Ultrashort pulse collapse in quadratic media

Experimental studies on spatiotemporal collapse of ultrashort pulse propagation in quadratic nonlinear media are reviewed. Two-dimensional multicolored transverse arrays are experimentally observed in a quadratic nonlinear medium based on cascaded non-collinearly quadratic couplings and spatial breakup of input pump beams. Furthermore, two-dimensional multicolored up-converted parametric amplifications are realized with preserved coherence. The observed two-dimensional arrays can be controlled by changing the boundary condition with a weak second harmonic beam along with the strong fundamental-wave pump pulses. As a result of spatiotemporal collapse of femtosecond pulses, colored conical emissions are observed under strong phase-matched fundamental pump, which are further amplified to support tunable broadband femtosecond pulse generation.