Intracavity laser absorption spectroscopy for flame diagnostics

Intracavity Laser Absorption Spectroscopy (ICLAS) is one of the most sensitive techniques in absorption spectroscopy. Application of this technique to combustion diagnostics offers many important advantages. Since ICLAS is an absorption-based method, it is not limited by the quenching and predissociation effects that compromise the sensitivity of Laser Induced Fluorescence (LIF), one of the most sensitive and widespread techniques applied in combustion diagnostics. For that reason, radicals that are subject to strong collisional quenching or predissociation, such as ¹CH₂ and HCO, can be measured by ICLAS with sensitivity much greater than that of LIF. For the same reason, ICLAS also possesses better sensitivity for NH and HNO. The present paper overviews the ICLAS measurements performed during the last decade in our laboratory and also presents recent results: first-time detection of the HSO radical in flames by ICLAS and application of Fiber Laser Intracavity Absorption Spectroscopy (FLICAS) based on Er-doped fiber laser for in-situ detection of ammonia and hydrogen cyanide in a low-pressure methane/air flame doped with a small amount of ammonia. Avenues for future research are discussed.