Silicon carbide (SiC), which is the leading representative of the third-generation of semiconductors, possesses many excellent physical properties. However, its advantages also incur difficulties in processing, which calls for special processing techniques, such as femtosecond laser machining. In addition, SiC has shown unprecedented potential for optoelectronic applications. Knowledge of the nonlinear absorption coefficient and the nonlinear refractive index coefficient of SiC is required in both of the fields. In this work, the nonlinear absorption coefficient and the nonlinear refractive index coefficient of semi-insulating (SI) 6H-SiC and SI 4H-SiC, the most pervasive SiC polytypes, are measured in an extensive spectral range from 400 nm to 1000 nm with the Z-scan technique. Besides, the spectral dependence of the nonlinear optical properties is analyzed, facilitated by linear absorption spectrum. Especially, two-photon absorption (2PA) and three-photon absorption (3PA) coefficients of SI 6H-SiC and SI 4H-SiC are characterized in the respective spectral ranges. From the characterization of SiC, we can observe self-focusing phenomenon for nonlinear refraction. In the end, we unravel the potential of SiC for ultrafast all-optical switching based on the measured nonlinear optical properties.
Silicon carbide (SiC) is one of the most promising wide-band gap semiconductors for future technological applications, with the potential for high-temperature and low-loss photonic devices. In this study, we investigated the ultrafast visible light all-optical switching in 6H-SiC, in which nondegenerate two-photon absorption appeared to be dominant. Using an 820 nm femtosecond laser beam as the modulation source, differential transmission on the order of 10% was achieved across the visible spectrum from 420 to 720 nm with the highest modulation depth reaching 27%. The dependence of the optical switching performance on wavelength, fluence, and polarization has been illustrated and analyzed in details. Our results provide an in-depth guideline for exploring SiC, of which the nonlinear optical properties could help to realize ultrafast all-optical switching devices in the visible regime.
Laser direct writing (LDW) is a promising approach for fabricating metallic micropatterns on transparent substrates for transparent electronic circuits that satisfy both electronic and optical criteria. However, high efficiency and precision patterning remain a challenge for both photochemical and photothermal LDW. Herein, a novel method is proposed with a femtosecond laser to achieve a highly‐efficient photothermal process via single‐photon absorption by photosensitive particles (SPA‐FsLDW). The dispersive photosensitive particles act as numerous heating sources, enabling simultaneous multiple‐location photothermal reactions and highly‐efficient metallization due to heat‐induced metal ion reduction. The new approach effectively exploits the excellent heat‐input regulation with the ultrashort pulse of the femtosecond laser to achieve great temperature controllability and precision. It is shown that, with a deposition rate of ≈107 µm3 s−1 and electrical resistivity of ≈10−7 Ω m, SPA‐FsLDW improves efficiency and electrical resistivity by at least one order of magnitude compared to previously reported FsLDW. A self‐powered sensor is fabricated using SPA‐FsLDW, demonstrating its practical applicability.
Transient grating spectroscopy (TGS) based on diffraction gratings is a powerful optical method for studying the transport of energy carriers such as phonons and electrons. The diffraction grating in a TGS system is a key component to form a large-area interference pattern, i.e., transient grating, and to study the mean free path distribution of energy carriers. In this work, a design method for polarization-insensitive diffraction gratings with periods in the range 2–50 µm for TGS by a combination of rigorous coupled wave analysis and genetic algorithm was discussed. The method was tested for pump/probe wavelength of 515/532 or 1030/808 nm. Each ±1st diffraction order carries 35%–40% of the incident energy and the diffraction efficiencies of the other orders are lower than 10%. The optimized diffraction gratings were fabricated by a combination of photolithography and inductively coupled plasma etching, with the processing parameters introduced in detail, and their optical characteristics were evaluated. Finally, as a demonstration, the diffraction gratings for 1030/808 nm were applied to TGS to study the thermal transport properties of Ge. This work provides a useful guide for future applications and the development of TGS.
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