Plasma diagnostics of a capillary plasma using pulse power

ABSTRACT We reported the production of a plasma channel in a capillary discharge-produced plasma. Plasma parameters of its channel were observed by use of both a laser interferometer and a hydrogen plasma spectrum. A time-resolved electron temperature was measured, and its maximum temperature of 3 eV with electron densities of the order of 10 17 cm  3 was observed at a discharge time of 150 ns and a maximum discharge current of 400 A. Intense laser pulse was guided over many vacuum Rayleigh lengths using its channel. Keywords: Capillary, plasma channel, di scharge-produced plasma waveguide, plasma parameters, laser guiding 1. INTRODUCTION The guiding of intense laser pulse in a plasma has applications which include high-order harmonic radiations [1], x-ray lasers [2], and laser-plasma-based electron acceleration [3]. These applications require intense laser pulse propagating, generally above the ionization threshold of at oms. Femtosecond laser technology generated by chirped-pulse-amplification, the high laser intensity and the high optical field are achieved in a tightly focused beam. For a focused Gaussian beam, the interaction length is approximately a Rayleigh length of less than 1 mm, which is attributed to the tightly focused beam. To overcome this sh ort interaction length, it is necessary to appropriate optical waveguides that are efficiently coupled with intense laser pulse. The choice of optical waveguides may thus become as important as that of high intensity laser. Intense laser pulse may be guided in a plasma if the refractive index along the optical pulse propagation direction can be in creased sufficiently to balance diffraction. There are several different kinds of optical plasma waveguides used in high-intensity laser-plasma interaction experiments, such as gas/cluster jets [4], hollow fibers [5], and discharge-produced plasma waveguides [6-10]. Among these, capillary-self-breakdown-ablated channel in vacuum [7,8] and hydrogen gas-filled channel [9,10] have actively been studied as possible efficient plasma channel to guide intense laser pulse. The hydrogen gas-filled capillary plasma waveguide forms a fully ionized. The plasma channel is formed by Ohmic heating to the capillary wall, which causes the electron density to be decreased, near the capillary centre. In order to understand the