Infrared Cavity Ringdown Spectroscopy

Abstract

Coherent two‐dimensional vibrational spectroscopies use multiple laser excitations at high intensities where nonlinear processes dominate. These new spectroscopies can potentially probe molecular structure and dynamics in complex systems like multidimensional nuclear magnetic resonance (NMR) methods. We describe the development of the optical analogue to two‐dimensional NMR and its unique capabilities for achieving spectral selectivity. The approach uses four‐wave mixing where three lasers are focused onto a sample and new beams are generated by nonlinear processes. Their intensity depends on whether there are vibrational resonances with the three lasers. We have named these methods doubly vibrationally enhanced four wave mixing (DOVE‐FWM). These methods are related to infrared and Raman spectroscopy, but they are capable of dissecting vibrational spectra into the components that they are made of. These methods offer the potential of a powerful new probe of intra‐ and intermolecular interactions, molecular structure, and molecular dynamics.

An Exploratory Study of Cavity Ringdown Spectroscopy as a Noninvasive Breath Diagnostic for Breast Cancer

“…However, for CRDS, as equation 2 demonstrates, the ringdown time will incorporate absorption due to the concentration of both SO 2 and mercury. The PI and associates noted [20][21][22][23][24][25][26] in related research, that the presence of isotopic structure during a scan of the mercury 253 nm line raised the possibility (later, confirmed) that absorbance components of complex mixtures can be separated (Fig 4a). 27,28 For example, using a gas mixture containing 1.2 ppb mercury and 2175 ppm SO 2 respectively (Fig.…”

“…The PI and associates noted [20][21][22][23][24][25][26] in related research, that the presence of isotopic structure during a scan of the mercury 253 nm line raised the possibility (later, confirmed) that absorbance components of complex mixtures can be separated (Fig 4a). 27,28 For example, using a gas mixture containing 1.2 ppb mercury and 2175 ppm SO 2 respectively ( By utilizing the fine absorption structure it has been demonstrated that accurate determination of individual components, down into the ppt range, can be successfully achieved.…”

“…However, whether for fundamental molecular structure studies or for applications in areas such as combustion studies, plasma processing, or environmental measurements, CRDS has proven its capability to detect and measure ultratrace molecular species or weak molecular absorptions under hostile environments (see Figure 3). Although a complete review of molecular spectroscopy using CRDS is beyond the scope of this report, reviews are available for further information concerning molecular spectroscopy using CRDS (20,23,(27)(28)(29)(30) .…”

“…Simply put, this means that a CRDS instrument has the 7 potential to improve sensitivity by a factor of up to 10,000 over commercially available absorption-based instruments. During early research by the PI's group, [20][21][22][23][24][25][26] However, in this proposal it is molecular CRDS that is of interest. At the time of writing the original proposal, as far as the authors were aware, CRDS had never been used for breath analysis.…”

“…However, whether for fundamental molecular structure studies or for applications in areas such as combustion studies, plasma processing, or environmental measurements, CRDS has proven its capability to detect and measure ultratrace molecular species or weak molecular absorptions under hostile environments (see Figure 3). Although a complete review of molecular spectroscopy using CRDS is beyond the scope of this report, reviews are available for further information concerning molecular spectroscopy using CRDS (20,23,(27)(28)(29)(30) .To provide small near-room temperature tunable light sources over the optimum spectral for the detection of formaldehyde, the choice of potential light sources was limited to either mid-IR Quantum Cascade diode lasers, Pb-salt or difference frequency generation (DFG) lasers (see 8 Table 1). 31 At the time of writing the initial proposal, the lasers with the most potential for this application appeared to be the QCLs, so we proposed to use such a laser for this effort.…”