Patent ID: 12188784

DETAILED DESCRIPTION

The present invention relates generally to sensor systems, and specifically to a vapor cell for atomic physics sensors. For example, the vapor cell can be implemented in nuclear magnetic resonance (NMR) sensors, electron paramagnetic resonance (EPR) sensors, interferometer sensors, and/or electrometer sensors. The vapor cell includes a cell wall formed from an approximately transparent material (e.g., a type of glass material, a transparent ceramic, or a crystal such as quartz). The cell wall can enclose an alkali metal vapor (e.g., rubidium (Rb) or cesium (Cs)), such as in an otherwise evacuated volume, and can include an inner surface and an outer surface. The vapor cell can also include at least one structural feature provided on at least one of the inner surface and the outer surface of the cell wall.

The structural feature(s) can extend along a portion of the respective at least one of the inner surface and the outer surface of the vapor cell, and can be formed in a variety of different ways (e.g., such as rings, ribs, bars, arches, fins, and combinations thereof). As one example, the structural feature(s) can provide structural integrity of the vapor cell, allowing the cell wall of the vapor cell to fabricated very thin to provide for higher transmission of signals (e.g., RF signals) through the cell wall, and thus approximate transparency to the signals, while still maintaining sufficient structural integrity to mitigate breaking based on pressure gradients between the inner and outer surfaces. As another example, the structural feature(s) can be chosen to modify signal propagation to improve sensor performance. For example, the structural feature(s) can present regions of varying dielectric constant that can modify electric, RF, and optical field properties within the vapor cell. In yet another example, the structural feature(s) can present regions of varying magnetic permeability, which can modify magnetic field properties within the cell

The structural feature(s) can be provided or formed in any of a variety of ways based on design goals. As a first example, the structural feature(s) can be implemented as integral with the cell wall of the vapor cell. For example, to form the structural feature(s), portions of the cell wall can be etched to a first thickness between the inner and outer surfaces. Therefore, the regions of the cell wall between the etched portions can correspond to the structural feature(s) having a thickness that is greater than the first thickness. As a second example, the structural feature(s) can be discrete components that are bonded to at least one of the inner and outer surfaces of the cell wall. As an example, such discrete components can have a higher tensile strength than the approximately transparent material from which the cell wall is formed and/or can be formed from a thicker material. In either example, the cell wall can have a lesser surface area devoted to portions of the total surface area on which the structural feature(s) are provided or formed than portions of the total surface area on which the structural feature(s) are absent. Accordingly, the thinner portions of the cell wall can be more prominent to facilitate approximate transparency of the signals (e.g., RF signals) through the cell wall and into the volume of the vapor cell that confines the alkali metal vapor.

FIG.1illustrates an example block diagram of a vapor cell100. The vapor cell100can be implemented in any of a variety of atomic physics-based sensors, such as nuclear magnetic resonance (NMR) sensors, electron paramagnetic resonance (EPR) sensors, interferometer sensors, and/or electrometer sensors. The vapor cell100can be configured to enclose an alkali metal vapor, such as rubidium (Rb) or cesium (Cs), such as in an otherwise evacuated volume.

In the example ofFIG.1, the vapor cell100includes a cell wall102formed from an approximately transparent material (e.g., a type of glass material, such as quartz). As described herein, the approximately transparent material can be sufficient to provide a high transmissivity of signals (e.g., optical or radio frequency (RF)) through the cell wall102, such as greater than or equal to approximately 95%. Therefore, optical beams and RF signals can thus interact with the alkali metal vapor therein. As an example, a detection beam corresponding to an optical beam (e.g., probe beam) exiting the vapor cell100can be monitored (e.g., via a detection system) to determine characteristics of the detection beam. The characteristics of the detection beam can be altered by the interaction of the signals with the alkali metal atoms, such as to facilitate measurement of a measurable parameter (e.g., time, rotation, acceleration, magnetic field, and/or electric field).

The cell wall102includes an inner surface, which is thus enclosed within the volume of the vapor cell100, and an outer surface, which is thus exposed to an exterior of the vapor cell100. In the example ofFIG.1, the vapor cell100includes at least one structural feature104provided on at least one of the inner surface and the outer surface of the cell wall102. The structural feature(s)104can extend along a portion of at least one of the inner surface and the outer surface of the vapor cell100. For example, the each of the structural feature(s)104can extend along a length of the cell wall102, can extend around (e.g., circumscribe) the cell wall102or can be provided in any of a variety of ways.

As one example, the structural feature(s)104can be configured to increase structural integrity of the cell wall102. The portions of the cell wall102on which the structural feature(s)104are absent can thus be fabricated to be very thin to provide for higher transmission of signals (e.g., RF signals) through the cell wall102, and thus approximate transparency to the signals. However, the presence of the structural feature(s)104can maintain sufficient structural integrity to mitigate breaking based on pressure gradients between the inner and outer surfaces of the cell wall102. The structural feature(s)104can be provided or formed in any of a variety of ways to provide the sufficient structural integrity while maintaining approximate transparency to incident signals (e.g., both optical and RF) passing through the cell wall102and into the vapor cell100.

As a first example, the structural feature(s)104can be formed from a material that is the same as the approximately transparent material that forms the cell wall102. As a further example, the structural feature(s)104can be integral with the cell wall102of the vapor cell100. For example, to form the structural feature(s)104, portions of the cell wall102can be chemically etched to a first thickness between the inner and outer surfaces. Therefore, the regions of the cell wall102between the etched portions can correspond to the structural feature(s) having a thickness that is greater than the first thickness. As a second example, the structural feature(s)104can be discrete components that are bonded to at least one of the inner and outer surfaces of the cell wall102. As an example, such discrete components can have a higher tensile strength than the approximately transparent material from which the cell wall102is formed and/or can be formed from a thicker material.

The cell wall102can have a lesser surface area devoted to portions of the total surface area on which the structural feature(s)104are provided or formed than portions of the total surface area on which the structural feature(s)104are absent. Therefore, the total surface area of the cell wall102that includes the thinner and more highly approximately transparent material can be more prevalent to facilitate greater transmissivity of signals provided through the cell wall102to interact with the alkali metal vapor enclosed therein. Accordingly, the cell wall102can facilitate approximate transparency of the signals (e.g., RF signals) through the cell wall102and into the volume of the vapor cell100that confines the alkali metal vapor (e.g., while maintaining sufficient structural integrity to mitigate breakage of the cell wall102based on pressure gradients between the inner and outer surfaces of the cell wall102). For example, given that the volume enclosed by the cell wall102is evacuated other than the alkali metal vapor, external pressure can cause the cell wall102to implode. Alternatively, for a sensor system that is used in space, the lack of atmospheric pressure can instead cause the cell wall102to explode. Regardless, vibrations and/or inertial shock can cause the cell wall102to break. However, by implementing structural feature(s)104, the vapor cell100can exhibit sufficient structural integrity to withstand environmental stresses while providing superior transmissivity based on a very thin cell wall102.

As another example, the structural feature(s)104can be alternatively or additionally implemented for a variety of other reasons besides structural integrity of the cell wall102. As an example, the structural feature(s)104can be implemented to affect the signals and/or fields that enter the volume within the vapor cell100in a variety of different ways. As an example, by implementing the structural feature(s)104as spatially-varying wall thickness of the cell wall102, a dielectric constant of the material of the cell wall102can likewise be spatially-varying. Therefore, the propagation direction, diffraction, and/or reflection properties of RF signals can be affected by the structural feature(s)104. As another example, by implementing the structural feature(s)104as spatially-varying wall thickness of the cell wall102, the magnetic permeability of the cell wall102can be affected in similar ways as to the dielectric described above. Therefore, magnetic fields that pass through the cell wall102can be manipulated. As an example, the magnetic permeability can be affected to provide for approximate uniformity of the magnetic fields within the volume of the cell wall102, or to block spurious magnetic fields from entering the volume within the cell wall102, thereby mitigating noise effects on the associated sensor or system. Accordingly, the structural feature(s)104can be provided for a variety of purposes.

FIG.2illustrates an example diagram of a vapor cell200. The vapor cell200can be implemented in any of a variety of atomic physics-based sensors, such as NMR sensors, EPR sensors, interferometer sensors, and/or electrometer sensors. The vapor cell200can be configured to enclose an alkali metal vapor, such as Rb or Cs, such as in an otherwise evacuated volume. The example ofFIG.2illustrates an exploded view202to provide a more magnified illustration of a portion (e.g., one end) of the vapor cell200. The vapor cell200can correspond to the vapor cell100in the example ofFIG.2. Therefore, reference is to be made to the example ofFIG.1in the following description of the example ofFIG.2.

In the example ofFIG.2, the vapor cell200is demonstrated as being cylindrical, and thus having a tubular shape. While the specific example ofFIG.2is demonstrated as cylindrical, other tubular arrangements (e.g., a rectangular, square, or triangular cross-sectional prism) are also possible. The vapor cell200includes a cell wall204formed from an approximately transparent material (e.g., a type of glass material, such as quartz). Therefore, optical beams and RF signals can thus interact with the alkali metal vapor therein. Similar to as described above in the example ofFIG.2, the cell wall204includes an inner surface, which is thus enclosed within the volume of the vapor cell200, and an outer surface, which is thus exposed to an exterior of the vapor cell200.

In the example ofFIG.2, the vapor cell200also includes a plurality of structural features206provided on the outer surface of the cell wall204. The structural features206are demonstrated as an array of rings periodically provided along the length of the tubular shape of the vapor cell100. The rings that constitute the structural features206are parallel with respect to each other and extend around the cross-section of the vapor cell100, such that the rings circumscribe the cell wall102. The portions of the cell wall204on which the structural features206are absent can thus be fabricated to be very thin to provide for higher transmission of signals (e.g., RF signals) through the cell wall204, and thus approximate transparency to the signals. However, as one example, the presence of the structural features206can maintain sufficient structural integrity of the cell wall204. As another example, the structural features206can affect the properties of the cell wall204, such as with respect to dielectric and/or magnetic permeability of the cell wall204. Therefore, the structural features206can also or instead be implemented to affect RF signals and/or magnetic fields that pass through the cell wall204.

As described above, the structural features206can be provided or formed in any of a variety of ways to provide the sufficient structural integrity while maintaining approximate transparency to incident signals (e.g., both optical and RF) passing through the cell wall204and into the vapor cell200. As a first example, the structural features206can be integral with the cell wall204of the vapor cell200. For example, to form the structural features206, the material that forms the vapor cell100can be etched about a cross-sectional periphery at periodic portions. Therefore, the unetched portions of the material can form the structural features206merely by being unetched, and therefore remaining thicker with respect to the cross-section of the vapor cell200. The etched portions can therefore correspond to the cell wall204between each of the structural features206. The etched portions corresponding to the cell wall204can therefore be much thinner with respect to the cross-section of the vapor cell200than the structural features206.

The portions of the cell wall204on which the structural features206are absent can constitute a much larger overall portion of the total surface area of the cell wall204than the portions of the cell wall204on which the structural features206are present. Stated another way, given that the structural features206and the cell wall204are integral with respect to each other, the cell wall204can constitute a much larger overall portion of the total surface area of the outer surface of the vapor cell200than the structural features206. Therefore, as one example, based on the much thinner material of the cell wall204combined with the larger surface area of the cell wall204relative to the structural features206, the vapor cell200can exhibit greater transmissivity of signals provided through the cell wall204to interact with the alkali metal vapor enclosed therein. Accordingly, the cell wall204can facilitate approximate transparency of the signals (e.g., RF signals) through the cell wall204and into the volume of the vapor cell200that confines the alkali metal vapor, such as while maintaining sufficient structural integrity to mitigate breakage of the cell wall204base on pressure gradients between the inner and outer surfaces of the cell wall204.

The vapor cell200is provided by example, and other arrangements are possible. For example, the structural features206can be implemented in any of a variety of other ways than the ring structures demonstrated in the example ofFIG.2. Examples include one or more elongated portions that extend along the tubular length of the vapor cell200, a helical or crisscross pattern along the tubular length of the vapor cell200, chevrons, patches, or other types of arrangements of the structural features206. Therefore, the vapor cell200can be implemented in any of a variety of ways.

FIG.3illustrates an example of an atomic physics-based sensor system300. The sensor system300can correspond to an NMR sensor, an EPR sensor, an interferometer sensor, or an electrometer sensor. Therefore, the sensor system300can be implemented to measure any of a variety of measurable parameters, such as time, rotation, acceleration, magnetic field, and/or electric field.

The sensor system300includes a vapor cell302that can be configured as a sealed glass container that includes a vapor of alkali metal atoms. The vapor cell302can correspond, for example, to the vapor cells100and/or200described above in the respective examples ofFIGS.1and2. The sensor system300also includes an optical signal system304that is configured to generate at least one optical beam, demonstrated in the example ofFIG.3as a signal OPT. As an example, the optical signal system304can include a probe laser and at least one coupling laser to generate a probe beam and at least one coupling beam, respectively. As another example, the optical signal system304can include a pump laser and a probe laser for generating separate respective pump and probe beams. Each of the optical beams OPT can be provided through the vapor cell302via optics (not shown), such as to provide interaction with the alkali metal vapor therein (e.g., to provide optical pumping and/or energy state transitions). In the example ofFIG.3, one of the optical beams OPT can exit the vapor cell302as a detection beam OPTDET.

The sensor system300also includes a signal system306that is configured to generate any of a variety of signals or fields, demonstrated in the example ofFIG.3as a signal SIG. As an example, the signal system306can include a splitting signal generator that is configured to generate the signal SIG as a splitting signal that is provided at a predetermined frequency and a predetermined amplitude through the vapor cell302to split a frequency-spectrum transparency peak corresponding to the first Rydberg energy state of the alkali metal atoms into a pair of Autler-Townes frequency-spectrum transparency peaks associated with the alkali metal atoms. As another example, the signal system306can include a tuning signal generator that can generate a tuning RF signal to adjust an energy difference between Rydberg energy states of the alkali metal atoms. The signal system306can also or instead include a magnetic field generator that is configured to generate one or more magnetic fields that are provided through the vapor cell302, such as to provide for precession of the alkali metal vapor contained in the vapor cell302. As described herein, the arrangement of the cell wall and the structural feature(s) of the vapor cell302can be such that the cell wall of the vapor cell302can be approximately transparent to the signal RF, thus providing greater interaction of the alkali metal vapor with the signal SIG, such as while maintaining sufficient structural integrity to mitigate breakage of the vapor cell302. As another example, the structural feature(s) of the vapor cell302can be such that the signal SIG (e.g., RF signal(s) and/or magnetic field(s)) can be manipulated as the signal SIG passes through the cell wall of the vapor cell302.

The sensor system300further includes a detection system308that is configured to monitor the detection beam OPTDET. For example, the detection system308can monitor a characteristic of the detection beam OPTDETthat is based on the interaction of the alkali metal atoms with the optical beam(s) OPT and the signal RF, as well as an external stimulus (e.g., acceleration, rotation, an external RF signal, an external magnetic field, etc.). As an example, the characteristic of the detection beam OPTDETcan be intensity, phase, Faraday rotation, or any of a variety of other optical beam characteristics. The detection system308can include a photodetector that can monitor the characteristic. Therefore, an associated processor (not shown) can be implemented to measure the measurable parameter based on the monitored characteristic.

Accordingly, based on the cell wall and the structural feature(s) of the vapor cell302as described herein, the sensor system300can be implemented in any of a variety of hostile environments to provide for accurate determination of the measurable parameter while maintaining sufficient structural integrity of the cell wall of the vapor cell302.

In view of the foregoing structural and functional features described above, a methodology in accordance with various aspects of the disclosure will be better appreciated with reference toFIG.4. It is to be understood and appreciated that the method ofFIG.4is not limited by the illustrated order, as some aspects could, in accordance with the present disclosure, occur in different orders and/or concurrently with other aspects from that shown and described herein. Moreover, not all illustrated features may be required to implement a methodology in accordance with an aspect of the present examples.

FIG.4illustrates an example of a method400for forming a vapor cell (e.g., the vapor cell100) for an atomic physics-based sensor system (e.g., the sensor system300). At402, a cell wall (e.g., the cell wall102) is formed from an approximately transparent material. The cell wall can include an inner surface and an outer surface. At404, at least one structural feature (e.g., the structural feature(s)104) is formed on at least one of the inner surface and the outer surface of the cell wall and extending along a portion of the respective at least one of the inner surface and the outer surface. At406, the vapor cell is sealed to enclose an alkali metal vapor (e.g., Rb or Cs) within the vapor cell.

What have been described above are examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art will recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Additionally, where the disclosure or claims recite “a,” “an,” “a first,” or “another” element, or the equivalent thereof, it should be interpreted to include one or more than one such element, neither requiring nor excluding two or more such elements. As used herein, the term “includes” means includes but not limited to, and the term “including” means including but not limited to. The term “based on” means based at least in part on.