Principle of laser gas analysis technique

1。 Lambert - Beer's law

DLAS technology is essentially a kind of spectral absorption technology, through the analysis of the laser is absorbed by gas selectivity for gas concentration. It with the traditional technique of infrared absorption spectrum of the difference is that the semiconductor laser spectral width is far less than that of gas absorption spectral lines broadening. Therefore, DLAS technology is a kind of high resolution spectral absorption technology, semiconductor laser through the gas being measured intensity attenuation lambert - available Bill ( 兰伯特- 啤酒) Law of expression of type IV, V 0 and IV respectively frequency laser incident and after pressure P, concentration and light path L X gas after light intensity; S（ T） Said gas absorption spectral line intensity; Linear function g ( v - v0） The shape of the characterization of the absorption lines. Normally gas absorption of small, can use type ( 4 - 2) To the approximate expression of gas absorption. The formula shows that the higher the gas concentration and light attenuation. Therefore, by measuring gas attenuation of laser to measure the concentration of the gas.

2。 Strong spectral line

the absorption of gas molecules and molecular internal always associated from low energy state to a high energy level transition. Strong line S ( T） Reflects the stimulated during the process of transition between absorption and spontaneous emission and stimulated radiation intensity, the net effect of absorption spectrum is the basic attribute of the spectrum, the energy level transition probability between the classics and the number of molecules in the upper and lower level decision. Molecules in the distribution between different level is affected by temperature, so the spectral line is also related to the temperature. If you know the strong reference line S ( T0） , other strong temperature line can be formed by the type and the type, Q ( T） As the molecular partition function; H is Planck's constant; C is the speed of light; K is the boltzmann constant; En energy for the next level. All kinds of gas absorption lines of strong line S ( T0） Can consult the relevant spectral database.

< br / >