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EP-4735853-A1 - MEASURING THERMAL RADIATION USING VAPOR CELL SENSORS

EP4735853A1EP 4735853 A1EP4735853 A1EP 4735853A1EP-4735853-A1

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.

Inventors

  • SCHMIDT, MATTHIAS
  • BOHAICHUK, STEPHANIE M.
  • VENU, Vijin
  • CHRISTALLER, Florian
  • LIU, CHANG
  • SHEN, PINRUI
  • Kübler, Harald
  • SHAFFER, JAMES P.

Assignees

  • Quantum Valley Ideas Laboratories

Dates

Publication Date
20260506
Application Date
20240627

Claims (20)

  1. CLAIMS What is claimed is: 1. A radiometer, comprising: a vapor cell sensor containing a vapor and configured to generate an optical signal in response to laser signals and thermal radiation interacting with the vapor, the vapor comprising a Rydberg electronic transition that is configured to interact with the thermal radiation, the optical signal based on a transmission of one of the laser signals through the vapor; and a computing system comprising one or more processors and a memory, the memory storing instructions that, when executed by the one or more processors, are configured to perform operations that comprise: generating, based on the optical signal, transmission data that represents the transmission of the one laser signal through the vapor, and determining, based on the transmission data, a temperature of a target body that generates the thermal radiation.
  2. 2. The radiometer of claim 1, comprising: an RF source configured to generate a reference RF electromagnetic field that is configured to interact with the Rydberg electronic transition.
  3. 3. The radiometer of claim 2, wherein the RF source comprises an RF attenuator configured to alter an amplitude of the reference RF electromagnetic field to a target amplitude, the target amplitude having a magnitude that places the vapor cell sensor in an amplitude regime when the reference RF electromagnetic field interacts with the Rydberg electronic transition.
  4. 4. The radiometer of claim 2 or claim 3, wherein the transmission data comprises first and second intensity values that are based on the one laser signal after passing through the vapor; wherein generating the transmission data comprises: generating the first intensity value as the laser signals and the thermal radiation interact with the vapor, and generating the second intensity value as the laser signals, the reference RF electromagnetic field, and the thermal radiation interact with the vapor.
  5. 5. The radiometer of claim 4, wherein determining the temperature of the target body comprises: calculating, based on the first and second intensity values, a magnitude of a parameter that is linearly dependent on the temperature of the target body; and determining the temperature of the target body based on the magnitude of the parameter.
  6. 6. The radiometer of claim 4, wherein the first and second intensity values are generated at different signal strengths of the one laser signal; and wherein determining the temperature of the target body comprises: calculating, based on the first and second intensity values at each signal strength, respective magnitudes of a parameter that represents a relationship between first and second absorption terms, wherein: the first absorption term represents an absorption of the one laser signal through the vapor as the laser signals and the thermal radiation interact with the vapor, and the second absorption term represents an absorption of the one laser signal through the vapor as the laser signals, the reference RF electromagnetic field, and the thermal radiation interact with the vapor; generating values of the first and second absorption terms based on the respective magnitudes of the parameter; and determining the temperature of the target body based on the generated values of the first and second absorption terms.
  7. 7. The radiometer of any one of claims 1-3, comprising: a laser system configured to produce the laser signals, the laser signals comprising probe and coupling laser signals; wherein: the optical signal is based on a transmission of the probe laser signal through the vapor, the probe laser signal is configured to interact with a probe optical transition of the vapor, and the coupling laser signal is configured to interact with a coupling optical transition of the vapor.
  8. 8. The radiometer of claim 7, wherein the vapor has electronic states that comprise: first and second electronic states, and first and second Rydberg electronic states; wherein the first electronic state, the second electronic state, and the first Rydberg electronic state are progressively higher in energy; and wherein: the probe optical transition is defined by the first and second electronic states, the coupling optical transition is defined by the second electronic state and the first Rydberg electronic state, and the Rydberg electronic transition is defined by the first and second Ryberg electronic states.
  9. 9. The radiometer of claim 7, wherein the coupling laser signal is a first coupling laser signal, and the laser signals comprise a second coupling laser signal; and wherein: the optical signal is based on a transmission of the probe laser signal through the vapor, the probe laser signal is configured to interact with a probe optical transition of the vapor, the first coupling laser signal is configured to interact with a first coupling optical transition of the vapor, and the second coupling laser signal is configured to interact with a second coupling optical transition of the vapor.
  10. 10. The radiometer of claim 9, wherein the vapor has electronic states that comprise: first, second, and third electronic states, and first and second Rydberg electronic states; wherein the first electronic state, the second electronic state, the third electronic state, and the first Rydberg electronic state are progressively higher in energy; and wherein: the probe optical transition is defined by the first and second electronic states, the first coupling optical transition is defined by the second electronic state and the third electronic state, the second coupling optical transition is defined by the third electronic state and the first Rydberg electronic state, and the Rydberg electronic transition is defined by the first and second Ryberg electronic states.
  11. 11. The radiometer of any one of claims 1-3, comprising: an optical detector that is configured to generate a detector signal in response to receiving the optical signal, the detector signal representing the transmission of the one laser signal through the vapor.
  12. 12. The radiometer of any one of claims 1-3, wherein the Rydberg electronic transition is configured to interact with thermal radiation corresponding to black body temperatures greater than 300 °C.
  13. 13. The radiometer of any one of claims 1-3, comprising: the target body, external to the vapor cell sensor and in thermal communication therewith.
  14. 14. A method of measuring thermal radiation, the method comprising: generating, by operation of a vapor cell sensor, an optical signal in response to laser signals and thermal radiation interacting with a vapor of the vapor cell sensor, the optical signal based on a transmission of one of the laser signals through the vapor, the vapor comprising a Rydberg electronic transition that is configured to interact with the thermal radiation; generating, based on the optical signal, transmission data that represents the transmission of the one laser signal through the vapor; and determining, based on the transmission data, a temperature of a target body that generates the thermal radiation.
  15. 15. The method of claim 14, comprising: generating, by operation of an RF source, a reference RF electromagnetic field that is configured to interact with the Rydberg electronic transition; and receiving the reference RF electromagnetic field at the vapor of the vapor cell sensor.
  16. 16. The method of claim 15, wherein the RF source comprises an RF attenuator; and wherein generating the reference RF electromagnetic field comprises altering, by operation of the RF attenuator, an amplitude of the reference RF electromagnetic field to a target amplitude, the target amplitude having a magnitude that places the vapor cell sensor in an amplitude regime when the reference RF electromagnetic field interacts with the Rydberg electronic transition.
  17. 17. The method of claim 15 or claim 16, wherein the transmission data comprises first and second intensity values that are based on the one laser signal after passing through the vapor; wherein generating the transmission data comprises: generating the first intensity value as the laser signals and the thermal radiation interact with the vapor, and generating the second intensity value as the laser signals, the reference RF electromagnetic field, and the thermal radiation interact with the vapor.
  18. 18. The method of claim 17, wherein determining the temperature of the target body comprises: calculating, based on the first and second intensity values, a magnitude of a parameter that is linearly dependent on the temperature of the target body; and determining the temperature of the target body based on the magnitude of the parameter.
  19. 19. The method of claim 17, wherein the first and second intensity values are generated at different signal strengths of the one laser signal; and wherein determining the temperature of the target body comprises: calculating, based on the first and second intensity values at each signal strength, respective magnitudes of a parameter that represents a relationship between first and second absorption terms, wherein: the first absorption term represents an absorption of the one laser signal through the vapor as the laser signals and the thermal radiation interact with the vapor, and the second absorption term represents an absorption of the one laser signal through the vapor as the laser signals, the reference RF electromagnetic field, and the thermal radiation interact with the vapor; generating values of the first and second absorption terms based on the respective magnitudes of the parameter; and determining the temperature of the target body based on the generated values of the first and second absorption terms.
  20. 20. The method of any one of claims 14-16, wherein generating transmission data comprises generating, over time, sets of transmission data at different, respective times; and wherein determining the temperature of the target body comprises: determining, based on the sets of transmission data, corresponding temperatures of the target body at the different, respective times, the corresponding temperatures defining a time series of temperatures, and calculating a final temperature based on the time series of temperatures, the final temperature defining the temperature determined for the target body.

Description

Measuring Thermal Radiation Using Vapor Cell Sensors CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application claims priority to U.S. Prov. Pat. App. No.63/510,604, which was filed on June 27, 2023, and entitled, “Measuring Thermal Radiation Using Vapor Cells.” The disclosure of the priority application is hereby incorporated herein by reference in its entirety. BACKGROUND [0002] The following description relates measuring thermal radiation using vapor cell sensors. [0003] Radiometers measure radiant flux and can operate in the microwave, infrared, and ultraviolet regimes. Commercially, radiometers can be used for remote sensing, although there are applications for temperature measurement and calibration as well. The radiometric services market is currently about $1B and projected to reach about $2B by 2027. Radiometers can operate on aerial, space, and ground-based platforms. The market for radiometers is large and growing, especially as environmental concerns drive monitoring and the desire to increase efficiency in agriculture. DESCRIPTION OF DRAWINGS [0004] FIG.1A is a schematic diagram of a first example of a radiometer that includes a vapor cell sensor; [0005] FIG.1B is a schematic diagram of an example of an energy level diagram for a vapor of the vapor cell of FIG.1A; [0006] FIG.2A is a schematic diagram of a second example of a radiometer that includes a vapor cell sensor; [0007] FIG.2B is a schematic diagram of an example set of electronic states for a vapor of Rb atoms; [0008] FIG.2C is a schematic diagram of an example set of electronic states for a vapor of Cs atoms; [0009] FIG.3 is a schematic diagram of an example computing system for a radiometer that includes a vapor cell sensor; [0010] FIG.4 is an example of a measured curve of parameter, ^, versus a black body temperature, ^; [0011] FIG.5 is an example of a simulated curve of ^ versus a signal strength of a probe laser without a coupling laser and reference a RF electromagnetic field present; and [0012] FIG.6 is a flowchart of an example method for determining the temperature of a target body using a radiometer that includes a vapor cell sensor. DETAILED DESCRIPTION [0013] In a general aspect, a vapor cell sensor may be used to measure thermal background radiation temperature and/or flux at a particular set of frequencies precisely. In this capacity, the vapor cell sensor may function as part of a radiometer. For example, a radiometer for measuring thermal radiation may include a laser system and a vapor cell sensor having a vapor therein. The laser system is configured to generate two or more input optical signals, and the vapor cell sensor is configured to generate an output optical signal in response to the two or more input optical signals interacting with its vapor. In some instances, the radiometer may also include a thermal source (e.g., a target body) that generates thermal radiation that interacts with the vapor of the vapor cell sensor. In some instances, the radiometer includes an RF source that is configured to generate an RF electromagnetic field (e.g., a reference RF field) that interacts with the vapor of the vapor cell sensor. In some instances, the radiometer includes a photodetector that is configured to receive the output optical signal from the vapor cell, and in response, generate a detector signal that represents a property of the thermal radiation (e.g., temperature, thermal flux, etc.). Radiometers are important for a number of applications such as, for example, calibration and environmental sensing. [0014] Radiometers are typically configured to measure the temperature and moisture content of objects, which may include objects measured from space (e.g., such as from orbit around the Earth). Measurements are typically taken over relatively long periods of time (e.g., such as during several orbits), making accuracy and drift free measurements important. The radiometers described herein are based on vapor cell sensors, and in some variations, these radiometers are configured as Rydberg vapor-based quantum sensors (e.g., Rydberg atom-based or Rydberg molecule-based quantum sensors). As such, the radiometers may extend the concept of Rydberg vapor-based quantum sensors to measure thermal emission from hot objects (e.g., objects have a temperature at least 300 °C). In some variations, the radiometers are configured to measure thermal emissions from targeted areas on the surface of the earth. In these variations, the radiometers may be configured as imaging radiometers. [0015] In some implementations, the radiometers are based on a vapor cell sensor that is configured to operate in the ‘so-called’ amplitude regime. The vapor cell may include a vapor that, in many variations, has at least two or more Rydberg electronic states (e.g., a Rydberg vapor). The vapor may include one or both of a vapor of Rydberg atoms and a vapor of Rydberg molecules. The vapor may include, for example, a vapor of Group IA atoms (e.g.