Yujing Huo

Optoelectronic system for high-speed flier velocity measurement based on laser scattering

High-speed flier velocity measurement is one of the key technologies in investigating collision sites on the surfaces of spacecraft structures impacted by high-speed space debris. We have designed and constructed an optoelectronic system to accurately determine the average velocity of a flier impacting on a spacecraft structure. The system is based on two parallel laser screens, which are crossed by the fliers before impact. This system utilizes scattered light as the start and the end signal to measure the time of flight between the two screens. A wideband optical sensor has been designed and evaluated, and an electronic circuit is used to accurately record the time of flight and calculate the velocity. Experimental results show this system is adequate to measure the velocity of a flier larger than 100 μm, in the range from 0.1 to 10 km/s, with accuracy better than 1.3%, and with low cost, simplicity, and high reliability.

Actively-controllable passively Q-switched laser

A new type of Q-switched pulsed lasers (CPQL, Controllable Passively Q-switched Laser) is presented. The laser is composite of a passively Q-switched laser with a saturable absorber and a controlling LD with a focus system. The performance of the laser output pulses, including the pulse energy, pulse width, pulse generation moment and repetition frequency, can be actively controlled by the operator with the controlling LD. The new type laser is discussed theoretically and the experiment results are present. Compare to the ordinary Q-switched laser, including passively Q-switched lasers and actively Q-switched lasers, CPQL’s have higher performance and will find important applications in many fields.

Second-harmonic generation using an a axis Nd:MgO:LiNbO3 single crystal fiber with Mg-ion indiffused cladding

We report the implementation of a low-loss core-cladding waveguide structure of an a axis Nd:MgO:LiNbO3 single-crystal fiber with a step refractive index profile and the demonstration of a frequency- doubled laser made from such a cladded crystal fiber. The laser-heated pedestal-grown a axis single-crystal fiber, with an elliptical crosssectional area of 200x 150?m, is further shown with a Mg ion indiffusion process. Electron probe microanalysis is used to measure the Mg ion concentration distribution in the Mg-diffused layer. After several trials, diffusion parameters suitable for achieving a core-cladding waveguide structure with a step refractive index profile are obtained. The optical and structural properties of the cladded crystal fibers are also characterized. Room-temperature second-harmonic generation with such a cladded crystal fiber is demonstrated. At room temperature, cw green laser output with a power of 10 ?W at the wavelength of 0.532 ?m is achieved. The origin of the relatively low conversion efficiency is discussed.

Time-of-flight measurement in self-triggering pulsed laser ranging

Self-triggering pulsed laser ranging, a novel pulsed laser ranging method, can ease the trade-off between ranging precision and measurement speed in the traditional laser ranging technique. Theoretical analysis and system design for time-of-flight measurement, which determines both the ranging precision and the measuring speed of self-triggering pulsed laser ranging, is performed. An experiment on self-triggering pulsed laser ranging is reported, in which submillimeter (better than 0.5 mm) precision is achieved over a 20-m range.

Surface modification investigation of lithium niobate single crystal fiber

Abstract In this paper, a Mg-ion indiffusion process is applied to LN single crystal fiber with MgO thin film deposited on its surface. After a large number of exploring experiments, we conclude that a core-cladding waveguide structure of crystal fiber with different refractive index profile can be obtained by selecting suitable diffusion parameters such as diffusion temperature, diffusion times and MgO film thickness. Other optical characteristics of the cladded fibers are investigated.

Self-triggering pulsed time-of-flight laser range-finding method

Based on the self-triggering pulsed technique, a novel pulsed time-of-flight (TOF) laser range-finding method is proposed to improve the accuracy and measuring speed of laser distance measurement. A theoretical analysis is carried out, and three basic equations are presented to describe the method. Furthermore, a measurement device is described and experimental evidence is presented to show the feasibility of measuring distance with 0.5-mm resolution over a 10-m range.

Cladding and characteristics of LiNbO 3 single crystal fibre

Abstract A magnesium ion indiffusion process is applied to LiNbO3 single crystal fibres deposited with MgO thin film on their surface. A core–cladding waveguide structure with different refractive index profile is formed in LiNbO3 single crystal fibres by selecting suitable diffusion parameters such as diffusion temperature, diffusion time and MgO film thickness. An electron probe microanalysis was used to measure the Mg-ion concentration distribution of the Mg diffused layer. The propagation loss of the clad crystal fibre (Mg-diffused crystal fibre) is measured to be 14 times lower than that of the unclad crystal fibre and the transmission modes were observed. The microstructural characteristics of the Mg diffused crystal fibres were also characterized by using Laue X-ray diffraction and scanning electron microscopy. It was shown that a good starting single crystal of the Mg diffused crystal fibres can be preserved by controlling suitable diffusion parameters and matching suitable crystal fibre diameter.

A-Axis Nd:MgO:LiNbO3 single crystal fibers with magnesium-ion indiffused cladding

Abstract A core-cladding waveguide structure for the a-axis Nd:MgO: LiNbO3 single crystal fiber with parabolic refractive index profiles was achieved by a Mg-ion indiffusion process. Propagation loss coefficient of the cladded crystal fiber was measured and is 7 times lower than the uncladded crystal fibers. Transmission modes of the 60μmlm × 45μmlm cladded crystal fiber were observed and the low order modes propagation was obtained

Multi-end-pumped nonplanar ring laser with a two-mirror resonator and output from a single point

A multi-end-pumped nonplanar ring laser with a two-mirror resonator has been demonstrated. Two important parameters of the beam loops are described, and simulation diagrams of the beam loops are shown. Using an output coupler with a fan-shaped distribution in reflectivity, multi-end-pumped operation with the output beam from a single point has been achieved, and the experimental results show that the laser could be multi-end-pumped to reduce thermal effects and multiply the fracture limit of the laser crystal.

Cladded optical fiber laser made from a-axis Nd:MgO:LiNbO3 single-crystal fiber with Mg-ion indiffussion

We report the implementation of a low loss core-cladding waveguide structure of an a-axis Nd:MgO:LiNbO3 single crystal fiber and the demonstration of a frequency-doubled laser made from such a cladded crystal fiber. The laser-heated pedestal grown a-axis single crystal fiber, which has an elliptical cross sectional area of about 200 micrometer X 150 micrometer, was further treated with a Mg-ion indiffusion process. An electron probe microanalysis was used to measure the Mg-ion concentration distribution of the Mg diffused layer. After a number of trials, the diffusion parameters suitable for forming a core-cladding waveguide structure have been obtained. The optical and structural properties of the cladded crystal fibers were also characterized. A diode pumped external cavity frequency doubled laser has been made from the cladded crystal fiber. At room temperature, CW green laser output with a power of 10 (mu) W at the wavelength of 0.532 micrometer has been obtained. The origins of the relatively low frequency-doubled conversion efficiency will also be discussed.