We have developed a 428 nm blue laser source based on resonator-enhanced frequency doubling of a GaAlAs diode laser and have used this source to demonstrate writing and reading on an MO disk. The power, beam quality, and noise of the blue laser are sufficient for high-density optical recording.

Measurements of the velocity and angular distributions for trapping-desorption scattering of argon from a clean, well characterized Pt(111) single crystal are reported. For certain experimental conditions, both the characteristic velocity and angular distributions deviate markedly from that predicted using equipartition arguments (i.e., a Maxwellian flux distribution in velocity and a cosine distribution in angle). The average kinetic energy for the flux exiting normal to the surface at 100 K is only 80% of that expected for a Maxwellian at TS. This kinetic energy deficit decreases and approaches zero as the detector is rotated away from the surface normal. The angular flux distribution is found to be broader than cosine. These results are discussed in terms of microscopic reversibility which permits estimates of the velocity dependent condensation coefficient to be obtained.

High resolution angularly resolved time of flight distributions are presented for a supersonic argon beam scattering from a clean well-characterized Pt(111) single crystal. A novel presentation of the resulting velocity and angular flux information in terms of iso-flux contour maps in Cartesian velocity space allows the scattering process to be decomposed into three mutually independent directions defined by the surface normal (z), parallel to the surface and in the scattering plane (y), and parallel to the surface but perpendicular to y and z(x). The iso-flux contour maps appear as nested ovals with principal axes oriented parallel to the above defined directions; axis length decreases in the order z, y, x. The corresponding variances in the x, y, and z velocities vary directly with the surface temperature. Three beam energy regimes are evident and are discussed in terms of the diminishing effect of the attractive well which occurs for increasing beam energies and the increasing effect of short range phenomena prevalent at high incident beam energies. Accomodation coefficients were defined and measured for the y and z directions and were 0.1 and 0.45, respectively, indicating the degree to which parallel and perpendicular momenta are not conserved in a single collision. Geometric scattering by instantaneous surface roughness is experimentally shown to be negligible for this system for beam energies <20 000 K indicating that the scattering is by the finite momentum of the surface.

Angle and velocity distributions for supersonic chopped beams of N 2 and CH 4 scattered from clean close-packed Pt(111) surfaces are reported. For specular direct-inelastic scattering N 2 and CH 4 velocity distributions can be characterized by empirical relationships used for Ar scattering. For instance, for specular scattering the following relation is found for Ar, N 2 and CH 4 : 〈KE f 〉 = A (KE i ) + B (2 kT s ), where 〈KE f 〉 is the average final kinetic energy, KE i is the incident kinetic energy and T s is the surface temperature. The beam and surface temperature independent coefficients A and B are, respectively: Ar 0.87, 0.17; N 2 0.79, 0.19 and CH 4 0.84, 0.25. Unlike Ar, N 2 desorbs from Pt with a Maxwell-Boltzmann velocity distribution near the surface temperature. Qualitatively the trapping probabilities for these molecules on Pt(111) are ordered: Xe > N 2 > CH 4 > Ar.

The rotationally inelastic scattering of HD(J = 0→, 1, 2, 3) from a clean Pt(111) surface is reported. Discrete peaks for each final J state are resolved in the in-plane angular distributions, with the inelastic peaks typically being large compared to the elastic peak. Sharp modulations of these inelastic transition probabilities were found as the incident angle was varied, suggesting bound level resonances. These resonances are inconsistent with G-vector mediated (elastic) selective adsorption, but are consistent with rotationally inelastic selective adsorption into the bound levels of the physisorption potential. Observation of bound level resonances can be used to determine molecule–surface potentials. However, unlike elastic selective adsorption, highly probable rotationally inelastic HD selective adsorption is applicable to metallic surfaces of low corrugation.

Velocity distributions for Ar atoms scattering from a clean, polycrystalline tungsten surface have been measured for a wide range of incident supersonic beam energies 300 K < (1/2) m〈v2〉/k<2000 K, and surface temperatures 350 K<Ts<1900 K. This work studies directly the nature of the scattering process of an intermediate mass atom on a clean metal surface over a very wide range of conditions. Direct inelastic scattering involving a single encounter of the gas atom with the surface is the most important process. No distinct elastic or quasielastic scattering occurs. Only at the lowest temperatures is a trapping–desorption scattering process observed. The direct inelastic scattering process is characterized by the linear proportional relationship 〈KEe〉=0.83 〈KEi〉+0.20 〈KETs〉 over the entire range of energies and temperatures for 45° angle of incidence and observation in the specular direction (KEe, KEi, and KETs are the kinetic energy of the exiting Ar, the incident Ar, and the Ar in equilibrium at the surfa...

Scattering of N 2 from a clean polycrystalline W surface is studied with a time-of-flight molecular beam apparatus. The time-of-flight spectra are used to characterize the N 2 -W energytransfer and condensation, allowing inferences to be made about the initial steps of N 2 chemisorption, thought to proceed via a molecular precursor state. The sticking coefficient on our sample for N 2 to chemisorb to an atomic nitrogen bound state was 0.5 ± 0.1 5 for a 600 K beam and a 450 K surface temperature. Unreacted N 2 scattered into direct and trapping-desorption channels. The direct channel is shown to be entirely inelastic with temperature independent differential energy accommodation coefficients that average 0.46 for normal and specular scattering at 45° incidence angle. The fraction of trapping-desorption scattering diminishes significantly with increasing surface and beam temperature. The observed decrease in sticking coefficient with increase in surface temperature is shown to be due to a diminution of the N 2 condensation coefficient as well as an increase in desorption of the N 2 , recursor relative to its migration-chemisorption.

Velocity and angular distributions for Xe scattered from clean Pt(111) have been observed which permit the scattering process to be experimentally divided into a direct inelastic channel and a trapping-desorption channel. The trapping-desorption channel leads to Maxwellian velocity distributions at the surface temperature and a $cos\ensuremath{\theta}$ angular dependence, while the direct inelastic channel exhibits a linear relationship between exit kinetic energy and both incident kinetic energy and surface temperature.