Nonlinear Reverse Saturable Absorption Research Articles

Electro-Induced Phase Transformation of a Conductive Metal-Organic Framework Film for Nonlinear Optical Switching.

Achieving metal-organic frameworks (MOFs) with nonlinear optical (NLO) switching is profoundly important. Herein, the conductive MOFs Cu-TCNQ phase I (Ph-I) and phase II (Ph-II) films were prepared using the liquid-phase-epitaxial layer-by-layer spin-coating method and steam heating method, respectively. Electronic experiments showed that the Ph-II film could be changed into the Ph-I film under an applied electric field. The third-order NLO results revealed that the Ph-I film had a third-order nonlinear reverse saturation absorption (RSA) response and the Ph-II film displayed a third-order nonlinear saturation absorption (SA) response. With increases in the heating time and applied voltage, the third-order NLO response realized the reversible transition between SA and RSA. The theoretical calculations indicated that Ph-I possessed more interlayer charge transfer, resulting in a third-order nonlinear RSA response that was stronger than that of Ph-II. This work applies phase-transformed MOFs to third-order NLO switching and provides new insights into the nonlinear photoelectric applications of MOFs.

Using femtosecond laser pulses to explore the nonlinear optical properties of a CR-39 polymer after being exposed to alpha particles

The effect of alpha particle radiation on nonlinear optical properties of poly(allyl diglycol carbonate) (CR-39) polymer has been investigated using the Z-scan technique. CR-39 polymers were exposed to alpha particles at different doses: 23.7 and 47.5 Gy. Alpha particles cause significant optical and chemical changes in the polymer CR-39. Data from UV-visible spectrometers revealed that when alpha particle doses increased, the absorption edge of polymer redshifted and the energy band gap decreased. Fourier transform infrared absorption spectra of alpha irradiation samples show a change in intensity and bond breakage in the chemical groups constituting the CR-39 polymer compared to the pristine one. With 100 fs laser pulses and 80 MHz repetition rate, the nonlinear absorption coefficient and nonlinear refractive index are measured for a pristine and irradiated polymer with different alpha doses at different excitation wavelengths and laser peak power. The samples displayed a negative nonlinear refractive index and reverse saturable absorption behavior with three photons absorption. The results reveal that the nonlinear optical properties of CR-39 were enhanced by alpha particle radiation.

Phthalocyanine covalent frameworks doped in PMMA matrix as high performance nonlinear optical limiter

Phthalocyanine compounds are a class of macrocyclic conjugated structures with 18 π-electrons. And have better photophysical properties. However, the π-π electron interactions lead to aggregation between phthalocyanine molecules, which affects optical limiting properties. In this work, the conjugated organic small molecule antiphenylenediamine (PDA) is grafted onto the phthalocyanine conjugate system through the azo condensation reaction, and the covalent organic framework polymer (PDA-InPc) was obtained. Then it is doped into the polymethyl methylmethacrylate (PMMA) matrix to produce a phthalocyanine solid device with different thickness (PMMA-PDA-InPc). The aggregation-free phthalocyanine covalent organic frameworks avoids intramolecular aggregation of the phthalocyanine units, and dispersing it in PMMA solid devices can also reduce intermolecular π-π stacking. As a result, the fluorescence lifetime of PMMA-PDA-InPc is τ1 = 0.52 ns (A1 = 95.71%) and τ2 = 11.5 ns (A2 = 4.29%), indicating that the phthalocyanine conjugated unit exists mainly as monomers (95.71%), while the proportion as aggregates is very small (4.29%). At the input laser energy of 9 μJ, the nonlinear absorption coefficient of PMMA-PDA-InPc device is (2.2 × 10−9 m/W), which is significantly better than PMMA-InPc device (1.0 × 10−9 m/W), indicating that PMMA-PDA-InPc has improved nonlinear absorption and reverse saturation absorption. This design idea of non-aggregated phthalocyanine covalent organic frameworks and its solid device expands a new idea for the development of useable phthalocyanine optical limiters.

Preparation and third order nonlinear optical properties of corrole functionalized GO nanohybrids

Three novel corroles, 5,15-bis(phenyl)-10-(3-methoxy-4-hydroxylphenyl)- corrole PC, 5,15-bis(naphthyl)-10-(3-methoxy-4-hydroxylphenyl)-corrole NAPC and 5,15-bis(pyrenyl)-10-(3-methoxy-4-hydroxylphenyl)-corrole PYPC, were designed and synthesized. Their graphene oxide (GO) nanohybrids, PC-GO, NAPC-GO and PYPC-GO, were prepared by a covalent functionalization method and characterized by various spectroscopic techniques. The third order nonlinear optical (NLO) behavior of the corroles and their corresponding nanohybrids was investigated using open aperture Z-scan technique at 532 nm with 4 ns laser pulses. The nanohybrids showed enhanced NLO properties in comparison to the corresponding corroles. In addition, the NLO properties of nanohybrids increase in the order of NAPC-GO < PC-GO < PYPC-GO, while the corrole molecules exhibit NLO performance in the same order of NAPC < PC < PYPC, implying the NLO response originating from the corrole moiety play a more important role in the NLO properties of the nanohybrids than that arising from the photo-induced electron or energy transfer process between GO and corrole molecules. Importantly, at same transmission intensity, all the corroles showed typical nonlinear reverse saturation absorption (RSA) behavior, while all the nanohybrids exhibited a flip over behavior from saturation absorption (SA) to RSA. The different NLO response between the corrole molecules and their nanohybrids implies their promising applications as NLO materials.

Low-order optical nonlinearities of PbS quantum dot liquids and films

We demonstrate the variations of the nonlinear optical parameters in the suspensions and thin films containing PbS quantum dots of different sizes (9 and 2.5 nm). We show that these colloidal quantum dots possess the thermal-lens induced negative nonlinear refraction and reverse saturable absorption in the case of the 532-nm, 10-ns probe pulses. The larger nonlinear absorption coefficients of 9-nm quantum dots compared with 2.5-nm species (1 × 10−7 and 8 × 10−9 cm W−1, respectively) in the case of 1064 nm, 10 ns probe pulses were determined. Similar relations between the nonlinear optical parameters of 9- and 2.5-nm species were maintained in the case of twice shorter wavelength (532 nm) of the probe pulses. The almost ten-fold growth of the nonlinear optical parameters in the visible range compared with the near infrared region was attributed to the stronger influence of the excitonic states on the propagation effects in the former case. We show that the thin films containing these quantum dots demonstrate saturable absorption, while the suspensions show mostly the reverse saturable absorption at 532 nm. A significant enhancement of the nonlinear refractive index of films compared with suspensions (−2 × 10−8 cm2 W−1 and -1 × 10−11 cm2 W−1), as well as a large negative nonlinear absorption coefficient (−3.2 × 10−5 cm W−1) in the former case are demonstrated. We discuss the signs of nonlinear refraction and nonlinear absorption of the quantum dots, as well as the role of the sizes of these species in variations of the nonlinear parameters.

Photoluminescence characterizations and nonlinear optical of PM-355 nuclear track detector film by alpha-particles and laser irradiation

The imaging processing technique was used for studying a laser beam nature that transmitted through films of PM-355. The thermal nonlinearity of PM-355 films was studied using a 635 nm cw diode laser at 15 mW as the source of excitation. Third order nonlinear optical properties of PM-355 films irradiated with α-particles at different times and pristine sample has been studied using Z-scan technique. The samples showed a negative and large nonlinear refractive index and reverse saturable absorption (RSA) with high values of the nonlinear absorption coefficient. The fluorescence spectra of PM-355 films were investigated at room temperature and wavelength range of 250–500 nm for a pristine film and in different times of exposure to α-particles. The broad peaks were between 350, 420 and 465 nm. All-optical switching property of PM-355 samples irradiated with α-particles at 20 min was also studied using the standard pump-probe technique.

Label-free superresolution effect of nonlinear reverse saturation absorption thin films through difference method.

Label-free superresolution effect of nonlinear reverse saturation absorption (NRSA) thin films was investigated through difference method, where a subdiffraction-limit spot signal was constructed by intensity subtraction of two spots obtained under different laser intensities. By using annealed InSb films as the NRSA thin films, we experimentally obtained the subdiffraction-limit spot signal, and the optimal reduction ratio was approximately 52.5% of the original spot. Experimental resultsagreedwell with theoretical simulations. The simulation results of a 9-point array sample showed the capability to achieve nonfluorescence superresolution imaging using the NRSA effect.

Comprehensive study on the nonlinear optical properties of few-layered MoSe2 nanosheets at 1 μm

The few-layered molybdenum diselenide (MoSe2) nanosheets were synthesized by the simple and low-cost ultrasonic-assisted liquid phase exfoliation (UALPE) method. The high quality of the two-dimensional nanostructures was verified by comprehensive characterization. The nonlinear optical properties including nonlinear absorption and refraction of the MoSe2 nanosheets were investigated by utilizing the open- and closed-aperture Z-scan technique. The MoSe2 nanosheets exhibits excellent nonlinear saturable and reverse saturable absorption for nanosecond laser pulses at 1 μm. The two photon absorption (TPA) coefficient, nonlinear refractive index n2, real and imaginary parts of the third-order nonlinear optical susceptibility were determined as 2.7 cm/MW, 2 × 10−4 cm2/GW, 8.2 × 10−12 esu and 1.61 × 10−12 esu, respectively. Finally, the passively Q-switched Nd:CNGG laser with MoSe2 saturable absorber at 1.06 μm was realized for the first time, showing the excellent satuable absorption properties.

Nonlinear optical switching behavior of nitrogen-doped carbon dots

Carbon dots (CDs), as an emerging class of carbon materials, have been recently demonstrated to possess nonlinear optical (NLO) behavior (e.g. nonlinear saturable absorption and reverse saturable absorption) which potentially expands CDs new application in optical limiting field. However, NLO switching behavior of CDs has not yet been reported in previous literature. In this paper, nitrogen-doped CDs (N-CDs) prepared from 2,3-diaminophenazine showed a switchable NLO behavior from saturable absorption (SA) to reverse saturable absorption (RSA) when the laser energy of incident picosecond pulse increased. By contrast, upon the irradiation of nanosecond pulse, the N-CDs exhibited only RSA behavior through excited state absorption (ESA) process. In mechanism, the switching behavior was probably resulted from competition between ground-state absorption and free carrier absorption (FCA) or two phonon absorption (TPA) processes, where both nitrogen doping and carbonyl groups of N-CDs were proved to be indispensable for the switching behavior.

Nonlinear reverse saturation absorption, self-defocusing behavior and structure-property relationship of a novel 2,3,4-trimethoxy-4'-nitrochalcone single crystal

The present work describes the crystal structure, third-order nonlinear optical (NLO) properties and Hirshfeld Surface (HFs) analysis of 1-(4-nitrophenyl)-3-(2, 3, 4,-trimethoxyphenyl) prop-en-1-one (2, 3,4TMNC). The synthesized material was characterised by FT-IR, FT-Raman, UV–Visible, NMR [1H, 13C{1H}] and single crystal X-ray diffraction techniques. TGA-DTA analysis revealed that crystal has higher thermal stability. HFs analysis is performed to visualize intra and intermolecular interactions (C–H⋯O). The third-order NLO properties were studied using standard open and closed aperture Z-Scan technique with a continuous wave (CW) DPSS laser (λ = 532 nm). The calculated values of nonlinear refraction coefficient (n2), third-order nonlinear susceptibility (χ(3)) and nonlinear absorption coefficient (β) were found to be of the order of -10−9 cm2/W, 10−7 esu and 10−5 cmW−1 respectively. Normalized transmittance is decreased with increased input intensity of laser i.e. 2, 3, 4 TMNC showed good optical limiting property. The optical limiting threshold was found to be 3.36 kJ/cm2. Thus, the title chalcone derivative is a potential material for optical limiting applications.

Optical materials: Studying the role of hetropolyacid to enhance the nonlinear optical responses of porphyrin in their hybrids system

Nonlinear optical responses are measured to investigate the role of hetropolyacid (HPA) in porphyrin-Lindqvist type {∼PM@HPA} hybrid systems, {where PM@HPA = [(TBA)8{(MTPPN4)(Mo6O18)4}]; M = 2H (1) and Mn (2)}. The well-known Z-scan technique with wavelength (λ) = 532 nm and pulse duration of τ = 6 ns is used. The results clearly show the significant enhancement in nonlinear self-defocusing effect and reverse saturable absorption under closed and open-aperture configuration for PM@HPA hybrids. It is also observed that the second hyperpolarizability γ values, {1 (4.639 × 10−29 esu) < 2 (5.214 × 10−29 esu)}, are directly proportional to the discrepancy of LUMO level (ΔE) values {1 (2.214 eV) < 2 (2.339 eV)} while they are inversely proportional to the HOMO−LUMO energy gap Eg values {1 (2.003 eV) > 2 (1.862 eV)} in the PM@HPA hybrid system where the porphyrin moiety acts as electron donor whilst HPA acts as electron acceptor. Therefore, the emergence of a facile electron transformation from the porphyrin moieties to the low-lying LUMO levels of HPA is mainly responsible for the enhancement in nonlinear optical responses of PM@HPA hybrids system. As a consequence the hybrid compounds can be fascinating for optical limiting applications.

Laser induced optical and microscopic studies of salicylic acid influenced KH2PO4 crystal for photonic device applications

The present communication is aimed to explore the characteristic properties of salicylic acid (SA) doped potassium dihydrogen orthophosphate (KDOP) crystal. The single SA doped KDOP crystal with optimum dimension of 10 × 08 × 04 mm3 has been grown from solution by slow evaporation at ambient temperature. The single crystal X-ray diffraction analysis has been employed to determine the structure and cell parameters of grown crystal. The Z-scan studies have been carried out at 632.8 nm to ascertain the influential third-order non-linear optical (TONLO) nature of SA doped KDOP crystal. The Z-scan transmittance data have been used to determine the magnitude of TONLO susceptibility (χ3), absorption coefficient (β) and refractive index (n2) of SA doped KDOP crystal. For grown crystal, the surface damage due to exposure of high intensity of Nd:YAG laser operating at 1064 nm has been determined and found of order MW cm−2. The growth tendency, etch pattern and surface quality of grown SA doped KDOP crystal has been investigated by means of etching studies. The thermal response of grown crystal has been examined by differential thermal analysis employed in the range of 23–800°C. The hardness number of SA doped KDOP crystal has been investigated by means of Vickers microhardness study by applying different load ranging from 25 to 100 gm. The work hardening index and elastic stiffness coefficient have been evaluated using the hardness data. The nature of photoconductivity exhibited by grown crystal has been determined in voltage range of 10–100 V.Highlights• Z-scan analysis revealed negative non-linear refraction and reverse saturable absorption effect in SA-KDOP crystal.• The laser damage threshold of SA-KDOP crystal at 1064 nm is found to be 274·74 MWcm−2.• SA-KDOP crystal exhibited positive photoconducting nature within 10–100 V.• The dopant SA facilitated large enhancement in hardness parameters of KDOP crystal.• Etching and thermal analysis has been performed.

Stoichiometric dependent optical limiting in PLD SiOx thin films

In this letter, optical limiting property of the insufficiently oxidized silicon oxide (SiOx) thin films is reported. Films were deposited by Pulsed Laser Deposition technique using Q-switched Nd: YAG laser (532 nm) onto fused silica substrate at a substrate temperature of 400 °C by varying the O2 pressure in the range of 5×10 -5 to 0.5 mbar. Energy Dispersive X-Ray spectra showed the increase in oxygen content with increasing O2 pressure. Raman spectra of SiOx films depicted the presence of micron sized clusters composed of nanocrystalline Silicon embedded in uniform matrix of oxidized amorphous Silicon. The open Z-scan of the thin films, under cw He-Ne laser irradiation, showed strong reverse saturation absorption (RSA) features and non linear absorption (NLA) coefficient, β, was found to be decreasing from 23.5 cm/W to 1.64 cm/W, with increase in O2 pressure from 5×10 -5 to 10 -1 mbar, respectively. Also, the SiOx films except that with maximum oxygen content showed optical limiting, where limiting threshold increases with increasing transparency controlled by oxygen content. The key feature of the present work is the tunability in linear absorption, nonlinear RSA and optical limiting in the SiOx films which can be used as novel material for optical switching application.

Investigation on Third-Order Nonlinear Optical Properties of Four Transition Metal Complexes Thin Films by Z-Scan Technique

In this work, four new transition metal complexes, [Zn(PTP)]12(1,4-NDA)12·2H2O (1), [Zn(PTP) (4,4′-ODA)]2 (2), [Ni(PTP)(4,4′-ODA)]2 (3) and [Ni(FTP)]2Cl4 (4), have been synthesized by the reaction between a metal salt, Zn(II) or Ni(II), a rigid polycarboxylic ligand, naphthalene-1,4-dicarboxylic acid (1,4-NDA) or 4,4′-oxydibenzoic acid (4,4′-ODA) and a co-ligand, 4′-phenyl-2,2′:6′,2″-terpyridine (PTP) or 4′-(furan-2-yl)-2,2′:6′,2″-terpyridine (FTP). Complex 1 based on {Zn(PTP)(1,4-NDA)}n intertwined chains characterized by three different configurations which form a chiral chain structure. Complexes 2 and 3 present a structure made of discrete rings containing two central metal atoms. In Complex 4, two complex Ni(FTP)2+ ions are found to be connected with the μ2–Cl bridge to form a binuclear cluster. The third-order nonlinear optical properties of each complex thin film were evaluated by the Z-scan technique, indicating a strong third-order nonlinear reverse saturable absorption effect, with a high absorption coefficient β 3.89 × 10−6 for 1, 40.50 × 10−6 for 2, 4.76 × 10−6 for 3, and 1.37 × 10−6 m W−1 for 1, respectively. Interestingly, Complex 1 exhibits an effective nonlinear refractive effect with a refractive coefficient of 7.16 × 10−13 m2 W−1. The third-order NLO susceptibilities χ (3) of each complexes were calculated.

Dielectric, etching and Z-scan studies of glycine doped potassium thiourea chloride crystal

Abstract Glycine doped potassium thiourea chloride (PTC) crystal has been grown by slow solution evaporation technique. The dielectric studies have been employed to examine substantial improvement in dielectric constant and dielectric loss of glycine doped PTC crystal. The etching studies have been performed to investigate the surface quality of this crystal. The z-scan studies have been carried out at 632.8 nm to explore the third order nonlinear optical nature. The negative nonlinear refraction of glycine doped PTC crystal was found to be of 7.27 × 10−12 cm2/W. The origin of high magnitude of third order nonlinear optical susceptibility and reverse saturable nonlinear absorption have been investigated. The obtained results were explored to discuss the nonlinear optical applications of PTC crystal.

“Closer is Better and Two is Superior to One”: Third-Order Optical Nonlinearities of a Family of Porphyrin–Anderson Type Polyoxometalate Hybrid Compounds

A family of covalently bonded hybrid compounds composed of Anderson type polyoxometalate (POM) moiety and porphyrin moiety have been synthesized and thoroughly characterized. The compounds all show remarkable nonlinear reverse saturable absorption and self-defocusing effect at 532 nm with a pulse duration τ = 6 ns, rendering them promising candidate materials for device applications in photonics and optoelectronics. More importantly, it is found that the hybrid wherein POM is coupled covalently to porphyrin through shorter bridge has an NLO response superior to the hybrid wherein POM is bonded via longer bridge to porphyrin, and the hybrid having two porphyrins connected to POM shows more enhancement than the hybrid having single porphyrin fused to POM. Disclosure of the inherent structure–property relationship is expected to be instructive for exploration of new porphyrin-POM based NLO materials. Meantime, the hybrid compounds have optical-limiting thresholds lower than 1.0 J/cm2, implying their high pot...

Nonlinear optical switching and optical limiting in colloidal CdSe quantum dots investigated by nanosecond Z-scan measurement

The semiconductor nanocrystals are found to be promising class of third order nonlinear optical materials because of quantum confinement effects. Here, we highlight the nonlinear optical switching and optical limiting of cadmium selenide (CdSe) quantum dots (QDs) using nanosecond Z-scan measurement. The intensity dependent nonlinear absorption and nonlinear refraction of CdSe QDs were investigated by applying the Z-scan technique with 532nm, nanosecond laser pulses. At lower intensities, the nonlinear process is dominated by saturable absorption (SA) and it is changed to reverse saturable absorption (RSA) at higher intensities. The SA behaviour is attributed to the ground state bleaching and the RSA is ascribed to free carrier absorption (FCA) of CdSe QDs. The nonlinear optical switching behaviour and reverse saturable absorption makes CdSe QDs are good candidate for all-optical device and optical limiting applications.

The physical understanding on dynamic readout/detection of super-resolution pits with nonlinear reverse saturation absorption thin films

The physical mechanism and understanding behind dynamic readout/detection of super-resolution pits with a nonlinear reverse-saturation absorption active layer, such as an InSb active layer, is presented on the basis of experimental results of open-aperture z-scan measurements and pump–probe transient time response analysis. The super-resolution of an InSb active layer is a result of the formation of a sub-wavelength scatterer region at the center of the focused spot. The frequency response function also verifies that the cutoff frequency with an InSb active layer is clearly extended compared to when an InSb active layer is not used. The findings are useful for understanding the physical process of the far-field super-resolution effect with nonlinear reverse-saturation absorption characteristics.

Self-assembled organic nanostructures and nonlinear optical properties of heteroleptic corrole–phthalocyanine europium triple-decker complexes

Two heteroleptic corrole–phthalocyanine europium triple-decker complexes were fabricated into organic nanostructures by the standard phase-transfer method. The investigated compounds are represented by Eu2(Pc)2[Cor(ClPh)3] (1) and Eu2[Pc(OC8H17)8]2[Cor(ClPh)3] (2), where Pc represents the dianion of phthalocyanine and Cor(ClPh)3 the trianion of 5,10,15-tri(4-chlorophenyl)corrole. Both compounds 1 and 2 show typical electronic absorption spectra for a non-aggregated molecular structure in chloroform or toluene. However, in methanol compound 1 self-assembled into belt-like nanostructures while compound 2, which possesses long OC8H17 alkoxy side chains, self-assembled into large scale sheet-like nanostructures. The third-order nonlinear optical properties of both triple-decker compounds were also investigated in toluene by the Z-scan technique and characterized as showing nonlinear reverse saturation absorption and self-defocusing behavior. A third-order nonlinear optical susceptibility, χ(3), of 3.18 × 10−10 and 3.35 × 10−10 esu was obtained for 1 and 2, respectively, thus indicating the potential application of these compounds in the field of optical devices.

Effect of Fe concentration on the nonlinear refraction and reverse saturable absorption in ferroelectric X-cut LiNbO3 crystal

In this Letter, the effects of the iron (Fe) dopant concentration on the nonlinear optical properties of iron-doped ferroelectric X-cut LiNbO3 crystals plates are studied by using the Z-scan technique with a cw laser at the wavelength of 532 nm. The amount of iron in the compound is varied from 0 to 0.15 mol%. Measurements of nonlinear refractive index n2 and the nonlinear absorption coefficient \beta are determined. The sign of the nonlinear refractive index is found to be negative and the magnitude is on the order of 10-8 cm2/W. This nonlinear effect increases as the concentration increases from 0 to 0.15 mol%. A good linear relationship is obtained between nonlinear refractive index, nonlinear absorption coefficient, and concentration.