Abstract: In a general aspect, vapor cell sensors are used to perform over-the-air (OTA) testing of cellular base stations. In some implementations, a vapor cell sensor including a vapor having Rydberg states is tuned to a carrier frequency of RF radiation emitted from a cellular base station. A first set of optical signals is generated based on an interaction between the vapor and a synchronization signal transmitted from the cellular base station. The vapor cell sensor is tuned to a harmonic of the carrier frequency. A second set of optical signals is generated based on an interaction between the vapor and the RF radiation. The first and second sets of optical signals are converted to digital data. The digital data is processed to detect a condition of the cellular base station.

Abstract: In a general aspect, a system is described herein for detecting the phase properties of a radio frequency (RF) wave. The system includes a vapor cell sensor that contains a vapor and is configured to generate an optical signal in response to laser signals that interact with the vapor. The vapor has a Rydberg electronic transition that interacts with a target RF electromagnetic field, and the optical signal is based on a transmission of one of the laser signals through the vapor. The system also includes an optical detection system and a signal processing system. The optical detection system is configured to generate a detector signal in response to receiving the optical signal, and the signal processing system is configured to receive the detector signal and perform operations that determine a phase change of the target RF electromagnetic field.

Abstract: In a general aspect, a method is described herein for detecting the phase properties of a radio frequency (RF) wave. The method includes generating an optical signal by interacting laser signals with a vapor of a vapor cell sensor. The optical signal is based on a transmission of one of the laser signals through the vapor. The method also includes altering an intensity of the optical signal by interacting a target RF electromagnetic field with a Rydberg electronic transition of the vapor. The target RF electromagnetic field includes a time series of RF pulses. The method additionally includes determining, by operation of a signal processing system, a magnitude of phase change in the time series of RF pulses. In some implementations, the method includes determining a phase of a target RF pulse in the times series of RF pulses.

Abstract: In a general aspect, a radiometer is disclosed that includes a vapor cell sensor. The vapor cell sensor contains a vapor and is configured to generate an optical signal in response to laser signals and thermal radiation interacting with the vapor. The vapor includes a Rydberg electronic transition that is configured to interact with the thermal radiation. The radiometer also includes a computing system having one or more processors and a memory. The memory stores instructions that, when executed by the one or more processors, are configured to perform operations that include generating, based on the optical signal, transmission data that represents the transmission of the one laser signal through the vapor. The operations also include determining, based on the transmission data, a temperature of a target body that generates the thermal radiation.

Abstract: In a general aspect, a radiometer is disclosed that includes a vapor cell sensor. The vapor cell sensor contains a vapor and is configured to generate an optical signal in response to laser signals and thermal radiation interacting with the vapor. The vapor includes a Rydberg electronic transition that is configured to interact with the thermal radiation. The radiometer also includes a computing system having one or more processors and a memory. The memory stores instructions that, when executed by the one or more processors, are configured to perform operations that include generating, based on the optical signal, transmission data that represents the transmission of the one laser signal through the vapor. The operations also include determining, based on the transmission data, a temperature of a target body that generates the thermal radiation.

Abstract: In a general aspect, vapor cell sensors are used to perform over-the-air (OTA) testing of cellular base stations. In some implementations, a vapor cell sensor including a vapor having Rydberg states is tuned to a carrier frequency of RF radiation emitted from a cellular base station. A first set of optical signals is generated based on an interaction between the vapor and a synchronization signal transmitted from the cellular base station. The vapor cell sensor is tuned to a harmonic of the carrier frequency. A second set of optical signals is generated based on an interaction between the vapor and the RF radiation. The first and second sets of optical signals are converted to digital data. The digital data is processed to detect a condition of the cellular base station.

Abstract: In a general aspect, vapor cell sensors are used to perform OTA testing of cellular base stations. In some implementations, a system for performing OTA testing of a cellular base station includes a vapor cell sensor including a vapor having Rydberg states and a control system communicably coupled to the vapor cell sensor and configured to tune the vapor cell sensor to a carrier frequency of RF radiation emitted from the cellular base station; receive a first set of optical signals generated based on an interaction between the vapor and a synchronization signal; tune the vapor cell sensor to a harmonic of the carrier frequency; receive a second set of optical signals generated by the vapor cell based on an interaction between the vapor and the RF radiation; convert the first and second sets of optical signals to digital data; and process the digital data to detect a condition of the cellular base station.

Abstract: In a general aspect, a system is described for sensing radio frequency (RF) electromagnetic fields. The system includes a laser system that generates probe and coupling laser signals. The system also includes an RF source that generates a reference RF electromagnetic field. The reference RF electromagnetic field is part of a combined RF electromagnetic field that also includes a perturbing RF electromagnetic field. A vapor cell sensor of the system generates an optical signal in response to the probe laser signal, the coupling laser signal, and the combined RF electromagnetic field interacting with a vapor of the vapor cell sensor. The system additionally includes a control system that tunes the coupling laser signal and the reference RF electromagnetic field relative to respective transitions of the vapor. The control system generates, based on the optical signal, a value that represents a property of the perturbing RF electromagnetic field.

Abstract: In a general aspect, a radio frequency (RF) measurement device includes first and second mode converters, each configured to convert a mode of the RF electromagnetic wave between a first RF waveguide mode and a second RF waveguide mode. The RF measurement device also includes an internal cavity between the first and second mode converters that contains a vapor or a source of the vapor. The vapor includes Ryberg atoms or molecules. The RF measurement device additionally includes an RF waveguide extending between the first and second mode converters and configured to carry the second RF waveguide mode through the internal cavity. In some variations, the RF waveguide includes first and second longitudinal portions disposed on respective, opposite sides of the device and configured to establish a target RF profile in an interaction region of the internal cavity.

Abstract: In a general aspect, a system for measuring radio frequency (RF) electromagnetic waves includes a laser system configured to generate plurality of input optical signals. The system also includes an RF measurement device having first and second mode converters and an internal cavity therebetween. The internal cavity contains a vapor that is configured to produce an output optical signal based on the plurality of input optical signals. The RF measurement device also includes an RF waveguide that extends between the first and second mode converters and is configured to carry the second RF waveguide mode through the internal cavity. The system also includes an optical detector system configured to generate a detector signal in response to receiving the output optical signal. The system additionally includes a signal processing system configured to generate data in response to receiving the detector signal.

Abstract: In a general aspect, a radio frequency (RF) measurement device includes first and second mode converters, each configured to convert a mode of the RF electromagnetic wave between a first RF waveguide mode and a second RF waveguide mode. The RF measurement device also includes an internal cavity between the first and second mode converters that contains a vapor or a source of the vapor. The vapor includes Ryberg atoms or molecules. The RF measurement device additionally includes an RF waveguide extending between the first and second mode converters and configured to establish a circular polarization of the RF electromagnetic wave in the internal cavity.

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 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 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.