A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which i...A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which include mirror filling efficiency, ~nterference fringes, and pattern stability. With a pattern of 174 passes, this cell gives a 22-m path length in a volume of 0.55 L. The results of an absorption measurement of oxygen at 13 091.7 cm-1 show that the fringe noise is lower than 6.54~10-4. The maximum allowed temperature change to keep the beam from exiting is 33 K, which indicates high stability against thermal drift.展开更多
An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prio...An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.展开更多
基金supported by the National Key Scientifc Instrument and Equipment Development Project under Grant No.2012YQ22011902
文摘A compact multipass cell with low fringes and high thermal stability is described. This cell is formed by two twisted cylindrical mirrors. The optical parameters are determined based on the selection criteria, which include mirror filling efficiency, ~nterference fringes, and pattern stability. With a pattern of 174 passes, this cell gives a 22-m path length in a volume of 0.55 L. The results of an absorption measurement of oxygen at 13 091.7 cm-1 show that the fringe noise is lower than 6.54~10-4. The maximum allowed temperature change to keep the beam from exiting is 33 K, which indicates high stability against thermal drift.
基金supported by the National Key Scientific Instrument and Equipment Development Project under Grant No.2012YQ22011902
文摘An adaptive filter for cancelling noise contained in the direct absorption spectra is reported. This technique takes advantage of the periodical nature of the repetitively scanned spectral signal, and requires no prior knowledge of the detailed properties of noises. An experimental system devised for measuring CH4 is used to test the performance of the filter. The measurement results show that the signal-to-noise （S/N） value is improved by a factor of 2. A higher enhancement factor of the S/N value of 5.4 is obtained through open-air measurement owing to higher distortions of the raw data. In addition, the response time of this filter, which characterizes the real-time detection ability of the system, is nine times shorter than that of a conventional signal averaging solution, under the condition that the filter order is 100.
