Shanghai Institute Of Optics And Fine Mechanics Research Articles

Recent Progress in Distributed Fiber Acoustic Sensing with Φ-OTDR.

Distributed fiber acoustic sensing (DAS) technology can continuously spatially detect disturbances along the sensing fiber over long distance in real time. It has many unique advantages, including, large coverage, high time-and-space resolution, convenient implementation, strong environment adaptability, etc. Nowadays, DAS becomes a versatile technology in many fields, such as, intrusion detection, railway transportation, seismology, structure health monitoring, etc. In this paper, the sensing principle and some common performance indexes are introduced, and a brief overview of recent DAS researches in Shanghai Institute of Optics and Fine Mechanics (SIOM) is presented. Some representative research advances are explained, including, quantitative demodulation, interference fading suppression, frequency response boost, high spatial resolution, and distributed multi-dimension localization. The engineering applications of DAS, carried out by SIOM and other groups, are summarized and reviewed. Finally, possible future directions are discussed and concluded. It is believed that, DAS has great development potential and application prospect.

Dynamic chromatic aberration pre-compensation scheme for ultrashort petawatt laser systems.

A novel chromatic aberration pre-compensation scheme for ultrashort petawatt laser systems was proposed. The pre-compensation scheme consists of a convex lens, group of concave lenses, and a spherical reflector combined with a conventional vacuum chamber. It provides a versatile method to accurately compensate the chromatic aberration of an entire laser system via controlling the amount of propagation time delay (PTD) induced by the compensator without changing the input and output beam size. A compensator, tailored based on the proposed scheme, was designed and experimentally evaluated for the Shen-Guang-II 5PW (SG-II 5PW) laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM). The experimental results verified that chromatic aberration in the laser system was almost fully compensated: the size of laser beam focused by an f/2.42 off-axis parabolic mirror (OAP) was reduced tremendously from 32×18μm2to about 4×4μm2at full width at half maximum (FWHM). The proposed scheme provides the flexibility to accurately correct chromatic aberration in high-power laser systems within a wide dynamic range.

Research and development of new neodymium laser glasses

This work presents a brief introduction on three kinds of newly developed $\text{Nd}^{3+}$ -doped laser glasses in Shanghai Institute of Optics and Fine Mechanics (SIOM), China. Two $\text{Nd}^{3+}$ -doped phosphate glasses with lower thermal expansion coefficient and thermal shock resistance 4 times higher than that of N31 glass are developed for laser processing. Nd:Silicate and Nd:Aluminate glasses with peak emission wavelength at 1061 and 1065 nm, effective emission bandwidth of 34 and 50 nm, respectively, are developed for Exawatt-class laser system application. Fluorophosphate glasses with low nonlinear refractive index ( $n_{2}=0.6{-}0.86$ ) and long fluorescence lifetime ( $430{-}510~\unicode[STIX]{x03BC}\text{s}$ ) are investigated for the purpose of decreasing B integral in high-power laser system. The properties of all these glasses are presented and compared with those of commercial neodymium laser glasses.

Research and development of neodymium phosphate laser glass for high power laser application

Neodymium phosphate laser glass is a key optical element for high-power laser facility. In this work, the latest research and development of neodymium phosphate laser glass at the Shanghai Institute of Optics and Fine Mechanics (SIOM), China, is addressed. Neodymium phosphate laser glasses, N31, N41, NAP2, and NAP4, for high peak power and high average power applications have been developed. The properties of these glasses are presented and compared to those of other commercial neodymium phosphate laser glass from the Schott and Hoya companies and the Vavilov State Optical Institute (GOI), Russia. Continuous melting and edge cladding are the two key fabrication techniques that are used for the mass production of neodymium phosphate laser glass slabs. These techniques for the fabrication of large-aperture N31 neodymium phosphate laser glass slabs with low stress birefringence and residual reflectivity have been developed by us The effect of acid etching on the microstructure, optical transmission, and mechanical properties of NAP2 glass is also discussed.

Improvement of the large aperture Ti:sapphire amplif iers in the petawatt femtosecond laser system at SIOM

We report the recent improvement on the petawatt (PW) femtosecond Ti:sapphire chirped pulse amplification (CPA) laser system at Shanghai Institute of Optics and Fine Mechanics (SIOM), Chinese Academy of Sciences. By enlarging the sizes of the pump and signal beams in the large aperture Ti:sapphire amplifiers and optimizing the whole laser system, the output laser energy before the pulse compressor is upgraded to 42.6 J. Accordingly, the peak power of the laser system exceeds 1 PW. The shot-to-shot instability of the output laser energy at about 40 J is less than ?%.

Neutron time of flight energy spectrometer for ICF ion temperature diagnostic

A current-mode neutron time-of-flight(nTOF) energy spectrometer for inertial confinement fusion(ICF) ion temperature measurements has been designed which will reduce measuring error of fusion neutron energy spectra when the neutron yield is low. The spectrometer consists of a shallow cup-shaped ST1422 fast plastic scintillator with a thickness of 3 mm and full effective volume of 104 cm3, a microchannel plate photomultiplier tube(MCP-PMT), a piece of coaxial cable(SUJ-50-7) with a length of 20 m, and a transient oscilloscope with a bandwidth of 7 GHz. The main performances of the spectrometer and its components have been calibrated. The rise-time and FWHM of the temporal response function are 260 ps and 850 ps, respectively. This spectrometer will be used to measure ion temperature in the direct-driven implosion experiments on Sheng-Guang 2 laser facility at Shanghai Institute of Optics and Fine Mechanics(SIOFM) next year.

Soft x-ray lasing and its spatial characteristics in a lithium-like silicon plasma

Experimental study of soft x-ray laser carried out on the LF12 Laser Facility of SIOM (Shanghai Institute of Optics and Fine Mechanics) is reported. Soft x-ray amplifications were observed in lithium-like silicon ions by line-focused laser irradiation of slab targets. Based on the time-integrated measurements, the gain coefficients are 1.5 and 1.4 cm−1 for the 5f–3d (88.9 Å) and the 5d–3p (87.3 Å) transitions of lithium-like silicon ions, respectively. In addition, the spatial characteristics of the laser lines are also presented.