Cadmium sulfide (CdS) has been studied for decades due to a variety of applications from photovoltaic cells to solid state lasers owing to its direct bandgap of 2.42 eV (512 nm) and a high radiative quantum efficiency. Recently it has been considered to be a potential candidate for radiation balanced lasing. In particular, nanoribbons (NRs) of CdS have been claimed to laser cool at 514 and 532 nm wavelengths, due to annihilation of phonons to produce antistokes fluorescence near the bandgap. In an effort to verify the claim, we demonstrate a novel optomechanical experimental technique for micro-thermometry of a single CdS-NR where the material’s Young’s modulus is the primary temperature-dependent observable. The eigenfrequency of individual cantilevers is measured as a function of the laser irradiance by processing the time-dependent photovoltage of an avalanche photodiode. We observe a red-shift in the cantilever’s eigenfrequency with increasing laser power, suggesting net heating at low laser irradiances. However, a heating effect combined with possible laser trapping forces has been hypothesized for higher powers based on a modified Euler-Bernoulli elastic-beam model. The experimental cantilever heating results are supported by a heat transfer analysis to obtain the temperature distribution in the cantilever and the time required to reach steady state (<1ms). This thermometry technique can be used to probe the effects of laser irradiation on CdS cantilevers fabricated from thin films grown by pulsed laser deposition.
Anupum Pant, Bennett E. Smith, Xuezhe Zhou, Stuart Frazier, E. James Davis, and Peter J. Pauzauskie, "Optomechanical thermometry of cadmium sulfide nanoribbon cantilevers (Conference Presentation)," Proc. SPIE 10550, Optical and Electronic Cooling of Solids III, 105500D (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2290421.5751542932001.
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