Large Nonlinear Refractive Index Research Articles

Studies of third order nonlinearity and thermal diffusivity of C3OC dye using thermal lens technique

An FT-IR spectrometer and a UV–Visible spectrometer were utilised in order to characterise the Cyanidin-3-O-glucoside chloride (C3OC) dye. The dye’s thermally induced optical nonlinearity was measured in a dimethylformamide solvent using an adjustable diode-pumped solid-state (DPSS) laser at 473 nm. The optical response was measured using the Z-scan technique. The dye showed negative and large nonlinear refractive index) NRX) values, with high nonlinear absorption coefficients (NBO). Because of its ability to change with concentration, the NRX is a viable candidate for applications in the field of nonlinear optics. Thermal lens (THS) technique was used to investigate thermo-optical properties and the NRX. The optical limiter capabilities of the C3OC dye are being investigated as a potential use.

Nonlinear metasurface engineering with disordered gold nanorods on ITO: a cost-effective approach to broadband response, polarization-independence, and weak nonlinear index dispersion.

The strong coupling of epsilon-near-zero materials with nanoantennas has demonstrated enhanced nonlinear optical responses, yet practical challenges persist. Here, we propose an alternative: an ultrathin metasurface featuring broadband response with a weakly dispersive nonlinear index, achieved through a simple implementation. Our metasurface, comprising a disordered gold nanorod array on indium tin oxide, exhibits polarization-independent behavior and a large average nonlinear refractive index of 5 cm2/GW across a broad wavelength range (1000-1300 nm). Enhanced performance is attributed to the weak coupling between gold nanorods and indium tin oxide, offering a cost-effective method for nonlinear optical metasurfaces and a flexible design in nanophotonic applications.

Determination of nonlinear refractive index of large area monolayer MoS2 at telecommunication wavelength using time-resolved Z-scan technique

The nonlinear refractive index of large area monolayer molybdenum disulfide (MoS2) thin film at the 1,550[Formula: see text]nm wavelength band is determined using time-resolved z-scan technique. MoS2 exhibits positive nonlinear phase shift with a large nonlinear refractive index, [Formula: see text] value of [Formula: see text]. The obtained value is similar to the [Formula: see text] value of monolayer MoS2 film measured at 2.0[Formula: see text][Formula: see text]m, and is approximately five and seven orders of magnitude larger than silicon and common bulk dielectrics. The large [Formula: see text] indicates that MoS2 can be used as nonlinear refractive 2D material for photonics applications operating in the 1,550[Formula: see text]nm optical telecommunications wavelength band.

Modulation of epsilon-near-zero wavelength and enhancement of third-order optical nonlinearity in ITO/Au multilayer films

We report the modulation of epsilon-near-zero (ENZ) wavelength and enhanced third-order nonlinearity in indium tin oxide (ITO)/Au multilayer films. The samples consisting of five-layer 40 nm ITO films spaced by four-layer ultrathin Au films of different thickness, i.e., ITO(40 nm)/[Au(x)/ITO(40 nm)]4, were prepared by magnetron sputtering at room temperature. The ENZ wavelength in the multilayer films is theoretically calculated and experimentally confirmed. The nonlinear refractive index and nonlinear absorption coefficient of the samples of x=0, 2, 3, 4 nm were determined using the Z-scan method at a wavelength of 1.064 µm. The large nonlinear refractive index n2=1.12×10-13 m2/W and nonlinear absorption coefficient β=-1.78×10-7 m/W in the sample of x = 4 nm are both four times larger than those in the single-layer ITO film. The large optical nonlinearity due to the ENZ enhancement and carrier concentration is discussed. The results indicate that the ITO/Au multilayer films are promising for advanced all-optical devices.

Nonlinear optical properties of graphdiyne/graphene van der Waals heterostructure for laser modulations

The construction of van der Waals heterostructures (vdWHs) is emerging as a promising approach for creating new materials with exotic functionalities and extraordinary optical properties in the field of laser modulations. However, the comprehensive research of vdWHs is still at an early stage that it needs further investigation of the corresponding optical properties and applications. In this paper, graphdiyne/graphene vdWH (GDY/G) is successfully fabricated through liquid-phase epitaxial growth method and its optical nonlinearities are investigated for both pulse laser generation and spatial self-phase modulation (SSPM). Using GDY/G as saturable absorber, the outputs of the passively Q-switched (PQS) Nd:Lu0.5Y0.5VO4 laser at 1343 nm under 878 nm direct pumping are investigated in detail, delivering a better performance than pristine graphdiyne or graphene. Moreover, as carrier for SSPM, GDY/G demonstrates a large nonlinear refractive index in the order of 10−5 cm2 W−1. These advantages can be attribute mainly to accelerated carrier relaxation and enhanced nonlinear optical properties due to synergistic effect of graphdiyne and graphene, which are stacked together to form the vdWH with interlayer coupling. The experimental results indicate that GDY/G possesses large potentials and bright prospects in laser modulations.

Four-wave mixing in graphdiyne-microfiber based on synchronized dual-wavelength pulses

We demonstrate four-wave mixing (FWM) in the graphdiyne (GDY) microfiber based on the synchronized dual-wavelength pump pulses that are transformed from a mode-locked fiber laser. Benefiting from the large nonlinear refractive index of GDY and the synchronized pump pulses, a maximum conversion efficiency of −39.05 dB can be achieved in GDY with only an average pump power of 6.9 mW, greatly alleviating the possible damage compared to previous investigations employing the continuous-wave pump. In addition, our proposal can be applied to measure the effective nonlinear coefficient γ of the GDY-microfiber, which could be extended as a practical measurement tool for γ of nanomaterials-based devices.

Superalkali (Li2F, Li3F) doped Al12N12 electrides with enhanced static, dynamic nonlinear optical responses and refractive indices

In the present work, superalkalis (Li2F and Li3F) doped Al12N12 nanocages have been designed and investigated theoretically to elucidate the correlations between geometric, electronic and nonlinear optical properties. All complexes (A-E) are stable inorganic electrides as indicated by their interaction energies (−52.97 to −87.58 kcal/mol). The decrease in HOMO-LUMO energy gaps (5.44–5.87 eV) has caused a remarkable increase in the nonlinear optical response of A-E complexes. The maximum values of first hyperpolarizability (1.20 × 104 a.u.) and second hyperpolarizability (1.65 × 107 a.u.) have been achieved for complex A. The highest dynamic hyperpolarizability coefficients including second harmonic generation (9.08 × 105 a.u.) and electro-optic Pockel's effect (9.56 × 105 a.u.) are obtained for complex A at 532 nm. The electric field-induced second harmonic generation (up to 3.52 × 108 a.u.) and dc-Kerr effect (up to 8.13 ×108 a.u.) along with a large quadratic nonlinear refractive index (up to 5.41 × 10−11 a.u.) of the designed electrides reflected their large NLO response.

Integrated Gallium Nitride Nonlinear Photonics

AbstractGallium nitride (GaN) as a wide bandgap material is widely used in solid‐state lighting. Thanks to its high nonlinearity and high refractive index contrast, GaN‐on‐insulator (GaNOI) is also a promising platform for nonlinear optical applications. Despite its intriguing optical proprieties, nonlinear applications of GaN are rarely studied owing to the relatively high optical loss of GaN waveguides (typically ≈2 dB cm−1). In this paper, GaNOI microresonators with intrinsic quality factor over 2.5 million are reported, corresponding to an optical loss of 0.17 dB cm−1. Parametric oscillation threshold power as low as 6.2 mW is demonstrated, and the experimentally extracted nonlinear index of GaN at telecom wavelengths is estimated to be n2 = 1.4 × 10−18 m2 W−1, which is several times larger than that of commonly used platform such as Si3N4, LiNbO3, and AlN. Single soliton generation in GaN is implemented by an auxiliary laser pumping scheme, so as to mitigate the high thermorefractive effect in GaN. The large intrinsic nonlinear refractive index, together with its broadband transparency window and high refractive index contrast, make GaNOI a promising platform for chip‐scale nonlinear applications.

Comprehensive study of -Alanine passivated colloidal gold nanoparticles and GNP-PVP thin films: Linear optical properties and very large nonlinear refractive index, absorption coefficient, third-order nonlinear susceptibility measurements and effect of passivation

We synthesized gold nanoparticles (GNPs) stabilized in various concentration of l-alanine by chemical reduction method. We measured NLO responses of GNPs when they are dispersed in the l-alanine stabilizer with 1, 2.5 and 5 mM concentrations and when they are implanted into the PVP matix, by using single beam Z- Scan technique with 632 nm He–Ne CW laser for excitation. GNPs exhibited blue shift in localised surface plasmon resonance (LSPR) peak with the l-alanine concentration. The fcc structured GNPs of reducing size with the stabilizer concentration were obtained and characterized by the TEM as well as XRD. The FTIR spectral investigation revealed the formation of strong bond between the surface of GNPs and the l-alanine functional groups and established that l-alanine is very good candidate for stabilization of MNPs. It was observed that these samples show very large nonlinear refractive index, absorption coefficient and third-order nonlinear susceptibility in the order of 10−8cm2W−1, 10−6 cmW−1 and 10−9esu respectively for colloidal suspension of GNPs, and for the GNP-PVP thin films these parameter values were found in the order of 10−6cm2W−1, 10−5cmW−1and 10−6esu respectively. The thermally stimulated, l-alanine concentration dependant, very large NLO responses attributed to the local field effect from Mie resonance and thermal lensing effect originated from thermo-optic phenomenon. The obtained results validate the influence of the stabilizer (l-alanine) on NLO properties.

Investigation of nonlinear optical properties of Eosin-B nanoparticles painted ‎

In this study the nonlinear optical properties of Eosin-B dye nanoparticles were studied using the ‎scanning-fluorescence spectrophotometer and fluorometer method. The nano water droplet in the ‎oil medium is prepared by a combination of hexane and surfactant water, which is painted inside ‎the drop by Eosin-B. The droplet size was studied on a nonlinear refractive index using a 532 nm ‎laser with a scanning power of 80 mW. The results show that the surface effects on the nano-‎droplets cause the droplets to have a larger nonlinear refractive index. This change was due to a ‎decrease in the accumulation of dyes inside the droplet as well as a decrease in the polarity of the ‎drop solvent relative to the water solvent.

Femtosecond infrared supercontinuum generation in 6H-SiC crystal

We report on supercontinuum generation in silicon carbide (6H-SiC), pumped by tunable femtosecond pulses in the wavelength range of 1.3 - 2.4 μm, which cover the regions of normal, zero, and anomalous group velocity dispersion of the material. More than an octave spanning infrared supercontinuum spectra were measured, demonstrating almost constant blue cut-offs around 0.9 μm. Low energy thresholds for supercontinuum generation (depending on the pump wavelengths, but generally below 200 nJ) were demonstrated due to large nonlinear refractive index of the material (n2 = 97 ± 19 × 10−16 cm2/W), which was experimentally evaluated by measurement of the nonlinear transmission at 2.0 μm.

Z-scan dosimetry of gamma-irradiated PMMA

Poly (methyl methacrylate) (PMMA) is widely used in scientific and industrial applications. Because of its favorable properties, it is used in various fields such as optical, medical, and nuclear applications. Effects of ionization radiations on physical properties of PMMA have greatly studied in recent years. However, to the best of our knowledge, there have been no reports on the effects of ionizing radiations, especially the gamma radiation, on the nonlinear optical properties of PMMA. In this paper, for the first time, detection of large and measurable nonlinear refractive index of PMMA after interaction with the gamma radiation is reported. The optical Z-scan technique is used for measuring the nonlinear optical properties of the gamma-irradiated PMMA samples in the 5–300 kGy dose range. It is shown that variation of the induced nonlinear refractive index in this dose range is more or less linear with deposited dose. A new dosimetry method is proposed, which is based on using the Z-scan technique for measuring the nonlinear refractive index of PMMA and obtaining the amount of absorbed dose using this linear response. The name Z-scan dosimetry is coined for this new dosimetry method.

Octave-spanning supercontinuum generation in infrared by MoS2-filled hollow core fiber

We report the generation of an infrared (IR) supercontinuum spanning over an octave using a centimeter (6 cm) length of photonic crystal fiber (PCF) filled with MoS2, which has a considerably large nonlinear refractive index. The fiber is pumped with a femto-second laser pulse with an infrared wavelength of 2080 nm, pumping intensity of 336.76 GW/cm2, peak power of 0.75 GW, and pulse width of 150 fs. With the assistance of highly nonlinear MoS2, a supercontinuum bandwidth that remarkably extends from 1400 to 2700 nm below 20 dB is achieved. This supercontinuum bandwidth significantly exceeds the previously reported spectra for other nonlinear glass-based optical fibers, even with a fairly short fiber length. Furthermore, this short fiber length allows PCF to be more efficiently utilized, and is expected to be suitable for various applications, such as broadband light source through liquid-based fibers and waveguide-based optical communications, especially in the IR region.

Broadband dispersive free, large, and ultrafast nonlinear material platforms for photonics

Abstract Broadband dispersion free, large and ultrafast nonlinear material platforms comprise the essential foundation for the study of nonlinear optics, integrated optics, intense field optical physics, and quantum optics. Despite substantial research efforts, such material platforms have not been established up to now because of intrinsic contradictions between large nonlinear optical coefficient, broad operating bandwidth, and ultrafast response time. In this work, a broadband dispersion free, large and ultrafast nonlinear material platform based on broadband epsilon-near-zero (ENZ) material is experimentally demonstrated, which is designed through a novel physical mechanism of combining structural dispersion and material dispersion. The broadband ENZ material is constructed of periodically nanostructured indium tin oxide (ITO) films, and the structure is designed with the help of theoretical predictions combined with algorithm optimization. Within the whole broad ENZ wavelength range (from 1300 to 1500 nm), a wavelength-independent and large average nonlinear refractive index of −4.85 × 10−11 cm2/W, which is enlarged by around 20 times than that of an unstructured ITO film at its single ENZ wavelength, and an ultrafast response speed at the scale of Tbit/s are experimentally reached simultaneously. This work not only provides a new approach for constructing nonlinear optical materials but also lays the material foundation for the application of nanophotonics.

Diffraction ring patterns and nonlinear measurements of the Tris(2′,2-bipyridyl)iron(II) tetrafluoroborate

The nonlinear optical properties of the Tris(2,2′-bipyridyl)iron(II) tetrafluoroborate in aqueous solution was investigated by the spatial self-phase modulation (SSPM) technique using CW laser at λ = 532 nm. The experimental results show large nonlinear refractive index (n2) and the thermo-optic coefficient (dn/dT) equal to −3.17 × 10−6 cm2/W and the 3.17 × 10−3 k−1, respectively. The effect of input power of excitation laser and the temporal evolution on the shape of the diffraction patterns were studied. Consequently, the collapse effect of the diffraction ring patterns was explained.

Enhancement of the linear, nonlinear and optical limiting properties of epoxy resin decorated by zinc oxide nanoparticles

Epoxy resin decorated by zinc oxide (ZnO) nanoparticles film was successfully prepared onto a glass substrate. Field-emission scanning electron microscopy was used to examine the surface morphology of the prepared film. It is clearly observed that these nanoparticles are adhered onto the surface of the epoxy resin and cover its entire area. The UV–vis measurements of the as-prepared ZnO/epoxy resin microstructures displayed the outstanding enhancement in the photocatalytic properties. The optical band gap of the obtained film shows a significant increase up to 3.7 eV due to the non-stoichiometric distribution of zinc and oxygen atoms in the obtained structure. The nonlinear optical properties of the film were investigated using the Z-scan technique. Large and negative nonlinear refractive index of the sample is determined. The optical limiting property of the film is reported, and the optical limiting mechanism is originated from the thermal effect and the nonlinear scattering. The obtained materials along with the high nonlinearities demonstrates the possibly of incorporating this material in many functions related to photonic applications.

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.

Nonlinear refraction in CH3NH3PbBr3 single crystals.

We measure both nonlinear absorption and nonlinear refraction in a ${{\rm CH}_3}{{\rm NH}_3}{{\rm PbBr}_3}$CH3NH3PbBr3 single crystal using the Z-scan technique with femtosecond laser pulses. At 1000 nm, we obtain values of 5.2 cm/GW and ${+}{9.5} \cdot {{10}^{ - 14}}\;{{\rm cm}^2}/{\rm W}$+9.5⋅10-14cm2/W for nonlinear absorption and nonlinear refraction, respectively. The sign and magnitude of the observed refractive nonlinearity are reproduced well by the two-band model. Our results suggest that the large nonlinear refractive index measured in perovskite nanostructures cannot be explained by an intrinsically high bound-electronic nonlinear refractive index in this emerging material class but is possibly caused by free carriers or quantum confinement effects.

Remarkably enhanced first hyperpolarizability and nonlinear refractive index of novel graphdiyne-based materials for promising optoelectronic applications: A first-principles study

A new functionalized graphdiyne-based structure was designed by adsorbing single and double AM3O (AM = Li, Na, K) on graphdiyne (GDY) surface, namely (AM3O)n@GDY (AM = Li, Na, K; n = 1, 2). Density-functional theory calculations have been used to unravel the relations between the geometric structure and nonlinear optical (NLO) properties, e.g., Hyper-Rayleigh Scattering coefficient (βHRS) and nonlinear refractive index (n2). The frequency-dependent electro-optic Pockel's effect (EOPE) and second-harmonic generation (SHG) were explored to design the efficient NLO materials. Our calculations reveal that the AM3O molecule has the strong interactions with the GDY unit, and the intramolecular charge transfer is significant for determining the NLO properties. Large first hyperpolarizabilities (βtot) for single-adsorbed GDY have been found, especially for K3O@GDY (∼3.06 × 105 a.u.), rather than double-adsorbed GDY. Moreover, the small transition energies with large oscillator strength are a decisive factor for enhancing the βtot values. In the dynamic NLO process, the EOPE and SHG resonances can be enhanced at ω = 0.10 a.u., while single-adsorbed GDY clusters have large nonlinear refractive index and improved Hyper-Rayleigh Scattering response. All of these results will inevitably stimulate further synthesis of GDY-based optoelectronic materials with high NLO properties for future applications.

Chalcogenide–Tellurite Composite Photonic Crystal Fiber: Extreme Non-Linearity Meets Large Birefringence

In this paper, we propose a novel design of a photonic crystal fiber (PCF) with tellurite-cladding, three rings of air-holes and elliptical concentration of As2S3 in the fiber core. The combined effect of tight mode confinement (an effective mode area of nearly 0.6 µm2), large non-linear refractive index of As2S3 and significant variation between the effective modal index values of the two orthogonal states of the fundamental guided mode leads to extreme non-linear coefficient and birefringence values, all achieved at the zero dispersion wavelength (ZDW) of 1550 nm. The corresponding birefringence and non-linear coefficient (7 × 10−3 and 28 W−1 m−1, respectively) are more than three orders of magnitude larger than that of the regular silica-based highly non-linear PCFs. In addition, we numerically demonstrate that by modifying the core and air-hole dimensions one can easily control the dispersion curve and tune the ZDW of the proposed fiber to any excitation wavelength ranging from near-infrared to short-wave-infrared, including optical telecommunication windows close to 1550 nm. The superior characteristics of the proposed elliptical-core composite PCF including extreme non-linearity, nearly-zero confinement loss (2.47 × 10−12 dB/cm), the ability to maintain polarization of light, and tunable ZDW can open the door to new possibilities in non-linear optics, optical telecommunications, optical signal processing, and sensing devices.