Sensitive and Selective Detection of Paramagnetic Species Using Cavity Enhanced Magneto-Optic Rotation

Cavity enhanced magneto-optic rotation spectroscopy (CEMOR) is a technique that utilizes a high-finesse cavity within a traditional magnetic rotation experimental setup to realize the benefits of both cavity ringdown and magneto-optic methods simultaneously. By observing Ga atoms at their resonance line of 417.204 nm, we demonstrate that CEMOR allows selective detection of paramagnetic species with lower detection limits than can be obtained through either flame atomic absorption or magnetic rotation spectroscopies. Quantitative CEMOR measurements of Ga in an air–acetylene flame reveal a 105 sensitivity increase over conventional flame atomic absorption in our experimental setup. Sample concentration is shown to impact the temporal behavior of transmitted signals, resulting in a significant time shift in transmission of peak signal intensity. Such time shifting has not been theoretically predicted, and we report its first experimental demonstration. The work discussed herein suggests that the CEMOR technique can be used to simplify the study of species such as combustion-generated radicals, which often absorb weakly and occur in spectral regions crowded by stronger molecular absorption lines.