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Vortex beams carrying optical angular momentum (AM) could drive the orbital motion of a small particle around the optical axis. In general, the orbital rotation speed of trapped particles increases linearly with the increasing laser power. Beyond the linear optics regime, in this work, we investigate both the optical force and torque on a two-photon absorbing Rayleigh particle produced by the tightly focused femtosecond-pulsed circularly polarized vortex beam. Different from the trapping dynamics of particles without two-photon absorption (TPA), it is shown that the orbital motion of trapped particles with TPA accelerates nonlinearly as the laser power increases. Moreover, the orbital motion acceleration of trapped particles is proportional to the TPA coefficient. The corresponding underlying mechanism is discussed in detail. Our results may find interesting applications in the characterization of the optical nonlinearity of a single nanoparticle, and AM manipulation and particle transportation in the nonlinear optics regime.Laguerre-Gaussian (LG) beams have orbital angular momentum (OAM). selleck chemicals A particle trapped in an LG beam will rotate about the beam axis, due to the transfer of OAM. The rotation of the particle is usually in the same direction as that of the beam OAM. However, we discovered that when the LG beam is strongly focused, the rotation of the particle and the beam OAM might be in the opposite direction. This anomalous effect is caused by the negative torque on the particle exerted by the focused LG beam, which is similar to the optical pulling force in the linear case. We calculated the optical radiation force distribution of a micro-particle trapped in optical tweezers formed by a strongly focused LG beam, and showed that there exist stable trajectories of the particle that are controlled by the negative torque. We propose several necessary conditions for observing the counter-intuitive trajectories. Our work reveals that the strongly trapped micro-particle exhibits diversity of motion patterns.Optical imaging for non-self-luminous objects surrounded by complex scattering environments is scientifically challenging and technologically important. We propose a non-invasive imaging method by externally sending the illuminating light through the scattering medium and by detecting and analyzing the speckle patterns. The imaging of the object is recovered by extending the application scope of the Fourier-domain shower-curtain effect. It is found that the imaging depth is substantially extended and that faster imaging restoration is realized with the improved illumination scheme assisted with optical lenses, hence making it possible to apply the non-invasive optical imaging technique for practical applications.The anisotropic thermal lens effect of a dual-polarization NdYLF laser is experimentally investigated by measuring the transverse beat frequency between TEM0,0 and TEM1,0 modes in the self-pulsing operation, and focal lengths of thermal lensing for both polarizations can be accurately determined. The focal length of the thermal lens for π polarization was observed to be negative and varies from -1.1 to -0.5m for the absorbed pump power increasing from 1.7 to 3.8 W. For σ polarization, the focal length of the thermal lens was determined to be positive and varies from 1.2 to 0.9 m for the absorbed pump power increasing from 8.4 to 10.9 W. The sensitivity factors of the thermal lens for both polarizations were evaluated to be Mπ=-0.54m-1/W and Mσ=0.1m-1/W, respectively.The performance of traditional chaotic optical communications depends on the matching parameters of the chaotic transmitter and receiver. The chaotic receiver based on the neural network (NN) can solve the dependence on matching parameters, but the analog-to-digital converter (ADC) has an effect on the decryption performance. In this paper, the effects of sampling rate and digitalizing bit for ADC on NN-based chaotic optical communication systems with different feedback strengths at different bit rates are numerically studied. The results show that the requirements for ADC will be higher if the feedback becomes stronger. In order to achieve higher speed chaotic optical communications, the ADC with higher performance is needed. These results can give guidance for the applications of NN-based high-speed chaotic optical communication systems.A detailed comparative study of heavily erbium-doped fiber laser generation features was carried out in the case of 1490 nm and 976 nm wavelength pumping. The laser cavity was designed using point-by-point fiber Bragg grating inscription technology with femtosecond laser pulses. The CW and Q-switched lasing regimes were achieved depending on temperature and heat sink performance. It was found experimentally for the first time, to the best of our knowledge, that the frequency and pulse duration of Q-switched laser operations are primarily determined by the output laser power and do not depend on the pump wavelength. The pulse formation is caused by the lasing process itself and depends on the up-conversion rate at the generation wavelength. Additionally, the level of laser cavity heating at the Q-switched generation regime was defined.We demonstrated a high-power Q-switched two-stage HoYAG master-oscillator power-amplifier (MOPA) system dual-end pumped by TmYLF lasers. A new method was introduced by rotating and swapping spatial axial directions of pump beams to improve the beam quality of the HoYAG oscillator and first-stage amplifier. Two parallel second-stage HoYAG amplifiers were employed to output high power. A total maximum average output power of 332 W at 2091 nm with pulse repetition frequency of 20 kHz was achieved. Then a ZnGeP2 MOPA system was demonstrated using the HoYAG MOPA as the pump source. A maximum average output power of 161 W at 3-5 µm was obtained with 290 W incident Ho pump power, corresponding to beam quality factors M2 of 3.42 and 3.83 for horizontal and vertical directions, respectively.A Mach-Zehnder silicon photonic switch with low random phase errors is proposed and demonstrated for the first time, to the best of our knowledge, by incorporating judiciously widened and shortened phase shifter waveguides. With a 180 nm complementary metal-oxide-semiconductor (CMOS) foundry process, more than one hundred 2×2 thermo-optic Mach-Zehnder switches (MZSs) with varied phase shifter widths have been designed, fabricated, and characterized on 14 silicon chips. The mean and standard deviation of the random phase errors of the MZSs with phase shifters widened to 2 µm are less than a third of those of the conventional design with 0.45-µm-wide single-mode phase shifters. This validates the improved fabrication tolerance and results in considerable reduction of the power consumption for the phase error compensation. Such elegant methodology paves the way to further scaling up N×N silicon thermo-optic switches and can be generalized for other phase-sensitive integrated photonic devices as well.
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