When an intense laser pulse interacts with homogeneous plasma embedded in a transverse magnetic field, transverse current density oscillating with frequency twice that of the laser field is set up. This leads to generation of second harmonic radiation with significant conversion efficiency.

There is evidence to suggest that organic cerebral changes occur in elderly depressed patients. Quantitative studies of elderly depressed patients have demonstrated that they have reduced ‘radio-attenuation’ on computerised tomography (CT) scans and as a group resembled more closely a group of demented patients than normal controls (Jacoby et al, 1983). Many biochemical changes associated with ageing are similar to the pathophysiological abnormalities in depression and in dementia (Alexopoulos et al, 1988). These changes, coupled with the high frequency of depressive syndromes in demented patients, suggest a complex relationship between depression and dementia in old age. Mahendra (1985) has suggested that a variety of brain abnormalities can produce a spectrum of clinical manifestations, ranging from depression with minimal cognitive dysfunction at one end to dementia with minimal depression at the other.

In this paper, evolution of spot size of an intense laser beam in cold, underdense, magnetized plasma has been studied. The plasma is embedded in a uniform magnetic field perpendicular to both, the direction of propagation and electric vector of the radiation field. Nonlinear current density is set up and the source dependent expansion method is used to determine the evolution of the spot size of a laser beam having a Gaussian profile. It is shown that transverse magnetization of plasma enhances the self-focusing property of the laser beam leading to reduction in critical power required to self-focus the beam.

A one-dimensional numerical model to study the evolution of longitudinal electrostatic wakefields, generated by propagation of a circularly polarized laser pulse in magnetized plasma has been presented. The direction of the external magnetic field is considered to be along as well as opposite to the axis of propagation of the laser pulse. Further, two-dimensional particle-in-cell code is used to obtain the generated wakefields. Separatrix curves are plotted to study the trapping and energy gain of an externally injected test electron, by the generated electrostatic wakefields, in the relativistic regime. Under appropriate conditions, an enhancement in the peak energy of an externally injected electron in magnetized plasma, as compared to the unmagnetized case, has been observed.