Negative Nonlinear Refraction Research Articles

Nonlinear properties of polyurethane-urea/multi-wall carbon nanotube composite films

The third-order nonlinear optical properties of polyurethane-urea/multiwalled carbon nanotube composites (PU/MWNT) films with different MWNT concentrations are investigated by the use of the Z-scan technique at a wavelength of 532 nm with a pulse duration of 8 ns. The results reveal that the nonlinear refraction and absorption coefficients are linearly dependent on the MWNT concentration. The negative nonlinear refraction effect is validated from the closed-aperture Z-scan measurements. We find that PU/MWNT films are promising nonlinear optical materials, and the nonlinear coefficients can be controlled.

The nonlinear optical response of a fluorine-containing azoic dye

The nonlinear optical nonlinearities of a fluorine-containing azoic dye in tetrahydrofuran have been investigated by using Z-scan technique with picosecond and nanosecond lasers. The experimental results reveal that the azoic dye has large optical nonlinearity under the excitations of picosecond and nanosecond 532 nm. At the picosecond 532 nm the solution presents negative nonlinear refraction due to the electronic effect, while the larger nonlinear refraction under nanosecond laser excitation is induced by thermal effect. Moreover, the different nonlinear absorption behavior under picosecond and nanosecond excitations is analyzed.

Mesoscale Self-Assembly of Highly Luminescent Zinc Tellurite Nanoclusters

Zinc tellurite (ZnTeO3 or ZTO) nanoclusters synthesized in aqueous medium from zinc acetate and sodium tellurite are amorphous in nature and exhibit intense photoluminescence when excited at the UV region. These nanoclusters assembled in two different compositions with different morphologies by refluxing in water, depending on the pH of the refluxing medium. At pH 5.5, the ZTO transformed to a crystalline phase with rod-like morphology. At pH 4.5, crystalline Zn2Te3O8 resulted and the as-obtained nanoplates of this compound self-assembled in oval-shaped microstructures. On further decreasing the pH to 3.5, the nanoplates self-assembled to rose-like patterns (nanorose). Very big microspheres and a mixture of microcrystals were formed on further reduction of pH to 3. Interestingly, all the crystalline products with different morphologies display luminescence properties. Further, these new materials exhibit three-photon absorption with positive third-order and negative fifth-order nonlinear refraction.

Ultrafast Switching Time and Third Order Nonlinear Coefficients of Microwave Treated Single Walled Carbon Nanotube Suspensions

Microwave treated water soluble and amide functionalized single walled carbon nanotubes have been investigated using femtosecond degenerate pump-probe and nonlinear transmission experiments. The time resolved differential transmission using 75 femtosecond pulse with the central wavelength of 790 nm shows a bi-exponential ultrafast photo-bleaching with time constants of 160 fs (130 fs) and 920 fs (300 fs) for water soluble (amide functionalized) nanotubes. Open and closed aperture z-scans show saturation absorption and positive (negative) nonlinear refraction for water soluble (amide functionalized) nanotubes. Two photon absorption coefficient, beta0 approximately 250 cm/GW (650 cm/GW) and nonlinear index, gamma approximately 15 cm2/pW (-30 cm2/pW) are obtained from the theoretical fit in the saturation limit to the data for two types of nanotubes.

Large Third-Order Optical Nonlinearity of Cadmium Sulphide Nanoparticles Embedded in Polymer Thin Films

A simple method for synthesis of well dispersed cadmium sulphide nanoparticles embedded in a polyethylene glycol matrix (PEG 400) in thin film form is presented. The large blue shift of the band gap energy of the CdS nanoparticles compared to the bulk semiconductors is observed via UV-vis absorption spectra. Photoluminescence spectra of CdS nanocomposite films show that the emission peaks shift towards the longer wavelength with the increase of annealing temperature. Transmission electron microscopic images as well as Raman scattering studies confirm the CdS nanometer size particle formation within the polymer matrix. The particle size is about 8 nm. Selected area electron diffraction (SAED) shows the cubic zinc blende polycrystalline rings. Third-order optical nonlinearity of the CdS nanoparticles embedded in polymer thin films is studied with the Z-scan technique under 1064 nm excitation. The results show that the CdS nanocomposite film exhibits negative nonlinear refraction index and positive absorption coefficient. The film shows large optical nonlinearity, and the magnitude of the third-order nonlinear susceptibility of the film is calculated to be 1.73 × 10−9 esu. The corresponding mechanism is discussed.

Nonlinear optical studies on 1,3-disubstituent chalcones doped polymer films

We report the measurements of the third-order nonlinear optical properties of recently synthesized and characterized two different 1,3-disubstituent chalcones doped PMMA films, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nanosecond Z-scan at 532 nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n 2 of the order 10 −11 esu and the molecular two photon absorption cross section is 10 −46 cm 4 s/photon. The doped films exhibit good optical power limiting property under nanosecond regime and the two photon absorption (TPA) is the dominating process leading to the nonlinear behavior. The improvement in the nonlinear properties has been observed when methylenedioxy group is replaced by dimethoxy group due to increase in conjugation length. The observed nonlinear parameters of chalcone derivatives doped PMMA film is comparable with stilbazolieum derivatives, a well-known class of optical materials for photonics and biophotonics applications, which suggests that, these moieties have potential for the application of all-optical limiting and switching devices.

Third‐order nonlinear optical properties and two‐photon absorption in polymers doped with p‐phenyl sydnone

AbstractWe report the measurements of the third‐order susceptibilities and two‐photon absorption in three different polymers doped with p‐phenyl sydnone moiety viz., 2‐benzylhydrazono‐5‐(3‐p‐tolylsydnone‐4‐yl)1,3,4,‐thiadiazine, which is recently synthesized and characterized, with the prospective of reaching a good compromise between processability and high nonlinear optical properties. The measurements were done using nano second Z‐scan at 532nm. The Z‐scan spectra reveal a large negative nonlinear refraction coefficient n2 of the order 10−14 cm2/W and a two‐photon absorption β, which is determined to be the order of cm/GW. The absorption cross section is 10−46 cm4 s/photon. The molecular second‐order hyperpolarizability in PMMA matrix was calculated to be 1.47 × 10−31 esu, comparable with stilbazolieum derivatives, a well‐known class of optical materials for photonics and biophotonics applications. The chromophore shows its optical power limiting behavior in all the three polymer matrices. All these results suggest that this moiety has potential for the application of all‐optical limiting and switching devices. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

THIRD-ORDER NONLINEAR OPTICAL PROPERTIES OF [(C2H5)4N][Co(dmit)2] USING Z-SCAN TECHNIQUE

A novel dmit 2- complex: [( C 2 H 5)4 N][Co(dmit) 2], abbreviated as EtCo , was synthesized and its third-order optical nonlinearities were characterized by Z-scan technique at the wavelength of 1064 nm with laser duration of 40 ps. Z-scan curves revealed a negative nonlinear refraction at 1064 nm and a positive absorption was observed. The nonlinear refraction coefficient n2, the nonlinear absorption coefficient β and the molecular second hyperpolarizability γ have been determined to be as large as 9.51×10-19 m 2/ W , 2.19×10-12 m/W and 5.41×10-31 esu respectively, suggesting that this material has potential applications in optical limiting.

Excited-State Absorption and Sign Tuning of Nonlinear Refraction in Porphyrin Derivatives

The nonlinear absorptions and nonlinear refractions of free-base porphyrin (P2) and Zn-porphyrin (ZnP2) were studied using the Z-scan technique at 532 nm with different pulse durations. Both P2 and ZnP2 exhibit reverse saturated absorption attributed to excited-state absorption. The coordination of P2 by Zn ion can alter the nonlinear refraction sign from negative to positive at 4 ns pulse. The results indicate that the sign of self-lensing can be tuned by the coordination of Zn in the porphyrin derivatives. In the case of longer pulse duration, the thermal effect was enhanced to dominate the nonlinear refraction sign, leading to the negative nonlinear refraction repeated appearance.

Third-order optical nonlinearity of a novel material: [(C4H9)4N][Co(dmit)2

A novel dmit organometallic complex—[(C4H9)4N][Co(dmit)2] (dmit2− = 4,5-dithiolate-1,3-dithiole-2-thione), abbreviated as BuCo, is synthesized and its third-order optical nonlinearity of the acetone solution is characterized using the Z-scan technique with a 40-ps pulse width at 1064 nm. Z-scan curves show that BuCo sample solution possesses the negative nonlinear refraction, exhibiting a self-defocusing effect. In addition, the two-photon absorption has been observed in BuCo. The effective molecular second-order hyperpolarizability γeff of the BuCo molecule was estimated to be as large as 5.60 × 10−31 esu, suggesting BuCo is a potential material for optical device applications.

Nonlinear optical response of silicon nanocrystals

Experimental results are presented related to the nonlinear optical response of silicon nanocrystals under visible nsec laser excitation. The nanocrystals were examined in water and glycerol suspensions and as was shown, they exhibit saturable absorption and negative nonlinear refraction. Finally, in the case of the glycerol suspensions and under sufficiently high incident intensity, the formation of bubbles was found to cause a serious modification of the sample’s transmission.

Negative nonlinear refraction obtained with ultrashort laser pulses

We present nonlinear refraction results for liquids methanol and acetic acid obtained with the Z-scan technique and 28 femtosecond (fs) 800 nm laser pulses. In contrast to the positive lensing effect obtained previously with picosecond and nanosecond laser pulses, a negative lensing effect is observed. The associated mechanism features the third-order polarization arising from the nonlinear response of the molecular skeletal motion that is driven into resonance through its electrostatic coupling to the valence electron cloud distorted by the fs laser field.

Third-order non-linear optical properties of tetra- n-propylammonium bis (4,5-dithiolato-1,3-dithiole-2-thione) nickel (III)

Tetra- n-propylammonium bis (4,5-dithiolato-1,3-dithiole-2-thione) nickel(III) was synthesized and its third-order optical non-linearity was characterized using Z-scan technique with 40 ps laser pulse at 1064 nm. The Z-scan curves have revealed that the complex exhibits a typical saturable absorption ( β=−4.3±0.3×10 −12 m/W) and a negative non-linear refraction ( n 2 =−2.7±0.2×10 −18 m 2/W). The molecular second-order hyperpolarizability γ was calculated to be 1.5×10 −30 esu. These relatively large non-linear optical properties of the complex may have much to do with its special π-electron structure.

Synthesis and optical properties of ZnSe∕95SiO2–5B2O3 nanocomposites by sol-gel method

Zn Se ∕ 95 Si O 2 – 5 B 2 O 3 nanocomposites were prepared by a sol-gel method and in situ growth technique. X-ray diffraction patterns showed the typical interplanar spacing corresponding to the cubic phase of ZnSe. Transmission electron microscopy studies indicated that an average particle size of the ZnSe nanocrystals is around 5.0nm. UV-visible spectroscopy was carried out to determine the band gap of the ZnSe nanocrystals and a blueshift was observed as compared to that of the ZnSe bulk materials. A single-beam Z-scan measurement showed that the nanocomposites have two-photon absorption (TPA) and a negative nonlinear refraction at the wavelength of 532nm; the TPA coefficient β and the nonlinear refractive index n2 are 19.94cm∕GW and 1.0×10−10esu, respectively. The nonlinearity of the nanocomposites is higher than that of the ZnSe bulk materials due to special surface structure and high surface activity of the ZnSe nanocrystals.

Nonlinear optical properties of [(CH 3 ) 4 N]Au(dmit) 2 using Z -scan technique

The third-order optical nonlinearities of [(CH3)4N]Au(dmit)2 (dmit = 4,5-dithiolate-1,3-dithiole-2-thione) at 532 nm and 1064 nm are investigated using the Z-scan technique with pulses of picoseconds duration. The Z-scan spectra reveal a strong nonlinear absorption (reverse saturable absorption) and a negative nonlinear refraction at 532 nm. No nonlinear absorption is observed at 1064 nm. The molecular second-order hyperpolarizability γ for the [(CH3)4N]Au(dmit)2 molecule at 532 nm is estimated to be as high as (2.1 ± 0.1) × 10−31 esu, which is nearly three times larger than that at 1064 nm. The mechanism responsible for the difference between the results is analysed. Nonlinear transmission measurements suggest that this material has potential applications in optical limiting.

Study on nonlinear optical properties of two novel dmit2− salts by Z-scan technique

Two novel dmit2− salts: [C16H33(CH3)3N]Co(dmit)2 and [C16H33(CH3)3N]Ni(dmit)2 (abbreviated as CTCo and CTNi, respectively, and dmit2−=4,5-dithiolate-1,3-dithiole-2-thione), are synthesized and their third-order optical nonlinearities of the acetone solutions are investigated using Z-scan technique with 40ps pulse width at 1064nm. The Z-scan spectra reveal both CTCo and CTNi sample solutions possess large negative nonlinear refraction, exhibiting a self-defocusing effect. In addition, slight two-photo absorption and strong saturable absorption have been found in CTCo and CTNi, respectively. The molecular second-order hyperpolarizability γeff of the CTNi molecule was estimated to be as high as (−4.6±0.2)×10−30esu, which was four times larger than that of CTCo. An explanation for this enhancement is given. All the results suggest that these materials may have potential applications in the field of nonlinear optics.

Nonlinear optical characteristics of carbon disulfide

The nonlinear refractive index γ of CS2 is studied using laser pulses of various durations (from 110 fs to 75 ns). It is found that γ increases with increasing pulse duration within the picosecond region (from (3 ± 0.6) × 10−15 cm2 W−1 at 110 fs to (3.5 ± 0.7) × 10−14 cm2 W−1 at 75 ns) due to orientational nonlinearities. Variations in the sign of γ caused by the thermal effect at different pulse durations and repetition rates are analyzed. It is demonstrated that the fast electronic component, the component associated with molecular processes, causing positive nonlinear refraction, and the acoustic component, responsible for negative nonlinear refraction, manifest themselves simultaneously. The results of a study of the nonlinear absorption of carbon disulfide are presented. The two-and three-photon absorption coefficients of CS2 are determined to be (5 ± 1.5) × 10−11 cm W−1 and (2.8 ± 0.8) × 10−23 cm3 W−2, respectively.

Third-order nonlinear optical properties of bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper

Bis(tetrabutylammonium)bis(4,5-dithiolato-1,3-dithiole-2-thione)copper (BCDT) was synthesized and its third-order optical nonlinearity was characterized using picosecond Z-scan at 1064 nm. The Z-scan spectra reveal a large negative nonlinear refraction coefficient n 2 as high as 4.0 × 10 −18 m 2/W and a slight two-photon absorption β, which is determined to be 3.4 × 10 −12 m/W. The molecular second-order hyperpolarizability γ was calculated to be 6.5 × 10 −32 esu. All these results suggest that this material has potential for the application of all-optical switching.

Nonlinear optical properties in SrTiO 3 thin films by pulsed laser deposition

Well-crystallized 250 nm-thick SrTiO 3 thin films on fused-quartz substrate were prepared by pulsed laser deposition. The band-gap of SrTiO 3 thin film by transmittance spectra is equal to 3.50 eV, larger than 3.22 eV for the bulk crystal. The nonlinear optical properties of the films were examined with picosecond pulses at 1.064 μm excitation. A large two-photon absorption (TPA) with absorption coefficient of 87.7 cm/GW was obtained, larger than 51.7 cm/GW for BaTiO 3 thin films. The nonlinear refractive index n 2 is equal to 5.7×10 −10 esu with a negative sign, larger than 0.267×10 −11 esu for bulk SrTiO 3. The large TPA is attributed to intermediate energy levels introduced by the grain boundaries, and the optical limiting behaviors stemming from both TPA and negative nonlinear refraction were also discussed.

Third-order nonlinearities of Bi12GeO20 crystal measured by nanosecond radiation

Negative nonlinear refraction is observed in the photorefractive crystal Bi12GeO20 (BGO) using 7-ns, 532-nm pulsed radiation. The nonlinear refractive index of BGO is measured to be γ=−3.8×10−13cm2W−1 using the z-scan technique. The self-defocusing of nanosecond pulses is attributed to the appearance of free carriers generated from defects, donors, and interband transitions. The nonlinear losses caused by two-photon absorption and self-scattering from dynamic grating are discussed. The nonlinear absorption coefficient is measured to be β=3.8×10−8cmW−1. Moreover, a variation of γ and β with intensity is observed. The comparison with self-focusing and two-photon absorption previously measured using 55-ps pulses is discussed.