Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances

R. Fenollosa; F. Ramiro-Manzano; M. Garín; R. Alcubilla

doi:10.1021/acsphotonics.9b01513

Research · Publication & note

Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances

Journal article

R. Fenollosa, F. Ramiro-Manzano, M. Garín and R. Alcubilla

ACS Photonics Volume 6 Issue 12 3174–3179 2019

Abstract

Planck’s law constitutes one of the cornerstones in physics. It explains the well-known spectrum of an ideal blackbody consisting of a smooth curve, whose peak wavelength and intensity depend on the temperature of the body. This scenario changes drastically, however, when the size of the emitting object is comparable to the wavelength of the emitted radiation. Here we show that a silicon microsphere (2–3 μm in diameter) heated to around 800 °C yields a thermal emission spectrum consisting of pronounced peaks that are associated with Mie resonances. We experimentally demonstrate in the near-infrared the existence of modes with an ultrahigh quality factor, Q, of 400, which is substantially higher than values reported so far, and set a new benchmark in the field of thermal emission. Simulations predict that the thermal response of the microspheres is very fast, about 15 μs. Additionally, the possibility of achieving light emission above the Planck limit at some frequency ranges is envisaged.

How to cite

Initials first

R. Fenollosa, F. Ramiro-Manzano, M. Garín and R. Alcubilla. Thermal emission of silicon at near-infrared frequencies mediated by Mie resonances. ACS Photonics 6(12), 3174–3179 (2019). DOI: 10.1021/acsphotonics.9b01513.

Family name first

Fenollosa, R., Ramiro-Manzano, F., Garín, M., & Alcubilla, R. (2019). Thermal emission of silicon at near-infrared frequencies mediated by Mie resonances. ACS Photonics, 6(12), 3174–3179. https://doi.org/10.1021/acsphotonics.9b01513

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Figures

Figure 1 from Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances — **Figure 1.** Experimental setup and FEM simulation of the temperature distribution and time response of the heating process of a silicon microsphere from room temperature to 750 °C. (a) Schematic of the setup utilized for the experiments, showing how a silicon microsphere supported on a SiO₂ substrate in air is heated by a blue laser and the thermal emission spectrum is collected at a plane parallel to the substrate. (b) Heating (black curve) and cooling (red curve) time evolution of the average temperature of the microsphere upon starting and stopping respectively the irradiation with the blue laser. (c) Cross section view at different scales of the temperature distribution at steady state condition.

Figure 2 from Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances — **Figure 2.** Thermal emission spectra of silicon microspheres. (a) Measured spectrum in the NIR for a 3595 nm diameter (Φ) silicon microsphere (black curve in right panel). It agrees with that spectrum obtained from fitting the experimental data to eq 1 (red curve) with a fitted temperature of 756 °C (see Table 1). The calculation indicates that the emission occurs in a much wider range of wavelengths toward the MIR (left panel), and it can reach intensities above the Planck limit (blue curve) at some frequency ranges. The spectra have been plotted against the size parameter, defined as (πΦ/λ), and wavelength. (b) The same as (a) but for a 2308 nm diameter silicon microsphere with a fitted temperature of 841 °C.

Figure 3 from Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances — **Figure 3.** Optical absorption parameters for silicon at high temperature. The green curve corresponds to the imaginary part of the refractive index at 756 °C, the temperature of the measurement of Figure 2a. It was obtained from the total absorption coefficient (black curve), which has two main contributions: band gap (blue curve) and free carriers (red curve) that are originated by the temperature and by the pumping laser. For comparison, the dashed red curve shows the absorption produced by the free carriers associated only with temperature. The position of the band gap, E_g, at 756 °C is indicated.

Figure 4 from Thermal Emission of Silicon at Near-Infrared Frequencies Mediated by Mie Resonances — **Figure 4.** Demonstration of a resonance tuning by temperature and its high Q. (a) Measured resonance TE_10,5 of the microsphere of Figure 2a at 756 °C (red dots) and at 792 °C (black dots). The continuous curves correspond to Lorentzian fits that yield a Q of 400 ± 40 in both cases. (b) Electric field intensity distribution of the mode at the resonance plane.