Investigation on optical switching behaviour of regenerated and non-regenerated silk by nanosecond Z-scan technique

The nonlinear optical behaviour of silk, a natural fibre, is investigated in this study. We have considered silk in the cocoon, fibre and film forms of bivoltine and multivoltine breeds. The nonlinear absorption and optical limiting studies were performed using the open aperture Z-scan technique at 1064nm. Interestingly, silk in cocoon and fibre form possess saturable absorption (SA), whereas silk in the film form exhibits reverse saturable absorption (RSA). This shift is attributed to the removal of sericin during the regeneration of silk into a film. Further, silk films exhibit optical limiting behaviour, whose limiting thresholds are in the order of 1012 W/cm2. Functional data analysis (FDA), a statistical approach, is employed to draw correlations amongst physical parameters. FDA offers good insight into the dependencies between silk varieties and their optical parameters. This helps in identifying the sample possessing the best properties.

Silver Nanoparticles under Nanosecond Pulsed Laser Excitation as an Intensity Sensitive Saturable Absorption to Reverse Saturable Absorption Switching Material

Optical nonlinearity involved switching draws an important consideration in nonlinear optical studies. Based on that, we explored nonlinear absorption processes in silver nanoparticles synthesized by liquid phase laser ablation technique employing a second harmonic wavelength (532 nm) of Q switched Nd:YAG laser pulses with 7 ns pulse width and 10 Hz repetition rates. The typical surface plasmon resonance induced absorption (~418 nm) confirmed the formation of Ag NPs. The Z-scan technique was used to study the nonlinear optical processes, employing the same laser system used for ablation. Our study reveals that there is an occurrence of a saturable to reverse saturable absorption switching activity in the Ag nanoparticles, which is strongly on-axis input intensity dependent as well. The closed aperture Z-scan analysis revealed the self-defocusing nature of the sample.

The Broadband Nonlinear Optical Response in Graphene/MoS2/Ag Thin Films at Near Infrared

Graphene/MoS2/Ag thin films were successfully prepared by the magnetron sputtering technique and liquid phase exfoliation. Structure, morphology, optical properties, and nonlinear optical characteristics of the graphene/MoS2/Ag and graphene/MoS2 thin films were studied by X-ray diffractometer, spectrophotometer, field-scanning electron microscope, and femtosecond (fs) Z-scan technique. The results of the fs Z-scan experiment indicate that the graphene/MoS2/Ag thin films exhibit reverse saturable absorption properties due to the free carrier absorption and two-photon absorption. More importantly, with the increase of DC magnetron sputtering power (from 5 to 15 W), the local surface plasmon resonance effect of the Ag thin films increases, which leads to the enhancement of nonlinear optical properties of the graphene/MoS2/Ag thin films. The nonlinear absorption coefficients of the graphene/MoS2/Ag thin films are increased from 1.14 × 10–10 to 1.8 × 10–10 m/W at 800 nm and from 4.79 × 10–11 to 6.79 × 10–11 m/W at 1,030 nm, and the nonlinear refraction index of the graphene/MoS2/Ag thin films is -4.37 × 10–17∼−4.18 × 10–16 m2/W under the excitation of 800 and 1,030 nm, respectively. Moreover, when the graphene/MoS2/Ag thin films were excited at 800 and 1,030 nm, respectively, the nonlinear figure of merit values of the graphene/MoS2/Ag thin films are increased from 1.23 to 2.91 and from 1.30 to 1.47, which are enough to support the application of the graphene/MoS2/Ag thin films in the field of all-optical switching applications.

Exfoliated Bi2Te3 nanoparticle suspensions and films: morphological and nonlinear optical characterization

Bismuth telluride nanoparticles (NPs) attract attention due to the growth of sensitivity of the Bi2Te3 NPs-containing registrars in the near- and mid-infrared ranges. We describe the synthesis and characterization of these structures and analyze the low-order nonlinear optical properties of the colloidal suspensions and thin films containing Bi2Te3 NPs using 1064 and 532 nm, 10 ns pulses. Colloidal Bi2Te3 NPs demonstrate saturable absorption and positive nonlinear refraction (saturation intensity 7 × 108 W cm−2, nonlinear absorption coefficient β SA = −7 × 10−8 cm W−1, nonlinear refractive index γ = 9 × 10−12 cm2 W−1), while at stronger excitation by 532 nm, 10 ns pulses the reverse saturable absorption dominates over other nonlinear optical processes. We achieved significant growth of the nonlinear optical parameters of the thin films containing these NPs (film thickness l = 60 nm, β SA = −1.2 × 10−4 cm W−1, γ = 5 × 10−7 cm2 W−1 in the case of 532 nm probe radiation and β = −5 × 10−5 cm W−1, γ = 6 × 10−8 cm2 W−1 in the case of 1064 nm probe radiation) compared with colloidal Bi2Te3 NPs and discuss the observed peculiarities of the nonlinear response of Bi2Te3 nanostructures.

Surface Plasmon Resonance Dependent Third-Order Optical Nonlinearities of Silver Nanoplates

A systematic study of the surface plasmon resonance (SPR)-dependent nonlinear optical response of Ag nanoplates is presented and discussed. The Ag nanoplates were synthesized using the well-known seed-mediated growth method. By performing the z-scan method with a nanosecond laser (532 nm, 5 ns), the optical nonlinearities of the Ag nanoplates, prepared tuning the SPR contribution in the 400–1000 nm range, were determined. The results showed a SPR-related competition between the saturable absorption and reverse saturable absorption mechanisms, while the nonlinear refraction changed from self-defocusing to self-focusing. Furthermore, the scattering effects contribute to determine the nature of the optical limiting response. The observed SPR-tunable third order optical nonlinearities make Ag nanoplates a suitable candidate to be used in different fields, i.e., laser pulse generation, optical limiting, or bio-imaging applications.

Tunable nonlinear optical responses of few-layer graphene through lithium intercalation

Intercalation has been demonstrated to be a powerful tool for tuning the physical and chemical properties of two-dimensional (2D) materials, providing the highest possible doping level and an ideal system to study various electronic states. In this work, we demonstrate that the nonlinear absorption effect of few-layer graphene (about 6–8 layers) is changed from saturable absorption (SA) to reverse saturable absorption (RSA) after lithium intercalation. This is attributed to the increase of Fermi energy owing to the charge transfer from Li to graphene layers in intercalated compounds (LiC6). And the change of nonlinear absorption effect is revisable after deintercalation. In addition, the modulation depth of RSA in lithiated graphene is found to rise with the decrease of incident laser wavelength, different from that of pristine graphene. Besides, the dispersion relationships of degenerate and nondegenerate two-photon absorption are analyzed from the results of nonlinear absorption and transient dynamics of lithiated graphene, indicating the 1.91–2.21 eV upshift of the Fermi surface. Our findings of the intercalation-tunable nonlinear optical absorption effect pave the way for the construction of nonlinear optical devices based on 2D intercalation compounds.

Study of Third-Order Nonlinear Optical Properties of Basic Violet 3 Dye in Polar Protic and Aprotic Solvents

The present work aims to study of third-order nonlinear optical (TONLO) behavior of basic violet 3 dye dissolved in polar protic and aprotic solvents, namely, ethanol, 1-propanol, acet0one and dimethyl sulfonate (DMSO), respectively. The polarity of the solvent used to have a substantial impact on the linear and TONLO properties of the dye sample. The dye exhibit self-defocusing nonlinearity due to thermally induced nonlinear refractive index and nonlinear absorption coefficient reveals the character of both saturable and reverse saturable absorption (RSA). The order of magnitude of nonlinear refractive index (n2) and nonlinear coefficient of absorption (β) of dye sample was determined to be 10–7 cm2/W and 10–3 cm/W, respectively. The real and imaginary factors of the TONLO susceptibility of basic violet 3 dye were measured to be the power of 10–5 esu. The results are revealed that the possibility of utilizing the dye sample in various photonics and optoelectronics applications.