Nonlinear Multiphoton Absorption Research Articles

Z-scan analytical solutions for thin media with high order refractive nonlinearity and multiphoton absorption

Considering that a thin media presents solely one type of nonlinearity, we obtain an analytical solution for far field on-axis Z-scan detection; a second solution is obtained for open aperture case. To find the analytical solutions, we propose a form for the nonlinear high order refractive and multiphoton absorption of the media. Z-scan curves are presented where the nonlinear high order refractive and multiphoton absorption are varied.

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.

Ultralow-threshold six-photon-excited upconversion lasing in a plasmonic microcavity.

Nonlinear multiphoton absorption (MPA) upconversion lasers have critical applications in fluorescence imaging probes and biological photonics. Here, we report the realization of ultralow-threshold six-photon-excited upconversion lasing through cavity quantum electrodynamics effects in a plasmonic microcavity. The value of the Purcell factor (Fp) in hybrid whisper-gallery mode (WGM) is enhanced five-fold relative to a bare microwire (MW), which enhances the nonlinear light-matter interactions dramatically. Compared with a MW, the threshold of six-photon upconversion WGM lasing is reduced by one order magnitude due to plasmonic enhancement effects. In addition, the temperature and polarization characteristics of upconversion lasing via a plasmonic-WGM approach show a distinct evolution, different from a bare MW. This work paves the way for extreme nonlinear optics, taking advantage of the processability and high Purcell factor of plasmonic microcavities.

Femtosecond-scale all-optical switching in oxyfluorogallate glass induced by nonlinear multiphoton absorption.

Herein, all-optical switching based on a new type of oxyfluorogallate glass with high switching efficiency and ultrafast response time was reported in the near-infrared wavelength range, which is of great importance for applications in optical telecommunication. The structural and optical properties, as well as the nonlinear optical effects, of the oxyfluorogallate glass were investigated, demonstrating a good figure of merit applicable to nonlinear optical devices. Using pump–probe experiments, we found that the switching time in the oxyfluorogallate glass due to nonlinear multiphoton absorption was approximately 350 fs, which was limited by the pulse duration of the near-infrared probe pulse. Additionally, the largest on–off amplitude of this optical switching device could reach ∼12%, which is in sharp contrast to that of quartz glass. Thus, this study provides a suitable material for the manufacture of integrated photonic devices, which are crucial for promoting the application of glass on-chip photonics.

Enhanced optical power limiting and visible luminescence in colloidal dispersion of ultra-small Au nanoclusters synthesized by single-pot chemical technique

Here, we present a detailed investigation on the synthesis and nonlinear multiphoton absorption properties of the colloidal solution of Au nanoclusters (AuNCs) which contains the atomic clusters, with the number of atoms per cluster (NAC) of only one (Au1NC) and two (Au2NC). These AuNCs are synthesized by an easy single step one-pot simple chemical process and by using dimethylformamide (DMF) both as reducer and stabilizer. The presence of both Au1NC and Au2NC are found in the sample by their distinct signature in the UV–Vis. absorption spectrum as well as in the high-resolution mass spectrum. The synthesized material has been found to exhibits a strong and stable blue-luminescence with a moderately high quantum yield (QY) of 12.4% when excited with UV light. The nonlinear optical two-photon absorption (2PA) properties of Au1, Au2NC solutions are being reported here by Z-scan studies, for the first time, by using both 10 ns and 100 fs pulse laser radiations having wavelength of 532 nm. It is significantly noted here that the synthesized AuNCs are found to exhibit reverse saturable absorption (RSA) when excited either by ns or by fs laser pulses. A high third-order nonlinear susceptibility (ꭓ(3)) of the order of 10−13 (esu) of the synthesized materials are obtained under fs laser excitation and it is attributed to the 2PA through electronic band to band transition. In contrast, the variation of the 2PA coefficient (β) with input intensity (I0) represents the footprint of free carrier involvement in the enhanced nonlinear absorption in the case of ns excitation. Furthermore, through the non-saturable nonlinear multiphoton absorption, the synthesized AuNCs exhibit excellent optical power limiting phenomenon with the limiting threshold (Fth) of 9.1 mJ/cm2 (fs excitation) and 2.02 J/cm2 (ns excitation) owing to their enhanced 2PA coefficient. Therefore, we believe that our synthesized ultra-small colloidal AuNCs can be used as the promising candidate material for advanced photonics application in the future.

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.

Low-temperature solution-processed flexible metal oxide thin-film transistors via laser annealing

Solution processed metal oxide thin-film transistors (MO-TFTs) have gained momentum in recent years and opened new horizons for their extended applications in thin-film optoelectronics. Unfortunately, the relatively high processing temperature has become the main limitation for their commercial application in flexible electronics. In this work, ultrashort femtosecond (fs) laser pulses were used for the annealing of printed InGaZnO TFT arrays with low temperature and fast processing. The high transient intensity and negligible heat-affected zone is beneficial to the effective conversion of precursor to metal-oxide lattices, which was also verified by the x-ray photoelectron spectroscopy analysis. Moreover, for the first time, based on optical engineering method, dielectric mirrors (DMs) is proposed to realize reflection of photon irradiation and protect the underlying polymer substrate. TFTs on polyethylene naphthalate (PEN) substrate with polymer insulator exhibited a mobility of 4.24 cm2 V−1 s−1, along with good mechanical stability. The mechanism of DMs for the improvement of the device performance was systematically investigated based on laser-matter interaction, optical structure and photon transport. DMs can reduce laser-induced pressure and variation of dielectric properties in PEN substrate resulting from the impact ionization due to a strong nonlinear multi-photon absorption. Our work clearly demonstrated that flexible MO-TFTs can be simply fabricated with fs-laser annealing. More importantly, this novel method is applicable for a wide range of MO and polymer substrates, by solving the incompatibility of solution processed MO and polymer substrates due to high processing temperature. Therefore, the proposed method showed tremendous potential to be applicable in flexible electronics such as sensors, display and circuits.

Ultra-Short Pulsed Laser Manufacturing and Surface Processing of Microdevices

Abstract Ultra-short laser pulses possess many advantages for materials processing. Ultrafast laser has a significantly low thermal effect on the areas surrounding the focal point; therefore, it is a promising tool for micro- and submicro-sized precision processing. In addition, the nonlinear multiphoton absorption phenomenon of focused ultra-short pulses provides a promising method for the fabrication of various structures on transparent material, such as glass and transparent polymers. A laser direct writing process was applied in the fabrication of high-performance three-dimensional (3D) structured multilayer micro-supercapacitors (MSCs) on polymer substrates exhibiting a peak specific capacitance of 42.6 mF·cm−2 at a current density of 0.1 mA·cm−2. Furthermore, a flexible smart sensor array on a polymer substrate was fabricated for multi-flavor detection. Different surface treatments such as gold plating, reduced-graphene oxide (rGO) coating, and polyaniline (PANI) coating were accomplished for different measurement units. By applying principal component analysis (PCA), this sensing system showed a promising result for flavor detection. In addition, two-dimensional (2D) periodic metal nanostructures inside 3D glass microfluidic channels were developed by all-femtosecond-laser processing for real-time surface-enhanced Raman spectroscopy (SERS). The processing mechanisms included laser ablation, laser reduction, and laser-induced surface nano-engineering. These works demonstrate the attractive potential of ultra-short pulsed laser for surface precision manufacturing.

Nonlinear optical and multi-photon absorption properties in graphene–ZnO nanocomposites

Graphene–ZnO (GZO) nanocomposites were synthesized by a modified solvothermal method, and characterized by transmission electron microscopy, x-ray diffraction, Raman spectra, and UV–vis absorption spectra. The controllable nonlinear optical (NLO) properties of as-prepared GZO nanocomposites were tested by an open-aperture Z-scan method with 1030 nm fs laser pulses; the tested results showed that there were five-photon absorption (5PA) at 46.8 GW cm−2, 3PA at 28.1 GW cm−2, 2PA at 18.7 GW cm−2, and a vital change from saturable absorption (SA) to reverse SA (RSA) with the increase of incident intensity. This was the first time that 5PA was found in GZO nanocomposites at such a low intensity, 46.8 GW cm−2. The tunable NLO property from SA to RSA and controllable multi-photon absorption provided a facile approach for their applications in optical, optoelectronic devices, and information storage.

Holes generation in glass using large spot femtosecond laser pulses

We demonstrate high-throughput, symmetrical, holes generation in fused silica glass using a large spot size, femtosecond IR-laser irradiation which modifies the glass properties and yields an enhanced chemical etching rate. The process relies on a balanced interplay between the nonlinear Kerr effect and multiphoton absorption in the glass which translates into symmetrical glass modification and increased etching rate. The use of a large laser spot size makes it possible to process thick glasses at high speeds over a large area. We have demonstrated such fabricated holes with an aspect ratio of 1:10 in a 1 mm thick glass samples.

Optical bandgap engineering in nonlinear silicon nitride waveguides.

Silicon nitride is a well-established material for photonic devices and integrated circuits. It displays a broad transparency window spanning from the visible to the mid-IR and waveguides can be manufactured with low losses. An absence of nonlinear multi-photon absorption in the erbium lightwave communications band has enabled various nonlinear optic applications in the past decade. Silicon nitride is a dielectric material whose optical and mechanical properties strongly depend on the deposition conditions. In particular, the optical bandgap can be modified with the gas flow ratio during low-pressure chemical vapor deposition (LPCVD). Here we show that this parameter can be controlled in a highly reproducible manner, providing an approach to synthesize the nonlinear Kerr coefficient of the material. This holistic empirical study provides relevant guidelines to optimize the properties of LPCVD silicon nitride waveguides for nonlinear optics applications that rely on the Kerr effect.

Progress in ultrafast laser processing and future prospects

AbstractThe unique characteristics of ultrafast lasers have rapidly revolutionized materials processing after their first demonstration in 1987. The ultrashort pulse width of the laser suppresses heat diffusion to the surroundings of the processed region, which minimizes the formation of a heat-affected zone and thereby enables ultrahigh precision micro- and nanofabrication of various materials. In addition, the extremely high peak intensity can induce nonlinear multiphoton absorption, which extends the diversity of materials that can be processed to transparent materials such as glass. Nonlinear multiphoton absorption enables three-dimensional (3D) micro- and nanofabrication by irradiation with tightly focused femtosecond laser pulses inside transparent materials. Thus, ultrafast lasers are currently widely used for both fundamental research and practical applications. This review presents progress in ultrafast laser processing, including micromachining, surface micro- and nanostructuring, nanoablation, and 3D and volume processing. Advanced technologies that promise to enhance the performance of ultrafast laser processing, such as hybrid additive and subtractive processing, and shaped beam processing are discussed. Commercial and industrial applications of ultrafast laser processing are also introduced. Finally, future prospects of the technology are given with a summary.

Femtosecond laser 3D fabrication of whispering-gallery-mode microcavities

Whispering-gallery-mode (WGM) microcavities with high-quality factors and small volumes have attracted intense interests in the past decades because of their potential applications in various research fields such as quantum information, sensing, and optoelectronics. This leads to rapid advance in a variety of processing technologies that can create high-quality WGM micro- cavities. Due to the unique characteristics of femtosecond laser pulses with high peak intensity and ultrashort pulse duration, femtosecond laser shows the ability to carry out ultrahigh precision micromachining of a variety of transparent materials through nonlinear multiphoton absorption and tunneling ionization. This review paper describes the basic principle of femtosecond laser direct writing, and presents an overview of recent progress concerning femtosecond laser three-dimensional (3D) fabrications of optical WGM microcavities, which include the advances in the fabrications of passive and active WGMs microcavities in a variety of materials such as polymer, glass and crystals, as well as in processing the integrated WGM-microcavity device. Lastly, a summary of this dynamic field with a future perspective is given.

Femtosecond laser-assisted selective reduction of neovascularization in rat cornea

Nonlinear multiphoton absorption induced by focusing near infrared (NIR) femtosecond (fs) laser pulses into a transparent cornea allows surgery on neovascular structures with minimal collateral damage. In this report, we introduce an fs laser-based microsurgery for selective treatment of rat corneal neovascularizations (in vivo). Contiguous tissue effects are achieved by scanning a focused laser pulse below the corneal surface with a fluence range of 2.2–8.6 J/cm2. The minimal visible laser lesion (MVL) threshold determined over the corneal neovascular structures was found to be 4.3 J/cm2. Histological and optical coherence tomography examinations of the anterior segment after laser irradiations show localized degeneration of neovascular structures without any unexpected change in adjacent tissues. Furthermore, an approximately 30 % reduction in corneal neovascularizations was observed after 5 days of fs laser exposure. The femtosecond laser is thus a promising tool for minimally invasive intrastromal surgery with the aid of a significantly smaller and more deterministic photodisruptive energy threshold for the interaction between the fs laser pulse and corneal neovascular structures.

Fabrication of 3D microfluidic structures inside glass by femtosecond laser micromachining

Femtosecond lasers have opened up new avenues in materials processing due to their unique characteristics of ultrashort pulse widths and extremely high peak intensities. One of the most important features of femtosecond laser processing is that a femtosecond laser beam can induce strong absorption in even transparent materials due to nonlinear multiphoton absorption. This makes it possible to directly create three-dimensional (3D) microfluidic structures in glass that are of great use for fabrication of biochips. For fabrication of the 3D microfluidic structures, two technical approaches are being attempted. One of them employs femtosecond laser-induced internal modification of glass followed by wet chemical etching using an acid solution (Femtosecond laser-assisted wet chemical etching), while the other one performs femtosecond laser 3D ablation of the glass in distilled water (liquid-assisted femtosecond laser drilling). This paper provides a review on these two techniques for fabrication of 3D micro and nanofluidic structures in glass based on our development and experimental results.

Measurement of nonlinear refractive index and multiphoton absorption by the subpicosecond z-scan method of tellurite multicomponent glassy matrixes having nonlinear susceptibility

New multicomponent tellurite glassy matrixes possessing high nonlinear susceptibility were developed and their optical properties were studied. The nonlinear refractive index n2 and multiphoton absorption β were measured by using the subpicosecond z-scan method. Second-harmonic generation was observed in poled glassy samples.

Shape of the photoacoustic signal generated due to multiphoton absorption of Gaussian laser pulses

Mathematical expressions for the shape and amplitude of a photoacoustic signal generated due to the multiphoton absorption of Gaussian laser pulses are derived. It was found that the sensitivity of a photoacoustic spectrometer increases in proportion to n 3/4 when changing from one-photon linear absorption to nonlinear multiphoton absorption, where n is the nonlinearity exponent. Calibration of the photoacoustic spectrometer used in the measurements of multiphoton absorption cross sections is discussed.

Designing novel chalcone single crystals with ultrafast nonlinear optical responses and large multi-photon absorption coefficients

A chalcone single crystal, 1-(4-chlorophenyl)-3-(4-methoxyphenyl)prop-2-en-1-one that is transparent over the visible to infrared region is introduced as a new potential material to third-order nonlinear optical applications. The crystal exhibits ultrafast optical response (≤90 fs) and large optical nonlinearity in the wavelength range 800–1200 nm. A very large effective two-photon absorption coefficient β eff exceeding 120 cm/GW can be obtained with this chalcone crystal, at a low intensity threshold of 41 MW/cm 2. The mechanism of nonlinear absorption at different levels of intensity has been discussed. The crystal shows no damage against the laser pulse intensity as high as 8 GW/cm 2. We discuss the molecular and crystal designing of chalcones with large and ultrafast optical nonlinearity combined with low optical cut-off (<450 nm).

The ultrafast nonlinear optical response and multi-photon absorption of a new metalcomplex in the near-infrared spectral range

A new coordination compound, chloro(1,10-phenanthroline-N, N′)(triphenylphosphine)copper(I) dichloromethane, incorporated in poly(methyl methacrylate)exhibits superior nonlinear optical properties in the near-infrared spectral region. Itsnonlinear response time and third-order nonlinear optical susceptibility at 800 nm are ≤ 90 fs and1.8 × 10 − 10 esu, respectively. Considerable nonlinear absorption is observed with this sample, near800 and 1250 nm. The contribution of the excited states to the total nonlinearabsorption process is discussed. The results reveal the potential of this newlydesigned compound for multi-photon absorption-based photonic applications.

Morphology of ablation craters generated by fs laser pulses in LiNbO 3

The surface morphology of the ablation craters generated in LiNbO 3 by 130 fs laser pulses at 800 nm has been investigated by AFM/SNOM microscopy. The single pulse fluence corresponding to the ablation threshold has been estimated to be ≈1.8 J/cm 2. A complex structure including random cone-shaped protrusions is observed inside the ablated crater. The scale of the protrusion spacing is in the submicron range and the heights are typically of a few tens of nanometers. At and outside the crater rim a novel quasi-periodic wave-like topography pattern is observed in both types of microscopy techniques. The average wavelength, that is slightly dependent on pulse fluence, is (500–800 nm) comparable to the light wavelength. This novel topography feature keeps a close similarity with a Fresnel diffraction pattern by an absorbing circular obstacle or impact wave pattern produced by a combination of heat and shock wave (resemble that of impact crater). It is proposed that the obstacle is associated to the strongly nonlinear multiphoton absorption at the peak of the pulse profile. The energy deposited by nonlinear absorption of such profile causes ablation of both the crater and the rippled structure.