Lasers, Spectrographs, and Detectors - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 1

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Lasers, Spectrographs, and Detectors
Fred LaPlant
Abstract The introduction of Raman spectroscopy into new fields has been driven
largely by advances in the underlying technology. While the spectrometer is still
comprised of a light source, a wavelength selector, and a detector, the improvement
in functionality of each of these components has had dramatic impacts on areas
where Raman was once thought impractical, if not impossible. In addition, eso-
teric techniques once confined to academic spectroscopy labs are now finding wide
application.
This chapter will briefly describe the basic function of a Raman spectrome-
ter, while focusing on the enabling advances in spectrometer components including
capability, flexibility, ease of use, and cost. Traditional laser sources have become
commodity items with air cooling, smaller forms, and lower cost in a variety of
wavelengths. Likewise, availability of high-power, tunable, and pulsed laser systems
have facilitated the use of higher-order techniques such as UV-resonance Raman
and CARS. The spectrograph form can be selected based on application, from tra-
ditional dispersive, to FT, to liquid crystal tunable filter, etc. Introduction of the
Raman signal to the spectrometer using fiber optics has seen similar advances, such
as SORS and other fiber bundle techniques. Detectors have become more sensitive,
with lower noise, better detection at longer wavelengths, and faster operation. Many
of these advances have resulted in miniaturization of the Raman system, so that sys-
tems once requiring an entire lab bench can now be handheld. Applications where
these advances have made significant impact will be highlighted.
1.1 Introduction
The evolution of Raman spectroscopy from a spectroscopic novelty, to a com-
plementary technique in niche applications, to an analytical powerhouse, has
closely paralleled the advancement of enabling technologies. While a sim-
ple block diagram of the components of a Raman spectrometer shown in
Figure 1.1 would still be comparable to the very early instruments built by
C.V. Raman [1], the improvement in functionality of each component has dra-
matically increased the impact of Raman spectroscopy in areas where it was