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多波长激光器的波长数理论模型如下所示[16]:
$ M = \frac{{\Delta {\nu _0}}}{{\Delta \nu }} = \frac{{2\Delta {\nu _0}nL}}{c} $
(1) 式中,M为晶体增益内波长数的最大值;Δν0为晶体的增益频宽;c为真空中光的传播速度;n为晶体的折射率;L为激光腔体的几何长度。
图 1为双频激光器模谱示意图。横坐标表示频率ν,纵坐标表示激光晶体增益g(ν)。通过设计激光墙体的几何长度,可以将模式间隔Δν=c/(2nL)控制在(0.5~1)Δν0之间,即可获得双频激光信号输出[17]。
均匀加宽增益介质的固体激光器的发射谱符合洛伦茨线型分布[18]。由于拍频效率受双频激光信号的功率均衡度的直接影响,而双频波长在增益介质发射谱内对应的发射截面不同是造成功率均衡度差异的主要因素。当双频激光信号的双频波长在发射谱峰值两侧对称位置时,其对应的发射截面值是相同的,进而其输出的双频信号是均衡的。
Nd:YVO4晶体的温度变化会对其折射率和腔体几何长度产生影响[19]。由于双频激光器的波长与腔体的光学长度相关,因此温度变化将导致双频波长变化。在实验中,可调节激光晶体温度,从而实现激光晶体发射谱与双频微片激光器谐振波长的相对移动,并且最终获得功率均衡的双频激光信号输出。
双频微片激光器的功率均衡机制实验研究
Experimental study about power balance mechanism in dual-frequency microchip lasers
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摘要: 为了研究双频Nd:YVO4微片激光器的功率均衡机制,利用实验研究分析了微片激光器的抽运电流、工作温度和谐振波长等参量之间关系。不断增大双频激光器抽运电流,通过降低晶体温度不断重新实现双频激光功率的均衡,最终获得了不同抽运电流下的双频激光器的功率均衡温度,以及双频功率积与抽运电流的关系数据。结果表明,双频激光信号功率均衡温度与抽运电流呈分段负相关,双频功率积与抽运电流呈正相关。此结果说明通过改变抽运电流和温控温度可以实现功率可调的功率均衡的双频激光信号输出。Abstract: In order to investigate output power balance mechanism of Nd:YVO4 microchip dual-frequency lasers (DFL), the relationships among pump current, operating temperature and dual-mode wavelengths of microchip lasers were analyzed by means of experiments. With the increase of pump current of DFL, the balance of DFL power was re-achieved by lowering the temperature of laser crystal. Finally, the power-balanced temperature of DFL with different pump currents and the relationship between dual-frequency power product and pump current of DFL were obtained. The result shows that, the power-balanced temperature of DFL signal is negatively correlated with pump current sectionally, and dual frequency power product is positively correlated with pump current. It indicated that, power-balanced power-adjustable dual-frequency laser signal output can be achieved by changing pump current and controlling temperature.
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Key words:
- lasers /
- power balance tuning /
- pump current /
- temperature control
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