Zhu Jianqiang

A 115-W Ytterbium-Doped Fibre Laser

We report a highly efficient ytterbium-doped double-clad fibre laser, one-end pumped by a 975-nm diode stack source and generating up to 115.6 W of cw output power at 1.1 μm. The maximum optical-to-optical conversion efficiency with respect to the launched pump power is 79% at 65-W output power, and the overall slope efficiency is about 69%.

A Lens Assisted Phase Microscope Based on Ptychography

Based on the recently developed ptychographical iterative engine (PIE), we suggest a lens assisted microscopy to realize quantitative phase imaging without using interferometry. The sample is imaged with a lens system; a pinhole on the image plane scans the image at a proper step interval; the diffraction pattern is recorded simultaneously by a CCD at Fresnel area. With a slightly changed PIE algorithm, the phase image of the sample can be accurately reconstructed from the recorded diffraction pattern. The main advantage of this suggested method lies in its capability to retrieve the phase information from the recorded intensity directly, and thus it has more flexibility over conventional interferometric techniques. The feasibility of the suggested method is verified by reconstructing the modulus and phase image of a biological sample from a set of 10 by 10 diffraction patterns, and the result matches the analysis well.

Negative-stiffness vibration isolation

A new kind of vibration isolator, which is base on negative-stiffness theory, is made out for nano manufacture. In this paper, vibration isolation theory is mentioned to further explain negative-stiffness, and then Euler Columns and another negative-stiffness structure are introduced. Furthermore, the stiffness expression is figured out. Finally, a negative-stiffness vibration isolator is made to prove the theory and experiments also shows that its nature frequency is 0.45Hz and can isolate 79% of vibration at 1.9Hz and 97% at 4.9 Hz.

Influence of the illumination coherency and illumination aperture on the ptychographic iterative microscopy

While ptychography is an algorithm based on coherent illumination, satisfactory reconstructions can still be generated in most experiments, even though the radiation sources that are used are not ideally coherent. The underlying physics of this phenomenon is that the diffraction patterns of partially coherent illumination can be treated as those of purely coherent illumination by altering the intensities of the diffracted beams relative to their real values. On the other hand, due to the inconsistency in the altering interference among all the diffraction beams, noise/distortion is always involved in the reconstructed images. Furthermore, for a weak object, the noise/distortion in the reconstruction can be mostly reduced by using a highly curved beam for illumination in the data recording and forcing the dark field diffraction to be zero in the reconstruction.

Super-Resolved Digital Holography Based on the Coherent Diffraction Imaging Scheme

An algorithm is proposed to enhance the resolution of digital holography by retrieving the frequency components lost in common holograms. A pinhole is placed directly behind the specimen to record the hologram, and an iterative scheme commonly used in coherent diffraction imaging is adopted for the reconstruction. Since some of the frequency components lost in common digital holography can be properly retrieved, the resolution of the reconstructed image is remarkably improved. Theoretical analysis and computer simulations are presented to demonstrate the feasibility of this proposed technique.

Far-Field Detection System of Laser Beams Alignment Based on Gratings Sampling and On-Axial Illumination

利用高功率激光装置空间滤波器小孔成像和取样光栅的衍射,结合插入的负透镜发散激光来同轴照明小孔,设计出一套新型光路远场监测方案.该方案利用光栅衍射可以灵活取样激光远场,并且在实验平台上进行了实验验证.实验结果表明,其远场监测系统的准直精度达到小孔直径的1.42%,能够满足准直系统远场调整精度(小于小孔直径5%)的要求.

808-nm Optical Parametric Amplification Based on DKDP Crystals

The optical parametric chirped pulse amplification (OPCPA)near the 800nm wavelength has gained significant popularity in the recent years.This can be attributed to the development of laboratory-scale Nd:glass lasers with their associated second harmonic generation (SHG),the mature nonlinear crystal growth technology, and the commercialized mode-locked Ti:sapphire oscillator.In this study,the characteristics of the 808-nm centered broad bandwidth signal OPCPA based on potassium dideuterium phosphate(DKDP)crystals are investigated.The phase mismatch in DKDP crystals for different deuteration levels of 0~99%is studied and a numerical simulation of the high energy optical parameric amplification(OPA)process with the considerations of absorption and several high deuteration levels is presented.Results show that the broadband bandwidth OPCPA at 808nm can be obtained when the deuteration level is more than 90%.

Precise diagnostics for SG-II facility

Diagnostics is important for large laser facilities to monitoring laser status and to analyzing physics phenomena on target. SG-II facility in Shanghai is setup in 2001 with eight beams. Each beams energy is 300J at 351nm, and its pulse width is 1ns. SG-II ninth beam is setup in 2005, its energy is 2700J at 351nm, and its pulse width is 1ns too. In recent years, it is an important international user facility for laser research with precise diagnostics system. With the development of SG-II, a new calorimeter is designed to 400 × 400mm2 in order to measure absolute energy up to 6400J at 351nm. Fast photodiode and 12GHz oscilloscope is used to analyze nanosecond pulse shape. In order to analyze petawatt laser pulse, a single shot auto-correlator is designed to measure pulse width between 0.5~18ps. And pulse contrast is obtained by a cross-correlation with fiber-array, which dynamic range is ~106 when pulse is 1mJ and 10ps. Quality of far-field measurement is 1.1DL for nanosecond pulse,and that is 1.5DL for picosecond pulse.

Highly stable, diode-pumped Nd : YLF regenerative amplifier

We present the design and experimental results for a diode pumped Nd:YLF regenerative amplifier applied to amplify a nanosecond laser pulse. Numerical simulation shows that the maximum output energy and the best stability can be obtained when the regenerative amplifier operates in a saturated mode for all pulse duration and temporal profiles. Using extra post-pulse is a good method to decrease the square-pulse distortion caused by gain saturation effect. The amplifier shows output energy of 4.2mJ with a total energy gain of more than 107 and output energy stability of better than 1% rms. When extra post-pulse is added, square-pulse distortion is decreased from 1.33 to 1.17 for the amplifier that is seeded with an optical pulse of 3 ns.