Some interesting phenomena: ions versus electrons

A collection of charged and neutral particles is referred to as plasma, if the ions and electrons stay there almost in equal number. These plasma species are connected with each other by electromagnetic forces because of which the plasmas show their collective behaviour. However, by applying an appropriate bias or field, we can control the motions of the ions and the electrons for the diverse applications of plasmas. The electrons can lead to several kinds of phenomena when they move in the background of the ions. For example, the electrons can be made to oscillate for exciting Langmuir wave /plasma wave when an intense laser is launched in the plasma. The same kind of wave can also be generated by beating two lasers having frequency difference the same as the plasma frequency. This way plasma can support a huge field called the wake field which can be used for the purpose of particle acceleration. On the other hand, nonlinear current can be generated by the electrons oscillations at a desired frequency with the application of lasers and this current is employed for the generation of Terahertz (THz) radiation. Plasmas have also been used for producing Free Electron Lasers, X-rays and other radiations. For the purpose of particle acceleration, lasers have proved to be very effective. However, we have shown that the microwave can also produce effective acceleration if the pulses of the microwave radiation are tailored. On the other hand, THz radiations have received huge applications in medicine, explosive and concealed weapon detection, material characterization, remote sensing, time domain spectroscopy, etc. In medical applications, we require the THz radiation to focus on multiple places for the diagnostics of cancerous cells. In this direction, we have developed theories for achieving bifocal and multifocal THz radiation with a control. There is another phenomenon also, which is related to the channel formation in the plasma which has ample applications in laser guiding and the laser fusion. In the present talk, main focus will be given to several interesting phenomena that have been explored at Plasma Science and Technology Laboratory of Indian Institute of Technology Delhi, India