Top-hat Z-scan Technique Research Articles

Nonlinear Properties Of Water-soluble Ag2S And PbS Quantum Dots Under Picosecond Laser Pulses

In this paper, the water-soluble Ag2S and PbS quantum dots(QDs) are synthesized by aqueous phase synthesis. The nonlinear optical properties of Ag2S and PbS QDs were investigated by Top-hat Z-scan technique under ps laser pulses (λ = 532 nm, t = 21 ps). The open Z-scan results show that Ag2S and PbS QDs all have a valley value which indicate that they have strong reverse saturable absorption(RSA). The nonlinear absorption coefficient of Ag2S QDs is 6.72×10-13 esu, however, the valley value of PbS QDs at the focal point is similar to 1, so its nonlinear absorption coefficient is small, is 7.13×10-14 esu. The close Z-scan results show that Ag2S QDs has self-defocusing effect and PbS QDs has self-focusing effect, their nonlinear refractive index are on the order of -6.13×10-13 esu and 2.41×10-13 esu. After fitting calculation, the third order nonlinear polarizability of Ag2S and PbS QDs are 2.40×10-14 esu and 6.02×10-15 esu respectively. The physical mechanisms responsible for the nonlinear optical response of the QDs are discussed in detail. In summary, the nonlinear absorption and refraction properties of Ag2S QDs are better than that of PbS QDs, but both of these materials are of great significance for the research of photoelectric, biosensor, optical limiting, and self-adaptive technologies.

Measurement of Nonlinear Properties for PEI Tetra Sulfonated Indium Phthalocyanine Compounds Self-Assembly Film Using Improved Tophat Z-Scan Technique

The nonlinear refraction and absorption properties of a PEI (phthalocyanine indium) tetrasulphonated chlorinated phthalocyanine electrostatic self-assembled film were studied using a simple and high sensitivity technique. We adopted picosecond laser pulses as source light and modified top-hat Zscan technique with a disk and a small aperture to explore the nonlinear refraction of the film. Experimental results show that the measuring sensitivity is increased by two orders of magnitude. Through theoretical fitting, we obtain the nonlinear refraction index and nonlinear absorption coefficients of the film are 2.1×10-14 m2/W and 2.4×10-7 m/W, respectively.

Fabrication and characterization of CaCuO2/CaCu2O3 thin films with enhanced third-order nonlinear properties

In this work, poly-crystalline CaCuO2/CaCu2O3 thin films were deposited on quartz substrates using radio frequency (RF) magnetron sputtering and subsequent annealing. The deposition process was performed at room temperature under an oxygen partial pressure of 4 × 10−2 Pa at a speed of 2 Å/s. The crystalline structure, distribution of the particles and size of the elements of the as-prepared and CaCuO2/CaCu2O3 thin films were individually acquired and discussed in detail. Subsequent annealing was found to modify the composition, structure and morphological characteristics of the as-prepared thin film, resulting in changes of the film quality and, thereby, improving the nonlinear optical (NLO) response of the film. The sign and magnitude of third-order nonlinear susceptibility χ(3) of the as-prepared and CaCuO2/CaCu2O3 thin films were determined using the top-hat Z-scan technique performed at 532 nm with a laser duration of 190 fs. The results show that annealed CaCuO2/CaCu2O3 thin film exhibits a fast NLO response with a third-order nonlinear susceptibility χ(3) of 1.1 × 10−12 esu, which is higher than that of the as-prepared thin film. The results indicate that CaCuO2/CaCu2O3 thin films have potential applications in nonlinear optics.

Facile synthesis of a glass film containing Ca2CuO3 micro-crystals and exhibiting a third-order non-linear property

A two-step synthetic method was used to obtain a Pb glass film containing micro-crystalline Ca2CuO3 particles on a K9 glass substrate. The Ca2CuO3 micro-crystals were prepared for the first time by a high-temperature solid state method. The synthesized films were obtained on K9 glass substrates by screen-printing and co-sintering techniques, using Pb glass powder and Ca2CuO3 micro-crystals as reagents under different sintering temperatures. Secondly, micro-crystalline Ca2CuO3 Pb-glass films with different thickness were obtained by mechanical polishing for various times. The analysis of the surface structure, purity of the Ca2CuO3 phase and confirmation of the Pb-glass components in the given composites were provided by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The interactions between phonons and atoms of the micro-crystalline Ca2CuO3 particles embedded in the Pb-glass matrix were characterized by means of Raman scattering spectra. Moreover, the nonlinear optical property of the film was detected by a top-hat Z-scan technique with a laser duration of 190ns at 532nm. The results showed that the film polished for 120min exhibited a large third-order non-linear susceptibility χ(3) of 6.1×10−12esu, suggesting its potential application in all-optical switches and integrated electron devices.

Effect of the mismatch structure on crystal packing, physical properties and third-order nonlinearity of unsymmetrical twistacenes

A novel family of unsymmetrical twistacene analogues were synthesized in a palladium-promoted cross-coupling reaction and fully characterized, where five-membered ring was embedded into the main skeleton in these molecules. The formed all-carbon compounds appreciate a series of promising photophysical properties such as good thermal stability and photostability than that of acenes consisting of all six-membered rings. All of them emitted strong solution fluorescence covered a wide range from cyan to yellow. In addition, the nonlinear optical properties were further investigated through the top-hat Z-scan technique at 515 nm, which indicates that all of them presented excellent third-order nonlinear absorption effects.

Donor–acceptor molecules based on benzothiadiazole: Synthesis, X-ray crystal structures, linear and third-order nonlinear optical properties

Three π-conjugated donor–acceptor molecules containing either N,N-dimethylaniline or carbazole as the electron donor and 2,1,3-benzothiadiazole as the electron acceptor were synthesized through either Suzuki or Sonogashira cross-coupling reactions. Their X-ray crystal structural, optical, electrochemical properties were investigated. These compounds showed blue-shifted emission in the solid state compared with those in organic solvents. HOMO–LUMO gaps of these compounds estimated from cyclic voltammetry experiments correlated well with those obtained from theoretical calculation results. The nonlinear optical properties of the three D–A molecules were studied using the top-hat Z-scan technique with 21 ps laser pulses at 532 nm. The compound with N,N-dimethylaniline as the donor featuring a more planar configuration makes π-electrons more delocalized, which exhibited large third-order nonlinear absorption and refraction effect.

Aggregation-induced emission on benzothiadiazole dyads with large third-order optical nonlinearity

Two kinds of D-A molecular of (4-(4-(9H-carbazol-9-yl)phenyl))-7-nitrobenzothiadiazole (BSC) and 4-((4-(9H-carbazol-9-yl)phenyl)ethynyl)-7-nitrobenzothiadiazole (BEC) containing carbazole moieties as the donor were synthesized. X-ray crystal data elucidated the multiple intermolecular interactions. They exhibit distinctly different self-assembly behaviours. The nonlinear optical properties were studied using the top-hat Z-scan technique at 532 nm with a 21 ps pulse. The results indicate that they exhibit large third-order nonlinear absorption effects. The nonlinear absorption coefficients α2 fitting the experimental data are 6.3 × 10(-12) m W(-1) for BSC and 3.6 × 10(-11) m W(-1) for BEC. The time-resolved pump-probe results show that both nonlinear absorption and nonlinear refraction of BEC in CH2Cl2 solution have rapid optical responses, which indicate the nonlinear absorption and nonlinear refraction mechanism are excited-state nonlinear. Moreover, both of these two compounds are observed to be aggregation-induced emission (AIE) active. The aggregates of the well-formed one-dimensional microrods of BEC and BSC endow the material with potential applications in the field of optical devices.

Concentration-dependent nonlinear refraction in tetrasulfonated copper phthalocyanine solution

By using the Gaussian Z-scan technique, a transition from the self-focusing property to the self-defocusing property with a decrease in concentration under 11 ns pulse excitation in tetrasulfonated copper phthalocyanine (CuPcTs) dissolved in dimethyl sulfoxide (DMSO) is observed, which is due to the coexistence of excited-state refraction and transient thermal-lens effect. The nonlinear optical properties of a CuPcTs/DMSO solution are investigated by using the top-hat Z-scan technique under different laser pulse excitations with the same fluence at 532 nm. The mechanism of the optical nonlinearities for the solution is studied by using an improved picosecond time-resolved pump–probe technique which can simultaneously measure the dynamic nonlinear absorption and refraction conveniently. The experimental results are described very well by using a simple three-level model and the theory of the transient thermal refraction in liquids. The values for the excited-state absorption and refraction cross section are also obtained.

ABSORPTION, EMISSION AND NONLINEAR SPECTROSCOPIC CHARACTERIZATION OF REACTIVE DYE

An optical spectroscopic characterization is carried out on a reactive dye (reactive orange 1). This dye is widely applied in textile coloration. It is a potential candidate for photonics applications. Its absorption cross-section spectra are measured. A fluorescence spectroscopic characterization is undertaken by measuring the fluorescence quantum distributions and fluorescence quantum yields. The saturable absorption is studied by nonlinear transmission measurements with intense picosecond laser pulses (second harmonic pulses of a mode-locked Nd :glass laser). The nonlinear optical absorption and refraction coefficients are measured by using the top-hat Z-scan technique at a wavelength of 532 nm with 35 ps duration pulses. Reactive orange 1 has the two-photon absorption coefficient of 1.20 cm/GW and the nonlinear refraction coefficient of -7.33 × 10-6 cm2/GW, respectively. In reactive orange 1, there occurs fast ground-state recovery by internal conversion likely via conical intersections. Low excited-state absorption and fast ground-state absorption recovery make it an ideal candidate for passive mode-locking of picosecond and femtosecond lasers as well as for fast nonlinear optical gating.