Lasers, Spectrographs, and Detectors - Emerging Raman Applications and Techniques in Biomedical and Pharmaceutical Fields - page 2

once thought impractical, if not impossible to perform. In addition, esoteric
techniques once confined to academic spectroscopy labs are now finding wide
application.
The principal difference in the current stage of Raman evolution, as ex-
emplified by this topic, is its breadth of application. From the earliest use of
mercury arc lamps and photographic plates to replace sunlight and the human
eye, to the introduction of the laser, to the rapid spread of multichannel detec-
tors, each technological advance represented a quantum leap in the capacity
of the Raman system to perform a wide range of useful experiments. But as
befits a maturing technology, the most impressive advances are now occurring
in specific disciplines, where the enabling technologies of the past allow new
technologies to be specialized and optimized for individual applications.
This chapter will briefly describe the Raman effect and the basic function
of a Raman spectrometer, while focusing on the advances in spectrometer com-
ponents including capability, flexibility, ease of use, and cost that have enabled
the emergence of new biomedical and pharmaceutical applications. 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 techniques such as
UV-resonance Raman and CARS (coherent anti-Stokes Raman spectroscopy).
The spectrograph form can be selected based on application, from traditional
dispersive, to FT, to liquid crystal tunable filter, etc. Detectors have become
more sensitive, with lower noise, wider wavelength range, and faster opera-
tion. These advances, coupled with improved laser line rejection, have pro-
duced miniaturized spectrometers suitable for measurements in the harshest
environments. Presentation of the sample to the spectrometer has seen similar
advances: Raman imaging can be performed rapidly or over large areas; the
use of fiber optics such as SORS (spatially offset Raman spectroscopy) and
other fiber bundle techniques has enabled greater sampling flexibility; SERS
(surface-enhanced Raman spectroscopy) has shown the potential for greatly
enhanced sensitivity and specificity. This chapter will describe the available
instrumental components that can be enlisted for the applications that will
be described in detail in upcoming chapters.
1.2 Raman Spectroscopy: Background
A variety of other excellent texts are available for in-depth review of the
fundamentals of Raman spectroscopy, including core technologies and ap-
plications [2, 3]. This is intended as a very brief, non-rigorous overview for
non-spectroscopists who may be unfamiliar with the principles of Raman, its
strengths, and practical limitations. For discussion of the experimental de-
tails of variant techniques such as ROA (Raman optical activity) or SERS,
the reader is directed to the appropriate chapters in this text.