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Based on the theory of vector diffraction and the principle of triangular modulation, the focusing characteristics and patterns of an axisymmetric Bessel-Gaussian beam with helical polarization with quadratic radial correlation are studied. The results show that both the beam parameters µ and the triangular modulation parameters n can significantly change the intensity distribution of the focusing region. Under the same spiral parameter C, obvious lateral changes of the focusing pattern can be observed by changing either of the above two parameters. The focusing pattern can be changed from focusing ring to two parallel focal spots extending horizontally, and moreover, some parameters have obvious “self-reduction” characteristics, which is of certain significance for the application of Bessel-Gaussian beams in the field of optical micromanipulation.In this theoretical study, a photonic crystal coupled-cavity waveguide created on polymer substrate was demonstrated to provide high-performance slow light with low group-velocity dispersion and large normalized delay-bandwidth product. Combined with structural-parameter optimization, the normalized delay-bandwidth product was enhanced to a large value of 0.809, and the group-velocity dispersion was on the order of 104(ps2/km). Furthermore, the optimized coupled-cavity waveguide had tunability capabilities by changing the external pump laser power. Importantly, while adjusting the slow light, the normalized delay-bandwidth product values remained above 0.8, which was necessary to maintain the performance of optical buffering devices.An all-optical Fredkin gate was proposed and designed. The Fredkin gate is a reversible logic gate. For designing the proposed structure we used three different optical nonlinear resonators. BSJ-4-116 The wide-bandwidth resonators do not have switching functionality. However, the proposed resonator was modified to act as an optical switch in the horizontal direction. The final structure was designed using four wide-band resonators, twelve sharp resonators, and four nonlinear ring resonators. Simulation results show that the maximum rise time for the proposed structure is about 5 ps.We present a 1/f noise model of 980 nm InGaAs/GaAs laser diodes (LDs) operated below the lasing threshold to study the correlation between 1/f noise and fluctuation of surface nonradiative recombination current I n r . In InGaAs/GaAs LDs, nonradiative recombination current components have been identified as being primarily related to surface recombination, which depends on surface oxide traps and lattice dislocation. An analysis of the experimental comparison of I n r and 1/f noise spectral density with constant current and temperature aging tests further shows the correlation and verifies the 1/f noise model, which can be interpreted as a change in carriers and trap density of a certain surface. This model permits facet stability to be investigated.Stimulated Raman scattering (SRS) is a powerful optical technique for probing the vibrational states of molecules in biological tissues and provides greater signal intensities than when using spontaneous Raman scattering. In this study, we examined the use of continuous wave (cw) and picosecond (ps) laser excitations to generate SRS signals in pure methanol, a carotene-methanol solution, acetone, and brain tissue samples. The cw-SRS system, which utilized two cw lasers, produced better signal-to-noise (S/N) than the conventional ps-SRS system, suggesting that the cw-SRS system is an efficient and cost-effective approach for studying SRS in complex systems like the brain. The cw-SRS approach will reduce the size of the SRS system, allowing for stimulated Raman gain/loss microscopy. In addition, we showed that there exists a resonance SRS (RSRS) effect from the carotene-methanol solution and brain tissue samples using cw laser excitations. The RSRS effect will further improve the signal-to-noise and may be utilized as an enhanced, label-free SRS microscopic tool for the study of biological tissues.To meet the requirements of the large sensing measurement range and high axial depth resolution for profile measurement, a dual differential confocal method (DDCM) is proposed in this paper. The DDCM uses the confocal signal to process separately the signal of two pinholes with axial offset, and it adds the two processed signals to obtain an axial response curve with a large slope and linear response range, thereby achieving a high-precision surface profile measurement with no axial scanning. Preliminary experiments show that the DDCM has a sensing measurement range of 0.54 µm and an axial resolution of 1 nm at the numerical aperture of 0.9. Furthermore, the sensing measurement range of the DDCM is approximately 2.9 times that of the differential confocal microscopy.We present a dual-channel mobile lidar system based on laser-induced fluorescence (LIF) for real-time standoff detection and concentration distribution analysis of tryptophan. The system employs an ultraviolet laser excitation source and signal detectors for receiving fluorescence signals within two different wavelength bands. The performed experiments measured tryptophan aerosols at two different standoff distances. Moreover, distilled water and ethanol solutions were also detected for comparison. The results show that the system can detect LIF signals of tryptophan, give early warnings, locate the diffusion sources, and monitor the variation of the aerosol concentration distribution in real time.In order to meet the needs of on-site, accurate, fast, and remote detection, we design a smartphone-based handheld dual-channel optical fiber fluorescence sensor (DOFFS), which is composed of a semiconductor laser for exciting fluorescence signals, a smartphone with a dual-bandpass filter for collecting fluorescence signals, a fiber coupler for transmitting light, and batteries for laser power supply. All the components are integrated into a 3D printed shell, on the side of which there are two fiber flanges used for fiber probe connection. The fluorescence signals of green and red quantum dots modified on the fiber probes can be captured by the smartphone camera and calculated by a self-developed Android application. The comparisons of single-channel and dual-channel fluorescence signals with pH show that the performance of the sensor is good. The proposed sensor not only can simultaneously detect dual-channel signals for fast detection needs, but it also is handheld with a small size of 79×57×154mm3 and inner power supply, and the fiber probes can be easily replaced, supporting remote and on-site applications.