Patent ID: 12230492

To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

Embodiments herein describe using compressed source material in an atom cooling and trapping apparatus. Source material is often refined and sold with dendritic or crystalline surfaces that result in a very large surface area. This surface area increases the likelihood that a large amount contaminants will form on the surface, which is especially true for reactive source materials. For example, when placed in an environment with oxygen or water, oxide and hydroxide layers can form on the surface of the source material.

To mitigate the risk of contamination, the embodiments herein compress the source material onto a substrate. This changes the material from having a dendritic or crystalline surface to a flat surface, which has a much smaller surface area and thus is less susceptible to contaminants which can improve the lifetime usage of the source material. Further, the compressed source material and the substrate can be heated using external lasers rather than an oven within the vacuum chamber of the apparatus. This can reduce the size of the atom cooling and trapping apparatus. Also, because the source material is compressed into a flat surface, it is easier to target the source material with the laser relative to targeting a dendritic or crystalline surface.

Moreover, the substrate can serve as a baffle to prevent the atoms emitted by the source material from coating a window used by the external laser to heat the source material. For example, the substrate can be transparent so that the external laser can pass through the substrate to heat the source material. The substrate also blocks the emitted atoms from the source material from coating the window used to couple the external laser into the vacuum chamber. In addition, the substrate can thermally isolate the source material from the other components in the apparatus.

In another embodiment, rather than using lasers to heat the compressed source material, a resistive heater can be integrated into the substrate. The resistive heater can use an electrical current to generate heat which then causes the source material to emit atoms into the vacuum chamber.

FIG.1illustrates a vacuum chamber100for atom cooling and trapping, according to one embodiment. As shown, the vacuum chamber100can use an array of lasers or magnetic fields to trap atoms emitted by a compressed source material130to generate an atom cloud105in the presence of a vacuum (e.g., an ultra-high vacuum (UHV)). That is, the compressed source material130is heated by a laser115which causes the material130to emit the vapor135(e.g., gaseous atoms of the source material130). While some source materials emit a vapor135at relatively low temperatures, e.g., 50 degrees Celsius, other may emit vapor135at much higher temperatures, e.g., 300-500 degrees Celsius such as Sr.

The atom vapor135can be used to perform many different kinds of quantum applications such as atomic clocks, GPS systems and navigation, research on fundamental constants, quantum information, and atom interferometry. The embodiments herein are not limited to any particular technique for slowing down the atoms in the vapor135to form the cloud105, nor is it limited to any particular application of the atom cloud105. For example, the atom vapor135can be slowed/cooled/trapped using techniques such as 2D magneto-optical trap (MOT), 3D MOT, and/or Zeeman slowing. As specific examples, the vapor135can be used to make an atomic vapor beam; or the vapor135is cooled using a Zeeman slower or a 2D MOT; or slowed/cooled atoms can be trapped in a MOT, a magnetic trap, or an optical trap. In one embodiment, the vacuum chamber100is (or is part of) a low size, weight, and power (SWaP) device that produces source atom vapor for use in an ultra-cold atom apparatus.

In contrast to an in-vacuum oven where the means for heating the source material130is disposed in the vacuum chamber100, here one or more external lasers115are used to heat the source material130. The vacuum chamber100includes a window110through which the laser115can pass in order to reach the compressed source material130. Further, the compressed source material130is disposed on a transparent substrate120so that the laser115can pass through the substrate120to reach the compressed source material. For example, the transparent substrate120can be sapphire or glass. However, the substrate120is not limited to any particular material so long as the material is transparent and can maintain structural integrity at the temperatures needed to cause the source material130to emit the vapor135.

In one embodiment, the material of the substrate120is thermally insulating, which can reduce the amount of energy used to generate the vapor135. That is, a thermally insulating substrate120helps to keep the source material140hot and mitigate the amount of heat that is lost to the surrounding components in the vacuum chamber100.

In another embodiment, the substrate120can be optically opaque. In that case, the heating laser is absorbed by the substrate120, which in turn heats the source material140.

In one embodiment, the laser115is a continuous wave (CW) laser. However, in another embodiment, the laser115is pulsed. For example, cold-atom experiments or applications are often periodic or pulsed. The pulsing of the laser115can be synchronized (but does not have to be) with the periodicity or pulse of the experiment or application (such as when the atom cloud105is being formed). This means that the vapor135is released only when it is used by the experiment or application, which can save power and extend the lifetime of the source material130(e.g., reduce the rate at which it is depleted). Another potential benefit is that reduced vapor pressure results in better cold atom lifetime (since cold atoms are less likely to be knocked off their trap by hotter ones from the source) during the off state. This can be beneficial for some scientific experiments.

The embodiments herein are not limited to any particular type of laser115. Moreover, the wavelength of the laser115may depend on the type of the source material130. Some suitable laser wavelengths include 808 nm and 980 nm.

WhileFIG.1illustrates using an external heating source (e.g., the laser115) to heat the compressed source material130, the embodiments herein can also be used in an in-vacuum oven. As discussed in more detail inFIG.8below, a heating element could be disposed in the substrate and used to heat the source material130. For example, a current could be used to heat a resistive heater in the substrate120. However, having to connect the heater in the substrate120to a power source may complicate the assembly of the vacuum chamber and cause the vacuum chamber to be larger relative to using the laser115as the heat source. Further, using a resistive heater creates a magnetic field which can impact the atom cloud105. As such, the substrate120(and the sourced material130) may be spaced farther apart from the area that includes the atom cloud105so that the magnetic field generated by the heating current does not negatively impact the atom cloud105. This can further impact the size and compactness of the vacuum chamber100. Put differently, using the laser115may allow the source to be placed closer to cold-atoms experiments for higher atomic flux without worrying about stray magnetic fields generated from heater wire. Moreover, the laser115may have lower power requirements than a resistive heater since the source is being heated directly, and using the laser115can lower the risk of failure.

The vacuum chamber100also includes a baffle125formed around the compressed source material130. The baffle125could be a part of either the vacuum chamber or the source holder and can help prevent the vapor135from traveling to other, undesired parts of the vacuum chamber100. That is, the baffle125can prevent the vapor135from going in undesired directions within the vacuum chamber100. For example, the baffle125may prevent the vapor135from coating windows (not shown) that are used by the array of lasers that slow down the vapor135in order to create the atom cloud105.

Further, the substrate120can serve as another baffle to prevent the compressed source material130for emitting the vapor135in a direction to the window110. Because of the substrate120, the compressed material130cannot emit atom vapor135in a direction towards the window110. As such, the vapor135does not coat the window110which would create a reflective mirror that reflects the laser115so that it cannot enter into the vacuum chamber100. However, the vapor135can coat the sides of the baffle125but this is acceptable since the vapor135will be emitted in the direction of the atom cloud105and not coat any other laser windows.

FIG.2illustrates a press200for pressing source material215onto a substrate120, according to one embodiment. In this example, the substrate120is loaded onto a base210of the press200. For instance, an upper portion205of the press200may be raised so that the substrate120can be placed on the base210.

The substrate120is not limited to any particular size. In one embodiment, the substrate120may have a diameter of ⅛ of an inch to ½ of an inch. Further, the thickness of the substrate120may range from 1-10 millimeters. Further, the substrate120can have different shapes such as cylindrical or cubic.

Once the substrate120is placed on the base210, the uncompressed source material215can be placed on the substrate120. In one embodiment, the uncompressed source material215has dendritic or crystalline surface, but is not limited to such. The embodiments herein can advantageously be used with any suitable source material that has a non-planar surface area.

The upper portion205of the press200is lowered to contact the uncompressed source material215and compress it onto the substrate120where the upper portion205of the press200, the substrate120and a die212reform the source material215into a desired shape that reduces the surface area of the material215. This pressure can cause the source material215to adhere to the substrate120. That is, there may not be a need for any kind of adhesive material to cause the source material215to stick or bond to the substrate120. However, in other embodiments, an adhesive layer or material (which may be transparent) is disposed between the substrate120and the uncompressed source material215to help bond or adhere the source material215to the substrate120.

The force applied by the press200can vary depending on the type of the source material and the size of the substrate120. As an example, an approximately 1 ton-force can be used to compress Sr to form a substantially even layer on a sapphire substrate120with a ¼ inch diameter.

After compression, the source material now forms a compressed layer on the substrate120, which can have a thickness of, e.g., 1-10 millimeters. This layer does not have to be perfectly flat, but can still include an uneven top surface. Nonetheless, the surfaces of the source material are much flatter when compared to a dendritic surface. This can result in the advantages mentioned above such as mitigating the likelihood the source material will be contaminated when being transported, makes it much easier (e.g., requires less time and heat) to precondition the source material to remove any contaminates, provides an easier target for laser heating, and the like.

In one embodiment, the process described inFIG.2occurs in a clean environment (e.g., under vacuum). For example, the press200may be in a glovebox, which can be filled with an inert gas (e.g., argon). For example, the substrate120and the uncompressed source material215can be introduced into the clean environment in sealed containers. For example, the uncompressed source material215may be transported in a vial filled with inert material (e.g., mineral oil) to prevent it from becoming contaminated. The vial can then be opened after it has been introduced into the clean environment. Thus, as the uncompressed source material215is placed on the substrate120, it will not become contaminated.

Further, after the press200has flattened the source material215onto the substrate, a technician may place the resulting sample into a sealed container so it can be removed from the clean environment without being exposed to contaminates in the air. For example, the source material215and the substrate can be hermetically sealed with an indium seal or submersed in an inert material such as mineral oil.

FIG.3illustrates compressing a dendritic material onto a substrate, according to one embodiment. That is, the left image inFIG.3illustrates a dendritic surface of Sr. This illustrates how Sr is typically produced and sold. The right image illustrates the result of pressing the Sr to form the compressed source material130on the substrate120. That is, the right image illustrates the results of using the press200inFIG.2to compress the source material.

While the embodiments herein discussing pressing the source material215to reduce its surface area, other types of techniques can be used to alter the source material to reduce its surface area. For example, the source material215may be machined into a cylindrical shape as shown inFIG.3. Or the source material215may be melted and put into a cast to form a desired shape. As such, the embodiments herein are not limited to using a press to reduce the surface area.

FIG.4is a flowchart of a method400for adding a compressed source material into a vacuum chamber, according to one embodiment. For example, the vacuum chamber may be part of an ultra-cold atom apparatus for laser cooling and trapping. However, the embodiments are not limited to such. This embodiments herein can be applied to any apparatus that uses an atom source such as gravimeters, accelerometers, gyroscopes, and trace gas detection. These sensors may not use an atom cloud as shown inFIG.1, or use laser cooling and trapping in order to perform their functions. For example, these sensors may use the atom vapor directly.

At block405, the source material is placed on a substrate. As mentioned inFIG.2, the substrate may first be placed in the base of a press. Further, the substrate and the source material may be disposed in a clean environment, such as a glovebox.

Moreover, the amount of source material placed on the substrate may depend on the desired lifetime of the device. Adding more source material extends the lifetime, but also requires more power to heat the material and may have a longer “turn on” time (e.g., the time it takes for the source material to be heated to a sufficient temperature to emit the atom vapor). Using less source material shortens the lifetime but saves power or can reduce the turn on time.

At block410, the press compresses the source material onto the substrate. This compression at least partially flattens the source material, which reduces its overall surface area. The source material may have a dendritic or a crystalline surface before it is compressed; however, the embodiments herein may be beneficial for any source material that has a non-flat surface. Moreover, the source material does not have to be perfectly flat after compression in order to benefit from the embodiments herein.

In one embodiment, compressing the source material onto the substrate causes the source material to adhere to the substrate.

While some source material can be malleable enough to be pressed at room temperature, other source materials may be heated before being compressed onto the substrate.

At block415, the compressed source material (now mounted on the substrate), is placed into a source holder. One example of a source holder will be discussed below inFIG.5. In general, the source holder can be any apparatus that permits the compressed source material to be mounted inside the vacuum chamber.

In another embodiment, rather than pressing the source material onto the same substrate that is then inserted into the source holder, the source material may be pressed to reduce surface area on a different substrate. The source material could then be removed from that substrate (e.g., a non-transparent substrate) and attached to the desired substrate (e.g., a transparent substrate120inFIG.1). Thus, the source material can be pressed to reduce surface area on any substrate but then removed from that substrate and placed on a desired substrate. This may be advantageous so that desired substrate is not damaged during the pressing process.

At block420, the source holder is placed into the vacuum chamber. For example, the source holder can include an aperture that permits the atoms emitted by the source material (when heated) to exit the source holder and enter into the vacuum chamber. For example, as shown inFIG.1, a source holder can include the baffle125which directs the vapor135into the area of the vacuum chamber100that creates the atom cloud105.

In one embodiment, the blocks405-420may be performed in a same clean environment (e.g., a glovebox). For example, the press, the source holder, and the vacuum chamber may be in the glovebox. However, in another embodiment, the blocks405-420may be performed in different environments. For example, blocks405and410may be performed in a first environment after which the compressed source material is transported to a different environment where it is placed into the source holder, and then the vacuum chamber.

The method400also includes preconditioning the source material (which is illustrated in a hashed box to indicate it is optional). Preconditioning can be done between (or part of) any of the steps410-420after the source material has been compressed onto the substrate. Preconditioning can include heating the source material in the presence of a vacuum so that contaminants (e.g., oxide and/or hydroxide layers) are removed from its reactive surface. This can be performed before the vacuum chamber is put into operation (e.g., before generating an atom cloud, using the vacuum chamber as part of a sensor, etc.).

However, preconditioning may not be performed if the source material is kept sufficiently free from contaminants as it is being processed. In that case, block425may be omitted.

FIG.5illustrates a source holder500, according to one embodiment. The top of the holder500includes a flange505that can be used to attach the source holder500to a vacuum chamber. For example, the source holder500can be inserted into a vacuum chamber where the flange505is used to attach the holder500to the outside surface of the vacuum chamber. The flange505can be a UHV flange that creates an air tight seal with the surface of the vacuum chamber.

FIG.5also illustrates a side view of the inside of the source holder500. Starting from the right, the side view illustrates an aperture550through which the laser (or multiple lasers) can pass through (along with a transparent substrate120) to heat the compressed source material130. In one embodiment, the aperture550may be aligned with the window110in the vacuum chamber100inFIG.1so that the laser can pass through both the window110, the aperture550, and the substrate120to reach the source material130.

The source holder500includes a sleeve515(or collar) that has an inner dimension that substantially matches the diameter of the substrate120so that the substrate120is held in place in the sleeve515.

Further, a spring-loaded clamp520applies a force to the compressed source material130to hold it and the substrate120in place in the sleeve515. That is, a spring525is placed between a lid510(which can be screwed or bolted onto the source holder500) to bias the clamp520which in turn holds the substrate120in the sleeve515. This force may help to prevent the substrate120from moving as the source holder500experiences any accelerations (e.g., vibrations, is dropped, jostled, etc.).

Moreover, as the source material130is expended over the lifetime of the apparatus (i.e., as the source material130is depleted) the spring525can continue to apply pressure using the clamp520to hold the substrate120in place. That is, as the compressed source material130thins as the vapor is created, the clamp520and the spring525continue to hold the substrate120in the same location.

In one embodiment, the sleeve515and the clamp520are made from thermally insulating material to reduce heat loss which in turn reduces the amount of laser power required to heat the source material130.

In this example, the lid510includes an aperture that permits the vapor emitted when the source material130is heated to exit the source holder500into the inner portion of the vacuum chamber. For example, the area to the left of the lid510may be the area where the atom cloud105shown inFIG.1is formed, or where some other measurement or experiment is performed, which can vary depending on the application (e.g., gravimeters, accelerometers, gyroscopes, etc.).

FIG.6is an exploded view of the source holder500inFIG.5, according to one embodiment. As shown, the lid510, spring525, clamp520, source material130, substrate120, and sleeve515are shown external to a housing610.FIG.6illustrates an order in which these components can be placed in the housing610. That is, the sleeve515may first be slid into the housing610, the combined substrate/source material can then be seated into the right side of the sleeve515, and the clamp520can then be slid into the sleeve515until it contacts the source material130. The spring525can be placed between the clamp520and the lid510, and finally, the lid510can be screwed or bolted into the housing610to hold the assembly in place and to compress the spring525so it applies the bias to the clamp520and the substrate120.

FIG.6also illustrates a baffle605(or aperture) in the lid510that permits the vapor emitted from the source material130to exit the housing and into the vacuum chamber. That is, the baffle605can be arranged to direct the vapor to a desired area within the chamber (e.g., the area where the atom cloud is formed). In one embodiment, a combination of the baffle605and the clamp520can serve as the baffle125shown inFIG.1which directs the vapor135to the desired area and prevents the vapor135from coating surfaces that it should not (e.g., windows or other apparatuses that may be in the vacuum chamber).

In addition,FIG.6illustrates that the spring525defines a first aperture through its center and the clamp520defines a second aperture through its center that are aligned with the aperture defined by the baffle605. These apertures provide a pathway through which the atom vapor can pass in order to exit the housing610and reach a desired area where an atomic experiment or atomic application is being performed (e.g., the area where an atom cloud is formed).

FIGS.7A-7Cillustrate heating a source material using a laser, according to several embodiments.FIG.7Aillustrates a vacuum chamber700similar to the chamber100shown inFIG.1. As such, the same reference numbers are used to reference to similar components. However, the vacuum chamber700differs from the chamber100in that the window110is not aligned with the substrate120. Instead, the vacuum chamber700includes mirrors705A and705B which redirect the laser115so that it ultimately aligns with the substrate120and the source material130.

While two mirrors705are shown, the vacuum chamber700can have any number of mirrors (e.g., only one, or three, four, five, etc.) for aligning the laser115with the substrate120and the source material130. In one embodiment, these mirrors may be disposed within the housing610of the source holder500as shown inFIG.6. Alternatively, the mirrors may be disposed in a region in the vacuum chamber between the housing610and the window110.

One advantage of using one or more mirrors705is that they provide additional flexibility for where the window110can be placed in the vacuum chamber700. That is, the source material130does not have to be disposed along an axis that extends through, and is orthogonal to, the window110. Using mirrors705, the window can potentially be placed on any side of the vacuum chamber700(regardless whether those sides are orthogonal or parallel with the source material130). Moreover, the substrate120(and potentially the baffle) prevents the atomic vapor from coating the mirrors705

FIG.7Billustrates a vacuum chamber720with a dual window/substrate725. In this case, the substrate725on which the source material130is compressed also serves as a window for the vacuum chamber720. That is, the transparent window/substrate725can be part of the outer surface of the vacuum chamber720.

In one embodiment, after the source material130is pressed onto the substrate725, this sample can then be attached to the surface of the vacuum chamber720. Alternatively, the source material130may be pressed onto an already installed window of a vacuum chamber—i.e., the window may already be assembled into the chamber720and then the source material is pressed onto the window. Advantageously, this omits the need for a separate substrate and it may be easier to ensure the laser115strikes the source material130since it is disposed on the outer surface or wall of the vacuum chamber720.

In another embodiment, rather than using the substrate as the window, the substrate can be directly pressed onto a vacuum window. For example, a transparent adhesive can be used to attach the substrate to the window of the vacuum chamber. In that case, the source material can first be compressed on to the substrate. This combined assembly can then be mounted or attached to a window of the vacuum chamber.

FIG.7Cillustrates a vacuum chamber750where the laser115strikes the source material130without passing through the substrate120. In this case, the substrate120can be a non-transparent material, which may increase the number of suitable materials that can be used as the substrate120. That is, both transparent and non-transparent substrate materials can be used in the embodiment shown inFIG.7C.

However,FIG.7Cmay not have a baffle, or if it has a baffle, the baffle is arranged (or has an aperture) so that the laser115can pass through the baffle to reach the source material130. Because neither the baffle nor the substrate120may block the vapor from reaching the window110, in one embodiment, the window110may be heated to prevent the atoms in the vapor from coating the window110. However, the windows110shown inFIGS.1,7A and7Bmay not be heated since the baffle and/or the substrate prevent the vapor from reaching the windows110.

FIG.8illustrates heating the source material130using a resistive heater810, according to one embodiment. In this example, instead of using a laser to heat the material130, the substrate805includes an integrated resistive heater810. The heater810can be disposed in the substrate805before the source material130is pressed onto the substrate805.

In one embodiment, the resistive heater810may be connected to electrodes in the vacuum chamber800that provide a current through the heater810. This current can cause the heater810to heat the source material130(similar to the laser) so that the atomic vapor135is released. As such,FIG.8illustrates that the embodiments herein are not limited to using a laser to heat the source material. Further, while the resistive heater810is disposed in the substrate805, it is not limited to such. In another example, the heater810can include a resistive coil that is wrapped around the periphery of the source material130and/or the substrate. However, as explained above, the current through the resistive heater810can create a magnetic field that may negatively affect the atom cloud105. As such, moving the resistive heater810to be as far away as way as possible from the atom cloud105can mean the atom cloud105can be formed closer to the source material130.

Also, becauseFIG.8is an example of an in-vacuum oven (because the heater810is inside the vacuum chamber800), the size of the vacuum chamber800may be larger than if a laser were used. For instance, the heater810may rely on an electrical feedthrough with increases complexity and limits design flexibility. However, the use of an in-vacuum oven also means the window110shown inFIG.1can be omitted.