Single beam Z-scan measurement of the third order optical nonlinearities of styryl7 dye

The optical nonlinearity of styryl7 dye in ethanol solution at different concentrations has been studied using pulsed Nd:YAG laser at 532 nm as the source of excitation. The optical responses were characterized by measuring the intensity dependent refractive index (n₂) of the medium using the Z-scan technique. The open aperture Z-scan trace of the dye in solution displayed saturable absorption. The closed aperture Z-scan trace of the dye exhibited a negative nonlinearity. The styryl7 dye at 1 mM concentration exhibited nonlinear refractive co-efficient n₂ = −1.24 × 10⁻⁸ cm²/W, nonlinear absorption coefficient β = − 3.9 × 10⁻⁴ cm/W and real and imaginary parts of third-order nonlinear optical susceptibility χ³ = 3.26 × 10⁻⁶ esu in ethanol. These results showed that the dye has potential application in nonlinear optics.     

Third-order nonlinear optical studies of new anthraquinone derivatives

Four new donor-acceptor-donor anthraquinone derivatives were synthesized and characterized by UV, IR, ¹H NMR and elemental analysis. Their off-resonant third-order nonlinear optical properties were measured using femtosecond laser and degenerate four-wave mixing technique. The third-order nonlinear optical susceptibilities χ⁽³⁾ were 3.36-3.76 × 10⁻¹³ esu. The nonlinear refractive indexes n₂ were 6.19-6.91 × 10⁻¹² esu. The second-order hyperpolarizabilities γ of the molecules were 3.36-3.76 × 10⁻³¹ esu. The response times were 101-115 fs. The results show that these compounds have potential nonlinear optical applications.     

Z-scan measurement for the nonlinear absorption and the nonlinear refraction of poly1,4-diazophenylene-bridged-tris(8-hydroxy-quinoline) aluminum (PDPAlq3)

The nonlinear optical properties of the poly1,4-diazophenylene-bridged-tris(8-hydroxy-quinoline) aluminum (PDPAlq₃) solution were studied using single beam Z-scan technique with a continuous-wave Diode laser radiation at 657.2 nm with 10 Hz repetition rate. The results show that the solution of PDPAlq₃ exhibits large nonlinear refractive index (n₂ = −1.7642 × 10⁻¹² m²/W) and nonlinear absorption coefficient (β = 1.12 × 10⁻⁶ m/W). The negative sign of the nonlinear refractive index n₂ indicates that the material exhibits self-defocusing optical nonlinearity. The evaluation of the figure of merit (W = 1.8) shows that the solution of PDPAlq₃ is sufficient for application in all-optical switching technology. These results show that the solution of PDPAlq₃ have potential application in nonlinear optics.     

χ measurement and optical limiting studies of urea picrate

The molecular charge complex urea picrate (UP) was synthesized and its third order nonlinear optical properties have been investigated using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data of the compound indicates two photon absorption at this wavelength. The nonlinear refractive index n₂, nonlinear absorption coefficient β, magnitude of effective third order susceptibility χ⁽³⁾, the second order hyperpolarizability γ_h and the coupling factor ρ have been estimated. The experimentally determined values of β, n₂, Re χ⁽³⁾ and Im χ⁽³⁾, γ_h and ρ of the compound UP are 2.146 cm/GW, −1.258×10⁻¹¹ esu, −1.347×10⁻¹³ esu, 0.377×10⁻¹³ esu, 0.69×10⁻³² esu and 0.28, respectively. The compound exhibits good optical limiting at 532 nm with the limiting threshold of 80 μJ/pulse. Our studies suggest that compound UP is a potential candidate for optical device applications such as optical limiters.     

Nonlinear optical properties of a D system in a spherical quantum dot

The nonlinear optical properties of a D⁻ system confined in a spherical quantum dot represented by a Gaussian confining potential are studied. The great advantage of our methodology is that the model potential possesses the finite height and range. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. We calculate the linear, third-order nonlinear and total optical absorption coefficients under the density matrix formalism. Numerical results for GaAs − Ga_1 − xAl_xAs QDs are presented. Our results show that the optical absorption coefficients in a spherical QD are much larger than their values for GaAs quantum wells. It is found that optical absorptions are strongly affected not only the confinement barrier height, dot radius, the electron-impurity interaction but also the position of the impurity.     

Photophysical and nonlinear optical properties of zincphthalocyanines with peripheral substitutions

Photophysical and nonlinear optical properties of zinc phthalocyanines (ZnPc) bearing peripheral phenoxy substituents containing different functionalized groups were studied. Fluorescence spectra corresponding to the optical transition S₁ → S₀ are found to be appeared at 684 or 686.4 nm. Z-scan technique reveals large nonlinearities, where the absorptive and refractive effects are separately evaluated. Saturation absorption of ZnPc-1 was observed at 632.8 nm, with a very large nonlinear absorption coefficient β = −1.36 × 10⁻² cm/W. However a strong nonlinear refractive effect was found in all ZnPcs (1-4). Transmitted versus incident irradiance measurements carried out on ZnPc-1 and ZnPc-2, showed a very clear optical limiting behavior with irradiance thresholds around be 44 W/cm² and 90 W/cm² respectively.     

3,3′-Benzene-1,4-diylbis[1-(substituted)phenylprop-2-en-1-one] derivatives: A new class of materials for third-order nonlinear optical applications

We have investigated the third-order nonlinear optical parameters of Bischalcones embedded in DMF solution and in solid PMMA matrix, by Z-scan technique using nanosecond laser pulse trains at 532 nm. Z-scan results reveal that the Bischalcones exhibits negative nonlinear refractive index as high as 10⁻¹¹ esu. The molecular two-photon absorption cross-section of Bischalcones were of the order 10⁻⁴⁶ cm⁴ s/photon, which is nearly two orders of magnitude larger than that of Rhodamine 6G which is 10⁻⁴⁸ - 10⁻⁵⁰ cm⁴ s/photon. We found that, the two-photon absorption (TPA) is the dominating nonlinear process leading to nonlinear absorption in both the cases in solution and as well as in solid medium. Based on TPA process, the Bischalcones exhibit good optical power limiting of nanosecond laser pulses at the input wavelength. The nonlinear optical parameters found to increase on enhancing the strength of the electron donor groups indicating the dependence and importance of electron donor/acceptor units on third-order nonlinear optical susceptibility χ⁽³⁾.     

Nonlinear optical studies of a newly synthesized copolymer containing oxadiazole and substituted thiophenes

We investigated the third-order nonlinear optical properties of a newly synthesized soluble copolymer containing oxadiazole and thiophene units 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 experiments. Z-scan results indicate a negative nonlinear refractive index, n₂, whose magnitude is of the order of 10⁻¹⁰ esu. The copolymer exhibits strong nonlinear absorption and good optical limiting properties at 532 nm, and hence may be a potential material for optical limiting applications.     

Investigation of third-order nonlinear optical properties of conjugated benzodioxal derivatives

An investigation of third-order nonlinear optical characterization of newly synthesized conjugated benzodioxal derivatives has been done by using nanosecond Z-scan technique at 532 nm. The molecules demonstrate self-defocusing effect with intensity dependent refractive index (n₂) of the order of 10⁻¹⁴ cm²/W. The measured molecular TPA cross-section is ranging from 2.47 ×10⁻⁴⁷ cm⁴ s/photon to 6.00 cm⁴ s/photon. Their input-output curves indicate that there is a clear optical power limiting behavior with the limiting threshold in the range 125-181 μJ. The main factor to exhibit the observed nonlinearity in these molecules is the presence of charge donor and acceptor groups. The increased conjugation length increases the nonlinear refraction and increased electron density enhances the nonlinear absorption. The molecules exhibit good nonlinear optical properties, comparable to those of regular azoaromatic compounds. Therefore, the molecules investigated here are promising candidates for optical power limiting devices.     

Nonlinear optical properties of periodic gold nanoparticle arrays

Periodic Au nanoparticle arrays were fabricated on silica substrates using nanosphere lithography. The identical single-layer masks were prepared by self-assembly of polystyrene nanospheres with radius R = 350 nm. The structural characterization of nanosphere masks and periodic particle arrays was investigated by atomic force microscopy. The nonlinear optical properties of the Au nanoparticle arrays were determined using a single beam z-scan method at a wavelength of 532 nm with laser duration of 55 ps. The results show that periodic Au nanoparticle arrays exhibit a fast third-order nonlinear optical response with the nonlinear refractive index and nonlinear absorption coefficient being n₂ = 6.09 × 10⁻⁶ cm²/kW and β = −1.87 × 10⁻⁶ m/W, respectively.     

Nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer

The nonlinear optical properties and photoinduced anisotropy of an azobenzene ionic liquid-crystalline polymer were investigated. The single beam Z-scan measurement showed the polymer film possessed a value of nonlinear refractive index n₂ = −1.07 × 10⁻⁹ cm²/W under a picosecond 532 nm excitation. Photoinduced anisotropy in the polymer was studied through dichroism and photoinduced birefringence. A photoinduced birefringence value Δn ∼ 10⁻² was achieved in the polymer film. The mechanism for the nonlinear optical response and the physical process of photoinduced anisotropy in the polymer were discussed.     

Third-order optical nonlinearity of (Ba0.7Sr0.3)TiO3 ferroelectric thin films fabricated by soft solution processing

(Ba_0.7Sr_0.3)TiO₃ (BST) ferroelectric thin films with perovskite crystal structure were fabricated by soft solution processing on a quartz substrate. The third-order nonlinear optical properties were investigated by using Z-scan technique. Positive nonlinear refractive index and nonlinear absorption coefficient were determined to be 4×10⁻⁷ esu and 1.2×10⁻⁶ m/w, respectively. The real part and imaginary part of third-order optical nonlinear susceptibility were calculated and the values were 6.43×10⁻⁸ and 5.14×10⁻⁸ esu, respectively. All of these results show ferroelectric BST thin film is promising for applications in nonlinear optical devices.     

Femtosecond Z-scan measurement of third-order optical nonlinearities in anatase TiO2 thin films

Anatase phase TiO₂ films have been grown on fused silica substrate by pulsed laser deposition technique at substrate temperature of 750 °C under the oxygen pressure of 5 Pa. From the transmission spectra, the optical band gap and linear refractive index of the TiO₂ films were determined. The third-order optical nonlinearities of the films were measured by Z-scan method using a femtosecond laser (50 fs) at the wavelength of 800 nm. The real and imaginary parts of third-order nonlinear susceptibility χ⁽³⁾ were determined to be −7.1 × 10⁻¹¹esu and −4.42 × 10⁻¹²esu, respectively. The figure of merit, T, defined by T=βλ/n₂, was calculated to be 0.8, which meets the requirement of all-optical switching devices. The results show that the anatase TiO₂ films have great potential applications for nonlinear optical devices.     

Diagnostic study of the roughness surface effect of zirconium on the third-order nonlinear-optical properties of thin films based on zinc oxide nanomaterials

Zinc oxide (ZnO) and zirconium doped zinc oxide (ZnO:Zr) thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 500 °C using zinc and zirconium chlorides as precursors. Effects of zirconium doping agent and surface roughness on the nonlinear optical properties were investigated in detail using atomic force microscopy (AFM) and third harmonic generation (THG) technique. The best value of nonlinear optical susceptibility χ⁽³⁾ was obtained from the doped films with less roughness. A strong third order nonlinear optical susceptibility χ⁽³⁾ = 20.12 × 10⁻¹² (esu) of the studied films was found for the 3% doped sample.     

Preparation and the optical nonlinearity of surface chemistry improved titania nanoparticles in poly(methyl methacrylate)-titania hybrid thin films

With 800-nm, 120-fs laser pulses, optical nonlinearity has been studied in a series of thin films containing poly(methyl methacrylate) (PMMA), filled with surfactant acetylacetone (Acac) capped TiO₂ nanoparticles, which were synthesized by a simple in situ sol-gel/polymerization process, assisted by spin coating and multi-step baking. The resulting nanohybrid thin films have highly optical transparency and demonstrate a unique nonlinear optical (NLO) response. The highest nonlinear refractive index (n₂) is observed up to 6.55 × 10⁻² cm² GW⁻¹ in the nanohybrid thin film of 60 wt% Ti(OBu)₄ in PMMA, with a negligible two-photon absorption (TPA), as confirmed by the Z-scan technique. The titanium precursor loading combined with the nature of the capping molecules are used to influence the ability of nanoparticles to nonlinear optical response. Indeed, the ligands at the nanoparticles’ surface can not only control the extent of the interaction between the organic molecules and the embedded nanoparticles but also influence the optical nonlinearities of nanoparticles.     

Synthesis and nonlinear optical characterization of SnO2 quantum dots

The present paper demonstrates the preparation and characterization of SnO₂ semiconductor quantum dots. Extremely small ∼1.1 and ∼1.4 nm SnO₂ samples were prepared by microwave assisted technique with a frequency of 2450 MHz. Based on XRD analysis, the phase, crystal structure and purity of the SnO₂ samples are determined. UV-vis measurements showed that, for the both size of SnO₂ samples, excitonic peaks are obtained at ∼238 and ∼245 nm corresponding to ∼1.1 nm (sample 1) and ∼1.4 nm (sample 2) sizes, respectively. STM analysis showed that, the quantum dots are spherical shaped and highly monodispersed. At first, the linear absorption coefficients for two different sizes of SnO₂ quantum dots were measured by employing a CW He-Ne laser at 632.8 nm and were obtained about 1.385 and 4.175 cm⁻¹, respectively. Furthermore, the nonlinear refractive index, n₂, and nonlinear absorption coefficient, β, were measured using close and open aperture Z-scan respectively using the same laser. As quantum dots have strong absorption coefficient to obtain purely effective n₂, we divided the closed aperture transmittance by the corresponding open aperture in the same incident beam intensity. The nonlinear refraction indices of these quantum dots were measured in order of 10⁻⁷ (cm²/W) with negative sign and the nonlinear absorption coefficients were obtained for both in order of 10⁻³ (cm/W) with positive sign.     

A study of nonlinear optical properties of a negative donor quantum dot

In this paper, we studied the nonlinear optical properties of a negative donor center (D⁻) in a disk-like quantum dot (QD) with a Gaussian confining potential. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A detailed investigation of the linear, third-order nonlinear, total optical absorptions and refractive index changes has been carried out for the D⁻ QD and the D⁰ QD. The linear, third-order nonlinear, total optical absorptions and refractive indices have been examined for a double-electron QD with and without impurity. Our results show that the optical absorption coefficients and refractive indices in a disk-like QD are much larger than their values for quantum wells and spherical QDs and the nonlinear optical properties of QDs are strongly affected not only with the confinement barrier height, dot radius, the number of electrons but also the electron-impurity interaction.     

Synthesis and third-order optical nonlinearities of nickel complexes of 8-hydroxyquinoline derivatives

A nickel complex of 5-(acrylamido)methyl-8-hydroxyquinoline, bis-(5-(acrylamido)methyl-8-hydroxyquinolino) nickel(II) (Ni(AAMQ)₂) has been synthesized and its third-order nonlinear optical properties was investigated with respect to that of bis-(8-hydroxyquinolino) nickel(II) (NiQ₂) by single beam Z-scan technique. The real parts (γ_R) of the molecular second-order hyperpolarizabilities were −6.0 × 10⁻⁴⁶ and −5.5 × 10⁻⁴⁶ m⁵/v² for NiQ₂ and Ni(AAMQ)₂, respectively, indicative of similar nonlinear refraction both in sign and in magnitude. After substitution of an acrylamidomethyl group to the 8-hydroxyquinoline (8-HQ) ligand, the nonlinear absorption coefficient of Ni(AAMQ)₂ was enhanced by more than two times. The corresponding imaginary part (γ_I) of the molecular second-order hyperpolarizability was 3.4 × 10⁻⁴⁶ m⁵/v² for Ni(AAMQ)₂ while 1.6 × 10⁻⁴⁶ m⁵/v² for NiQ₂. The increase in nonlinear absorption was attributed to the substitution effect and the enhanced transition dipole moment due to the participation of δ-donor group of CH₂ in the molecular conjugation.     

Method for measurements of second-order nonlinear optical coefficient based on Z-scan

The method for measuring second-order nonlinear optical coefficients based on well-known Z-scan is presented. The influence of linear absorption coefficients on normalized transmittance is discussed. Using this method, we obtained the second-order nonlinear coefficient d₃₁(5%MgO:LiNbO₃) = 4.5 × 10⁻¹² m/v at 1064 nm, which agrees well with theoretical calculations and previous well-known values.     

Nonlinear refraction and photoinduced birefringence in chlorophosphonazo I doped polymer thin films

The nonlinear refraction and photoinduced birefringence of chlorophosphonazo I (CPA I ) doped PVA thin films were investigated. The single-beam Z-scan measurement showed that CPA I doped PVA thin film possessed a large value of nonlinear refractive index (n₂=1.82×10⁻¹² cm²/W) under a pulse 532 nm excitation, and the mechanism accounting for the process of nonlinear refraction was discussed in term of resonant electronic effect. Moreover, fast and stable molecular reorientation was observed when investigating the photoinduced birefringence of CPA I doped PVA thin film with a CW 532 nm laser as pump light and a CW 650 nm laser as probe light.