Dual Resonant Sum Frequency Generations from Two-Dimensional Materials

We propose dual resonant optical sum frequency generation (SFG), where the two most singular resonances could be selected, and report for the monolayer (1L-) WSe2 when one (omega(1)) of two excitation pulses is resonant to A exciton and their sum frequency (omega(1) + omega(2)) to D exciton. The dual resonant SFG confirms that, under an irradiation of re, and m2 pulses with the same fluence of similar to 1.4 X 10(10) W /m(2), its signal intensity could be enhanced about 20 times higher than the resonant SFIG (i.e., 2 omega(1) to the D excitonic absorption). Further, the dual resonant SFG intensity of lL-WSe2 is found to be 1 order of magnitude higher than the single resonant SFG intensity of 1L-WS2 under the same condition of two-pulse irradiation. Finally, observations of the dual resonant SFG are thoroughly examined using real-time time-dependent density functional theory (rt-TDDFT), and the relevant nonlinear optical characteristics are scrutinized using the Greenwood-Kubo formalism.