Extremely nondegenerate two-photon absorption in direct-gap semiconductors [Invited]

Abstract

Two-photon absorption (2PA) spectra with pairs of extremely nondegenerate photons are measured in several direct-gap semiconductors (GaAs, CdTe, ZnO, ZnS and ZnSe) using picosecond or femtosecond pulses. In ZnSe, using photons with a ratio of energies of ~12, we obtain a 270-fold enhancement of 2PA when comparing to the corresponding degenerate 2PA coefficient at the average photon energy (ηω1 + ηω2)/2. This corresponds to a pump photon energy of 8% of the bandgap. 2PA coefficients as large as 1 cm/MW are measured. Thus, by using two widely different wavelengths we are able to access the large 2PA observed previously only in narrow gap semiconductors. We also calculate the corresponding enhancement of nonlinear refraction, consisting of two-photon, AC-Stark and Raman contributions. The net effect is a smaller enhancement, but exhibits very large dispersion within the 2PA regime.

Nonlinear optics of two‐dimensional transition metal dichalcogenides

“…It was reported that monolayer MoS 2 had the TPA coefficient of 7.62 × 10 3 cm/GW, and a TPA coefficient of 1 × 10 4 cm/GW was reported in 1 to 3 layers WS 2 . The reported TPA coefficient is 10 3 to 10 4 order higher than the conventional bulk semiconductors such as GaAs, CdS, and ZnO . The giant TPA in few layers TMDs is attributed to the 2D confinement, band edge resonance, and strong excitonic effect.…”

“…115 The reported TPA coefficient is 10 3 to 10 4 order higher than the conventional bulk semiconductors such as GaAs, CdS, and ZnO. 140 The giant TPA in few layers TMDs is attributed to the 2D confinement, band edge resonance, and strong excitonic effect. The TPA coefficient decreases with increasing layer numbers ( Figure 3D).…”

Nondegenerate two-photon absorption in GaAs/AlGaAs multiple quantum well waveguides

“…(C4)). With this experimental support for our model, we can re-examine ND-2PA for extremely nondegenerate photon pairs [17,18,38]. Fig.…”

Temporally Resolving Synchronous Degenerate and Nondegenerate Two‐Photon Absorption in 2D Semiconducting Monolayers

“…Besides high light intensity applications, nondegenerate TPA of 2D semiconducting monolayers are potentially important for subband photodetections involving extremely low light intensity. Previously, it has been demonstrated that performances of infrared detections with traditional semiconductors of wide band gap via nondegenerate TPA were comparable to or even better than that of commercial infrared detectors via one‐photon absorption . For instance, Fishman et al.…”

“…Previously, it has been demonstrated that performances of infrared detections with traditional semiconductors of wide band gap via nondegenerate TPA were comparable to or even better than that of commercial infrared detectors via one-photon absorption. [38][39][40] For instance, Fishman et al have realized sensitive detection of weak midinfrared radiation in GaN via nondegenerate TPA of a gated visible photon and an infrared photon, [39] facilitated by strongly enhanced nondegenerate TPA coefficients. Comparing with traditional semiconductors, intense excitonic resonances of 2D semiconducting monolayers are expected to further enhance nondegenerate TPA coefficients, making them promising candidates of novel subband photodetectors.…”