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We present an optical pump-probe technique to optimise the all-optical photonic switching based on Bi2S3-xSex/PMMA nanocomposite films. Bi2S3-xSex/PMMA nanocomposite films were prepared using a microwave-assisted synthesis with different compositions of x. Crystal structure, surface morphology, and optical properties were performed to characterise the prepared nanocomposite films. The crystallinity and optical band gap of the prepared Bi2S3-xSex/PMMA were affected by x. The prepared samples showed a blue shift in the absorption edge. The optical nonlinearity of the films exhibited switchover from self-defocusing to focusing effect, and saturable absorption to reverse saturable absorption, investigated using the Z-scan technique. The all-optical switching performance of the Bi2S3-xSex/PMMA nanocomposite films under different compositions x was investigated. The results showed that the Bi2S3-xSex/PMMA at x = 0.4 and 1.0 can demonstrate an all-optical switching at threshold pump power of 13 mW and lead to the realisation with maximum modulation depth of 76% and 80% with minimum switching contrast of 6.2 dB and 7 dB at switching time of 14 ms and 13 ms, respectively. [ABSTRACT FROM AUTHOR]

We present an optical pump-probe technique to optimise the all-optical photonic switching based on Bi2S3-xSex/PMMA nanocomposite films. Bi2S3-xSex/PMMA nanocomposite films were prepared using a microwave-assisted synthesis with different compositions of x. Crystal structure, surface morphology, and optical properties were performed to characterise the prepared nanocomposite films. The crystallinity and optical band gap of the prepared Bi2S3-xSex/PMMA were affected by x. The prepared samples showed a blue shift in the absorption edge. The optical nonlinearity of the films exhibited switchover from self-defocusing to focusing effect, and saturable absorption to reverse saturable absorption, investigated using the Z-scan technique. The all-optical switching performance of the Bi2S3-xSex/PMMA nanocomposite films under different compositions x was investigated. The results showed that the Bi2S3-xSex/PMMA at x = 0.4 and 1.0 can demonstrate an all-optical switching at threshold pump power of 13 mW and lead to the realisation with maximum modulation depth of 76% and 80% with minimum switching contrast of 6.2 dB and 7 dB at switching time of 14 ms and 13 ms, respectively. [ABSTRACT FROM AUTHOR]

• Obtaining ultra-narrowband, electrically switchable, and high-efficiency absorption in graphene remains a challenge. • For the first time, we study how to utilize lattice plasmon resonance to obtain ultra-narrowband and electrically switchable near-infrared absorption enhancement in graphene. • The lattice plasmon resonance can enhance electromagnetic fields at graphene surface, with the absorption bandwidth being only several nanometers. • The graphene absorption has nearly 100% modulation depth and thus exhibits switching property by changing Fermi energy. We propose a novel approach to obtain the ultra-narrowband, electrically switchable, and high-efficiency absorption in the monolayer graphene. The monolayer graphene is sandwiched between the silica substrate and a square array of silver nanospheres, which is covered by a very thick silica layer. The fundamental role of the thick silica cover layer is to homogenize the surrounding medium of the silver nanospheres, and thus efficiently exciting the lattice plasmon resonance. The lattice plasmon resonance arising from the coupling between the dipolar plasmon resonance of silver nanospheres and the zero-order diffraction wave at Wood anomaly can enhance the electromagnetic fields at the graphene surface, and thus greatly improve the near-infrared light absorption of the monolayer graphene with the maximum absorption efficiency up to 45%. Owing to the low radiation loss of the lattice plasmon resonance, the absorption linewidth of the monolayer graphene can be largely compressed to only several nanometers (3.2 nm ∼ 7.4 nm). Moreover, the absorption of the monolayer graphene in our proposed nanostructures has a nearly 100% modulation depth to exhibit an excellent switching property. Our work will be helpful for some graphene-based photoelectric devices. [ABSTRACT FROM AUTHOR]

The paper presents the results of a homogeneous Mathieu equation studies. Mathieu equation solutions are oscillations, modulated in amplitude and frequency. In the computational experiments we found dependences of the given oscillations on the ratio of the coefficients. These dependences are shown in graphs that can be used for an approximate estimation of the Mathieu equation solutions without integration. [ABSTRACT FROM AUTHOR]

Sb 2 Te 3 /GeTe bilayer films with different thickness ratios have been deposited on silicon substrate and fused quartz substrates by radio-frequency magnetron sputtering. Linear optical properties and optical bandgap of sample films were investigated firstly. With the thickness ratio changes, their transmittance differences decrease a lot at the wavelength range of 1500–1600 nm. Besides, the modulation depth of saturable absorption of samples will increase along to the incident power density or thickness ratio. Besides incident power density, interface states between topological insulation characteristic Sb 2 Te 3 and ferroelectric GeTe layers will also affect the modulation depth greatly. [ABSTRACT FROM AUTHOR]

Summary: Background: A plethora of investigations have studied the acoustic characteristics of vibrato such as the rate, extent, onset (time from initiation of phonation until the first peak of vibrato), and periodicity. Despite extensive research, the degree to which various parameters of vibrato contribute to its acceptability remain unclear. Purpose: The present study sought to determine the psychoacoustical relationship of mean fundamental frequency (f 0), modulation frequency (f f0m), modulation depth (d f0m), and intensity to the appropriateness or inappropriateness of vibrato. Method: Phonation samples of eight voice majors singing at low, middle, and high pitches were obtained. A high fidelity vocoder (STRAIGHT; Kawahara, 1997) was used to resynthesize these vowels with systematic manipulations of f f0m and d f0m of the f 0 contours resulting in a total of 600 stimuli (8 singers×3 pitches×5 f f0m levels×5 d f0m levels). Nine listeners (four experts and five students) evaluated these stimuli for appropriateness of vibrato at two different presentation levels (70 and 90dB sound pressure level). Results: Statistical analyses of the perceptual data suggest that appropriateness of vibrato tends to increase with mean f 0 and decrease with d f0m. Appropriateness of vibrato is greatest for f f0m value of 6Hz, but decreases both above and below this frequency. Conclusion: perceived appropriateness of vibrato results from an interaction of mean f 0, f f0m, and d f0m of the vowel waveform. [Copyright &y& Elsevier]