Two-photon and three-photon excitation in GaN by spectrally broadband and few-cycle laser pulses

Abstract

Nonlinear interactions between ultrashort laser and semiconductors become increasingly important for frequency conversion, lightwave petahertz (PHz) photocurrent, or PHz electronic signal processing. Under the excitation of the spectrally broadband and few-cycle pulses, a complete characterization of multiple nonlinear processes in GaN is revealed in high temporal resolution, including coherent second (third) harmonics and multiphoton induced photoluminescence (MPL). Two-dimensional interferometric frequency-resolved autocorrelation and its Fourier transformed microscopy show that MPL dominates at GaN near-band-edge emission, which is attributed to the simultaneous two-photon and three-photon excitation within a spectrally broadband pulse. Spatial intensity fluctuations of these nonlinear signals are demonstrated as sensitive indicators of surface morphology and film quality.