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12 February 2008 Nanogap experiments for laser cooling
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Abstract
One of the challenges of laser cooling a semiconductor is its typically high index of refraction (greater than 3), which limits efficient light output of the upconverted photon. This issue is addressed with a novel concept of coupling the photon out via a thin, thermally insulating vacuum gap that allows light to pass efficiently by frustrated internal reflection. Although silicon technology is mature and inexpensive, the indirect nature of the bandgap of silicon makes it unsuitable for laser cooling. The material of choice is the binary compound semiconductor GaAs, which can be fabricated with high quality necessary for laser cooling experiments. Moreover, process technology exists that enables a relatively simple fabrication of a thin vacuum gap in this material system. This paper will present an investigation of heat transport and light transmission across a "nanogap" consisting of a thin epitaxial film supported over a substrate by an array of nanometer-sized posts. The structure is manufactured by crystal growth of a sacrificial Al0.98Ga0.02As layer on a single crystal GaAs substrate. After lithographically defining holes in the Al0.98Ga0.02As layer, the holes are filled with GaAs and a top GaAs layer is deposited. Lateral selective etching of the Al0.98Ga0.02As will create a nanogap between two GaAs layers separated by GaAs posts. We are demonstrating the successful fabrication of various size nanogaps in this material system, as well as their properties with respect to reduced heat transfer across the gap. We are also presenting data supporting that the interface quality is high enough to allow evanescent tunneling of light at angles otherwise forbidden by total internal reflection. The implications for semiconductor laser cooling will be discussed.
© (2008) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Andreas Stintz, Richard I. Epstein, Mansoor Sheik-Bahae, Kevin J. Malloy, Michael P. Hasselbeck, and Stephen T. P. Boyd "Nanogap experiments for laser cooling", Proc. SPIE 6907, Laser Refrigeration of Solids, 690709 (12 February 2008); https://doi.org/10.1117/12.761962
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