Fan Zhongwei

High-power blue light generation by external frequency doubling of an optical parametric oscillator

We report on an all-solid-state high-power quasi-continuous blue light source by the frequency doubling of a signal wave from an optical parametric oscillator (OPO). A 50-mm-long LiB3O5 (LBO) crystal is used for the OPO, which is pumped by a diode-pumped Nd:YAG green laser (10 kHz, 50 ns). Tunable blue emission in a new nonlinear crystal BiB3O6 (BiBO) is obtained with a wavelength range from 450 to 495 nm. The average power of the signal output is as high as 9.3 W from 924 to 970 nm. The maximum output of the blue laser with the second harmonic walk-off compensation is 1.3 W average power at 470 nm for 6.2 W of OPO signal light at 940 nm.

A 1342-nm Passively Mode-Locked Picosecond Oscillator with a Semiconductor Saturable Absorber Mirror

A 1342-nm oscillator was successfully demonstrated by using a semiconductor saturable absorber mirror with the repetition rate of 65 MHz. The output coupler with appropriate transmission was chosen to suppress Q-switched mode-locking. At the pumping power of 1.7 W, the stable continuous-wave mode locked pulse was observed. The average output power was 140mW and pulse width was measured to be 17.2 ps.

Design of MM-wave Fresnel zone plate reflector antenna with continuous phase structure

The phase Fresnel zone plate, whose diffraction efficiency is up 97%, has been made. Because of the advantages of thinner thickness, lighter weight and design flexibility, the phase Fresnel zone plate has been considered for use as a MM-wave antenna so as to increase the diffraction efficiency. However, zone plates with only four phase steps are generally made up to now, so the diffraction efficiency is only about 80%, and the highest gain is no more than 35 dB. To overcome this weakness, a new kind of Fresnel zone plate antenna with a continuous phase structure is designed, and the authors call it a diffraction antenna.

A 46-W Laser Diode Stack End-Pumped Slab Amplifier with a Pulse Duration of Picoseconds

A 46-W laser diode end-pumped amplifier is demonstrated by using a SESAM passively mode-locked oscillator and a compact LD stack end-pumped slab amplifier. For the oscillator, a 5-W picosecond mode-locked laser with a repetition frequency of 79 MHz is obtained with beam quality factors of M2 < 1.3. A beam shaping system made up of cylindrical lens is designed according to different sizes of the active medium in both directions, and a plane-plane cavity is used in the amplifier for high efficiency. At the absorbed pumping power of 174 W, the highest output power of 46 W is obtained with the slope efficiency of 29.5%. The beam quality factors M2 in both directions are measured to be 1.43 and 1.76, respectively.

Spherical distribution structure of the semiconductor laser diode stack for pumping

A semiconductor laser diode stack is used for pumping and 8 semiconductor laser diode arrays of the stack are put on a sphere, and the output of every bar is specially off-axis compressed to realize high coupling efficiency. The output beam of this semiconductor laser diode stack is shaped by a hollow duct to the laser active medium. The efficiency of the hollow light pipe, which is used for semiconductor laser diode stack coupling, is analyzed by geometric optics and ray tracing. Geometric optics analysis diagnoses the reasons for coupling loss and guides the design of the structure. Ray tracing analyzes the relation between the structural parameters and the output characteristics of this pumping system, and guides parameter optimization. Simulation and analysis results show that putting the semiconductor laser diode arrays on a spherical surface can increase coupling efficiency, reduce the optimum duct length and improve the output energy field distribution.

Self-Compensated Thermal Effect Points in Laser Rod

Thermal effect in all solid-state lasers is a bottleneck for improving output average power and beam quality. In general, the focal length or optical path difference of laser rod are calculated in order to compensate thermal effect through extremity ground, lens inserted, or especial resonator designed. We regarded laser rod as a gradient index rod in my paper and got an equaling focal length equation of thermal lens of laser rod. Our equation contrasting to Koechners in literature [1] was gone along. From our equation self-compensated thermal effect points (SCTEPs) in laser rod were found when certain equation is satisfied. The phenomenon of SCTEP was research in detail.

DESIGN OF mm-WAVE PHASE-CORRECTING FRESNEL ZONE PLATE REFLECTOR ANTENNA WITH CONTINUOUS STRUCTURE

Based on scalar diffraction optics theory, a new type of mm-wave antenna(diffraction antenna) phase-correcting Fresnel zone plate with continuous structure is described in this paper. It has the advantages of thinner thickness, lighter weight and design flexibility. The design theory and space shadow are discussed in details, and the measured results are presented. The results show that the properties of this kind of antenna is closed to paraboloid reflector.