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A Closed-Cycle Optical Cryostat and Improved Optical Elements for Studies of Dissipation at the Molecular Scale

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Technical Report,01 Aug 2014,31 Jul 2015

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William Marsh Rice University Houston United States

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Simultaneous electronic and optical measurements provide a means of accessing microscopic information about the electronic and vibrational energy distributions in atomic- and molecular-scale systems driven out of equilibrium. These distributions and their evolution as a function of temperature, bias, and optical intensity are directly relevant to understanding the flow of energy and the origins of dissipation atthe nanoscale, a topic of direct interest to the DoD. In support of a full research proposal awarded by ARO, proposal 63808CH in September, 2013, we sought critical integrated upgrades to our Raman microscopy system. The first was acquisition of a closed-cycle cryocooled microscope cryostat system from Montana Instruments. The CryoStation allows optical and electronic measurements in high vacuum at sample temperatures down to 3 K, with no helium cost and vibrations limited to the few-nm scale. The instrument was integrated with our existing custom-built Raman microscope and software, previously demonstrated to allow single-molecule sensitivity Raman spectroscopy. The second component of our upgrade was a revamped ultranarrow optical notch filter and ultrastable laser source for measurements down to extremely low wave number Raman shifts. These upgrades have been incredibly valuable, and the new capabilities have transformed the way we are able to perform simultaneous electronic and optical measurements at the molecular scale.

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