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1

Ponderomotive self-focusing of a short laser pulse under a plasma density ramp

Kant N., Saralch S., Singh H.

Nukleonika

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2011

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Vol. 56, No. 2

149-153

EN

The ponderomotive self-focusing of a short laser pulse in an underdense plasma under a plasma density ramp is analyzed. The pulse may acquire a minimum spot size due to the ponderomotive self-focusing. Beyond the focus, the nonlinear refraction starts weakening, and the spot size of the laser pulse increases, resulting in an oscillatory self-focusing and defocusing behavior of the beam with the propagation distance. In order to minimize the defocusing, we introduce a localized upward plasma density ramp. Due to the upward plasma density ramp, the laser beam retains a minimum spot size. Self-focusing becomes stronger with a mild ripple as the propagation distance increases. The conditions for the ponderomotive self-focusing for suitable parameters of the laser beam and the plasma are determined. The plasma density ramp of the considered type may be observed in gas jet plasma experiments.

2

Resonator Transients of all Solid-State Cr: LiSAF and Nd:YVO4 Lasers-Generation of Single Short Laser Pulse

Van Hao N., Trong Nghia N., Khoa Quang N., Dai Hung N.

Computational Methods in Science and Technology

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2010

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Vol. spec. iss. (2)

xx-xx

EN

The resonator transients and, in particular, the phenomenon of relaxation oscillations of diode end-pumped solid-state Cr:LiSAF and Nd:YVO4 lasers have been investigated at 850 nm and 1064 nm, respectively. The obtained results allow to understand clearly the resonator transients and show a generation of single laser pulses from the Cr:LiSAF and Nd:YVO4 lasers at near-threshold pumping levels. By proper choices of solid-state laser resonator and pumping parameters, obtainable duration of single solid-state laser pulses is computationally studied to be in nanosecond range and much shorter than the diode laser pumping pulse (100 mi s). As a result, a technique of single short laser pulse generation at high repetition rate of diode pumping pulses has been experimentally demonstrated. In our Nd:YVO4 laser pumped by 100 mi s diode laser pulse, single laser pulses as short as 93 ns at 1064 nm and pulse repetition rate as high as 3 kHz has been produced. The superior limit (about 3 kHz) in repetition rate of single Nd:YVO4 laser pulse mainly resulted from the fluorescence lifetime of active ion Nd3+.

3

A Short Pulse Laser System to Detect Concentration of Polychloro-Dibenzodioxine, -Furans

Hoa D. Q., Hoang N. D., Imasaka T.

Computational Methods in Science and Technology

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2010

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Vol. spec. iss. (2)

xx-xx

EN

The method based on the multiphoton Ionization Mass Spectroscopy/Supersonic Jet (MPI-MS/SSJ) technique for determination of trace concentration of toxic organic substances in the air is studied and applied in many laboratories in the world. A short pulse laser system with Fourier transform – limited bandwidth is suitable to the alternatively ionization process of the cold molecules. The Distributed Feedback Dye Laser (DFDL) pumped by a Nd:YAG picosecond laser is setup and employed to this purpose. The short laser pulse of 12 ps, which is exactly adjusted to wavelength of 316.14 nm and 315.83 nm with bandwidth of 0.05 nm, is corresponding to detect polychlorodibenzofuran and polychlorodibezodioxine.