Giant photothermal nonlinearity in a single silicon nanostructure

Abstract

Silicon photonics have attracted significant interest because of their potential in integrated photonics components and all-dielectric meta-optics elements. One major challenge is to achieve active control via strong photon–photon interactions, i.e. optical nonlinearity, which is intrinsically weak in silicon. To boost the nonlinear response, practical applications rely on resonant structures such as microring resonators or photonic crystals. Nevertheless, their typical footprints are larger than 10 μm. Here, we show that 100 nm silicon nano-resonators exhibit a giant photothermal nonlinearity, yielding 90% reversible and repeatable modulation from linear scattering response at low excitation intensities. The equivalent nonlinear index is five-orders larger compared with bulk, based on Mie resonance enhanced absorption and high-efficiency heating in thermally isolated nanostructures. Furthermore, the nanoscale thermal relaxation time reaches nanosecond. This large and fast nonlinearity leads to potential applications for GHz all-optical control at the nanoscale and super-resolution imaging of silicon.

Quantitative Imaging of Single Light-Absorbing Nanoparticles by Widefield Interferometric Photothermal Microscopy

“…The heated and nonheated samples scatter light differently due to at least two reasons. First, the heated light absorber itself may exhibit different optical properties due to thermal expansion and the change of refractive index. − Second, the absorbed light eventually generates heat that dissipates into the surrounding region of the particle, resulting in a change of optical properties of the local environment that is known as the thermal lens effect. − With proper design of the experiment, a laser point-scanning photothermal microscopy can be extremely sensitive: single metallic nanoparticles (as small as 1.4 nm) and single light-absorbing pigment molecules were successfully detected whose absorption cross sections were on the order of 10 –16 cm 2 .…”

All-dielectric thermonanophotonics

“…Remarkably, typical raising time of the thermal nonlinearity is governed by electron-phonon scattering timescale laying in the interval of 1-10 ps [210]. The relaxation time in this case is slower than for optically induced nonlinearities caused by Kerr effects [211] or free carriers [212,213] generation being usually about 1-100 ns [129] strongly depending on the thermal conductivity of surrounding medium.…”

“…VO 2 ) demonstrated considerably tunable scattering spectra owing to strong variation of optical properties of their surrounding media, [128] yielding temperature resolution around 1 K. Because of high thermo-refractive coefficients for such materials as silicon, light scattering from Si nanoparticles at high temperatures can be also used for nanothermometry with high spatial resolution. [129] In contrast to plasmonic nanoparticles, which are also demonstrated thermaldependent scattering behavior due to strong increase of imaginary part of metal dielectric permittivity [130], the all-dielectric approach might have higher potential because of more degrees of freedom related to thermal tunability of far-field response caused by the interplay between magnetic and electric Mie-like resonances.…”

“…Stronger laser-induced heating of silicon allowed more than +400% to -90% nonlinear deviation of scattering from a single Mie-resonant silicon nanoparticle under continuous-wave (CW) illumination via enhanced thermorefractive nonlinearity. [129] The nanostructure can exhibit a strong nonlinear response (saturation of scattering). With a Gaussian focus, the nonlinear response should start from the center of point-source function, and thus, by extracting the nonlinear part, the resulting point-source function becomes smaller than its linear counterpart.…”

Theory of Non-equilibrium "Hot" Carriers in Direct Band-gap Semiconductors Under Continuous Illumination

“…Our formulation provides a unique prediction for the partition between the two channels by which the electron/hole sub-system dissipates its energy, viz., interband recombination and energy transfer to the lattice via phonons. This is crucial for the correct prediction of semiconductor heating and associated photo-thermal nonlinearlity in SC nanostructures (for example, recently studied in Silicon nanostructures; notably an indirect band-gap SC), 70,71 quantification of the strength of PL, applications relying on these quantities such as thermometry and imaging, and most importantly, lighting applications of semiconductors. 29,72,73 Thus, we define η ph are quantitatively the same as that of the electrons).…”