Nonlinear Optical Absorption Research Articles

A comparative analysis on electrical and nonlinear optical properties of pure and Co–Ni co-doped SnO2 nanoparticles

Compared to bulk materials, nanostructured materials possess ultrafast optical response and strong two-photon absorption which leads to the utility of materials in various laser related applications. Hence, Cobalt (Co)-Nickel (Ni) co-doped SnO2 nanoparticles were synthesized via co-precipitation technique and its optical limiting behavior was studied. PXRD confirms the formation of tetragonal rutile SnO2with space group P42/mnm with decrease in crystallite size due to co-doping. Shift in PXRD peak position towards higher angle and suppression of Sn–O–Sn vibrational peaks confirm the intervention of Co2+ and Ni2+ ions into the SnO2 lattice. Upon co-doping, the band gap decreases (3.35, 3.28 and 3.20 eV) and the PL intensity of blue-green emission increases due to the increase in density of oxygen vacancies on the surface of SnO2. Low dielectric constant, dielectric loss and ac conductivity indicates the prepared materials are having lesser defects. Nonlinear optical (NLO) absorption and optical limiting behavior of developed NPs were recorded by Z-scan method (open aperture) using nano pulsed green laser excitation. Open aperture Z-scan curves with a valley-like pattern indicate the presence of reverse saturable nonlinear absorption due to the sequential two-photon absorption (2PA) process. The 2PA coefficient increases (0.27–0.56 ×10−10W/m) and onset optical limiting threshold decreases (4.5 –1.7 ×10−12W/m2) with increasing dopant concentration of Co–Ni (2 & 4 wt%) in SnO2 NPs. These results demonstrate that Co–Ni (4 wt%) NPs have virtuous dielectric and efficient NLO absorption and limiting properties which suggest that it could be an eminent candidate for the potential applications such as high-performance dielectric material and optical limiting components in optical devices.

Optical properties of Al x Ga1−x As/GaAs Woods–Saxon quantum well in the presence of hydrostatic pressure and applied electric field

The third harmonic generation (THG), linear and nonlinear optical absorption coefficients (OACs), and refractive index changes (RICs) are investigated in a Woods–Saxon quantum well (QW) modulated by the hydrostatic pressure and applied electric field. The effect of non-uniform aluminum doping (position-dependent effective mass (PDEM)) on the mass of the system is discussed, and further to explore the influence of PDEM on the nonlinear THG, OACs, and RICs of the Woods–Saxon QW. These nonlinear optical properties above are obtained using the compact-density matrix formalism. The electron states in a Woods–Saxon QW under the constant effective mass (CEM) and PDEM are calculated by solving the Schrödinger equation via the finite difference technique. The contributions from competing effects of the hydrostatic pressure and applied electric field to the nonlinear optical properties with CEM and PDEM are reported, as well as the comparison with each other. The observations reveal that the regulation of external fields and the influence of PDEM play an important role in the photoelectric properties of QW.

The role of defects in the nonlinear optical absorption behavior of pristine and Co-doped V2O5 layered 2D nanostructures

V2O5 nanostructures doped with 1% Co have been successfully synthesized by simple hydrothermal method. Structural and morphological aspects, vibrational spectra and optical properties (linear and nonlinear) of pristine as well as Co-doped V2O5 (V2O5:Co) nanoparticles are investigated. X-ray diffraction patterns indicate that both V2O5 and Co doped V2O5 are stabilized in an orthorhombic structure. Energy band gaps measured using the Tauc plot give 2.24 eV for V2O5 and 2.16 eV for Co doped V2O5. When excited using 5 ns laser pulses at 532 nm in the open aperture Z-scan configuration, pristine as well as Co-doped V2O5 nanoparticles are found to show excellent nonlinear absorption, which arises from strong reverse saturable absorption occurring in the sample at this wavelength. The corresponding effective two-photon absorption coefficients are in the range of 10−11 to 10−12 m/W, and effective three-photon absorption coefficients are in the range of 10−22 to 10−23 m3/W2. When excited at the same wavelength using a continuous wave laser beam, the effective two-photon absorption coefficient gets enhanced to 10−6 m/W. These results confirm the suitability of V2O5 and Co-doped V2O5 nanoparticles for the fabrication of optical limiter devices for the protection of human eyes and sensitive optical detectors from hazardous laser radiation.

Third-order optical nonlinearity of indium-doped rutile TiO2 thin films

Rutile TiO2 and Ti0.9In0.1O2 thin films were fabricated using a pulsed laser deposition method. We employed the optical transmission spectra to reveal the good transparency of the films in the visible spectral range of 330 to 900 nm. The absorption edge of the Ti0.9In0.1O2 film is blue-shifted compared with that of undoped TiO2 film. The third-order optical nonlinearity of the films was investigated by using a z-scan method with a pulse laser operating at 532 nm with a duration of 55 ps. The results show that the Ti0.9In0.1O2 and TiO2 films exhibit nonlinear saturable absorption and negative nonlinear refraction. The doping of In ions does not change the nonlinear optical absorption of the TiO2 film significantly. However, the nonlinear refractive index of Ti0.9In0.1O2 film is about two times larger than that of undoped TiO2 film. The local electron-pinned defect-dipoles and widening bandgap in the Ti0.9In0.1O2 film can be used to explain the observed results.

Passively Q-Switched and Mode-Locked Fiber Laser Based on a Zeolitic Imidazolate Framework-67 Saturable Absorber

Exploring new saturable absorber (SA) materials with excellent performance to achieve Q-switching and mode-locking operations is a hot topic in ultrafast laser research. The impressive specific surface areas, structural tunability, and high thermal and chemical stability of the zeolitic imidazolate framework (ZIF) materials make them promising candidates as high-performance SAs. In this work, we demonstrated the potential of the ZIF-67 SAs for ultrafast fiber laser applications. The nonlinear optical absorption characteristics of the ZIF-67 SAs at the telecommunication band were investigated by using the balanced twin-detector method. By incorporating the ZIF-67 SAs into the Er3+-doped fiber laser cavity, stable Q-switching and mode-locking operations were achieved. The research results are essential for promoting the application of novel hybrid nanomaterials in ultrafast lasers.

2D BP/InSe Heterostructures as a Nonlinear Optical Material for Ultrafast Photonics.

The BP/InSe heterojunction has attracted the attention of many fields in successful combined high hole mobility of black phosphorus (BP) and high electron mobility of indium selenide (InSe), and enhanced the environmental stability of BP. Nevertheless, photonics research on the BP/InSe heterostructure was insufficient, while both components are considered promising in the field. In this work, a two-dimensional (2D) BP/InSe heterostructure was fabricated using the liquid-phase exfoliation method. Its linear and non-linear optical (NLO) absorption was characterized by ultraviolet−visible−infrared and Open-aperture Z-scan technology. On account of the revealed superior NLO properties, an SA based on 2D BP/InSe was prepared and embedded into an erbium-doped fiber laser, traditional soliton pulses were observed at 1.5 μm with the pulse duration of 881 fs. Furthermore, harmonic mode locking of bound solitons and dark-bright soliton pairs were also obtained in the same laser cavity due to the cross-coupling effect. The stable mode-locked operation can be maintained for several days, which overcome the low air stability of BP. This contribution further proves the excellent optical properties of 2D BP/InSe heterostructure and provides new probability of developing nano-photonics devices for the applications of double pulses laser source and long-distance information transmission.

A passively Q-switched operation of Tm:YAP laser with a zeolite imidazole framework-8 saturable absorber

A passively Q-switched (PQS) Tm:YAP solid laser using a zeolite imidazole framework (ZIF-8) as saturable absorber (SA) was reported systematically. The nonlinear optical absorption properties of ZIF-8 SA was characterized. The modulation depth and saturable absorption were calculated to be 4.6% and 0.38 MW/cm2, respectively. Under a pumped power of 9.49 W, an average power of 649 mW was generated with a narrowest pulse width of 961 ns and a pulse repetition frequency (PRF) of 44.59 kHz, corresponding to a single pulse energy of 14.55 μJ that at the central wavelength of 1988 nm. The results well demonstrate the great potential of ZIF-8 as a SA in achieving high performance mid-infrared pulsed lasers.

Effects of Magnetic Field on Nonlinear Optical Absorption in Quantum Dots Under Parabolic-Inverse Squared Plus Modified Gaussian Potential

Effects of Magnetic Field on Nonlinear Optical Absorption in Quantum Dots Under Parabolic-Inverse Squared Plus Modified Gaussian Potential

Nonlinear Optical Absorption in Nanoscale Films Revealed through Ultrafast Acoustics.

Herein we describe a novel spinning pump-probe photoacoustic technique developed to study nonlinear absorption in thin films. As a test case, an organic polycrystalline thin film of quinacridone, a well-known pigment, with a thickness in the tens of nanometers range, is excited by a femtosecond laser pulse which generates a time-domain Brillouin scattering signal. This signal is directly related to the strain wave launched from the film into the substrate and can be used to quantitatively extract the nonlinear optical absorption properties of the film itself. Quinacridone exhibits both quadratic and cubic laser fluence dependence regimes which we show to correspond to two- and three-photon absorption processes. This technique can be broadly applied to materials that are difficult or impossible to characterize with conventional transmittance-based measurements including materials at the nanoscale, prone to laser damage, with very weak nonlinear properties, opaque, or highly scattering.

Layered gallium telluride for inducing mode-locked pulse laser in thulium/holmium-doped fiber

In this work, layered gallium telluride (GaTe) was used as a saturable absorber (SA) to initiate the generation of mode-locked pulses in a Thulium/Holmium-doped fiber (THDF) laser. The GaTe solution has been embedded onto the surface of fabricated D-shaped fiber by using the drop-casting method. This action was taken to allow the strong nonlinear interaction between the GaTe solution and the evanescent field of the wave propagating in the D-shaped fiber. The nonlinear optical absorption for the prepared GaTe/D-shaped based SA exhibits a modulation depth of 31.35%, saturation intensity of 3.35 kW/cm2, and a non-saturable loss of 68.65%. A stable mode-locked pulse laser was observed with a repetition rate of 10.71 MHz at a threshold pump power of 281.0 mW. The soliton pulse generated from the proposed THDFL cavity centered at 1946.24 nm with a spectral bandwidth of 2.92 nm. The mode-locked pulse produced pulse duration of 1.396 ps and a signal-to-noise ratio (SNR) value of 63 dB. Overall, the excellent output performance of the laser-generated in this work has shown the credibility of the GaTe/D-shaped based SA device as another possibility for ultrafast laser application.

Investigation of transient optical nonlinearity in pyrene-based ferrocene and its optical limiting potential for ultrafast laser absorption

The ultrafast optical nonlinearity of a pyrene-based ferrocene derivative (Py-Fc) is systematically studied via Z-scan, transient absorption spectrum (TAS), and phase object pump probe (POPP). An ultrafast broadband absorption in visible wavelength region is observed via TAS. Based on this finding, nonlinear optical absorption of the material is investigated at various wavelengths. Results indicate that different absorption mechanisms, including reverse saturable absorption and two-photon induced excited state absorption involve in the nonlinear absorption in visible spectrum. The cooperation between the two mechanisms brings strong optical limiting properties. In addition, negative nonlinear optical refraction from the excited state is observed in POPP experiment and its dynamics is discussed. These results demonstrate that the molecular Py-Fc exhibits strong optical limiting, suggesting it is a potential material for ultrafast laser protection.

Optical absorption coefficients of spherical quantum dots system with inversely quadratic Yukawa-Hellmann potential

In this paper, the effects of hydrostatic pressure, temperature, Al-concentration and other structural parameters on the optical absorption coefficients (OACs) in inversely quadratic Yukawa-Herman potential (IQYHP) GaAs/AlηGa1−ηAs spherical quantum dots are studied theoretically. The Nikiforov-Uvarov (N–U) solution is used to solve the Schrödinger equation corresponding to this structure, and the energy levels and wave functions can be obtained. We also get nonlinear optical absorption coefficients by using compact density matrix theory and iterative method. The results show that various parameters play an essential role in OACs, including the red shift (blue shift) of OACs resonance peaks and the change of peaks size.

Boosting optical nonlinearities of graphene oxide films by laser direct writing

In this work, we study the boosted optical nonlinearities of graphene oxide (GO) films by laser direct writing with femtosecond laser (532 nm, 330fs) excitation. We firstly prepare the uniform GO films by vacuum filtration method, which are then partly reduced by commercial carbon dioxide laser machine. The morphology, structure and luminescence traits of both the pristine and reduced GO are further characterized by SEM, XRD, Raman spectra, XPS, PL and UV–Vis absorption spectrum. Moreover, their third-order optical nonlinearities (TONs) are measured by the femtosecond laser Z-scan technique. The experimental results show that the reduced GO films take on stronger TONs and the related degree of enhancement depends on the spot size of laser processing. In particular, when the processed diameter is around 400 μm, the optical nonlinear absorption and refraction coefficients of the reduced GO are −2.9 × 10−7 m/W and 2.5 × 10−15 m2/W, respectively, which are in turn 4 and 2 times higher than that of GO film. Our results provide powerful backing for the GO-based applications, such as ultra-fast optical devices, super-resolution imaging technology and photodetector.

Effects of Intense Laser Field on Electronic and Optical Properties of Harmonic and Variable Degree Anharmonic Oscillators

In this paper, we calculated the electronic and optical properties of the harmonic oscillator and single and double anharmonic oscillators, including higher-order anharmonic terms such as the quartic and sextic under the non-resonant intense laser field. Calculations are made within the effective mass and parabolic band approximations. We have used the diagonalization method by choosing a wave function based on the trigonometric orthonormal functions to find eigenvalues and eigenfunctions of the electron confined within the harmonic and anharmonic oscillator potentials under the non-resonant intense laser field. A two-level approach in the density matrix expansion is used to calculate the linear and third-order nonlinear optical absorption coefficients. Our results show that the electronic and optical properties of the structures we focus on can be adjusted to obtain a suitable response to specific studies or aims by changing the structural parameters such as width, depth, coupling between the wells, and applied field intensity.

Effect of laser ablated gold nanoparticles on the nonlinear optical properties of π-extended BODIPY dyes

Dipyrromethene boron difluoride (BODIPY) and its derivatives have attracted considerable interest due to their remarkable photophysical properties beneficial for developing fluorescent sensors, biolabels, photodynamic therapy agents, photonic materials, and so on. Herein, we report gold nanoparticles (AuNPs) induced modulation of nonlinear optical properties of π-extended BODIPY derivatives BPA and BDIPA. The spherical gold nanoparticles with an average particle size of 11 ± 3.5 nm were synthesized by pulsed laser ablation technique and characterized by transmission electron microscopy and dynamic light scattering. The interaction of AuNPs with the dye molecules was confirmed by UV/vis absorption and steady-state emission spectroscopy studies. Further, the dual-beam thermal lens technique was used to validate dye-nanoparticle interaction. The thermal diffusivity values of the samples at an excitation wavelength of 532 nm were measured and found that the overall heat diffusion was slower in the AuNPs added samples than that of the dye alone sample, corroborating dye-nanoparticle interaction. The third-order nonlinear optical absorption properties of the samples were investigated by using the Z-scan technique in the infrared region (1064 nm). The open aperture configuration shows significant reverse saturable absorption characteristics for all the samples. Determination of nonlinear absorption coefficient for the dye samples at different input intensities identified two-photon absorption as the important mechanism that produces reverse saturable absorption. The AuNPs incorporated dye samples showed a substantial enhancement in the nonlinear optical behavior. The nonlinear absorption coefficient of the AuNPs incorporated dye samples (10 cm/GW) was enhanced almost two times than that of dye alone samples (5 cm/GW). The enhanced nonlinearity is attributed to the intense local field effect of AuNPs.

Optical absorption in core-shell quantum antidot under applied co-directed electric and magnetic fields

Using the matrix diagonalization method within the effective mass approximation and the rectangular potential profile, we investigate optical absorption coefficients (OAC) in the core-shell quantum antidot (QAD) Al0.3Ga0.7 As/GaAs/Al0.3Ga0.7 As in the presence of applied co-directed electrical and magnetic fields. The electric field effect on the electron wave functions, energy spectrum, oscillator strength of the intersubband electronic transitions is calculated for different size of QAD core and different value of the magnetic field induction. The total, linear and nonlinear optical absorption coefficients in QAD are obtained by considering 1 s-1p and 1p-1d electron quantum transitions as functions of the incident photon energy.

Enhanced optical nonlinearity and ultrafast carrier dynamics of TiO2/CuO nanocomposites

Transition metal oxides (TMOs) are drawing multitudinous interest due to their strong thermochemical stability. In the present work, we proposed a facile strategy to fabricate TiO 2 /CuO nanocomposites. By using the conventional open- and closed-aperture Z-scan technology, the eminent nonlinear optical (NLO) properties of the as-prepared TiO 2 /CuO nanocomposites were demonstrated. In order to deeply investigate the NLO enhancement mechanism, we established a theoretical model to study the photogenerated carriers transfer dynamics at the interface with rate equations and the fouth-order Runge-Kutta algorithm. The simulation results indicated that under pumping irradiation, the carriers transferring from CuO to TiO 2 promoted the nonlinear optical absorption of CuO nanosheets and increased the modulation depth. Experimentally, the transient absorption spectroscopy and broadband time-resolved pump-probe measurements were presented to study the role of the carrier dynamics in the broadband near-infrared region. To further confirm the enhanced NLO response in TiO 2 /CuO nanocomposites, a highly stable dissipative soliton mode-locked Yb-doped fiber laser with TiO 2 /CuO saturable absorber was constructed at 1 μm for the first time. Our work manifested the key effects of the interface in TiO 2 /CuO nanocomposites to boost the NLO features which can be applied in ultrafast photonics applications.

Study of ultrafast nonlinear optical response and transient dynamics of pyrene derivatives with intramolecular charge transfer characteristics

Two pyrene derivatives 1906 and 1936 with typical charge transfer characteristics were designed and synthesized to study the influence of intramolecular charge transfer (ICT) on the ultrafast nonlinear optical (NLO) absorption. Frontier molecular orbital distribution and hole-electron analysis show that compound 1906 has stronger ICT characteristics than 1936 by introducing the halogen effect. Intense ESA signals in the green region of these pyrene derivatives were observed in the transient absorption spectrum (TAS). The excited state dynamics clearly show singlet-based electronic transitions and relaxation processes. Femtosecond Z-scan experiment at 480 nm indicates the ultrafast NLO absorption performance of these pyrene derivatives can be significantly improved by enhancing the ICT characteristics. The photophysical mechanism is one-photon absorption (OPA) induced excited-state absorption (ESA). As the input intensity is 46.8 GW cm−2, the effective NLO absorption coefficient of 1906 is 7.6 × 10−13 W m−1 which is 6.3 times that of 1936. Our results indicate that these pyrene derivatives are promising potential candidates for ultrafast laser protection applications.

Low power Z-scan study and photoacoustic behavior of synthesized conjugated organic compounds based on carbazole derivatives

Third-order nonlinear optical (NLO) properties of the synthesized conjugated organic molecules based on carbazole derivatives were studied at different input intensities and wave lengths, by the Z-scan method and using continuous wave (CW) lasers. The normalized transmittance results are explained by fitting the data with theoretical models of the open and close aperture Z-scan technique. Measurements demonstrated the influence of saturation in absorption and thermal lensing effects on the nonlinear optical coefficients and also indicate a strong correlation between linear and nonlinear optical absorption. Also, photoacoustic behaviour and photoluminescence of the components were investigated which shows the high optical potential of these organic molecules in different optical fields and devices. It was found that frequency spectra of photoacoustic signals were the same for all derivatives, but with different amplitudes.

Study on Excited State Kinetics and Optical Limiting Performance of Triphenylamine-Based Chalcone Derivatives: Effect of the Molecular π-Conjugated Structure.

Optical limiting (OL) is an important application of nonlinear optics. Summarizing the structure-property relationship of organic materials is an effective means to develop superior optical limiters. In this work, two triphenylamine-based chalcone derivatives T1 and T2 with different peripheral substituent groups were synthesized to study their transient kinetics and nonlinear optical (NLO) absorption performance. The transient absorption spectrum (TAS) of compounds T1 and T2 in solvents of varying polarities visualizes the intramolecular charge transfer (ICT) processes between the local excited state (LES) and the charge transfer state (CTS). Nanosecond Z-scan experiment and hole-electron analysis indicate that all compounds have excellent reverse saturated absorption (RSA) performance at 532 nm and T1 exhibits stronger RSA than T2 due to the stronger ICT performance of T1 caused by the halogen effect. Degenerate pump-probe experiment shows that the ESA of T2 at 532 nm is significantly enhanced by expanding the molecular π-conjugation. Under the premise of consistent linear transmittance (78%), compound T2 shows better OL performance than compound T1 at 532 nm in the nanosecond time domain. The OL thresholds of T1 and T2 are 3.72 and 0.72 J cm-2, respectively, which are better than those of the most reported OL materials. Our research shows that simple and common chalcone derivatives exhibit amazing NLO performance through a reasonable design.