Study on the optical limiting properties of the mixed liquid of carbon black suspensions and green tea solution by multi-pulse laser

The optical limiting properties of the mixed liquid of carbon black suspensions （CBS） and green tea solution were studied by using an 8 ns laser pulse at 532 nm. The optical limiting effects of the CBS and mixed liquid have been compared between 5 and 10 Hz repetition frequencies with nanosecond laser pulse. The experimental results indicate that the optical limiting threshold of the sample with the incidence laser at 10 Hz repetition frequency is lower than at 5 Hz repetition frequency. The possible reasons for the influence of the repetition frequency on the samples are discussed. And by observing the optical radiant distributions when the laser pulse passing through different samples, a possible mechanism for the observed effects is suggested. At the same time, the result shows that the optical limiting of CBS is the dominant factor to optical limiting of the mixed liquid.

Measurement of stimulated Brillouin scattering(SBS) threshold based on waveform variation of SBS optical limiting

This paper proposes a method for measuring the stimulated Brillouin scattering （SBS） threshold based on waveform variation of SBS optical limiting. The output waveforms for different pump power densities are numerically simulated, and validated in the Nd：YAG seed-injected laser system. The results indicate that SBS does not take place in the case of a low pump power density and thus the output power scales up linearly with pump power. Once the pump power density exceeds the SBS threshold, SBS takes place and thereby the energies are transferred from pump to Stokes. As a result, a small shoulder appears in the trailing edge of the output waveform, which provides another method to determine the SBS threshold.

Optical Limiting Response in Er^(3+)-Doped TeO_2-Nb_2O_5-ZnO Glass

The nonlinear absorption properties of Er^3＋ doped telluride glass were investigated with picosecond laser pulses. The optical limiting response was measured with a transmission technique and reverse saturable absorption （RSA） with a Z-scan technique, which proved that the glass was a promising material for practical optical limiters. The experimental resulted showed that the excited absorption was responsible for the measured RSA, resulting in the optical limiting response. The measured data could be well simulated with a rate equation model to obtain the absorption cross sections of the excited state.

PREPARATION OF SOLUBLE SUBSTITUTED POLYACETYLENE OPTICAL LIMITING MATERIAL

Two novel polyacetylenes bearing nonlinear optical chromophoric group poly（3-（4-[4-（n-butyloxy） phenylazophenyl]carbonyl）oxy-1-propyne） （poly（1a）） and poly（3-（4-[4-（n-heptyloxy）phenylazophenyl]carbonyl）-oxy-l- propyne） （poly（lb）） were synthesized with [Rh（nbd）Cl]2-EtaN as catalysts. These polyacetylenes are soluble by using an alkyl spacer and an alkyloxyl group as a substituent. They were characterized by FTIR, NMR, GPC and UV-Vis and their optical limiting and nonlinear optical properties were investigated using 8 ns pulse at 532 nm wavenumber. The results show that these soluble functional polyacetylenes possess optical limiting properties and large nonlinear optical properties and poly（1b） possesses better optical limiting and nonlinear optical properties than poly（ 1 a）.

Spectroscopic Properties and Three-photon Absorption Induced Optical Limiting of Series of Novel Nonlinear Chromophores

Three novel nonlinear chromophores with symmetric D-π-D molecular structure and extended conjugated length were synthesized. Solvatochromism analysis shows great symmetric intramolecular charge transfer occurring in chromophores by the enhancement in the dipole moment between the ground and excited states. The properties of optical power limiting induced by three-photon absorption （3PA） are demonstrated. Large 3PA coefficients and the corresponding molecular cross sections as high as 10^-74 cm^6s^2 were obtained for nanosecond laser pulses at 1.06μm from nonlinear transmission measurements.

Investigation on the effect of beam divergence angle upon output waveform based on stimulated Brillouin scattering optical limiting

This paper investigates the effect of beam divergence angle on output waveform based on stimulated Brillouin scattering optical limiting.Output waveforms in the case of different pump divergence angles are numerically simulated,and validated in a Nd：YAG seed-injected laser system.The results indicate that a small pump divergence angle can lead to good interaction between pump and Stokes,and a platform can be easily realized in the transmitted waveform.In contrast,a peak followed by the platform appears when the divergence angle becomes large.

Theoretical Analysis on Optical Limiting Properties of Newly Synthesized Graphene Oxide-Porphyrin Composites

Optical limiting （OL） properties and two-photon absorption （TPA） of a series of covalently linked graphene oxide-porphyrin composite materials have been investigated by numerically solving the rate equations and field intensity equation with an iterative predictor-corrector finite-difference time-domain technique in nanosecond time domain. Our results show that graphene oxide-porphyrin composites exhibit enhanced OL behavior and possess larger TPA cross section compared with individual porphyrins. Interestingly~ unlike the previous result that porphyrin with heavier central metal shows better nonlinear abilities than that with- out metal substitute, graphene oxide-metal free porphyrin composite has stronger nonlinear absorption properties compared with graphene oxide-metal porphyrin composite. The com- putational results are in reasonable agreement with the experimental ones. Special attention has been paid to the influence of thickness of the medium and pulse width on TPA cross sections, which presents that larger TPA cross sections are obtained as the medium is thicker or the pulse duration is wider.

Variation of Two-photon Absorption Cross Sections and Optical Limiting of Compounds Induced by Static Electric Field

By numerically solving the Maxwell-Bloch equations using an iterative predictor-corrector finite-difference time-domain technique, we investigate propagating properties of a few-cycle laser pulse in a 4,4＇-bis（di-n-butylamino） stilbene （BDBAS） molecular medium when a static electric field exists. Dynamical two-photon absorption （TPA） cross sections are obtained and optical limiting （OL） behavior is displayed. The results show that when the static electric field intensity increases, the dynamical TPA cross section is enhanced and the OL behavior is improved. Moreover, both even- and odd-order harmonic spectral components are generated with existence of the static electric field because it breaks the inversion symmetry of the BDBAS molecule. This work provides a method to modulate the nonlinear optical properties of the BDBAS compounds.

Numerical analyses on optical limiting performances of chloroindium phthalocyanines with different substituent positions

Optical limiting properties of two soluble chloroindium phthalocyanines with a- and β-alkoxyl substituents in nanosecond laser field have been studied by solving numerically the coupled singlet-triplet rate equation together with the paraxial wave field equation under the Crank-Nicholson scheme. Both transverse and longitudinal effects of the laser field on photophysical properties of the compounds are considered. Effective transfer time between the ground state and the lowest triplet state is defined in reformulated rate equations to characterize dynamics of singlet-triplet state population transfer. It is found that both phthalocyanines exhibit good nonlinear optical absorption abilities, while the compound with a-substituent shows enhanced optical limiting performance. Our ab-initio calculations reveal that the phthalocyanine with a-substituent has more obvious electron delocalization and lower frontier orbital transfer energies, which are responsible for its preferable photophysical properties.

Synthesis, Structure, and Optical Limiting Properties of an Axial Substituted Bis(8-oxide quinoline)zirconium Phthalocyanine

A novel bis(8-oxide quinoline)zironium phthalocyanine [(OQ)2 Zr Pc] with two 8-oxide quinolone anions at the same axial positions has been successfully synthesized and its chemical structure has been assigned by the 1 H NMR, MS and two-dimensional correlation infrared(2D-IR) spectroscopy as well as by single-crystal X-ray structural analysis. It possessed a moderately effective nonlinear absorption coefficient βeff of 6.69×10-14cm/GW at 532 nm in DMF solution, implying it is a promising candidate for nonlinear optical materials.

Nonlinear optical limiting effect of graphene dispersions at 3.8μm

We investigate the nonlinear optical limiting effect of novel graphene dispersions and graphene dispersions in carbon tetrachloride at a wavelength of 3.8μm.The transmittances of graphene dispersions in carbon tetrachloride under two different concentrations(0.004 and 0.008 mg/mL)and two different solution thicknesses(10 and 20 mm)are measured.The influences of concentration and thickness on the optical limiting effect of graphene dispersion are analyzed.Theoretical analysis of the experimental data shows that the main optical limiting mechanism of the new graphene dispersions is Mie scattering.The limiting capacity coefficient of the new graphene dispersion in carbon tetrachloride reaches 0.405 and the minimum transmittance reaches 0.292 when the concentration is 0.004 mg/mL and the thickness is 20 mm.The graphene dispersions in carbon tetrachloride can be used to achieve good nonlinear optical limiting effects at the wavelength of 3.8μm.

The largest aluminum molecular rings:Phenol-thermal synthesis,photoluminescence,and optical limiting

It is of great interest to modulate the photophysical properties by atomically precise chemical control.The incorporation of conjugated ligands into crystalline materials provides a platform for molecular-level interpretation of the structure-activity relationship.Herein,we reported the phenol-thermal and scale-up synthesis of a new family of remarkably stable aluminum molecular rings.They are assembled by twenty Al^(Ⅲ) ions with large conjugated ligands and phenols,representing the currently largest sizes(up to 4 nm in diameter)in the field of main group metal oxo clusters.Phenols are not only reaction medium but also auxiliary bridging ligands on the surface of macrocyclic molecules.In addition,they are either parallel to the center of the molecular ring or inserted into the molecular ring,or form dimers/tetramers that bind macrocyclic molecules to form supramolecular structures.These macrocyclic rings are hydrophobic and ultra-stable,evidenced by retaining their morphology and crystalline when exposed to air for more than a year.Compared with the pristine conjugated ligands,they exhibit coordination-enhanced fluorescence.By dispersing them into a polydimethylsiloxane(PDMS)matrix,we prepared transparent and flexible PDMS thin films for coupling flexible display and nonlinear optical application.Our discovery of such atomically precise rings provides a platform for the fine-tuning of photo-related performances.

Laser shaping and optical power limiting of pulsed Laguerre–Gaussian laser beams of high-order radial modes in fullerene C60

We study the strong nonlinear optical dynamics of nanosecond pulsed Laguerre–Gaussian laser beams of high-order radial modes with zero orbital angular momentum propagating in the fullerene C60molecular medium. It is found that the spatiotemporal profile of the incident pulsed Laguerre–Gaussian laser beam is strongly reshaped during its propagation in the C60molecular medium. The centrosymmetric temporal profile of the incident pulse gradually evolves into a noncentrosymmetric meniscus shape, and the on-axis pulse duration is clearly depressed. Furthermore, the field intensity is distinctly attenuated due to the field-intensity-dependent reverse saturable absorption, and clear optical power limiting behavior is observed for different orders of the input pulsed Laguerre–Gaussian laser beams before the takeover of the saturation effect;the lower the order of the Laguerre–Gaussian beam, the lower the energy transmittance.

Optical limiting performances of transitional metal dichalcogenides MX_(2)(M = V, Nb, Ta;X = S, Se) with ultralow initial threshold and optical limiting threshold

The optical limiting performances of few-layer transitional metal dichalcogenides (TMDs) nanosheets in the VB group(VS_(2),VSe_(2),NbS_(2),NbSe_(2),TaS_(2),and TaSe_(2)) were systematically investigated for the first time,to the best of our knowledge.It was found that these TMDs nanosheets showed a normalized transmittance in the range of 20%–40%at the input energy of 1.28 GW/cm^(2).Ultralow initial threshold F_(S)(0.05–0.10 J/cm^(2)) and optical limiting threshold F_(OL)(0.82–2.23 J/cm^(2)) were achieved in the TMDs nanosheets,which surpassed most of the optical limiting materials.This work showed the potential of TMDs beyond MoS_(2)in optical limiting field.

Nonlinear optical and optical limiting properties of new structures of organic nonlinear optical materials for photonic applications

The nonlinear optical （NLO） and optical limiting （OL） properties of three new structures of organic NLO guest host Poly（N-vinylcarbozole）/disperse orange 3 （PVK/DO3）, PVK/disperse orange 13 （PVK/DO13）. and PVK/disperse orange 25 （PVK/DO25） as a solution at different concentrations and as a thin-film sample are studied using continuous wave z-scan system at 532 nm. The open-aperture z-scan data of the NLO materials in the solution and thin-film samples displayed two-photon and saturable absorptions, respectively. The PVK/DO13 exhibites the largest and best values of the nonlinearities, such as n2, β, X（3） compared with those of PVK/DO3 and PVK/DO25. This nonlinearity increases as the concentration increases. Tile results indicate that these NLO materials are good candidates for optical switching and OL devices.

Tailoring optical properties of TiO_2 in silica glass for limiting applications

We present the linear and nonlinear optical studies on TiO2-SiO2 nanocomposites with varying compositions. Opti- cal band gap of the material is found to vary with the amount of SiO2 in the composite. The phenomenon of two-photon absorption （TPA） in TiO2/SiO2 nanocomposites has been studied using open aperture Z-scan technique. The nanocom- posites show better nonlinear optical properties than pure TiO2, which can be attributed to the surface states and weak dielectric confinement of TiO2 nanoparticles by SiO2 matrix. The nanocomposites are thermally treated and similar studies are performed. The anatase form of TiO2 in the nanocomposites shows superior properties relative to the amorphous and rutile counterpart. The involved mechanism is explained by rendering the dominant role played by the excitons in the TiO2 nanoparticles.

Two-photon Absorption and Optical Power Limiting Properties of Two Novel Dibenzothiophene-based Chromophores

Two novel V-shaped symmetric chromophores： E-2,8-bis（4-vinyl-4-carbazol-9-yl）diben- zothiophene （abbreviated as SK-G1） and E-2,8-bis（4-vinyl-4-triphenylamino） dibenzothiophene （abbreviated as ST-G1） have been synthesized and characterized. Their two photon absorption properties were measured by the open-aperture femtosecond Z-scan technique and the nanosecond nonlinear optical transmission （NLT）, respectively, when pumped by Ti： sapphire laser at 750 nm and 800 nm.

Infrared broadband nonlinear optical limiting technology based on stimulated Brillouin scattering in As_(2)Se_(3) fiber

A novel infrared broadband nonlinear optical limiting[NOL]technology based on stimulated Billouin scattering(SBS)in As_(2)Se_(3) fiber is proposed.The As_(2)Se_(3) fiber alows a weak infrared laser to pass through,but blocks an intense laser with the same wavelength due to the SBS effect.This NOL technology has been experimentally proved to have excellent NOL per-formance for incident pulsed lasers with a typical infrared wavelength of 3.6μm.The linear transmissions of 1 m and 0.5 m As_(2)Se_(3) fibers are higher than 90%,and the lowest nonlinear transmissions are reduced to 0.89%and 1.23%,respectively.

Synthesis,Structure and Optical Limiting (OL) Properties of a Novel Incomplete Cubane-like Cluster [PPh_4][(η~5-C_5Me_5) WS_3-(CuBr)(CuI)_2(μ-dppm)]

Reaction of [PPh_4][(η 5-C_5Me_5)WS_3] with CuI,CuBr and bis^(diphenylphosphino)methane (dppm) (molar ratio=1∶2∶1∶1) in MeCN gave rise to [PPh_4][(η 5-C_5Me_5)WS_3(CuBr)(CuI)_2-(μ-dppm)] (1) in high yield. Compound 1 crystallizes in the monoclinic,space group P2_1/n with lattice parameters:a=1.2906(4) nm, b=1.5006(8) nm,c=3.1484(6) nm,β= 92.12(2)°,V=6.093(3) nm 3,Z=4. The structure of the anion of 1 contains an incomplete WS_3Cu_3 cubane-like core in which two CuI units are bridged by a dppm ligand. The W—Cu distances vary in the range of 0.2644(1)—0.2793(1) nm. The optical limiting (OL) properties of 1 in MeCN were measured with the laser pulse-width of 12-ns at 532 nm,and the nanosecond OL effect may be due to the reverse saturable absorption (RSA) related to the excited triplet states.

Optical power limiting of ultrashort hyper-Gaussian pulses in cascade three-level system

Propagation of strong femtosecond hyper-Gaussian pulses in a cascade three-level molecular system is studied by solving numerically the Maxwell–Bloch equations by the iterative predictor-corrector finite-difference time-domain method.Optical power limiting behavior induced by strong nonlinear two-photon absorption is observed for different orders of the femtosecond hyper-Gaussian pulses. Pulses of a higher order temporal profile are found to have a wider power range of optical limiting but a larger output saturation intensity. Both the output saturation value and the damage threshold of optical power limiting decrease with pulse duration increasing. The decrease of the pulse area along the pulse propagation is much slower than that obtained from the two-photon area theorem due to invalidity of the slowly varying amplitude approximation and the monochromatic field hypothesis.