Multiphoton Absorption Research Articles

Multiphoton characterization and live cell imaging using fluorescent adenine analogue 2CNqA.

Fluorescent nucleobase analogues (FBAs) are established tools for studying oligonucleotide structure, dynamics and interactions, and have recently also emerged as an attractive option for labeling RNA-based therapeutics. A recognized drawback of FBAs, however, is that they typically require excitation in the UV region, which for imaging in biological samples may have disadvantages related to phototoxicity, tissue penetration, and out-of-focus photobleaching. Multiphoton excitation has the potential to alleviate these issues and therefore, in this work, we characterize the multiphoton absorption properties and detectability of the highly fluorescent quadracyclic adenine analogue 2CNqA as a ribonucleotide monomer as well as incorporated, at one or two positions, into a 16mer antisense oligonucleotide (ASO). We found that 2CNqA has a two-photon absorption cross section that, among FBAs, is exceptionally high, with values of σ2PA(700 nm) = 5.8 GM, 6.8 GM, and 13 GM for the monomer, single-, and double-labelled oligonucleotide, respectively. Using fluorescence correlation spectroscopy, we show that the 2CNqA has a high 2P brightness as the monomer and when incorporated into the ASO, comparing favorably to other FBAs. We furthermore demonstrate the usefulness of the 2P imaging mode for improving detectability of 2CNqA-labelled ASOs in live cells.

Near-infrared multiphoton absorption and third harmonic generation with CsPbBr3 quantum dots embedded in micro-particles of metal–organic frameworks

A hybrid compound of CsPbBr3 quantum dots embedded in ZIF-8 microparticles shows both multiphoton excited (MPE) photoluminescence and third harmonic generation (THG) when excited by near-infrared femtosecond laser pulses.

Ultrafast laser deposition of powder materials on glass

The deposition of various powder materials on borosilicate glass was demonstrated using high-repetition-rate (frep = 1.5 MHz) femtosecond laser light. Melting of the glass substrate was caused by the heat-accumulation effect following multi-photon absorption, while powder materials were melted primarily through linear absorption. This novel processing approach allows the simultaneous melting of glass and powders leading to the formation of either a mechanical joint or fusion welds. The deposition of continuous material tracks was demonstrated for nickel, tin, stainless steel, copper, silicon, as well as silicon oxide powders. Effects of the varying average laser power and focus position on the deposited track morphology were studied. Laser-deposited tin and copper layers with thicknesses up to 60–70 µm were produced.

Micropattern of Silver/Polyaniline Core-Shell Nanocomposite Achieved by Maskless Optical Projection Lithography.

With the development of device miniaturization, a flexible and fast preparation method is in demand for achieving microstructures with desired patterns. We develop a novel photoreduction-polymerization method for preparing conductive metal-polymer patterns. Ag/polyaniline (PANI) nanocomposites have been successfully synthesized by maskless optical projection lithography (MOPL) technology, which is based on multiphoton absorption and the localized surface plasmon resonance (LSPR) effect. The individualized design and synthesis of the nanocomposite patterns at the micro-nano scale are flexibly realized on a variety of substrates. The surface-enhanced Raman scattering (SERS) effect of Rhodamine 6G (R6G) is demonstrated on the microstructure of a square maze-shaped Ag/PANI nanocomposite. The electrical conductivity of the as-prepared nanocomposite is obtained. The preparation protocol proposed in this study opens up new avenues for the fabrication of micro-nano devices such as sensors and detectors.

EMReact: a tool for modelling electromagnetic field induced effects in chemical reactions by solving the discrete stochastic master equation

The effects of electromagnetic fields (EMF) have been widely debated concerning their role in chemical reactions. Reactions, usually took hours or days to complete, have been shown to happen a thousand times faster using EMF radiations. This work develops a formalism and a computer program to evaluate and quantify the EMF effects in chemical reactions. The master equation employed in this program solves the internal energy of the reaction under EMFs while including collisional effects. Multiphoton absorption and emission are made possible with the transitioning energy close to the EMF and are influenced by the dielectric properties of the system. Dimethyl Sulfoxide and Benzyl Chloride are simulated under different EMF intensities. The results show that EMF absorption is closely related to the collisional redistribution of energy in molecules. The EMF effect can be interpreted as a shift of the thermodynamic equilibrium. Under such nonequilibrium energy distribution, the ‘temperature’ is not a reliable quantity for defining the state of the system.

Quantitatively identifying the upconversion luminescence mechanisms of Er3+:NaYF4 nanocrystals in aluminosilicate glass ceramics under femtosecond laser field

Upconversion luminescence of lanthanide ion doped nanocrystals under ultrashort laser pulse excitation can find significant applications in areas like super-resolution nonlinear microscopic imaging and attracts increasing attention. Though major excitation mechanisms, such as excited state absorption (ESA), energy transfer upconversion (ETU) and multi-photon absorption (MPA), have been analyzed and discussed intensively, quantitative differentiation of their respective contributions with convincing experimental proof has seldom been reported however. Here we report experimental demonstration of a simple but effective way to quantitatively identify simultaneous MPA from other mechanisms like ESA and ETU involved in the Er3+ doped NaYF4 nanocrystals in aluminosilicate glass ceramics under femtosecond laser field excitation. Comparative studies using laser pulses of the same spectral bandwidth but different time duration or repetition rate are performed and convincing experimental evidences for their respective contribution weights are obtained. The dependence of the MPA excitation efficiency on the spectral bandwidth of the femtosecond laser pulse is also explored for maximizing the upconversion luminescence yield. And predictions from a theoretical model agree well with experimental observations.

Quantum amplification of spin currents in cavity magnonics by a parametric drive induced long-lived mode

Cavity-mediated magnon-magnon coupling can lead to a transfer of spin-wave excitations between two spatially separated magnetic samples. In this paper, we present a scheme to substantially amplify this transfer efficiency through the application of a two-photon parametric drive on the cavity. Further, we enunciate the physical origin of the enhancement. The recurrent multiphoton absorption by the cavity opens up an infinite ladder of accessible energy levels, which can induce higher-order transitions within the magnon Fock space. This is reflected in a heightened spin-current response from one of the magnetic samples when the neighboring sample is coherently pumped. The enhancement induced by the parametric drive can be considerably high within the stable dynamical region. Specifically, near the periphery of the stability boundary, the spin current is amplified by several orders of magnitude. Such striking enhancement factors are attributed to the emergence of parametrically induced strong coherences precipitated by a long-lived mode, which is analogous to a bound state in continuum. While contextualized in magnonics, the generality of the principle would allow applications to energy transfer between systems contained in parametric cavities.

A New Insight into High-Aspect-Ratio Channel Drilling in Translucent Dielectrics with a KrF Laser for Waveguide Applications.

A new insight into capillary channel formation with a high aspect ratio in the translucent matter by nanosecond UV laser pulses is discussed based on our experiments on KrF laser multi-pulse drilling of polymethyl methacrylate and K8 silica glass. The proposed mechanism includes self-consistent laser beam filamentation along a small UV light penetration depth caused by a local refraction index increase due to material densification by both UV and ablation pressure, followed by filamentation-assisted ablation. A similar mechanism was shown to be realized in highly transparent media, i.e., KU-1 glass with a multiphoton absorption switched on instead of linear absorption. Waveguide laser beam propagation in long capillary channels was considered for direct electron acceleration by high-power laser pulses and nonlinear compression of excimer laser pulses into the picosecond range.

Enhanced energy deposition and carrier generation in silicon induced by two-color intense femtosecond laser pulses

We theoretically investigate the optical energy absorption of crystalline silicon subject to dual-color femtosecond laser pulses, using the time-dependent density functional theory (TDDFT). We employ the modified Becke-Johnson (mBJ) exchange-correlation potential which reproduces the experimental direct bandgap energy $E_g$. We consider situations where the one color is in the ultraviolet (UV) range above $E_g$ and the other in the infrared (IR) range below it. The energy deposition is examined as a function of mixing ratio $\eta$ of the two colors with the total pulse energy conserved. Energy transfer from the laser pulse to the electronic system in silicon is dramatically enhanced by simultaneous dual-color irradiation and maximized at $\eta\sim 0.5$. Increased is the number of generated carriers, not the absorbed energy per carrier. The effect is more efficient for lower IR photon energy, or equivalently, larger vector-potential amplitude. As the underlying mechanism is identified the interplay between intraband electron motion in the {\it valence} band (before excitation) driven by the IR component and resonant valence-to-conduction interband excitation (carrier injection) induced by the UV component. The former increases excitable electrons which pass through the $k$ points of resonant transitions. The effect of different multiphoton absorption paths or intraband motion of carriers generated in the conduction band play a minor role.

Control of Electron Wave Packets Close to the Continuum Threshold Using Near-Single-Cycle THz Waveforms.

The control of low-energy electrons by carrier-envelope-phase-stable near-single-cycle THz pulses is demonstrated. A femtosecond laser pulse is used to create a temporally localized wave packet through multiphoton absorption at a well defined phase of a synchronized THz field. By recording the photoelectron momentum distributions as a function of the time delay, we observe signatures of various regimes of dynamics, ranging from recollision-free acceleration to coherent electron-ion scattering induced by the THz field. The measurements are confirmed by three-dimensional time-dependent Schrödinger equation simulations. A classical trajectory model allows us to identify scattering phenomena analogous to strong-field photoelectron holography and high-order above-threshold ionization.

Production of polarized particle beams via ultraintense laser pulses

High-energy spin-polarized electron, positron, and $$\gamma$$ -photon beams have many significant applications in the study of material properties, nuclear structure, particle physics, and high-energy astrophysics. Thus, efficient production of such polarized beams attracts a broad spectrum of research interests. This is driven mainly by the rapid advancements in ultrashort and ultraintense laser technology. Currently, available laser pulses can achieve peak intensities in the range of $$10^{22}$$ – $$10^{23}$$ $$\hbox {Wcm}^{-2}$$ , with pulse durations of tens of femtoseconds. The dynamics of particles in laser fields of the available intensities is dominated by quantum electrodynamics (QED) and the interaction mechanisms have reached regimes spanned by nonlinear multiphoton absorption (strong-field QED processes). In strong-field QED processes, the scattering cross-sections obviously depend on the spin and polarization of the particles, and the spin-dependent photon emission and the radiation-reaction effects can be utilized to produce the polarized particles. An ultraintense laser-driven polarized particle source possesses the advantages of high brilliance and compactness, which could open the way for the unexplored aspects in a range of researches. In this work, we briefly review the seminal conclusions from the study of the polarization effects in strong-field QED processes, as well as the progress made by recent proposals for production of the polarized particles by laser–beam or laser–plasma interactions.

Fourier-Transform Atomic Force Microscope-Based Photothermal Infrared Spectroscopy with Broadband Source.

The mechanical detection of photothermal expansion from infrared (IR) absorption with an atomic force microscope (AFM) bypasses Abbe's diffraction limit, forming the chemical imaging technique of AFM-IR. Here, we develop a Fourier transform AFM-IR technique with peak force infrared microscopy and broadband femtosecond IR pulses. A Michelson interferometer creates a pair of IR pulses with controlled time delays to generate photothermal signals transduced by AFM to form an interferogram. A Fourier transform is performed to recover IR absorption spectra. We demonstrate the Fourier transform AFM-IR microscopy on a polymer blend and hexagonal boron nitride. An intriguing observation is the vertical asymmetry of the interferogram, which suggests the presence of multiphoton absorption processes under the tip-enhancement and femtosecond IR lasers. Our method demonstrates the feasibility of time-domain detection of the AFM-IR signal in the mid-IR regime and paves the way toward multiphoton vibrational spectroscopy at the nanoscale below the diffraction limit.

Oxygen vacancy levels mediated photophysical pathways of NIR-II responsive broadband upconversion

The photon upconversion (UC) is the process that has been known for a long time. Especially, lanthanide-based UC materials recently have attracted huge interest of scientific community due to their narrow visible emission bands upon near-infrared (NIR) excitation. However, the excitation in the high excitation power of NIR can cause highly bright and broad emission (B-UC). Such explosive B-UC was distinct at high excitation condition with UC wavelength encompassing the entire visible range. Previously, the proposed model of B-UC origination includes heat, multi-photon absorption, and accumulated thermal energy transfer. In this article, we will show various experimental and theoretical evidence supporting the idea that B-UC arises from photophysical pathways. Here, the key experimental evidence for photophysical pathways model of B-UC is to measure B-UC in the low-temperature environment (22 K). In addition, the density functional theory was used to regenerate energy levels which would be compared to the absorption spectral bands in Er2O3. As a result, we are confident of an electron tunneling model from 2P3/2 of Er3+ to oxygen vacancy level (VO) of Er2O3. Then, VO electrons are sequentially excited to the conduction band of Er2O3 by energy transfer from 4F9/2 of Er3+. Finally, the electrons return to the VO of Er2O3 with concomitant B-UC.

Asymmetric encryption by optical Kerr nonlinearities exhibited by electrochromic NiO thin films.

Herein is analyzed how an electric field can induce a band gap shift in NiO films to generate an enhancement in their third-order optical nonlinearities. An electrochromic effect seems to be responsible for changes in absorbance and modification in off-resonance nonlinear refractive index. The optical Kerr effect was determined as the dominant physical mechanism emerging from the third-order optical susceptibility processes present in a nanosecond two-wave mixing configuration at 532 nm wavelength. Absence of any important multi-photonic absorption was validated by the constant trace of high-irradiance optical transmittance in single-beam mode. The inspection of nonlinear optical signals allowed us to propose an exclusive disjunctive logic gate assisted by an electrochromic effect in an optical Kerr gate. Asymmetric encryption by our XOR system with the influence of a switchable probe beam transmittance and electrical signals in the sample was studied. Immediate applications for developing multifunctional quantum systems driven by dynamic parameters in electrochromic and nonlinear optical materials were highlighted.

Thermal feature-size enhancement in multiphoton photoresists

We demonstrate a new approach for decreasing the feature size in multiphoton absorption polymerization (MAP). Acrylic photoresists containing the photoinitiator KL68 (bis-[4-(diphenylamino) stryl]-1-(2-ethylhexyloxy), 4-(methoxy)benzene) exhibit a proportional velocity (PROVE) dependence, yielding smaller feature sizes at lower fabrication speeds. The feature size in this photoresist decreases substantially with a temperature increase of less than 10°C when all other fabrication parameters are kept constant, suggesting that the PROVE behavior results from local heating. Although higher temperatures have previously been associated with decreased feature sizes in MAP, the effect observed here is considerably stronger than in previous work, and is shown to be a property of the photoinitiator. This discovery opens the door to exploiting thermal gradients to improve resolution in MAP lithography.

Two-photon absorption in semiconductors: A multiband length gauge analysis

The simplest approach to deal with light excitations in direct-gap semiconductors is to model them as a two-band system: one conduction and one valence band. For such models, particularly simple analytical expressions are known to exist for the optical response such as multi-photon absorption coefficients. Here we show that generic multi-band models do not require much more complicated expressions. Our length-gauge analysis is based on the semiconductors Bloch equations in the absence of all scattering processes. In the evaluation, we focus on two-photon excitation by a pump-probe scheme with possibly non-degenerate and arbitrarily polarized configurations. The theory is validated by application to graphene and its bilayer, described by a tight-binding model, as well as bulk Zincblende semiconductors described by k.p theory.

Beyond third-order optical nonlinearities in liquid suspensions of metal-nanoparticles and metal-nanoclusters

Various nonlinear optical (NLO) phenomena observed in liquid suspensions of metal nanoparticles (NPs) and metal nanoclusters (NCs) have received considerable attention in the past few years. For example, multiphoton absorption, modulational instability, optical solitons, and parametric processes, benefit from research on soft-matter systems. Thus, many results are still being published providing support for earlier theoretical predictions and new discoveries. In particular, colloids containing NPs and NCs of noble-metal atoms present outstanding NLO responses and have been exploited to study for studying various phenomena and applications. Indeed, when illuminated with intense optical fields, such colloids can exhibit effective high-order nonlinearities (HONs) with large magnitudes which can dominate their NLO behavior. In this article, we review experiments with liquid suspensions of noble-metal NPs and noble-metal NCs, in which an appropriate methodology has been applied to study effective HONs for different sizes and morphologies of metal-nanostructures. In addition, a nonlinearity management procedure is discussed as a valuable tool to control for controlling the NLO response of metal-colloids through constructive and destructive interference among the nonlinearities of different orders. Because of the strong NLO behavior of metal-colloids, various phenomena associated to effective HONs were investigated such as: self-action effects, saturated multiphoton absorption, NLO scattering, bright and vortex spatial solitons, and operation of Random Lasers. Perspectives for further studies and photonic applications of metal-colloids exploring their effective nonlinearities are also discussed.

Parameterization of a Refined Model Aimed at Simulating Laser-Induced Incandescence of Soot Using a Visible Excitation Wavelength of 532 nm

Laser-induced incandescence (LII) is one of the most powerful techniques for soot detection in combustion media. It is therefore commonly used to perform experiments in lab-scale flames and industrial combustors with a view to elucidating the formation mechanisms leading to combustion-generated fine carbonaceous particles while assessing their intrinsic properties. Quantitatively interpreting LII measurements, however, requires a firm knowledge of the optical properties of soot, including their wavelength-dependent absorption function (). Among the approaches used to evaluate such a crucial parameter, one can implement a LII model to derive the value which has to be set to reproduce a series of LII signals measured in a well-characterized environment. In this context, the present work aims at parameterizing a refined LII model built upon a comprehensive version of soot heat- and mass-balance equations for assessment when using a visible excitation wavelength of 532 nm. The proposed model integrates terms representing the saturation of linear, single- and multi-photon absorption processes, cooling by sublimation, conduction, radiation and thermionic emission, in addition to mechanisms depicting soot oxidation and annealing, non-thermal photodesorption of carbon clusters, as well as corrective factors accounting for the shielding effect and multiple scattering (MS) within aggregates. To parameterize this advanced simulation tool, an optimization procedure coupling design of experiments with a genetic algorithm-based solver was implemented. Doing so allowed to estimate the values of different factors involved in absorption and sublimation terms, including the multi-photon absorption cross-section for C2 photodesorption, the saturation coefficients for linear- and multi-photon absorption, as well as the value. Obtained parameters turned out to be well-suited to reproduce a set of LII signals acquired in a Diesel flame. While leading to predictions merging on a single curve with measured data, the so-parameterized model notably led to infer values of 0.3 and 0.38 when considering or neglecting MS within aggregates, respectively. Finally, the / ratio estimated based on data collected herein and in a former modeling work was found to be consistent with results issued from two-excitation wavelength LII measurements previously reported in the literature.

Nucleation in situ of perylene crystal by femtosecond laser induced cavitation

Organic semiconductor single crystal materials have broad application prospects in the field of high-performance optoelectronic devices because of their highly ordered structure, few defects, and high carrier mobility. However, it is difficult to control the nucleation location of crystal formation in the current commonly used crystal growth methods including physical vapor transport and solution processing, which makes it difficult to manufacture organic crystal devices. Laser-induced crystallization technology is expected to solve this problem. In this study, we demonstrated nucleation in situ of a perylene crystal by femtosecond laser induced cavitation. The results show that the crystallization of perylene crystals induced by the femtosecond laser is mainly due to the aggregation effect by laser cavitation bubbles caused by multiphoton absorption. This strategy facilitates the application of organic single crystals to optoelectronic devices.

Theoretical investigation of electron dynamics driven by laser pulses in graphene nanoribbons

Control of electron dynamics in graphene nanoribbons (GNRs) is critically important for the future applications of graphene-based nanoelectronic devices. Based on real-time simulations, we investigate the manipulation of electronic transport by femtosecond laser pulses in armchair GNRs. The simulation results show that the multiphoton absorption process can drive the photon-excited electron flow along a GNR. The corresponding transferred charges are determined by the order of multiphoton absorption and depend on the central frequency and energy distribution of few-cycle laser pulses. Furthermore, the transferred charge can be controlled by the carrier-envelope phase of pulses; this dependence vanishes as the duration time of laser pulses increases. These results also provide insights into the manipulation of electron dynamics using lasers and the design of optoelectronic devices based on graphene materials.