Large Nonlinear Refractive Index Research Articles

Studying of Nonlinear Optical Properties of Binary Bi2S3 and Bi2Te3/PMMA Nanocomposite Films by Z-Scan Technique

For measuring the nonlinear refraction index n2 and absorption index β, we have used modified Z-scan technique with the single laser beam. The media is a nanocomposite films made from the binary (Bi2S3 and Bi2Te3) with PMMA. The material is prepared via the microwave-assisted chemical method. The Characterization of the nanocomposite films was carried out using X-ray diffraction (XRD), and U-V spectroscopy. The band gaps of Bi2S3 and Bi2Te3 are 2.6ev and 2.38ev respectively. XRD shows that Bi2S3 and Bi2Te3 have orthorhombic and trigonal (hexagonal axes) structures respectively. The optical non-linearity is intensity dependent. The nanocomposite films exhibit self-defocusing nonlinearity beneath the empirical conditions. Both samples exhibit a large negative nonlinear refractive index and good nonlinear absorption coefficient with increasing laser input power. The spotted nonlinear refraction and absorption are related to thermal in nature and reverse Saturable absorption, respectively. The obtained results indicate that the nanocomposite films may open several new possibilities of using these materials in all-optical element devices.

Linear and femtosecond nonlinear optical properties of soluble pyrrolo[1,2-a] quinoxalines

We report our results from the investigations of linear and ultrafast nonlinear optical properties of a set of pyrrolo[1,2-a]quinoxalines. Using the steady state optical techniques and density functional theory calculations the linear optical properties were investigated while the non-resonant ultrafast nonlinear optical properties were studied using the degenerate four-wave mixing technique at a wavelength of 800 nm with 70 fs pulses. The investigated molecules demonstrated large off-resonant second hyperpolarizability (γ) and nonlinear refractive index (n2) values compared to similar molecular moieties with potential application in optical devices.

Theoretical simulations of the soliton self-frequency shift of mid-infrared femtosecond pulses in step-index tellurite optical fibers: broadband tunability and high efficiency

Broadband tunable ultrafast lasers using mid-infrared (MIR) fibers operating at a 3-5 µm atmospheric transmission window are attractive sources because of their numerous applications. Tellurite fibers possess the merits of large linear and nonlinear refractive indices, sufficient chemical stability, and wide transparency range up to ∼5 µm; also, they are highly suitable for high efficiency MIR ultrafast fiber laser sources based on soliton self-frequency shift (SSFS). We numerically simulate SSFS of MIR femtosecond pulses in step-index tellurite optical fibers. A femtosecond erbium-doped fluoride fiber laser at 3.5 µm is employed as the pump source. Parameters including the peak power of the input pulse and nonlinear fiber length are optimized for high efficiency broadband tunable MIR ultrafast laser performance. Our results show that a high-efficiency 3.5-6 µm wavelength-tunable femtosecond laser can be realized by employing SSFS in a 22-cm-long segment of tellurite step-index fiber pumped by femtosecond pulses with 10-300 kW peak powers at 3.5 µm. Ultra-high energy ratios of the most redshifted solitons to the input pulses of >50% are obtained across the 3.5-5 µm tuning range. The presented numerical study provides valuable guidance for SSFS of MIR femtosecond pulses in step-index tellurite fibers and is valuable for future high efficiency wavelength-tunable MIR ultrafast fiber laser development.

Third-order optical nonlinearity in nonstoichiometric amorphous silicon carbide films

This study investigated the third-order nonlinear optical properties of amorphous silicon carbide (SiC) films prepared via magnetron sputtering at room temperature (RT) and annealed at 200 °C–800 °C. The third-order optical nonlinearity was investigated by Z-scan measurement at a wavelength of 1064 nm and a pulse duration of 25 ps. The self-defocusing behaviour was observed in a large nonlinear refractive index n2 ∼10−14 m2/W, which was five orders of magnitude larger than the value of SiC crystals. By fitting the open-aperture data of the Z-scan, we determined the two- and three-photon absorption in the SiC films prepared at RT and in the annealed samples, respectively. The different nonlinear absorption behaviour was probably ascribed to the intermediate states between the conduction and valence bands.

Fifth- and third- order nonlinear optical responses of olive oil blended with natural turmeric dye using z-scan technique

In this study, nonlinear optical responses of olive oil as a pure material and also blended with turmeric powder at different concentrations are demonstrated using z-scan technique. This material is found to be a novel natural nonlinear medium with large nonlinear refractive index. The modified Newton-Raphson method was used to solve the formula obtained from Gaussian Decomposition method for transmission of beam light in z-scan technique. It shows a negative third order nonlinear refractive index (n2) on the order of 10−7cm2/w under irradiation of maximum 50 mw continuous wave (CW) He-Ne laser at 632.8 nm wavelength. The third order nonlinear susceptibility (χ3) of olive oil was calculated on the order of 10−5 (esu). The fifth order nonlinear refractive index (n4) of this oil was calculated positive and on the order of 10−9cm4w2 for the first time according to the authors' knowledge. It is worth noting that the fifth order nonlinear susceptibility occurs at lower intensity with regards to other nonlinear materials. The thermal nonlinear refractive index of the olive oil is also calculated for pure olive oil and different concentrations of olive oil blended with turmeric.

High Repetition-Rate Laser Z-Scan Measurements: Criterion for Recognizing Adverse Thermal Effects

This study reports z-scan measurements in which high-repetition-rate and reduced repetition-rate (pulse-picked) laser beams were employed using a standard sample, carbon disulfide (CS2) contained in supposedly high damage-threshold spectroscopic-grade pristine fused-quartz cuvettes. The results suggest that at reduced repetition rates, the closed aperture z-scan profile for CS2 displays the expected configuration. However, at high repetition-rates the closed aperture z-scans are distinctly different resulting in unexpectedly large nonlinear refractive index of CS2 due to thermal effects that resulted in below-threshold laser-induced damage of the cuvettes. Normaski microscope images confirm the damage and open aperture z-scan study of the damaged fused-quartz cuvettes yielded about two orders of magnitude enhancement in the nonlinear absorption coefficient of silica. Based on these findings, the necessary criterion for recognizing below-threshold laser-induced damage in any high-repetition-rate laser z-scan measurement has been formulated in order to help avoid erroneous interpretation of the origin and strength of nonlinear response in such studies.

Third-order optical nonlinearity in silicon nitride films prepared using magnetron sputtering and application for optical bistability

We investigate the third-order optical nonlinearity in silicon nitride (SiN) films prepared using magnetron sputtering. The large nonlinear refractive index n2 in SiN prepared at room temperature of a value of −2.00 × 10−16 m2/W and the nonlinear absorption coefficient β of 1.44 × 10−9 m/W are determined by the Z-scan method at a wavelength of 1064 nm and a pulse duration of 25 ps. The n2 is three orders of magnitude larger than that in SiN films prepared by the chemical vapor deposition method and at a wavelength of 1.55 μm. The enhanced n2 up to −6.27 × 10−16 m2/W and the slightly changed β, indicating an enhanced ratio of |Reχ(3)|/|Imχ(3)|, are further obtained in the annealed samples. Such a change is probably due to the crystallization of the films. The optical bistability in SiN resonant waveguide grating (RWG) is numerically studied. The low threshold intensity around 300 MW/cm2 in the RWG is obtained.

Linear and nonlinear optical properties of chlorophyll-a extracted from Andrographis paniculata leaves

This paper reports the linear and third-order nonlinear optical (NLO) properties of chlorophyll-a, a natural pigment extracted from the medicinal plant Andrographis paniculata. Silica column chromatography technique was used to extract the chlorophyll-a from the plant leaves. The functional groups present in the extracted sample were recognized by Fourier transform infrared (FT-IR) spectra. The sample was also characterized by UV–Vis, fluorescent spectra and Z–scan techniques. Z–scan study reveals that the extracted natural pigment chlorophyll-a evinces a large negative nonlinear refractive index n2 and nonlinear absorption coefficient β respectively owing to self-defocusing and saturable absorption behaviors. Third-order NLO susceptibility χ(3) of chlorophyll-a was measured to be of the order of 10–6 esu. The sample fulfilled the conditions for figure of merit and we believe that the natural pigments extracted from the Andrographis paniculata leaves may be suitable for all-optical switching applications.

Enhanced photostability and optical nonlinearity of nickel and cobalt organometallic complexes

Nonlinear optical and limiting properties of nickel, cobalt metal-organic complexes and ligand (L) {L = N,N′-o-phenylenebis (4-hyrdoxy-salicylideneimine)} were studied using Z-scan technique using Q-switched Nd: YAG laser with nanosecond pulses at 532 nm. The results reveal that metal complexes exhibit large negative nonlinear refractive index (n2) of the order of 10−11 esu. The metal complexes displays large nonlinearity than the ligand due to effective charge delocalization between metal ion and ligand. The magnitude of ground state absorption cross section is small compared to the effective excited-state absorption cross section implying the observed nonlinearity is due to reverse saturable absorption. Further, metal-organic complexes exhibit enhanced optical limiting behaviour at nanosecond laser pulses.

Kerr Nonlinearity in 2D Graphdiyne for Passive Photonic Diodes

Graphdiyne is a new carbon allotrope comprising sp- and sp2 -hybridized carbon atoms arranged in a 2D layered structure. In this contribution, 2D graphdiyne is demonstrated to exhibit a strong light-matter interaction with high stability to achieve a broadband Kerr nonlinear optical response, which is useful for nonreciprocal light propagation in passive photonic diodes. Furthermore, advantage of the unique Kerr nonlinearity of 2D graphdiyne is taken and a nonreciprocal light propagation device is proposed based on the novel similarity comparison method. Graphdiyne has demonstrated a large nonlinear refractive index in the order of ≈10-5 cm2 W-1 , comparing favorably to that of graphene. Based on the strong Kerr nonlinearity of 2D graphdiyne, a nonlinear photonic diode that breaks time-reversal symmetry is demonstrated to realize the unidirectional excitation of Kerr nonlinearity, which can be regarded as a significant demonstration of a graphdiyne-based prototypical application in nonlinear photonics and might suggest an important step toward versatile graphdiyne-based advanced passive photonics devices in the future.

Coherent ultra-broadband laser-assisted injection radiation from a laser plasma accelerator

The injection of electrons into a laser wakefield accelerator (LWFA) is observed to generate an intense coherent ultra-broadband and ultrashort pulse radiation flash, consistent with the acceleration of electrons from rest to nearly the speed of light in a distance < ~ 1 $\mu$m. The flash is sufficiently bright to induce large nonlinear refractive index shifts in optical materials; we estimate a source brightness temperature of ~$10^{18}$ K. We present measurements of the flash spectra, coherence, pulse duration, polarization and angular distribution, providing a detailed picture of electron injection dynamics in LWFA. These are characteristic of laser-assisted injection of off-axis electrons, which preserves wake coherence.

Period doubling and route to chaos in reduced graphene oxide, an experimental evidence

We use Nonlinear Schrödinger Equation (NLSE) to investigate chaotic dynamics inside a graphene-based optical system. Numerical results show that with increasing the control parameters, the character of Modulation instability (MI) is changed from convective to absolute. In consequence, a hyper-chaotic map is more expressive to explain the dynamical state of the system. It is also indicated that a reverse transition from the chaotic regime to the stable state can be resulted if the optical input intensity is further increased. The optical input intensity and feedback strength are distinguished as the two control parameters of the system. We then use Reduced Graphene Oxide (RGO) dispersion with large nonlinear refractive index to verify if a transition to instability and chaotic behavior is experimentally realized for the visible input light wave. The observation begins with saturation in the nonlinear response followed by an Optical Bistability (OB) phenomena. Afterward, a quasi-periodic fluctuations appear expressing the absolute MI. In agreement with our simulation result based on the period doubling bifurcation diagram, this quasi-periodic state is recognized as a route to the chaos. We infer that the graphene Quantum Dots (QDs) which are formed as a result of reduction process are responsible for energy transfer through the optical near-field interactions and thus, strengthen the required feedback.

Study of nonlinear optical properties and optical limiting of acid green 5 in solution and solid film

Experimental investigation of the nonlinear optical properties of aqueous solution of acid green 5 and acid green 5 doped polyvinyl alcohol film, by Z-scan technique using continuous wave (CW) laser is presented. Both samples exhibit large negative nonlinear refractive index. The optical limiting properties were also studied. The efficiency of the optical limiting was found to depend on the diameter of the detector aperture and the position of the sample. The dye exhibits good optical limiting properties in solution and solid PVA host. The mechanism of optical limiting is found to be predominantly of a thermal origin.

Synthesis, surface profile, nonlinear reflective index and photophysical properties of curcumin compound

Curcumin and other three curcuminoids (bisdemethoxycurcumin, α-chlorocurcumin and α-methylcurcumin) were synthesized. Fourier transform infrared spectroscopy, Fluorescence quantum yields, AFM analysis and image surface profiles were characterized. All compounds possessed electron donor moieties at both ends of the conjugated π-system and an electron acceptor moiety in the middle of the molecules (D-A-D system) and should exhibit different optical properties depending on substituents on the benzene rings. The third order nonlinear optical properties of the curcuminoids have been investigated by z-scan technique. The optical response was characterized by measuring the refractive index (n2) of the derivatives of curcumin using the Z-scan technique. The compounds showed negative and large nonlinear refractive index values of the order of 10−7 cm2/W and reverse saturable absorption with high values of the nonlinear absorption coefficient of the order of 10−4 cm/W. The nonlinear refractive index was found to vary with the different compound. The optical constants of the different compound films were studied and the dispersion of the refractive index was discussed in terms of the Wemple-DiDomenico single oscillator model. The photo-physical properties of these compounds are compared to those of native curcumin, in order to provide a rationale to the design of samples with molecular structures optimized for a photosensitizer. These types of materials may be considering new photonic applications.

Large Third-Order Optical Susceptibility with Good Nonlinear Figures of Merit Induced by Octupole Plasmon Resonance of Asymmetric Au–Ag Core–Shell Nanorods

The Au–Ag core–shell nanorods with asymmetric transverse cross section are synthesized, and their tunable linear and nonlinear optical responses are investigated. After the overgrowth of the asymmetric Ag shell on the Au nanorods, (i) a strong transverse octupole (TO) plasmon resonance at 390 nm is observed; (ii) the nonlinear refractive index γ at the TO resonance wavelength significantly increases from −0.15 × 10–4 to −0.85 × 10–4 cm2/GW, and the γ at the longitudinal dipole (LD) resonance wavelength slightly increases from −0.42 × 10–4 to −0.58 × 10–4 cm2/GW; (iii) but the nonlinear absorption coefficient β induced by the TO resonance is approximately 1 order of magnitude smaller than the one induced by the LD resonance. Consequently, the asymmetric Au–Ag core–shell nanorods at the TO resonance wavelength demonstrate a very large nonlinear refractive index as well as excellent nonlinear figures of merit (W = 4.4 > 1 and T = 0.14 < 1), which satisfy the demands for waveguide all-optical switching.

Coexistence of bound soliton and harmonic mode-locking soliton in an ultrafast fiber laser based on MoS2-deposited microfiber photonic device

As the typical material of two-dimensional transition metal dichalcogenides (TMDs), few-layered MoS2 possesses broadband saturable absorption and a large nonlinear refractive index, which could be regarded as a promising candidate for dual-function photonic device fabrication. In this work, the coexistence of a bound soliton and harmonic mode-locking soliton was demonstrated in an ultrafast fiber laser based on a MoS2-deposited microfiber photonic device. Through a band-pass filter, each multi-soliton state was investigated separately. The bound soliton has periodic spectral modulation of 1.55 nm with a corresponding pulse separation of 5.16 ps. The harmonic mode-locking soliton has the repetition rate of 479 MHz, corresponding to the 65th harmonic of the fundamental repetition rate. The results indicated that there exist more possibilities of different multi-soliton composites, which would enhance our understanding of multi-soliton dynamics.

Third-order nonlinear optical response of CH_3NH_3PbI_3 perovskite in the mid-infrared regime

The third-order nonlinear optical properties of CH3NH3PbI3 perovskite film have been investigated by the Z-scan technique in the mid-infrared (mid-IR) region. We prepared the high-quality CH3NH3PbI3 films with the precursor solutions, and experimentally observed its broadband saturable absorption behavior and large Kerr nonlinearity. The CH3NH3PbI3 perovskite film exhibited a large nonlinear refractive index (~10−12 m2/W) in the mid-IR regime. Our study indicates the great potential of the organic-inorganic perovskite material in the mid-IR nonlinear optics, and might provide some new sights for Kerr nonlinearity based mid-IR nonlinear optical application.

Mid-infrared optical properties of chalcogenide glasses within tin-antimony-selenium ternary system.

In this work, we investigated the mid-infrared (MIR) optical properties of selenide (Se-based) chalcogenide glasses (ChGs) within an As- and Ge-free system, namely the environment-friendly and low-cost tin-antimony-selenium (Sn-Sb-Se, SSS) ternary system, which has not been systematically studied to the best of our knowledge. As compared to ChGs within those conventional Se-based systems, SSS ChGs were found to exhibit extended infrared transmittance range as well as larger linear refractive index (n0). Femtosecond Z-scan measurements show the presence of evident three-photon absorption from Urbach absorption of the SSS ChGs at MIR wavelength, which resonantly enhanced the nonlinear refractive behavior and resulted in large nonlinear refractive index (n2).

Third Order Optical Nonlinearity of Silver Nanoparticles Prepared by Chemical Reduction Method

In this study, silver colloidal nanoparticles have been prepared by chemical reduction of silver nitrate by trisodium citrate as a reduction agent. The adding time of the reduction agent was held constant while the time of stirring was varied. The resulting silver nanoparticles were characterized by UV-VIS absorption spectroscopy. The non-linear refractive index and absorption coefficient of silver nanoparticles were investigated using a single beam z-scan technique. The excitation source was a continuous wave (CW) of 532 nm diode laser with a beam power of 40 mW. All investigated samples showed negative and large thermally-induced non-linear refractive indices. Other nonlinear optical parameters (i.e.β,χ_r^((3)),χ_i^((3))) were also calculated. Our measurements confirm that the non-linear parameters are caused by self-defocusing process making them potential candidates for nonlinear optical devices.

Development of thermally stable glass from SiO2-Bi2O3-PbO-ZnO-BaO oxide system suitable for all-solid photonic crystal fibers

The series of SiO2-Bi2O3-PbO-ZnO-BaO and SiO2-TiO2-Bi2O3-PbO-Na2O glasses were synthetized to obtain non-crystallizing materials, dedicated to fabrication of photonic crystal fibers. During composition development, the thermal properties were investigated according to the change of chemical composition. The glasses contain high concentrations of heavy metal oxides for high refractive index, large nonlinear refractive index and spectrally broad transmission window from 0.5 to 4.5 μm. Their thermal properties are optimized to enable drawing of all-solid glass photonic crystal fibers in tandem with previously designed highly nonlinear glass PBG81 based on SiO2-Ga2O3-Bi2O3-PbO-CdO system. This creates novel dual glass combinations for PCF fibers. We have also investigated influence of melting conditions on the final thermal and optical properties, including absorption from water contamination at around 2.8 μm.