Principle for second- and third-order nonlinearities (2nd- and 3rd-NL) for generating vis-NIR white laser via CPPLN nonlinear crystal. (a) Bandwidth expansion of femtosecond lasers via 3rd-NL processes. (b) Simultaneous broadband SHG and THG via cascaded 2nd-NL QPM upconversion upon near-infrared pump femtosecond laser in CPPLN. (c) Synergic action of 2nd- and 3rd-NL for generating SHG and THG with much broadened bandwidth, leading to white laser with spectrum covering the whole visible band. (d) Schematic diagram of the structural geometry of a CPPLN structure. The up or down arrows indicate positive or negative domains, respectively, which enables upconversion of near-IR femtosecond into white laser. Under the pump of NIR femtosecond laser with arbitrary polarization, the CPPLN crystal can generate vis-NIR white laser. (e) Calculated distributions of the effective nonlinear coefficient as a function of the RLV for designed CPPLN sample. (f, g) Combined plots of the phase-mismatch curves for various three-wave mixing processes in a homogeneous LN crystal and the effective nonlinear coefficient curve for CPPLN structure in SHG and THG processes.