Phase-matching effect on the second harmonic and terahertz generations in β-barium borate

Nonlinear optics is of fundamental importance for frequency conversion and nonlinear optical spectroscopy. For instance, the second harmonic (SH) and terahertz (THz) generations are commonly utilized as frequency-conversion methodologies, and they are also employed as spectroscopic approaches. SH is generated through frequency doubling and THz through optical rectification (OR) in β-barium borate (BBO). Although the frequency doubling and OR are second-order nonlinear optical processes resulting from the same second-order susceptibility tensor, these two processes generate waves in totally different wavelength ranges. It is also interesting to find out other differences between these two nonlinear optical processes. This paper theoretically and experimentally investigates how phase matching affects the SH and THz generations. The theoretical results successfully explain the experimental ones.