Two-photon Intensity Research Articles

Rashba Effect and Spin-Dependent Excitonic Properties in Chiral Two-Dimensional/Three-Dimensional Composite Perovskite Films.

Among various chiral semiconductor materials, chiral two-dimensional (2D)/three-dimensional (3D) composite perovskites (CPs) offer the benefits of strong interface asymmetry and energy transfer between 2D and 3D phases, making the chiral CPs promising for spintronic devices. Therefore, understanding their spintronic properties will be greatly important for expanding their relevant applications. In this work, we synthesized one pair of chiral 2D/3D CP films. Their Rashba effect and spin relaxation process have been investigated by polarization-dependent femtosecond transient absorption spectroscopy. Interestingly, under left- and right-handed circularly polarized light (CPL) excitation, a two-photon emission intensity difference is observed in chiral 2D/3D CP films at 298 K. This work sheds light on the spin-dependent excitonic characteristics of chiral 2D/3D CPs and confirms the feasibility of their application in near-infrared CPL detection.

Accuracy of One- and Two-Photon Intensities with the Extended Polarizable Density Embedding Model.

The recently developed extended polarizable density embedding (PDE-X) model is evaluated for the spectroscopic properties of organic chromophores solvated in water, including both one- and two-photon absorption properties. The PDE-X embedding model systematically improves vertical excitation energies over the preceding polarizable density embedding model (PDE). PDE-X shows more modest improvements over existing embedding models for oscillator strengths and two-photon absorption cross-sections, which are more sensitive properties. We argue that the origin of these discrepancies is related to the description of polarization effects, suggesting directions for future development of the embedding model.

Abstract 3703: Multimodal metabolic imaging and proteomics of radiation resistance in head and neck squamous cell carcinoma

Abstract Radiation resistance can halt a well-curated treatment plan in its tracks, but it may take weeks to realize this lack of efficacy resulting in lost time and unnecessary side effects. In this study, we sought to elucidate novel biomarkers of radiation resistance to predict treatment response in head and neck squamous cell carcinoma (HNSCC) at much earlier timepoints. We grew tumor xenografts from radiation-resistant UM-SCC-47 (n=25) and -sensitive UM-SCC-22B (n=37) cells in nude athymic mice. Each group was randomly divided into treatment and control groups, which were further subdivided into four timepoints for tumor excision: pre-treatment baseline, 1-, 24-, and 48-hours post-treatment. Prior to excision, we injected pimonidazole to quantify tumor hypoxia. We determined the two-photon excited fluorescence intensity and lifetime of NADH and FAD and quantified the optical redox ratio, ratio of free to bound NADH, and mean NADH lifetime of frozen sections of each tumor. We observed spatial and temporal heterogeneity in these high-resolution optical maps that indicated different metabolic programs in radiation-resistant and -sensitive tumors. A histogram-based heterogeneity analysis revealed time dependent shifts toward glycolysis in the radiation-resistant UM-SCC-47 treatment group, while the sensitive UM-SCC-22B treatment group showed the opposite trend. Proteomics performed on both cell lines identified multiple dysregulated proteins that are often implicated in HNSCC and associated with metabolic reprogramming — specifically, EGFR and SMAD4. We also found elevated levels of hypoxia and HIF-1 in the UM-SCC-47 tumors compared with the UM-SCC-22B tumors prior to and post-radiation. Using spatially co-registered optical imaging and immunohistochemical maps of the same field of view, we will present correlations between our optical markers and EGFR, SMAD4, and HIF-1. These studies will provide evidence of how protein dysregulation causes changes to optical metabolic imaging markers. Citation Format: Jesse D. Ivers, Sina Dadgar, Narasimhan Rajaram. Multimodal metabolic imaging and proteomics of radiation resistance in head and neck squamous cell carcinoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3703.

Quantum interferometric two-photon excitation spectroscopy

Two-photon excitation spectroscopy is a nonlinear technique that has gained rapidly in interest and significance for studying the complex energy-level structure and transition probabilities of materials. While the conventional spectroscopy based on tunable classical light has been long established, quantum light provides an alternative way towards excitation spectroscopy with potential advantages in temporal and spectral resolution, as well as reduced photon fluxes. By using a quantum Fourier transform that connects the sum-frequency intensity and N00N-state temporal interference, we present an approach for quantum interferometric two-photon excitation spectroscopy. Our proposed protocol overcomes the difficulties of engineering two-photon joint spectral intensities and fine-tuned absorption-frequency selection. These results may significantly facilitate the use of quantum interferometric spectroscopy for extracting the information about the electronic structure of the two-photon excited-state manifold of atoms or molecules without any requirement for precise and complicated scanning in the spectral domain. This may be particularly relevant for photon-sensitive biological and chemical samples.

Quantum Wiener-Khinchin Theorem for Spectral-Domain Optical Coherence Tomography

The Wiener-Khinchin theorem, the fact that the autocorrelation function of a time process has a spectral decomposition given by its power-spectrum intensity, can be used in many disciplines. However, the applications based on a quantum counterpart of the Wiener-Khinchin theorem that provides a translation between time-energy degrees of freedom of biphoton wave function still remains relatively unexplored. Here, we use a quantum Wiener-Khinchin theorem (QWKT) to state that two-photon joint spectral intensity and the cross-correlation of two-photon temporal signal can be connected by making a Fourier transform. The mathematically defined QWKT is experimentally demonstrated in frequency-entangled two-photon Hong-Ou-Mandel (HOM) interference with the assistance of spectrally resolved detection. We apply this method to spectral-domain quantum optical coherence tomography that detects thickness-induced optical delays in a transparent sample, and show that our method suffices to achieve great advantages in measurement precision within a wide dynamic range and capturing time over the conventional HOM interferometric schemes. These results may significantly facilitate the use of QWKT for quantum information processing and quantum interferometric spectroscopy.

Broadband strong photon correlations of frequency-resolved single-atom resonance fluorescence generated by two equal-frequency laser fields with different amplitudes

Frequency-resolved photon statistics of resonance fluorescence generated from a two-level system driven by a strong laser field and a weak laser field with equal frequencies are studied. The frequency resolution of fluorescent radiation is described by quantum filtering dynamics, which is simulated theoretically by two single-mode quantum optical cavities with tunable frequencies to scan the incident fluorescent radiation. By calculating the two-photon intensity–intensity correlation functions in terms of the cavity modes, we demonstrate that two-color strong correlations of resonance fluorescence can be generated not only between the opposite sidebands, but also between the central band and one of the sidebands: although both sidebands are broadened due to the perturbation of the weak laser field on the strong-field dressed atom. We emphasize that these properties are in contrast to the conventional case of the standard single-atom Mollow triplet. Moreover, if the resonance frequencies of the two filtering cavities are tuned appropriately, broadband two-color strong correlations are predicted, and the physical origin is revealed from the perspective of quantum interference of photon emission dynamics. This can be considered as a feasible scheme for the design of broadband non-classical light sources, and may be beneficial to the quantum precise detection of atomic and molecular dynamics via quantum optical spectroscopy.

In vivo fluorescence lifetime imaging of macrophage intracellular metabolism during wound responses in zebrafish.

The function of macrophages in vitro is linked to their metabolic rewiring. However, macrophage metabolism remains poorly characterized in situ. Here, we used two-photon intensity and lifetime imaging of autofluorescent metabolic coenzymes, nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) and flavin adenine dinucleotide (FAD), to assess the metabolism of macrophages in the wound microenvironment. Inhibiting glycolysis reduced NAD(P)H mean lifetime and made the intracellular redox state of macrophages more oxidized, as indicated by reduced optical redox ratio. We found that TNFα+ macrophages had lower NAD(P)H mean lifetime and were more oxidized compared to TNFα- macrophages. Both infection and thermal injury induced a macrophage population with a more oxidized redox state in wounded tissues. Kinetic analysis detected temporal changes in the optical redox ratio during tissue repair, revealing a shift toward a more reduced redox state over time. Metformin reduced TNFα+ wound macrophages, made intracellular redox state more reduced and improved tissue repair. By contrast, depletion of STAT6 increased TNFα+ wound macrophages, made redox state more oxidized and impaired regeneration. Our findings suggest that autofluorescence of NAD(P)H and FAD is sensitive to dynamic changes in intracellular metabolism in tissues and can be used to probe the temporal and spatial regulation of macrophage metabolism during tissue damage and repair.

The Optimization of Cold Rubidium Atom Two-Photon Transition Excitation with an Erbium-Fiber Optical Frequency Comb

We demonstrated the observation of cold rubidium atom two-photon transition excitation by a fiber optical frequency comb. In addition to this, we optimized the repetition rate of optical frequency comb to enhance two-photon intensity by controlling cavity length and pump source of optical comb. This technique can fine tune repetition rate to corresponding stepwise two-photon transition resonance frequency and improve the transition intensity by three times. This method is useful in Doppler laser cooling and detection of macromolecules.

Imaging of latent three-dimensional exposure patterns created by direct laser writing in photoresists

A technique to visualize latent three-dimensional photoexposure patterns recorded in photoresist using direct laser writing technique is described. Owing to photoluminescence quenching in the regions of photoresist previously exposed to intense laser radiation, spatial mapping of two-photon excited photoluminescence intensity across the laser-processed region was found to reveal size, shape, and geometric parameters of the exposed patterns prior to their development. Fast, non-destructive preliminary diagnostics of the laser-written structures may improve the versatility and applicability of direct laser writing technique for fast prototyping of micro- and nano-structures.

Effects of donor position and number on two-photon absorption properties of tetraphenylethylene derivatives

Organic materials with strong two-photon absorption response and aggregation induced emission have aroused a great deal of interest in recent years, for their many potential applications such as two-photon fluorescence microscopy, up-conversion laser, photodynamic therapy, etc. The tetraphenylethylene units are usually employed in two-photon absorption and aggregation induced emission materials because of their good electron-donating capability and special propeller starburst structures. Theoretical study on the relationship between molecular structure and two-photon absorption property is of great importance for guiding the experimental design and synthesis of functional materials. In this paper, the two-photon absorption properties of a series of organic molecules containing tetraphenylethylene and cyano groups are studied by employing the density functional response theory in combination with the polarizable continuum model. The molecular geometries are optimized at a hybrid B3LYP level with 6-31g(d, p) basis set in the Gaussian 16 program. The two-photon absorption cross sections are calculated by response theory through using the CAM-B3LYP functional with 6-31g(d) basis set in the Dalton program. The effect of donor position and number on two-photon absorption properties are investigated. In addition, by increasing the planarity and conjugated length of the molecule, as well as by enhancing the strength of the electron donor, we design three molecular structures and calculate their two-photon absorption properties. The results show that the donor position and number have important effects on two-photon absorption properties. The methoxy donor at the end of the molecule can increase the two-photon absorption intensity effectively. As the number of substituents increases, the position of the two-photon absorption peak is red-shifted. The effects of adding electron donor groups on different side positions have a significant difference in the two-photon absorption property. Comparing with the experimental molecules, the two-photon absorption cross sections of the designed molecules are greatly enhanced. When the tetraphenylethylene group is replaced by the triphenylamine group, the two-photon absorption peak is greatly red-shifted, and the two-photon absorption intensity is significantly increased. Since all of these molecules contain tetraphenylethylene or triphenylamine group with propeller structure, they can have both two-photon absorption and aggregation induced emission properties. This study provides theoretical guidelines for synthesizing a new type of active two-photon absorption and aggregation induced emission material.

Quantum manipulation of biphoton spectral distributions in a 2D frequency space toward arbitrary shaping of a biphoton wave packet.

Arbitrary shaping of optical waveform is fundamental interest from basic science to advanced optical technologies. However, it is still challenging task for shaping a biphoton wave packet. Here we experimentally manipulate the spectrum and phase of a biphoton wave packet in a two-dimensional frequency space. The spectrum is shaped by adjusting the temperature of the crystal, and the phase is controlled by tilting the dispersive glass plate. The manipulating effects are confirmed by measuring the two-photon spectral intensity (TSI) and the Hong-Ou-Mandel (HOM) interference patterns. The technique in this work paves the way for arbitrary shaping of a multi-photon wave packet in a quantum manner.

Site-Specific Photodecomposition in Conjugated Energetic Materials.

Nonadiabatic excited-state molecular dynamics (NEXMD) has been used to study photodecomposition in a class of recently synthesized bicyclic conjugated energetic materials (CEMs) composed of fused tetrazole and tetrazine derivatives with increasing oxygen substitutions. Modification by oxygen functionalization has already been demonstrated to increase the two-photon absorption intensity in the target CEMswhile simultaneously improving oxygen balance. Photodecomposition mechanisms in materials that undergo nonlinear absorption could be used to achieve controlled, direct optical initiation. Here, we use NEXMD simulations to model the nonradiative relaxation and photodecomposition in CEMs following photoexcitation by a simulated Nd:YAG laser pulse. Excess electronic energy is quickly converted into vibrational energy on a sub-100 fs time scale resulting in bond dissociation. We find that, for the studiedtetrazine derivatives, the bicyclic framework is an important structural feature that enhances the photochemical quantum yield and the high atomic oxygen content increases the relaxation lifetime and opens additional photodissociation pathways targeting the oxygen-substituted sites. The presented analysis scheme based on bond orders in the swarm of NEXMD trajectories is a useful tool for determining photochemical reactions.

Dye confined in metal-organic framework for two-photon fluorescent temperature sensing

In order to expand the application range of luminescent dye, metal-organic framework (MOF) is applied as a carrier to solve the problem such as low luminescent efficiency and poor stability. Here a two-photon luminescent dye-confined ionic metal-organic framework (iMOF) ZJU-68⊃DMASM was prepared through size confinement and electrostatic interaction. The dye loading content was investigated to obtain maximum luminescent efficiency and it was found that the change of two-photon emission intensity was consistent with that of quantum efficiency. In addition, the composite showed excellent physiological temperature sensing performance from 20 °C to 60 °C with a high relative sensitivity, good water stability and good biocompatibility, possessing great potential to be applied in biological field.

Site-Selective, Two-Photon Plasmonic Nanofocusing on a Single Quantum Dot for Near-Room-Temperature Operation

Although the study of single quantum dot (QD) properties without the background noise and dephasing processes caused by surrounding carriers is a crucial issue, the spatial-selective excitation of a single QD is still challenging, due to the diffraction nature of light. Here, we demonstrate a deep subwavelength excitation of a single QD using two-photon plasmonic nanofocusing. Self-aligned plasmonic nanofocusing on a single QD was achieved using metal coated nanopyramid structures. The highly enhanced local electric field generated by the plasmonic nanofocusing gives rise to a large increase in the optical nonlinear effect (i.e., two-photon excitation). As a result of the enhanced field enhancement on the metal-pyramid hybrid structure, the two-photon luminescence intensity was enhanced by a factor of 5000, and the selective excitation of a single QD enabled us to observe InGaN QD emission at near room temperature, due to the large suppression of the background emission. Our approach opens promising persp...

A Two-Photon Luminescent Dye-Loaded Metal-Organic Framework for Physiological Temperature Sensing within Biological Windows.

Luminescent temperature sensing in biological windows is uniquely superior compared to traditional temperature sensing methods because the scattering and absorption by skin, tissue and blood is minimal. In this study, the two-photon luminescence from dyes loaded into a metal-organic framework was utilised to achieve physiological temperature sensing within two biological windows. A composite was prepared that can be excited at 1064 nm to emit at 650 nm, well within the two biological windows. The two-photon luminescence intensity at 650 nm has a linear relationship with temperature over the range 20 to 60 °C. In addition, the stability and quantum efficiency were significantly improved after loading into the MOF and, with high temperature resolution, excellent repeatability and low biological toxicity, measurements with this composite has great potential to be applied to physiological temperature sensing in cells or tissues.

Coherent source interaction, third-order nonlinear response of synthesized PEG coated magnetite nanoparticles in polyethylene glycol and its application

Third-order nonlinear response of synthesized polyethylene glycol coated Fe3O4 nanoparticles dispersed in a suitable solvent, polyethylene glycol has been studied. The structural characterization of the synthesized magnetite nanoparticles were carried out. The linear optical property of the synthesized magnetite nanoparticles was investigated using UV-visible technique. Both closed and open aperture Z-scan techniques have been performed at 532nm with pulse width 5ns and repetition rate 10Hz. It was found that polyethylene glycol coated magnetite exhibits reverse saturable absorption, with significant nonlinear absorption coefficient. Two-photon absorption intensity dependent positive nonlinear refraction coefficients indicate self focusing phenomena. Results show that higher concentration gives better nonlinear and optical limiting properties.

Bridging length scales to measure polymer assembly

Time-resolvable quantitative measurements of polymer concentration are very useful to elucidate protein polymerization pathways. There are numerous techniques to measure polymer concentrations in purified protein solutions, but few are applicable in vivo. Here we develop a methodology combining microscopy and spectroscopy to overcome the limitations of both approaches for measuring polymer concentration in cells and cell extracts. This technique is based on quantifying the relationship between microscopy and spectroscopy measurements at many locations. We apply this methodology to measure microtubule assembly in tissue culture cells and Xenopus egg extracts using two-photon microscopy with FLIM measurements of FRET. We find that the relationship between FRET and two-photon intensity quantitatively agrees with predictions. Furthermore, FRET and intensity measurements change as expected with changes in acquisition time, labeling ratios, and polymer concentration. Taken together, these results demonstrate that this approach can quantitatively measure microtubule assembly in complex environments. This methodology should be broadly useful for studying microtubule nucleation and assembly pathways of other polymers.

Ruthenium(II) Complex Incorporated UiO-67 Metal–Organic Framework Nanoparticles for Enhanced Two-Photon Fluorescence Imaging and Photodynamic Cancer Therapy

Ruthenium(II) tris(bipyridyl) cationic complex (Ru(bpy)32+) incorporated UiO-67 (Universitetet i Oslo) nanoscale metal-organic frameworks (NMOFs) with an average diameter of ∼92 nm were developed as theranostic nanoplatform for in vitro two-photon fluorescence imaging and photodynamic therapy. After incorporation into porous UiO-67 nanoparticles, the quantum yield, luminescence lifetime, and two-photon fluorescence intensity of Ru(bpy)32+ guest molecules were much improved owing to the steric confinement effect of MOF pores. Benefiting from these merits, the as-synthesized nanoparticles managed to be internalized by A549 cells while providing excellent red fluorescence in cytoplasm upon excitation with 880 nm irradiation. Photodynamic therapeutic application of the Ru(bpy)32+-incorporated UiO-67 NMOFs was investigated in vitro. The Ru(bpy)32+-incorporated UiO-67 NMOFs exhibited good biocompatibility without irradiation while having good cell-killing rates upon irradiation. In view of these facts, the developed Ru(bpy)32+-incorporated NMOFs give a new potential pathway to achieve enhanced two-photon fluorescence imaging and photodynamic therapy.

Optimizing single-nanoparticle two-photon microscopy by in situ adaptive control of femtosecond pulses

Single-nanoparticle two-photon microscopy shows great application potential in super-resolution cell imaging. Here, we report in situ adaptive optimization of single-nanoparticle two-photon luminescence signals by phase and polarization modulations of broadband laser pulses. For polarization-independent quantum dots, phase-only optimization was carried out to compensate the phase dispersion at the focus of the objective. Enhancement of the two-photon excitation fluorescence intensity under dispersion-compensated femtosecond pulses was achieved. For polarization-dependent single gold nanorod, in situ polarization optimization resulted in further enhancement of two-photon photoluminescence intensity than phase-only optimization. The application of in situ adaptive control of femtosecond pulse provides a way for object-oriented optimization of single-nanoparticle two-photon microscopy for its future applications.

Investigating Two-Photon-Induced Fluorescence in Rhodamine-6G in Presence of Cetyl-Trimethyl-Ammonium-Bromide.

We investigate the effect of cetyl-trimethyl-ammonium-bromides (CTAB) concentration on the fluorescence of Rhodamine-6G in water. This spectroscopic study of Rhodamine-6G in presence of CTAB was performed using two-photon-induced-fluorescence at 780nm wavelength using high repetition rate femtosecond laser pulses. We report an increment of ∼10% in the fluorescence in accordance with ∼12% enhancement in the absorption intensity of the dye molecule around the critical micellar concentration. We discuss the possible mechanism for the enhancement in the two-photon fluorescence intensity and the importance of critical micellar concentration.