ABSTRACT
The use of Raman spectroscopy in the study of microscopic particles (micrometer-size particles) was suggested in the midsixties (1 ,2) as a consequence of the rapid development in the laser-excited Raman technique (3). Shortly after, Raman spectra from an effective scattering volume of 0.04 microliter ( 4) was reported experimentally, and in 1969 a volume of 7 nanoliters was found sufficient for obtaining a useful Raman signal (5). However, the idea which was going to revolutionize the microRaman experiment was originally published by Hirschfeld in 1973 (6): the laser power contained in a diffraction limited spot should permit the detection of the Raman signal from a 1 J.Lm 3 sample volume. This analysis was experimentally confirmed a year later by two separate research groups which revealed their first experimental data at the fourth International Conference on Raman Spectroscopy (ICORS)(7,8)- one of these two laboratories, which was from the National Bureau of Standards, showed (7,9) that Raman signals of micrometer-size particles could be detected by simply modifying the fore-optics of a conventional Raman spectrometer using a sophisticated micropositioning system. The device was formed of a microscope objective that focuses the laser beam onto the particle, another microscope objective at 90' to view the microsample and finally a conventional 90' Raman configuration system to collect the scattered light.
