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The nature of linear photophysical and nonlinear optical properties of a new squaraine derivative 2,4-bis[4-(azetidyl)-2-hydroxyphenyl]squaraine (

The two-photon absorption (2PA) properties are investigated for two series of organic, π-conjugated, fused-ring, quadrupolar A-π-D-π-A chromophores of the type originally developed as nonfullerene acceptors for organic photovoltaics. These molecules are found to exhibit large nondegenerate two-photon absorption (ND2PA) cross-sections (ca. 6-27 × 103 GM) in the near-infrared (NIR). In the first series, involving molecules of varying core size, ND2PA spectra and cross-sections characterized by femtosecond ND2PA spectroscopy in chloroform solutions reveal that increases in core size, and thus conjugation length, leads to substantially red-shifted and enhanced 2PA. In a second series, variation of the strength of the terminal acceptor (A) with constant core size (seven rings, indacene-based) led to less dramatic variation in the 2PA properties. Among the two core types studied, compounds in which the donor has a thieno[3,2-b]thiophene center demonstrate larger 2PA cross-sections than their indacene-centered counterparts, due to the greater electron-richness of their cores amplifying intramolecular charge transfer. Excited-state absorption (ESA) contributions to nonlinear absorption measured by open-aperture Z-scans are deduced for some of the compounds by analyzing the spectral overlap between 2PA bands and NIR ESA transitions obtained by ND2PA and transient absorption measurements, respectively. ESA cross-sections extracted from transient absorption and irradiance-dependent open-aperture Z-scans are in reasonable agreement, and their moderate magnitudes (ca. 10-21 m2) suggest that, although ESA contributions are non-negligible, the effective response is predominantly instantaneous 2PA.

Twisted intramolecular charge transfer (TICT) chromophores exhibit a promising third-order nonlinear optical (NLO) response, γ, which is potentially useful for all-optical switching. Here we explor...

International audience; The fast relaxation processes in the excited electronic states of functionalized aza-boron-dipyrromethene (aza-BODIPY) derivatives (1-4) were investigated in liquid media at room temperature, including the linear photophysical, photochemical, and nonlinear optical (NLO) properties. Optical gain was revealed for nonfluorescent derivatives 3 and 4 in the near infrared (NIR) spectral range under femtosecond excitation. The values of two-photon absorption (2PA) and excited-state absorption (ESA) cross-sections were obtained for 1-4 in dichloromethane using femtosecond Z-scans, and the role of bromine substituents in the molecular structures of 2 and 4 is discussed. The nature of the excited states involved in electronic transitions of these dyes was investigated using quantum-chemical TD-DFT calculations, and the obtained spectral parameters are in reasonable agreement with the experimental data. Significant 2PA (maxima cross-sections ∼2000 GM), and large ESA cross-sections ∼10(-20) m(2) of these new aza-BODIPY derivatives 1-4 along with their measured high photostability reveal their potential for photonic applications in general and optical limiting in particular.

We develop a common path interferometer to measure the refractive index of liquids from the visible to infrared. In this work, we present experimental data for several organic solvents from visible wavelengths to 2µm.

Space-time (ST) wave packets are a class of pulsed optical beams whose spatio-temporal spectral structure results in propagation invariance, tunable group velocity, and fascinating refractive phenomena. Here, we investigate the refraction of ST wave packets at a planar interface between two dispersive, homogeneous, isotropic media. We formulate a new refractive invariant for ST wave packets in this configuration, from which we obtain a law of refraction that determines the change in their group velocity across the interface. We verify this new refraction law in ZnSe and CdSe, both of which manifest large chromatic dispersion at near-infrared frequencies in the vicinity of their band edges. ST wave packets can thus be a tool in nonlinear optics for bridging large group-velocity mismatches in highly dispersive scenarios., 5 pages, 4 figures

Non-degenerate two-photon absorption (ND-2PA) across the indirect gap of silicon is theoretically and experimentally investigated. Three theoretical pathways for the two photons and a phonon are explained, and the most dominant process is determined by comparing to our measurements and the enhancement of ND-2PA was observed.

We develop a common path interferometer to measure the refractive index in liquids. This technique can measure the refractive index from the visible to infrared. In this work, we present experimental data in four wavelengths for several organic solvents.

We performed a comprehensive study of the fast relaxation processes in three metal–organic Ir(III)-complexes in liquid solutions at room temperature in order to estimate their singlet–triplet conve...

Epsilon-near-zero (ENZ) materials have emerged as viable platforms for strong nonlinear optical (NLO) interactions. The NLO phase shift in materials exhibiting an ENZ condition is extremely large; however, direct experimental measurements of the magnitude and time dynamics of this phenomenon, particularly nondegenerate NLO phase shifts, have so far been lacking. Here, we directly measure the NLO phase shift of an Indium-Tin-Oxide (ITO) thin film using three different techniques. By characterizing the excitation-induced, time-resolved beam deflection (BD) of a probe beam, we measure the nondegenerate NLO effects, allowing a separate determination of the effects of excitation and probe wavelengths on the NLO phase shift as they are varied across the ENZ region. These experiments reveal that having the probe pulse centered at ENZ greatly contributes to this enhancement; however, the NLO phase shift is less sensitive to the excitation wavelength, which only slightly enhances the nonlinearity for obliquely incident TM-polarized light. We also find that the spectral shift of the probe pulse induced by the excitation follows both the magnitude and time dynamics of the NLO phase shift measured via the BD experiments. We observe large, ultrafast cross-phase modulation in agreement with a redistribution of carriers in the conduction band. Finally, using the Z-scan method, we measure the degenerate nonlinear refraction at ENZ near normal incidence. The results of all three measurements agree, revealing a gigantic sub-picosecond NLO phase shift in ITO. At its largest, we consistently measure an effective induced index change greater than the linear index.

International audience; Aza-boron dipyrromethenes (aza-BODIPYs) presenting a benzothiadiazole substitution on upper positions are described. The strong electron-withdrawing effect of the benzothiadiazole moiety permits enhancement of the accepting strength and improves the delocalization of the aza-BODIPY core to attain a significant degree of electronic communication between the lower donating groups and the upper accepting groups. The nature of the intramolecular charge transfer is studied both experimentally and theoretically. Linear spectroscopy highlighted the strongly redshifted absorption and emission of the synthesized molecules with recorded fluorescence spectra over 1000 nm. Nonlinear optical properties were also investigated. Strong enhancement of the two-photon absorption of the substituted dyes compared with the unsubstituted one (up to 4520 GM at 1300 nm) results in an approximately 15-20 % improvement of the optical power limiting performances. These dyes are therefore a good starting point for further improvement of optical power limiting in the short-wave IR range.

We report the nonlinear-optical properties of functionalized aza-borondipyrromethene chromophores in the near infrared. The fluorescence efficiencies are low, and they exhibit excited- state absorption and two-photon absorption at these wavelengths.

The ultrafast response function of air is used to predict the pulsewidth dependence of 2, ff from our measurements in the near and mid-infrared. We predict 2, ff in the atmosphere, showing agreement with multiple literature measurements.

The third-order nonlinear optical coefficients of Si and GaAs have been characterized in the near-infrared using a comprehensive approach to ensure accuracy and to address the large variation in the published coefficients.

Materials with vanishing real part of permittivity, also known as epsilon-near-zero (ENZ), have emerged as a new paradigm to obtain large optical nonlinearities. Transparent conducting oxides such as indium tin oxide (ITO) naturally exhibit an ENZ condition in the near-infrared and close to their plasma frequency. The peculiarity of ENZ materials is their highly dispersive nature explained by Drude model, allowing to obtain reduced group velocity at frequencies where the phase velocity is enhanced. This condition can dramatically increase the phase sensitivity caused by any given changes in material permittivity. To accurately address the NLO mechanism in such materials, we present a generalized formalism for the nonlinear phase shift for a dispersive material, where it includes contributions from both group velocity and phase velocity. We experimentally demonstrate that the nonlinear phase can reach to the values close to π/2 when the probe beam is at ENZ, while the index change in the conventional definition is not enhanced necessarily. In this work, we present nonlinear optical measurements using the nondegenerate Beam Deflection (BD) methodology at normal incident together with cross-phase modulation experiments. BD is a pump-probe method that directly characterizes the ultrafast response of the nonlinear phase-shift, hence nonlinear refraction. We see no polarization dependence proving that bound electronic third-order nonlinearities are negligible compared to the sub-picosecond fast carrier effects. We also present that frequency shift is highly sensitive to the temporal dynamics of the nonlinear phase shift suggesting that short pulses may help to improve the magnitude of frequency shift.

We present direct measurements of the nonlinearly induced phase-shift and spectral shift via beam-deflection technique and cross-phase modulation measurements. The optical nonlinearities are enhanced due to the highly dispersive nature of epsilon-near-zero materials, which allows obtaining reduced group velocity and enhanced phase velocity.

This paper presents three-photon absorption (3PA) measurement results for nine direct-gap semiconductors, including full 3PA spectra for ZnSe, ZnS, and GaAs. These results, along with our theory of 3PA using an 8-band Kane model (4 bands with double spin degeneracy), help to explain the significant disagreements between experiments and theory in the literature to date. 3PA in the 8-band model exhibits quantum interference between the various possible pathways that is not observed in previous 2-band theories. We present measurements of degenerate 3PA coefficients in InSb, GaAs, CdTe, CdSe, ZnTe, CdS, ZnSe, ZnO, and ZnS. We examine bandgap, Eg, scaling using 2-band tunneling and perturbation theories that show agreement with the predicted Eg^-7 dependence; however, For those semiconductors for which we measured full 3PA spectra, we observe significant discrepancies with both 2-band theories. On the other hand, our 8-band model shows excellent agreement with the spectral data. We then use our 8-band theory to predict the 3PA spectra for 15 different semiconductors in their zincblende form. These results allow prediction and interpretation of the 3PA coefficients for various narrow to wide bandgap semiconductors., 20 pages

Materials with vanishing real part of permittivity, also known as epsilon-near-zero, have emerged as a new paradigm to obtain large optical nonlinearities. In this region, light-matter interaction enhances significantly, which gives rise to an unprecedentedly large nonlinear phase shift. The phase sensitivity enhancement is due to the strong dispersion in this spectral region. We present nonlinear optical measurements via the Beam Deflection technique, to directly measure the spectral dependence of the ultrafast nonlinear phase shift of an Indium Tin Oxide thin film. We present simultaneously cross-phase modulation induced frequency changes that depend on how fast the nonlinear phase changes.

Here, we present our development of several experimental methods, which, when applied together, can provide a thorough characterization of the nonlinear refraction and absorption properties of materials. We focus mainly on time-resolved methods for studying both transient absorption and refraction that reveal molecular dynamics including excited-state absorption, singlet-triplet transfer, instantaneous electronic nonlinear refraction, and molecular reorientation. In particular, we will describe our recent studies of new materials including organometallic compounds and organic solvents such as Tetrachloroethylene (C2Cl4).

By exciting in both the Near-IR and Mid-IR and probing in the mid-IR, using the polarization-resolved Beam Deflection Technique, the bound electronic nonlinear refractive index of air is measured below the ionization threshold.

We use the ultrafast response function of air to predict the pulsewidth dependence of from measurements in the near and mid-infrared showing no dispersion. This allows predictions of the dependence of n nnnnn on altitude.

We present measurements of the nonlinear absorption and refraction of GaAs/AlGaAs quantum wells, and explore the fitness of this material system for nonlinear photonic devices.

We study the nonlinear absorption properties of aza-borondipyrromethene dyes using the Z-scan and transient absorption methods. Near 1200 nm, excited-state absorption due to two-photon excitation appears, which is more pronounced in the brominated dyes.

We present 3-photon-absorption (3PA) measurements of 9 direct-gap semiconductors, including the 3PA spectra of ZnS, GaAs, and ZnSe and use a Kane 4-band model to fit the spectra and show the bandgap dependence.

We present Beam-Deflection experiments, to measure the temporal and spectral dependence of the nonlinear phase-shift of ITO at ENZ. Our measurements suggest that group and phase velocity contribute to the enhanced nonlinearities observed at ENZ. © 2020 The Author(s)

A comprehensive experimental and theoretical study of linear photophysical properties, such as excited-state relaxation, two-photon absorption, and stimulated emission spectra of the symmetrical fluorene derivative 2,2′-((1E,1′E)-(9,9-diethyl-9H-fluorene-2,7-diyl)bis(ethene-2,1-diyl))bis(1-methyl-1H-pyrrole) (1), is presented. The steady-state absorption, fluorescence, excitation, and excitation anisotropy spectra of 1 in organic solvents of different polarities are investigated experimentally and modeled. The fluorescence solvatochromism of 1 suggests the occurrence of symmetry breaking in the first excited state. The nature of fast relaxation processes in the excited state of 1, with the characteristic times of several picoseconds, is investigated by transient absorption femtosecond pump–probe spectroscopy. The spectral properties of 1 are satisfactorily described by an essential-state model that, accounting for electron–vibration coupling and for polar solvation, addresses spectroscopic features not on...

Linear steady-state and time-resolved spectroscopic properties, degenerate two-photon absorption (2PA) spectra, and photochemical stability of IrIII complexes TCQ[IrIII(ppz)2]n, (TCQ = tricycloquinazoline; ppz = 1-phenylpyrazole; n = 1 (1), n = 2 (2), and n = 3 (3)) are presented for liquid solutions. The analysis of the linear photophysical properties revealed the nature of the observed dual-component fluorescence–phosphorescence emission of 1–3 at room temperature. The values of 2PA cross sections were determined by open aperture Z-scans using a 1 kHz femtosecond laser system. The specific dependence of the 2PA efficiency on the number of ppz ligand units in 1–3 was determined. The quantum yields, Φph, for photochemical decomposition of TCQ[IrIII(ppz)2]n complexes were obtained for the first time using the absorption method [Corredor, C. C.; J. Photoch. Photobio. A 2006, 184, 105−112] with continuous wave laser irradiation, and the highest stability of Φph ≈ 4 × 10–6 was shown for 2 in toluene.

With the objective of developing new near-infrared fluorescent probes and understanding the effect molecular structure exerts on physical properties, a series of aniline-based squaraine dyes with different number and position of methoxy substituents adjacent to the squaraine core were synthesized and investigated. Using both computational and experimental methods, we found that the subtle changes of the number or position of the methoxy substituents influenced the twisting angle of the structure and led to significant variations in optical properties. Moreover, the methoxy substituent also affected aggregation behavior due to steric effects. The X-ray crystal structure of one of the key members of the series, SD-2a, clearly demonstrates the distortion between the four-membered squaraine core and the adjacent aniline ring due to methoxy substitution. Structure-related fast relaxation processes were investigated by femtosecond pump–probe experiments and transient absorption spectra. Quantum chemical calcula...

Gold dipole nanoantennas embedded in an organic molecular film provide strong local electromagnetic fields to enhance both the nonlinear refractive index (n2) and two-photon absorption (2PA) of the molecules. An enhancement of 53× for 2PA and 140× for nonlinear refraction is observed for BDPAS (4,4′-bis(diphenylamino)stilbene) at 600 nm with only 3.7% of gold volume fraction. The complex value of the third-order susceptibility enhancement results in a sign change of n2 for the effective composite material relative to the pure BDPAS film. This complex nature of the enhancement and the tunability of the nanoantenna resonance allow for engineering the effective nonlinear response of the composite film.

Typically, strong gain saturation and gain dynamics play a crucial role in semiconductor laser mode-locking. While there have been several investigations of the ultrafast gain dynamics in vertical-external-cavity surface-emitting lasers (VECSELs), little is known about the associated refractive index changes. Yet, such refractive index changes do not only have a profound impact on the pulse formation process leading to self-phase modulation, which needs to be compensated by dispersion, but they are also of particular relevance for assessing the feasibility of Kerr-lens mode-locking of VECSELs. Here, we measure both refractive index as well as gain dynamics of a VECSEL chip using the ultrafast beam deflection method. We find that, in contrast to the gain dynamics, the refractive index dynamics is dominated by an instantaneous ($\sim$100~fs) and a very slow component ($\sim$100~ps). The time-resolved measurement of nonlinear refraction allows us to predict a pulse-length dependent, effective nonlinear refractive index $n_{2,eff}$, which is shown to be negative and in the order of $10^{-16}$ $m^2/W$ for short pulse lengths ($\sim$100~fs) . It becomes positive for large excitation fluences and large pulse lengths (few ps). These results agree with some previous reports of self-mode-locked VECSELs for which the cavity design and pulse properties determine sign and strength of the nonlinear refractive index when assuming Kerr-lens mode-locking.

Comprehensive investigations of the linear and nonlinear optical properties of new Ir(III)-complexes [Ir(pbt)2(dbm)] (1), [Ir(pbt)2(dmac)] (2), and [Ir(pbt)2(minc)] (3) (pbt=2-phenylbenzothiazole; dbm=dibenzoyl methane; dmac=(1E,4Z,6E)-1,7-bis(4-(dimethylamino)phenyl)-5-hydroxyhepta-1,4,6-trien-3-one; minc=(1E,4Z,6E)-5-hydroxy-1,7-bis(1-methyl-1H-indol-3-yl)hepta-1,4,6-trien-3-one) are reported, including, photostability, two-photon absorption, and femtosecond transient absorption spectroscopy. The steady-state and time-resolved spectral properties of 1-3 revealed the electronic nature of the absorption bands, and photoluminescence emission of 2 and 3 shows both fluorescence and phosphorescence processes occurring simultaneously in liquid solution at room temperature. This unusual behavior of 2 and 3 can be explained by a dual-minimum potential surface of the excited electronic state resulting in two independent fluorescence and phosphorescence emission channels. The degenerate 2PA spectra of 1-3 were obt...

We present femtosecond pump-probe measurements of the nondegenerate (1960$\,$nm excitation and 1176--1326$\,$nm probe) two-photon absorption spectra of 8 $\,$nm GaAs/12$\,$nm Al$_{0.32}$Ga$_{0.68}$As quantum well waveguides. Experiments were performed with light pulses co-polarized normal and tangential to the quantum well plane. The results are compared to perturbative calculations of transition rates between states determined by the $\mathbf{k}\cdot\mathbf{p}$ method with an 8 or 14 band basis. We find excellent agreement between theory and experiment for normal polarization, then use the model to support predictions of orders-of-magnitude enhancement of nondegenerate two-photon absorption as one constituent photon energy nears an intersubband resonance., 13 pages, 8 figures

In this work, a new phosphonium-containing cationic polyelectrolyte (PE1) has been rationally designed and developed via a facile click-chemistry type postfunctionalization, which can form complexe...

We present beam deflection measurements to study the nondegenerate nonlinear refraction of highly doped semiconductors at epsilon-near-zero (ENZ) for several different pump and probe polarizations. Beam deflection is sensitive to induced optical path length as small as 1/20,000 of a wavelength, which enables us to resolve NLR in the presence of large nonlinear absorption backgrounds. The optically induced index changes in these materials can be both very large (on the order of unity) and fast (on the order of 100 fs). Our results show that carrier redistribution effects dominate the nonlinear refraction, and by independently tuning the pump and probe wavelengths, we find that the strong wavelength dependence of nonlinearities around the ENZ point is different for pump and probe waves. These nonlinear optical properties, where the ultrafast index change can be larger than the linear index, offer new paradigms for dynamically switchable diffractive elements that respond to structured light, allowing manipulation of optical beams in transmission and reflection not only along the two spatial dimensions but also in time. This is a revolutionary change in the field of nonlinear optics allowing a myriad of potential applications, ranging from rapid all-optical beam steering and switching, to spectral scanning, spatial mode conversion, as well as pulse shaping and suppression, all on sub-picosecond time scales.

Fast optical limiters are needed to protect sensors from intense short laser pulses. An optical limiter design based on a conducting-oxide grating with a large nonlinear refractive index at the plasma frequency is proposed and investigated.

We studied the effects of bromine substitution on the nonlinear absorption properties of aza-dipyrromethene dyes. Nonlinear absorption is measured at wavelengths of 1200, 1500, and 1700nm At 1200nm, excited-state absorption due to two-photon excitation appears, and it is more pronounced in the brominated polymethine cyanine.

We present measurements of nonlinear refraction and absorption in transparent conductive oxides (TCO), which are essentially highly-doped semiconductors, at Epsilon-Near-Zero (ENZ). In this spectral region, where the real part of the permittivity crosses zero, materials demonstrate interesting nonlinear properties such as enhanced harmonic generation, nonlinear absorption (NLA), and nonlinear refraction (NLR). We find that induced changes in the refractive index of Indium Tin Oxide, can be very large with respect to the initial index. This means that the even the Fresnel coefficients are highly irradiance-dependent. Therefore, the nonlinear transmission, reflection, and absorption of the material will be significantly different from conventional materials which means that it is challenging to use conventional methods such as Z-Scan and time-resolved transmission and reflection techniques to accurately determine the underlying nonlinear optical coefficients. We have studied optical nonlinearities of TCOs using the Beam-Deflection (BD) method to independently characterize the temporal dynamics and polarization dependence of the NLR. This method enables us to resolve NLR in the presence of large NLA backgrounds. In addition, we can also study the dependence on relative polarization and incidence angle of excitation and probe waves to characterize the enhancement mechanism and the physical origin of the nonlinear response. We conduct these BD measurements in conjunction with Z-Scan and transient reflection and transmission at different wavelengths, incidence angle, and polarization. Our measurements reveal that there is a strong wavelength dependence of nonlinearities around the ENZ point. We find that the wavelength dependence is quite different for excitation and probe waves.

For bioimaging purposes, non-cytotoxic fluorescent labels, stable in biological media and capable of site-specific labeling are in upsurging demand. However, many fluorescent dyes with promising properties, such as fluorescent organic dyes, are poorly water-soluble and often lose their properties in water, limiting their use for bioapplications. The weak signals, poor photobleaching resistance, short fluorescence life time and low chemical stability are continuous challenges for the development of optimal fluorescent probes. The use of aqueous colloidal structures, such as nanovesicles, as nanocarriers for the loading of the organic dyes offers a promising strategy to overcome this limitation. As a matter of fact, we have engineered a new class of fluorescent organic nanoparticles (FONs) using thermodynamically stable nanovesicles named quatsomes (QS) [1-4]. QSs are new class of exceptionally stable small unilamellar vesicles with sizes smaller than 100nm, and formed by the self-assembly of sterols and quaternary ammonium surfactants. [5,6] Dye-loaded QSs can be prepared by a one-step method using compressed CO2, named depressurization of expanded liquid organic solution-suspension (DELOS-susp).[7] Indeed, it is a green technology leading to a formation of a highly homogenous dispersion of nanovesicles stables in an aqueous environment. The loading of water-insoluble carbocyanines dyes into QSs, has successfully proved the photostability of the obtained FONs in aqueous solutions, as well as, their valuable brightness [6]. They show excellent colloidal stability and structural homogeneity along with superior optical properties, in comparison with the fluorophores in solution. Dye-loaded QSs have enhanced optical properties, demonstrating the absence of non-fluorescent aggregates due to the Aggregation Caused Quenching (ACQ) effect, neither the formation of J- and H-aggregates was produced, in contrary to the well-known tendency of cyanines to aggregate [8]. Different methods for obtaining dye loaded nanoparticles were compared pointing the advantages of dye-loaded QS over other dye-based FONs, in terms of both, optical and colloidal properties. The effect of the dye loading on the physicochemical properties were studied as well as the brightness, showing higher brightness when dyes were located at the QS membrane. Moreover, experimental results were supported by molecular dynamics (MD) simulations which give information on the configuration of the dyes within the membrane. The potential of dye-loaded QSs for biological imaging was studied using a superresolution microscopy technique, the stochastic optical reconstruction microscopy (STORM). This study determine that dye-based QS are remarkable candidates as nanostructured probes for biological imaging, not only because of their photophysical properties but also, for their capabilities to be precisely decorated at their surfaces with targeting groups3 and to integrate small drugs or large biomolecules. All such benefits represent a certainly promising probe for bioimaging and, especially, for theragnostic nanomedicine. 1. Elizondo, E. et al. Influence of the Preparation Route on the Supramolecular Organization of Lipids in a Vesicular System. J. Am. Chem. Soc. 134, 1918–1921 (2012). 2. Ferrer-Tasies, L. et al. Quatsomes: Vesicles Formed by Self-Assembly of Sterols and Quaternary Ammonium Surfactants. Langmuir 29, 6519–6528 (2013). 3. Cabrera, I. et al. Multifunctional Nanovesicle-Bioactive Conjugates Prepared by a One-Step Scalable Method Using CO2-Expanded Solvents. Nano Lett. 13, 3766–3774 (2013). 4. Grimaldi, N. et al. Lipid-based nanovesicles for nanomedicine. Chem. Soc. Rev. 45, 6520–6545 (2016). 5. Silbaugh, D. A. et al. Highly Fluorescent Silicon Nanocrystals Stabilized in Water Using Quatsomes. Langmuir 33, 14366–14377 (2017). 6. Antonio, A. et al. Nanostructuring Lipophilic Dyes in Water Using Stable Vesicles, Quatsomes, as Scaffolds and Their Use as Probes for Bioimaging. Small 14, 1703851 (2018). 7. Ventosa, Nora; Veciana, Jaume; Sala, Santiago; Cano, M. Method for Obtaining Micro- and Nano-disperse systems. (2006). doi:WO/2006/079889 8. Gadde, S., Batchelor, E. K. & Kaifer, A. E. Controlling the Formation of Cyanine Dye H- and J-Aggregates with Cucurbituril Hosts in the Presence of Anionic Polyelectrolytes. Chem. – A Eur. J. 15, 6025–6031 (2009).

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We used the polarization-resolved beam-deflection technique to separate the bound-electronic and molecular-rotational components of the transient nonlinear refraction (NLR) of ambient air in the Mid-infrared spectral range below the ionization threshold.

We report Z-scan and beam-deflection measurements of Indium-Tin-Oxide at epsilon- near-zero. We observe near unity change in the index. Nondegenerate beam-deflection measurements at different incident angles are used to characterize the coupling efficiency to longitudinal plasmons.

Current Editor-in-Chief Alexandra Boltasseva and inaugural Editor-in-Chief David Hagan look back over the decade and celebrate the tenth anniversary of Optical Materials Express.

We use the polarization-sensitive, time-resolved Beam-Deflection technique to measure the nonlinear refraction of air, exciting in both the near and mid-IR and probing in the mid-IR. This gives us the first measurements for air using both excitation and probe in the mid-IR, and we find no dispersion of the bound-electronic nonlinear refractive index, n2,el(λ p ;λ e ), assuming, as has been shown earlier, that the nuclear rotational nonlinear refraction is nearly dispersionless. From these data, we can model the pulsewidth dependence of the effective nonlinear refractive index, n2,eff, i.e., as would be measured by a single beam. Interestingly, n2,eff is maximized for a pulsewidth of approximately 0.5 ps. The position of this maximum is nearly independent of pressure while its magnitude decreases with increasing pressure and temperature. From the measurements and modeling, we predict the nonlinear refraction in the atmosphere at different altitudes.

Cyanines with long conjugation length such as heptamethines are well known to have strong intramolecular and/or intermolecular interactions (i.e., ion paring and aggregation), which can affect their structures (i.e., symmetry breaking) and optical properties remarkably. In this paper, we report a covalently linked complementary cyanine complex of cationic and anionic heptamethines forming a highly polarizable zwitterionic cyanine–cyanine salt. The effect of the modification was studied in detail on both its electronic structure and its optical properties. This novel zwitterionic salt was found to exhibit a decreased ion-pairing-induced charge localization but with an increased electronic coupling between the excited states of the cyanine cation and the anion, resulting in unusual optical properties compared to closely related noncovalent complementary cyanine salts. The dual-arm Z-scan technique was used to study their third-order NLO properties, suggesting the electronic coupling in such preorganized zwi...

The synthesis, comprehensive linear photophysical and photochemical study, two-photon absorption (2PA) spectrum, ultrafast relaxation kinetics in the excited states, and efficient superluminescence properties of a new symmetrical three-armed star-shaped squaraine derivative (1) are presented. The steady-state spectral parameters of 1 in a number of organic solvents, including fluorescence excitation anisotropy spectra, revealed a weak interaction between the squaraine branches and the effect of symmetry breaking in the ground electronic state. The degenerate 2PA spectrum of 1 was obtained over a broad spectral range with a maximum cross section of ∼8000 GM using the open aperture Z-scan technique. The nature of the fast dynamic processes in the excited electronic states of 1 was investigated by the femtosecond transient absorption pump–probe method, revealing characteristic relaxation times of ∼3–4 ps. The efficient superluminescence emission of 1 was observed in relatively low concentration solution (≈ 2...