We report an alternative random laser (RL) architecture based on a flexible and ZnO-enriched cellulose acetate (CA) fiber matrix prepared by electrospinning. The electrospun fibers, mechanically reinforced by polyethylene oxide and impregnated with zinc oxide powder, were applied as an adsorbent surface to incorporate plasmonic centers (silver nanoprisms). The resulting structures – prepared in the absence (CA-ZnO) and in the presence of silver nanoparticles (CA-ZnO-Ag) - were developed to support light excitation, guiding and scattering prototypes of a RL. Both materials were excited by a pulsed (5 Hz, 5 ns) source at 355 nm and their fluorescence emission monitored at 387 nm. The results suggest that the addition of silver nanoprisms to the ZnO- enriched fiber matrix allows large improvement of the RL performance due to the plasmon resonance of the silver nanoprisms, with ~80% reduction in threshold energy. Besides the intensity and spectral analysis, the RL characterization included its spectral and intensity angular dependences. Bending the flexible RL did not affect the spectral characteristics of the device. No degradation was observed in the random laser emission for more than 10,000 shots of the pump laser.

Intensity dependent self-action of a continuous wave (CW) or pulsed optical beam can lead to spatial or spectral effects upon propagation through a nonlinear medium, which can be described as an intensity dependence of the refractive index, known as self-phase modulation (SPM). In this work, we revisit the nonlinear optical propagation of a CW and a CW mode-locked (CW-ML) high repetition rate [ ∼ megahertz (MHz)] laser propagating through pure ethanol in regions of very low optical absorption (800 nm) or very high absorption (1480 nm, 1560 nm). Spatial and spectral SPM and Z -scan experiments were performed to clarify the origin of the third-order nonlinear optical response in the different optical excitation regimes. From spatial SPM and Z -scan at either CW or CW-ML MHz regime, a thermal nonlinear response was determined to be the origin of the nonlinearity at 800 nm or 1480 nm, 1560 nm region, with the nonlinear refractive index response of the order of 10 − 4 − 10 − 9 c m 2 / W . From the spectral SPM, the non-thermal origin of the nonlinearity, arising from electronic or nuclear processes in the ethanol, was determined, and values of the order of 10 − 13 − 10 − 16 c m 2 / W were obtained, depending upon the spectral region. The results were supported by theoretical calculations using the nonlinear Schrödinger equation for the spectral behavior or Fresnel–Kirchhoff integral for the spatial results and clarify some of the misinterpreted results reported in the literature, besides complementing other nonlinear refraction data available at different wavelengths from 355 nm to 1560 nm.

We report experimental studies of spatial self-phase modulation (SSPM) in liquid suspensions of semiconducting MoS 2 , MoSe 2 , MoTe 2 , WS 2 , semimetallic ZrTe 2 , WTe 2 , and metallic NbS 2 , NbSe 2 using linearly and circularly polarized light with CW or CWmode-locked (ML) excitation lasers. For the semiconducting suspension of nanoflakes, excitation above and below the bandgap was performed. The results show that the intensity-dependent changes in the refractive index responsible for SSPM and associated ring formation are explained as arising from thermal origin. Measured values of the effective thermal nonlinear coefficient, n 2,th , range from ∼4.3 × 10 −7 to ∼4.2 × 10 −5 cm 2 /W, depending on the absorption strength of the suspension, and are independent of the optical excitation regime (polarization and laser mode of operation). The use of circularly polarized light to obtain the same results as seen with linearly polarized light is fundamental to complement the results, demonstrating that at the spectro-temporal regimes studied, thermal nonlinearity explains well the ring formation, in addition to providing the original SSPM results for NbS 2 , ZrTe 2 , and WTe 2 .

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We report the first-hyperpolarizability, β-(−2ω;ω,ω), of gold nanoclusters Au 6 (GSH) 2 (MPA) 2 having six gold atoms capped by 3-mercaptopropionic acid and glutathione (GSH) that is unprecedented. Here, we used the concentration of 2.1 × 10 16 nanoclusters/mL in experiments to determine β(−2ω;ω,ω), applying the hyper-Rayleigh scattering technique by using a 1064 nm laser and analyzing the scattered light at 532 nm. The measured hyperpolarizability is found to be β(−2ω;ω,ω) = 760 × 10 −30 esu. The static hyperpolarizability, β(0) = 300 × 10 −30 esu, was determined by using a two-level model approximation. The large β(−2ω;ω,ω) is attributed to the quantum confinement effect and the geometry of the nanoclusters that have no inversion symmetry. Computer calculations based on the density functional theory method were performed, and the numerical results present the same order of magnitude than the experimental values.