脉冲激光在水中激发声脉冲的光声能量转换效率

利用TEA-CO_2脉冲激光在水中激发热弹光声信号,采用压电陶瓷水听器接收并将光声信号转换成电信号送入数字存储示波器,计算出声脉冲的能量,从而获得该激发条件下激光能量转换成声波能量的效率η。结果表明不采用凹面镜聚焦激光脉冲能量密度低于2 J/cm~2时,光声转换效率η为10~(-7)～10~(-5),聚焦之后η增大一个数量级;激光脉冲谱线宽度固定时,能量越高,η越高;激光脉冲能量相同时,激光脉冲谱线宽度越大,η越高。故可以通过聚焦、增加激光脉冲谱线宽度、提高激光能量等方法来提高光声转换效率η,获得强的热弹光声信号。

Laser Acoustic Energy Conversion Efficiency Induced by Pulse Laser in Water

To get the laser acoustic energy conversion efficiency, TEA-CO2 pulse laser, a spherical piezoelectric ceramic hydrophone and a digital oscilloscope were used to receive, demonstrate and store the optoacoustic signal induced in water. And energy conversion efficiency η was calculated. The results showed that when the laser pulse energy varied below 2 J/cm2, the conversion efficiency η was in the range 10-7～10-5, and increased ten times when the laser beam was focused. If the spectrum width of the laser pulse was fixed, η increased with the pulse energy, on the other hand if the pulse energy was fixed, η decreased when the spectrum width increased. As a result, methods of laser focusing, laser pulse compression and laser energy increasing can be used to enhance the conversion efficiency η, and to get strong thermoelastic optoacoustic signal.