Zhiwei Lv

Polarization and polarization control of random lasers from dye-doped nematic liquid crystals

A polarimetric study of random laser (RL) emitted from dye-doped nematic liquid crystals (NLCs) is presented. We observed linearly polarized light, the orientation of which is in proximity to the bisection between the polarization direction at the maximal scattering in NLCs and the nematic director. Any arbitrary linear polarization of RLs can be obtained by rotating the NLC sample. The efficiency and output uniformity over the complete direction angle of 2π can be optimized by choosing a proper pump polarization.

Research on stimulated Brillouin scattering suppression based on multi-frequency phase modulation

The method of generating equal-amplitude spectral lines by multi-frequency phase modulation is used in stimulated Brillouin scattering (SBS) suppression. The spectra of three, five, seven, and eleven equal-amplitude spectral lines are obtained in experiment with flatnesses less than 0.3 dB. Theoretical research on SBS suppression shows that the threshold power after modulation is in reverse proportion to the maximum square of amplitude moduli of fundamental frequency and the nth harmonic wave. The threshold powers of three, five, seven, and eleven equal-amplitude spectral lines are improved by 5.21, 8.36, 9.39, and 10.76 dB, respectively.

Using an active temporal compensating system to achieve the super-Gaussian pulses in high-power lasers

In high-power solid-state laser, initiative pulse shaping can help improve the output laser’s performance. The evaluation for output laser pulse is also incomplete. In this paper, we propose a method of initiative pulse shaping by using arbitrary waveform generator (AWG), and establish a relatively complete evaluation system for the output pulses shape simultaneously. It achieves the super-Gaussian pulse output with high SNR (signal-to-noise ratio). As a consequence, a square laser pulse with pulse adjustable width ~5ns, rising time 197ps is obtained. The power imbalance of the output square pulse is 3.72%. The similarity between the eight-order super-Gaussian pulse and the one we get from experiment reached 99%.

Novel Optical Fiber Magnetic Sensor Based on Magnetic Fluid

A novel fiber optic F-P electromagnetic sensor is developed based on magnetic fluid as the medium in F-P interference cavity. A signal demodulation method based on fiber Bragg grating wavelength scanning is proposed. Theory and principle of electromagnetic-controlled refractive index of the magnetic fluid is described as well as the structure of the sensor system. Preliminary experiments are carried out, and the results indicate that there is a fairly good linearity of the measurement characteristic, and the thickness of magnetic fluid film and environmental temperature will affect the measurement results.

Orbital angular momentum mode division filtering for photon-phonon coupling

Stimulated Brillouin scattering (SBS), a fundamental nonlinear interaction between light and acoustic waves occurring in any transparency material, has been broadly studied for several decades and gained rapid progress in integrated photonics recently. However, the SBS noise arising from the unwanted coupling between photons and spontaneous non-coherent phonons in media is inevitable. Here, we propose and experimentally demonstrate this obstacle can be overcome via a method called orbital angular momentum mode division filtering. Owing to the introduction of a new distinguishable degree-of-freedom, even extremely weak signals can be discriminated and separated from a strong noise produced in SBS processes. The mechanism demonstrated in this proof-of-principle work provides a practical way for quasi-noise-free photonic-phononic operation, which is still valid in waveguides supporting multi-orthogonal spatial modes, permits more flexibility and robustness for future SBS devices.

Synthesis, crystal structure and catalytic performance of bis (imino)pyridyl nickel complexes

Two new Ni(II) complexes of 2,6-bis[1-(2,6-diethylphenylimino)ethyl]pyridine (L1), 2,6-bis[1-(4-methylphenylimino)ethyl]pyridine (L2 ) have been synthesized and structurally characterized. Complex Ni(L1)Cl2 · CH3CN (1), exhibits a distorted trigonal bipyramidal geometry, whereas complex Ni(L1)(CH3CN)Cl2 (2), is six-coordinate with a geometry that can best be described as distorted octahedral. The catalytic activities of complexes 1, 2, Ni{2,6-bis[1-(2,6-diisopropyl-phenylimino)ethyl]pyridine} Cl2 · CH3CN (3), and Ni{2,6-bis[1-(2,6-dimethylphenylimino) ethyl]pyridine}Cl2 · CH3CN (4), for ethylene polymerization were studied under activation with MAO.

Analysis and optimization of mounting configuration of large aperture optics

With the aim to decrease the gravitational distortion and stress for the large aperture optics, a novel mounting configuration was proposed, analyzed and optimized. The effects of the design factors of external load, supporting surface topography and supporting width were studied by using the Finite Element Method (FEM), the changing trends of the distortion and stress with these varying factors were obtained, respectively. More over, orthogonal tests of the influence of these factors were carried out, consequently, the regression analysis of the test results were processed, and the mathematical models for comprehensively considering the coupling effects of these factors were received. Further more, the optimization of the mounting configuration, based on the mathematical models and additionally considered the engineering specifications, was performed, and the optimal configuration was figured out. The numerical results showed the feasibility of the mounting configuration in the aspects of decreasing the gravitational distortion and stress.

Core Technique Research on Optoelectronics and Control System in Target Area for ICF Laser Driver

This paper will introduce in detail how to adopt the technique of the match between light beams and the target on optoelectronics and control system to realize the full closed loop control of light beam leading and target precisely fixed position, auto program flow of shooting target practice process, make the system shooting practice preparative time less than 30 minutes and shooting target practice accuracy better than 30μm (RMS). Its performance superiority will decide operation efficiency and success or failure of physics experiment on the whole ICF laser driver facility.

Effect of hydroxyl group upon optical fiber sensors used in permanent downhole

Fibers in the optical fiber sensors would react with water and hydrogen in permanent downhole measurement under the high temperature and pressure. This reaction would change the absorption loss of the fibers, which would affect the reliability of the measurement system. To analyze this problem, the course of hydroxyl penetrating through fibers was investigated. The source of penetrating hydroxyl was discussed. The penetration changes the chemical bond combination inner the fibers, which causes the increase of the absorption loss and the reduction of useful life of the fibers. The results show that at the wavelength of 1.38μm, when the content of the hydroxyl group is about 0.0001, the absorption loss can reach 33dB/km. The analyses also point out that carbon-coated fiber could increase the static fatigue resistance parameter, thus increasing the useful life of the fibers exponentially.

A new circulating two-cell structure for stimulated Brillouin scattering phase conjugation mirrors with 1-J load and 10-Hz repetition rate

A new approach to realize high-energy and high-power stimulated Brillouin scattering phase conjugation mirrors (SBS-PCMs) is described. The reflectivity of SBS-PCM is investigated under a 10-Hz repetition rate and a high energy load. The relationship between reflectivity and input energy is examined experimentally with different PCM structures, focus lengths, and medium cell structures. A medium cell with a circulating structure is designed, and its advantage is demonstrated through an experimental comparison with traditional PCM structures. The 30-cm focus lens and 150-cm collimation lens are optimized when the input energy reaches 1010 mJ at 10-Hz repetition rate. Therefore, a reflectivity of 84.7% and a higher energy load using the circulating two-cell structure are achieved.