The single-filament schlieren method was based on the beam deflection in non-uniform medium. In this paper, a fourelement photodiode was used to acquire the deflection of the probing beam. The effects of electromagnetic interference (EMI) and the vibration of the blower on the output of the photodiode were investigated in detail and they have little impact on the measurements of the flowing characteristic after discharge. Then the perturbation in the discharge region was investigated. The heated gas in the discharge region can be easily detected and the gas velocity can be calculated by tracing the drift of the heated gas. This method also showed a high sensitivity and convenience to observe the acoustic waves originated from fast energy deposition. The results showed that the reflective acoustic wave existed for about 4 ms after discharge and it had a major effect on the non-uniformity of gas medium before the subsequent pulsed discharge.
Recent studies on signal enhancement of spontaneous Raman scattering for developing of sensitive Raman gas detectors
are reported. Raman scattering is a gas detecting method with high feasibility, but usually its signal is very low. To
improve the level and the quality of the Raman signal, the effects of pumping laser source, sample cell, and optical
arrangement are studied in detail. It is found that not only the wall of sample cell will give a wide Raman or fluorescence
background which will decrease the sensitivity, but the dichroic beam splitter will also contribute considerable
background if it is not aligned properly. The sample cell of hollow fiber is characterized by its high responsibility as well
as its high background and low signal contrast. When the hollow fiber is replaced by a free-space sample cell consisted
of metal-coated parabolic reflector, the wide background is largely suppressed. If there is no common optical elements
between the pumping and collecting optical systems, the wide background will be cut down obviously, which is proved
by the intracavity-enhanced Raman scattering in a He-Ne laser. These experimental results will be helpful for the
research and developing of highly sensitive Raman gas detectors.
The evolution of shock wave generated by discharge in laser chamber is one of the key factors which affect laser beam
quality, discharge stability, and repetition rate of TEA gas laser. In this paper, Mach-Zehnder interferometer is applied to
observe both the longitudinal and transversal shock waves between electrodes as well as the acoustic waves originated
by preionization in the discharge pumping zone of TEA gas laser. By changing the discharge voltage, gas pressure and
gas composition concentration, the developing processes in different conditions are compared and analyzed. It is
observed that the shock waves originating from cathode is different from the anode's ones even in the symmetric
electrode construction. And the carbon dioxide concentration in helium-buffered working gas can affect the speed of the
wave obviously. However, the increasing trend of shock wave speed, when increasing discharge voltage or reducing
discharge gas pressure, is inconspicuous.
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