The use and general applicability of Raman spectroscopy for both fundamental and applied problem solving has always been closely tied to advances in technology. The most notable instrumentation development, of course, which transformed the practical significance of the Raman effect, was the incorporation of laser excitation for the observation of spontaneous Raman signals. This occurred some 35 years after the first observations of this inelastic scattering phenomenon. Other critical advances include the development of detectors, evolving from photographic plates to photoelectric tube, photon counting and various forms of multichannel detection (e.g. photodiode arrays and most recently, charge coupled device (CCD) cameras). What is quite clear from an historical perspective is that improvements in Raman instrumentation due to advances in optical technologies, allow the range of Raman applications to expand as a consequence.
The articles gathered in this special issue highlight some of the most recent advances in Raman instrumentation and demonstrate the resulting innovative applications of Raman spectroscopy which take advantage of these new technological developments. A number of common elements run through the papers collected here. The use of fibre optic Raman probes is clearly a marriage of technologies which combines the chemical selectivity of Raman spectroscopy with the spatial resolution and convenience of remote sensing possible with these optical guides. In addition, the use of fibre-related probes greatly expands the applications of Raman spectroscopy both in terms of portability and in the flexibility of sampling it offers. In addition, other techniques described here, such as near-field and confocal Raman imaging and array-based probes, offer additional examples of the use of Raman to obtain spatially-resolved chemical information.
A perusal of the range of molecular and material samples of interest in the articles of this issue clearly reveals that one of the most important and expanding areas where advances in Raman instrumentation are being exploited is in the study of biological materials. Topics in this area appearing in this collection range from the continuing development of Raman optical activity spectrometers as probes of structures and dynamics of biological chromophores, to the biomedical diagnostics of DNA mapping and sequencing. The inherent non-invasive character and the absence of problems from water interference continue to underscore the importance of Raman spectroscopy as a probe of biological systems and are reflected in several of the applications described here.
Finally, as demonstrated by the evolution (or revolution) from Toronto arcs to laser excitation, practitioners of Raman spectroscopy will continue to incorporate advances in excitation sources as they develop. In particular, three of the papers here exploit various aspects (pulse duration, power and tunability) of Ti : sapphire-based laser systems for novel applications of Raman spectroscopy.
In summary, this collection of articles demonstrates how developments in optical technology are currently being absorbed into the practice of Raman spectroscopy and, one can, with complete certainty, anticipate the continued growth of applications for this spectroscopic technique as a result of continuing technological advances.