Nonlinear Transmission Method Research Articles

Two-photon absorption cross-section investigation of visible-light photoinitiators under Q-switched Nd:YAG nanosecond pulse laser at 1064 nm

Two-photon polymerization (TPP) technologies commonly rely on femtosecond lasers such as Ti:sapphire which limits their accessibility due to high costs and complexities. Recently, multiple reports showed TPP under near-infrared irradiation which enables the use of alternative light sources such as Neodymium-doped lasers known to be affordable and efficient for a nanosecond and picosecond pulsed generation. 4,4′-Bis(dimethyl-amino) benzophenone or Michler’s ketone (MK), one of the photoinitiators commonly used for photopolymerization under UV irradiation, also shows an absorption band in the visible region which allows for two-photon polymerization at the fundamental wavelength of Neodymium-doped lasers at 1064 nm. In this report, we investigated the two-photon absorption (TPA) of MK in contrast with Irgacure-784 and Indane-1,3-dione, reported to also be promising photoinitiators for the same TPP process. Among them, MK showed a large TPA cross-section measured via the nonlinear transmission method and Z-scan technique with Q-switched Nd:YAG nanosecond pulse laser at 1064 nm, demonstrating MK as a promising photoinitiator for the low-cost two-photon polymerization.

Two‐Photon Absorption in Monolayer MXenes

AbstractTwo‐photon absorption (2PA) is a nonlinear optical (NLO) effect that typically occurs in a conventional semiconductor whose bandgap is larger than the energy of one excited photon but smaller than the energy of two photons. In this work, the experimental observation of strong 2PA in gapless MXene monolayers is reported. This phenomenon is verified by a nonlinear transmission method and ultrafast dynamic studies based on a wavelength‐degenerate, non‐collinear pump‐probe technique. The unconventional 2PA is attributed to the structures of the MXene energy bands near the Fermi level, which favors two‐photon transitions and suppresses one‐photon transitions due to parallel band absorption effects. These results, as well as the measured NLO parameters including the 2PA coefficient, absorption cross‐section, excited carrier lifetimes, and third‐order NLO susceptibility, provide a systematic understanding of the unusual NLO effect in MXenes and may be applied in advanced photonic and optoelectronic devices.

Effective control of two-photon absorption of DCM dye by solvent manipulation

The imaginary part of third-order nonlinear optical susceptibility (Imχ<3>) and two-photon absorption cross-section (σ2) of DCM dye dissolved in tetrahydrofuran, chloroform and dimethyl sulfoxide were obtained using nonlinear transmission method at 635 nm in ps regime.The Imχ<3> and σ2 values change with changing the solvent polarity parameter in the following way: and . However, in the case of DCM dissolved in chloroform, these values are about four times higher comparing with the parameters obtained for DCM dissolved in polar solvents. Therefore, using different solvents one can change, influence, enhance and control the nonlinear optical properties of DCM dye.

Spontaneous Symmetry Breaking Facilitates Metal-to-Ligand Charge Transfer: A Quantitative Two-Photon Absorption Study of Ferrocene-phenyleneethynylene Oligomers.

Change of the permanent molecular electric dipole moment, Δμ, in a series of nominally centrosymmetric and noncentrosymmteric ferrocene-phenyleneethynylene oligomers was estimated by measuring the two-photon absorption cross-section spectra of the lower energy metal-to-ligand charge-transfer transitions using femtosecond nonlinear transmission method and was found to vary in the range up to 12 D, with the highest value corresponding to the most nonsymmetric system. Calculations of the Δμ performed by the TD-DFT method show quantitative agreement with the experimental values and reveal that facile rotation of the ferrocene moieties relative to the organic ligand breaks the ground-state inversion symmetry in the nominally symmetric structures.

Two-photon absorption spectra of fluorescent isomorphic DNA base analogs.

Fluorescent DNA base analogs and intrinsic fluorophores are gaining importance for multiphoton microscopy and imaging, however, their quantitative nonlinear excitation properties have been poorly documented. Here we present the two-photon absorption (2PA) spectra of 2-aminopurine (2AP), 7-methyl guanosine (7MG), isoxanthopterin (IXP), 6-methyl isoxanthopterin (6MI), as well as L-tryptophan (L-trp) and 3-methylindole (3MI) in aqueous solution and some organic solvents measured in the wavelength range 550 - 810 nm using femtosecond two-photon excited fluorescence (2PEF) and nonlinear transmission (NLT) methods. The peak 2PA cross section values range from 0.1 GM (1 GM = 10-50 cm4 s photon-1) for 2AP to 2.0 GM for IXP and 7MG. Assuming typical excitation conditions for a scanning 2PEF microscope, we estimate a maximum image frame rate of ~175 frames per second (FPS).

CW Optical Limiting Study in Disperse Yellow Dye-doped PMMA-MA Polymer Films

&lt;div&gt;&lt;p&gt;&lt;em&gt;Molecules with high two-photon absorption (TPA) cross section and the molecules which have reverse saturation absorption (RSA) cross section are of great interest today because of their application in three-dimensional optical data storage and photonic switches. During last forty years, several techniques have been developed to determine the two-photon absorption cross-sections and reverse saturation absorption cross-sections of the materials. This includes direct methods, such as nonlinear transmission and Z-scan methods and indirect methods, such as two-photon excited fluorescence and two-photon pump-probe transient absorption spectroscopy. During recent years, the organic dye-doped polymer films getting more attention due to their advantages to fabricate photonics devices. In this paper, we have studied the nonlinear optical properties like nonlinear absorption and nonlinear refraction of an azo dye Disperse yellow-7 (DY-7) doped in Polymethyl methacrylate-methacrylic acid (PMMA-MA) polymer matrix using open aperture and closed aperture Z-scan experimental methods using continuous wave (CW) laser. The optical limiting properties of these films are also studied in Type 1 and Type 2 configurations at different input power using continuous wave (CW) laser beams of 532 nm wavelength.&lt;/em&gt;&lt;/p&gt;&lt;/div&gt;

Saturable absorption of silver nanoparticles in glass for femtosecond laser pulses at 400 nm

The commercially available glass BK7 was chosen to prepare silver-rich layer within the glass by the silver (Ag) ion exchange method in order to enhance its nonlinear optical properties. The glass substrates were doped with Ag at 320°C by a 50-minute Ag+↔Na+ ion exchange in a melt of NaNO3 and KNO3 containing 14mol% of AgNO3. Then, one piece of glass BK7 containing Ag ions (as-exchanged sample) was annealed in air for 1h at 600°C to prepare the as-annealed sample. The thickness of the layer containing Ag in the as-exchanged glass BK7 was measured to less than 1μm. It was found that during the post-exchanged annealing most silver diffused deeply into the glass substrate leading to increase the thickness of the layer to 110μm. However, some amount of Ag nucleated during the annealing, thus creating small nanoparticles (NPs) with an average size of 2nm. The linear and nonlinear optical properties of the as-exchanged and as-annealed glass BK7 were studied. The as-exchanged sample showed no absorption in the visible spectral region whereas, as-annealed glass BK7 showed a peak absorption at 420nm which can be attributed to the presence of Ag NPs formed in this glass. The nonlinear optical behavior of the samples was investigated using 800nm and 400nm femtosecond pulses. Strong saturable absorption was observed in the as-annealed sample at 400nm. This feature promises an efficient way for designing all optical switching devices appropriate for the second harmonic of the Ti-sapphire laser. Using nonlinear transmission (NLT) method the saturation intensity for the as-annealed sample was determined 8.5×1011W·cm−2. An intensity dependent switching from saturable absorption (SA) to reverse saturable absorption (RSA) was also observed when the as-annealed sample was irradiated simultaneously by 800nm and 400nm femtosecond pulses.

Symmetry Breaking in Platinum Acetylide Chromophores Studied by Femtosecond Two-Photon Absorption Spectroscopy.

We study instantaneous two-photon absorption (2PA) in a series of nominally quasi-centrosymmetric trans-bis(tributylphosphine)-bis-(4-((9,9-diethyl-7-ethynyl-9H-fluoren-2-yl) ethynyl)-R)-platinum complexes, where 11 different substituents, R = N(phenyl)2(NPh2), NH2, OCH3, t-butyl, CH3, H, F, CF3, CN, benzothiazole, and NO2, represent a range of electron-donating (ED) and electron-withdrawing (EW) strengths, while the Pt core acts as a weak ED group. We measure the 2PA cross section in the 540-810 nm excitation wavelength range by complementary femtosecond two-photon excited fluorescence (2PEF) and nonlinear transmission (NLT) methods and compare the obtained values to those of the Pt-core chromophore and the corresponding noncentrosymmetric side group (ligand) chromophores. Peak 2PA cross sections of neutral and ED-substituted Pt complexes occur at S0 → Sn transitions to higher energy states, above the lowest-energy S0 → S1 transition, and the corresponding values increase systematically with increasing ED strength, reaching maximum value, σ2 ∼ 300 GM (1 GM = 10-50 cm4 s), for R = NPh2. At transition energies overlapping with the lowest-energy S0 → S1 transition in the one-photon absorption (1PA) spectrum, the same neutral and ED-substituted Pt complexes show weak 2PA, σ2 < 30-100 GM, which is in agreement with the nearly quadrupolar structure of these systems. Surprisingly, EW-substituted Pt complexes display a very different behavior, where the peak 2PA of the S0 → S1 transition gradually increases with increasing EW strength, reaching values σ2 = 700 GM for R = NO2, while in the S0 → Sn transition region the peak 2PEF cross section decreases. We explained this effect by breaking of inversion symmetry due to conformational distortions associated with low energy barrier for ground-state rotation of the ligands. Our findings are corroborated by theoretical calculations that show large increase of the permanent electric dipole moment change in the S0 → S1 transition when ligands with strong EW substituents are twisted by 90° relative to the planar chromophore. Our NLT results in the S0 → S1 transition region are quantitatively similar to those obtained from the 2PEF measurement. However, at higher transition energy corresponding to S0 → Sn transition region, the NLT method yields effective multiphoton absorption stronger than the 2PEF measurement in the same systems. Such enhancement is observed in all Pt complexes as well as in all ligand chromophores studied, and we tentatively attribute this effect to nearly saturated excited-state absorption (ESA), which may occur if 2PA from the ground state is immediately followed by strongly allowed 1PA to higher excited states.

Two-photon absorption and optical power limiting properties of ladder-type tetraphenylene cored chromophores with different terminal groups

A series of soluble ladder-type tetraphenylene cored chromophores with different terminal groups have been synthesized and their structure–property relationship with regards to various linear optical and nonlinear optical properties has been established. By using the two-photon excited fluorescence method and the nonlinear transmission method, the two-photon absorption (2PA) properties of these chromophores were determined, and they were found to be strongly dependent on the electron-richness of the ladder-type tetraphenylene core, as well as the terminal groups. The introduction of strong electron donors (N-alkyl) in both the central core and the terminals led to a chromophore with a high 2PA cross-section value of 2137 GM. Optical limiting behaviors of the synthesized chromophores in THF were investigated by using a femto-second ultra-fast laser. 2PA coefficients for these chromophores in THF (5 mM) ranged from 0.131–0.256 cm GW−1. The ladder-type tetraphenylene cored chromophore with the highest 2PA cross-section value exhibited the best optical limiting performance, as evidenced by light transmission as low as 19.1% at 770 nm under an intensity of 99.6 GW cm−2. The excellent optical limiting performance of these chromophores makes them useful in photonic or optoelectronic devices for protecting human eyes and optical sensors, as well as for stabilizing light sources in optical communications.

Phenylene Vinylene Platinum(II) Acetylides with Prodigious Two-Photon Absorption

The linear and nonlinear optical properties of a series of linear and cross-conjugated platinum(II) acetylide complexes that contain extended p-(phenylene vinylene) chromophores are reported. The complexes exhibit very high femtosecond two-photon absorption (2PA) cross section values (σ(2) up to 10,000 GM), as measured by nonlinear transmission (NLT) and two-photon excited fluorescence (2PEF) methods. The large 2PA cross sections span a broad range of wavelengths, 570-810 nm, and they overlap with the triplet excited state absorption. Spectral coincidence of high cross section 2PA and triplet absorption is a key feature giving rise to efficient dual-mode optical power limiting (OPL).

Photophysical properties of octupolar chromophore based on triazine core and fluorene divinylene conjugated bridge

Abstract A novel octupolar chromophore with 1,3,5-triazine as core, 2,7-divinylene-9,9-dimethylfluorene as extended π-conjugated bridge, triarylamine as the electron-donating end-groups was successfully synthesized and characterized. Their linear photophysical and two-photon absorption (TPA) properties were investigated by UV absorption, excited fluorescence (SPEF) spectra and nonlinear transmission method, respectively. The absorption cut-off of the chromophore is below 520 nm and it has stronger fluorescence emission in a nonpolar solvent. In addition, the chromophore exhibits larger TPA cross-section (226.0 GM) in the femtosecond regime at 800 nm.

Three-photon absorption in a push–pull type chromophore containing tricyanofuran acceptor

Abstract Three-photon absorption (3PA) of a push–pull chromophore, 2-(3-cyano-(3-(4-(dimethylamino)styryl)-5, 5-dimethylcyclohex-2-enylidene)methyl)-5, 5-dimethylfuran-2-ylidene) malononitrile (CFM) including TCF group was measured by the nonlinear transmission method using a femto-second Ti:Sapphire oscillator-amplifier laser system. Its three-photon absorption cross-sections at 1300 nm were 36.8 × 10−79 cm6 s2 in the solution of DMF and 12.3 × 10−79 cm6 s2 in the solution of CH2Cl2, respectively. The large values were got by experiments in this paper, which is a new exploration for these kinds of materials. The molecule has the potential application foreground of 3PA areas and optical power limiting.

Synthesis and properties of tribranched chromophores with triazine and fluorene units

Abstract Two tribranched chromophores, 1,3,5-triazine as electron deficient core, 9,9-dimethylfluorene as π -conjugated bridge, diphenylamino ( 4a ) and naphthylamino ( 4b ) as electron-donating end-groups, were successfully prepared via Buchwald–Hartwig coupling reaction. Their linear photophysical and two-photon absorption (TPA) properties were investigated by absorption, fluorescence and nonlinear transmission method, respectively. The absorption cut-offs of the chromophores are below 550 nm and both chromophores have strong fluorescence emission. The compound 4a (206.3 GM) exhibits larger TPA cross-section than 4b (57.8 GM) in the femtosecond regime at 800 nm.

A novel near IR two-photon absorbing chromophore: Optical limiting and stabilization performances at an optical communication wavelength

Materials with large two-photon absorption (TPA) capability are highly useful not only for optical power limiting, but also for laser pulses’ stabilization in an optical communication system. A novel dipyrromethene boron difluoride (BODIPY) chromophore was synthesized and its TPA characteristic was investigated by the direct nonlinear transmission method in femto-second regime. This chromophore was found to have a broad TPA spectral distribution in the near-IR range, and a fairly large TPA cross-section of 101 GM at around 1310 nm. Using the BODIPY chromophore, both good optical limiting and optical stabilization performances were achieved at the wavelength of 1310 nm.

新型双光子吸收生色分子的电化学、热性能和光物理性质

Electrochemical, thermal, and photophysical properties of novel two- (BPODPA), four- (BBPOPA), and six-branch (TBPOA) triphenylamine chromophores are studied. The decomposition temperature of chromophores reaches 373-412 C. The electrochemical properties is explored by cyclic voltammetry. The ionization potential of chromophores is in the range of 5.14-5.18 eV. Excitation at 400 nm reveals emission peaks at 483-487 nm and the fluorescence quantum yields are 0.73-0.75 in CH2Cl2 Two-photon absorption (TPA) properties of chromophores are measured by nonlinear transmission method. The maximum TPA cross-section values are measured at 758 nm to be 20369 GM (1 GM=10^{-50} cm4s/photon) for TBPOA, 7024 GM for BBPOPA, and 1227 GM for BPODPA, respectively. When pumped with 800-nm laser irradiation, chromophores show strong two-photon excited blue-green fluorescence at 502-518 nm. These results provide a basis for understanding the electronic and optical properties of the conjugated multi-branch chromophore in terms of the underlying molecular and electronic structures.

Water-soluble benzylidene cyclopentanone dye for two-photon photopolymerization

A novel water-soluble benzylidene cyclopentanone dye was synthesized by introducing four sodium carboxylate groups into 2,5-Bis-[4-(diethylamino)-benzylidene]-cyclopentanone (BDEA). Its two-photon absorption (TPA) cross-section in water solution was determined by nonlinear transmission method with Ti:sapphire femtosecond laser as exciting light source. 287 GM at 800 nm was obtained, which was quite larger than TPA cross-section of water-soluble xanthene dyes. Using this new dye as initiator, two-photon polymerization (TPP) of water-soluble acrylate could be induced directly. Low threshold energy of 0.51 mW and a high resolution of 400 nm were achieved, indicating this dye would have extensive application prospects in TPP under aqueous environments.

Linear Multiuser MIMO Transceiver Design With Quality of Service and Per-Antenna Power Constraints

Joint design of linear multiuser multiple-input-multiple-output (MIMO) transceiver subject to different quality of service (QoS) constraints per user and with per-antenna or antenna group power constraints is considered. Solutions for two linear transceiver optimization problems are proposed, i.e., balancing the weighted signal-to-interference-plus-noise ratio (SINR) per data stream and balancing the weighted rate for each scheduled user with minimum rate requirements per user. The proposed joint transceiver optimization algorithms are compared to corresponding optimal nonlinear transmission methods as well as to generalized zero-forcing transmission solutions. Unlike the optimal nonlinear schemes, the optimization problems employed in the linear multiuser MIMO transceiver design are not convex in general. However, the proposed algorithms are shown to provide very efficient solutions despite of the fact that the global optimum cannot be guaranteed due to nonconvexity of the problems.

Two-Photon Frequency-Upconversion Fluorescence of Multibranch Chromophores with Nitrogen-Coupling Center

Two-photon absorption (TPA) properties of multibranch chromophores with nitrogen coupling center, N-[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N,N-diphenylamine (BPODPA), N,N-bis[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl]-N-phenylamine (BBPOPA) and N,N,N-tris[4-{2-(3,5-di-{5-[4-(tert-butyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl)-1-ethenyl}phenyl] amine (TBPOA),were measured by nonlinear transmission method. Single photon excited fluorescence and two-photon excited fluorescence (TPEF) of the chromophores were studied. The effect of dendronization on the TPA and TPEF characters of triphenylamine-based chromophores was investigated. When pumped with 800 nm laser irradiation, chromophores BPODPA, BBPOPA, and TBPOA showed strong two-photon excited blue green fluorescence at 502, 515, and 518 nm, respectively. These multibranched chromophores showed large TPA cross-section. The enhanced two-photon absorption found in these chromophores was attributed to the fact that the multibranched chromophores had both an extended -conjugated system and an increased intramolecular cooperative effect compared to the one-branched chromophore.

Design, Fabrication, Linear and Nonlinear Optical Properties of Metal-Dielectric Photonic Bandgap Structures

The linear and the nonlinear optical properties of metallodielectric photonic bandgap (MD-PBG) structures were studied by using linear absorption spectroscopy and a femtosecond nonlinear transmission method. The MD-PBG structure consisted of three bilayers of MgF2(250 nm)/Ag(30 nm). It was prepared by evaporating MgF2 and Ag layers alternatively onto a glass plate. The optical transmission spectrum of the prepared MD-PBG structure was found to exhibit several pass bands and a broad photonic bandgap. The photonic bandgap extended throughout most of the visible region from 475 nm to 780 nm. Interestingly, there existed transmissive pass bands corresponding to the Bragg resonances: λ1 = 410 nm (T = 53.9 %), λ2 = 449 nm (T = 42.9 %), λ3 = 802 nm (T = 39.6 %) and λ4 = 878 nm (T = 16.9 %). The observed transmission spectra could be described by applying the optical transfer matrix formalism to the periodic metallodielectric multilayer. The number of pass bands was found to increase with increasing number of metal-dielectric pairs, and the band width of PBG was found to increase with increasing dielectric layer thickness. At high laser intensity, the MD-PBG structure exhibited a large nonlinear absorption. The enhanced optical nonlinearity is thought to be due to a bathochromic shift of the low-energy band edge of PBG by the saturable absorption of each metallic layer.

Synthesis and two-photon absorption properties of 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles

Two symmetrical 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles that exhibit strong two-photon absorption and enhanced two-photon excited fluorescence were designed and synthesized based on “push-core-pull-core-push” molecules built from embedding electron-transporting 1,3,4-oxadiazole in aromatic conjugated system through Wittig–Horner reaction. Pumped by nanosecond laser at 800 nm, strong up-conversion emissions with the central wavelength at 507 nm (green) of 2,5-bis[4-(2- N, N-diphenylaminostyryl)phenyl]-1,3,4-oxadiazole and 475 nm (blue) of 2,5-bis[4-{2-(3- N-ethylcarbazolyl)vinyl}phenyl]-1,3,4-oxadiazole in the solution of CHCl 3 have been observed. Their two-photon absorption cross-sections obtained by nonlinear transmission method are 107 × 10 −48 cm 4 s photon −1 and 66 × 10 −48 cm 4 s photon −1. A very effective energy transfer from the excited terminal units to the π-conjugated bridging units of the 2,5-bis[4-(2-arylvinyl)phenyl]-1,3,4-oxadiazoles is the dominant contribution to the two-photon absorption.