Two-photon Absorption Effect Research Articles

Nonlinear Optical Properties of Aurintricarboxylic Acid Compound(B)Using Z-Scan Technique

In the present work, the spectral properties (absorption and fluorescence) for liquid Aurintricarboxylic Acid compound (B) dissolve in dimethy sulfoxide (DMSO) were studied at different concentrations(1×10−4 and 1×10−5)M, nonlinear optical parameters was study by use technique of z-scan represented by the nonlinear refractive index and nonlinear absorption coefficients, several testing were done including, Fourier-transform infrared spectroscopy(FTIR), nuclear magnetic resonance (NMR),results showed the effect of self-focusing in the material at higher intensities, which evaluated n2,the effect of two-photon absorption was studied which evaluated β. In addition, the optical limiting behavior has been studied, the results confirmed the capability of the sample to be used as optical limiter device.

Picosecond pulse pumped supercontinuum generation in silicon waveguide with a weak continuous wave trigger

We numerically demonstrate that picosecond pulse pumped supercontinuum (SC) generation in a silicon waveguide can be enhanced with the assistance of a weak continuous-wave (CW) trigger. The bandwidth of the resulting SC is greatly improved. The effects of two-photon absorption, free-carrier absorption, and free-carrier dispersion on SC generation in the silicon waveguide are studied. The optimized trigger position is close to the modulation instability peak. The results help us understand the details of SC generation in silicon waveguides in the presence of a CW trigger and noise. By tuning the wavelength of the CW trigger, we reach a good temporal coherence and intensity stability in the picosecond pulse pumped SC generation in a silicon waveguide.

Plasmon coupling interactions and inhibition of nonlinear absorption in a complex system with Ag and Pt nanoparticles in silica.

The optical response exhibited by a complex hybrid system integrated by Pt ultrasmall fluorescent particles and plasmonic Ag nanoparticles is reported. The system was synthesized by coimplantation of Ag and Pt ions into a silica matrix followed by a proper thermal annealing. The energies and fluences were chosen in order to overlap the spatial regions of the Ag and Pt ion distributions below the silica surface. Optical absorption and emission spectroscopies show that the complex nanostructures exhibit an important plasmonic response, together with photoluminescence excited at 355 nm, which is enhanced when compared to the reference sample with only Pt particles. Off-resonance nonlinear transmission and Z-scan measurements were undertaken using ultrafast pulses. High-irradiance excitation at 1064 nm with picosecond pulses shows that the Pt or Ag nanoparticles exhibit a two-photon absorption effect, while the complex system shows the absence of any nonlinear absorption. Similar observations were made using femtosecond pulses at 800 nm wavelength. This inhibition of the two-photon absorption effect and enhancement in the emission of the complex hybrid samples by the synergic participation of Ag and Pt particles can be explained as a result of a plasmon coupling via the near-field interaction between plasmonic and emitting sources.

Anisotropic two-photon absorbers measured by the Z-scan technique and its application in laser beam shaping

We investigate anisotropic two-photon absorption (TPA) effects in a cubic-symmetry crystal excited by scalar and vectorial optical fields. First, we present the anisotropic TPA coefficient, which depends on the anisotropy coefficient, the dichroism coefficient, the crystal orientation angle, and the ellipticity of the polarized ellipse. Second, we develop the elliptically polarized light Z-scan technique for characterizing anisotropic two-photon absorbers, which is demonstrated experimentally. Last, we present the laser beam shaping of vectorial optical fields with Gaussian intensity distribution into a flat-top profile through anisotropic TPA effects. It is shown that the anisotropic TPA offers a new avenue to manipulate the intensity distribution of the polarization-structured light field, which may find interesting applications in beam shaping, optical limiting, and photodetection.

MZI-based all-optical serial-to-parallel conversion circuit by free-carrier dispersion effect

Device applications of nonlinear optical phenomena on the silicon-on-insulator platform are attracting significant attention in silicon photonics. We report a novel on-chip Mach–Zehnder interferometer-type serial-to-parallel converter aimed at all-optical label processing of optical packets. We focus on the free-carrier dispersion effect during phase modulation of the serial probe signal, and a pump signal is used to generate sufficient free-carriers within the waveguide structure. By leaving out a delay between the pump and probe pulses, we avoid the effects of pump-induced cross-phase modulation and two-photon absorption, and perform serial-to-parallel conversion at a lower pump power. In the theoretical analysis, serial-to-parallel conversion of a 10-Gbps probe signal is considered. By numerical simulations, the shortest arm length of the Mach–Zehnder interferometric structure required for operation is calculated. When doing so, the pump pulse width and delay between the pulses are varied while the pulse energy of the pump is held constant at 25 pJ, and the combination of values that corresponds to the shortest arm length is taken as optimum values. Our study reveals that the optimum values for delay and pump pulse width are 30 ps and 25 ps, respectively. Finally, we also demonstrate single-bit serial-to-parallel conversion experimentally on a Mach–Zehnder interferometric device. Phase modulation due to free-carrier dispersion was observed at peak pump power levels of 1.0 W at the waveguide input.

Neural-network-assisted femtosecond laser pulse duration measurement using two-photon absorption

In this work, a neural network (NN) method is developed for pulse duration inferring for an erbium-doped fiber laser at 1550 nm. Experimentally, the interferometric autocorrelation trace is observed clearly with the use of the two-photon absorption (TPA) effect in a GaAs photodiode. The intensity autocorrelation function is curve-fitted by the NN with an appropriate performance, and the measuring accuracy is consistent with a commercial autocorrelator. Compared with the Levenberg–Marquardt curve-fitting method, the NN can retrieve the intensity autocorrelation function more stably and has a certain noise reduction ability, simplifying the signal processing for a TPA photodiode-based autocorrelator.

Femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles

We investigate femtosecond laser trapping dynamics of two-photon absorbing hollow-core nanoparticles with different volume fractions and two-photon absorption (TPA) coefficients. Numerical simulations show that the hollow-core particles with low and high-volume fractions can easily be trapped and bounced by the tightly focused Gaussian laser pulses, respectively. Further studies show that the hollow-core particles with and without TPA can be identified, because the TPA effect enhances the radiation force, and subsequently the longitudinal force destabilizes the trap by pushing the particle away from the focal point. The results may find direct applications in particle sorting and characterizing the TPA coefficient of single nanoparticles.

Solitonic Fixed Point Attractors in the Complex Ginzburg–Landau Equation for Associative Memories

It was recently shown that the nonlinear Schrodinger equation with a simplified dissipative perturbation features a zero-velocity solitonic solution of non-zero amplitude which can be used in analogy to attractors of Hopfield’s associative memory. In this work, we consider a more complex dissipative perturbation adding the effect of two-photon absorption and the quintic gain/loss effects that yields the complex Ginzburg–Landau equation (CGLE). We construct a perturbation theory for the CGLE with a small dissipative perturbation, define the behavior of the solitonic solutions with parameters of the system and compare the solution with numerical simulations of the CGLE. We show, in a similar way to the nonlinear Schrodinger equation with a simplified dissipation term, a zero-velocity solitonic solution of non-zero amplitude appears as an attractor for the CGLE. In this case, the amplitude and velocity of the solitonic fixed point attractor does not depend on the quintic gain/loss effects. Furthermore, the effect of two-photon absorption leads to an increase in the strength of the solitonic fixed point attractor.

Giant and Multistage Nonlinear Optical Response in Porphyrin-Based Surface-Supported Metal-Organic Framework Nanofilms.

Benefitting from the strong intrinsic nonlinear optical (NLO) property of the individual porphyrin molecule, the integration of porphyrin molecules into tightly aligned arrays may lead to intuitively promising high-performance materials of tailorable NLO effect. In order to verify this speculation, we prepare crystalline and highly oriented porphyrin-based surface-supported metal-organic framework nanofilms (SURMOFs) and then characterize their NLO performance. Results reveal that porphyrin-based SURMOFs exhibit the highest saturable absorption (SA) yet recorded with a third-order NLO absorption coefficient up to -10-3 cm/W, about 7 orders stronger than porphyrin solvents in which the porphyrin molecules are disordered, under a certain excitation strength. Further increasing the excitation strength shows that the NLO absorption property of the porphyrin-based SURMOFs can be effectively modulated from SA to reverse saturable absorption, followed by a reemerging SA. The multiple-stage NLO switching is assigned to the interplay of simultaneous one-photon SA, two-photon absorption, and two-photon SA effects. The superior and modulatable NLO property as well as the designable and ordered crystalline structure suggest that porphyrin-based SURMOFs might be employed as a new class of high-performance NLO materials with potential applications in novel optical switches or logic gates to realize the all-optical information process.

Superbunching effect of classical light with a digitally designed spatially phase-correlated wave front

Superposition of multiple indistinguishable two-photon paths is introduced by means of a digital wave front encoding technique to design a spatially phase-correlated wave front of a light field, which could result in a superbunching effect with a bunching peak much larger than 2, the theoretical bunching peak of thermal light. Experimentally, we demonstrated a bunching peak of $11.72\ifmmode\pm\else\textpm\fi{}0.05$ with the digitally designed phase-correlated wave front of classical light, which can be improved further on. A significant improvement of the visibility of the second-order interference fringes and ghost imaging was also experimentally demonstrated. Our method provides a convenient digitally controllable way to implement superposition of multiple different but indistinguishable two-photon paths, and therefore to modify the optical coherence properties of photons. Such a superbunching effect may have potential applications in improving the visibility of correlation interference and imaging, and enhancing the efficiency of two-photon nonlinear effects such as two-photon absorption effect.

Self-phase modulation-induced modulation instability in silicon-on-insulator nano-waveguides

We present an investigation of the impact of two-photon absorption and free-carrier effects on modulation instability (MI) in silicon-on-insulator (SOI) nano-waveguide. We have analyzed nano-waveguide with both the anomalous and the normal group velocity dispersion (GVD) parameters at telecommunication wavelength. The power dependence of MI gain spectra in these waveguides has been explored. Also, we have studied the nonlinear losses and carrier density in the two dispersion regimes. Further, the impact of carrier lifetime on the MI gain spectrum is discussed in detail.

Cavity-enhanced harmonic generation in silicon rich nitride photonic crystal microresonators

We report second and third harmonic generation in photonic crystal cavities fabricated in a suspended silicon-rich nitride membrane under resonant continuous-wave excitation at telecom wavelength. Two-dimensional photonic crystal cavities with a far-field optimized line-width modulated design were employed. A quality factor at fundamental wavelength as high as Q = 1.3 × 104 and a coupling efficiency ηc ≈ 30% enabled us to exploit the cavity field enhancement to achieve the generation efficiencies ρSH = (4.7 ± 0.2) × 10−7 W−1 and ρTH = (5.9 ± 0.3) × 10−5 W−2. The absence of saturation effects at high power and the transparency of the device at the second harmonic wavelength suggest the absence of two-photon absorption and related detrimental effects.

Influence of two-photon absorption and free-carrier effects on all-optical logic gates in silicon waveguides

We investigate the impact of two-photon absorption (TPA) and free-carrier effects on all-optical logic gates in silicon waveguides, in which the conversion efficiency is greatly reduced and the waveform is seriously distorted. A silicon–organic hybrid dual-slot waveguide without TPA is proposed for all-optical logic gates and could offer an extremely large nonlinear parameter higher than 1.4 × 107 W−1 km−1. The all-optical logic AND, OR, and XOR gates based on four-wave mixing in this waveguide are realized for 100 Gb s−1 data signals in the C-band. These results provide potential applications for all-optical signal processing in integrated optics, optical communications, and optical computation.

Impact of exponential saturable nonlinearity on modulation instability in silicon-on-Insulator nano-waveguides

We present a theoretical study of modulation instability (MI) in silicon-on-insulator (SOI) nano-waveguides in the presence of exponential saturable nonlinearity (SNL). The study incorporates two-photon absorption and free-carrier effects in the normal dispersion regimes at telecommunication wavelength. Also, we have shown the impact of SNL on the power dependence of MI gain spectra, and carrier density. Further, the effects of carrier lifetime and fourth order dispersion on MI gain spectra have been discussed in the presence of SNL.

Ultrafast Broadband Nonlinear Spectroscopy of a Colloidal Solution of Gold Nanoparticles

The generation of supercontinuum radiation at the filamentation of femtosecond laser pulses (800 nm) with a supercritical gigawatt peak power in pure water and colloidal solutions of plasmon gold nanoparticles (perturbative regime) has been studied experimentally. After correction to the extinction of the fluid behind a filament, the supercontinuum radiation yields from the active filamentation zone in water (broadband radiation source) and in colloidal solution (broadband radiation source modified by various in situ interactions with nanoparticles) have been compared and analyzed for various peak radiation powers. As a result, the proposed method of ultrafast broadband nonlinear spectroscopy has allowed the observation of effects of the saturated two-photon interband absorption of gold nanoparticles in the spectral range of supercontinuum generation and the enhancement of this generation in the range of plasmon resonance of nanoparticles.

Quadratic detection of an enhanced self-mixing laser Doppler signal with two-photon absorption

A new detection scheme is proposed for an enhanced self-mixing laser Doppler velocimeter (SLDV) using two-photon absorption (TPA), which is based on the TPA-induced quadratic photoconductivity dependence of a photodiode on the incident radiance at 1550 nm with self-mixing interference (SMI). The harmonics of the SMI signal in the frequency spectrum are enhanced simultaneously, as for a fiber-Bragg-grating-based enhanced SLDV. The quadratic response induced by TPA can suppress the undesirable harmonics, making their amplitude into the same level as the noise. From the experimental results presented in this paper, the TPA effect in a commercial Si photodiode implements a sort of ultra-wide bandwidth filter without passively adjusting the cutoff frequencies for an unknown Doppler frequency, which simplifies Doppler signal processing. The signal-to-noise ratio (SNR) is also improved to a considerable level of 15 dB for a Doppler frequency of 4 kHz due to the amplification of an erbium-doped fiber amplifier. This paper provides guidance for the design of the enhanced SLDV with optical filtration.

Two-photon absorption in quantum dot semiconductor optical amplifiers-based all-optical XOR gate at 2 Tb/s

The nonlinear effect of two-photon absorption (TPA) on the performance of all-optical XOR gate using quantum dot semiconductor optical amplifiers (QDSOAs)-assisted Mach–Zehnder interferometer is numerically analyzed and investigated at a data rate of 2 Tb/s. The dependence of the quality factor (QF) on the critical parameters of the input signal and QDSOA is examined and assessed. The obtained QFs for the all-optical XOR gate using QDSOAs-MZI at 2 Tb/s with TPA and without TPA are 14 and 8, respectively.

2 Tb/s all-optical gates based on two-photon absorption in quantum dot semiconductor optical amplifiers

The performance of all-optical AND, OR, and NAND gates based on quantum dot semiconductor optical amplifiers (QDSOAs), which are either incorporated in properly configured Mach-Zehnder interferometer or combined with a delayed interferometer, is theoretically investigated at a data rate of 2 Tb/s when the nonlinear effect of two-photon absorption (TPA) is exploited in these active devices. The impact of the input signal and QDSOA key parameters on the quality factor (QF) is assessed. The obtained results indicate that these Boolean functions can be executed at 2 Tb/s with almost as twice as high QF than without TPA.

Growth and characterization of an efficient semi organic single crystal: Sodium hydrogen oxalate monohydrate

A highly proficient nonlinear optical compound Sodium Hydrogen Oxalate Monohydrate (SHOM) single crystal under semi organic category has been grown-up by the process of slow solvent evaporation. The triclinic structure and cell parameters of SHOM was revealed from X-ray diffraction analysis. The examination of FTIR was done to determine the existence of various functional groups present in the SHOM crystal. The mechanical stability is evaluated from Vicker's microhardness tester and related mechanical parameters were assessed. The multiple shot laser damage threshold was examined to be 2.65 GW/cm2. TG/DTA analysis is carried out to appraise the thermal limit of the grown material. The absorbance spectrum was analyzed from UV–vis analysis which verifies high transparency of the grown crystal and various optical constants were also estimated. The third order nonlinearity, two-photon absorption and self-defocussing effect of the grown material was established from the Z-Scan approach. The results favoring the materials suitability over nonlinear optical applications are reported.

Third harmonic generation on silicon surface induced by femtosecond laser

The emission spectra of silicon (Si) surface have been studied by a Ti: sapphire femtosecond laser amplification system. The third optical harmonic and plasma emission were detected. The third harmonic generation (THG) is sensitive to the laser fluence and negatively correlated with the fluence. The nonlinear loss on the THG conversion efficiency at high laser fluence is mainly due to the two-photon absorption (TPA) effect. The micro-nanoparticles around the ablated area increase with decreasing laser fluence, which may be one of the reasons for the enhancement of the THG signal. Compared with the theoretical calculation of the THG (266.67 nm), the slight spectral blue-shift (<2 nm) can be attributed to the nonlinear optical processes of the self-phase modulation.