Diamonds continue to amaze
Department of Materials, Imperial College London
Tuesday 22 May
The solid-state maser, invented in the 1950s, had a far less impressive career than its younger sibling, the laser. This was mainly due to its dependence on cryogenic refrigeration and high-vacuum systems. Despite this, the maser found application in deep-space communications and radio astronomy due to its unparalleled performance as a low-noise amplifier and oscillator. In 2012, the first room-temperature solid-state maser was demonstrated, exploiting the photo-excited triplet state of organic pentacene molecules doped into a p-terphenyl host . Since then, this new class of maser has been miniaturized , characterized on nanosecond timescales  and shown to exhibit strongly coupled ensemble spin-photon polaritons . However, p-terphenyl has very poor thermal and mechanical properties, and the triplet sublevel decay rates of pentacene mean that only pulsed operation has been observed in this system to date. Alternative inorganic materials that contain spin-defects have been proposed as viable maser gain media, such as diamond [5,6] and silicon carbide .
In this talk, I will discuss how the organic solid-state room-temperature maser came about, its subsequent development and how the quest for continuous operation naturally led towards diamond and nitrogen-vacancy centres. I will conclude by reporting the recently demonstrated continuous-wave (CW) room-temperature maser oscillator using optically pumped charged nitrogen-vacancy (NV−) defect centres in diamond . This demonstration unlocks the potential of masers for use in a new generation of microwave devices that could find new applications in spectroscopy, medicine, security, sensing and quantum technologies.
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