测量激光喇曼分光计杂散光的几点考虑

Some Considerations in Testing of the Stray Light of a Raman Spectrometer

本文对激光喇曼分光计杂散光的测试方法提出了几点考虑。为了使测量结果正确地反映出仪器本身的性能,讨论了测试用的激光光源、光的入射方式、光强衰减方法和微弱光讯号检测等方面应注意的几个问题,并给出了相应的实验结果。

The key problem to a spectrometer suilable in the studies of Ramanscattering is that the stray light of the spectrometer must be weaker than Raman sig-nal of the sample,at the corresponding wave number.In this article,some conside-rations in testing of the stray light of a Raman spectrometer are proposed,and thecorresponding experimental results are given.A He-Ne laser used as the light source with output power of only lmw is enough in the test.However,it is worthy to no-tice that,besides the stimulated radiation involved,spontaneous radiation backgroundexists in the output of the laser beam.This spontaneous radiation will make sone unrea-lity on the curve of stray light versus wave number.Therefore,narrow-bandpass filtersmust be placed at the output end of the laser in order to obtain the best monochr-omaticity as far as possible.In order to avoid the effects of the circumstances on theresults of the stray light measurements,it seems that the filtered laser beam focused bya collector illuminates directly into the slit of spectrometer is prefered than via cer-tain seattering sample.In testing,three polarizers are adopted to vary the light inten-sity in the range of four to five orders of magnitude,and then a D.C.digital rolt-meter or a lock-in amplifier can be selected to measure the light intensity variationsafter passing those polarizers in the range;of eight orders of magnitude,instead of us-ing a series of high density neutral filter to attenuate the light intensity.As a result,twelve to thirteen orders of magnitude of measurement range can be obtained.Theresults have shown that this method is simpler than others,and the error is smaller.