LASER SPECTROMETERS FOR ATMOSPHERIC ANALYSIS

摘要

Before starting the discussion, it's worth reminding that the target molecule for laser spectrometer is a light molecule, exhibiting discrete absorptions in the near- or middle-IR. Benzene-type molecules are not good targets, unless they include some radicals, having the above type of behaviour. Most hydrocarbons, even having linear structures, have quasi-continuum absorptions, so are not visible with the described devices. Coming back to the initial question, hopefully the reader should have got convinced that the scientific bases of laser spectrometers are firmly established, and that whatever the experimental condition, the technology is able to provide the right solution. The "best" technique doesn't exist, but for each kind of application it is possible to select that one, which is most suitable. This leads to one conclusion: the quality/price ratio of laser spectrometers is still too low, compared to other kinds of devices. The reason lies most times in the high cost or in the requirements of the lasers (e.g. liquid nitrogen). So, even if the device is simple, even if the prices of electronics and optics can be made almost negligible, a laser spectrometer is often very far from being practically useful for a particular purpose. The competition is open when the price of alternative devices is high, or when they lack some useful features, like selectivity, or when the safety regulations require such high sensitivities or resolutions, or such low detection limits, that they cannot be achieved by standard devices. This is the case of the leak finder in chapter 12.5. Its higher cost, compared to that of standard devices, can be acceptable because it allows a much higher speed of inspection. Moreover, the lack of false positive avoids waste of manpower. A significant impulse towards the diffusion of laser spectrometers could arrive from the governments. New regulations about pollution could require more sensitive analyzers, beyond the capabilities of standard techniques. Of course, the producers of lasers should develop both cheaper production methods, and new kinds of sources, like QCL.