Multiphoton Absorption Research Articles

Multiphoton Absorption and Graphitization in Poly(methyl methacrylate)-Coated Aluminum Nanoantenna Arrays

Collective electron oscillations, termed surface plasmons, in subwavelength metallic nanostructures can be excited by light, giving rise to an enhanced optical near-field at the surface of the meta...

Ultra-high aspect ratio pores milled in diamond via laser, ion and electron beam mediated processes

Microfabrication techniques are critical for the rapid prototyping and development of applications for cutting edge materials. Recently diamond has gained considerable interest for quantum photonic, biosensing, inertial confinement fusion and magnetometer applications. In this article, ultra-high aspect ratio milling of diamond micropores by photon, ion and electron based methods is reported. A multiphoton absorption laser ablation approach is revealed to rapidly produce sub-10 μm diameter micropores in diamond with an aspect ratio of 14:1 and a tapered profile at the surface interface. Chemically active, oxygen focused ion beam milling produces high-aspect ratio pores in diamond with an aspect ratio of 65:1 and minimal tapering over the length of the pore, overcoming the physical interaction volume limitations imposed in conventional gallium based focused ion beam milling and laser ablation methods. Oxygen-mediated electron beam induced etching is revealed to negate the limitations imposed by physical sputtering mechanisms utilized in focused ion beam milling via the direct initiation of chemical reactions at the receding surface, producing aspect ratios on the order of 200:1. Numerical simulations reveal the physical basis for the superior aspect-ratio pore milling of the oxygen focused ion beam milling and electron beam induced etching methods. Our results demonstrate direct-write methods for the fabrication of ultra-high aspect micropores in diamond and provide insight into the underlying mechanisms of these physical processes. The three methods demonstrated here can be interchanged for applications based on the desired characteristic aspect ratio and process throughput.

O-FIB: far-field-induced near-field breakdown for direct nanowriting in an atmospheric environment

Nanoscale surface texturing, drilling, cutting, and spatial sculpturing, which are essential for applications, including thin-film solar cells, photonic chips, antireflection, wettability, and friction drag reduction, require not only high accuracy in material processing, but also the capability of manufacturing in an atmospheric environment. Widely used focused ion beam (FIB) technology offers nanoscale precision, but is limited by the vacuum-working conditions; therefore, it is not applicable to industrial-scale samples such as ship hulls or biomaterials, e.g., cells and tissues. Here, we report an optical far-field-induced near-field breakdown (O-FIB) approach as an optical version of the conventional FIB technique, which allows direct nanowriting in air. The writing is initiated from nanoholes created by femtosecond-laser-induced multiphoton absorption, and its cutting “knife edge” is sharpened by the far-field-regulated enhancement of the optical near field. A spatial resolution of less than 20 nm (λ/40, with λ being the light wavelength) is readily achieved. O-FIB is empowered by the utilization of simple polarization control of the incident light to steer the nanogroove writing along the designed pattern. The universality of near-field enhancement and localization makes O-FIB applicable to various materials, and enables a large-area printing mode that is superior to conventional FIB processing.

Photophysical Properties of Water-Soluble CdTe/CdSe/ZnS Core/Shell/Shell Nanocrystals Emitting at 820 nm

The photophysical properties of near-infrared-I (NIR-I)-emissive type-II semiconductor nanocrystals (NCs), such as their excitonic properties and multiphoton absorption (MPA), have been rarely repo...

Comparison studies of excitonic properties and multiphoton absorption of near-infrared-I-emitting Cu-doped InP and InP/ZnSe nanocrystals.

Cu-doped InP (Cu:InP) and InP/ZnSe nanocrystals (NCs) with near-infrared-I (NIR-I) emission were prepared and characterized. Femtosecond transient absorption spectra revealed that the epitaxial growth of a ZnSe diffusion barrier onto the Cu:InP core can amplify its exciton-dopant coupling strength, with the energy transfer times of $\sim{220}\;{\rm ps}$∼220ps for Cu:InP NCs and $\sim{183}\;{\rm ps}$∼183ps for Cu:InP/ZnSe NCs. Importantly, the Cu:InP/ZnSe NCs exhibit much larger two- and three-photon absorption cross sections, reaching $\sim{10162}$∼10162 GM at 1030 nm and $\sim{1.06} \times {{10}^{ - 77}}\;{{\rm cm}^6}\,{{\rm s}^2}\,{{\rm photon}^{ - 2}}$∼1.06×10-77cm6s2photon-2 at 1600 nm, compared with Cu:InP NCs.

Nonlinear optical properties of Sponge Si/Au nanoparticle

Plasmon sponge nanostructures have occupied a special role in the field of plasmonics and nanophotonics: sensors and advanced source of white emission. If the pores of a golden spongy nanostructure are filled with silicon, the result will be a promising source of broadband radiation with high efficiency due to the localization of the field by a structure with a high surface-to-volume ratio. This paper presents the results of photoluminescence generation with multiphoton absorption and second-harmonic generation obtained from hybrid sponge Si/Au nanoparticles. The particles have been fabricated by femtosecond laser ablation at room temperature in the air. Experiments have shown the ability to generate broadband photoluminescence in the range of 500 – 800 nm (0.93 eV). The obtained results can be applied for creation of white light luminescent metasurfaces and advanced nanophotonic spectroscopy devices.

Controlling photocurrent channels in scanning tunneling microscopy

We investigate photocurrents driven by femtosecond laser excitation of a (sub)-nanometer tunnel junction in an ultrahigh vacuum low-temperature scanning tunneling microscope (STM). The optically driven charge transfer is revealed by tip retraction curves showing a current contribution for exceptionally large tip-sample distances, evidencing a strongly reduced effective barrier height for photoexcited electrons at higher energies. Our measurements demonstrate that the magnitude of the photo-induced electron transport can be controlled by the laser power as well as the applied bias voltage. In contrast, the decay constant of the photocurrent is only weakly affected by these parameters. Stable STM operation with photoelectrons is demonstrated by acquiring constant current topographies. An effective non-equilibrium electron distribution as a consequence of multiphoton absorption is deduced by the analysis of the photocurrent using a one-dimensional potential barrier model.

Giant Nonlinear Optical Response in Triple Cation Halide Mixed Perovskite Films

AbstractThe versatility of perovskites through chemical composition modification is critical for enhancing performance of a range of potential applications such as light emitters and integrated photovoltaics. However, a systematic study on the nonlinear optical (NLO) responses of these perovskites is still lacking. Here, for the first time, the NLO properties of triple cation mixed halide perovskite (TCMHP) films, (Cs0.06FA0.79MA0.15)Pb (I0.85Br0.15)3, using Z‐scan and time‐resolved spectroscopy, are investigated. It is found that TCMHP film shows strong saturable absorption at 395 nm, reverse saturable absorption such as two‐ and three‐photon absorption (2PA, 3PA) at 790 nm (near the bandgap), and 3PA at 1200 nm. The 3PA phenomena at 790 nm are attributed to the phonon‐assisted anti‐Stokes process. The 2PA and 3PA coefficients are estimated to be ≈2.1 cm MW−1 and ≈900 cm3 GW−2, respectively, which are an order of magnitude larger than those of MAPbI3 and other perovskites. Moreover, it is demonstrated that these giant 2PA and 3PA coefficients of TCMHP can be used to realize optical stabilization. The observed strong multiphoton absorption response will enable TCMHP materials to be suitable for various nonlinear optical applications such as multiphoton‐based imaging, optical modulator, and all‐optical switching devices.

Harnessing Multi-Photon Absorption to Produce Three-Dimensional Magnetic Structures at the Nanoscale

Three-dimensional nanostructured magnetic materials have recently been the topic of intense interest since they provide access to a host of new physical phenomena. Examples include new spin textures that exhibit topological protection, magnetochiral effects and novel ultrafast magnetic phenomena such as the spin-Cherenkov effect. Two-photon lithography is a powerful methodology that is capable of realising 3D polymer nanostructures on the scale of 100 nm. Combining this with postprocessing and deposition methodologies allows 3D magnetic nanostructures of arbitrary geometry to be produced. In this article, the physics of two-photon lithography is first detailed, before reviewing the studies to date that have exploited this fabrication route. The article then moves on to consider how non-linear optical techniques and post-processing solutions can be used to realise structures with a feature size below 100 nm, before comparing two-photon lithography with other direct write methodologies and providing a discussion on future developments.

Protein Crosslinking and Immobilization in 3D Microfluidics through Multiphoton Absorption

This study used laser multiphoton absorption (MPA) to crosslink and immobilize protein in 3D microfluidics. MPA can be used to crosslink proteins to form smaller crosslinked-protein structures than those formed through single-photon absorption. However, studies on MPA protein crosslinking in 3D microfluidics are lacking. In this study, the MPA was implemented using pulse laser to induce bovine serum albumin (BSA) crosslinking. We also applied (3-glycidyloxypropyl)trimethoxysilane to increase the adhesion of crosslinked BSA. Also, the width of crosslinked-BSA structure was measured, and then curve-fitting and optical equation were used to predict heights of the crosslinked-BSA structures formed under various laser powers. At last, BSA structures were effectively crosslinked in the three-layered glass or polydimethylsiloxane microchannels. In contrast to studies on single-photon absorption in 3D microfluidics or MPA protein crosslinking in 2D microfluidics, we obtained relatively small crosslinked-BSA structures through MPA and immobilize BSA in 3D microfluidics. In the future, this method can be applied in monolithic 3D microfluidics for protein crosslinking to avoid misalignment and leakage in layer-by-layer 3D microchannels and form more compact 3D microfluidics. These features are conducive to enhance the diversity and convenience of microfluidics in biomedical testing.

Interaction of (CCl4)n clusters with nanosecond and picosecond laser pulses at discrete wavelengths spanning from IR to UV region: A comparative study using TOFMS

Using time-of-flight mass spectrometer (TOFMS), photochemistry of carbon tetrachloride clusters ((CCl4)n) has been investigated upon interaction with nanosecond and picosecond Nd:YAG laser pulses (266, 355, 532 and 1064 nm) spanning over intensity range of ∼1.2 × 109 to 7.9 × 1012 W/cm2. At all the laser wavelengths upon interaction of (CCl4)n clusters with laser pulse, multiphoton excitation leads to excessive fragmentation of cluster constituents, which are subsequently ionized by multiphoton absorption process. Depending on laser wavelength and pulse duration, at 266 and 355 nm these clusters exhibit dominant ion signal corresponding to singly charged fragment ions i.e. Cl+, CCl+, CCl2+ and CCl3+ in the mass spectra. In addition, for studies carried out at 266 nm using picosecond laser pulses minor ion signal corresponding to C2Cl+ and C2Cl2+ were also observed. Generation of these ions has been ascribed to intra-cluster radical chemistry resulting in generation of neutral precursors, which subsequently are multiphoton ionized. At 532 and 1064 nm, dominant ion signal corresponding to multiply charged atomic ions of carbon (up to C4+/C5+) and chlorine (up to C11+) have been observed. Though multiphoton absorption is the primary process driving the photochemistry of (CCl4)n clusters, observation of multiply charged atomic ions at 532 and 1064 nm has been ascribed to dominant role played by quasi-free electrons which are confined within the ionized cluster, in efficient coupling of laser energy at longer laser wavelengths via inverse Bremsstrahlung process.

Dynamics and stability of cw and pulse lasers in Kerr optical media with K-photon absorption

The laser dynamics in inscription processes involving transparent media is carried out, by considering an optical field propagating in a transparent medium with Kerr nonlinearity. The study takes into account multi-photon absorption phenomena, as well as a possible modification of the material structure resulting in the generation of a plasma of nearly free electrons. The model is described by a complex Ginzburg–Landau equation governing the laser dynamics, in which an extra Kth-order nonlinear term is induced by K-photon absorption processes. The model also takes into consideration the electron plasma generation via a linear term in the optical field. A global stability analysis of the system dynamics reveals a rich variety of fixed points consisting of no, one or two singular points in the amplitude-frequency plane. The modulational instability of plane waves gives rise to period-halving bifurcations in the continuous-wave amplitude growth rate, reminiscent of dominant multi-pulse structures in the nonlinear regime at large multi-photon absorption rate K. Pulses and multi-pulses are observed in numerical simulations of the nonlinear equations for the full system dynamics, the first structures are clearly associated with the case K = 2 whereas multi-pulse structures of increasing amplitudes and shorter perioids are dominant at larger values of K.

Investigation of laser-induced damage and related multiphoton absorption changes in lithium niobate crystals at high repetition rate femtosecond pump

An R-on-1 laser-induced damage-threshold (LIDT) testing method was applied to test coated and uncoated magnesium oxide-doped periodically poled lithium niobate samples pumped by femtosecond Yb:KGW laser pulses at kilohertz and megahertz pulse repetition rates. LIDT values decreased by ∼1.5 and ∼38 times when increasing repetition rate from 100 to 571 kHz and to 76 MHz, respectively. We also investigated nonlinear absorption changes in lithium niobate crystals at the pulse repetition range from 60 to 600 kHz with trains consisting of 100 identical femtosecond pulses. Laser beam transmission in the crystal experienced a drop of ∼18 % from initial pulses of train to the next 40 pulses at intensities 40% to 15% lower than LIDT due to nonlinear absorption of 220 fs duration pulses at 1.03 μm.

Clusters formation and fragmentation of nitromethane at 266 nm

We carry out experiments on the fragmentation of nitromethane by multiphoton absorption at the wavelength 266 nm. This was conducted in a reflectron (Jordan), modified in the laboratory. Due to the large number of fragments, special care has been taken into the calibration of the system, in the simultaneity between the laser pulse and the sample, and the associated electronics to ensure that produced fragment spectra arise from the interaction laser-sample. We emphasize the next aspects of the method:•Simple design for introducing a gas sample at laser interaction region to facilitate the cluster formation•Astonishing number of fragments produced by multiphoton absorption.

Energy selective time of flight spectrometer to study low energy dissociation channels of PAHs

SynopsisDissociation channels induced by sequential UV multiphoton absorption of vapour phase fluorene cation is investigated using energy selective ToF mass spectrometer. Neutral fluorene molecule is ionized by resonantly enhanced multiphoton absorption and dissociated in the same photon field. The main goal of this experiment is to determine the rate constants of statistical dissociation channels of PAH cations for a wide range of internal energies.

Multiphoton absorption in low-dimensional cesium copper iodide single crystals

Two kinds of all-inorganic lead-free cesium copper iodide (CsCu2I3 and Cs3Cu2I5) single crystals (SCs) are synthesized and their multiphoton absorption (MPA) properties are comparatively investigated for the first time.

Five-photon absorption upconversion lasing from on-chip whispering gallery mode.

In the progress of ultrafast optics, nonlinear interactions between light and matter are very important in scientific and technical fields. In particular, the high-order nonlinear effect induced by multi-photon absorption (MPA) upconversion lasing has injected new impetus into the research on short-wavelength laser sources. Here, we report the realization of amplified spontaneous emission (ASE) by MPA simultaneously in an epitaxy thin film. In addition, by virtue of the excellent optical confinement of cylindrical microcavities with high Q (∼4 × 103) on-chip, we demonstrated, for the first time, low-threshold upconversion lasing of five-photon absorption enhanced by a microcavity at room temperature. The resonant whispering-gallery mode (WGM) distribution in cylindrical microcavities was simulated comprehensively by the finite difference time domain (FDTD) method. We found that the high-order nonlinear optical process could be significantly enhanced in the microcavity with an increase in the lifetime of radiation photons.

Star-shaped triazine-cored ladder-type ter(p-phenylene)s for high-performance multiphoton absorption and amplified spontaneous blue emission

Lacking high-performance blue emissive multiphoton absorption (MPA) materials particularly for frequency up-converted amplified spontaneous emission (ASE) or lasing hampers novel breakthroughs in a wide-range of laser-based applications.

Near-Infrared-Excitable Organic Ultralong Phosphorescence through Multiphoton Absorption.

Organic ultralong room-temperature phosphorescence (OURTP) with a long-lived triplet excited state up to several seconds has triggered widespread research interests, but most OURTP materials are excited by only ultraviolet (UV) or blue light owing to their unique stabilized triplet- and solid-state emission feature. Here, we demonstrate that near-infrared- (NIR-) excitable OURTP molecules can be rationally designed by implanting intra/intermolecular charge transfer (CT) characteristics into H-aggregation to stimulate the efficient nonlinear multiphoton absorption (MPA). The resultant upconverted MPA-OURTP show ultralong lifetimes over 0.42 s and a phosphorescence quantum yield of ~37% under both UV and NIR light irradiation. Empowered by the extraordinary MPA-OURTP, novel applications including two-photon bioimaging, visual laser power detection and excitation, and lifetime multiplexing encryption devices were successfully realized. These discoveries illustrate not only a delicate design map for the construction of NIR-excitable OURTP materials but also insightful guidance for exploring OURTP-based nonlinear optoelectronic properties and applications.

The interaction of 355nm laser light on Adenine and Uracil

SynopsisDissociation and ionization of adenine and uracil were investigated in the multiphoton absorption re-gime using laser pulse at 355nm in conjunction with TOF mass spectrometry in reflectron mode (R-TOF). In contrast of previous investigations where a notorious amount of low mass ions was detected arising from both molecules.