High Third-order Nonlinear Susceptibility Research Articles

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.

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.

Enhanced optical power limiting and visible luminescence in colloidal dispersion of ultra-small Au nanoclusters synthesized by single-pot chemical technique

Here, we present a detailed investigation on the synthesis and nonlinear multiphoton absorption properties of the colloidal solution of Au nanoclusters (AuNCs) which contains the atomic clusters, with the number of atoms per cluster (NAC) of only one (Au1NC) and two (Au2NC). These AuNCs are synthesized by an easy single step one-pot simple chemical process and by using dimethylformamide (DMF) both as reducer and stabilizer. The presence of both Au1NC and Au2NC are found in the sample by their distinct signature in the UV–Vis. absorption spectrum as well as in the high-resolution mass spectrum. The synthesized material has been found to exhibits a strong and stable blue-luminescence with a moderately high quantum yield (QY) of 12.4% when excited with UV light. The nonlinear optical two-photon absorption (2PA) properties of Au1, Au2NC solutions are being reported here by Z-scan studies, for the first time, by using both 10 ns and 100 fs pulse laser radiations having wavelength of 532 nm. It is significantly noted here that the synthesized AuNCs are found to exhibit reverse saturable absorption (RSA) when excited either by ns or by fs laser pulses. A high third-order nonlinear susceptibility (ꭓ(3)) of the order of 10−13 (esu) of the synthesized materials are obtained under fs laser excitation and it is attributed to the 2PA through electronic band to band transition. In contrast, the variation of the 2PA coefficient (β) with input intensity (I0) represents the footprint of free carrier involvement in the enhanced nonlinear absorption in the case of ns excitation. Furthermore, through the non-saturable nonlinear multiphoton absorption, the synthesized AuNCs exhibit excellent optical power limiting phenomenon with the limiting threshold (Fth) of 9.1 mJ/cm2 (fs excitation) and 2.02 J/cm2 (ns excitation) owing to their enhanced 2PA coefficient. Therefore, we believe that our synthesized ultra-small colloidal AuNCs can be used as the promising candidate material for advanced photonics application in the future.

Generation of tunable ultraviolet femtosecond pulse in MgO crystal by cascaded four wave mixing

Ultraviolet femtosecond laser pulse is an important tool in studying ultrafast chemical and physical processes. Realizing broadband ultraviolet laser pluses with a wide tunable range would significantly facilitate the study of ultrafast processes. As an effective and convenient method, the cascaded four-wave mixing (CFWM) has been widely adopted to generate broadband and tunable ultraviolet femtosecond laser pulses. In this work, we carry out CFWM in MgO crystal by using two 400-nm pulses to generate tunable ultraviolet femtosecond pulse. The MgO crystal is chosen due to its high third-order nonlinear susceptibility, large band gap and high transmittance in the ultraviolet region. In the experiment, nine frequency up-converted and five frequency down-converted sidebands are observed. The measured wavelength and scattering angle of each sideband are consistent with the CFWM theory predictions. The wavelength range of the sidebands covers 350–450 nm. The total conversion efficiency of the ultraviolet sidebands is 1.2%, which is higher than the reported values with visible/near infrared driven lasers. Meanwhile, the spectra of the high-order sidebands present a Gaussian profile and can support a Fourier-transform-limited pulse duration of less than 50 fs. Besides, the central wavelengths of the sidebands can be effectively tuned by adjusting the time-delay between the two pre-chirped pump pulses. Our study provides an efficient and convenient scheme to generate short ultraviolet femtosecond pulses with a wide tunable range.

Structural investigation of new tellurite glasses belonging to the TeO2-NbO2.5-WO3 system, and a study of their linear and nonlinear optical properties

The glass-forming domain, density, thermal, structural and optical properties of new glasses within the TeO2-NbO2.5-WO3 system have been investigated. By means of Raman spectroscopy, a thorough structural analysis of these glasses has been undertaken on the basis of a full-scale spectral decomposition process. The optical transmission window, refractive index dispersion and third-order nonlinear susceptibilities χ(3) were measured by UV–Vis-NIR spectroscopy, spectroscopic ellipsometry and Z-scan method respectively. Consistent correlations are successfully established between the measured structural, linear and nonlinear optical properties. In general, the structural features of the glass network are found to evolve mildly upon adding NbO2.5 or WO3. Nonetheless, a weak structural depolymerization of the TeOTe bond network as a result of adding NbO2.5 is evidenced and discussed in detail. Upon continuous addition of NbO2.5 and/or WO3, the glass network becomes progressively richer in NbO2.5-rich and/or WO3-rich regions before the crystallization of Nb6TeO17 (NbO2.5:TeO2 ratio of 6:1) and WO2.83 compounds respectively. The studied glasses exhibit high linear refractive indices with an average of ~2.13 and very high third-order nonlinear susceptibilities χ(3) with an average of 5.48 *10−13 esu (~37 times higher than that of SiO2 glass).

Correlation between induced changes in the structural properties of nanostructured boron subphthalocyanine chloride thin films and their linear and nonlinear optical properties

Metal phthalocyanines (MPcs) are widely used in optoelectronic applications thanks to their high absorption in the visible region, durability, tunability and chemical stability. This paper aims to address the induced changes in the structure of boron subphthalocyanine chloride (BsubPc-Cl) thin films – before and after annealing processes – and correlate these changes with their linear and nonlinear optical properties. The BsubPc-Cl thin films have been characterized via the differential scanning calorimeter (DSC), X-ray diffraction (XRD), atomic force microscope (AFM) and UV–Vis.-IR spectroscopy. The DSC thermograph curve through a wide range of temperatures (20–340 °C) has proved the thermal stability of BsubPc-Cl films. The XRD calculations have revealed the nanostructure of the films. In addition, the particle size is a temperature dependent and it increases with increasing annealing temperature. In context, the AFM images have declared that the roughness of the films’ surfaces increases with increasing annealing temperature. The absorbance spectra of BsubPc-Cl thin films have elucidated two peaks at λ = 300 and 603 nm which are assigned to B and Q bands, respectively. Further, the pristine film had a peak centered at 1550 nm which underwent a blue shift to 1185 nm due to annealing. The BsubPc-Cl films have showed high third-order nonlinear susceptibility χ3 = 8×10-12 esu. Moreover, χ3 values have increased between visible and NIR regions which may suggest employing BsubPc-Cl as an optical switch.

Polymer-Free Carbon Nanotubes Saturable Absorbers for Nanosecond Pulse Generation

Hereby we present the results of investigations of nonlinear optical properties of single-walled carbon nanotube (CNT) thin-film saturable absorbers without binding polymers. Developed CNT-based polymer-free saturable absorbers exhibit high third-order nonlinear susceptibility: esu, low absorption saturation intensity: Is∼30 mW/cm2, and high photostability. Using CNT-based polymer-free saturable absorbers for passive Q-switching mode of Nd:YAG laser, 25 ns laser pulses have been obtained.

Efficient phase-matched third harmonic generation in a metal-clad plasmonic double-slot waveguide

We propose a metal-clad plasmonic double-slot waveguide with DDMEBT integrated into the slot region as the interactive material for third harmonic generation (THG) from the mid-IR (3600 nm) to the near-IR (1200 nm) region. Typically, an efficient THG process in a waveguide platform relies on three key aspects: high third-order nonlinear susceptibility of the interactive material, fulfillment of the phase-matching condition (PMC), and large pump-harmonic modal overlap. Although it has been theoretically predicted to be possible, designing waveguides to achieve the three key aspects simultaneously is still a major challenge. In the metal-clad plasmonic double-slot waveguide, the PMC between the zeroth mode at the fundamental wave (FW) and the second mode at the third harmonic (TH) is achieved. Taking advantage of the channel plasmon polariton (CPP), the electric fields at both FW and TH are tightly confined in the slot region. The specific slot waveguide structure is exploited to significantly enhance the pump-harmonic modal overlap by greatly reducing the counteractive electric field portion of the second mode at TH. According to our simulation, THG conversion efficiency reaches 1.4732 × 10−5 with 3 W pump power at a waveguide length of 12.3 μm. This THG efficiency is greatly enhanced because of the high third-order nonlinear optical susceptibility of the DDMEBT, the specific plasmonic slot waveguide structure, and the CPP nature of the guided modes—it is more than two times that obtained by simply considering a single slot under the same slot-width condition.

Microfiber-Based Highly Nonlinear Topological Insulator Photonic Device for the Formation of Versatile Multi-Soliton Patterns in a Fiber Laser

We reported on the observation of versatile multi-soliton patterns in an erbium-doped fiber laser with a microfiber-based topological insulator (TI) photonic device. Taking advantage of both the high third-order nonlinear susceptibility and excellent saturable absorption of TI, various multi-soliton formations, such as soliton molecules, bound solitons, and soliton rains could be easily obtained at a low pump power. These results might deepen the understanding of nonlinear dynamics of multi-soliton patterns, and further demonstrate that the TI deposited microfiber could operate as a high-performance photonic device with both highly nonlinear effect and saturable absorption for the related optics applications.

Synthesis and properties of multifunctional poly(2-trimethylsilyl-1,4-phenylenevinylene): a novel, silicon-substituted, soluble PPV derivative

The novel, silicon-substituted, soluble PPV derivative, poly(2-trimethylsilyl-1,4-phenylenevinylene)(TMS–PPV), is prepared in a solution elimination process and shows high electrical conductivity after I2 doping, high third-order nonlinear susceptibility and green light-emitting properties.