The research group, led by Prof. Zhengping Wang, from State Key Laboratory of Crystal Materials, Shandong University, realized Q-switched output of 0.9-um laser with graphene as the saturable absorber. The graphene was prepared on K9 glass substrate with liquid phase exfoliation method. To elevate pulse energy and shorten pulse width, a mixed crystal, Nd:La0.11Y0.89VO4, was utilized as the laser medium whose emission cross section is smaller than that of Nd:YVO4 crystal. At an absorbed pump power of 7.62 W, the maximum average output power was 0.62 W, and the highest pulse energy, minimum pulse width were 2.58 uJ, 84 ns, respectively. The wavelength was 915 nm, corresponding to the 4F3/2 4I9/2 quasi-three-level transition of Nd:La0.11Y0.89VO4 crystal. Such laser has important applications in water vapor detection, ozone detection, and differential absorption radar. Its second harmonic generation can supply blue coherent light, which can be employed for biomedicine, underwater optical communication, high density optical storage, and laser color display. It is reported in Chinese Optics Letters Vol. 12, No.1, 2014 .
As a novel developed photoelectric material, the zero band-gap structure of graphene leads its saturable absorption (SA) characteristic that is wavelength insensitive, so full wave band saturable absorber can be fabricated. While the current popular SA materials such as Cr4+:YAG crystal or GaAs semiconductor just respond to certain wave bands, which have no universality. WhatÃ¢â‚¬â„¢s more, compared with Cr4+:YAG or GaAs, graphene owns shorter fabrication period and lower production cost, which are favorable for large scale promotion. Here it is the first time to the best of our knowledge that graphene is used to the pulse modulation for the laser with wavelength shorter than 1 um, which fully demonstrates the advantages of preparation convenience, wavelength non-selectivity, short recovery time, and small loss. The present research manifests graphene possesses great potential and broad prospects for short wavelength laser modulation.
Next, the overall laser performance is planned to be improved by further optimizing the graphene, the laser medium, and the resonator parameters. Combing with nonlinear frequency doubling technique, new type solid-state blue laser source will be developed. At the same time, the graphene saturable absorber will be applied to more wave bands.
山东大学晶体材料国家重点实验室王正平教授课题组利用液相剥离方法制备的石墨烯，实现了0.9 m激光的调Q输出。激光工作介质选用Nd:La0.11Y0.89VO4晶体, 其受激发射截面比Nd:YVO4更小，能够提高脉冲能量、缩短脉冲宽度。在7.62 W的吸收抽运功率下，获得了平均功率为0.62W，单脉冲能量为2.58 uJ，脉冲宽度为84 ns的准三能级激光输出，波长为915 nm。这种光源在水蒸汽探测、臭氧探测以及差分吸收雷达等方面都有重要应用。此外，经过非线性倍频可以产生蓝色激光，应用于生物医学、水下光通信、高密度光信息存储、激光彩色显示等领域。该研究成果将发表在Chinese Optics Letters 2014年第1期上（http://www.opticsinfobase.org/col/abstract.cfm?uri=col-12-1-011401）。