponsive bilayer that actuation performance is controlled by the bilayer stiffness rather than the photochrome incorporation of DASA. Finally, we report and compare the light-induced property changes in Tg and the elastic modulus between the materials comprising the open or closed forms of DASAs. Our results demonstrate the importance of designing a material that is stiff enough to provide the mechanical strength required for actuation under load, but soft enough to reversibly switch at the operational temperature and provide key considerations for the development of application-geared photoswitchable materials.}, author = {Sroda, Miranda M. and Lee, Jaejun and Kwon, Younghoon and Stricker, Friedrich J and Park, Minwook and Valentine, Megan T. and Read de Alaniz, Javier}, issn = {2637-6105}, journal = {ACS Applied Polymer Materials}, keywords = {donor−acceptor Stenhouse adducts, photothermal actuation, photo-induced property changes, negative photochromism, glass transition temperature}, number = {1}, pages = {141--149}, publisher = {American Chemical Society}, title = {{Role of material composition in photothermal actuation of DASA-based polymers}}, doi = {10.1021/acsapm.1c01108}, volume = {4}, year = {2022}, } @article{21827, author = {Stricker, Friedrich J and Julie, Peterson and Javier, Read de Alaniz}, issn = {2333-3553}, journal = {Organic Syntheses}, pages = {79--91}, publisher = {Organic Syntheses}, title = {{Preparation of a donor-acceptor Stenhouse Adduct (DASA): 5-((2Z,4E)-5-(diethylamino)-2-hydroxypenta-2,4-dien-1-ylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione}}, doi = {10.15227/orgsyn.099.0079}, volume = {99}, year = {2022}, } @inbook{21828, abstract = {Donor–acceptor Stenhouse adducts (DASA) are a reported class of visible-light-activated photoswitches. DASA synthesis involves two steps using furfural as starting material, while their complex photoswitching mechanism consists both of actinic and thermal steps. As a result of their visible-light activation, negative photochromism, large volume and polarity change, and wavelength tunability, DASAs present significant promise toward light-activated materials. In the years since their first report in 2014, a number of applications have utilized DASA ranging from selective cargo release over controlled phase transfer to directed flow in solution.}, author = {Stricker, Friedrich J and Seshadri, Serena and de Alaniz, Javier Read}, booktitle = {Molecular Photoswitches: Chemistry, Properties, and Applications}, editor = {Pianowski, Zbigniew}, isbn = {9783527347681}, pages = {303--324}, publisher = {Wiley}, title = {{Donor-Acceptor Stenhouse Adducts}}, doi = {10.1002/9783527827626.ch14}, year = {2022}, } @article{13445, abstract = {Rotation is typically assumed to induce strictly symmetric rotational splitting into the rotational multiplets of pure p- and g-modes. However, for evolved stars exhibiting mixed modes, avoided crossings between different multiplet components are known to yield asymmetric rotational splitting, in particular for near-degenerate mixed-mode pairs, where notional pure p-modes are fortuitously in resonance with pure g-modes. These near-degeneracy effects have been described in subgiants, but their consequences for the characterization of internal rotation in red giants have not previously been investigated in detail, in part owing to theoretical intractability. We employ new developments in the analytic theory of mixed-mode coupling to study these near-resonance phenomena. In the vicinity of the most p-dominated mixed modes, the near-degenerate intrinsic asymmetry from pure rotational splitting increases dramatically over the course of stellar evolution, and it depends strongly on the mode-mixing fraction ζ. We also find that a linear treatment of rotation remains viable for describing the underlying p- and g-modes, even when it does not for the resulting mixed modes undergoing these avoided crossings. We explore observational consequences for potential measurements of asymmetric mixed-mode splitting, which has been proposed as a magnetic-field diagnostic. Finally, we propose improved measurement techniques for rotational characterization, exploiting the linearity of rotational effects on the underlying p/g-modes, while still accounting for these mixed-mode coupling effects.}, author = {Ong, J. M. Joel and Bugnet, Lisa Annabelle and Basu, Sarbani}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {1}, publisher = {American Astronomical Society}, title = {{Mode mixing and rotational splittings. I. Near-degeneracy effects revisited}}, doi = {10.3847/1538-4357/ac97e7}, volume = {940}, year = {2022}, } @article{13451, abstract = {We characterize massive stars (M > 8 M⊙) in the nearby (D ∼ 0.8 Mpc) extremely metal-poor (Z ∼ 5% Z⊙) galaxy Leo A using Hubble Space Telescope ultraviolet (UV), optical, and near-infrared (NIR) imaging along with Keck/Low-Resolution Imaging Spectrograph and MMT/Binospec optical spectroscopy for 18 main-sequence OB stars. We find that: (a) 12 of our 18 stars show emission lines, despite not being associated with an H ii region, suggestive of stellar activity (e.g., mass loss, accretion, binary star interaction), which is consistent with previous predictions of enhanced activity at low metallicity; (b) six are Be stars, which are the first to be spectroscopically studied at such low metallicity—these Be stars have unusual panchromatic SEDs; (c) for stars well fit by the TLUSTY nonlocal thermodynamic equilibrium models, the photometric and spectroscopic values of $\mathrm{log}({T}_{\mathrm{eff}})$ and $\mathrm{log}(g)$ agree to within ∼0.01 dex and ∼0.18 dex, respectively, indicating that near-UV/optical/NIR imaging can be used to reliably characterize massive (M ∼ 8–30 M⊙) main-sequence star properties relative to optical spectroscopy; (d) the properties of the most-massive stars in H II regions are consistent with constraints from previous nebular emission line studies; and (e) 13 stars with M > 8M⊙ are >40 pc from a known star cluster or H II region. Our sample comprises ∼50% of all known massive stars at Z ≲ 10% Z⊙with derived stellar parameters, high-quality optical spectra, and panchromatic photometry.}, author = {Gull, Maude and Weisz, Daniel R. and Senchyna, Peter and Sandford, Nathan R. and Choi, Yumi and McLeod, Anna F. and El-Badry, Kareem and Götberg, Ylva Louise Linsdotter and Gilbert, Karoline M. and Boyer, Martha and Dalcanton, Julianne J. and GuhaThakurta, Puragra and Goldman, Steven and Marigo, Paola and McQuinn, Kristen B. W. and Pastorelli, Giada and Stark, Daniel P. and Skillman, Evan and Ting, Yuan-sen and Williams, Benjamin F.}, issn = {1538-4357}, journal = {The Astrophysical Journal}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, publisher = {American Astronomical Society}, title = {{A panchromatic study of massive stars in the extremely metal-poor local group dwarf galaxy Leo A}}, doi = {10.3847/1538-4357/aca295}, volume = {941}, year = {2022}, } @article{13452, abstract = {Magnetic fields can drastically change predictions of evolutionary models of massive stars via mass-loss quenching, magnetic braking, and efficient angular momentum transport, which we aim to quantify in this work. We use the MESA software instrument to compute an extensive main-sequence grid of stellar structure and evolution models, as well as isochrones, accounting for the effects attributed to a surface fossil magnetic field. The grid is densely populated in initial mass (3–60 M⊙), surface equatorial magnetic field strength (0–50 kG), and metallicity (representative of the Solar neighbourhood and the Magellanic Clouds). We use two magnetic braking and two chemical mixing schemes and compare the model predictions for slowly rotating, nitrogen-enriched (‘Group 2’) stars with observations in the Large Magellanic Cloud. We quantify a range of initial field strengths that allow for producing Group 2 stars and find that typical values (up to a few kG) lead to solutions. Between the subgrids, we find notable departures in surface abundances and evolutionary paths. In our magnetic models, chemical mixing is always less efficient compared to non-magnetic models due to the rapid spin-down. We identify that quasi-chemically homogeneous main sequence evolution by efficient mixing could be prevented by fossil magnetic fields. We recommend comparing this grid of evolutionary models with spectropolarimetric and spectroscopic observations with the goals of (i) revisiting the derived stellar parameters of known magnetic stars, and (ii) observationally constraining the uncertain magnetic braking and chemical mixing schemes.}, author = {Keszthelyi, Z and de Koter, A and Götberg, Ylva Louise Linsdotter and Meynet, G and Brands, S A and Petit, V and Carrington, M and David-Uraz, A and Geen, S T and Georgy, C and Hirschi, R and Puls, J and Ramalatswa, K J and Shultz, M E and ud-Doula, A}, issn = {1365-2966}, journal = {Monthly Notices of the Royal Astronomical Society}, keywords = {Space and Planetary Science, Astronomy and Astrophysics}, number = {2}, pages = {2028--2055}, publisher = {Oxford University Press}, title = {{The effects of surface fossil magnetic fields on massive star evolution: IV. Grids of models at Solar, LMC, and SMC metallicities}}, doi = {10.1093/mnras/stac2598}, volume = {517}, year = {2022}, } @article{13991, abstract = {The prediction and realization of topological insulators have sparked great interest in experimental approaches to the classification of materials1,2,3. The phase transition between non-trivial and trivial topological states is important, not only for basic materials science but also for next-generation technology, such as dissipation-free electronics4. It is therefore crucial to develop advanced probes that are suitable for a wide range of samples and environments. Here we demonstrate that circularly polarized laser-field-driven high-harmonic generation is distinctly sensitive to the non-trivial and trivial topological phases in the prototypical three-dimensional topological insulator bismuth selenide5. The phase transition is chemically initiated by reducing the spin–orbit interaction strength through the substitution of bismuth with indium atoms6,7. We find strikingly different high-harmonic responses of trivial and non-trivial topological surface states that manifest themselves as a conversion efficiency and elliptical dichroism that depend both on the driving laser ellipticity and the crystal orientation. The origins of the anomalous high-harmonic response are corroborated by calculations using the semiconductor optical Bloch equations with pairs of surface and bulk bands. As a purely optical approach, this method offers sensitivity to the electronic structure of the material, including its nonlinear response, and is compatible with a wide range of samples and sample environments.}, author = {Heide, Christian and Kobayashi, Yuki and Baykusheva, Denitsa Rangelova and Jain, Deepti and Sobota, Jonathan A. and Hashimoto, Makoto and Kirchmann, Patrick S. and Oh, Seongshik and Heinz, Tony F. and Reis, David A. and Ghimire, Shambhu}, issn = {1749-4893}, journal = {Nature Photonics}, keywords = {Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials}, number = {9}, pages = {620--624}, publisher = {Springer Nature}, title = {{Probing topological phase transitions using high-harmonic generation}}, doi = {10.1038/s41566-022-01050-7}, volume = {16}, year = {2022}, }