Abstract

Dispersive wave (DW) emission occurs when a laser pulse propagating in a Kerr nonlinear medium in presence of group-velocity dispersion (GVD) scatters through a resonant-like process to a shifted frequency [1]. It has recently been pointed out that DW emission may also arise during the interaction of co-propagating pulses, rather than from the instability of a single pulse, e.g. a weak seed and an intense pump. If the two pulses have different frequencies (and hence group velocities) the weak pulse may catch up with the intense pump and lead to a Cross-Pulse DW originating from the weak pulse (see e.g. [2]). This process is governed by a constant phase condition: D(ω_DW)=D(ω_seed) where D is the dispersion defined as: D(ω) = k(ω) − ω/v_p, with v_p the pulse group velocity. We have here considered the extreme case of a weak Terahertz pulse co-propagating with an intense 800 nm pulse in diamond [3]. According to the constant phase conditions, the expected blue-shifted emission should occur for a wavelength of nearly 425 nm, as shown in Fig. 1(a). A pseudospectral space domain (PSSD) algorithm [4] confirms this analytical prediction as shown in Fig 1(b), yet two signals appear in the blue-side of the spectrum. By decomposing the nonlinear contributions in the code we identify the 400 nm signal as the Electric Field Induced Second Harmonic (a known effect), and the 428 nm one as the Cross-Pulse DW.

© 2015 IEEE