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Temporally Resolving Synchronous Degenerate and Nondegenerate Two‐Photon Absorption in 2D Semiconducting Monolayers
Author(s) -
Cui Qiannan,
Li Yuanyuan,
Chang Jianhua,
Zhao Hui,
Xu Chunxiang
Publication year - 2019
Publication title -
laser and photonics reviews
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.778
H-Index - 116
eISSN - 1863-8899
pISSN - 1863-8880
DOI - 10.1002/lpor.201800225
Subject(s) - degenerate energy levels , monolayer , femtosecond , absorption (acoustics) , materials science , two photon absorption , physics , molecular physics , optics , optoelectronics , laser , nanotechnology , quantum mechanics
Abstract Degenerate and nondegenerate two‐photon absorption (TPA) in WS 2 and MoSe 2 monolayers are synchronously induced and temporally resolved by femtosecond laser pump‐probe. Differential transmission signals in the first 500 fs consist of negative and positive components, that originate from direct probe depletion via nondegenerate TPA and carrier accumulation via degenerate TPA, respectively. Temporal cross‐correlation of pump and probe pulses allows us to fully decouple the ultrafast nondegenerate and degenerate TPA signals. Subsequently, degenerate and nondegenerate TPA coefficients are calculated as a function of pump irradiance. Under nonresonant pumping, 100 ± 10 and 250 ± 25 cm GW −1 are obtained for degenerate and nondegenerate TPA coefficients of monolayer WS 2 , respectively, which both present linearly decreasing trends as increasing pump irradiances. However, under resonant pumping of 2 p excitonic states in monolayer MoSe 2 , degenerate TPA coefficients exponentially decrease from 800 to 80 cm GW −1 as increasing pump irradiances, due to the interplay between band‐renormalization and band‐filling effects, while nondegenerate TPA coefficient is about 650 ± 50 cm GW −1 . For comparison, a trilayer MoSe 2 is also investigated. These results set a foundation for precisely measuring TPA coefficients and actively controlling nonlinear excitonic dynamics via TPA in 2D semiconducting monolayers.