Coherent Excitations and Raman Effect

At first sight measurement of the intensity ratio of antistokes to stokes Raman lines offers a straight forward method for determining the above thermal excitation required by theory. Early measurements /l/, in fact, have confirmed such excitation in the 100 cm-1 region. Clearly much more spectacular enhancement should be expected in the higher frequency region near 1000 cm-1, but, so far, stokes spectra only have been taken /2/. Figure 1 shows our result on the time dependence of the E.coli spectra indicating the appearance, and disapperance, of lines as the activity of the bacteria developes. The neighbourhood of the waterband at 1640 cm-1 provides the possibility for a rough estimate of intensities. At the high dilution required for the maintainance of the activity of the bacteria, an intensity enhancement of the order 105 would be required to find lines of the measured intensity /3/. As a consequence it can be concluded that a number of cells must oscillate coherently, for then the intensity is proportional to the square of the number of oscillating centers. This should explain why, in the time available to us, we were unable to reproduce this result.