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前曾报导[1],用紫外记录示波器测量热透镜信号的方法,研究了激光热透镜效应的基本物理特性,并使用1.2 mW He—Ne激光,在5mc样品池中测得PAN—Co(111)氯仿溶液的Co浓度下限为12ppb。本实验在此基础上进一步改进测量装置,用稳频切光器调制通过样品池后的光束,由置于远场光斑中心的光敏二极管探测器转换成咏冲光电流。将此光电流信号和来自切光器的参考信号输入锁定放大器,用测量微弱信号变化的方法,测量加入样品后稳态光电流信号相对于空白时光电流信号(I’_o)的微小变化(△I)。用双笔X—Y函数记录仪同时记录△I和参考光束功率P_1。结果在He—Ne激光功率为4mW和1.2mW时,测得氯仿中PAN—Co(111)
Previously reported [1], using UV recording oscilloscope measuring thermal lens signal method to study the laser thermal lens effect of the basic physical properties and the use of 1.2 mW He-Ne laser in a 5mc sample cell measured PAN-Co (111 ) The lower limit of the Co concentration of the chloroform solution is 12 ppb. On the basis of this experiment, we further improve the measuring device, modulate the light beam passing through the sample cell with a frequency-stabilized light chopper, and convert it into an emissive flashlight by a photodiode detector placed in the center of the far-field light spot. The photocurrent signal and the reference signal from the chopper were input to a lock-in amplifier and the slight change in the photocurrent signal (I’_o) of the steady-state photocurrent signal after the addition of the sample was measured by the method of measuring the change of the weak signal I). Record the ΔI and reference beam power P_1 simultaneously with a dual-pen X-Y function recorder. Results When the He-Ne laser power was 4mW and 1.2mW, the PAN-Co (111)