Anomalous, low-frequency Raman scattering from localized acoustic vibrations of roughness features on a metal surface are observed. The observed mode frequency shifts with excitation frequency and with the index of refraction of the surrounding medium. The shifts arise from resonant laser excitation of localized dipolar plasmons. This resonant optical coupling is a key to the phenomenon of enhanced Raman scattering from molecules adsorbed on rough metal surfaces.

Hole burning, which is attributed to optical pumping of nuclear-quadrupole levels, has been observed in the stoichiometric rare-earth compound, EuP5O14. The long lifetime of these holes (∼60 min) implies slow nuclear-spin flip-flop rates. The small magnetic moment of Eu3+ has prevented conventional magnetic-resonance measurements on Eu3+ compounds, but hole burning provides a sensitive method for the optical detection of nuclear-magnetic resonance and nuclear-quadrupole resonance. We have used hole burning and optically detected nuclear-quadrupole resonance to determine quadrupole splittings in the ground (7F0) and excited (5D0) states.

A novel coherent transient effect is observed following a rapid shift in the relative phase of an exciting laser and sample polarization. An analytical expression is derived for the signal which is a sum of exponentially decaying terms with characteristic times involving both T1 and T2. Phase switching is a powerful approach to the study of optical relaxation and is applied here to measure dephasing in LaCl3: Pr3+.

A theory for inelastic Mie scattering from rough metal surfaces or metal sols is proposed. A resonant excitation of a localized dipolar plasmon can enhance the cross section, and experimental data relating to the phenomenon in silver and copper are presented. Two distinct effects are noted. One is inelastic light scattering from the rough metal surface or bare metal sol. The other is related to Reyleigh scattering from adsorbed molecules as modified by the presence of the substrate. Both involve frequency shifts determined by the characteristic mechanical vibrations of the metal. A striking feature of this inelastic Mie scattering is that for a distribution of particle sizes and shapes the frequency shift changes as the incident laser frequency is changed or as the index of refraction of the surrounding medium is changed. Inelastic Mie scattering is shown to yield important information on the surface roughness required for the observation of surface-enhanced Raman scattering.

We have observed Raman spectra of a very low frequency mode involving surface adsorbed molecules. Scattering from this mode appears to be sensitive to adsorbate orientation. With pyrazine as the adsorbate, the frequency shifts with electrochemical voltage, possibly because of changes in orientation of the molecule on the surface. With pyridine as the adsorbate, we find that the frequency of the peak in the scattered light intensity increases linearly with excitation frequency, suggesting that light is resonantly scattered from the surface adsorbed species.​​​​​​