Fig. 1. Schematic experimental setup. Beam splitters (not shown) separated the laser pulses into three pulses, denoted as the pump, seed, and probe. The forward 353.8 nm radiation was recombined with the probe pulse by a dichroic mirror (DM).

Fig. 2. Dependence of 353.8 nm signal intensity as a function of the rotation angle of the quarter wave-plate. The angles 0° and 45° correspond to circular polarization and linear polarization, respectively.

Fig. 3. Amplified spectra of the seed pulse inside nitrogen plasma. The spectrum of seed pulse and that from pump pulse are also presented, multiplied by a factor of 100 for visibility.

Fig. 4. Dependence of 353.8 nm signal intensity on gas pressure without seeding and with seeding.

Fig. 5. Dependence of 353.8 nm signal intensity on the time delay between the pump and seed pulses for different gas pressures.

Fig. 6. (a) Temporal profile of the amplified 353.8 nm signal for different gas pressures. (b) Dependence of pulse delay, pulse width, and peak intensity on gas pressure.