Patent Description:
The present invention relates generally to sensor systems, and specifically to a vapor cell for atomic physics sensors.

A variety of high-precision sensor systems implement atomic physics for measuring any of a variety of parameters, such as time, inertial parameters, magnetic fields, and electric fields. Such high-precision sensor systems typically include optical and/or radio frequency (RF) signals that interact with atoms (e.g., alkali metal atoms) that are provided in a vapor matter state within a vapor cell. Examples of such sensor systems include nuclear magnetic resonance (NMR) sensors, electron paramagnetic resonance (EPR) sensors, interferometer sensors, and/or electrometer sensors. The sensor systems typically include one or more optical beams that are provided through the vapor cell, such that a characteristic of a detection beam exiting the vapor cell is monitored. The interaction of the optical beam(s) and some external stimulus (e.g., a magnetic field, RF signal, etc.) with the atoms contained in the vapor cell can provide for the measurable parameter of the monitored detection beam to facilitate the measurement of a measurable parameter (e.g., rotation, acceleration, magnetic field, electric field, and/or time). <NPL>, <NPL>, <NPL>, <NPL>. Anonymous: "Triad Technology Inc. | Spectroscopy Solutions", <NUM> December <NUM> (<NUM>-<NUM>-<NUM>), as well as <NPL>, disclose a vapor cell for an atomic physics-based sensor system, the vapor cell comprising a cell wall formed from an approximately transparent material, the cell wall enclosing an alkali metal vapor and comprising an inner surface and an outer surface and at least one structural feature provided on the inner surface of the cell wall and extending along a portion of the inner surface.

One embodiment includes a vapor cell for an atomic physics-based sensor system. The vapor cell includes a cell wall formed from an approximately transparent material. The cell wall can enclose an alkali metal vapor 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 and extending along a portion of the respective at least one of the inner surface and the outer surface.

Another example includes a method for forming a vapor cell for an atomic physics-based sensor system. The method includes forming a cell wall from an approximately transparent material. The cell wall includes an inner surface and an outer surface. The method also includes forming at least one structural feature 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. The method further includes sealing the vapor cell to enclose an alkali metal vapor within the vapor cell.

Another example includes an atomic physics-based sensor system. The system includes a vapor cell. The vapor cell includes a cell wall formed from an approximately transparent material. The cell wall can enclose an alkali metal vapor 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 and extending along a portion of the respective at least one of the inner surface and the outer surface. The system also includes at least one laser configured to provide a respective at least one optical beam through the vapor cell and at least one radio frequency (RF) signal generator configured to provide an RF signal through the vapor cell. The system further includes a detection system configured to monitor a detection beam corresponding to one of the at least one optical beam exiting the vapor cell to determine a measurable parameter.

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. According to a first aspect of the invention, a vapor cell is provided as set forth in appended independent claim <NUM>. According to a second aspect of the invention, a method for forming a vapor cell is provided as set forth in appended independent claim <NUM>. 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 encloses an alkali metal vapor (e.g., rubidium (Rb) or cesium (Cs)), such as in an otherwise evacuated volume, and includes an inner surface and an outer surface. The vapor cell also includes at least one structural feature provided on at least one of the inner surface and the outer surface of the cell wall.

According to the claimed invention , the at least one structural feature is formed as rings that circumscribe a respective one of the inner surface and the outer surface of the cell wall and are arranged parallel with respect to each other along a length of the tubular vapor cell. 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. In examples not covered by the claimed invention, the structural feature(s) can be formed in a variety of different ways (e.g., such as 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> illustrates an example block diagram of a vapor cell <NUM>. The vapor cell <NUM> can 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 cell <NUM> is configured to enclose an alkali metal vapor, such as rubidium (Rb) or cesium (Cs), such as in an otherwise evacuated volume.

In the example of <FIG>, the vapor cell <NUM> includes a cell wall <NUM> formed 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 wall <NUM>, such as greater than or equal to approximately <NUM>%. 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 cell <NUM> can 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 wall <NUM> includes an inner surface, which is thus enclosed within the volume of the vapor cell <NUM>, and an outer surface, which is thus exposed to an exterior of the vapor cell <NUM>. In the example of <FIG>, the vapor cell <NUM> includes at least one structural feature <NUM> provided on at least one of the inner surface and the outer surface of the cell wall <NUM>. The structural feature(s) <NUM> can extend along a portion of at least one of the inner surface and the outer surface of the vapor cell <NUM>. For example, the each of the structural feature(s) <NUM> can extend along a length of the cell wall <NUM>, can extend around (e.g., circumscribe) the cell wall <NUM> or can be provided in any of a variety of ways.

As one example, the structural feature(s) <NUM> can be configured to increase structural integrity of the cell wall <NUM>. The portions of the cell wall <NUM> on which the structural feature(s) <NUM> are absent can thus be fabricated to be very thin to provide for higher transmission of signals (e.g., RF signals) through the cell wall <NUM>, and thus approximate transparency to the signals. However, the presence of the structural feature(s) <NUM> can maintain sufficient structural integrity to mitigate breaking based on pressure gradients between the inner and outer surfaces of the cell wall <NUM>. The structural feature(s) <NUM> can 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 wall <NUM> and into the vapor cell <NUM>.

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

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

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

<FIG> illustrates an example diagram of a vapor cell <NUM>. The vapor cell <NUM> can 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 cell <NUM> can be configured to enclose an alkali metal vapor, such as Rb or Cs, such as in an otherwise evacuated volume. The example of <FIG> illustrates an exploded view <NUM> to provide a more magnified illustration of a portion (e.g., one end) of the vapor cell <NUM>. The vapor cell <NUM> can correspond to the vapor cell <NUM> in the example of <FIG>. Therefore, reference is to be made to the example of <FIG> in the following description of the example of <FIG>.

In the example of <FIG>, the vapor cell <NUM> is demonstrated as being cylindrical, and thus having a tubular shape. While the specific example of <FIG> is demonstrated as cylindrical, other tubular arrangements (e.g., a rectangular, square, or triangular cross-sectional prism) are also possible. The vapor cell <NUM> includes a cell wall <NUM> formed 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 of <FIG>, the cell wall <NUM> includes an inner surface, which is thus enclosed within the volume of the vapor cell <NUM>, and an outer surface, which is thus exposed to an exterior of the vapor cell <NUM>.

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

As described above, the structural features <NUM> can 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 wall <NUM> and into the vapor cell <NUM>. As a first example, the structural features <NUM> can be integral with the cell wall <NUM> of the vapor cell <NUM>. For example, to form the structural features <NUM>, the material that forms the vapor cell <NUM> can be etched about a cross-sectional periphery at periodic portions. Therefore, the unetched portions of the material can form the structural features <NUM> merely by being unetched, and therefore remaining thicker with respect to the cross-section of the vapor cell <NUM>. The etched portions can therefore correspond to the cell wall <NUM> between each of the structural features <NUM>. The etched portions corresponding to the cell wall <NUM> can therefore be much thinner with respect to the cross-section of the vapor cell <NUM> than the structural features <NUM>.

The portions of the cell wall <NUM> on which the structural features <NUM> are absent can constitute a much larger overall portion of the total surface area of the cell wall <NUM> than the portions of the cell wall <NUM> on which the structural features <NUM> are present. Stated another way, given that the structural features <NUM> and the cell wall <NUM> are integral with respect to each other, the cell wall <NUM> can constitute a much larger overall portion of the total surface area of the outer surface of the vapor cell <NUM> than the structural features <NUM>. Therefore, as one example, based on the much thinner material of the cell wall <NUM> combined with the larger surface area of the cell wall <NUM> relative to the structural features <NUM>, the vapor cell <NUM> can exhibit greater transmissivity of signals provided through the cell wall <NUM> to interact with the alkali metal vapor enclosed therein. Accordingly, the cell wall <NUM> can facilitate approximate transparency of the signals (e.g., RF signals) through the cell wall <NUM> and into the volume of the vapor cell <NUM> that confines the alkali metal vapor, such as while maintaining sufficient structural integrity to mitigate breakage of the cell wall <NUM> base on pressure gradients between the inner and outer surfaces of the cell wall <NUM>.

Other arrangements of a vapor cell, not covered by the claimed invention, are possible. For example, structural features can be implemented in any of a variety of other ways than the ring structures demonstrated in the embodiment of <FIG>. Examples not covered by the claimed invention is include one or more elongated portions that extend along the tubular length of the vapor cell, a helical or crisscross pattern along the tubular length of the vapor cell, chevrons, patches, or other types of arrangements of the structural features.

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

The sensor system <NUM> includes a vapor cell <NUM> that can be configured as a sealed glass container that includes a vapor of alkali metal atoms. The vapor cell <NUM> can correspond, for example, to the vapor cells <NUM> and/or <NUM> described above in the respective examples of <FIG>. The sensor system <NUM> also includes an optical signal system <NUM> that is configured to generate at least one optical beam, demonstrated in the example of <FIG> as a signal OPT. As an example, the optical signal system <NUM> can 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 system <NUM> can 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 cell <NUM> via 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 of <FIG>, one of the optical beams OPT can exit the vapor cell <NUM> as a detection beam OPTDET.

The sensor system <NUM> also includes a signal system <NUM> that is configured to generate any of a variety of signals or fields, demonstrated in the example of <FIG> as a signal SIG. As an example, the signal system <NUM> can 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 cell <NUM> to 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 system <NUM> can 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 system <NUM> can also or instead include a magnetic field generator that is configured to generate one or more magnetic fields that are provided through the vapor cell <NUM>, such as to provide for precession of the alkali metal vapor contained in the vapor cell <NUM>. As described herein, the arrangement of the cell wall and the structural feature(s) of the vapor cell <NUM> can be such that the cell wall of the vapor cell <NUM> can 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 cell <NUM>. As another example, the structural feature(s) of the vapor cell <NUM> can 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 cell <NUM>.

The sensor system <NUM> further includes a detection system <NUM> that is configured to monitor the detection beam OPTDET. For example, the detection system <NUM> can monitor a characteristic of the detection beam OPTDET that 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 OPTDET can be intensity, phase, Faraday rotation, or any of a variety of other optical beam characteristics. The detection system <NUM> can 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 cell <NUM> as described herein, the sensor system <NUM> can 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 cell <NUM>.

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 to <FIG>. It is to be understood and appreciated that the method of <FIG> is 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> illustrates an example of a method <NUM> for forming a vapor cell (e.g., the vapor cell <NUM>) for an atomic physics-based sensor system (e.g., the sensor system <NUM>). At <NUM>, a cell wall (e.g., the cell wall <NUM>) is formed from an approximately transparent material. The cell wall can include an inner surface and an outer surface. At <NUM>, at least one structural feature (e.g., the structural feature(s) <NUM>) 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. At <NUM>, the vapor cell is sealed to enclose an alkali metal vapor (e.g., Rb or Cs) within the vapor cell.

Claim 1:
A vapor cell (<NUM>, <NUM>, <NUM>) for an atomic physics-based sensor system (<NUM>), wherein the vapor cell (<NUM>, <NUM>, <NUM>) comprises:
a cell wall (<NUM>, <NUM>) arranged as a tubular vapor cell (<NUM>, <NUM>, <NUM>) and formed from an approximately transparent material, the cell wall (<NUM>, <NUM>) enclosing an alkali metal vapor and comprising an inner surface and an outer surface; characterized in that the vapor cell further comprises:
at least one structural feature (<NUM>, <NUM>) provided on at least one of the inner surface and the outer surface of the cell wall and formed as rings that circumscribe a respective one of the inner surface and the outer surface of the cell wall (<NUM>, <NUM>) and are arranged parallel with respect to each other along a length of the tubular vapor cell (<NUM>, <NUM>, <NUM>).