In a general aspect, a system for generating radio frequency (RF) electromagnetic radiation includes a maser having a photonic crystal structure and a vapor. The photonic crystal structure is formed of dielectric material and includes an array of cavities having a defect region disposed therein and an elongated slot disposed in the defect region. The array of cavities and the elongated slot define a waveguide having a waveguide mode. The vapor is disposed in the elongated slot and includes one or more input electronic transitions and an output electronic transition coupled to the one or more input electronic transitions. The output electronic transition is operable to emit a target RF electromagnetic radiation and is resonant with the waveguide mode. The system also includes a laser system configured to provide input optical signals to the elongated slot and signal processing electronics in communication with the laser system.

In a general aspect, a system for generating radio frequency (RF) electromagnetic radiation includes a maser having a photonic crystal structure and a vapor. The photonic crystal structure is formed of dielectric material and includes an array of cavities having a defect region disposed therein and an elongated slot disposed in the defect region. The array of cavities and the elongated slot define a waveguide having a waveguide mode. The vapor is disposed in the elongated slot and includes one or more input electronic transitions and an output electronic transition coupled to the one or more input electronic transitions. The output electronic transition is operable to emit a target RF electromagnetic radiation and is resonant with the waveguide mode. The system also includes a laser system configured to provide input optical signals to the elongated slot and signal processing electronics in communication with the laser system.

In a general aspect, a photonic crystal maser includes a dielectric body having an array of cavities ordered periodically to define a photonic crystal structure in the dielectric body. The dielectric body also includes a region in the array of cavities defining a defect in the photonic crystal structure. An elongated slot through the region extends from a slot opening in a surface of the dielectric body at least partially through the dielectric body. The array of cavities and the elongated slot define a waveguide having a waveguide mode. The photonic crystal maser also includes a vapor or source of the vapor in the elongated slot and a laser configured to generate an optical signal capable of exciting one or more input electronic transitions of the vapor.

In a general aspect, a photonic crystal maser includes a dielectric body having an array of cavities ordered periodically to define a photonic crystal structure in the dielectric body. The dielectric body also includes a region in the array of cavities defining a defect in the photonic crystal structure. An elongated slot through the region extends from a slot opening in a surface of the dielectric body at least partially through the dielectric body. The array of cavities and the elongated slot define a waveguide having a waveguide mode. The photonic crystal maser also includes a vapor or source of the vapor in the elongated slot and a laser configured to generate an optical signal capable of exciting one or more input electronic transitions of the vapor.

Some variations provide an atomic vapor-cell system comprising: a vapor-cell region configured with vapor-cell walls for containing an atomic vapor; and a coating disposed on at least some interior surfaces of the walls, wherein the coating comprises magnesium oxide, a rare earth metal oxide, or a combination thereof. The atomic vapor-cell system may be configured to allow at least one optical path through the vapor-cell region. In some embodiments, the coating comprises or consists essentially of magnesium oxide and/or a rare earth metal oxide. When the coating contains a rare earth metal oxide, it may be a lanthanoid oxide, such as lanthanum oxide. The atomic vapor-cell system preferably further comprises a device to adjust vapor pressure of the atomic vapor within the vapor-cell region. Preferably, the device is a solid-state electrochemical device configured to convey the atomic vapor into or out of the vapor-cell region.

Masing at room temperature is achieved by an apparatus and method that utilize a microwave cavity which exhibits a resonance of sufficiently high Q-factor for maser oscillation, and a resonator structure comprising a masing medium located within a resonant element. The masing medium comprises spin-defect centres. The resonator structure is disposed within the microwave cavity. A magnetic field is applied across the masing medium. An input of microwave radiation to be amplified is coupled to the resonator structure. An optical pump pumps the masing medium, thereby causing stimulated emission of microwave photons. The microwave cavity has an effective magnetic mode volume matching the volume of the masing medium.

In a general aspect, a vapor cell is presented that includes a dielectric body. The dielectric body has a surface that defines an opening to a cavity in the dielectric body. The vapor cell also includes a vapor or a source of the vapor in the cavity of the dielectric body. An optical window covers the opening of the cavity and has a surface bonded to the surface of the dielectric body to form a seal around the opening. The seal includes metal-oxygen bonds formed by reacting a first plurality of hydroxyl ligands on the surface of the dielectric body with a second plurality of hydroxyl ligands on the surface of the optical window.

In a general aspect, a vapor cell is presented that includes a dielectric body. The dielectric body has a surface that defines an opening to a cavity in the dielectric body. The vapor cell also includes a vapor or a source of the vapor in the cavity of the dielectric body. An optical window covers the opening of the cavity and has a surface bonded to the surface of the dielectric body to form a seal around the opening. The seal includes metal-oxygen bonds formed by reacting a first plurality of hydroxyl ligands on the surface of the dielectric body with a second plurality of hydroxyl ligands on the surface of the optical window.

Masing at room temperature is achieved by an apparatus and method that utilize a microwave cavity which exhibits a resonance of sufficiently high Q-factor for maser oscillation, and a resonator structure comprising a masing medium located within a resonant element. The masing medium comprises spin-defect centres. The resonator structure is disposed within the microwave cavity. A magnetic field is applied across the masing medium. An input of microwave radiation to be amplified is coupled to the resonator structure. An optical pump pumps the masing medium, thereby causing stimulated emission of microwave photons. The microwave cavity has an effective magnetic mode volume matching the volume of the masing medium.

Low power MASER (Microwave Amplification by Stimulated Emission of Radiation) radiation is used to non-invasively record molecular activity in a biological object such as a brain. Low power MASER radiation is also used to neuromodulate molecular targets via Rabi coupling, resulting for example in conformational and function change in specific molecular targets such as ligand-gated ion channels, voltage-gated ion channels, G-proteins, or dopamine receptors. The method can be used to change the energy state of targeted molecules via energization or enervation, or to ablate targeted molecules.