基于铋纳米片可饱和吸收被动调Q中红外单晶光纤激光器

Bismuth nanosheets based saturable-absorption passively Q-switching mid-infrared single-crystal fiber laser

铋纳米片作为一种新型二维材料,具有合适的带隙、较高的载流子迁移率和较好的室温稳定性,加上优异的电学和光学特性,是实现中红外脉冲激光的有效调制器件.中红外单晶光纤兼备晶体和光纤的优势,是实现高功率激光的首选增益介质.本文采用超声波法成功制备了铋纳米片可饱和吸收体,并首次将其用于二极管抽运Er:CaF2单晶光纤中红外被动调Q脉冲激光器中.在吸收抽运功率为1.52 W时,获得平均输出功率为190 mW的脉冲激光,最窄脉冲宽度为607 ns,重复频率为58.51 kHz,对应的单脉冲能量和峰值功率分别为3.25μJ和5.35 W.结果表明,使用铋纳米片作为可饱和吸收体,是实现结构紧凑的小型中红外单晶光纤脉冲激光的有效技术途径.

As a new two-dimensional material, bismuth nanosheet is an effective modulator for realizing a midinfrared pulsed laser, which benefits from its suitable band gap, higher carrier mobility and better room temperature stability, as well as its excellent electrical and optical properties. The mid-infrared single-crystal fiber is a preferable gain medium for high-power laser because of its advantages of both crystal and fiber. In this paper, a bismuth nanosheet saturable absorber is successfully prepared by the ultrasonic method and used for the first time in a diode-pumped Er:CaF2 single-crystal fiber mid-infrared passively Q-switching pulsed laser. A compact concave planar linear resonator is designed to study the Q-switching Er:CaF2 single-crystal fiber laser with bismuth nanosheets serving as saturable absorbers. The pump source is a fiber-coupled semiconductor laser with a core diameter of 105 μm, a numerical aperture of 0.22, and a central emission wavelength of 976 nm. The pump light is focused onto the front end of the gain medium through a coupled collimating system with a coupling ratio of 1∶2. The gain medium is a 4 at.% Er3+:CaF2 single-crystal fiber grown by the temperature gradient method, and this fiber has two polished but not coated ends, a diameter of 1.9 mm, and a length of 10 mm. To reduce the thermal effect, the single-crystal fiber is tightly wrapped with indium foil and mounted on a copper block with a constant temperature of 12 ℃. The input mirror has a high reflection coating at 2.7 –2.95 μm and an antireflection coating at 974 nm, with a curvature radius of 100 mm. A group of partially transmitting plane mirrors are used as output couplers, respectively, with transmittances of 1%, 3%, and 5% at 2.7–2.95 μm. The total length of the resonant cavity is 26 mm. By inserting the bismuth nanosheet into the resonator and carefully adjusting its position and angle, a stable mid-infrared Q-switching laser is obtained. At the absorbed pump power of 1.52 W, a pulsed laser with an average output power of 190 mW is obtained for an output mirror with a transmittance of 3%. The shortest pulse width is 607 ns, the repetition frequency is58.51 kHz, and the corresponding single pulse energy and peak power are 3.25 μJ and 5.35 W, respectively.