Cavity Ring-Down Spectroscopy
Abhijit Maity, Mithun Pal, and Manik Pradhan
Abstract Cavity ring-down spectroscopy (CRDS), one of the most fascinating
analytical techniques, has found widespread applications in a variety of research
fields. It is a direct, ultra-sensitive and quantitative laser absorption spectroscopy
technique which measures the rate of absorption of molecular species instead of
the magnitude of absorption in an optical cavity where the light moves to and fro
several times. CRDS is an extremely powerful analytical method which can measure
weak as well as strong absorptions of trace and abundant molecular species in a
variety of environments. Recently, the technique has been modified in a great extent
and consequently several variants of CRDS are available. In this chapter, we briefly
discuss an overview of the CRDS technique and some of its important applications
in the field of high-resolution fundamental molecular spectroscopy and trace detection of molecules in the atmosphere. The application of CRDS in medical science
through breath test is also discussed followed by future trends and a perspective on
the technique.
Keywords Cavity ring-down spectroscopy · Cavity enhanced technique ·
Molecular spectroscopy · Trace gas sensing · Non-invasive medical diagnosis
1 Introduction
Conventional absorption spectroscopy is based on the Beer-Lambert law which
essentially provides information about the attenuation of light beam when it is passed
through a sample. The absorption coefficients are estimated by measuring the ratios
of the intensities of the transmitted and incident light. The traditional spectroscopy
has a very limited sensitivity as the measured change in light intensities is very
small and the actual signal is detected against a large background signal. Therefore, the conventional spectroscopy is sensitive to laser intensity fluctuations and the
measurements of low concentrations in the levels of parts per billion (ppb) to parts
A. Maity · M. Pal · M. Pradhan (B)
S. N. Bose National Centre for Basic Sciences, Salt Lake, JD Block, Sector III, Kolkata 700106,
India
e-mail: manik.pradhan@bose.res.in
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
D. K. Singh et al. (eds.), Modern Techniques of Spectroscopy, Progress in Optical Science
and Photonics 13, https://doi.org/10.1007/978-981-33-6084-6_11
287
Abhijit Maity, Mithun Pal, and Manik Pradhan
Abstract Cavity ring-down spectroscopy (CRDS), one of the most fascinating
analytical techniques, has found widespread applications in a variety of research
fields. It is a direct, ultra-sensitive and quantitative laser absorption spectroscopy
technique which measures the rate of absorption of molecular species instead of
the magnitude of absorption in an optical cavity where the light moves to and fro
several times. CRDS is an extremely powerful analytical method which can measure
weak as well as strong absorptions of trace and abundant molecular species in a
variety of environments. Recently, the technique has been modified in a great extent
and consequently several variants of CRDS are available. In this chapter, we briefly
discuss an overview of the CRDS technique and some of its important applications
in the field of high-resolution fundamental molecular spectroscopy and trace detection of molecules in the atmosphere. The application of CRDS in medical science
through breath test is also discussed followed by future trends and a perspective on
the technique.
Keywords Cavity ring-down spectroscopy · Cavity enhanced technique ·
Molecular spectroscopy · Trace gas sensing · Non-invasive medical diagnosis
1 Introduction
Conventional absorption spectroscopy is based on the Beer-Lambert law which
essentially provides information about the attenuation of light beam when it is passed
through a sample. The absorption coefficients are estimated by measuring the ratios
of the intensities of the transmitted and incident light. The traditional spectroscopy
has a very limited sensitivity as the measured change in light intensities is very
small and the actual signal is detected against a large background signal. Therefore, the conventional spectroscopy is sensitive to laser intensity fluctuations and the
measurements of low concentrations in the levels of parts per billion (ppb) to parts
A. Maity · M. Pal · M. Pradhan (B)
S. N. Bose National Centre for Basic Sciences, Salt Lake, JD Block, Sector III, Kolkata 700106,
India
e-mail: manik.pradhan@bose.res.in
© The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2021
D. K. Singh et al. (eds.), Modern Techniques of Spectroscopy, Progress in Optical Science
and Photonics 13, https://doi.org/10.1007/978-981-33-6084-6_11
287