Abstract
Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. Advanced functionalities are enabled by modulation of the harmonic generation efficiency, which can be achieved with electrical or all-optical triggers. Electrical control of the harmonic generation efficiency offers large modulation depth at the cost of low switching speed, by contrast to all-optical nonlinear devices, which provide high speed and low modulation depth. Here we demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration. This result arises from a combination of D3h crystal symmetry and the deep subwavelength thickness of the sample, it can therefore be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms.
Highlights
Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization
Second-harmonic generation (SHG) is a second-order nonlinear process widely used for frequency conversion, self-referencing of frequency combs[2], crystal symmetry and Rashba effect studies[3,4], sensing[5], interface spectroscopy[6] and ultrashort pulse characterization[7]
Large efforts have been devoted to the integration of nonlinear crystals such as lithium niobate[8,9], or to symmetry breaking in Si and Si3N4, for instance, via strain[10], electric fields[11] or the photogalvanic effect[12]
Summary
Second-harmonic generation is of paramount importance in several fields of science and technology, including frequency conversion, self-referencing of frequency combs, nonlinear spectroscopy and pulse characterization. We demonstrate all-optical modulation of second-harmonic generation in MoS2 with a modulation depth of close to 100% and speed limited only by the fundamental pulse duration This result arises from a combination of D3h crystal symmetry and the deep subwavelength thickness of the sample, it can be extended to the whole family of transition metal dichalcogenides to provide great flexibility in the design of advanced nonlinear optical devices such as high-speed integrated frequency converters, broadband autocorrelators for ultrashort pulse characterization, and tunable nanoscale holograms. This approach offers high modulation speed and is limited in principle only by the excited state/exciton lifetime (approximately tens of picoseconds); the largest depth in all-optical SHG modulation reported[29] so far in TMDs is 55%, with a strong dependence on the excitation wavelength and fluence This scheme for all-optical SHG modulation is only effective for excitation and frequency conversion above-gap or at excitonic resonances and it is not applicable for below-gap excitation, leading to a naturally limited spectral bandwidth
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