The dynamics of ultrashort laser plasmas demand single shot temporal measurements on fast time scales. We describe a method to record the plasma expansion on picosecond (ps) timescales continuously over hundreds of ps, in single shot. The method uses the chirp of a Ti:sapphire laser as a time-resolved optical diagnostic tool. Using this technique, the evolution of the plasma expansion had been recorded with ps time resolutions, by probing with a chirped laser pulse of 200 ps duration. A peak expansion velocity of 1.8×107 cm/s is observed and its evolution in time is obtained for ∼300 ps.
Self-generated magnetic fields produced in laser plasmas at moderate laser intensities have been measured using a three-channel polaro-interferometer. The main elements of this device are two birefringent calcite wedges placed between two crossed polarizers. Using this device, the spatial profiles of (a) the rotation angle (polarometry), (b) the electron density (interferometry), and (c) the transmitted probe beam intensity (shadowgraphy) are recorded simultaneously using a digital camera with a large format CCD in a single laser shot. Magnetic fields of 2-4 MG had been estimated in aluminum plasma at laser intensities ~10(13) W/cm(2). It is also possible to use this device in other configurations to get time resolved information.
fast capillary discharge scheme, which has been demonstrated by several groups worldwide [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. This is based on collisional excitation pumping through a fast heating of the plasma. Such a soft X-ray laser has several applications in different areas of science and technology [16][17][18][19][20][21][22]. In fact, there exists a strong interest in extending the lasing wavelength toward shorter side. It is worth mentioning here that directed EUV emission has also been reported from discharge plasma at shorter wavelengths ranging from 12 to 16 nm [23]. Efforts are presently going on in this direction in various laboratories worldwide to demonstrate X-ray lasing at a wavelength of 13.4 nm in nitrogen z-pinch plasma using a capillary discharge system [24][25][26][27]. Unlike the 46.9-nm X-ray laser, this is based on recombination pumping scheme which requires fast heating of the plasma followed by fast cooling of the hot plasma. Whether it is collisional excitation pumping scheme or recombination pumping scheme, both require faster pumping of the plasma to achieve population inversion, which can be done using a fast current pulse having high rate of rise (dI/dt) to excite the plasma.The generation of X-ray laser through the fast capillary discharge scheme is based on passing a fast rising electrical current through a pre-ionized gas column in a ceramic capillary. The magnetic field generated by the discharge current exerts strong magnetic force acting radially inwards on the plasma column. As a result, the plasma column gets pinched to a highly ionized hot and dense column, which may have sufficient population of required ionization state for lasing under suitable conditions. With argon gas filled inside the capillary, Ar 8+ ions are the lasing species and collectively form the gain medium for X-ray laser at 46.9 nm. Collisional electron excitation of these ions creates population inversion between 3p 1 S 0 and 3s 1 P 1 energy levels, which leads to soft X-ray lasing at 46.9 nm Abstract The rate of rise in discharge current (dI/dt) is an important parameter in an X-ray laser pumped by fast capillary discharge. The effect of this parameter on the energy of an argon plasma-based 46.9-nm soft X-ray laser pulse has been experimentally studied. It was found that an X-ray laser pulse with ~2 μJ energy, which can be obtained at a discharge current of ~40 kA with dI/dt value of ~7.1 × 10 11 A/s, can also be obtained at a much lower peak current of ~26 kA if the quarter period (T/4) of the discharge current is made shorter to achieve a comparable dI/dt value. For a fixed T/4, the laser energy could be enhanced from 2 to 4 μJ for an increase in the dI/dt value from 7.1 × 10 11 to 1.3 × 10 12 A/s by increasing the peak current from 26 to 44 kA. It was also observed that for a fixed dI/dt, mere increase in the discharge current does not increase the laser energy.
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