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Three distinctly different regimes of photoelectric emission are observed over a wide fluence range of uv-laser pulses irradiating single-crystal silicon samples. The role of the electron-hole plasma in the nonlinear photoemission is demonstrated by temporal correlation measurements. The diffusion properties of hot carriers are analyzed by investigating the influence of energy transport by hot carrier diffusion on the fluence threshold for melting with uv photons.

The changes in reflectivity of a silicon surface, irradiated by a green picosecond pulse, are probed during and following that pulse with a spatial resolution of 10 µm. The data indicate the development of a liquid phase, and a resolidification either into a single crystal or an amorphous phase. The latter has a characteristic ring-type pattern, and occurs only at locations where the incident picosecond laser fluence lies between 0.2 and 0.26 J/cm2. The reflectivity data appear to be in good quantitative agreement with a “simple heating” model, in which the electrons and phonons maintain a local thermodynamic equilibrium on a picosecond time scale.

Picosecond time-resolved reflectivity measurements on bare silicon surfaces and silicon surfaces with oxide layers reveal very fast heat diffusion and material evaporation on subnanosecond time scales. With a thick oxide layer resolidification of a molten silicon surface can take place in a few hundred picoseconds. At high laser fluences, vaporization processes take only a couple of 100 ps.

Basic properties of propagation of electromagnetic waves in nonlinear media are a direct consequence of classical conservation laws for energy, and for components of momentum and angular momentum.

The collisionless infrared multiphoton excitation of small molecules, OCS, SO2, NO2and DN3is discussed. Despite the small absorbance of IR photons by these molecules, evidence for the population of highly excited vibronic levels below the dissociation threshold is obtained. Multiphoton dissociation is observed, as well. The average number of photons absorbed and dissociation yields depend predominately on the laser intensity. High order multiphoton processes couple the ground vibrational level with the quasicontinuum of excited levels below and above the dissociation threshold.

The intensity patterns produced by a Gaussian (TEM_00 mode) laser beam propagating in the vicinity of the optical axis of α-iodic acid have been photographed. Densitometric profiles for different polarization conditions have been obtained. The theory of Portigal and Burstein has been extended to permit a quantitative comparison between theory and experiment for conical refraction in noncentrosymmetric crystals.

Detailed measurements of the conical intensity pattern aragonite have been carried out with an incident Gaussian beam (TEM_00) of a helium neon laser. Quantitative agreement with theoretical calculations is found. It is shown that the integrated intensities on either side of the Poggendorff dark circle are not equal, unless the far-field condition for Fraunhofer diffraction is satisfied.

The two-photon absorption coefficients of some uv transmitting window and coating materials are measured at 355 nm and 266 nm. In materials with band gaps larger than 2ħω, the nonlinear absorption is below the detection limit of 3 × 10^−6 cm/MW. CdF_2 has a two-photon absorption coefficient 1.6 × 10^−3 cm/MW at 266 nm, which is comparable with that of the alkali-halides. The newly developed window material LiYF_4 has no detectable nonlinear loss at 266 nm.

Four-photon photoemission is observed from tungsten using carefully controlled and calibrated single pulses produced by a passively mode-locked Nd:YAG laser system. The results are shown to be in quantitative agreement with a four-photon generalization of the Fowler and DuBridge theories of photoemission.

Detailed measurements of the conical intensity pattern aragonite have been carried out with an incident Gaussian beam (TEM_00) of a helium neon laser. Quantitative agreement with theoretical calculations is found. It is shown that the integrated intensities on either side of the Poggendorff dark circle are not equal, unless the far-field condition for Fraunhofer diffraction is satisfied.

Two-beam coupling is demonstrated in CS_2 and other transparent Kerr liquids by use of frequency chirped, picosecond 532-nm-wavelength pulses with several polarization combinations. As the temporal delay between pulses is varied within the coherence time, the first pulse always loses energy while the second pulse gains this energy. The transferred energy at a fixed delay varies linearly with irradiance. The results are consistent with energy transfer from transient refractive gratings that are due to stimulated Rayleigh-wing scattering.

Three distinctly different regimes of photoelectric emission are observed over a wide fluence range of uv-laser pulses irradiating single-crystal silicon samples. The role of the electron-hole plasma in the nonlinear photoemission is demonstrated by temporal correlation measurements. The diffusion properties of hot carriers are analyzed by investigating the influence of energy transport by hot carrier diffusion on the fluence threshold for melting with uv photons. [ABSTRACT FROM AUTHOR]

Picosecond time-resolved reflectivity measurements on bare silicon surfaces and silicon surfaces with oxide layers reveal very fast heat diffusion and material evaporation on subnanosecond time scales. With a thick oxide layer resolidification of a molten silicon surface can take place in a few hundred picoseconds. At high laser fluences, vaporization processes take only a couple of 100 ps. [ABSTRACT FROM AUTHOR]

The concentration of the electric field strength in the neighborhood of micropores and cracks may lower the nominal external intensity for electric avalanche breakdown by a factor 2–100 depending on the geometry of the crack and the dielectric constant. The presence of absorbing inclusions at the edge of microcracks will often be the dominant mechanism giving the lowest surface damage threshold. Inclusions and cracks with characteristic dimensions less than about 10^−6 cm will not lower the breakdown threshold appreciably.

The linewidth and intensity of the four-wave degenerate mixing signal in Na vapor have been observed as functions of He buffer-gas pressure with cw single-mode dye-laser beams. The width is independent of He pressure, and a quantitative comparison with theory is made. We also report the observation of a new effect, a four-wave mixing Raman-type resonance between two equally populated hyperfine levels.

Phase-matched four-wave mixing in sodium vapor with a helium buffer gas is carried out in a noncoplanar geometry. The directions of the four light beams remain nondegenerate even if all frequencies are equal. A sharp zero-difference frequency resonance in the intensity of the parametrically generated fourth beam by three incident beams is observed that is proportional to the square of the pressure of the buffer gas. A theoretical interpretation of this effect caused by elimination of destructive interference between two coherent pathways is presented.