Under these conditions, it becomes the center of a luminous phenomenon (electroluminescence). In fact, this is an electromagnetically induced plasma. A plasma is a collection of charged particles ; In this case, the plasma consists of a stream of argon. This process being an emission technique, it is very useful for quantitative analysis. This technique is not new, but the recent advances in semiconductors as well as in optical coating and devices, make it easier to develop an instrument based on this technology, without the cost normally associated with this category of analytical instruments.

Once the gas is ionized (charged), many spectral lines are emitted.

Here, we think a few words regarding the technique used to create the plasma are necessary. There are many ways of producing light from an argon stream for analytical purposes. The electroluminescence phenomenon includes luninescence from all kinds of electrical discharges, such as sparks, arcs or tubes of different kinds, operating on direct or alternating current of low or high frequency. Recently, some experiments were conducted in the microwave range by surface-wave-induced plasma.

Excitation in these cases results mostly from electron or ion collisions ; it is the kinetic energy of electrons or ions accelerated in an electric field to which the atoms or molecules of the gas are subjected that causes emissions of light.

By any of the previous methods, characteristic emission spectra can be obtained for argon and each substance in it. They usually vary for a given substance, depending on the mode of excitation.

We developed our plasma generator and plasma cell as to minimize the heat generation inside the cell and get a clear spectral line for the substance of interest, i.e. nitrogen.

Once the intense line is identified, we must use a system to filter it out. In our case, instead of a grating, prism or tunable filter, we use an custom made optical filter with special coating that lessens background noise considerably and reduces spectral interference. This filter show an exceptional bloking range. Its main characteristic is its great stability : temperature and humidity and time will not affect its performance it is coupled with a special lens that focuses the optical beam.

The resulting light is directed to a special photodiode, where an electrical current is generated. This current is proportional to the nitrogen level in the gas stream. (Argon or helium).

By regulating the power of the plasma and having close control of plasma position, with the focusing electrodes, we can optimize the sensitivity for a particular spetral ray.