Abstract: In a general aspect, a vapor cell includes a body defined by a stack of layers that includes electrically conductive layers and electrically insulating layers. The stack of layers are bonded to each other and have first and second end layers at respective opposite ends of the body. The stack of layers also has intermediate layers between the first and second end layers that define an internal cavity of the body. The internal cavity extends through the body between the first and second end layers and includes a vapor or a source of the vapor disposed therein. Adjacent electrically conductive layers are separated by at least one electrically insulating layer. Moreover, each electrically conductive layer defines an electrode of the vapor cell and includes a contact surface on an exterior side of the body. The contact surface defines an electrical contact of the electrode.

Abstract: In a general aspect, radio frequency (RF) electromagnetic radiation can be detected using vapor cell sensors. In some aspects, a system includes a laser system that is configured to generate laser signals that comprise first and second laser signals. The system also includes an optical comb generator and a vapor cell sensor. The optical comb generator is configured to generate a comb spectrum based on the first laser signal. The comb spectrum includes comb lines at respective comb frequencies. The vapor cell sensor contains a vapor and is configured to generate an optical spectrum based on interactions of the vapor with the comb spectrum and the second laser signal. The system also includes an optical detector that is configured to detect the property of the optical spectrum at one or more of the comb frequencies.

Abstract: In a general aspect, a system for sensing pulses of radio frequency (RF) fields includes a laser system and a vapor cell sensor. The laser system is configured to generate beams of light that include a probe beam of light. The vapor cell sensor has a vapor therein and is configured to allow the beams of light to pass through the vapor. The system also includes an optical detector configured to generate a detector signal based on the probe beam of light. The system includes a signal processing system configured to perform operations that include receiving the detector signal from the optical detector over a time period. The operations also include generating a digital signal based on the detector signal and applying a matched filter to the digital signal to generate a filtered signal. The filtered signal is processed to determine properties of an RF field experienced by the vapor.

Abstract: In a general aspect, a method includes interacting a beam of light with a vapor in a vapor cell. The vapor cell includes a body defined by a stack of layers that includes electrically conductive layers and electrically insulating layers. The stack of layers are bonded to each other and have first and second end layers at respective opposite ends of the body. The stack of layers also has intermediate layers between the first and second end layers that define an internal cavity of the body. A vapor is disposed in the internal cavity. The method includes applying respective voltages to one or more electrodes to alter an electric field in the internal cavity. The method also includes measuring one or both of an ion signal based on charged particles in the vapor and an optical property of the beam of light after interacting with the vapor.

Abstract: In a general aspect, radio frequency (RF) electromagnetic radiation can be detected using vapor cell sensors. In some aspects, a system includes a laser system that is configured to generate laser signals that comprise first and second laser signals. The system also includes an optical comb generator and a vapor cell sensor. The optical comb generator is configured to generate a comb spectrum based on the first laser signal. The comb spectrum includes comb lines at respective comb frequencies. The vapor cell sensor contains a vapor and is configured to generate an optical spectrum based on interactions of the vapor with the comb spectrum and the second laser signal. The system also includes an optical detector that is configured to detect the property of the optical spectrum at one or more of the comb frequencies.

Abstract: In a general aspect, a radar system includes a vapor cell sensor system and a radio frequency (RF) optic. The vapor cell sensor system includes a vapor cell sensor, and the RF optic is configured to direct an RF field onto the vapor cell sensor. The RF field includes one or more RF pulses that define a radar signal. The radar system also includes a signal processing system configured to perform operations that include generating a digital signal based on a signal from the vapor cell sensor system. The digital signal represents a measured response of the vapor to the RF field over a time period. The operations also include applying a matched filter to the digital signal to generate a filtered signal and processing the filtered signal to determine properties of the RF field sensed by the vapor cell sensor over the time period.

Abstract: In a general aspect, a radar system includes a vapor cell sensor system and a radio frequency (RF) optic. The vapor cell sensor system includes a vapor cell sensor, and the RF optic is configured to direct an RF field onto the vapor cell sensor. The RF field includes one or more RF pulses that define a radar signal. The radar system also includes a signal processing system configured to perform operations that include generating a digital signal based on a signal from the vapor cell sensor system. The digital signal represents a measured response of the vapor to the RF field over a time period. The operations also include applying a matched filter to the digital signal to generate a filtered signal and processing the filtered signal to determine properties of the RF field sensed by the vapor cell sensor over the time period.

Abstract: In a general aspect, a laser system includes a laser and a frequency comb generator system. The laser is configured to generate a laser signal, and the frequency comb generator system is configured to generate a frequency comb based on the laser signal. The frequency comb includes frequency comb signals at respective comb frequencies. The laser system also includes a frequency comb dispersion system configured to spatially separate the frequency comb signals onto respective optical channels of the frequency comb dispersion system. The laser system additionally includes a frequency selector system configured to generate a selected frequency signal from the frequency comb signals after separation. The selected frequency signal includes a target separated frequency comb signal. The laser system also includes a frequency shifter configured to alter the selected frequency signal toward a target output frequency of the laser system.

Abstract: In a general aspect, a communication system comprises a first station and a second station. The first station includes a photonic crystal maser, a laser subsystem, and a tracking subsystem. A photonic crystal structure of the photonic crystal maser is formed of dielectric material and has an array of cavities and an elongated slot. The elongated slot is disposed in a defect region of the array of cavities. The photonic crystal maser also includes a vapor disposed in the elongated slot and operable to emit a target RF electromagnetic radiation in response to receiving an optical signal. The array of cavities and the elongated slot define a waveguide configured to form the target RF electromagnetic radiation, when emitted, into a beam. The second station includes a receiver configured to couple to the beam of target RF electromagnetic radiation.

Abstract: 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 elongated slot and the array of cavities define a waveguide of the dielectric body. The dielectric body additionally includes an input coupler aligned with an end of the elongated slot and configured to couple a reference radiofrequency (RF) electromagnetic radiation to the waveguide. The photonic crystal maser also includes a vapor or source of the vapor in the elongated slot and an optical window covering the elongated slot.

Abstract: In a general aspect, a method is presented for increasing the measurement precision of an optical instrument. The method includes determining, based on optical data and environmental data, a measured value of an optical property measured by the optical instrument. The optical instrument includes an optical path and a sensor configured to measure an environmental parameter. The method also includes determining a predicted value of the optical property based on a model representing time evolution of the optical instrument. The method additionally includes calculating an effective value of the optical property based on the measured value, the predicted value, and a Kalman gain. The Kalman gain is based on respective uncertainties in the measured and predicted values and defines a relative weighting of the measured and predicted values in the effective value.

Abstract: In a general aspect, a method is presented for increasing the measurement precision of an optical instrument. The method includes determining, based on optical data and environmental data, a measured value of an optical property measured by the optical instrument. The optical instrument includes an optical path and a sensor configured to measure an environmental parameter. The method also includes determining a predicted value of the optical property based on a model representing time evolution of the optical instrument. The method additionally includes calculating an effective value of the optical property based on the measured value, the predicted value, and a Kalman gain. The Kalman gain is based on respective uncertainties in the measured and predicted values and defines a relative weighting of the measured and predicted values in the effective value.

Abstract: In a general aspect, a communication system comprises a first station and a second station. Each station includes a transceiver and a control subsystem. The transceiver includes having one or more photonic crystal masers and one or more photonic crystal receivers. The control subsystem includes one or more lasers optically coupled to the one or more photonic crystal masers and the one or more photonic crystal receivers. The control subsystem also includes modulation electronics in communication with the one or more lasers and configured to control one or more properties of a first input optical signal received by each photonic crystal maser. The control subsystem additionally includes demodulation electronics in communication with the one or more lasers and configured to control one or more properties of a second input optical signal received by each photonic crystal receiver.

Abstract: In a general aspect, a vapor cell includes a body defined by a stack of layers bonded to each other. The stack of layers includes a first end layer disposed at a first end of the body and a second end layer disposed at a second, opposite end of the body. Intermediate layers extend between the first and second end layers and define an internal cavity extending through the body between the first end layer and the second end layer. The stack of layers also includes first and second sets of tabs. The first set of tabs extends outward from the intermediate layers on a first exterior side of the body, and the second set of tabs extends outward from the intermediate layers on a second exterior side of the body. The vapor cell also includes a vapor or a source of the vapor disposed in the internal cavity.

Abstract: 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.

Abstract: In a general aspect, a vapor cell includes a body defined by a stack of layers bonded to each other. The stack of layers includes a first end layer disposed at a first end of the body and a second end layer disposed at a second, opposite end of the body. Intermediate layers extend between the first and second end layers and define an internal cavity extending through the body between the first end layer and the second end layer. The stack of layers also includes first and second sets of tabs. The first set of tabs extends outward from the intermediate layers on a first exterior side of the body, and the second set of tabs extends outward from the intermediate layers on a second exterior side of the body. The vapor cell also includes a vapor or a source of the vapor disposed in the internal cavity.

Abstract: In a general aspect, a vapor cell includes a body defined by a stack of layers bonded to each other. The stack of layers includes a first end layer disposed at a first end of the body and a second end layer disposed at a second, opposite end of the body. Intermediate layers extend between the first and second end layers and define an internal cavity extending through the body between the first end layer and the second end layer. Each intermediate layer includes a through-hole that defines a portion of the internal cavity through the intermediate layer. The vapor cell also includes a vapor or a source of the vapor disposed in the internal cavity.

Abstract: In a general aspect, a vapor cell includes a body defined by a stack of layers bonded to each other. The stack of layers defines an array of cavities that includes first and second subsets of cavities. The first subset of cavities extends through intermediate layers of the stack of layers and the second subset of cavities extends entirely through the stack of layers. The vapor cell includes a vapor or a source of the vapor disposed in each of the first subset of cavities. The stack of layers includes a first end layer disposed at a first end of the body and a second end layer disposed at a second, opposite end of the body. The intermediate layers are positioned between the first and second end layers.

Abstract: 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.

Abstract: 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.