石墨烯在3-5μm中红外波段的光限幅效应研究

Using the self-developed 3-5 μm wavelength tunable mid-infrared solid-state optical parametric oscillator (repetition frequency of 1 - 1000 Hz, pulse width of less than 10 ns, single pulse energy of more than 2 mJ at 1 kHz), the mid-infrared 2D automatic Z-scan device and the integral sphere, it is planned to conduct out closed-aperture, open-aperture Z-scan experiments and scattering light intensity detection experiments on the graphene, which is prepared by CVD or oxidation-reduction method. Under the conditions of different laser parameters (wavelength, pulse width, repetition frequency rate, the incident angle), the nonlinear optical parameters of graphene, included qualitative and semi-quantitative characterization of the linear absorption coefficient, nonlinear absorption coefficient, nonlinear refractive index, nonlinear scattering rate, optical Limiting transmittance, limiting band, cut-off light intensity, attenuation factor and limiting threshold, will be studied in 3-5μm mid-infrared range of graphene. On this basis, we will also explore and study optical limiting effect and its production mechanism of graphene in 3-5 μm mid-infrared band, influence mechanism of laser parameters change and two different preparing methods on the optical limiting effect of the graphene in 3-5 μm mid-infrared band. The research will provide experimental and theoretical basis for the optimization preparation methods of graphene optical limiting materials, and the mechanism on infrared CCD detector against strong laser in 3-5 μm mid-infrared band.

利用本项目自制的3-5μm波长可调谐的全固态中红外光学参量振荡激光器、中红外波段二维自动Z-扫描装置和积分球，开展石墨烯的开孔、闭孔Z扫描探测和散射光强探测。在不同的激光参量（波长、脉冲宽度、重复频率、入射角度）条件下，对两种不同方法(CVD法和氧化还原法)制备出的石墨烯在3-5μm中红外波段的线性吸收系数、非线性吸收系数、非线性折射率、非线性散射率以及与光限幅相关的透过率、限幅波段、截止光强、限幅阈值等参量进行定性半定量表征，从而探索石墨烯在3-5μm中红外波段的光限幅效应及其产生机理、激光参量变化和两种不同制备方法对石墨烯光限幅性质的影响机理。本项目的研究成果能够为中红外波段石墨烯光限幅材料制备方法的优化、特别是为红外CCD精密制导武器对抗3-5μm中红外强激光的抗干扰、抗损伤研究提供必要的实验及理论支持。

激光在民用、军用领域获得了广泛的和应用。例如激光焊接、激光打孔、激光切割、激光致盲、激光制导、激光测距和激光目标指示等。但是随着激光输出功率不断向大功率、大能量发展，其对人眼视力和各种光电传感器的威胁也日趋严重。采用非线性光限幅材料对高能量强激光低透射率，而对低能量的外界辐射和目标反射光的高透射率的非线性光学特性来提高激光防护能力成为研究热点。基于独特的热、机械、电子及光学性能和宽光谱范围内的非线性光学性能，在可见光和近红外光学波段，石墨烯因具有良好的光限幅效应而成为了国内外在光限幅材料领域研究的热点，并且多侧重于其在液相体系中光限幅效应的研究，而很少针对石墨烯薄膜化器件的光限幅开展研究。但是随着激光应用波长向中红外波段方向发展，在3~5µm中红外波段，探索石墨烯是否同样具有良好的光限幅性质，那么将大幅地拓展石墨烯的光限幅应用范围。. 本研究成功研制出的脉冲重复频率10Hz，脉冲宽度6ns、单脉冲能量超过8mJ的3~5µm中红外波段光参量振荡器和一台针对3~5µm波长可调谐的激光二维Z-扫描装置，开展了器件化的石墨烯CaF2镜片开孔、闭孔Z扫描探测和积分球散射实验，发现石墨烯在3~5µm中红外波段存在较强的光限幅特性，其光限幅效应是非线性反饱和吸收和非线性散射的协同作用的结果。在石墨烯层数相同的条件下，非线性反饱和吸收效应随探测光波长的增加而逐渐减弱；在相同激光参数条件下，非线性反饱和吸收效应随层数增加而加强；在相同的入射光能量下，石墨烯散射能量的增长率与入射波长成反比关系，与石墨烯层数成正比关系。由于CVD法制备石墨烯相比于氧化还原法制备的石墨烯具有更为完整的晶体结构、电子共轭体系和高抗损伤特性，因而CVD法制备的石墨烯在3-5μm中红外波段具有实用化的光限幅效应。本研究成果对于利用石墨烯材料的光限幅效应来提高红外波段激光人眼安全防护和光电探测器件的抗干扰、抗损伤能力具有重要的参考意义。

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