[Show abstract][Hide abstract] ABSTRACT: Energy exchange between two filament-forming pulses with initially free chirp in air was experimentally studied. It occurs because of the change of delayed nonlinear refractive index, which slightly chirps the incident filament-forming laser pulses. Accompanying energy exchange process, spectral characteristics of output laser pulses shows dramatic blueshift and supercontinuum generation. Nonlinear absorptive effect introduces an inbalance between energy exchange at the negative delays and that at the positive delays, and affects the energy exchange efficiency. These results may provide a more comprehensive understanding of energy exchange process between filament-forming laser pulses.
[Show abstract][Hide abstract] ABSTRACT: We experimentally demonstrate energy exchange up to 32% between a probe femtosecond beam and two pump ones as the probe filament interacted with an one-dimensional plasma grating formed by two pump ones as they spatiotemporally overlapped and experienced filamentation in air. A two-dimensional plasma grating would be built when three pulses overlapped, which elongates the energy exchange process in an extent. The lifetime of energy exchange is up to 100 picoseconds, corresponding to the decay time of plasma grating. The energy exchange ratio increased when the energy of the probe pulse and pump ones approached. PACS numbers: 52.38.Hb, 42.65.Jx, 42.60.Fc, 42.65.Sf Femtosecond filamentation in air is an interesting phenomenon 1 , and has intensively applications includ-ing few-cycle pulse generation 4 , THz radiation 3 , lighting 5 and discharge triggering 6 , remote-sensing of atmospheric pollution 2 . Recently, much attention has been given to the interaction between few crossing filaments. Because laser field interference, a one-dimensional plasma grating is formed in the intersection region when two noncollinear filamentary pulses overlap in time and space. In addi-tion, A two-dimensional plasma grating can be formed when three laser pulses spatiotemporal overlapped. This plasma grating plays an important role in the inter-action between filaments. For instance, the traveling plasma grating formed at the intersection of two fila-mentary pulses with slightly different central frequency is responsible for an efficient energy exchange between the filaments 7 . Energy exchange between two laser beams has been demonstrated in several experiments including filamentation in air and liquid methanol 7,9–11 . It has been found that the direction of energy transfer depends on the relative time delay between filamentary pulses, the chirp and the laser intensity. In addition, it oscillates at increments of an optical period (2.6 fs) in the rela-tive time delay 10 , and an fine spectral structure of en-ergy transfer was observed by using 12 fs laser pulses 11 . All these works were done by using two femtosecond pulses filamentation and the presence of one-dimensional plasma grating. In this letter, we experimentally study the filamen-tary coupling between a delay-tuned probe beam and two delay-fixed pump beams, keeping in mind potential ap-plications to atmospheric sensing. Our results are con-sistent with those of previous works demonstrating en-ergy coupling between two filaments in air and liquid methanol, when the relative delay between the delay-tuned probe beam and the two delay-fixed pump ones a) Electronic mail: email@example.com
[Show abstract][Hide abstract] ABSTRACT: A plasma grating is formed by two femtosecond filaments, and the influence of probe filament on the plasma grating is shown. By using the plasma grating, the enhancement of the third harmonic (TH) generated from the probe filament is studied, and more than three orders of magnitude enhancement of TH generation is demonstrated as compared with that obtained from a single filament. The dependences of TH generation on the time delay, the spatial period of plasma grating, the relative polarization and the crossing position between the probe beam and the two pump beams are investigated. The spectral broadening of TH generated from the probe filament induced by the interaction between the probe filament and the plasma grating is also studied.