Third-order Nonlinear Effects Research Articles

Enhancing silicon wafer ablation using passive Q-switch [formula omitted] lasers with third-order nonlinear effects

We show that a passive Q-switch nanosecond Tm:Yap laser operating at 1.940μm is a promising candidate for conducting ablation process at the surface of silicon wafers. By modulating the fluence intensity of the lasing source, we can engrave the surface with a short series of pulses and obtain sharp and regular craters with a high level of repeatability. Our results show that we can get highly repeatable craters of diameters ranging from D=10.0μm up to D=40.0μm with a laser operating We easily manage the hole depth by choosing the correct fluence repetition rate between pulses, reducing the waste deposition on the borders of the holes. For fluences greater than 3.8J/cm2, third-order nonlinear effects, such as the lens converging Kerr n2 and the two-photon absorption βTPA effects, turn the silicon into an absorbing medium, improving the ablation process. At a room temperature of 300°K, n2=12.0×10−5±2.0×10−5cm2/GW and βTPA=0.56±0.02cm/GW, the resulting nonlinear factor of merit NFOM=2.1±2.0 is very large; conferring a self-focusing lensing action on the silicon. We also observe that these latter nonlinear effects modify the regular linear regression relating the ablated surface to the logarithm of the fluence, enhancing the efficiency of the ablation process at higher fluences due to these effects.

High-order effect on the transmission of two optical solitons

For optical solitons with the pulse width in the subpicosecond and femtosecond scales in optical fibers, a modified model containing higher-order effects such as third-order dispersion and third-order nonlinearity is needed. In this paper, in order to study the dynamic mechanism of femtosecond solitons in different media, we take the nonlinear Schrödinger equation considering higher-order effects as the theoretical model, discuss the propagation of solitons in single-mode fibers, and explore the third-order dispersion and third-order nonlinear effects on the generation of optical solitons. The exact solution of the theoretical model is obtained through the bilinear method, and the transmission characteristics of two solitons with exact soliton solutions in actual fiber systems are analyzed and studied. The influence of various conditions on the transmission and interaction of optical solitons is explored. Methods for optimizing the transmission characteristics of optical solitons in optical communication systems are suggested. The relevant conclusions of this paper have guiding significance for improving the quality of fiber optic communication and increasing bit rates.

Cascaded four-wave mixing all-optical wavelength converter based on highly nonlinear fiber deposited graphene oxide

The all-optical wavelength conversion using cascaded four-wave mixing (FWM) phenomena with graphene oxide (GO) and a highly nonlinear fiber (HNLF) device is demonstrated experimentally. GO has a strong third-order nonlinear effect and is an excellent nonlinear optical material for nonlinear optical wavelength conversion. The group velocity matching of pump and signal, HNLF, and GO amplification promote the cascaded nonlinear frequency mixing process. From the experimental and analytical results, the maximum spacing between signal and pump is 21 nm, and specifically, the order of cascaded FWM light increases from order 1 to order 2 with increasing GO, and the first-order FWM conversion efficiency increases to a maximum of −14.5 dB. To the best of our knowledge, this is the first time that cascaded FWM-based all-optical wavelength conversion in HNLF–GO with wide wavelength selectivity is investigated with combined pump and signal light. Our findings not only provide an effective method for achieving all-optical wavelength conversion in cascaded FWM but also offer the possibility of fabricating high-performance nonlinear optical devices.

Zero-refractive-index waveguide by using layered structures

In this paper, we proposed a layered structure composed of two kinds of materials. The interface of this structure has zero-refractive-index (ZRI) frequencies in near-infrared regime at which the relative dielectric constant or permeability is zero. We analyze the dispersion relation of various materials, design a layered structure, and explore the possibility of realizing ZRI by using metal and two-dimensional materials. The results show that at the interface between borophene and chromium film (BP-Cr) there are ZRI points in a large range from visible to near-infrared. On this basis, the third-order nonlinear effects of two-layer structure based on BP-Cr are examined. The particularity of the ZRI-frequency point of the structure meets phase matching very well, which greatly enhances the intensity of the third-harmonic generation. It is also 10–100 times that of silicon under the same conditions, indicating that Bp-Cr combination will have a potential application prospect in nonlinear optical field.

Intensity-dependent transition from saturation absorption to reverse saturable absorption ways in TiSxSe2-x (0 ≤ x ≤ 1)

• Different atom ratios of TiS 2-x Se x were regulated by sulfur doping. • A laser intensity-dependent transition from SA to RSA in TiS x Se 2-x nanosheets was observed. • With the increase of S 2− contents in TiS x Se 2-x , the SA effect became weaker while the RSA effect became stronger. The third-order nonlinear effects in the TiS x Se 2-x (0 ≤ x ≤ 1) nanosheets were investigated via the open-aperture (OA) Z-scan technique. An input fluence dependent transition from saturation absorption (SA) to reverse saturable absorption (RSA) ways in TiS x Se 2-x was discovered. Under lower laser intensities, only SA existed in the TiS x Se 2-x . Higher incident laser intensities caused the transition from SA to RSA, due to the competition between ground state absorption and excited state absorption. This unique intensity-dependent absorption transition can be applied in all-optical logic gates, fast optical switch, optical limiter, mode storage.

X-ray third-order nonlinear diffraction in the asymmetric reflection geometry.

X-ray third-order nonlinear asymmetrical diffraction has three independent parameters: the asymmetry angle, the incident wave intensity and the deviation from the exact Bragg orientation. In contrast to the linear case, in the nonlinear case the total reflection region does not exist for all intensity values and asymmetry angles. Theoretical consideration leads to analytical conditions of the total reflection region, and the analysis can be carried out by a graphical method. An exact solution in the total reflection region is found. The numerical solutions of the third-order nonlinear diffraction allow one to find the reflection curves for a fixed asymmetry angle or for a fixed intensity. For very large or very small asymmetry factors the third-order nonlinear effects can be observed for beams with very low intensities.

Applications of thin-film lithium niobate in nonlinear integrated photonics

Photonics on thin-film lithium niobate (TFLN) has emerged as one of the most pursued disciplines within integrated optics. Ultracompact and low-loss optical waveguides and related devices on this modern material platform have rejuvenated the traditional and commercial applications of lithium niobate for optical modulators based on the electro-optic effect, as well as optical wavelength converters based on second-order nonlinear effects, e.g., second-harmonic, sum-, and difference-frequency generations. TFLN has also created vast opportunities for applications and integrated solutions for optical parametric amplification and oscillation, cascaded nonlinear effects, such as low-harmonic generation; third-order nonlinear effects, such as supercontinuum generation; optical frequency comb generation and stabilization; and nonclassical nonlinear effects, such as spontaneous parametric downconversion for quantum optics. Recent progress in nonlinear integrated photonics on TFLN for all these applications, their current trends, and future opportunities and challenges are reviewed.

Theoretical design, synthesis and third-order non-linear optical properties of thiophene and tetrafluorobenzene based low band gap conducting polymers

Low band gap donor-acceptor type π-conjugated conducting polymers P(BT-4FPH), P(3METH-4FPH) and P(TH-4FPH) were theoretically designed using Gaussian 09 with two hybrid functionals B3LYP, HSE06/6–31 G (d,p) basis set. Oscillator strength and excitation energy of the monomers were determined by TD-DFT/B3LYP/6–31 G (d,p) method. Copolymers were synthesized by the direct arylation polymerization method. Structural characterization was done by FTIR and 1H NMR spectra. Thermal stabilities of the copolymers were evaluated by TG. The molecular weights of the copolymers were obtained by Gel permeation chromatography. Cyclic voltammetry (CV) was used to observe the electrochemical band gaps of the copolymers. Theoretical observations from HSE06/6–31 G (d,p) method supported the experimental results. Third-order non-linear optical properties and optical limiting effect of the copolymers were studied at different laser intensities using the open-aperture Z-scan technique at 532 nm in DMSO. P(BT-4FPH) exhibited strong optical non-linearity with reverse saturable absorption when compared with P(3METH-4FPH) and P(TH-4FPH) with non-linear absorption coefficient β = 1.20 × 10−8 m/W at 20 µJ. Optical threshold values obtained for the copolymers were low which indicated that the polymers could be used for optical power limiting devices. Among the three synthesized copolymers, P(BT-4FPH) exhibited higher molecular weight, lowest electrochemical band gap and showed strong non-linear absorption with lowest optical threshold value of 0.009 GW/cm2 at 10 µJ due to the increased delocalization of π- electrons over the conjugated backbone of donor-acceptor units.

Ultrabroadband nonlinear Raman–Nath diffraction against femtosecond pulse laser

Nonlinear Raman–Nath diffraction (NRND) offers an effective way to realize multiple noncollinear parametric processes based on the partially satisfied transverse phase-matching conditions in quadratic nonlinear media. Here, the realization of ultrabroadband NRND (UB-NRND) driven by a high-peak-power ultrashort femtosecond pump laser in two types of nonlinear crystals is reported: periodically poled lithium niobate (PPLN) and chirped PPLN (CPPLN). Multi-order ultrabroadband Raman–Nath second-harmonic (SH) signal outputs along fixed diffraction angles are simultaneously observed. This distinguished transversely phase-matched supercontinuum phenomenon is attributed to the synergic action of natural broad bandwidth of an ultrashort femtosecond pump laser and the third-order nonlinear effect induced spectral broadening, in combination with the principal ultrabroadband noncollinear second-harmonic generation processes. The NRND process with multiple quasi-phase matching (QPM) interactions from CPPLN leads to the SH output covering a wide range of wavelengths between 389 and 997 nm and exhibiting an energy conversion efficiency several orders of magnitude higher than previous studies. This UB-NRND scheme would bring better techniques and tools for applications ranging from ultrashort pulse characterization and nondestructive identification of domain structures to accurate parameter monitoring of second- and third-order nonlinear susceptibilities within solid-state nonlinear microstructured materials.

Near-infrared all-fiber mode-locked laser based on vanadium carbide nanosheets

Vanadium carbide (V2C), a newly developed MXene, has been theoretically predicted to be an excellent nonlinear optical materials. Here, few-layer V2CTx nanosheets were synthesized by liquid phase exfoliation (LPE) method. Z-scan measurement was performed to explore their third-order nonlinear optical properties, highlighting the strong nonlinearities of few-layer V2CTx nanosheets. And the effective nonlinear absorption coefficient was determined to be − 98.3 cm/MW, corresponding to the imaginary part of the third-order nonlinear effects was obtained to be − 1.106 × 10−8 esu. In addition, microfiber-based few-layer V2CTx saturable absorber (SA) was fabricated by optical deposition method and the saturable absorption characteristic was measured by I-scan technique. The Yb-doped and Er-doped fiber lasers (YDFLs and EDFLs) were performed by inserting microfiber-based few-layer V2CTx SA into the ring cavity. And the stable mode-locked operation was realized with super high signal- noise ratio (SNR). Our work systematically reveals that few-layer V2CTx nanosheets should be an excellent SA for ultrafast photonics in the near-infrared band.

Boosting the SiN nonlinear photonic platform with transition metal dichalcogenide monolayers.

In the past few years, we have witnessed increased interest in the use of 2D materials to produce hybrid photonic nonlinear waveguides. Although graphene has attracted most of the attention, other families of 2D materials such as transition metal dichalcogenides have also shown promising nonlinear performance. In this work, we propose a strategy for designing silicon nitride waveguiding structures with embedded MoS2 for nonlinear applications. The transverse geometry of the hybrid waveguide is optimized for high third-order nonlinear effects using optogeometrical engineering and multiple layers of MoS2. Stacking multiple monolayers results in an improvement of two orders of magnitude compared to standard silicon nitride waveguides. The hybrid waveguide performance is then investigated in terms of four-wave mixing enhancement in micro-ring resonator configurations. A signal/idler conversion efficiency of -6.3 dB is reached for a wavelength of around 1.55 µm with a 5 mW pumping level.

Integrable high-efficiency generation of three-photon entangled states by a single incident photon

Generation of multi-photon entangled states with high efficiency in integrated photonic quantum systems is still a big challenge. The usual three-photon generation efficiency based on the third-order nonlinear effect is extremely low. Here, we propose a scheme to generate three-photon correlated states, which are entangled states in frequency space and bound states in real space, with high efficiency. This method relies on two crucial processes. On one hand, by employing a Sagnac interferometer, an incident photon can be transformed into a symmetric superposition of the clockwise and counterclockwise modes of the Sagnac loop, which can then be perfectly absorbed by the emitter. On the other hand, the coupling strengths of the two transition paths of the emitter to the Sagnac loop are set to be equal, under which the absorbed photon can be emitted completely from the cascaded transition path due to quantum interference. By adjusting the coupling strengths among the three transition paths of the emitter and the waveguide modes, we can control the spectral entanglement and spatial separation among the three photons. Our proposal can be used to generate three-photon entangled states on demand, and the efficiency can be higher than 90% with some practical parameters, which can find important applications in integrated quantum information processing.

Third-order nonlinear optical properties and thermal lens effect of 5-hydroxyquinoline azo dyes

In this research, the third-order nonlinear characteristics of some novel azo dyes based on 5-hydroxyquinoline (containing quinoline skeleton in their structure) were studied via Z-scan technique and by means of a continuous wave of a diode-pumped laser at the wavelength 532 nm with an intensity of 38.72 × 103 W/m2. The nonlinear absorption coefficient and nonlinear refractive index (β and n2, respectively) were calculated by fitting the theoretical model and experimental data obtained from the Z-scan technique. The open aperture component of this technique illustrated reverse saturable absorption phenomenon. Thermal nonlinear phase shift affected the shapes of closed-aperture Z-scan curves, and they did not fit well with the common theoretical models. The forms of peak-to-valley in these plots did behave like a modified aberrant thermal lens model. The substituent effect on the values of β and n2 was also investigated and demonstrated that the azo dyes bearing electron-withdrawing groups offer higher values of β and n2 than the other azo dyes with or without electron-donating groups. The calculated values of third-order susceptibility of these azo dyes were from the order 10-6esu, indicating their potential capability for the use in optical devices.

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.

Synthesis and Third-Order Nonlinear Synergistic Effect of ZrO2/RGO Composites.

Tuning the third-order nonlinear properties of graphene by hybrid method is of great significance in nonlinear optics research. ZrO2/reduced graphene oxide (RGO) composites with different ZrO2 concentrations were prepared by a simple hydrothermal method. The morphology and structure show that ZrO2 nanoparticles were uniformly dispersed on the surface of graphene nanosheets. The nonlinear optical (NLO) characteristics of composites with different ZrO2 concentrations were studied by the Z-scan technique of 532 nm picosecond pulsed laser. The results showed that ZrO2/RGO composites had saturated absorption and positive nonlinear refraction characteristics. Meanwhile, the third-order nonlinear susceptibility of the ZrO2/RGO composite with a 4:1 mass ratio of ZrO2 to graphene oxide could reach 23.23 × 10−12 esu, which increased tenfold compared to RGO, and the nonlinear modulation depth reached 11.22%. Therefore, the NLO characteristics could be effectively adjusted by controlling the concentration of ZrO2, which lays a foundation for further research on the application of ZrO2/RGO composites in NLO devices.

Transformation from Self-Focusing to Self-Defocusing of Silver Nanoparticles.

The nonlinear refraction of silver nanoparticles (AgNPs) in n-hexane was studied by using the closed-aperture Z-scan technique with a 532 nm nanosecond laser. It was found that, the nonlinear refraction of AgNPs shows the coexistence and transformation from self-focusing to self-defocusing. Specifically, self-focusing occurs at low excitation intensity, self-defocusing occurs at high excitation intensity, and coexistence of self-focusing and self-defocusing occurs at relatively moderate excitation intensity. The experimental results were analysed and discussed in terms of third-order and fifth-order nonlinear refractive effect. Specifically, the self-focusing is caused by the positive third-order nonlinear refraction, the self-defocusing is induced by the negative fifth-order nonlinear refraction, and the transformation from the self-focusing to self-defocusing at medium excitation intensity is caused by the competition of third-order and fifth-order nonlinear refraction. Finally, the third-order refractive index and fifth-order refractive index were obtained.

Laser-frequency-comb calibration for the Extremely Large Telescope: an OPO-based infrared astrocomb covering the H and J bands

The Extremely Large Telescope (ELT) will address an unprecedented optical wavelength range from 370 to 2400 nm, and its high-resolution spectrograph (HIRES) will require a laser frequency comb calibrator of comparable coverage. An architecture based around a Ti:sapphire master comb in principle enables wavelengths across this range to be obtained by a combination of second- and third-order nonlinear effects. In this scheme, near-infrared wavelength coverage can be addressed by downconversion of the comb to 1600 nm using an optical parametric oscillator (OPO), followed by broadband supercontinuum generation in highly nonlinear fiber. Here we present an example of this approach in the form of a 10 GHz astrocomb comprising a Fabry–Perot-filtered supercontinuum derived from a degenerate OPO and spanning 1.15–1.80 µm. We characterize the astrocomb using Fourier-transform spectroscopy, enabling the mode orders within the filtered comb to be identified.

Deterministic generation of parametrically driven dissipative Kerr soliton

Abstract We theoretically study the nature of parametrically driven dissipative Kerr soliton (PD-DKS) in a doubly resonant degenerate micro-optical parametric oscillator (DR-DμOPO) with the cooperation of χ (2) and χ (3) nonlinearities. Lifting the assumption of close-to-zero group velocity mismatch (GVM) that requires extensive dispersion engineering, we show that there is a threshold GVM above which single PD-DKS in DR-DμOPO can be generated deterministically. We find that the exact PD-DKS generation dynamics can be divided into two distinctive regimes depending on the phase matching condition. In both regimes, the perturbative effective third-order nonlinearity resulting from the cascaded quadratic process is responsible for the soliton annihilation and the deterministic single PD-DKS generation. We also develop the experimental design guidelines for accessing such deterministic single PD-DKS state. The working principle can be applied to different material platforms as a competitive ultrashort pulse and broadband frequency comb source architecture at the mid-infrared spectral range.

Emergence of fifth-order optical nonlinearity in 2-(2-Quinolyl)-1,3-indandione with strong third-order nonlinear effect under low power CW laser excitation

The present work reports the presence of fifth-order optical nonlinearity in 2-(2-Quinolyl)-1,3-indandione, an organic dye, at low intensity level. Photophysical, structural and vibrational properties were studied by theoretical and experimental methods. Z-scan study of the dye revealed that the compound has a self-defocusing behaviour at continuous Nd:YAG 532 nm laser excitation and exhibited reverse saturable absorption. The positive fifth-order nonlinear refractive index (n4) is of the order of 10−10 cm4/W2. The nonlinearities present in the compound has both thermal and electronic origin. This study reveals that the material is a potential candidate as an optical limiter at low power.

Circular photogalvanic effect from third-order nonlinear effect in 1T’-MoTe2

The two-dimensional layered material MoTe2 has aroused extensive research interests in its rich optoelectronic properties in various phases. One property of particular interest is the circular photogalvanic effect (CPGE): a conventional second order nonlinear optical effect that is related to the chirality of materials. It has been demonstrated in Td-MoTe2, a type-II topological Weyl semimetal candidate, while it has been unclear so far whether it exists in the semimetallic 1T’ phase, another interesting phase that hosts a quantum spin hall state. In this article, we report a clear experimental observation of in-plane CPGE in 1T’-MoTe2. The observation is confirmed under various experimental designs with excitation by normally incident mid-infrared laser, and we find it to be related to an in-plane internal DC electric field. We attribute the circular photogalvanic response to a third-order nonlinear optical effect involving this DC electric field, which is consistent with the crystal symmetry of the lattices and present in both the 1T’ and Td phases of the material.