摘要: Ultrafast modulation of light is of great importance in optical communications, optical spectroscopy, precision measurement and so on. To achieve better modulation performance, various materials platforms including photonic crystals, two-dimensional materials and plasmonic metasurfaces have been extensively explored. In this work, we demonstrate that a thin β-BaB₂O₄ which has wide band transparence and large nonlinear coefficient can be used to realize ultrafast modulation of second harmonic waves (SHWs). Under the pumping of two femtosecond laser pulses with perpendicular polarizations and variable time delay, the modulation of SHWs exhibits either slow or fast varying characteristics by using the concept of polarization selective interferometric autocorrelation. Interestingly, these two kinds of modulation behaviors depend on the real and imaginary parts of the pulse-width parameter of the chirped laser pulse. The observed physical mechanism is then utilized to generate and modulate the SHWs carrying orbital angular momentum. The proposed strategy in this work may have important applications in parallel ultrafast optical information processing and optical computing.