Cavity ring-down spectroscopy

Cavity ring-down spectroscopy (CRDS) has become increasingly popular in the last few years. This is a highly sensitive method of absorption spectroscopy that uses a pair of highly reflecting mirrors (> 99%) to form a high-finesse ("high Q") optical cavity. Light that is coupled into the cavity will slowly leak out at the mirrors because they are not 100% reflecting. If the light leaking out is measured, an exponential decay (the "ring-down") can be observed. The rate of exponential decay will depend not only on the mirror reflectivities, but also on the presence of absorbing media in the cavity. We have developed and applied CRDS to solid and liquid media. To date there have only been a handful of studies that have achieved this aim. The problem lies in the losses incurred by scattering of the solid/liquid media. However, it is possible to circumvent some of these losses by careful design of the cavity, and the point of interaction between the light and the medium of interest.

 
Using optical components placed at the Brewster Angle inside the cavity, we have demonstrated sub-monolayer detection sensitivity for dyes adsorbed on glass [1]. We have also measured photo-induced reactions of nitrate (NO3) radicals in solution for the first time with single-shot ring-downs [2]. More recently, we have developed a unique flowing liquid jet for studies of liquid-air interfaces [3].

Relevant publications:

  1. R. N. Muir, A. J. Alexander, Phys. Chem. Chem. Phys.5, 1279 (2003): "Structure of monolayer dye films studied by Brewster angle cavity ringdown spectroscopy". doi:10.1039/b212790c.
  2. A. J. Alexander, Chem. Phys. Lett. 393, 138 (2004): "Reaction kinetics of nitrate radicals with terpenes in solution studied by cavity ring-down spectroscopy". doi:10.1016/j.cplett.2004.06.027.
  3. A. J. Alexander, Anal. Chem. 78, 5597 (2006): "Flowing Liquid-Sheet Jet for Cavity Ring-Down Absorption Measurements". doi:10.1021/10.1021/ac060571v.
 

See poster on CRDS

CRDS poster
© 2009 Andrew J. Alexander