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Flash laser heating using short-pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1 μm. This is very useful because micron- and submicron-sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser-cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laser irradiation. This permits the effective removal of particles smaller than ∼20 μm, down to as small as 0.1 μm, from a solid surface using a modest ultraviolet laser fluence of ∼0.1 J/cm2.

It was recently discovered that when there are sufficiently rapid spin-exchange collisions in an alkali-metal vapor, the rf magnetic-resonance frequency of the ground-state atoms becomes a constant fractional value (e.g., 4/11 for Cs) of the Larmor frequency, and the linewidth becomes inversely proportional to the spinexchange rate. These properties are in complete contrast to those in the slow spin-exchange limit. We present a theoretical analysis of these properties, and we predict some additional new effects for rapid spin exchange. Four theories are presented: an intuitive-vector model, a perturbation treatment, numerical solutions of complex non-Hermitian matrices, and a statistical analysis of the effect of rapid transfers between two Zeeman multiplets. These theories all provide, to varying degrees, consistent quantitative answers to the problem of how spin exchange affects magnetic resonance in an alkali vapor.

Laser cleaning with pulsed ultraviolet and infrared lasers is successfully employed to remove particulate contamination from silicon wafer surfaces and from delicate lithography membrane masks. Particulate material investigated include latex, alumina, silicon, and gold. Gold particles as small as 0.2 μm can be effectively removed. This new and highly efficient laser cleaning is achieved by choosing a pulsed laser with short pulse duration (without causing substrate damage), and a wavelength that is strongly absorbed by the surface; the removal efficiency is further enhanced by depositing a liquid film of thickness on the order of micron on the surface just before the pulsed laser irradiation.