Large-Scale Spectral Broadening of Femtosecond Optical Parametric Oscillators by MoTe2 Films

Spectral broadening is desirable in optical parametric oscillators (OPOs) for their tunability and generation of short pulses, which typically entails more complex systems and increased costs. Here, we report large-scale spectral broadening through the simple insertion of a MoTe2 film into the cavity of a femtosecond OPO for the first time. The OPO offers a tunable output ranging from 1245 to 1552 nm, and comparable broadening effects are observed in most of the operating wavelengths. The broadest spectrum is achieved at 1524 nm by inserting a low-concentration 1T′-MoTe2 film, exhibiting a spectral broadening factor exceeding 22. Spectral broadening results in a time compression correspondingly. The narrowest pulse is obtained by using a low-concentration 2H-MoTe2 film with a pulse duration of 88 fs, and a temporal compression of 20 of pulse duration is obtained at 1417 nm. The experimental results show that the nonlinear properties and the film structure of MoTe2 induce a local modulation of the signal in the space–time domain, representing the main contribution to spectral broadening. This approach will offer new insights to enhance the practical application of 2D materials and benefit the development of OPO devices.