Quantum Cascade Laser Spectroscopy
Mithun Pal and Manik Pradhan
Abstract Over the past few decades, the progress in applications of quantum cascade
laser (QCL) spectroscopy has accelerated with breathtaking way since its discovery
in 1994. The unique properties of QCL such as certain access in mid-IR spectral
range, narrow emission pure spectrum, and wide tuning capabilities have enabled
to develop new-generation analytical tools, which have been utilizing rigorously in
several spectroscopic applications like atmospheric science, biomedical diagnostics
and imaging purposes, industrial process monitoring as well as explosive detection.
Moreover, the unique features of QCL have resulted in developing several miniaturized and portable spectrometers in mid-IR spectral range. This book chapter provides
an overview of some unique applications of QCL spectroscopy in the field of trace gas
sensing in the atmosphere, human exhaled breath analysis for non-invasive disease
detection and isotope ratios measurements in a variety of environments. The chapter
also provides the application of QCL in microscopy and infra-red imaging. The
application of QCL in terahertz region has also been elaborated.
Keywords Quantum cascade laser (QCL) · Mid-IR laser spectroscopy · Trace gas
detection · Biomedical imaging · Terahertz spectroscopy · Application
1 Introduction
In recent years, the development of quantum cascade laser (QCL) technology has
paved the revolution in infrared-spectroscopic applications as it can easily access
the entire mid-infrared (mid-IR) spectral region, covering 4–12 μm. This spectral
window is known as the molecular fingerprint region where the fundamental and
combinational vibrational bands of important trace molecules can be probed with
unprecedented molecular selectivity and sensitivity. Moreover, other salient features
of QCL such as room-temperature operation, high-optical output power, spectral
purity, compactness, mode-hop-free (MHF) wide tunability (≥100 cm
−1 ), extremely
M. Pal · M. Pradhan (B)
Department of Chemical, Biological and Macromolecular Sciences, 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_14
363
Mithun Pal and Manik Pradhan
Abstract Over the past few decades, the progress in applications of quantum cascade
laser (QCL) spectroscopy has accelerated with breathtaking way since its discovery
in 1994. The unique properties of QCL such as certain access in mid-IR spectral
range, narrow emission pure spectrum, and wide tuning capabilities have enabled
to develop new-generation analytical tools, which have been utilizing rigorously in
several spectroscopic applications like atmospheric science, biomedical diagnostics
and imaging purposes, industrial process monitoring as well as explosive detection.
Moreover, the unique features of QCL have resulted in developing several miniaturized and portable spectrometers in mid-IR spectral range. This book chapter provides
an overview of some unique applications of QCL spectroscopy in the field of trace gas
sensing in the atmosphere, human exhaled breath analysis for non-invasive disease
detection and isotope ratios measurements in a variety of environments. The chapter
also provides the application of QCL in microscopy and infra-red imaging. The
application of QCL in terahertz region has also been elaborated.
Keywords Quantum cascade laser (QCL) · Mid-IR laser spectroscopy · Trace gas
detection · Biomedical imaging · Terahertz spectroscopy · Application
1 Introduction
In recent years, the development of quantum cascade laser (QCL) technology has
paved the revolution in infrared-spectroscopic applications as it can easily access
the entire mid-infrared (mid-IR) spectral region, covering 4–12 μm. This spectral
window is known as the molecular fingerprint region where the fundamental and
combinational vibrational bands of important trace molecules can be probed with
unprecedented molecular selectivity and sensitivity. Moreover, other salient features
of QCL such as room-temperature operation, high-optical output power, spectral
purity, compactness, mode-hop-free (MHF) wide tunability (≥100 cm
−1 ), extremely
M. Pal · M. Pradhan (B)
Department of Chemical, Biological and Macromolecular Sciences, 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_14
363