The Study Of 632.8nm Notch Filter Of Laser Raman Spectrometer

The notch filter of Laser Raman spectrometer is a special optical element, belonging to reflection holographic filter. It can stop the Raleigh scattering but allow the Raman scattering in Raman spectrum detection, so it plays a vital role for the maximum detection of Raman signal. The notch filer is made of photosensitive material, and it has a certain useful time about 1 to 2 years. Currently there is not formal product in china, and the main source is importing from foreign countries, but the price is expensive. Therefore, it is meaningful to study the optical and chemical characteristics and the process of the notch filter, for analytical instrument and element can made in china.First of all, the absorption spectrum functions of foreign Raman notch filters were studied by ultraviolet and visible spectrophotometer, and the optical characteristics and filtering function were treated in this paper. On this ground, try to make the reflection holographic filters by holofilm which is made in china, and make a primary success. The influence of the performances of reflection holographic filters which were made of two different silver halides holofilms and in two different laboratories was discussed. The influence of the angle of two writing light beam, the time of exposure, the time of development, the time of bleaching and the drying way in making reflection holographic filters was also discussed. At last, the best experiment conditions were chose. Besides, the stability of the filters kept in different conditions, which were made by us, was studied.The result can be concluded as follow:(1) The optical properties of the notch filter of Laser Raman spectrometer is the same as the reflective hologram. Both of them are obey the Bragg equation. After 4 years’ use, the filtering functions of the notch filters in laboratory are different. The filter of 785nm still works well. For the filter of 514nm, when the Raman signal is weak, there will be some influences. But the filter of 632.8nm has already been inefficient in Raman spectrum detection.(2) The resolution of holofilm must be or higher than 7000 l/mm. The optical platform must cut off the vibration, which is come from circumstances, in maximum degree. The laser should have high stability and appropriate intensity. The laboratory should be far away from the vibratory source.(3) When the angle of two laser beams is 178°, the time of exposure is 4s, the time of development is 60s, the time of bleaching is 6.2min, and drying in the air, the best optical performance of the reflection holographic filter can be obtained. (4) When the filter is completely dry, the optical performance will not change by the preservative time. Although the filter is in damp conditions, the optical performances still not change after dry.(5) The redivivus wavelength can be controlled by changing the angle of the incident light and controlling the moisture of the filter.