Articles de revistahttp://hdl.handle.net/2117/32152024-03-19T08:02:15Z2024-03-19T08:02:15ZControlling monoterpene isomerization by guiding challenging carbocation rearrangement reactions in engineered squalene-hopene cyclasesLudwig, JulianCurado Carballada, ChristianHammer, Stephan C.Schneider, AndreasDiether, SvenjaKress, NicoRuiz Barragán, SergioOsuna Oliveras, SilviaHauer, Bernhardhttp://hdl.handle.net/2117/4047252024-03-18T01:59:13Z2024-03-15T12:02:26ZControlling monoterpene isomerization by guiding challenging carbocation rearrangement reactions in engineered squalene-hopene cyclases
Ludwig, Julian; Curado Carballada, Christian; Hammer, Stephan C.; Schneider, Andreas; Diether, Svenja; Kress, Nico; Ruiz Barragán, Sergio; Osuna Oliveras, Silvia; Hauer, Bernhard
The interconversion of monoterpenes is facilitated by a complex network of carbocation rearrangement pathways. Controlling these isomerization pathways is challenging when using common Brønsted and Lewis acid catalysts, which often produce product mixtures that are difficult to separate. In contrast, natural monoterpene cyclases exhibit high control over the carbocation rearrangement reactions but are reliant on phosphorylated substrates. In this study, we present engineered squalene-hopene cyclases from Alicyclobacillus acidocaldarius (AacSHC) that catalyze the challenging isomerization of monoterpenes with unprecedented precision. Starting from a promiscuous isomerization of (+)-ß-pinene, we first demonstrate noticeable shifts in the product distribution solely by introducing single point mutations. Furthermore, we showcase the tuneable cation steering by enhancing (+)-borneol selectivity from 1¿% to >90¿% (>99¿% de) aided by iterative saturation mutagenesis. Our combined experimental and computational data suggest that the reorganization of key aromatic residues leads to the restructuring of the water network that facilitates the selective termination of the secondary isobornyl cation. This work expands our mechanistic understanding of carbocation rearrangements and sets the stage for target-oriented skeletal reorganization of broadly abundant terpenes.
2024-03-15T12:02:26ZLudwig, JulianCurado Carballada, ChristianHammer, Stephan C.Schneider, AndreasDiether, SvenjaKress, NicoRuiz Barragán, SergioOsuna Oliveras, SilviaHauer, BernhardThe interconversion of monoterpenes is facilitated by a complex network of carbocation rearrangement pathways. Controlling these isomerization pathways is challenging when using common Brønsted and Lewis acid catalysts, which often produce product mixtures that are difficult to separate. In contrast, natural monoterpene cyclases exhibit high control over the carbocation rearrangement reactions but are reliant on phosphorylated substrates. In this study, we present engineered squalene-hopene cyclases from Alicyclobacillus acidocaldarius (AacSHC) that catalyze the challenging isomerization of monoterpenes with unprecedented precision. Starting from a promiscuous isomerization of (+)-ß-pinene, we first demonstrate noticeable shifts in the product distribution solely by introducing single point mutations. Furthermore, we showcase the tuneable cation steering by enhancing (+)-borneol selectivity from 1¿% to >90¿% (>99¿% de) aided by iterative saturation mutagenesis. Our combined experimental and computational data suggest that the reorganization of key aromatic residues leads to the restructuring of the water network that facilitates the selective termination of the secondary isobornyl cation. This work expands our mechanistic understanding of carbocation rearrangements and sets the stage for target-oriented skeletal reorganization of broadly abundant terpenes.Mode-cleaning in antisymmetrically modulated non-Hermitian waveguidesAkhter, Mohammad NayeemBotey Cumella, MurielHerrero Simon, RamonStaliunas, Kestutishttp://hdl.handle.net/2117/4041582024-03-18T01:55:40Z2024-03-11T16:23:51ZMode-cleaning in antisymmetrically modulated non-Hermitian waveguides
Akhter, Mohammad Nayeem; Botey Cumella, Muriel; Herrero Simon, Ramon; Staliunas, Kestutis
We demonstrate all-optical spatial mode-cleaning in non-Hermitian waveguides. The effect is accounted by a unidirectional coupling among the modes resulting from a simultaneous modulation of the refractive index and the gain/loss along graded index multimodal waveguides. Depending on the spatial delay between the real and imaginary part of the potential modulation, higher or lower order modes are favored, which in latter case eventually leads to an nearly-monomode propagation. In this way, for any arbitrary initial field distribution an antisymmetric non-Hermitian modulation results in an effective mode-cleaning. The effect is demonstrated analytically, based on coupled mode theory in 1D waveguides, and numerically proven by solving the wave propagation equation with the antisymmetric non-Hermitian potential. The proposal is also generalized to the more involved case of 2D waveguides, leading to a significant reduction of the beam quality factor and improvement of beam spatial quality.
2024-03-11T16:23:51ZAkhter, Mohammad NayeemBotey Cumella, MurielHerrero Simon, RamonStaliunas, KestutisWe demonstrate all-optical spatial mode-cleaning in non-Hermitian waveguides. The effect is accounted by a unidirectional coupling among the modes resulting from a simultaneous modulation of the refractive index and the gain/loss along graded index multimodal waveguides. Depending on the spatial delay between the real and imaginary part of the potential modulation, higher or lower order modes are favored, which in latter case eventually leads to an nearly-monomode propagation. In this way, for any arbitrary initial field distribution an antisymmetric non-Hermitian modulation results in an effective mode-cleaning. The effect is demonstrated analytically, based on coupled mode theory in 1D waveguides, and numerically proven by solving the wave propagation equation with the antisymmetric non-Hermitian potential. The proposal is also generalized to the more involved case of 2D waveguides, leading to a significant reduction of the beam quality factor and improvement of beam spatial quality.An equivalent lattice-modified model of interfering Bragg bandgaps and Locally Resonant Stop Bands for phononic crystal made from Locally Resonant elementsRedondo Pastor, Francisco JavierGodinho, LuisStaliunas, KestutisSanchez Perez, Juan Vicentehttp://hdl.handle.net/2117/4015442024-02-12T01:38:05Z2024-02-08T19:22:58ZAn equivalent lattice-modified model of interfering Bragg bandgaps and Locally Resonant Stop Bands for phononic crystal made from Locally Resonant elements
Redondo Pastor, Francisco Javier; Godinho, Luis; Staliunas, Kestutis; Sanchez Perez, Juan Vicente
The design and development of advanced devices based on metamaterials to control the transmission of acoustic waves is a hot topic. An important class of these metamaterials is based on phononic crystals with Locally Resonant Structure, included in those commonly known as Locally Resonant Sonic Materials. In these metamaterials, wave control is basically performed by two mechanisms: internal (or local) resonances in the scatterers that form the phononic crystal, and Bragg bandgaps due to structural periodicity. Their main control feature is the resonance peaks forming additional stop-bands away from the Bragg frequency, mainly in the low frequency regime. For some applications, coupling of the two phenomena is necessary to create a broad transmission gap. However, when both are located in close frequency ranges, some destructive interferences can occur. In this paper, the authors develop a comprehensive numerical model of periodic arrays of Hemholtz resonators, which explains in detail the physical mechanisms of this destructive interference and, simultaneously, allows the reproduction of the consequences of the interference. The numerical results are supported by experimental tests.
2024-02-08T19:22:58ZRedondo Pastor, Francisco JavierGodinho, LuisStaliunas, KestutisSanchez Perez, Juan VicenteThe design and development of advanced devices based on metamaterials to control the transmission of acoustic waves is a hot topic. An important class of these metamaterials is based on phononic crystals with Locally Resonant Structure, included in those commonly known as Locally Resonant Sonic Materials. In these metamaterials, wave control is basically performed by two mechanisms: internal (or local) resonances in the scatterers that form the phononic crystal, and Bragg bandgaps due to structural periodicity. Their main control feature is the resonance peaks forming additional stop-bands away from the Bragg frequency, mainly in the low frequency regime. For some applications, coupling of the two phenomena is necessary to create a broad transmission gap. However, when both are located in close frequency ranges, some destructive interferences can occur. In this paper, the authors develop a comprehensive numerical model of periodic arrays of Hemholtz resonators, which explains in detail the physical mechanisms of this destructive interference and, simultaneously, allows the reproduction of the consequences of the interference. The numerical results are supported by experimental tests.Spatially structured optical pump for laser generation tuningKontenis, GabrieliusGailevicius, DariusTaranenko, VictorStaliunas, Kestutishttp://hdl.handle.net/2117/4015382024-02-12T01:40:48Z2024-02-08T18:27:28ZSpatially structured optical pump for laser generation tuning
Kontenis, Gabrielius; Gailevicius, Darius; Taranenko, Victor; Staliunas, Kestutis
The goal and essential parameter of laser light conversion is achieving emitted radiation of higher brightness. For many applications, the laser beam must have the highest available beam quality and highest achievable power. However, lasers with higher average power values usually have poorer beam quality, limiting the achievable brightness. Here, we present a method for improving the beam quality by using a spatially structured optical pump for a membrane external cavity laser resonator. An increase in brightness is achieved under fixed focusing conditions just by changing the pump intensity profile. A controllable output laser mode can be achieved by using a dynamically changing pump pattern.
2024-02-08T18:27:28ZKontenis, GabrieliusGailevicius, DariusTaranenko, VictorStaliunas, KestutisThe goal and essential parameter of laser light conversion is achieving emitted radiation of higher brightness. For many applications, the laser beam must have the highest available beam quality and highest achievable power. However, lasers with higher average power values usually have poorer beam quality, limiting the achievable brightness. Here, we present a method for improving the beam quality by using a spatially structured optical pump for a membrane external cavity laser resonator. An increase in brightness is achieved under fixed focusing conditions just by changing the pump intensity profile. A controllable output laser mode can be achieved by using a dynamically changing pump pattern.Resonant x-ray difference frequency generationSerrat Jurado, Carleshttp://hdl.handle.net/2117/4008602024-02-04T23:03:38Z2024-02-02T11:18:52ZResonant x-ray difference frequency generation
Serrat Jurado, Carles
Resonantly enhanced x-ray difference-frequency generation (re-XDFG) is a second-order nonlinear effect that involves illuminating a molecule with two-color x-ray pulses with photon energies O1 and O2. The energy difference $\Omega_1-\Omega_2$ is tuned to match an x-ray absorption edge of an atom in the molecule. We have numerically studied the re-XDFG effect considering different individual molecules in the gas phase using density functional theory calculations and have verified the non-centrosymmetric character of the target transitions. Two-level molecular systems with permanent dipoles are evaluated for the description of re-XDFG taking into account different two-color input pulse geometries. This innovative nonlinear x-ray methodology offers a means to measure the K-edge NEXAFS spectrum of light elements, such as carbon, nitrogen, or oxygen, in dense media using non-resonant x-rays. It can also be used to investigate chemical material dynamics that are inaccessible by linear spectroscopy. These findings enable the combination of atomic-scale structure with chemical specificity and the selective and local access to x-ray excitations using hard x-ray pulses.
2024-02-02T11:18:52ZSerrat Jurado, CarlesResonantly enhanced x-ray difference-frequency generation (re-XDFG) is a second-order nonlinear effect that involves illuminating a molecule with two-color x-ray pulses with photon energies O1 and O2. The energy difference $\Omega_1-\Omega_2$ is tuned to match an x-ray absorption edge of an atom in the molecule. We have numerically studied the re-XDFG effect considering different individual molecules in the gas phase using density functional theory calculations and have verified the non-centrosymmetric character of the target transitions. Two-level molecular systems with permanent dipoles are evaluated for the description of re-XDFG taking into account different two-color input pulse geometries. This innovative nonlinear x-ray methodology offers a means to measure the K-edge NEXAFS spectrum of light elements, such as carbon, nitrogen, or oxygen, in dense media using non-resonant x-rays. It can also be used to investigate chemical material dynamics that are inaccessible by linear spectroscopy. These findings enable the combination of atomic-scale structure with chemical specificity and the selective and local access to x-ray excitations using hard x-ray pulses.All-regions tunable high harmonic enhancement by a periodic static electric fieldSerrat Jurado, CarlesBiegert, Jenshttp://hdl.handle.net/2117/4003332024-01-28T22:22:46Z2024-01-26T08:43:03ZAll-regions tunable high harmonic enhancement by a periodic static electric field
Serrat Jurado, Carles; Biegert, Jens
Simulations show that a static electric field periodically distributed in space can be used to control the production of coherent light by high-order harmonic generation in a wide spectral range covering extremeultraviolet and soft x-ray radiation. The radiation yield is selectively enhanced due to symmetry breaking induced by a static electric field on the interaction between the driving laser and the medium. The spectral position of the enhancement is tuned by varying the periodicity of the static electric field which matches twice the coherence length of the harmonics in the desired region. We find that the static electric field strength inducing enhancement decreases for shorter wavelengths and predict an increase of more than two orders of magnitude for harmonics in the water window spectral range with a static electric field as weak as 1:12 MV/cm.
2024-01-26T08:43:03ZSerrat Jurado, CarlesBiegert, JensSimulations show that a static electric field periodically distributed in space can be used to control the production of coherent light by high-order harmonic generation in a wide spectral range covering extremeultraviolet and soft x-ray radiation. The radiation yield is selectively enhanced due to symmetry breaking induced by a static electric field on the interaction between the driving laser and the medium. The spectral position of the enhancement is tuned by varying the periodicity of the static electric field which matches twice the coherence length of the harmonics in the desired region. We find that the static electric field strength inducing enhancement decreases for shorter wavelengths and predict an increase of more than two orders of magnitude for harmonics in the water window spectral range with a static electric field as weak as 1:12 MV/cm.Permutation entropy-based characterization of speckle patterns generated by semiconductor laser lightTirabassi, GiulioDuque Gijón, MaríaTiana Alsina, JordiMasoller Alonso, Cristinahttp://hdl.handle.net/2117/4002172024-02-20T09:54:27Z2024-01-24T19:02:08ZPermutation entropy-based characterization of speckle patterns generated by semiconductor laser light
Tirabassi, Giulio; Duque Gijón, María; Tiana Alsina, Jordi; Masoller Alonso, Cristina
Semiconductor lasers with optical feedback are stochastic nonlinear systems that can display complex dynamics and abrupt changes when their operation conditions change. Even very small changes can lead to large variations in the spatial and spectral properties of the laser emission. This makes a semiconductor laser with feedback an ideal system for conducting controlled experiments to test data analysis tools to detect and characterize transitions. Here, we identify feedback-induced transitions by analyzing speckle patterns that are generated after the laser light propagates in an optical fiber. Speckle patterns result from the interference of multiple modes, and their statistical properties are understood, but a direct mathematical model does not exist. Here we show the versatility of the correlation length and the permutation entropy as measures for characterizing speckle patterns. Combining entropy and correlation analysis with speckle contrast analysis, we uncover changes that occur when the laser current increases from below to well above the threshold, which unveils the effects of optical feedback on the coherence of the laser emission.
2024-01-24T19:02:08ZTirabassi, GiulioDuque Gijón, MaríaTiana Alsina, JordiMasoller Alonso, CristinaSemiconductor lasers with optical feedback are stochastic nonlinear systems that can display complex dynamics and abrupt changes when their operation conditions change. Even very small changes can lead to large variations in the spatial and spectral properties of the laser emission. This makes a semiconductor laser with feedback an ideal system for conducting controlled experiments to test data analysis tools to detect and characterize transitions. Here, we identify feedback-induced transitions by analyzing speckle patterns that are generated after the laser light propagates in an optical fiber. Speckle patterns result from the interference of multiple modes, and their statistical properties are understood, but a direct mathematical model does not exist. Here we show the versatility of the correlation length and the permutation entropy as measures for characterizing speckle patterns. Combining entropy and correlation analysis with speckle contrast analysis, we uncover changes that occur when the laser current increases from below to well above the threshold, which unveils the effects of optical feedback on the coherence of the laser emission.Spectral shift and split of harmonic lines in propagation affected high harmonic generation in a long-interaction gas tubeSeres, JozsefSeres, EnikoeSerrat Jurado, CarlesDinh, Thanh HungHasegawa, NoboruIshino, MasahikoNishikino, MasaharuNamba, Shinichihttp://hdl.handle.net/2117/4000732024-01-28T22:13:24Z2024-01-23T18:43:07ZSpectral shift and split of harmonic lines in propagation affected high harmonic generation in a long-interaction gas tube
Seres, Jozsef; Seres, Enikoe; Serrat Jurado, Carles; Dinh, Thanh Hung; Hasegawa, Noboru; Ishino, Masahiko; Nishikino, Masaharu; Namba, Shinichi
While generating high harmonics in long media of helium gas, at certain laser intensities and chirp, the spectral shift and split of the harmonic lines were experimentally observed, sometimes exceeding one harmonic order. Beyond reporting these results, numerical simulations were performed to understand the phenomenon. A 3D propagation model was solved under the strong field approximation. According to the simulations, the distortion of the laser beam profile during propagation and the consequently accused change in the conditions of phase matching are responsible for the observations. The observed phenomena can be an excellent tool to produce tunable narrow band harmonic sources covering a broad range around 13.5 nm for spectroscopy and for seeding X-ray lasers, and to understand non-desired detuning of the seed wavelength.
2024-01-23T18:43:07ZSeres, JozsefSeres, EnikoeSerrat Jurado, CarlesDinh, Thanh HungHasegawa, NoboruIshino, MasahikoNishikino, MasaharuNamba, ShinichiWhile generating high harmonics in long media of helium gas, at certain laser intensities and chirp, the spectral shift and split of the harmonic lines were experimentally observed, sometimes exceeding one harmonic order. Beyond reporting these results, numerical simulations were performed to understand the phenomenon. A 3D propagation model was solved under the strong field approximation. According to the simulations, the distortion of the laser beam profile during propagation and the consequently accused change in the conditions of phase matching are responsible for the observations. The observed phenomena can be an excellent tool to produce tunable narrow band harmonic sources covering a broad range around 13.5 nm for spectroscopy and for seeding X-ray lasers, and to understand non-desired detuning of the seed wavelength.Timing jitter reduction in semiconductor lasers induced by optical injectionDuque Gijón, MaríaQuirce Teja, AnaTiana Alsina, JordiMasoller Alonso, CristinaValle Gutierrez, Ángelhttp://hdl.handle.net/2117/3957382023-11-03T09:10:17Z2023-11-03T09:01:33ZTiming jitter reduction in semiconductor lasers induced by optical injection
Duque Gijón, María; Quirce Teja, Ana; Tiana Alsina, Jordi; Masoller Alonso, Cristina; Valle Gutierrez, Ángel
We present an experimental study of the effect of continuous-wave optical injection (OI) from a vertical-cavity surface-emitting laser (VCSEL) on the timing jitter of a gain-switched discrete-mode semiconductor laser (DML). Timing jitter was analyzed over a wide range of temperatures of the DML, which allowed tuning the detuning between the lasers emissions, and it was compared with the inter-pulse timing jitter. We have found that there is a range of detunings in which OI diminishes the jitter by 70% with respect to the jitter of the solitary DML. However, within this region, there are some detunings for which OI significantly increases the jitter.
2023-11-03T09:01:33ZDuque Gijón, MaríaQuirce Teja, AnaTiana Alsina, JordiMasoller Alonso, CristinaValle Gutierrez, ÁngelWe present an experimental study of the effect of continuous-wave optical injection (OI) from a vertical-cavity surface-emitting laser (VCSEL) on the timing jitter of a gain-switched discrete-mode semiconductor laser (DML). Timing jitter was analyzed over a wide range of temperatures of the DML, which allowed tuning the detuning between the lasers emissions, and it was compared with the inter-pulse timing jitter. We have found that there is a range of detunings in which OI diminishes the jitter by 70% with respect to the jitter of the solitary DML. However, within this region, there are some detunings for which OI significantly increases the jitter.Entropy-based early detection of critical transitions in spatial vegetation fieldsTirabassi, GiulioMasoller Alonso, Cristinahttp://hdl.handle.net/2117/3939042024-02-11T05:46:50Z2023-09-22T09:39:31ZEntropy-based early detection of critical transitions in spatial vegetation fields
Tirabassi, Giulio; Masoller Alonso, Cristina
In semiarid regions, vegetated ecosystems can display abrupt and unexpected changes, i.e., transitions to different states, due to drifting or time-varying parameters, with severe consequences for the ecosystem and the communities depending on it. Despite intensive research, the early identification of an approaching critical point from observations is still an open challenge. Many data analysis techniques have been proposed, but their performance depends on the system and on the characteristics of the observed data (the resolution, the level of noise, the existence of unobserved variables, etc.). Here, we propose an entropy-based approach to identify an upcoming transition in spatiotemporal data. We apply this approach to observational vegetation data and simulations from two models of vegetation dynamics to infer the arrival of an abrupt shift to an arid state. We show that the permutation entropy (PE) computed from the probabilities of two-dimensional ordinal patterns may provide an early warning indicator of an approaching tipping point, as it may display a maximum (or minimum) before decreasing (or increasing) as the transition approaches. Like other spatial early warning indicators, the spatial permutation entropy does not need a time series of the system dynamics, and it is suited for spatially extended systems evolving on long time scales, like vegetation plots. We quantify its performance and show that, depending on the system and data, the performance can be better, similar or worse than the spatial correlation. Hence, we propose the spatial PE as an additional indicator to try to anticipate regime shifts in vegetated ecosystems.
2023-09-22T09:39:31ZTirabassi, GiulioMasoller Alonso, CristinaIn semiarid regions, vegetated ecosystems can display abrupt and unexpected changes, i.e., transitions to different states, due to drifting or time-varying parameters, with severe consequences for the ecosystem and the communities depending on it. Despite intensive research, the early identification of an approaching critical point from observations is still an open challenge. Many data analysis techniques have been proposed, but their performance depends on the system and on the characteristics of the observed data (the resolution, the level of noise, the existence of unobserved variables, etc.). Here, we propose an entropy-based approach to identify an upcoming transition in spatiotemporal data. We apply this approach to observational vegetation data and simulations from two models of vegetation dynamics to infer the arrival of an abrupt shift to an arid state. We show that the permutation entropy (PE) computed from the probabilities of two-dimensional ordinal patterns may provide an early warning indicator of an approaching tipping point, as it may display a maximum (or minimum) before decreasing (or increasing) as the transition approaches. Like other spatial early warning indicators, the spatial permutation entropy does not need a time series of the system dynamics, and it is suited for spatially extended systems evolving on long time scales, like vegetation plots. We quantify its performance and show that, depending on the system and data, the performance can be better, similar or worse than the spatial correlation. Hence, we propose the spatial PE as an additional indicator to try to anticipate regime shifts in vegetated ecosystems.