Room temperature solid-state maser
Since its discovery, the laser has resulted in many innovations and become a ubiquitous technology. The maser (microwave amplification by stimulated emission of radiation), on the other hand, whilst instrumental to the laser’s birth, has not.
The maser’s relative obscurity to date has been due to the inconvenience of the operating conditions needed for its various realizations. Atomic and free-electron masers require vacuum chambers and pumping. Solid-state masers, though excelling as low-noise amplifiers and occasionally incorporated within ultra-stable oscillators, have required cryogenic refrigeration. Most realizations have also required strong magnets and/or magnetic shielding.
Overcoming these obstacles would pave the way for significant new innovations such as more sensitive chemical assays, more precise determinations of bio-molecular structure and function, and more accurate medical diagnostics (incl. tomography) based on enhanced magnetic resonance spectrometers incorporating maser amplifiers and oscillators. Here we report the first experimental demonstration of a solid-state maser operating at room temperature in pulsed mode. It works on a lab bench, in air, in the earth’s magnetic field and amplifies at around 1.45 GHz.
In contrast to the cryogenic ruby maser, its gain medium is an organic mixed molecular crystal, namely p-terphenyl doped with pentacene, where the latter species is photo-excited by yellow light. The maser’s pumping mechanism exploits spin-selective molecular intersystem crossing (ISC) into pentacene’s triplet ground state. When configured as an oscillator, the solid-state maser’s measured output power of around -10 dBm is approximately 100 million times greater than that of an atomic hydrogen maser, which oscillates nearby in frequency (~1.42 GHz).
By exploiting the high levels of spin polarization readily generated via ISC in photo-excited pentacene and other aromatic molecules, this new type of maser appears capable of amplifying with a residual noise temperature far below room temperature.