High Nonlinear Susceptibility Research Articles

One- and Two-Photon Photophysical Properties, Ultrafast Dynamics, and DFT Study of Three Modified Zinc Phthalocyanines.

As two-photon absorption (TPA) materials, phthalocyanine molecules have promising application prospects due to their large TPA absorption cross-section, high third-order nonlinear optical susceptibility, and ultrafast response characteristics. In this work, optical properties and the ultrafast response of three modified zinc phthalocyanine molecules (P-HPcZn, Pc-P-Pc, and (DR1)4PcZn) were analyzed. No obvious side-shoulder absorption peaks in the Q-band can be observed from the steady-state absorption spectra of the three molecules, confirming the lack of aggregation products in the solutions of our measurement. Open-aperture Z-scan results show relatively large TPA cross-section values of 136.4 and 55.3 GM for Pc-P-Pc and (DR1)4PcZn, respectively. The nonlinear optical results show that the absorption process observed under the excitation of femtosecond pulses is a reverse saturable absorption (RSA) mechanism. Up-conversion fluorescence spectra of (DR1)4PcZn in THF solution indicate that the fluorescence emission mechanism is TPA. In the study of ultrafast dynamics, the transient absorption spectra were investigated and the decay lifetime of the dynamic traces corresponding to some representative probe wavelengths was obtained through data fitting with a multi-exponential function. Finally, the charge transfer and excited state properties of the modified zinc phthalocyanine molecules were discussed in depth by the DFT method. The energy gaps of P-HPcZn, Pc-P-Pc, and (DR1)4PcZn are 2.16, 1.39, and 2.13 eV, respectively. The results indicate that the Pc-P-Pc of donor-acceptor-donor (D-A-D) structure has the smallest energy gap as well as the best charge transfer properties.

Second harmonic generation in monolithic gallium phosphide metasurfaces

Abstract Gallium phosphide (GaP) offers unique opportunities for nonlinear and quantum nanophotonics due to its wide optical transparency range, high second-order nonlinear susceptibility, and the possibility to tailor the nonlinear response by a suitable choice of crystal orientation. However, the availability of single crystalline thin films of GaP on low index substrates, as typically required for nonlinear dielectric metasurfaces, is limited. Here we designed and experimentally realized monolithic GaP metasurfaces for enhanced and tailored second harmonic generation (SHG). We fabricated the metasurfaces from bulk (110) GaP wafers using electron-beam lithography and an optimized inductively coupled plasma etching process without a hard mask. SHG measurements showed a high NIR-to-visible conversion efficiency reaching up to 10−5, at the same level as typical values for thin-film-based metasurface designs based on III–V semiconductors. Furthermore, using nonlinear back-focal plane imaging, we showed that a significant fraction of the second harmonic was emitted into the zeroth diffraction order along the optical axis. Our results demonstrate that monolithic GaP metasurfaces are a simple and broadly accessible alternative to corresponding thin film designs for many applications in nonlinear nanophotonics.

Second-harmonic generation of ultrashort pulses in refractive index linearly modulating quantum dot structure

While other works use segments of nonlinear crystal to compensate for walk-off, this work utilizes a quantum dot (QD) nanostructure for such compensation. Such nanocrystal structures allow two benefits: the high nonlinear susceptibility in these nanocrystals and the high surface density of QDs in the structure. Good results are obtained for pre-chirping and modulation parameters. The results are computed at 10 and 100 kV/cm applied electric fields. Compared to ordinary nonlinear crystals, the pulse width, intensity, and efficiency of the second harmonic (SH) pulse are all higher in QD nanocrystals, even with a low electric field applied. Higher applied fields give higher results.

Extraordinary Enhancement of Nonlinear Optical Interaction in NbOBr2 Microcavities.

2D materials are burgeoning as promising candidates for investigating nonlinear optical effects due to high nonlinear susceptibilities, broadband optical response, and tunable nonlinearity. However, most 2D materials suffer from poor nonlinear conversion efficiencies, resulting from reduced light-matter interactions and lack of phase matching at atomic thicknesses. Herein, a new 2D nonlinear material, niobium oxide dibromide (NbOBr2) is reported, featuring strong and anisotropic optical nonlinearities with scalable nonlinear intensity. Furthermore, Fabry-Pérot (F-P) microcavities are constructed by coupling NbOBr2 with air holes in silicon. Remarkable enhancement factors of ≈630 times in second harmonic generation (SHG) and 210 times in third harmonic generation (THG) are achieved on cavity at the resonance wavelength of 1500nm. Notably, the cavity enhancement effect exhibits strong anisotropic feature tunable with pump wavelength, owing to the robust optical birefringence of NbOBr2. The ratio of the enhancement factor along the b- and c-axis of NbOBr2 reaches 2.43 and 5.27 for SHG and THG at 1500nm pump, respectively, which leads to an extraordinarily high SHG anisotropic ratio of 17.82 and a 10° rotation of THG polarization. The research presents a feasible and practical strategy for developing high-efficiency and low-power-pumped on-chip nonlinear optical devices with tunable anisotropy.

Structural Study of alumino(boro)silicate glasses containing tin-doped indium oxide (ITO) nanocrystals with nonlinear optical and enhanced UV/ NIR-shielding properties

Transparent alumino(boro)silicate glasses containing tin-doped indium oxide nanocrystals were fabricated using conventional melt-casting and heat treatment. Structural characterization was carried out by Raman spectroscopy to study glass-forming species, coordination, type and number of oxygens, and possible connectivity of silicate, aluminate, and borate species. A changing role of indium, acting as a modifier in the glass structure, but leaving a less modified glass after clustering and crystallization was also revealed. X-ray photoelectron spectroscopy confirmed that indium was in the trivalent state only. HR-TEM provided insights into the distribution and morphology of the nanocrystals in the glass ceramic sample, yielding a mean size of 4.75 nm. The nonlinear optical behavior of aluminoborosilicate glass samples was evaluated using the Z-scan technique, demonstrating high third-order nonlinear optical susceptibility for both glass and glass ceramic samples, accompanied by a change in the signs of nonlinear refractive indices before and after crystallization from negative to positive.

Crystal design of novel Piperazinum Isophthalate (PIP): Growth, Structural, Thermal, Spectral, Mechanical and Optical properties for NLO application

Novel organic single crystal Piperazinum Isophthalate (PIP) has been synthesized and grown by the slow evaporation solution growth technique. The structural analysis of the single crystal was assessed by the single crystal X-ray diffraction and from a thorough literature survey, it is confirmed that the structure is claims to be the reported for the first time. The FT-IR analysis is used to confirm the different vibrational modes present in the crystal. Utilizing Vicker's Microhardness tester, the mechanical behavior of the crystal was examined and its related constants were computed. Mechanical analysis reveals that the grown crystal exhibits Reverse Indentation Size Effect (RISE) and also found that it belongs to the soft material category with n = 8. The TG/DTA technique is used to analyze the thermal property of the grown crystal and found that PIP is thermally stable up to 271°C. The optical property of the PIP crystal is analyzed using the UV–Vis NIR Spectroscopy, it is observed that PIP has good transparency in the entire visible region with a cutoff wavelength of 281 nm. The Laser Damage Threshold (LDT) of the PIP single crystal was studied by the Q-switched Nd-YAG laser of the wavelength 532 nm and the computed LDT value is 7.3047 GW/cm2. The third order non-linear optical properties of the grown crystal were analyzed by Z - scan technique and the obtained results confirm high nonlinear susceptibility(X(3) = 1.2728× 10−7esu) with self-defousing nature. From the above discussion, we may infer that the grown PIP crystal will be a promising material for optoelectronic device fabrication.

Self-consistent simulations of intracavity terahertz comb difference frequency generation by mid-infrared quantum cascade lasers

Portable terahertz (THz) frequency comb sources are highly desired for applications in rotational molecular spectroscopy and sensing. To date, direct THz quantum cascade laser (QCL) frequency comb generation is not achievable at room temperature. However, THz comb generation based on intracavity difference frequency generation (DFG) in mid-infrared (mid-IR) QCLs is a promising alternative. Here, we present a numerical study of THz DFG-QCL comb formation in mid-IR QCLs based on a self-consistent multi-domain simulation approach. The dynamical simulations are performed using our open-source software tool mbsolve, which provides a flexible and efficient codebase for solving the generalized full-wave Maxwell–Bloch equations. Here, DFG in the active region of a dual-wavelength mid-IR QCL is considered for the generation of THz radiation. The mixing process and, thus, THz generation require a high second-order intersubband nonlinear susceptibility in the QCL active region and can be obtained by targeted quantum engineering. The associated nonlinear effects are included in the Hamiltonian of our Maxwell–Bloch simulation approach. All necessary input parameters for the description of the quantum system are determined self-consistently using our in-house ensemble Monte Carlo software tool for stationary carrier transport simulations. Notably, such simulations require a full-wave Maxwell–Bloch solver that does not employ the common rotating wave approximation, as a broadband optical field extending from the THz to the mid-IR region is investigated. Our modeling approach and the obtained simulation results for two THz DFG-QCL comb setups are validated against experimental data, showing reasonable agreement. Furthermore, we obtain a locked frequency modulated comb state for mid-IR and THz regimes.

Chitosan, a Cationic Polymer-Loaded CuS:Ni Nanoparticles Well Suited for Pseudocapacitors, Optical Switching and Spintronic Devices

Chitosan, a cationic polymer, is loaded on Ni-doped copper monosulfide (CuS) NPs with optimal Ni doping concentration, and electrochemical, third-order nonlinear, magnetic and antibacterial characteristics of chitosan unloaded and loaded CuS:Ni nanoparticles are compared. The crystallite size of pure CuS increased with Ni doping and the 10[Formula: see text]wt.% Ni-doped CuS NPs exhibit a maximum crystallite size of 41[Formula: see text]nm. The presence of Ni in the doped samples was acknowledged by the existence of Ni 2p[Formula: see text] and Ni 2p[Formula: see text] peaks at binding energies 851[Formula: see text]eV and 873.1[Formula: see text]eV, respectively from the XPS spectrum. Optical reflectance decreased with Ni doping and the optical band gap varied from 2.56[Formula: see text]eV to 2.4[Formula: see text]eV. Specific capacitance increased with Ni doping. Diamagnetic nature of CuS changed to ferromagnetic with Ni doping. The 10[Formula: see text]wt.% Ni-doped CuS exhibits a high third-order nonlinear absorption coefficient and susceptibility value. Bacterial growth inhibition nature of CuS improved with Ni doping. Among the doped samples, the 10[Formula: see text]wt.% Ni-doped sample exhibits improved electrochemical, third-order nonlinear, magnetic and antibacterial properties. Keeping this as the optimized Ni concentration, chitosan was loaded. Chitosan-loaded samples exhibited a reduction in crystallite size and an increase in band gap. A high specific capacitance of 96[Formula: see text]F/g was realized for the chitosan-loaded sample. Saturation magnetization of 10[Formula: see text]wt.% CuS:Ni decreased with chitosan loading.

Magneto-optic and mechanical properties of TeO2 with K2TeO3 doped with rare earth

The novel glasses within composition: 62TeO2-5K2TeO3-20ZnO-10Nb2O5-3PbF2 and 62TeO2-5K2TeO3-20ZnO-10Nb2O5-3PbF2-2Er2O3 in mol% were fabricated by using meltquenching technique. The magnetic properties Viz; Faraday effect and the Verdet constant at wavelength of laser beam (λ = 632 nm) were measured. The prepared sample with doped Er3+ has the highest value of Verdet constant (= 0.104min/G.cm) which depends on the polarizability of Er3+ ions. Moreover, the optical properties of present glass estimated by using UV-Vis-NIR spectroscopy. The oxygen-packed densities, molar volumes, the polarizability of the oxygen molar volume, the linear refractive index (n), third-order nonlinear susceptibility, (3)  , and nonlinear index (n2) of produced glasses were evaluation. It was found that the linear refractive index decreases otherwise the optical energy gap increased with doped Er3+ ions in the glasses network. Also, the Vickers microhardness increase with increasing Er2O3 in the glass matrix. Hence, these glasses may be use in optical isolator with high third-order non-linear susceptibility.

Improving the nonlinear electro-optical responses of doped nematic liquid crystals with chiral dopants

Liquid crystals with considerable optical and electro-optical responses play important roles in photonics and optoelectronics. In this research, the electro-optical responses of pure and doped nematic liquid crystal with left-handed S-1011 chiral dopant with different percentages were investigated at different temperatures for the first time. According to the results, nematic liquid crystal with 4 wt% of chiral dopant indicates high electro-optical Kerr constat and third-order nonlinear susceptibility. In this case, various molecular interactions enhance the average order of nematic liquid crystal. By increasing the temperature, gradually the Kerr constant is deecreased, but this decreasing is slow for liquid crystal with 9 wt% of chiral dopant. Moreover, the temperature dependence of Kerr constant was used for calculating the pre-transition temperature. Therefore, these results provide a precise and simple method for improving the electro-optical responses of a nematic liquid crystal, which is an important step in the design of optoelectronic devices.

Towards high nonlinear optical susceptibility of Acid Fuchsin dye deposited on FTO substrate for optoelectronic applications

Towards high nonlinear optical susceptibility of Acid Fuchsin dye deposited on FTO substrate for optoelectronic applications

Demonstration of DC Kerr effect induced high nonlinear susceptibility in silicon rich amorphous silicon carbide

In this study, we demonstrate the DC Kerr effect in plasma-enhanced chemical vapor deposition silicon rich amorphous silicon carbide (a-SiC). Using the resonance shift of the transmission spectra of a ring resonator, we experimentally extract the third order nonlinear susceptibility χ3 to be 6.90×10−19 m2/V2, which is estimated to be more than six times higher than previous reported values in stoichiometric a-SiC. The corresponding induced second order nonlinear susceptibility χ2 of 44.9 pm/V is also three times higher than the reported value in silicon and silicon rich nitride utilizing the DC Kerr effect. The high nonlinearity makes silicon rich a-SiC a good materials candidate for nonlinear photonic applications.

Characterization of optical and nonlinear properties of individual GaP nanowires using optical tweezers

Semiconductor nanowires (NWs) offer multiple advantages for designing novel optoelectronic devices, such as small footprint, high quantum efficiency, high nonlinear susceptibility. Gallium phosphide (GaP) is one of the attractive materials owing to its low optical absorption and high nonlinear susceptibility. However NWs should be transferred to planar substrates for optical studies, which do not allow efficient signal outcoupling. We demonstrate efficient second harmonic generation in individual GaP nanowires trapped using optical tweezers. Such vertically arranged configuration of NW allows to both efficiently generate second harmonic and to probe linear optical response using broadband light source. Such experiment allows to examine interplay between harmonic generation efficiency and NW dimensions.

Nonlinear optical single crystals for terahertz generation and detection

Nonlinear optical (NLO) single crystals with high quality are the pillars for the development of new devices that fulfil the demands of society. Nowadays, NLO single crystals are very attractive for the photonic applications particularly for terahertz (THz) photonics. The reason for their popularity is that these crystals can produce very powerful and ultra wideband THz waves due to their high nonlinear susceptibility. In this review paper, we deal with the challenges and progresses in the evolution of NLO single crystals for THz wave generation and detection. Here, we review the single crystal growth that how and by which method single crystal is grown. We summarize the structures, intermolecular and intramolecular interactions, their properties and how they generate and detect the THz waves. Widely used single crystals at present are DAST, BNA, OH1, amino acid-based single crystals, etc.

Single GaP nanowire nonlinear characterization with the aid of an optical trap.

Semiconductor nanowires exhibit numerous capabilities to advance the development of future optoelectronic devices. Among the III-V material family, gallium phosphide (GaP) is an attractive platform with low optical absorption and high nonlinear susceptibility, making it especially promising for nanophotonic applications. However, investigation of single nanostructures and their waveguiding properties remains challenging owing to typically planar experimental arrangements. Here we study the linear and nonlinear waveguiding optical properties of a single GaP nanowire in a special experimental layout, where an optically trapped structure is aligned along its major axis. We demonstrate efficient second harmonic generation in individual nanowires and unravel phase matching conditions, linking between linear guiding properties of the structure and its nonlinear tensorial susceptibility. The capability to pick up single nanowires, sort them with the aid of optomechanical manipulation and accurately position pre-tested structures opens a new avenue for the generation of optoelectronic origami-type devices.

Bloch Surface Wave‐Assisted Ultrafast All‐Optical Switching in Graphene

AbstractGraphene has ultrafast charge carrier dynamic and shows strong light–matter interaction allowing the use in photovoltaic devices, fast photodetectors, saturable absorbers, and electro‐optical modulators. However, despite the high nonlinear optical susceptibilities, the small amount of material significantly limits the use of graphene for nonlinear optical applications. In this work, Bloch surface waves (BSWs) are employed, enhancing the graphene–light interaction, for all‐optical switching realization. By placing a graphene monolayer on top of a 1D photonic crystal, it is shown that for the wavelength corresponding to the BSW resonance, the reflection coefficient is modulated on the sub‐picosecond time scale by an order of magnitude larger than that for bare graphene. The magnitude of the reflection change reaches 0.3% at the fluence of 40 µJ cm−2. The reported results are proof of priciple possibility of BSW‐assisted enhancing the reflection modulation of any 2D materials and transparent thin films while maintaining their inherent ultrafast dynamics, which is useful for the further development of all‐optical switches.

Nonresonant CARS Imaging of Porous and Solid Silicon Nanoparticles in Human Cells.

Coherent anti-Stokes Raman scattering (CARS), a nonlinear optical method for rapid visualization of biological objects, represents a progressive tool in biology and medicine to explore cells and tissue structures in living systems and biopsies. In this study, we report efficient nonresonant CARS imaging of silicon nanoparticles (SiNPs) in human cells as a proof of concept. As both bulk and porous silicon exhibit a high third-order nonlinear susceptibility, χ(3), which is responsible for the CARS intensity, it is possible to visualize the SiNPs without specific labels. Porous and solid SiNPs were obtained from layers of porous and nonporous silicon nanowires and mesoporous silicon. Electron microscopy and Raman spectroscopy showed that porous SiNPs consisted of ∼3 nm silicon nanocrystals (nc-Si) and pores, whereas solid nanoparticles comprised ∼30 nm nc-Si. All types of SiNPs were nontoxic at concentrations up to 500 μg/mL after 24 h of incubation with cells. We demonstrated that although nc-Si possesses a distinguished narrow Raman band of about 520 cm-1, it is possible to detect a high CARS signal from SiNPs in the epi-direction even in a nonresonant regime. 3D CARS images showed that all types of studied SiNPs were visualized as bright spots inside the cytoplasm of cells after 3-6 h of incubation because of the contrast provided by the high third-order nonlinear susceptibility of SiNPs, which is 1 × 104 to 1 × 105 times higher than that of water and typical biological media. Overall, CARS microscopy can provide localization of SiNPs within biological structures at the cellular level and can be a powerful tool for in vitro monitoring of silicon-based drug delivery systems or use SiNPs as labels to monitor various bioprocesses inside living cells.

Mode-locked fiber laser based on [formula omitted]-Fe2O3 nanosheets as saturable absorbers

With broadband saturable absorption properties and a high third-order nonlinear optical susceptibility, α-Fe2O3 exhibits potential applications in nonlinear optics. In this study, α-Fe2O3 nanosheets are embedded into polyvinyl alcohol (PVA) films to fabricate thin-film saturable absorbers (SAs) that feature an uninterrupted broad absorption band spanning over 2000 nm and a modulation depth of 16.13%. In α-Fe2O3-PVA SA-based erbium-doped fiber lasers, two stable mode-locked operations are achieved: dark-bright pulse pairs and bright solitons. The results indicate that α-Fe2O3 nanosheets are excellent candidates for two-dimensional saturable absorption materials.

Intracavity second harmonic generation from a WSe2 monolayer in a passively mode-locked picosecond fiber laser

A single layer WSe2 crystal is transferred on the tip of a single mode fiber that is placed in the cavity of a Yb3+ doped picosecond fiber oscillator. This intracavity monolayer generates second harmonics without affecting the stable mode-locking and laser output of the fiber oscillator. This method utilizes the higher intracavity optical intensities to increase the SHG conversion efficiency, thus combining the high nonlinear susceptibility and the phase-matching independence of a monolayer with the versatility of a fiber laser in an all-fiber integrated system. We also demonstrated a procedure to verify the monolayer placement on the fiber core by hyperspectral mapping. This intracavity SHG has possible applications for self-referencing f-2f interferometry in fiber-laser frequency combs.

High-efficiency generation of harmonics in polythiophene

High-efficiency harmonic generation is observed in a semiconducting polymer RR-P3HT [regioregular poly(3-hexylthiophene)], which exhibits a high nonlinear susceptibility [χ (2) > 10−6 m V−1] under pumping by a pulsed fibre laser. The harmonic generation efficiency in RR-P3HT is comparable or higher than that observed for liquid crystals, which are used in reference experiments to estimate the susceptibility [the quadratic susceptibility of a nematic liquid crystal NLC 1289 is χ (2) ≈ 2 × 10−6 m V−1]. No generation is observed in polythiophene with a random structure, RRa-P3HT [regiorandom poly(3-hexylthiophene)], at the same pump power. It is experimentally demonstrated that a necessary condition for generating the second and third harmonics in a polymer, along with a high pump power density, is the presence of a large power density gradient (exceeding 1013 W m−3). Based on a preliminary theoretical analysis, we can suggest that the quadrupole mechanism, which is a consequence of the regularity of RR-P3HT structure in the thin near-wall layer, may contribute significantly to the nonlinear radiation conversion in semiconducting polymers.