N. Bloembergen

Laser-induced electric breakdown in solids

A review is given of recent experimental results on laser-induced electric breakdown in transparent optical solid materials. A fundamental breakdown threshold exists characteristic for each material. The threshold is determined by the same physical process as dc breakdown, namely, avalanche ionization. The dependence of the threshold on laser pulse duration and frequency is consistent with this process. The implication of this breakdown mechanism for laser bulk and surface damage to optical components is discussed. It also determines physical properties of self-focused filaments.

NONLINEAR OPTICAL PROPERTIES OF PERIODIC LAMINAR STRUCTURES

Some novel phase‐matching schemes are suggested for nonlinear processes occurring in a composite layered structure of GaP and GaAs.

Controlled stimulated Raman amplification and oscillation in hydrogen gas

The gain of the Q(1) vibrational stokes line of H 2 has been measured as a function of pressure in a Raman amplifier cell of variable length. The threshold power for stimulated emission of the Q(1) vibrational and S(1) rotational stokes line of H 2 has been measured in a transverse resonator as a function of pressure. Both geometries give results in good agreement with theory, without invoking any other nonlinear instabilities.

Dependence of laser‐induced breakdown field strength on pulse duration

Field strengths at which optical damage is initiated in NaCl have been measured with a mode‐locked Nd: YAG laser with pulse durations of 15 and 300 psec. Comparison with previously reported data with a Q‐switched laser shows that the field strength required for intrinsic optical damage increases by almost one order of magnitude from 106 V/cm at 10−8 sec to over 107 V/cm at 1.5 × 10−11 sec. This is in qualitative agreement with published estimates based on the electron avalanche breakdown mechanism.

Purely refractive transient energy transfer by stimulated Rayleigh-wing scattering

Two-beam coupling is demonstrated in CS2 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.

TRANSIENT STIMULATED ROTATIONAL AND VIBRATIONAL RAMAN SCATTERING IN GASES

Using a mode‐locked ruby laser, stimulated rotational and vibrational Raman scattering has been observed in a variety of high‐pressure gases, where previously no stimulated scattering has been reported. Pulse energy conversion efficiencies as high as 70% have been obtained. Evidence for a strong optical Stark effect is seen in the gases producing rotational scattering. Self‐focusing in a collimated beam is observed in N2O and CO2.

Magnetic Resonance in Ferrites

Ferromagnetic resonance in ferrites is reviewed. The concept of tensor permeability, the influence of magnetic anisotropy, demagnetizing fields, and damping mechanisms are discussed. Special consideration is given to coupled magnetic systems and the behavior in ferrites with compensation points. The general theoretical results are compared with a few illustrative examples. The behavior in polycrystalline material, g-value, line width, and anisotropy as a function of temperature and external magnetic field are outlined.

Nonlinear optics - Past, present, and future

Some introductory remarks and historical comments on the field of nonlinear optics are made.

Multiplex coherent anti‐Stokes Raman spectroscopy study of infrared‐multiphoton‐excited OCS

The vibrational energy distribution following ν2 overtone excitation of OCS by a pulsed CO2 laser is studied by monitoring the coherent anti‐stokes Raman spectrum of the ν1 mode. Because of the slow energy transfer from the pumped mode to other modes, and because the anharmonicity of the ν2 mode is small, OCS is an ideal system for studying the interaction of an intense infrared laser field with a single, nearly harmonic, oscillator. From the spectra the cross anharmonicities of the ν1 mode are determined to be x12=−6.0 cm−1 and x13=−2.7 cm−1, respectively. The time dependence of the spectra provides information on V–V energy transfer rates. In particular, the measurements put a lower limit of kν2→ν2=1 μs−1 Torr−1 on the vibrational relaxation rate within ν2 mode. At high excitation, the temperature of the ν2 mode rises up to 2000 K, and hot bands are observed up to the n=4 level. This fourth overtone peak is split because of either a Fermi resonance or vibrational angular momentum splitting.

Brief history of laser-induced breakdown (Abstract Only)

Breakdown of air by a focused pulse from a Q-switched ruby laser was first observed in 1962. This marked the beginning of studies on laser-generated plasmas and of laser-induced breakdown in solids, liquids and gases. A historical overview will be presented of major developments in the basic physical processes involved, including multiphoton ionization and avalanche breakdown. Recent experiments on plasma creation and damage induced by femtosecond pluses have thrown new light on this subject, which continues to be of great technical interest.