Giant and Tunable Optical Nonlinearity in Single-Crystalline 2D Perovskites due to Excitonic and Plasma Effects

Materials with large optical nonlinearity, especially in the visible spectral region, are in great demand for applications in all-optical information processing and quantum optics. 2D hybrid Ruddlesden-Popper-type halide perovskites (RPPs) with tunable ultraviolet-to-visible direct bandgaps exhibit large nonlinear optical responses due to the strong excitonic effects present in their multiple quantum wells. Using a microscopic Z-scan setup with femtosecond laser pulses tunable across the visible spectrum, it is demonstrated that single-crystalline lead halide RPP nanosheets possess unprecedentedly large nonlinear refraction and absorption coefficients near excitonic resonances. A room-temperature insulator (exciton)-metal (plasma) Mott transition is found to occur near the exciton resonance of the thinnest qunatum-well RPPs, boosting the nonlinear response. Owing to the rapidly changing refractive index near resonance, a single RPP crystal can exhibit different nonlinear functionalities across the excitation spectrum. The results suggest that RPPs are efficient nonlinear materials in the visible waveband, indicating their potential use in integrated nonlinear photonic applications such as optical modulation and switching.

NLOphoric benzyl substituted BODIPY and BOPHY: A comprehensive linear and nonlinear optical study by spectroscopic, DFT and Z-scan measurement

BOPHY (BPY) and BODIPY (BDY) dye bearing benzyl group (Bn) at 4,4' and 2,6 position respectively were synthesized and characterized. The fluorescence decay measurements were performed which reveal that benzyl BOPHY (Bn-BPY) has shorter fluorescence lifetime compared to benzyl BODIPY (Bn-BDY). The difference in transition dipole moment is found to be 6.93 and 11.3 D for Bn-BDY and Bn-BPY respectively in toluene. The molecular electrostatic potential (MEP) plot shows Bn-BDY is more polarised compared to Bn-BPY. The nonlinear optical (NLO) property was evaluated using Z-scan measurement. The molecular electronic arrangement of Bn-BPY significantly affects the nonlinear absorption properties resulting into reverse saturable absorption (nonlinear absorption coefficient β = 0.256 × 10^-11 m/W). In contrast, the Bn-BDY displays saturable absorption character. The calculated third-order nonlinear susceptibility χ⁽³⁾ value is 12.23 × 10^-13 esu and 2.49 × 10^-13 esu for Bn-BDY and Bn-BPY respectively. The power limiting behaviour of Bn-BPY displays limiting threshold energy around 70 Jcm^-2 with clamped output at ~35 Jcm^-2.

Application of the Z-scan technique for the detection of CFCDNA (cell-free circulating DNA) and urine DNA (uDNA) in patients with bladder cancer

BACKGROUND

Patients with BC have a higher amount of cell-free circulating DNA (CFCDNA) in the blood and urine than healthy people. We aimed to verify if the Z-Scan method could analyze the concentrations of uDNA (urinary) and pDNA (plasma) in relation to the time of collection during treatment for patients with bladder cancer.

METHODS

Peripheral blood and urine samples were obtained from 30 patients with BC at the time of diagnosis, 45, 90 and 180 days after initiating treatment; 5 μL of k-DNA (k = u or p) was added in 250 μL a solution of 1:1000 Ethidium Bromide dye (EtBr) in water. Continum laser Nd:YVO4, wavelength λ = 532 nm was used. Samples of uDNA and pDNA in water were submitted to the laser with an incident power of 84.5 mW and an exposure time of 30 ms.

RESULTS

There was a different concentration of pDNA and uDNA during the treatment of patients using both optical techniques. However, the reaction rate of pDNA and uDNA was similar with spectrophotometry, whereas the z-scan technique presented different values.

CONCLUSION

Z-scan technique has potential for use in the differentiation of pDNA and uDNA concentrations, which are distinct in patients with BC and healthy people.

Non-linear optical response of meso hybrid BODIPY: Synthesis, photophysical, DFT and Z scan study

Hybrid meso BODIPY dyes are synthesized and their linear and non-linear optical properties are studied. Time-resolved fluorescence lifetime decay is found to be identical for all dyes irrespective of meso substituents. The Z-scan experiment performed to calculate the nonlinear absorption coefficient (β) and third-order nonlinear susceptibility (χ³). Global hybrid (B3LYP and BHHLYP) and range-separated hybrid (CAM-B3LYP) functional with the basis set 6-311++G(d,p) was employed to determine the theoretical linear and non-linear optical properties. The computed β₀ value of all the three dyes was found to be superior to that of urea (βo = 0.371 × 10^-30 esu). Introduction of meso substituent directly affects the polarizability and second-order hyperpolarizability of the dyes. Thermal and reorientational effect of the investigated NLOphoric dyes were studied.

Optical limiting properties of 3,5-dipyrenylvinyleneBODIPY dyes at 532nm

The optical limiting (OL) properties of 3,5-dipyrenylvinyleneBODIPY dyes that contain both electron withdrawing and donating moieties have been investigated by using the z-scan technique at 532nm in the nanosecond pulse range. The extension of the π-conjugation at the 3,5-positions with pyrenylvinylene groups results in a ca. 200nm red shift of the main BODIPY spectral band to ca. 700nm, so there is relatively weak absorbance at 532nm under ambient light conditions. Reverse saturable absorbance (RSA) profiles are observed in response to incident pulsed laser light that is consistent with a two photon absorption-assisted excited state absorption (ESA) mechanism in CH₂Cl₂ solution and when the dyes are embedded in poly(bisphenol carbonate A) (PBC) polymer thin films. This demonstrates that 3,5-divinyleneBODIPY dyes are potentially suitable for use in OL applications, since limiting threshold fluence (I_lim) values of below 0.95Jcm^-2 are observed when thin films are prepared.

Hydrogen bonded charge transfer molecular salt (4-chloro anilinium-3-nitrophthalate) for photophysical and pharmacological applications

Radical scavenging activity against DPPH radical and binding properties of a hydrogen bonded charge transfer molecular salt 4-chloro anilinium-3-nitrophthalate(CANP) with calf thymus DNA has been studied by electronic absorption and emission spectroscopy. The molecular structure and crystallinity of the CANP salt have been established by carried out powder and single crystal X-ray diffraction analysis which indicated that cation and anion are linked through strong N⁺H^…O^- type of hydrogen bond. FTIR spectroscopic study was carried out to know the various functional groups present in the crystal. ¹H and ¹³C NMR spectra were recorded to further confirm the molecular structure of the salt crystal. The thermal stability of the title salt was established by TG/DTA analyses simultaneously on the powdered sample of the title crystal. Further, the CANP salt was examined against various bacteria and fungi strains which showed a remarkable antimicrobial activity compared to that of the standards Ciproflaxin and Clotrimazole. The results showed that the CANP salt could interact with CT-DNA through intercalation. Antioxidant studies of the substrates alone and synthesized CANP salt showed that the latter has been better radical scavenging activity than that of the former against DPPH radical. The third order nonlinear susceptibility of the CANP salt was established by the Z-scan study.

Non-linear Optical Responses of Low-Density Lipoprotein are Associated with Intima-Media Thickness of Carotid Artery in Athletes

We investigated the association between the degree of oxidative modification of LDL particles by non-linear optical response of LDL (Z-scan technique) and the presence of subclinical atherosclerosis in different segments of the carotid artery. We recruited high-intensity athlete runners (n = 44) and controls (n = 51) to participate in the study. The carotid intima-media thickness (cIMT), interleukin 10 (IL-10), TNF-alpha, and the non-linear optical responses of LDL particle (Z-scan) were assessed. In athletes, the mean cIMT differed between genders, with higher values observed in female athletes compared to male athletes (P < 0.05). Higher mean values for cIMT were seen in the right carotid arteries of female athletes as compared to female controls (P < 0.05). Higher levels of TNF-alpha and IL-10 were found in athletes (P < 0.05). Yet, ΔΓpv (transmittance curve) of Z-scan in athletes was higher than in the non-athletes, indicating less oxidation in LDL particles of athletes (P < 0.05). There was an inverse association between the ΔΓpv and cIMT in the right internal carotid segments (β = -0.163, P < 0.05) in all subjects, and between the VO2max and the mean cIMT (β = -0.003, P < 0.05) in male subjects. The present study shows that the Z-scan technique enabled to detect less oxidative modifications in LDL particles from athletes. This effect was associated with cIMT in a gender-dependent mode.

Shape-Dependent Nonlinear Optical Properties of Anisotropic Gold Nanoparticles

This Letter reports the shape-dependent third-order nonlinear optical properties of anisotropic gold nanoparticles. We characterized the nonlinear absorption coefficients of nanorods, nanostars, and nanoshells using femtosecond Z-scan measurements. By comparing nanoparticle solutions with a similar linear extinction at the laser excitation wavelength, we separated shape effects from that of the localized surface plasmon wavelength. We found that the nonlinear response depended on particle shape. Using pump-probe spectroscopy, we measured the ultrafast transient response of nanoparticles, which supported the strong saturable absorption observed in nanorods and weak nonlinear response in nanoshells. We found that the magnitude of saturable absorption as well as the ultrafast spectral responses of nanoparticles were affected by the linear absorption of the nanoparticles.

Shape-Dependent Nonlinear Optical Properties of Anisotropic Gold Nanoparticles

This Letter reports the shape-dependent third-order nonlinear optical properties of anisotropic gold nanoparticles. We characterized the nonlinear absorption coefficients of nanorods, nanostars, and nanoshells using femtosecond Z-scan measurements. By comparing nanoparticle solutions with a similar linear extinction at the laser excitation wavelength, we separated shape effects from that of the localized surface plasmon wavelength. We found that the nonlinear response depended on particle shape. Using pump-probe spectroscopy, we measured the ultrafast transient response of nanoparticles, which supported the strong saturable absorption observed in nanorods and weak nonlinear response in nanoshells. We found that the magnitude of saturable absorption as well as the ultrafast spectral responses of nanoparticles were affected by the linear absorption of the nanoparticles.

Assessment on third order non linearity and other optical analyses of L-Asparagine Monohydrate single crystal: An efficient candidate for harmonic conversions

Single crystal of l-Asparagine Monohydrate, an organic material has been successfully grown by slow evaporation solution growth technique at ambient condition. The lattice parameters and its strain of the grown crystal have been evaluated from powder X-ray diffraction and found that it belongs to orthorhombic crystal system. The polarizability has been measured by using the Clausius-Mossotti relation. The crystalline perfection of grown single crystal has been examined by high resolution X-ray diffraction and its imperfection in the diffraction plane was clearly visible by recording topographical image of the plane. From the high resolution XRD, it confirms that the crystal contained high crystalline perfection. The optical behavior was analyzed by photoluminescence and birefringence methods. In the photoluminescence, a broad peak has been observed at 475 nm which suggest that it emits blue light. The decay tendency of the material has also been observed by calculating decay constant. The optical homogeneity has been determined by the dispersion pattern of the material. The two photon absorption coefficient was further calculated by Z-scan, which gives the information about the third order non linear optical behavior of the material. The value of two-photon absorption coefficient is 4.25 × 10(-12)m/W. The thermal parameters like thermal effusivity, thermal diffusivity, specific heat and thermal conductivity was obtained by using photopyroelectric technique. The ferroelectric behavior of the grown specimen was analyzed from PE (polarization VS electric field) loop. The loop suggests that the material was a nearly equivalent to ideal capacitor.

Direct Observation of Degenerate Two-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films

The optical nonlinearity of WS2 and MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS2 and MoS2 films and their dependences on excitation wavelength were studied. WS2 films with 1-3 layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 ± 0.8) × 10(4) cm/GW. TPA saturation was observed for the WS2 film with 1-3 layers and for the MoS2 film with 25-27 layers. The giant nonlinearity of WS2 and MoS2 films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA.

Crystal growth, morphology, spectrographic characterization and thermal properties of Glycine Barium Bromo Chloride crystals

Glycine Barium Bromo Chloride material was purified by repeated recrystallization. Single crystal was grown by the slow evaporation solution technique (SEST). The presence of functional groups in the grown crystals was confirmed by Fourier transform infrared spectrum analysis. Thermal properties of the crystals were investigated using thermogravimetric (TG) and differential thermal analyses (DTA). The dielectric studies were carried out to identify the phase transition temperature and the dielectric constant was found. The transparency of crystal was tested using UV-visible spectra. Single crystal X-ray diffraction study has been carried out to find the crystal system and unit cell parameters.

Ethylenediaminium di(4-nitrophenolate): a third order NLO material for optical limiting applications

Single crystals of ethylenediaminium di(4-nitrophenolate) [EDA4NP] were grown by slow evaporation solution growth technique using ethanol as solvent at constant temperature. It crystallizes in monoclinic centrosymmetric space group C2/c with cell dimension a=11.326Ǻ, b=7.264Ǻ, c=20.036Ǻ; β=93.55°. Fourier Transform Infra Red (FT-IR) spectrum was recorded to identify various functional groups present in EDA4NP. Nuclear Magnetic Resonance (NMR) spectral studies were performed to confirm the functional groups. Thermogravimetric analysis and differential thermal analysis showed that the compound melts at 142.9°C. The material possesses a wide optical transparency window in the visible and near IR region (500-1200nm). The nonlinear refractive index, nonlinear absorption coefficient and third-order nonlinear susceptibility of EDA4NP were estimated to be n2=5.46×10(-8)cm(2)W(-1), β=0.65×10(-3)cmW(-1) and χ((3))=2.96×10(-6)esu respectively. The limiting behavior observed with the sample is attributed mainly to nonlinear refraction.

Third-order nonlinear optical investigations of meso-tetrakis(2,3,5,6-tetrafluoro-N,N-dimethyl-4-anilinyl)porphyrin and its metal complexes

We report here the experimental investigation on third-order nonlinear optical parameters of 5,10,15,20-tetrakis(2,3,5,6-tetrafluoro-N,N-dimethyl-4-anilinyl)porphyrin and its various metal complexes, using Z-scan technique at 532 nm. The third-order nonlinear optical susceptibilities (χ(3)) were of the order 10(-12) esu and are compared through degenerate four wave mixing (DFWM). The operating mechanism is reverse saturable absorption (RSA) as the effective excited-state absorption cross-section was found higher than ground state absorption cross-section as well as the magnitude of nonlinear absorption coefficient was found decreasing with on-axis input intensity. The compounds found to exhibit good optical limiting at 532 nm, 7 ns excitation steering applications in laser safety.

Growth, spectral, anisotropic, second and third order nonlinear optical studies on potential nonlinear optical crystal anilinium perchlorate (AP) for NLO device fabrications

A new semiorganic nonlinear optical material anilinium perchlorate was grown by the slow evaporation technique using water as solvent. The solubility and meta stable zone width were determined. The anilinium perchlorate crystal belongs to orthorhombic system with noncentrosymmetric space group P2₁2₁2₁. The presence of various functional groups was identified by FT-IR FT-Raman spectrum. The morphology of the anilinium perchlorate crystal was studied. From this morphology, anilinium perchlorate crystal plate was cut along three prominent planes, such as (001), (010) and (20-1). The thermal stability of the crystal was determined using TG-DTA studies. The hardness, laser damage threshold, transmittance, reflectance, experimental refractive index of the crystal was found. The particle size dependent second harmonic generation efficiency for anilinium perchlorate was evaluated by Kurtz-Perry powder method using Nd:YAG laser, which established the existence of phase matching. The third order nonlinear refractive index and nonlinear absorption coefficient of the grown crystal were measured by Z-scan studies.

Linear and nonlinear optical, mechanical, electrical and surface studies of a novel nonlinear optical crystal - manganese mercury thiocyanate (MMTC)

The highly efficient nonlinear optical single crystal of manganese mercury thiocyanate has been grown from slow evaporation solvent technique. The second harmonic generation and optical transmittance of the grown crystal are studied by Kurtz and Perry powder technique and spectroscopic absorbance spectrum. Mechanical behaviour is analyzed using Vickers microhardness test. The dielectric response of the grown crystal is studied as a function of the temperature and the results are discussed. Further, electronic properties such as plasma energy, Penngap, Fermi energy and electronic polarizability are evaluated. Third order nonlinear optical studies are performed using by single beam Z-scan technique using Nd:YAG laser and parameters such as nonlinear refractive index n2, absorption co-efficient β and nonlinear optical susceptibility χ((3)) are evaluated for the grown crystal. The surface of the grown crystal is analyzed with field emission scanning electron microscope and atomic force microscope analyses.

Growth, molecular structure, NBO analysis and vibrational spectral analysis of l-tartaric acid single crystal

Single crystal of l-tartaric acid (LTA) has been grown by slow evaporation technique. The experimental and theoretical studies on molecular structure, vibrational spectra, electronic absorption spectra and non-linear optical property of the crystal are studied. The FT-IR, FT-Raman and UV-Vis-NIR experimental spectra of LTA crystal have been recorded in the range 400-4000cm(-1), 100-3700cm(-1) and 190-1100nm, respectively. Density functional theory calculations with B3LYP/6-311++G(d,p) basis sets was used to determine ground state molecular geometries, vibrational frequencies, ICT interactions, Mulliken population analysis on atomic charge, HOMO-LUMO analysis, non-linear optical response properties and thermodynamic properties for LTA and the results were discussed. Vibrational analysis confirms the formation of intramolecular OH⋯O hydrogen bonding. The stability of the molecule has been analyzed using NBO analysis. The results of electronic absorptions in gas phase and water phase LTA were calculated using TD-DFT method. The third-order nonlinear absorption behaviour of LTA was studied using open aperture Z-scan technique, with 5ns laser pulses at 532nm and the nonlinear absorption coefficient of the grown crystal was measured. The predicted NLO properties, UV absorption and Z-scan studies indicate that LTA is an attractive material for laser frequency doubling and optical limiting applications.

Study of self-defocusing, reverse saturable absorption and photoluminescence in anthraquinone PMMA nanocomposite film

The nanocomposite film of 1,5-diamino-9,10-anthraquinone in poly methyl methacrylate has been fabricated by following guest-host method. Intense reverse saturable absorption and self-defocusing effect have been investigated by employing Z-scan technique with low power CW laser at 532 nm with different intensities for the dye-polymer composite film. The estimated values of nonlinear absorption coefficient β, nonlinear refractive index n2 and third order susceptibility χ((3)) of the composite film are of the order of 10(-3) (m/W), 10(-11) (m(2)/W) and 10(-4) (esu), respectively. The dye molecules have been encapsulated uniformly between molecules of polymer as a nanocomposite with average roughness ∼7.96 nm as characterized by AFM technique. The nanocomposite film also exhibited strong photoluminescence emission when excited with 532 nm. The second order hyperpolarizability of composite film has also been estimated. The evaluated figure of merit W having a value greater than 1, and the results obtained suggest that the composite film of 1,5-diamino-9,10-anthraquinone-PMMA has potential applications in nonlinear optical devices.

Experimental and theoretical investigations of nonlinear optical properties of 1,4-Diamino-9,10-Anthraquionone

Nonlinear optical properties of 1,4-Diamino-9,10-Anthraquinone dye in solution at different concentrations are investigated by utilizing single beam Z-scan technique using a low power continuous wave laser (λ=532 nm). The anthraquinone dye is found to exhibit self-defocusing and reverse saturable absorption behavior. Effect of concentration on nonlinear refractive index and nonlinear absorption coefficient are also studied. The nonlinear absorption coefficient (β) and nonlinear refractive index (n2) have been evaluated from the open aperture and closed aperture Z-scan data and are found to increase with increase in concentration. The order of magnitude obtained for nonlinear refractive index and nonlinear absorption coefficient are found to be 10(-6) esu and 10(-4) m/W, respectively. The optical limiting behavior and induced self-diffraction patterns are also observed. To have a theoretical insight of nonlinear optical properties of 1,4-Diamino-9,10-Anthraquinone, first hyperpolarizability (β) is also evaluated by using quantum chemical calculations employing DFT method using 6-311 G basis set. The results obtained confirm the nonlinear optical behavior of 1,4-Diamino-9,10-Anthraquinone dye.

Graphene Oxides as Tunable Broadband Nonlinear Optical Materials for Femtosecond Laser Pulses

Graphene oxide (GO) thin films on glass and plastic substrates were found to display interesting broadband nonlinear optical properties. We have investigated their optical limiting activity for femtosecond laser pulses at 800 and 400 nm, which could be tuned by controlling the extent of reduction. The as-prepared GO films were found to exhibit excellent broadband optical limiting behaviors, which were significantly enhanced upon partial reduction by using laser irradiation or chemical reduction methods. The laser-induced reduction of GO resulted in enhancement of effective two-photon absorption coefficient at 400 nm by up to ∼19 times and enhancement of effective two- and three-photon absorption coefficients at 800 nm by ∼12 and ∼14.5 times, respectively. The optical limiting thresholds of partially reduced GO films are much lower than those of various previously reported materials. Highly reduced GO films prepared by using the chemical method displayed strong saturable absorption behavior.