We show that multifocal 1064 nm Raman microscopy based on Hadamard-coded multifocal arrays is useful for imaging carbon nanotubes (CNTs) that would otherwise be damaged if a conventional single focus microscope design is used. The damage threshold for CNTs, dependent on laser power density and exposure time, limits the spectral detection sensitivity of single focus Raman imaging. With multifocal detection, the signal-to-noise ratio of the Raman spectra were improved by more than a factor of three, allowing for the G and D Raman bands of CNTs to be detected while avoiding specimen damage. These results lay the foundation for developing multifocal 1064 nm Raman microscopy as a tool for in situ imaging of CNTs in plant material.High optical quality (Q) factors are critically important in optical microcavities, where performance in applications spanning nonlinear optics to cavity quantum electrodynamics is determined. Here, a record Q factor of over 1.1 billion is demonstrated for on-chip optical resonators. Using silica whispering-gallery resonators on silicon, Q-factor data is measured over wavelengths spanning the C/L bands (100 nm) and for a range of resonator sizes and mode families. A record low sub-milliwatt parametric oscillation threshold is also measured in 9 GHz free-spectral-range devices. The results show the potential for thermal silica on silicon as a resonator material.In this Letter, the electron-blocking-layer (EBL)-free AlGaN ultraviolet (UV) light-emitting diodes (LEDs) using a strip-in-a-barrier structure have been proposed. The quantum barrier (QB) structures are systematically engineered by integrating a 1 nm intrinsic AlxGa(1-x)N strip into the middle of QBs. The resulted structures exhibit significantly reduced electron leakage and improved hole injection into the active region, thus generating higher carrier radiative recombination. Our study shows that the proposed structure improves radiative recombination by ∼220%, reduces electron leakage by ∼11 times, and enhances optical power by ∼225% at 60 mA current injection compared to a conventional AlGaN EBL LED structure. Moreover, the EBL-free strip-in-a-barrier UV LED records the maximum internal quantum efficiency (IQE) of ∼61.5% which is ∼72% higher, and IQE droop is ∼12.4%, which is ∼333% less compared to the conventional AlGaN EBL LED structure at ∼284.5nm wavelength. Hence, the proposed EBL-free AlGaN LED is the potential solution to enhance the optical power and produce highly efficient UV emitters.Focusing regions, also known as caustic regions, are the singular solutions to the amplitude function of optical fields. Focusing regions are generated by the envelope curve of a set of critical points, which can be of attractor or repulsor type. The nature of the critical point depends on the refractive index. An important property of the critical points is that they present charge-like features. When a focusing region is generated in media with a random refractive index, current-like effects appear, and the evolution of the focusing regions follows a diffusion behavior. The morphology of the focusing regions may generate vortices or "eternal solutions" of solitonic type in a nonlinear medium. Herein, the condition under which these effects occur is analyzed and experimentally corroborated.The neural network (NN) has been widely used as a promising technique in fiber optical communication owing to its powerful learning capabilities. The NN-based equalizer is qualified to mitigate mixed linear and nonlinear impairments, providing better performance than conventional algorithms. Many demonstrations employ a traditional pseudo-random bit sequence (PRBS) as the training and test data. However, it has been revealed that the NN can learn the generation rules of the PRBS during training, degrading the equalization performance. In this work, to address this problem, we propose a combination strategy to construct a strong random sequence that will not be learned by the NN or other advanced algorithms. The simulation and experimental results based on data over an additive white Gaussian noise channel and a real intensity modulation and direct detection system validate the effectiveness of the proposed scheme.We report a compact source of high power, tunable, ultrafast yellow radiation using fourth-harmonic generation of a mid-IR laser in two-stage frequency-doubling processes. Using Cr2+ZnS laser at 2360 nm frequency-doubled in a multi-grating MgOPPLN crystal, we have generated near-IR radiation tunable across 1137-1200 nm with average output power as high as 2.4 W and pulse width of ∼60fs. Subsequently, the near-IR radiation is frequency-doubled using a bismuth triborate (BIBO) crystal to produce coherent yellow radiation tunable across 570-596 nm with a maximum average power of ∼1W.  https://www.selleckchem.com/products/apx2009.html  The source has a maximum mid-IR to yellow (near-IR to yellow) single-pass conversion efficiency as high as ∼29.4% (∼47%). Without any pulse compression, the yellow source has output pulses at a repetition rate of 80 MHz with a pulse width of ∼130fs in Gaussian-shaped and a spectral width of ∼4nm corresponding to a time-bandwidth product of 0.45. The generated output beam has a Gaussian transverse beam profile with measured M2 values of Mx2∼1.07 andMy2∼1.01.We demonstrate an on-chip high-sensitivity photonic temperature sensor based on a GaAs microdisk resonator. Based on the large thermo-optic coefficient of GaAs, a temperature sensitivity of 0.142 nm/K with a measurement resolution of 10 mK and low input optical power of only 0.5 µW was achieved. It exhibits great potential for chip-scale biological research and integrated photonic signal processing.Wavefront shaping is increasingly being used in modern microscopy to obtain high-resolution images deep inside inhomogeneous media. Wavefront shaping methods typically rely on the presence of a "guide star" to find the optimal wavefront to mitigate the scattering of light. However, the use of guide stars poses severe limitations. Notably, only objects in the close vicinity of the guide star can be imaged. Here, we introduce a guide-star-free wavefront shaping method in which the optimal wavefront is computed using a digital model of the sample. The refractive index model of the sample, that serves as the input for the computation, is constructed in situ by the microscope itself. In a proof of principle imaging experiment, we demonstrate a large improvement in the two-photon fluorescence signal through a diffuse medium, outperforming state-of-the-art wavefront shaping by a factor of two in imaging depth.