Light scattering in physics, chemistry and biology - Concluding remarks

The papers presented at this conference have demonstrated the extraordinary range of information that can be deduced from experimental studies of the spectrum and the intensity of light scattered by matter. Indeed, these experiments provide detailed information on the energy level structure, dynamical motion and spatial structure of atoms, molecules, solids, fluids and synthetic and biological macromolecules. Each of the participants in this conference has given us the detailed analysis of his experimental studies on these various systems. I see it as my function to remind you, in the briefest way, of those physical findings which stand out most clearly in my own mind, without an effort to be complete. When considering atoms, the work of Dr Svanberg on resonance scattering provides detailed knowledge of the energy level structure of the electronic multiplets. Dr Cohen-Tannoudji has discussed the possibility of, and the theoretical basis for, an understanding of the precise dynamics of the radiation process using ‘antibunching’ experiments. For molecules, experimental studies of the Raman effect, and measurements of molecular polarizability by Dr Jones, Dr Madden, Dr Knaap and Professor Buckingham have provided accurate information on the moments of inertia and interatomic distances in molecules, the lifetimes of rotational and vibrational states and the electronic charge distribution through the polarizability. For solids, Dr Patel has shown how the Landau levels in indium antimonide can be used to produce a laser light source with great monochromaticity and high power. By combining this 'spin-flip ’ Raman laser with the sensitive detection techniques of opto-acoustic spectroscopy he has been able to measure the temporal variation in the very low concentration of NO and NO2 in the atmosphere and the stratosphere. Dr Cummins has shown how Raman and Brillouin scattering experiments in ferroelectric crystals can provide knowledge on structural phase transitions by detecting the softening of specific normal modes of the lattice vibrations as the transition is approached. Dr Pusey has created a uniquely interesting ‘solid’ made up of highly charged polystyrene latex spheres. By studying the spectrum and angular dependence of the intensity of light scattered from this system as a function of the degree of order, he can observe the development of the diffusive motion and the time average pair correlation function as the system of spheres evolves from a solution to a solid lattice. For fluids, Dr Vinen has explained how his work and that of Dr Greytak on the spectrum of light scattered from liquid helium provides information on the rich variety of elementary excitation such as phonons, rotons (including a roton bound state), and second sound in this fascinating quantum fluid. Dr Pike has shown how optical mixing, or photon correlation spectroscopy of the Doppler shift in the light scattered from macroscopic motion in a fluid can be used to provide information on velocity profiles and turbulent motion in fluids. These methods are applied to systems as diverse as chimney stacks, vortices behind jet aircraft on takeoff and landing, and flames. In addition he uses these techniques to observe blood flow in the retinal microcirculation in the living eye as was first demonstrated by Dr Riva and his collaborators. At the conclusion of his talk he showed some vivid, beautiful moving pictures of light scattered from a variety of dynamical fluid motions.