Shaolan Zhu

Single- and dual-pulse oscillation in a passively Q-switched Nd:YAG microchip laser

Experimental investigation of single and dual pulses in a passively Q-switched Nd:YAG microchip laser with a Cr4+:YAG saturable absorber has been reported. The dual pulses consist of a main and a satellite pulse with respective spectra, intensities, and durations. It is found that the preponderant oscillating mode gives birth to the main pulse, and the other oscillating mode corresponds to the satellite pulse. Our results demonstrate that the dual-pulse emission results from double-longitudinal-mode oscillation in high pump regime.

Optimization and Comparison of Single- and Dual-Pump Fiber-Optical Parametric Amplifiers with Dispersion Fluctuations

Solutions for fiber-optical parametric amplifiers (FOPAs) with dispersion fluctuations are derived using matrix operators. On the basis of the propagation matrix product and the hybrid genetic algorithm, we have optimized and compared single- and dual-pump FOPAs with zero-dispersion-wavelength variations. The simulations prove that the design of FOPAs involves multimodal function optimization problems. The numerical results show that dual-pump FOPAs are highly sensitive to dispersion fluctuations whereas dispersion variations have less impact on the gain of single-pump FOPAs. To increase signal gain and reduce ripple, dual-pump FOPAs, instead of single-pump FOPAs, have to be carefully optimized with a suitable multisegment fiber structure rather than a one-segment fiber structure. The different combinations of multisegment fibers can provide highly different gain properties. The increase in gain is at the cost of the ripple.

All fiber supercontinuum light source using photonic crystal fibers pumped by nanosecond fiber laser pulses

A novel compact supercontinuum (SC) source using the single mode photonic crystal fibers (PCF) pumped with an all fiber MOPA fiber laser is demonstrated experimentally. A bandwidth of 700 nm is achieved by operating the pumping fiber laser at a wavelength of 1064 nm, pulse duration of 10 ns, repetition rate of 50 kHz and peak power of 1 kW. The SC generation is initiated through modulation instability (MI) which breakups the nanosecond pump pulses into picosecond or femtosecond pulses, and further broadened through nonlinear effects of PCF.

Influence of the time modulation of the pump laser caused by mode beating on optical parametric process

Numerical simulation and analysis about the influence of the time modulation of the pump laser caused by mode beating on optical parametric process are presented with OPA and OPG as examples. It is shown that the output power of the generated beams from optical parametric process is modulated in the time domain and exhibits large power fluctuations, when a Q-switched laser oscillating on several random longitudinal modes is used as the pump laser. Irregular spike sequences of the generated beams are observed. We also find that the output power of the light from optical parametric process becomes more stable and exhibits a less fluctuation, when the number of the longitudinal modes (n) increases.

Passive Q-switched fiber laser with SESAM in ytterbium-doped double-clad fiber

A passively Q-switched ytterbium-doped double-clad fiber laser with SESAM as a saturable absorber is demonstrated experimentally. This system showed up to 18.7mW output power, up to 29.4 kHz repetition rate, a maximum pulse energy of 0.636μJ and a minimum pulse duration of 3.148 μs. The characteristics of pulse were investigated, and the theoretical analysis agree well with the experimental results.

A sub-nanosecond narrow-linewidth pulsed laser source with controllable repetition rate

A compact all-fiber sub-nanosecond narrow-linewidth Yb-doped fiber amplifier with a controllable repetition rate has been investigated. Tunable temporal pulses ranging from sub-nanoseconds to 10 ns with repetition rates from 10 kHz to 1 MHz are obtained by controlling the waveform of the injected electrical-pulse signal. Due to the practical requirements of our intended applications, a distributed feedback semiconductor laser with a wavelength of 1064 nm, pulse duration of 802 ps, repetition rate of 500 kHz and average power of 20 μW is used to seed a dual-stage single mode Yb-doped fiber amplifier. The characteristics of the amplified pulses are measured and exhibit a temporal duration of 810 ps with an average power of 31.2 mW. The gain of the amplified pulse is about 32 dB at the maximum output power. A notable feature of the amplifier pulses is that the spectral linewidth can be maintained to less than 0.1 nm during the dual-stage amplifier process. The noise level lies more than 22 dB below the peak value of the amplified spectrum, which represents an excellent signal-to-noise ratio.

Applications of digital IF receivers and under-sampling technique in ladar

The traditional technique of phase laser range finder is mixing high frequency signals with analog circuits and filtering them to obtain the useful signal with low frequency. But the analog mixing circuits are susceptible to interference and will bring amplitude attenuation, phase jitter and offset and this way has difficulties in achieving high precision ranging and fast speed ranging at the same time. The method of this paper is based on under-sampling technique with digital synchronous detection and referring to Digital down converter technique of digital IF receiver in radar system. This method not only reduces the complexity of data processing, improves the speed and accuracy of phase detection at the same time, but also reduces requirements for ADC devices and DSP chips in the ladar system by a lower sampling rate. At the same time, the structure of electronic system is global simplified compared with traditional analog ladar system and the anti-jamming is greatly enhanced. So this method has important research value.

The pulsed all fiber laser application in the high-resolution 3D imaging LIDAR system

An all fiber laser with master-oscillator-power-amplifier (MOPA) configuration at 1064nm/1550nm for the high-resolution three-dimensional (3D) imaging light detection and ranging (LIDAR) system was reported. The pulsewidth and the repetition frequency could be arbitrarily tuned 1ns~10ns and 10KHz~1MHz, and the peak power exceeded 100kW could be obtained with the laser. Using this all fiber laser in the high-resolution 3D imaging LIDAR system, the image resolution of 1024x1024 and the distance precision of ±1.5 cm was obtained at the imaging distance of 1km.

Probability of acquisition of three-dimensional imaging laser radar

Three-dimensional imaging laser radar (3-D ladar) is widely used in area of modern military, scientific research, agriculture and industry. Because of its many features such as angle-angle-range capturing, high resolution, anti-jamming ability and no multipath effect ,but it has to scan for target searching, acquiring and tracking. This paper presents a novel probability model of target acquiring which provides a theoretical basis for optimizing the scanning mechanism. The model combines space and time, target moving velocity and ladar scanning velocity together. Then the optimum scanning mechanism to obtain the maximum probability of acquisition and associated with different targets can be gained. The result shows that this model provides a method to optimize parameter for designing of the scanner.

Optimization of the high repetition rate all-fiber two-stage ytterbium-doped fiber amplifier

Based on the technique of master oscillator power amplifier (MOPA), a two-stage ytterbium-doped fiber amplifier (YDFA) with all-fiber structure is theoretically simulated. The seed signal operating at the wavelength of 1064 nm has the characteristic of high repetition rate (10 MHz), ultrashort pulse duration (10 ps), low signal power input (20μW) and single longitudinal mode. The gain (and amplification stimulation emission power) is calculated at the different pump powers and gain fiber lengths of YDFA pumped by 975 nm. In addition, the amplifications at the different signal power inputs (1-25μW) are also simulated. The numerical results can be used to optimize the YDFA.