Abstract

For second-harmonic generation (SHG) the phase mismatch is given by Δk=k₂-2k₁ For Δk>>0 a large negative Kerr-like nonlinear phase shift may be induced on the fundamental wave (FW). This self-defocusing nonlinearity together with normal dispersion may compress a pulse, and problems normally encountered due to self-focusing in cubic media are avoided. Thus, having no power limit, in bulk media a self-defocusing soliton compressor can create high-energy near single-cycle fs pulses [1]. Here we present a theoretical and numerical investigation of pulse- compression in a nonlinear crystal. We introduce an SHG soliton number and show that compression only takes place when it is larger than the “usual” Kerr soliton number. This can be achieved by adjusting Ak, but only if the quadratic material nonlinearity is sufficiently stronger than the cubic Kerr nonlinearity. Also the group-velocity mismatch (GVM) between the FW and second harmonic (SH), given by the inverse group velocity difference d_u=1/v_g1-1/v_g2, limits the compression regime [la,lc]. We show that in a typical nonlinear crystal, efficient, good-quality compression down to <2 optical cycles may be observed when optimizing Ak within the compression regime.

© 2007 IEEE