研究目的
The measurement of gas pressure is normally, and very effectively, achieved using transducers which are usually mounted in the wall of the containing vessel. In some situations, however, such as hostile or rapidly changing environments, or where a local pressure fluctuation occurs remote from the walls, such devices will not be able to record accurately any localised or dynamic pressure variations. In such cases a non-invasive or remote sensing capability can be advantageous.
研究成果
This work has demonstrated that LITGS provides a viable method for space- and time-resolved measurement of pressure in both static and dynamic conditions. Accurate and precise measurements have been shown to be possible especially under conditions of ambient temperatures and pressures in excess of 1 bar. These properties should allow application of the method in a range of situations where remote and non-invasive measurement of local pressure is required.
研究不足
The method was found to be of limited utility for measurements in high temperature flames at around ambient pressures. The rapid diffusion at the elevated temperatures results in much shorter signal duration and consequently reduced precision in the measurement of the decay times. Furthermore, a high degree of uncertainty in the relevant gas kinetic and dynamic parameters in flames results in significant experimental error in deriving the pressure under conditions of high temperature and (relatively) low pressure.
1：Experimental Design and Method Selection:
The process involves the interference of two degenerate frequency pump beams crossing at a small angle to produce a grating pattern. This grating is written into a gas medium by the mechanism of absorption and quenching or by electrostriction.
2：Sample Selection and Data Sources:
The signals were generated in NO at a partial pressure of
3：5 mbar in N2 added at pressures in the range 5–0 bar. The gas mixture was contained in a stainless steel cell fitted with fused silica windows to transmit the input pump and probe beams and the output signal beam. List of Experimental Equipment and Materials:
The laser system used consisted of a Q-switched Nd:YAG laser (Continuum Powerlite 8000) operating at 10 Hz and emitting both the second and third harmonics at 532 nm and 355 nm, respectively. The second harmonic was used to pump a modeless dye laser whose output was spectrally narrowed to a linewidth of approximately
4：3 cm?Radiation at 226 nm was generated by sum frequency mixing, in a BBO crystal, the output of the dye laser, tuned to a wavelength of 624 nm, with the third harmonic of the pump laser at 355 nm. Experimental Procedures and Operational Workflow:
The resulting output consisted of pulses of 5 ns duration and 1 mJ energy which was sufficient to generate LITGS signals with adequate signal-to-noise ratio.
5：Data Analysis Methods:
The model-fitting method, MFM, relies on fitting of a theoretically modelled signal to the experimental data using pressure-dependent parameters to obtain a best-fit value for the pressure.
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