A rigid, monolithic but still scannable cavity ring-down spectroscopy cell

A novel cell for continuous wave cavity ring-down spectroscopy (cw-CRDS) is described and tested. The cell is monolithic and maintains a rigid alignment of the two cavity mirrors. Two high-resolution and high-force piezoelectric transducers are used to sweep the length of the cell by elastic deformation of the 2.86 cm outer diameter stainless steel tube that makes up the body of the cell. The cavity length is scanned more than 1/2 wavelength of the near-IR light used, which ensures that at least one TEM00 mode of the cavity will pass through resonance with the laser. This allows the use of a frequency-locked-laser cw-CRDS technique, which increases the precision of the measurements compared to the alternative of sweeping the laser more than one free spectral range of the cavity. The performance of the cell is demonstrated by using it to detect the absorption spectrum of methane (CH4) at the wavenumber regions of around 6051.8-6057.7 cm(-1). (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3700978]