Strong Reverse Saturable Absorption Research Articles

Nonlinear optical properties of p-( N, N-dimethylamino)dibenzylideneacetone doped polymer

A bis-chalcone derivative, p-( N, N-dimethylamino) dibenzylideneacetone was synthesized. Its third-order nonlinear susceptibility was determined to be as high as 10 −12 esu by employing single beam Z-scan and degenerate four wave mixing techniques using Nd:YAG 7 ns laser pulses at 532 nm. The compound was doped in to poly(methylmethacrylate) matrix and the third-order nonlinearity was investigated by using Z-scan technique. The nonlinear refractive index of the doped polymer is found to be negative, and its magnitude is of the order of 10 −10 esu. The results show that the compound exhibits strong reverse saturable absorption and a good optical limiting property and hence may be used as a promising dopant material. The study on concentration dependence of nonlinear optical parameters has been presented.

Large third-order optical nonlinearities of ultrathin films containing octacarboxylic copper phthalocyanine

Abstract An ultrathin composite film with alternating layers containing anionic octacarboxylic copper phthalocyanine [CuPc(COONa)8] and cationic polyethylenimine (PEI) has been prepared by the electrostatic layer-by-layer self-assembly technique. The alternating multilayer assemblies of CuPc(COONa)8/PEI were characterized by UV–Vis spectroscopy, showing the regularly consecutive adsorption process. The film surface was smooth and homogeneous as indicated by atomic force microscopy. The closely packed nanoparticles, with the average diameter of 36 nm and the mean interface roughness of 2.984 nm, can be easily seen on the film surface uniformly. Further structure investigation was carried out by using small angle X-ray diffraction. Third-order nonlinear properties of the film and CuPc(COONa)8 aqueous solution were studied by Z-scan measurements at 532 nm with 8 ns pulses. The ultrathin film depicted strong nonlinear reverse saturable absorption and excellent self-defocusing performance. The second-order molecular hyperpolarizability γ value of the film was 68 times larger than that of solution sample.

Third-order nonlinear optical studies of newly synthesized polyoxadiazoles containing 3,4-dialkoxythiophenes

The third-order nonlinear optical properties of newly synthesized soluble polyoxadiazoles containing 3,4-dialkoxythiophenes were investigated by using Z-scan and degenerate four-wave mixing (DFWM) techniques. The measurements were performed at 532 nm with 7 ns pulses from a Nd:YAG laser. We found a good agreement between the values of χ (3) determined from both the experiments. Z-scan results indicate a negative nonlinear refractive index, n 2, whose magnitude is of the order of 10 −10 esu for all the copolymers. The variation of nonlinear response among the copolymers clearly indicates the dependence of χ (3) on donor and acceptor type of units present in these copolymers. The copolymers exhibit strong reverse saturable absorption and good optical limiting properties at 532 nm.

Z-scan and degenerate four wave mixing studies on newly synthesized copolymers containing alternating substituted thiophene and 1,3,4-oxadiazole units

The third-order nonlinear optical properties of newly synthesized copolymers containing alternating substituted thiophene and 1,3,4-oxadiazole units have been studied in DMF solution at 532 nm by using single beam Z-scan and degenerate four wave mixing techniques with nanosecond laser pulses. The variation of nonlinear response among the copolymers clearly indicates the dependence of χ(3) on donor and acceptor type of units present in the copolymers. The nonlinear refractive index, n2, of the investigated copolymers is found to be negative and the magnitude is as high as 10−10 esu. All samples exhibit strong reverse saturation absorption at the wavelength used and show good optical limiting of nanosecond pulses. The concentration dependence of n2 and the two-photon absorption coefficient (β) has been studied.

Third-order nonlinear optical properties of bromo［tri-α-(2,4-dimethyl-3-pentyloxy) subphthalocyanine］ boron

The third-order nonlinear optical properties of a new subphthalocyanine complexe (bromo［tri-α-(2,4-dimethyl-3-pentyloxy) subphthalocyanine］ boron) was studied by Z-scan using 8ns laser pulses at 532nm. It was found that the compound shows a strong reverse saturation absorption (β=3.7×10-10 m/W) and nonlinear self-focusing refraction effects (n2=7.2×10-11 esu). The third-order nonlinear susceptibility (χ(3)) is 1.1×10-11esu.The effects of cone-chaped molecular structure and axially heavy-atom (Br) substitution on third-order nonlinear optical properties are also discussed.

Photophysical studies on axially substituted indium and gallium phthalocyanines upon UV–Vis laser irradiation

A series of results from different photophysical experiments on indium and gallium phthalocyanine (Pc) compounds is reported. Gallium Pc's have much longer singlet and triplet excited state lifetimes in comparison with indium Pc's. The strong reverse saturable absorption observed at 532 nm excitation is a consequence of the increase in absorbance of Pc's in the triplet excited state in the optical window comprised between Q- and B-bands, as verified upon laser irradiation with ns pulses at 355 nm. Using C 60 as a reference, the intersystem cross quantum yields of tBu 4PcInCl and tBu 4PcGaCl are 0.70 and 0.36, respectively.

Reverse saturable absorption of copper phthalocyanines in toluene and sol-gel tetraethyl orthosilicate/polyvinyl butyral hybrid film

Materials with strong reverse saturable absorption have been searched for power limiting applications, and metallophthalocyanine molecules are one of them. Here we report our investigations of reverse saturable absorptive properties of copper phthalocyanines with three different side substitutions. By dissolving them in toluene or incorporating them in polymer-silica hybrid material using a sol-gel process with polyvinyl butyral and tetraethyl orthosilicate as precursors, we found that substitution of copper phthalocyanines influence the optical nonlinearities. Regarding the preparation process of phthalocyanines in the solids, a new route has been successfully used.

Third-order optical nonlinearities of α,ω-dithienylpolyenes and oligo(thienylvinylene)

Abstract α,ω-Dithienylpolyenes and oligo(thienylvinylene) are interesting third-order nonlinear optical materials for a variety of device applications. To better understand the third-order nonlinear response of these materials, the third-order susceptibilities ( χ (3) ) and nonlinear absorption behaviors of two α,ω-dithienylpolyenes with different conjugation length and two oligo(thienylvinylene) with different substituents on the thiophene rings have been studied using degenerate four wave mixing (DFWM) and nonlinear transmission techniques at 532 nm. The χ (3) values of 1×10 −3 mol/l solutions are all of the order of 10 −13 esu. The χ (3) values increase with the increase of the linear absorption coefficient. In addition, these compounds exhibit reverse saturable absorption for nanosecond laser pulses. The strength of reverse saturable absorption varies when the conjugation length and substituents change. Moreover, the nonlinear absorption characteristics of these compounds in the picosecond regime differ from those in the nanosecond regime. The different nonlinear absorption behavior is due to the relative contributions from excited singlet–singlet and triplet–triplet absorption. The strong reverse saturable absorption characteristics of two of the compounds suggest that they could be potential candidates for optical limiting applications in the nanosecond regime.

Optical limiting and picosecond relaxation of carbocyanines upper electronic states

Nonlinear absorption, anomalous fluorescence and relaxation of high-lying electronic states in six carbocyanine dyes, including cryptocyanine (DCI), DDI, DTDCI, DTTCI, DOTCI and HDIDCI, in solution and in polymer, were studied by means of picosecond transient absorption spectroscopy and nonlinear transmission experiments. Absorption cross-sections of the S 1→S n transition, and decay rates of the second singlet excited state, S 2, were measured. All dyes showed strong reverse saturable absorption in the 450–600 nm region with large excited to ground state absorption cross-section ratios. For DTDCI this ratio, at 470 nm, was measured to be 350, which is the largest ever reported. All molecules have shown strong optical limiting effect. However, in all molecules except DCI a saturation of the optical limiting process was observed as expected, owing to relatively long, up to 17.5 ps, lifetime of the S 2 state. The S 2 state fluorescence quantum yields were also measured.

Optical switching in organometallic phthalocyanine

The strong reverse saturation absorption (optical limiting) which has been observed with high-peak-power, short-pulse lasers in Pt-phthalocyanine solutions can also be observed at low intensity with continuous-wave lasers. The origin of the effect is a strong triplet state absorption as in the case of pulse excitation. We demonstrate that this phenomenon can be utilized to generate various types of all-optical switching.

Third-order nonlinear optical properties of an expanded porphyrin cadmium complex

The third-order nonlinear optical properties of a pentaazadentate porphyrin-like cadmium complex, [(DBP–APPC)Cd]Cl, have been investigated using 40-ps and 5-ns laser pulses at 532 nm. The molecular second-order hyperpolarizability of this complex is 9.7×10−31 esu, and the nonlinearity is predominantly electronic in origin with picosecond laser pulses. Temporal response of the nonlinear process is composed of at least two components with different time responses and shows a strong fluence dependence that indicates the participation of excited states in the nonlinear process. Nonlinear absorption measurements demonstrate that this complex shows strong reverse saturable absorption for nanosecond laser pulses, but exhibits a transformation from reverse saturable absorption to saturable absorption at high fluence for picosecond pulses. These results suggest that [(DBP–APPC)Cd]Cl is a very promising candidate for optical limiting of nanosecond laser pulses.

Femtosecond to Nanosecond Characterization of Optical Limiting Mechanisms in Power Limiting Liquids and Solids

AbstractWe present our recent advances toward the development of high-performance solid-state optical limiting devices using reverse saturable absorption (RSA) dyes doped into optical host materials. Femtosecond transient absorption spectroscopy was employed to determine both the spectral regions of strong RSA, and the singlet-triplet excited-state dynamics. The optical limiting in the visible spectrum in both metallo-phthalocyanines and metallo-porphyrins is due to a combination of singlet and triplet RSA. Optical limiting performance was studied for RSA dyes in dual tandem limiters (both in solution and solid-state). Our best results in the solid-state yielded an attenuation of 400x, and a damage threshold of up to several mJ at f/5 focusing. The optical limiting at f/5 is further enhanced, particularly in the solid-state, by self-defocusing thermal nonlinearities.