Hongming Zhao

Beam conditions for radiation generated by an electromagnetic J 0 -correlated Schell-model source

Based on the 2x2 (electric field) cross-spectral density matrix, a model for an electromagnetic J0-correlated Schell-model beam is given that is a generalization of the scalar J0-correlated Schell-model beam. The conditions that the matrix for the source to generate an electromagnetic J0-correlated Schell-model beam are obtained. The condition for the source to generate a scalar J0-correlated Schell-model beam can be considered as a special case.

Stable pulse-compressed acousto-optic Q-switched fiber laser

A novel acousto-optic switch operation by a simple laser-diode pumped acousto-optic, Q-switched, ytterbium-doped, double-clad fiber laser is reported. Stable compressed Q-switched sub-40 ns pulses with a beam quality factor (M(2)=2) are achieved at the repetition rate of 1-50 kHz. Q-switched pulses of ~20 microJ pulse energy and 35 ns pulse width are obtained at the repetition rate of 50 kHz. Finally, a reasonable explanation of the novel Q-switched operation is presented.

High-Repetition-Rate MHz Acoustooptic

A simple actively Q-switched double-clad fiber laser combining an amplifying cavity is reported by using a dynamic acoustooptic Q-switching as a beam splitter. Sub-100-ns pulses independence of the repetition rate of acoustooptic modulator are almost changeless with repetition rate varied from 50 kHz to 1.5 MHz. With 4.5-W absorbed power, 9.4-W peak-power pulses at 1.5-MHz repetition rate with 75-ns pulse duration are generated.

Q

A pulsed master-oscillator fiber power amplifier system with near diffraction-limited output by use of China-made large-mode-area fiber and a (2+1)×1 multimode combiner is reported. The effect of the seed power on the amplification performance is found. For the seed power, there exists a range within which the pulsed fiber amplifier can operate safely and reliably at a certain pump power. With the seed average power of 70 mW, the amplification performances of the fiber amplifier are investigated.

-Switched Fiber Laser

Laser-diode pumped Q-switched ytterbium-doped fiber laser is studied experimentally by controlling the switching time of acousto-optic modulator (AOM). The characteristics of Q-switched pulses with different rise time of AOM regulated by the laser beam size along the window of AOM are presented. Meanwhile, the behaviors of Q-switched pulses are achieved by regulating the switching time of AOM. The single-repetition-rate and half-repetition-rate phenomena are described and discussed. The experimental results confirm that the fiber laser with lower level inversion population can be more easily operated for half-repetition-rate generation.

Impacts of seed power on amplification performance in pulsed double-clad fiber amplifier

The authors report stable short high-repetition-rate Q-switched pulses in acousto-optic Q-switched ytterbium-doped double-clad fiber lasers. This device uses a diode pumped at 975 nm to end pump the large mode area double-clad fiber laser. In the experiment acousto-optic modulator is used as a special Q-switching in the F-P cavity. As a result, sub 100 nanosecond pulses are obtained with varying the acoustic-optic repetition rate from 1 kHz to 100 kHz. The Q-switching technique provides a novel method to generate short pulses at high repetition rate.

Characteristic of pulsed fiber laser induced by switching time

A narrow-linewidth master-oscillator fiber power amplifier system with homemade large-mode-area fiber is demonstrated. Some fundamental characteristics of this system, including the output power characteristics, the emission spectrum characteristics, as well as the confirmation of single-frequency operation are investigated in detail. The system generates up to 7.3 W of single-frequency radiation at a wavelength of 1064 nm with 39% slope efficiency and 26% optical-optical power conversion efficiency.