Giant Two-Photon Absorption in Monolayer MoS2

TL;DR

This paper demonstrates that monolayer MoS2 exhibits a giant two-photon absorption effect with high damage threshold, contrasting with saturable absorption in multilayer MoS2, revealing its potential for nonlinear optical applications.

Contribution

It reports the first observation of giant two-photon absorption in monolayer MoS2 and compares its nonlinear optical properties with multilayer MoS2.

Findings

Monolayer MoS2 shows a giant TPA coefficient larger than conventional semiconductors.

Two-photon pumped luminescence is directly observed in monolayer MoS2.

Monolayer MoS2 has a higher laser damage threshold than multilayer MoS2.

Abstract

Strong two-photon absorption (TPA) in monolayer MoS2 is demonstrated in contrast to saturable absorption (SA) in multilayer MoS2 under the excitation of femtosecond laser pulses in the near infrared region. MoS2 in the forms of monolayer single crystal and multilayer triangular islands are grown on either quartz or SiO2/Si by employing the seeding method through chemistry vapor deposition. The nonlinear transmission measurements reveal that monolayer MoS2 possesses a giant nonsaturation TPA coefficient, larger than that of conventional semiconductors. As a result of TPA, two-photon pumped frequency up-converted luminescence is observed directly in the monolayer MoS2. For the multilayer MoS2, the SA response is demonstrated with the ratio of the excited-state absorption cross section to ground-state cross section of 0.18. In addition, the laser damage threshold of the monolayer MoS2 is 97 GW/cm2, larger than that of the multilayer MoS2 of 78 GW/cm2.