Optoelectronic Sensor of NO2 Detection using Cavity Ring Down Spectroscopy and 414 nm GaN Diode Laser

Abstract

For a long time detection of volatile chemicals traces contained in the atmosphere, especially NO2 has been a serious problem. Strict environmental standards restricted acceptable limits of atmospheric traces, furthermore it brought in an obligation of constant atmospheric traces monitoring. That is why a special method that enables different requirements has to be created. One of a few methods that enables to fulfill requirements in range of detection limit of volatile chemicals traces, moreover one that gives results in the real time is CRDS. The cavity ring down spectroscopy (CRDS) is a sensitive "in situ" laser absorption spectroscopy method developed by O 'Keefe (1988). It is the youngest spectroscopy technique nearly unknown in Poland. All over the world it has been applied for several years in laboratory conditions to perform measurements of very low absorption cross section values of volatile chemicals (10-19+10-18 cm2). Recent years a significant progress in GaN / InGaN blue diode laser technology has been made. Moreover, great progress in multilayer dielectric mirrors based on technology of interference stacks has been made. Thanks to it super reflection coefficient has been received. Those discoveries make CRDS technique possible to both detect and monitor volatile chemical traces contained in the atmosphere at limit of single ppb. This paper describes modern optoelectronic methods of atmospheric trace detection. Their advantages and disadvantages have been shown. Special attention has been paid to CRDS method (pol. Spekrtoskopia Strat We Wnece). Intensive research on CRDS are being taken in Laboratorium Sygnalow Optycznych, Instytut Optoelektroniki WAT.