General formalism of parametric excitation

Production of lower hybrid waves and field-aligned plasma density striations by whistlers

Soon after lasers were invented, there was tremendous curiosity on the nonlinear phenomena which would result in their interaction with a fully ionized plasma. Apart from the basic interest, it was realized that it could be used for the achievement of nuclear fusion in the laboratory. This led us to a paper on the propagation of a laser beam into an inhomogeneous fusion plasma, where it was first demonstrated that light would go up to the critical layer (where the frequency matches the plasma frequency) and get reflected from there with a reflection coefficient of order unity. The reflection coefficient was determined by collisional effects. Since the wave was expected to slow down to near zero group speed at the reflection point, the dominant collision frequency determining the reflection coefficient was the collision frequency at the reflection point. It turned out that the absorption of light was rather small for fusion temperatures. This placed a premium on investigation of nonlinear phenomena which might contribute to the absorption and penetration of the light into high-density plasma. An early investigation showed that electron jitter with respect to ions would be responsible for the excitation of decay instabilities which convert light waves into electrostatic plasma waves and ion waves near the critical frequency. These electrostatic waves would then get absorbed into the plasma even in the collisionless case and lead to plasma heating which is nonlinear. Detailed estimates of this heating were made. Similar nonlinear processes which could lead to stimulated scattering of light in the underdense region $$(\omega >\omega _p)$$
 were investigated together with a number of other workers. All these nonlinear processes need a critical threshold power for excitation. Another important process which was discovered around the same time had to do with filamentation and trapping of light when certain thresholds were exceeded. All of this work has been extensively verified in laser plasma experiments and have become the backbone of our present understanding of how lasers nonlinearly interact with fully ionized fusion plasmas. A review of this early work will be presented. We shall also present a review of our involvement in the recent work on nonlinear
penetration of light into overdense plasmas with gradual and sharp interfaces.

Nonlinear laser–plasma interactions

The ionospheric modification facility at Arecibo, Puerto Rico, has been used to study Langmuir waves excited in the lower ionosphere by a high-power HF radio wave. Measurements of HF-enhanced plasma lines have been made in the lower F region (less than 160 km altitude) and in the E region using the 430-MHz radar at Arecibo Observatory. These measurements complement observations made in the past at higher altitudes. Enhanced plasma line spectra observed in the lower F region peak at the so-called 'decay line' and contain additional spectral structure similar to that found in the upper F region. In the E region the spectra exhibit narrow peaks located at 430 MHz + or - f(HF), where f(HF) is the frequency of the modifying HF wave. While strong plasma line enhancements are commonly observed in sporadic E, only weak enhancements have been detected in the normal daytime E layer. Candidate mechanisms for the E region enhancements include the oscillating two-stream instability and direct conversion of the HF wave into Langmuir waves.

HF‐enhanced plasma lines in the lower ionosphere

The growth rates and thresholds of modulational instabilities associated with whistler waves are obtained. The formation of whistler solitons and their stability are discussed.

A note on the stability and evolution of whistler waves

During the last decades active and increasingly important research has been carried out in the field of nonlinear plasma physics, like in the field of nonlinear optics

General formalism of parametric excitation

Citations

Production of lower hybrid waves and field-aligned plasma density striations by whistlers

Nonlinear laser–plasma interactions

HF‐enhanced plasma lines in the lower ionosphere

A note on the stability and evolution of whistler waves

Some Remarks on Coherent Nonlinear Coupling of Waves in Plasmas

Related Papers (5)

Nonlinear propagation of lower-hybrid waves in an inhomogeneous plasma

The nonlinear interaction between waves in an inhomogeneous plasma

Parametric excitation of high-frequency electrostatic waves in a homogeneous cold plasma

Decay instabilities in an inhomogeneous plasma with trapped waves

Nonlinear theory for the modulation instability of plasma waves