We investigate theoretically the optical bistability of reflection at the interface between graphene and Kerr-type nonlinear substrates. We derive a simple procedure to calculate the nonlinear reflectivity with graphene, and discuss the influence of the graphene sheets on the hysteretic response of the TM-polarization reflected light. It is found that the bistable behavior of the reflected light can be electrically controlled via suitably varying the applied voltage on the graphene. In THz, the bistable thresholds can be lowered markedly by increasing the Fermi energy. However, in near-infrared frequency, it requires multiple graphene layers to exhibit significant influence on the bistable thresholds.

Yuanjiang Xiang;Xiaoyu Dai;Jun Guo;双春 文;定元 汤

Applied Physics Letters

2014

Transparent polycrystalline ceramics have found various applications, such as laser hosts, infrared (IR) windows/domes, lamp envelopes and transparent armors, instead of their single crystal counterparts, due mainly to their processing flexibility in fabricating items with large sizes and complex shapes and more importantly cost-effectiveness. High optical transparent ceramics require high purity and high density. To achieve high purity final products, it is necessary to use high purity precursor powders. To get high density, various sintering technologies have been employed, such as high-pressure (HP) sintering, high isostatic pressure (HIP) sintering, vacuum sintering and spark plasma sintering (SPS). At the same time, various wet chemical synthesis routes have been used to produce precursor powders at submicron or even nanometer scales, with significantly improved sinterability. Transparent ceramics for armor and IR window/dome applications should have superior mechanical and thermal properties. Therefore, nanosized ceramics and nanocomposite ceramics have attracted much attention more recently. This review was aimed to summarize the latest progress in processing, materials and applications of transparent ceramics. It is arranged by starting with a brief introduction, followed by a detailed description on various sintering technologies used to develop transparent ceramics. After that, potential applications of transparent ceramics, together with their optical, mechanical and thermal properties, will be discussed. It will be concluded with discussions on future trend and perspectives, as well as some important issues, of transparent ceramic materials.

S. F. Wang;J. Zhang;D. W. Luo;F. Gu;定元 汤;Z. L. Dong;G. E.B. Tan;W. X. Que;T. S. Zhang;S. Li;L. B. Kong

Progress in Solid State Chemistry

2013-5

The properties of multi-hump (-pulse) temporal solitons in passively mode-locked fiber lasers have been investigated. All the features reported before on soliton operation have been discovered on multi-hump soliton operation for the first time.

B. Zhao;定元 汤;P. Shum;Y. D. Gong;W. S. Man;H. Y. Tam

2003

This paper reports on the influence of rapid rate sintering (RRS) on densification and microstructure evolution of yttria transparent ceramics by using vacuum sintering. The presence of temperature gradient has been confirmed during the RRS process. The higher the heating rate (HR), the larger the temperature gradient in the samples would be. By using RRS, e.g., HR = 40°C/min, the samples could be densified very fast to a relative density of 99.6%. However, these samples could not be further densified, due to the presence of difference in densification caused by a heating rate-induced temperature gradient. By using a two-step RRS with an intermediate-temperature thermal treatment, this problem has been successfully addressed. The intermediate-temperature treatment allowed for the particle neck growth, so that effective thermal conductivity of the compacts was increased greatly. Therefore, the temperature gradient and differentiate densification were effectively prevented. Samples sintered using the two-step RRS process could be fully densified and excellent in-line optical transmittance was achieved. It is believed this strategy is applicable to other transparent ceramics, as well as other engineering ceramics.

Jun Wang;Kaijie Ning;Jian Zhang;Dewei Luo;Jie Ma;Danlei Yin;定元 汤;Ling Bing Kong;H. J. Kleebe

Journal of the American Ceramic Society

2016-6-1

Coexistence of scalar dissipative solitons along the two orthogonally polarized directions of a fiber laser is observed. Due to the large cavity birefringence, the dissipative solitons along different polarization axes have different group velocities.

L. M. Zhao;定元 汤;X. Wu;H. Zhang;H. Y. Tam

2010

In this letter, a diode-pumped passively mode-locked Nd:Lu _1.5Y_1.5Al₅O₁₂ (Nd:LuYAG) laser is demonstrated for the first time, to the best of our knowledge. With a semiconductor saturable-absorber mirror, a maximum output power of 0.85 W at 1064 nm was obtained under an absorbed power of 8.51 W, corresponding to a high slope efficiency of 44%. The mode-locked pulses were estimated to be 6.6 ps. The results of our experiment show that Nd:LuYAG crystal could be a promising material for diode-pumped ultra-short laser generation.

J. Q. Di;X. D. Xu;W. D. Tan;J. Zhang;定元 汤;D. Z. Li;D. H. Zhou;F. Wu;军 徐

Laser Physics Letters

2013-9

A passively mode-locked Tm:YAG ceramic laser was demonstrated. Employing a 6 at.% Tm³⁺-doped sample with a length of 2.7 mm, we have realized stable mode-locked pulses with a repetition rate of 109 MHz by a semiconductor saturable absorber. A maximum output power of 116.5 mW was obtained at the central wavelength of 2007 nm. The corresponding pulse duration was determined to be 55 ps by a self-built noncollinear intensity auto-correlation setup. It is shown that Tm:YAG ceramics are excellent laser materials which can be used in ultrafast lasers with high-power and high-efficiency output.

Min Jie Zhan;Yu Wan Zou;Qing Feng Lin;Zhao Hua Wang;Hai Nian Han;Liang Lü;Zhi Yi Wei;Jian Zhang;定元 汤

Wuli Xuebao/Acta Physica Sinica

2014-1-5

An integrated MEMS tunable laser of ∼ 2 mm × 1.5 mm size is demonstrated in this paper. The tunable laser is formed by the integration of a surface-micromachined 3D micromirror with a Fabry-Perot laser diode and an optical fiber. The micromirror can be driven to translate by a comb drive to change the external cavity length of laser diode, enabling the wavelength tuning. A tunable range of 16 nm is obtained, which covers 20 channels of WDM systems spaced by 100GHz. The three-mirror Fabry-Perot cavity model is modified to explain the continuous wavelength change as well as the mode hopping. An array of the tunable laser is potential to supply light sources for multiple channels of WDM systems.

X. M. Zhang;A. Q. Liu;C. Lu;定元 汤

Proceedings of SPIE - The International Society for Optical Engineering

2001

We observe a novel type of vector dark soliton in a fiber ring laser. The vector dark soliton consists of stable localized structures separating the two orthogonal linear polarization eigenstates of the laser emission and is visible only when the total laser emission is measured Numerical simulations based on the coupled complex Ginzburg-Landau equations have well reproduced the results of the experimental observation.

H. Zhang;定元 汤;L. M. Zhao;R. J. Knize

Optics Express

2010-3-1

We report on the continuous wave (CW) and passive Q-switching performance of a high-power diode-pumped Nd:GGG laser. A CW output power of 7.20 W was obtained under an absorbed pump power of 14.97 W. which gives a stop efficiency of 52.7%. With a Cr⁴⁺ doped yltrium aluminum garnet crystal as the saturable absorber, the shortest passively Q-switched pulse width, largest pulse energy, and highest peak power achieved were 7.7 ns. 126.25 μJ. and 15.5 kW. respectively. A graph is presented. Oscilloscope trace of a typical Q-switched pulse train.

L. J. Qin;定元 汤;G. Q. Xie;C. M. Dong;Z. T. Jia;绪堂 陶

Laser Physics Letters

2008-2