Multiple Photon Absorption Research Articles

(Invited) Near-Infrared Triggered Theranostics

In the last decade, the field of luminescent lanthanide doped nanoparticles has had a meteoric rise, progressing from the basic understanding of the photophysical properties governing their nanoscale luminescence, in particular upconversion, to their use in a plethora of applications, with considerable focus in biology and medicine. This interest stems primarily from the ability to stimulate these luminescent nanoparticles with near-infrared (NIR) light as well as their diverse emission wavelengths spanning the UV to the NIR. Therefore, with a single NIR excitation wavelength, it is possible to observe higher energy multiphoton luminescence, known as upconversion, or single photon NIR emission (known as down-shifted luminescence). The former upconversion process proceeds through the sequential absorption of multiple NIR photons through the long-lived 4f electronic energy states of the tri-positive lanthanide ions. As a result, upconversion is several of orders more efficient than conventional multiphoton absorption processes. This is especially interesting for applications in theranostics (therapy + diagnostics on the same platform) where the upconverted light can be used to trigger another light activated modality (therapy) while the NIR luminescence can be used for bioimaging and nanothermometry (diagnostics). Here, we present our work on the synthesis and development of various NIR excited (and emitting) core/shell lanthanide-doped nanostructures/nanoplatforms and demonstrate how their various emissions could be harnessed for applications in biology and nanomedicine.

Tunable Nonlinear Optical Properties Based on Metal–Organic Framework Single Crystals

AbstractSolid‐state hybrid materials with designability in topology and tunable photo‐responsiveness hold great promise for multitudinous applications from optoelectronics to information storage/communication. However, the judicious design and synthesis of metal–organic frameworks (MOFs) with intrinsically custom‐made nonlinear optical (NLO) properties including multiple photon absorption and harmonic generation effects suitable for miniaturized devices remain highly challenging. Herein, the design and synthesis of a novel pillared framework named after Zn‐TCPE‐DPNI MOF coordinated by zinc ions (Zn2+), aggregation induced emission (AIE) featured [1,1′‐biphenyl]‐4‐carboxylic acid (H4TCPE), and N,N′‐di(4‐pyridyl)‐1,4,5,8‐naphthalenetetracarboxydiimide (DPNI) are reported. The highly ordered Zn‐TCPE‐DPNI MOF single crystal exhibits tunable NLO responses by switching incident excitation wavelengths of a femtosecond laser from 900 to 1500 nm. The noticeable transformation from two‐ or three‐photon excited photoluminescence (2PL or 3PL) to the concurrent occurrence of 3PL and third harmonic generation (THG), and eventually to the mere emergence of THG with a high effective susceptibility χ(3) (3ω) of 2.9 × 10−12 esu is observed. This study paves a novel avenue for the design and synthesis of photoluminescent MOF crystals with tunable NLO responses toward the fabrication of multifunctional NLO devices targeted for optoelectronics and information communication.

GOALS-JWST: Small Neutral Grains and Enhanced 3.3 μm PAH Emission in the Seyfert Galaxy NGC 7469

We present James Webb Space Telescope (JWST) Near Infrared Spectrograph (NIRSpec) integral field spectroscopy of the nearby luminous infrared galaxy NGC 7469. We take advantage of the high spatial/spectral resolution and wavelength coverage of JWST/NIRSpec to study the 3.3 μm neutral polycyclic aromatic hydrocarbon (PAH) grain emission on ∼200 pc scales. A clear change in the average grain properties between the star-forming ring and the central AGN is found. Regions in the vicinity of the AGN, with [Ne iii]/[Ne ii] > 0.25, tend to have larger grain sizes and lower aliphatic-to-aromatic (3.4/3.3) ratios, indicating that smaller grains are preferentially removed by photodestruction in the vicinity of the AGN. PAH emission at the nucleus is weak and shows a low 11.3/3.3 PAH ratio. We find an overall suppression of the total PAH emission relative to the ionized gas in the central 1 kpc region of the AGN in NGC 7469 compared to what has been observed with Spitzer on 3 kpc scales. However, the fractional 3.3 μm–to–total PAH power is enhanced in the starburst ring, possibly due to a variety of physical effects on subkiloparsec scales, including recurrent fluorescence of small grains or multiple photon absorption by large grains. Finally, the IFU data show that while the 3.3 μm PAH-derived star formation rate (SFR) in the ring is 27% higher than that inferred from the [Ne ii] and [Ne iii] emission lines, the integrated SFR derived from the 3.3 μm feature would be underestimated by a factor of 2 due to the deficit of PAHs around the AGN, as might occur if a composite system like NGC 7469 were to be observed at high redshift.

Influence of an atomic resonance on the coherent control of the photoionization process

In coherent control schemes, pathways connecting an initial and a final state can be independently controlled by manipulating the complex amplitudes of their transition matrix elements. For paths characterized by the absorption of multiple photons, these quantities depend on the magnitude and phase between the intermediate steps, and are expected to be strongly affected by the presence of resonances. We investigate the coherent control of the photoemission process in neon using a phase-controlled two-color extreme ultraviolet pulse with frequency in proximity of an excited energy state. Using helium as a reference, we show that the presence of such a resonance in neon modifies the amplitude and phase of the asymmetric emission of photoelectrons. Theoretical simulations based on perturbation theory are in fair agreement with the experimental observations.Received 25 July 2021Revised 1 August 2022Accepted 5 August 2022DOI:https://doi.org/10.1103/PhysRevResearch.4.033231Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasMultiphoton or tunneling ionization & excitationPhotoemissionSingle- and few-photon ionization & excitationUltrafast phenomenaUltrashort pulsesAtomic, Molecular & Optical

Isomer Differentiation of Trapped C16H10+ Using Low-Energy Collisions and Visible/VUV Photons.

Polycyclic aromatic hydrocarbons are major species in astrophysical environments, and this motivates their study in samples of astrochemical interest such as meteorites and laboratory analogues of stardust. Molecular analyses of carbonaceous matter in these samples show a dominant peak at m/z = 202.078 corresponding to C16H10. Obtaining information on the associated isomeric structures is a challenge for the molecular analysis of samples available in very small quantities (mg or less). Here we show that coupling laser desorption ionization mass spectrometry with ion trapping opens up the possibility of unraveling isomers by activating ion fragmentation via collisions or photon absorption. We report the best criteria for differentiating isomers with comparable dissociation energies, namely pyrene, fluoranthene, and 9-ethynylphenanthrene, on the basis of the parent dissociation curve and the ratio of dehydrogenation channels. Photoabsorption schemes (multiple photon absorption in the visible range and single photon absorption at 10.5 eV) are more effective in differentiating these isomers than activation by low energy collisions. The impact of the activation scheme on the fragmentation kinetics and dehydrogenation pathways is discussed. By analyzing the 10.5 eV photodissociation measurements with a simple kinetic model, we were able to derive a branching ratio for the H and 2H/H2 loss channels of the parent ions. The results suggest a role in the formation of H2 for bay hydrogens that are present in both fluoranthene and 9-ethynylphenanthrene. In addition, we suggest for the latter the presence of a highly competitive 2H loss channel, possibly associated with the formation of a pentagonal ring.

Laser-assisted charged Higgs boson decay in Two Higgs Doublet Model - type II

In this paper, we investigate the charged Higgs boson decay in the context of the type-II two-Higgs-doublet model in the presence of a circularly polarized electromagnetic field of laser radiation. The calculations are performed by adopting the Furry picture approach of non-perturbative interactions with the external electromagnetic field. Using the method of exact solutions for charged particles states in the presence of a circularly polarized electromagnetic wave field and evaluating the S-matrix elements, an exact analytic expression is derived for the decay width of leptonic, hadronic and bosonic decay modes. The branching ratios of different decay modes with multiple photon emission and absorption from the laser beam are analyzed and found to be dramatically modified in the region of superstrong fields. The dependencies of the decay width on the laser field strength and frequency are also examined. The results obtained may be interesting for future experimental and theoretical investigations.

Multiphoton ionization of standard optical fibers

Atoms ionization by the simultaneous absorption of multiple photons has found applications in fiber optics, where it leads to unique nonlinear phenomena. To date, studies of the ionization regime have been limited to gas-filled hollow-core fibers. Here, we investigate multiphoton ionization of standard optical fibers, where intense laser pulses ionize the atoms constituting the fiber structure itself, instead of that of the filling gas. We characterize material modifications produced by optical breakdown. Their formation affects laser beam dynamics over hours long temporal scales. The damage features are studied by means of optical microscopy and X-ray microtomography. In the framework of glass photonics, our results pave the way for a novel glass waveguide micromachining technique.

Multi-photon multi-quantum transitions in the spin- 32 silicon-vacancy centers of SiC

Silicon vacancy centers in silicon carbide are promising candidates for storing and manipulating quantum information. Implementation of fast quantum gates is an essential requirement for quantum information processing. In a low magnetic field, the resonance frequencies of silicon vacancy spins are in the range of a few MHz, the same order of magnitude as the Rabi frequencies of typical control fields. As a consequence, the rotating wave approximation becomes invalid and nonlinear processes like the absorption and emission of multiple photons become relevant. This work focuses on multi-photon transitions of negatively charged silicon vacancies driven by a strong RF field. We present continuous-wave optically detected magnetic resonance (ODMR) spectra measured at different RF powers to identify the 1-, 2-, and 3-RF photon transitions of different types of the silicon vacancy in the 6$H$-SIC polytype. Time-resolved experiments of Rabi oscillations and free induction decays of these multiple RF photon transitions were observed for the first time. Apart from zero-field data, we also present spectra in magnetic fields with different strength and orientation with respect to the system's symmetry axis.

Impact ionization and multiple photon absorption in the two-dimensional photoexcited Hubbard model

We study the non-equilibrium response of a 4x3 Hubbard model at U=8 under the influence of a short electric field pulse, with the main focus on multiple photon excitations and on the change of double occupancy after the pulse. The behavior mainly depends on the driving frequency of the electric field. The largest change of double occupancy occurs during the pulse. For frequencies below the Mott gap, we observe multiphoton excitations at large field intensities. For frequencies beyond the gap energy, there is a region where Auger recombination reduces the double occupancy after the pulse. Impact ionization (Multi Exciton Generation), namely a growing double occupancy after the pulse, occurs for frequencies larger than twice the Mott gap. From the Loschmidt amplitude we compute the eigenstate spectrum of the quantum state after the pulse, observing multiple distinct photon excitation peaks, in line with expectations from a quasiparticle picture. We introduce a technique with which we analyze the time evolution of double occupancy in each peak individually. The long-term behavior of the double occupancy almost only depends on the absorbed energy, and we explore the connection of this property to the Eigenstate Thermalization Hypothesis.

Development of the laser isotope separation method to study for the neutrino-less double beta decay of 48Ca

Search for the ultra-rare process, neutrino-less double beta decay, is a powerful tool to test the Majorana nature of neutrinos. Among the potential double beta decay nuclei, 48Ca has the largest Q-value, hence we can expect the measurement with least background. On the other hand, due to its low natural abundance, isotope enrichment is essential to achieve the sensitivity in the region of interest (inverted/normal mass hierarchy of neutrinos).We have been developing a laser isotope separation method using a tunable semiconductor laser that can excite only a specific isotope (48Ca). The laser is irradiated perpendicular to the collimated calcium vapor beam. Only 48Ca atoms are separated by deflecting them from the original atomic beam by momentum transfer due to multiple absorption and emission of laser photons. The isotope separation is confirmed by irradiating an ionization laser and time-of-flight measurement.Following the success of the proof-of-principle experiment, we are now developing the mass production system which include efficient generation of atomic beams, frequency-stabilized high-power laser, efficient laser irradiation method, and collection method of deflected isotope beams. In this paper, we report on the status and prospects of these developments.

Slow Auger Recombination of Trapped Excitons Enables Efficient Multiple Electron Transfer in CdS-Pt Nanorod Heterostructures.

Solar-to-fuel conversion reaction often requires multiple proton-coupled electron transfer (PCET) processes powered by the energetic electrons and/or holes generated by the absorption of multiple photons. The effective coupling of multiple electron transfer from the light absorber with the multiple PCET reactions at the catalytic center is one of the key challenges in efficient and selective conversion of solar energy to chemical fuels. In this paper, we examine the dynamics of multiple electron transfer in quantum confined CdS nanorods with a Pt tip, in which the CdS rod functions as the light absorber and the Pt tip the catalytic center. By excitation-fluence-dependent transient absorption spectroscopic measurements, we show that the multiexciton Auger recombination rate in CdS rods follows a carrier-collision model, knA = n2(n - 1)/4k2A, with a biexciton lifetime (1/k2A) of 2.0 ± 0.2 ns. In CdS-Pt nanorods, electron transfer kinetics from the CdS conduction band edge to the Pt show negligible dependence on the excitation fluence, occurring with a half-life time of 5.6 ± 0.6 ps. The efficiency of multiple exciton dissociation by multiple electron transfer to Pt decreases from 100% in biexciton states to ∼41% at 22 exciton state due to the competition with Auger recombination. The half-lifetime of the n-charge separated state recombination (with n electrons in the Pt and n holes in the CdS) decreases from 10 μs in the single charge separated state to 42 ns in nine charge separated states. Our findings suggest the possibility of driving multielectron photocatalytic reactions under intense illumination and controlling product selectivity through multielectron transfer.

Kinetics of near-infrared-to-visible upconversion in rubrene: An initial excitation of triplets

Upconversion (UC) in a molecular system is a process in which excitons produced by a multiple absorption of low-energy photons at long wavelengths undergo fusion to produce high energy excitons that consequently recombine to emit anti-Stokes shifted photons. Molecular systems for UC typically require a sensitizer. However, recent experiments show that UC in rubrene occurs even without the presence of the sensitizer. In this system, intermediate states are assumed to absorb photons at near-infrared wavelengths, which either absorb additional photons to populate the emissive singlet state or undergo fusion to generate triplets. The triplets can again undergo fusion to populate the excited singlet state. The final emission is around 600 nm. These models have been tested against the intensity dependence of the UC emission. Here, we have measured the kinetics of UC in rubrene by using intensity modulated photoexcitation at 800 nm to better understand the underlying mechanism. The models of UC that have been proposed so far do not agree with our measurements. Our results show that the yield of UC lags behind excitation significantly, indicating that triplet states are directly excited from the ground state, and their fusion, which depends on the population, becomes prominent after a certain build up time. While the intermediate states could form dynamically after the UC has been initiated and enhance the process, further sensitive absorption measurements are necessary to understand the role of the intermediate states in the process. Our results are important in finding new routes to enhance UC in pristine organic semiconductors for applications in photovoltaics, lasers, bioimaging, optical devices, and lighting.

Fabrication and Characterization of Inverted Silicon Pyramidal Arrays with Randomly Distributed Nanoholes

We report the fabrication, electromagnetic simulation and measurement of inverted silicon pyramidal arrays with randomly distributed nanoholes that act as an anti-reflectivity coating. The fabrication route combines the advantages of anisotropic wet etching and metal-assisted chemical etching. The former is employed to form inverted silicon pyramid arrays, while the latter is used to generate randomly distributed nanoholes on the surface and sidewalls of the generated inverted silicon pyramidal arrays. We demonstrate, numerically and experimentally, that such a structure facilitates the multiple reflection and absorption of photons. The resulting nanostructure can achieve the lowest reflectance of 0.45% at 700 nm and the highest reflectance of 5.86% at 2402 nm. The average reflectance in the UV region (250–400 nm), visible region (400–760 nm) and NIR region (760–2600 nm) are 1.11, 0.63 and 3.76%, respectively. The reflectance at broadband wavelength (250–2600 nm) is 14.4 and 3.4 times lower than silicon wafer and silicon pyramids. In particular, such a structure exhibits high hydrophobicity with a contact angle up to 132.4°. Our method is compatible with well-established silicon planar processes and is promising for practical applications of anti-reflectivity coating.

Laser-nucleus interactions in the sudden regime

The interaction between medium-weight nuclei and a strong zeptosecond laser pulse of MeV photons is investigated theoretically. Multiple absorption of photons competes with nuclear equilibration. We investigate the sudden regime. Here the rate of photon absorption is so strong that there is no time for the nucleus to fully equilibrate after each photon absorption process. We follow the temporal evolution of the system in terms of a set of rate equations. These account for dipole absorption and induced dipole emission, equilibration (modeled in terms of particle-hole states coupled by the residual nuclear interaction), and neutron decay (populating a chain of proton-rich nuclei). Our results are compared with earlier work addressing the adiabatic regime where equilibration is instantaneous. We predict the degree of excitation and the range of nuclei reached by neutron evaporation. These findings are relevant for planning future experiments.

The quantized chemical reaction resonantly driven by multiple MIR-photons: From nature to the artificial

Biochemical reactions in vivo occur at the temperature usually lower than that in vitro, however the underlying mechanism still remains a challenge. Inspired by our recent studies of adenosine triphosphate (ATP) releasing photons to resonantly drive DNA replication in a quantum way, we propose a quantized chemical reaction driven by multiple mid-infrared (MIR) photons. The space confinement effect of enzymes on a reactant molecule increases the lifetime of excitation state of its bond vibration, providing a chance for the bond to resonantly absorb multiple photons. Although the energy of each MIR photon is significantly lower than that of chemical bond, the resonant absorption of multiple photons can break the appointed bond of confined molecules. Different from the traditional thermochemistry and photochemistry, the quantized chemical reactions could have a high energy efficiency and ultrahigh selectivity. In addition, we also suggest a quantum driving source for our quantum-confined superfluid reactions proposed previously. The quantized chemical reaction resonantly driven by multiple MIR photons holds great promise to develop novel approaches for the chemical engineering in future.

Energetics of Formation of Cyclacenes from 2,3-Didehydroacenes and Implications for Astrochemistry.

The carriers of the diffuse interstellar bands (DIBs) are still largely unknown although polycyclic aromatic hydrocarbons, carbon chains, and fullerenes are likely candidates. A recent analysis of the properties of n‐acenes of general formula C4n+2H2n+4 suggested that these could be potential carriers of some DIBs. Dehydrogenation reactions of n‐acenes after absorption of an interstellar UV photon may result in dehydroacenes. Here the reaction energies and barriers for formation of n‐cyclacenes from 2,3‐didehydroacenes (n‐DDA) by intramolecular Diels–Alder reaction to dihydro‐etheno‐cyclacenes (n‐DEC) followed by ejection of ethyne by retro‐Diels–Alder reactions are analyzed using thermally assisted occupation density functional theory (TAO‐DFT) for n=10–20. It is found that the barriers for each of the steps depend on the ring strain of the underlying n‐cyclacene, and that the ring strain of n‐DEC is about 75 % of that of the corresponding n‐cyclacene. In each case, ethyne extrusion is the step with the highest energy barrier, but these barriers are smaller than CH bond dissociation energies, suggesting that formation of cyclacenes is an energetically conceivable fate of n‐acenes after multiple absorption of UV photons.

Imaging multiphoton ionization dynamics of CH3I at a high repetition rate XUV free-electron laser

XUV multiphoton ionization of molecules is commonly used in free-electron laser experiments to study charge transfer dynamics. However, molecular dissociation and electron dynamics, such as multiple photon absorption, Auger decay, and charge transfer, often happen on competing time scales, and the contributions of individual processes can be difficult to unravel. We experimentally investigate the Coulomb explosion dynamics of methyl iodide upon core–hole ionization of the shallow inner-shell of iodine (4d) and classically simulate the fragmentation by phenomenologically introducing ionization dynamics and charge transfer. Under our experimental conditions with medium fluence and relatively long XUV pulses (∼75 fs), we find that fast Auger decay prior to charge transfer significantly contributes to the charging mechanism, leading to a yield enhancement of higher carbon charge states upon molecular dissociation. Furthermore, we argue for the existence of another charging mechanism for the weak fragmentation channels leading to triply charged carbon atoms. This study shows that classical simulations can be a useful tool to guide the quantum mechanical description of the femtosecond dynamics upon multiphoton absorption in molecular systems.

Visible light responsive 2DCeO2-CdSQDs binary hybrid towards photocatalytic degradation of phenol

Environmental pollutions are now regarded as a major catastrophe for society, so the scientific community in search of efficient technology which can tackle this issue. Photocatalysis has emerged as one of the cost effective, clean and eco-friendly approach, which efficiently deals the various type of environmental pollutants. In this contest, different semiconductor materials have gained much more popularity. In this regard, we have modified 2D-CeO2 with CdSQDs with a simple deposition precipitation technique. As CdSQDs posses high cross-sections for multiple photon absorption and large oscillator strengths as compared with their bulk CdS counterparts makes it a suitable candidate for hybrid material with CeO2 which extends the spectral range of the absorption from UV to UV-visible range. Further, the formation of type-II heterostructure in between CdSQDs and 2D-CeO2 efficiently enhances the interfacial charge transfer and chemical stability. Structural, optical and morphological characterization of the fabricated samples were carried out by XRD, UV, PL and TEM analysis. The photocatalytic activity of the fabricated samples was tested towards phenol degradation where the degradation efficiency of hybrid CeO2NS-CdSQDs was found to be 71% in 2 h.

Luminescent materials as spectral converters: Power dependent profiling of solid NaYF4:Yb[formula omitted], Er[formula omitted] UCNP reveals highly efficient UVA–Blue emission

Upconversion is a common process in lanthanides-based materials in which absorption of multiple low energy photons result in a high energy one. The emission spectrum is frequently tuned by changing the composition of the material. However, a commonly overlooked aspect is the non-linear power dependence which can influence the spectral and temporal properties of the emission. Moreover, as upconverting materials have been shown to increase the output current density in photovoltaic cells when used as spectral converters, the complete power profile is required to calculate the improved efficiency and needs to be incorporated in the design process.In this work, we show that solid β-NaYF4:Yb3+, Er3+upconversion nanoparticles, well known for the green–red emission, can also emit efficiently in the UVA–blue range. These bands are often neglected in the literature in nanosized particles despite having promising applications. In addition, we characterized their stationary and dynamic luminescence features as a function of incident power to reveal the relevant intra-band mechanisms. Our results demonstrate that the red emission at high incident power is explained by back-energy transfer. Finally, by simultaneously acquiring time resolved decays and power dependent emission slopes, we classified the spectral information to build a visual summary of the system providing a description at a glance of its complex dynamics.

The Sequence of Coronene Hydrogenation Revealed by Gas-phase IR Spectroscopy

Abstract Gas-phase coronene cations ( ) can be sequentially hydrogenated with up to 24 additional H atoms, inducing a gradual transition from a planar, aromatic molecule toward a corrugated, aliphatic species. The mass spectra of hydrogenated coronene cations show that molecules with odd numbers of additional hydrogen atoms (n H) are dominant, with particularly high relative intensity for “magic numbers” n H = 5, 11, and 17, for which hydrogen atoms have the highest binding energies. Reaction barriers and binding energies strongly affect the hydrogenation sequence and its site specificity. In this contribution, we monitor this sequence experimentally by the evolution of infrared multiple-photon dissociation (IRMPD) spectra of gaseous with n H = 3–11, obtained using an infrared free electron laser coupled to a Fourier transform ion cyclotron mass spectrometer. For weakly hydrogenated systems (n H = 3, 5) multiple-photon absorption mainly leads to loss of H atoms (and/or H2). With increasing n H, C2H2 loss becomes more relevant. For n H = 9, 11, the carbon skeleton is substantially weakened and fragmentation is distributed over a large number of channels. A comparison of our IRMPD spectra with density functional theory calculations clearly shows that only one or two hydrogenation isomers contribute to each n H. This confirms the concept of hydrogenation occurring along very specific sequences. Moreover, the atomic sites participating in the first 11 steps of this hydrogenation sequence are clearly identified.