A vapour containment structure

Abstract

This invention provides a vapour containment structure comprising: a first vapour containment structure segment; a second vapour containment structure segment; a first connector comprising: a first portion defining an interior passageway extending between a first interface and a second interface, wherein the first interface of the first portion of the first connector is configured to connect with the first vapour containment structure segment and the second interface is configured to connect with the second vapour containment structure segment, wherein an optical path passes from the first vapour containment structure segment to the second vapour containment structure segment via the interior passageway of the first portion of the first connector, and a second portion defining an interior passageway, the interior passageway of the second portion of the first connector being connected to the interior passageway of the first portion of the first connector at a junction between the first and second interfaces of the first portion of the first connector, wherein a major axis of the first portion of the first connector is offset to a major axis of the second portion of the first connector; and a first vapour reservoir connected to the first portion of the first connector via the second portion of the first connector such that the first vapour reservoir is in fluidic communication with the first and a second vapour containment structure segments via the interior passageway of the first portion of the first connector and the interior passageway of the second portion of the first connector.

Description

[0001] A VAPOUR CONTAINMENT STRUCTURE

[0002] Field of the Invention

[0003] The present invention relates to a vapour containment structure.

[0004] Background

[0005] It is desirable to contain an atomic vapour, such as a vapour of alkali and alkali earth metals, for use in a variety of quantum technologies, such as an atomic receiver or atomic clock, and a variety of optical technologies, such as an optical reference or gas laser. Typically, a containment of atomic vapour is provided as a vessel. However, it is desirable to confine the containment of atomic vapour to a low-aspect ratio structure, such as a Hollow Core Fibre (HCF) or other waveguide, to enable direct integration with quantum and / or optical technologies. The ability to create an optical waveguide which ensures the optical path intercepts a volume of vapour is challenging for several reasons.

[0006] Firstly, the material that is typically contained for use in many quantum applications, such as Rubidium, tends to be highly reactive. For example, Rubidium exposed to air and / or water reacts violently and irreversibly, leading to compounds that no longer have the useful electronic configurations of the unreacted Rubidium vapour.

[0007] Secondly, the material is typically contained at a low pressure to ensure the material is in its vapour phase. This presents a challenge when filling low aspect ratio structures, such as an HCF or other waveguide, as the narrow aperture limits the rate of filling and the low aspect ratio along the length of the structure increases the time taken for the vapour pressure to equilibrate.

[0008] Thirdly, when the material is contained within an HCF (or similar structure), there is a high surface area to volume ratio between the contained material and the surrounding structure. The resulting interactions between the surrounding structure and the material must be mitigated or managed.

[0009] It is therefore desirable to alleviate at least some of the above problems. Summary of the Invention

[0010] According to a first aspect of the invention, there is provided a vapour containment structure comprising: a first vapour containment structure segment; a second vapour containment structure segment; a first connector comprising: a first portion defining an interior passageway extending between a first interface and a second interface, wherein the first interface of the first portion of the first connector is configured to connect with the first vapour containment structure segment and the second interface is configured to connect with the second vapour containment structure segment, wherein an optical path passes from the first vapour containment structure segment to the second vapour containment structure segment via the interior passageway of the first portion of the first connector, and a second portion defining an interior passageway, the interior passageway of the second portion of the first connector being connected to the interior passageway of the first portion of the first connector at a junction between the first and second interfaces of the first portion of the first connector, wherein a major axis of the first portion of the first connector is offset to a major axis of the second portion of the first connector; and a first vapour reservoir connected to the first portion of the first connector via the second portion of the first connector such that the first vapour reservoir is in fluidic communication with the first and second vapour containment structure segments via the interior passageway of the first portion of the first connector and the interior passageway of the second portion of the first connector.

[0011] The vapour containment structure may further comprise a third vapour containment structure segment; and a second connector comprising: a first portion defining an interior passageway extending between a first interface and a second interface, wherein the first interface of the first portion of the second connector is configured to connect with the second vapour containment structure segment and the second interface is configured to connect with the third vapour containment structure segment, wherein an optical path passes from the second vapour containment structure segment to the third vapour containment structure segment via the interior passageway of the first portion of the second connector, and a second portion defining an interior passageway, the interior passageway of the second portion of the second connector being connected to the interior passageway of the first portion of the second connector at a junction between the first and second interfaces of the first portion of the second connector, wherein a major axis of the first portion of the second connector is offset to a major axis of the second portion of the second connector; and a second vapour reservoir connected to the first portion of the second connector via the second portion of the second connector such that the first vapour reservoir is in fluidic communication with the second and third vapour containment structure segments via the interior passageway of the first portion of the second connector and the interior passageway of the second portion of the second connector.

[0012] The first interface of the first portion of the first connector may be configured as a seal between the first portion of the first connector and the first vapour containment structure segment and / or the second interface of the first portion of the first connector may be configured as a seal between the first portion of the first connector and the second vapour containment structure segment.

[0013] The first interface of the first portion of the second connector may be configured as a seal between the first portion of the second connector and the second vapour containment structure segment and / or the second interface of the first portion of the second connector may be configured as a seal between the first portion of the second connector and the third vapour containment structure segment.

[0014] The first vapour reservoir may comprise one of a group comprising: a solid material, the solid material having a property so as to provide vapour via sublimation, and a liquid material, the liquid material having a property so as to provide vapour via vapourisation or evaporation.

[0015] The second vapour reservoir may comprise one of a group comprising: a solid material, the solid material having a property so as to provide vapour via sublimation, and a liquid material, the liquid material having a property so as to provide vapour via vapourisation or evaporation.

[0016] The first and / or second vapour reservoir may be connected to an external vapour source.

[0017] The vapour containment structure may further comprise a vacuum pump configured to evacuate the first vapour reservoir, first vapour containment structure segment, and second vapour containment structure segment. The vacuum pump may be configured to evacuate the second vapour reservoir and third vapour containment structure segment.

[0018] The first vapour containment structure segment may comprise a first end and a second end, and the second vapour containment structure segment may comprise a first end and a second end, the first interface of the first portion of the first connector may be configured to configured to connect to the second end of the first vapour containment structure segment and the second interface of the first portion of the first connector may be configured to connect to the first end of the second vapour containment structure segment, the vapour containment structure may further comprise: a first termination segment comprising a first interface configured to connect to a first end of the first vapour containment structure segment; and a second termination segment comprising a first interface configured to connect to a second end of the second vapour containment structure segment.

[0019] Brief Description of the Figures

[0020] In order that the present invention may be better understood, embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which:

[0021] Figure 1 is a schematic diagram of a vapour containment structure;

[0022] Figure 2 is a schematic diagram illustrating a connection between two Hollow Core Fibre (HCF) segments of the vapour containment structure of Figure 1 ;

[0023] Figure 3 is a schematic diagram illustrating a termination of the vapour containment structure of Figure 1 ; and

[0024] Figure 4 is a schematic diagram of the vapour containment structure 100 connected to a vacuum pump.

[0025] Detailed Description

[0026] Figure 1 illustrates a vapour containment structure 100 comprising a plurality of vapour containment structure segments each, in this example, being a Hollow Core Fibre (HCF) segment. The plurality of HCF segments collectively use reference 1 10, and comprise a first HCF segment 1 10-1 , a second HCF segment 1 10-2 and a third HCF segment 1 10- 3. Figure 1 further illustrates a first Single-Mode Fibre (SMF) 120 and a second SMF The first, second and third HCF segments 110-1 , 110-2, 1 10-3 are hollow waveguides having a hollow core and therefore defining an interior passageway throughout their respective lengths. The interior passageways of the hollow cores may be filled with a vapour, such as a vapour of an alkali metal such as Rubidium, via a process discussed in more detail below. The first, second and third HCF segments 110-1 , 1 10-2, 110-3 are designed to guide an optical signal having a particular wavelength.

[0027] In one example, the HCF segments may have an outer diameter of 125um (although 250um is another common option). The hollow cores of the HCF segments may have diameters in the range of 30pm to 60pm, and therefore be considered a large core. The large cores of the HCF segments allow for faster diffusion of the vapour material and also have longer Rayleigh coupling lengths enabling large distances between two interfaces while maintaining efficient coupling.

[0028] Figure 1 further illustrates a plurality of connectors comprising: a first HCF connector 160 connecting the first and second HCF segments 110-1 , 1 10-2; a second HCF connector 170 connecting the second and third HCF segments 1 10-2, 1 10-3; a first HCF termination connector 180 connecting the first HCF segment 1 10-1 and the first SMF 120; and a second HCF termination connector 190 connecting the third HCF segment 110-3 and the second SMF 130.

[0029] Figure 2 illustrates the connection between the first and second HCF segments 110-1 , 110-2 via the first HCF connector 160 in more detail. The first HCF connector 160 comprises a first elongate section 160-1 , a second elongate section 160-2 and a vapour reservoir 160-3. The second elongate section 160-2 extends between the first elongate section 160-1 and the vapour reservoir 160-3. The first elongate section 160-1 is hollow and therefore defines an interior passageway extending between a first port 160-4 and a second port 160-5. Similarly, the second elongate section 160-2 is hollow and defines an interior passageway extending from the interior passageway of the first elongate section 160-1 to the vapour reservoir 160-3. The interior passageways of the first elongate section 160-1 and second elongate section 160-2 are therefore connected via an open junction to enable fluidic communication therebetween. Similarly, the interior passageway of the second elongate section 160-2 and an interior of the vapour reservoir 160-3 are connected via an open junction to enable fluidic communication therebetween. Vapour contained in the vapour reservoir 160-3 may therefore be communicated throughout the interior passageways of the first and second elongate sections 160-1 , 160-2.

[0030] The first HCF connector 160 is therefore shaped as a T-junction. However, a perpendicular alignment of the first and second elongate sections 160-1 , 160-2 is non- essential, and the second elongate section 160-2 may extend between the first elongate section 160-1 and the vapour reservoir 160-3 at a variety of angles such that a major axis of the first elongate member 160-1 (defining a part of an optical path between the first and second HCF segments 1 10-1 , 1 10-2) is offset from a major axis of the second elongate member 160-2 (defining a part of a vapour path between the vapour reservoir 160-3 and the first and second HCF segments 110-1 , 1 10-2).

[0031] The first port 160-4 and section of the interior passageway adjacent the first port 160-4 are shaped and dimensioned so as to receive the first HCF segment 110-1. In one example, the diameter of the first port 160-4 may be 125pm to match the outer diameter of the first HCF segment 110-1. The first HCF segment 1 10-1 therefore extends into and within the interior passageway of the first HCF connector 160 via the first port 160-4. The first HCF segment 110-1 extends into the interior passageway of the first elongate section 160-1 of the first HCF connector 160 up to a first insertion point. The first insertion point is between the first port 160-4 of the first HCF connector 160 and the open junction between the interior passageways of the first and second elongate sections 160- 1 , 160-2. In this example, the first insertion point is adjacent the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2. That is, the first HCF segment 1 10-1 is inserted up to the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2 without blocking any portion of said open junction (which would otherwise limit or prevent fluidic communication between the interior passageways of the first and second elongate sections 160-1 , 160-2). The first HCF segment 110-1 is hermetically sealed to the inner wall of the interior passageway of the first HCF connector 160, such as by fusing the glass of the first HCF segment 110-1 to the inner wall of the interior passageway of the first elongate section 160-1 and / or by applying adhesive that is resistant to corrosion by the vapour contained in the vapour reservoir 160-3. Similarly, the second port 160-5 and section of interior passageway adjacent the second port 160-5 are shaped and dimensioned so as to receive the second HCF segment 1 10- 2. In one example, the diameter of the second port 160-5 may be 125pm to match the outer diameter of the second HCF segment 1 10-2. The second HCF segment 110-2 therefore extends into and within the interior passageway of the first HCF connector 160 via the second port 160-5. The second HCF segment 1 10-2 extends into the interior passageway of the first elongate section 160-1 of the first HCF connector 160 up to a second insertion point. The second insertion point is between the second port 160-5 of the first HCF connector 160 and the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2. In this example, the second insertion point is adjacent the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2. That is, the second HCF segment 1 10-2 is inserted up to the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2 without blocking any portion of said open junction (which would otherwise limit or prevent fluidic communication between the interior passageways of the first and second elongate sections 160-1 , 160-2). The second HCF segment 110- 2 is hermetically sealed to the inner wall of the interior passageway of the first HCF connector 160, such as by fusing the glass of the second HCF segment 1 10-2 to the inner wall of the interior passageway of the first elongate section 160-2 and / or by applying adhesive that is resistant to corrosion by the vapour contained in the vapour reservoir 160-3.

[0032] By inserting the first and second HCF segments 110-1 , 1 10-2 up to the respective first and second insertion points adjacent the open junction between the interior passageways of the first and second elongate sections 160-1 , 160-2 (but without blocking any portion of said open junction), the respective inserted ends of the first and second HCF segments 110-1 , 110-2 are as close as possible without limiting or preventing fluidic communication between the interior passageways of the first and second elongate sections 160-1 , 160-2. This close proximity is desirable so as to maximise optical coupling of an optical signal being communicated between the first and second HCF segments 110-1 , 110-2. To further optimise this optical coupling, the hollow cores of the first and second HCF segments 1 10-1 , 110-2 are of the same or similar diameter. In the configuration illustrated in Figure 2, vapour may be communicated from the vapour reservoir 160-3 along the interior passageway of the second elongate section 160-2, through the open junction between interior passageways of the first and second elongate sections 160-1 , 160-2, along the interior passageway of the first elongate section 160-1 , and into and along the respective hollow cores of the first and second HCF segments 110-1 , 1 10-2. Vapour of the vapour reservoir 160-3 may therefore be communicated to and throughout the respective hollow cores of the first and second HCF segments 110- 1 , 1 10-2.

[0033] The outer diameter of the first elongate section 160-1 may be around 2-5mm. The first HCF connector 160 may be constructed out of glass, or any material that may be bonded to glass by the application of heat or adhesive (e.g. fused silica or graphite) and will not react with the vapour material. The second elongate section 160-2 may have any suitable inner or outer diameters so long as it is mechanically stable. The vapour reservoir may have a volume of around 1cm3.

[0034] The second elongate section 160-2 is as short as possible to minimise a volume of its interior passageway. This maximises the amount of vapour that may be communicated from the vapour reservoir 160-3 to the respective hollow cores of the first and second HCF segments 110-1 , 110-2 which would otherwise occupy the interior passageway of the second elongate section 160-2. There may be a minimum length for the second elongate section 160-2 due to, for example, limitations in the glass blowing process or a requirement to enable burn off points along the length of the second elongate section 160-2 (which may be used to burn off the vapour reservoir 160-3 at some point in the device lifetime) such as 20mm from the junction between the first and second elongate sections 160-1 , 160-2.

[0035] In this example, the vapour reservoir 160-3 contains a solid material that may sublimate / vapourise (e.g. by the application of heat and / or reduced pressure) to provide a vapour source.

[0036] Turning back to Figure 1 , the vapour containment structure 100 further comprises a connection between the second HCF segment 1 10-2 and third HCF segment 1 10-3 via the second HCF connector 170. This connection is the same or substantially similar to the connection between the first HCF segment 1 10-1 and the second HCF segment 1 10- 2 via the first HCF connector 160, as described above with reference to Figure 2.

[0037] The vapour containment structure 100 therefore comprises vapour reservoirs at multiple points along the length of the vapour containment structure 100, which each provide vapour into respective hollow cores of each segment of the vapour containment structure 100 via interior passageways that are sealed from an external environment. The vapour filling process is therefore contamination free such that no contaminants from the external environment enter the respective hollow cores of the hollow segments of the vapour containment structure 100. Furthermore, by providing vapour at multiple points along the length of the vapour containment structure 100, the vapour containment structure 100 may be filled at a faster rate and achieve a vapour pressure equilibrium more quickly relative to a conventional vapour containment structure being filled at one end.

[0038] The hollow core of the vapour containment structure 100 is filled with vapour from the vapour reservoirs and may thereafter be used in any quantum or optical application. Furthermore, the vapour reservoirs may periodically or continuously provide additional vapour to the hollow core of the vapour containment structure 100 subsequent to the initial fill of vapour from the vapour reservoirs. Any subsequent fill may be performed before, during or after use of the vapour containment structure in a quantum or optical application. This is beneficial as one or more properties of the vapour containment structure 100, such as the vapour pressure within the hollow core, may degrade due to, for example, interactions between the vapour and an inner wall of the interior passageway of the first or second elongate section of the first or second HCF connector 160, 170, and / or an inner wall of the hollow core of the first, second or third HCF segment 110-1 , 1 10-2, 110-3. Therefore, by providing additional vapour from one or more vapour reservoirs, the property of the vapour containment structure 100 (e.g. vapour pressure) may be maintained.

[0039] Figure 3 illustrates a termination of the vapour containment structure 100 between the first HCF segment 110-1 and the first termination connector 180. The first termination connector 180 is an elongate glass capillary being hollow so as to define an interior passageway extending between a first port 180-1 and a second port 180-2. The first port 180-1 and section of the interior passageway adjacent the first port 180-1 are shaped and dimensioned so as to receive the first SMF 120. The first SMF 120 therefore extends into and within the interior passageway of the first termination connector 180 via the first port 180-1. The first SMF 120 extends into the interior passageway of the first termination connector 180 up to a first insertion point. The first SMF 120 is hermetically sealed to an inner wall of the interior passageway of the first termination connector 180, such as by fusing glass and / or applying adhesive.

[0040] The second port 180-2 and section of the interior passageway adjacent the second port 180-2 are shaped and dimensioned so as to receive the first HCF segment 1 10-1 (that is, an opposing end of the first HCF segment 110-1 to the end of the first HCF segment 110-1 inserted into the first HCF connector 160 as described above with reference to Figure 2). The first HCF segment 1 10-1 therefore extends into and within the interior passageway of the first termination connector 180 via the second port 180-2. The first HCF segment 1 10-1 extends into the interior passageway of the first termination connector 180 up to a second termination point. The first HCF segment 1 10-1 is hermetically sealed to an inner wall of the interior passageway of the first termination connector 180, such as by fusing glass and / or applying adhesive.

[0041] In the example shown in Figure 3, the first and second termination points are at equal points along the length of the first termination connector 180 such that the first SMF 120 and first HCF segment 110-1 are inserted into the interior passageway so as to abut one another. That is, an end of the first SMF 120 abuts an end of the first HCF segment 1 10- 1. Minimising the distance between the respective ends of the first SMF 120 and first HCF segment 1 10-1 is desirable so as to maximise optical coupling of an optical signal communicated between the first SMF 120 and first HCF segment 110-1 and further so as to minimise any volume of vapour that would otherwise occupy the interior passageway of the first termination connector 180 between the first SMF 120 and first HCF segment 1 10-1.

[0042] In the event that optimal optical coupling between the first SMF 120 and first HCF segment 1 10-1 cannot be achieved by abutting their respective ends (due to, for example, a mismatch of the respective core sizes), then a lens (such as a solid core graded index fibre or a Gradient-index (GRIN) lens) may be positioned in the interior passageway of the first termination connector 180 so as to optically couple an optical signal communicated between the first SMF 120 and first HCF segment 110-1. In this scenario, both the first SMF 120 and first HCF segment 110-1 are inserted up to the lens so as to abut the lens on opposing sides thereof.

[0043] T urning back to Figure 1 , the apparatus 100 further comprises a connection between the third HCF segment 1 10-3 and second SMF 130 via the second termination connector 190. This connection is the same or substantially similar to the connection between the first SMF 120 and first HCF segment 1 10-1 via the first termination connector 180, as described above with reference to Figure 3.

[0044] A method of manufacturing the vapour containment structure 100 will now be described. The vapour reservoir of each HCF connector is initially cleaned and placed in an inert normal pressure environment. The solid material source is then placed inside the vapour reservoir and the reservoir is sealed.

[0045] The first and second elongate segments of each HCF connector are then filled with an inert gas and the vapour reservoir and second elongate segment are joined by application of heat.

[0046] As shown in Figure 4, the vapour reservoir of each HCF connector is initially connected to a vacuum pump 200. The vapour containment structure 100 is constructed by connecting the HCF segments via the assembly of HCF connectors and termination connectors. The vapour containment structure 100 is then flushed with an inert gas. The vacuum pump 200 is then operated so as to lower the pressure throughout the vapour containment structure 100. As the pressure drops, the solid material source sublimates and therefore acts as a vapour source.

[0047] The vacuum pump 200 may be separated from the remainder of the vapour containment structure 100 by application of heat (e.g. by blow torch or tungsten wire) at suitable burn off points on the connectors between the vapour reservoirs and the vacuum pump 200 (resulting in the vapour containment structure 100 of Figure 1 . Alternatively, the vacuum pump 200 may also act as a vapour source so as to provide (additionally or alternatively to the solid material source) vapour to the vapour containment structure. The vapour containment structure 100 is modular such that one or more vapour containment structure segments may be added to the vapour containment structure 100. For example, a fourth HCF segment may be added to the vapour containment structure 100 by: 1 ) disconnecting a first end of the third HCF segment 1 10-3 from the second termination connector 190, 2) providing a third HCF connector (the same or similar to the first HCF connector 160 described above with reference to Figure 2), 3) inserting the first end of the third HCF segment 1 10-3 into a first port of a first elongate section of the third HCF connector, 4) inserting a first end of the fourth HCF segment into a second port of the first elongate section of the third HCF connector, and 5) inserting a second end of the fourth HCF segment into the second termination connector 190. In this way, the vapour containment structure 100 comprises four HCF segments including the first, second, third and fourth HCF segments. A similar method may be used to insert an additional HCF segment between the first termination connector 180 and the first HCF segment 1 10-1 , or between any adjacent pair of HCF segments (e.g. between the first and second HCF segments 1 10-1 , 110-2 or between the second and third HCF segments 110-2, 110-3). A plurality of additional HCF segments may be inserted in the same operation.

[0048] As the process of adding additional HCF segments involves a step of disconnecting an HCF segment from a termination connector or an HCF connector, then the process may be performed before sealing the HCF segment and connector.

[0049] Furthermore, the modular construction of the vapour containment structure 100 enables one or more segments of the vapour containment structure 100 to be removed. For example, the first HCF segment 110-1 may be removed by: 1 ) disconnecting a first end of the first HCF segment 1 10-1 from the first termination connector 180, 2) disconnecting a first end of the second HCF segment 110-2 from the first HCF connector 160, and 3) inserting the first end of the second HCF segment 1 10-2 into the first termination connector 180. A similar method may be used to remove the third HCF segment 1 10-3 from the second termination connector 190, or to remove the second HCF segment 110- 2 (such that the first HCF segment 1 10-1 is thereafter connected to the third HCF segment 110-3). A plurality of HCF segments may be removed in the same operation.

[0050] The skilled person will understand that the method and apparatus described above is not limited to HCF. That is, vapour containment structure 100 may comprise segments of other hollow elongate containment structures, such as a capillary or an optical waveguide. These structures are characterised as being relatively narrow in two dimensions relative to a third dimension, and further characterised as having a narrow aperture to their hollow interior (in which the aperture is narrow in two dimensions relative to a third dimension).

[0051] Furthermore, the skilled person will understand that the method and apparatus described above may be used to fill the HCF (or other containment structure) with alternative materials, such as any atomic, molecular, gas or suspended powder vapour.

[0052] As noted above, the vapour source may be via a solid material in the vapour reservoir or vapour from an external source. Additionally, the vapour reservoir may contain a liquid material which provides vapour via evaporation / vapourisation. The skilled person will understand that any combination of features is possible within the scope of the invention, as claimed.

Claims

CLAIMS1 . A vapour containment structure comprising: a first vapour containment structure segment; a second vapour containment structure segment; a first connector comprising: a first portion defining an interior passageway extending between a first interface and a second interface, wherein the first interface of the first portion of the first connector is configured to connect with the first vapour containment structure segment and the second interface is configured to connect with the second vapour containment structure segment, wherein an optical path passes from the first vapour containment structure segment to the second vapour containment structure segment via the interior passageway of the first portion of the first connector, and a second portion defining an interior passageway, the interior passageway of the second portion of the first connector being connected to the interior passageway of the first portion of the first connector at a junction between the first and second interfaces of the first portion of the first connector, wherein a major axis of the first portion of the first connector is offset to a major axis of the second portion of the first connector; and a first vapour reservoir connected to the first portion of the first connector via the second portion of the first connector such that the first vapour reservoir is in fluidic communication with the first and second vapour containment structure segments via the interior passageway of the first portion of the first connector and the interior passageway of the second portion of the first connector.

2. A vapour containment structure as claimed in Claim 1 , further comprising: a third vapour containment structure segment; and a second connector comprising: a first portion defining an interior passageway extending between a first interface and a second interface, wherein the first interface of the first portion of the second connector is configured to connect with the second vapour containment structure segment and the second interface is configured to connect with the third vapour containment structure segment, wherein an optical path passes from the second vapour containment structure segment tothe third vapour containment structure segment via the interior passageway of the first portion of the second connector, and a second portion defining an interior passageway, the interior passageway of the second portion of the second connector being connected to the interior passageway of the first portion of the second connector at a junction between the first and second interfaces of the first portion of the second connector, wherein a major axis of the first portion of the second connector is offset to a major axis of the second portion of the second connector; and a second vapour reservoir connected to the first portion of the second connector via the second portion of the second connector such that the first vapour reservoir is in fluidic communication with the second and third vapour containment structure segments via the interior passageway of the first portion of the second connector and the interior passageway of the second portion of the second connector.

3. A vapour containment structure as claimed in either Claim 1 or Claim 2, wherein the first interface of the first portion of the first connector is configured as a seal between the first portion of the first connector and the first vapour containment structure segment and / or the second interface of the first portion of the first connector is configured as a seal between the first portion of the first connector and the second vapour containment structure segment.

4. A vapour containment structure as claimed in Claim 2 or Claim 3 when dependent on Claim 2, wherein the first interface of the first portion of the second connector is configured as a seal between the first portion of the second connector and the second vapour containment structure segment and / or the second interface of the first portion of the second connector is configured as a seal between the first portion of the second connector and the third vapour containment structure segment.

5. A vapour containment structure as claimed in any preceding claim, wherein the first vapour reservoir comprises one of a group comprising: a solid material, the solid material having a property so as to provide vapour via sublimation, and a liquid material, the liquid material having a property so as to provide vapour via vapourisation or evaporation.

6. A vapour containment structure as claimed in Claim 2 or any one of Claims 3 to 5 as dependent on Claim 2, wherein the second vapour reservoir comprises one of a group comprising: a solid material, the solid material having a property so as to provide vapour via sublimation, and a liquid material, the liquid material having a property so as to provide vapour via vapourisation or evaporation.

7. A vapour containment structure as claimed in any one of the preceding claims, wherein the first vapour reservoir is connected to an external vapour source.

8. A vapour containment structure as claimed in Claim 2 or any one of Claims 3 to 7 as dependent on Claim 2, wherein the second vapour reservoir is connected to an external vapour source.

9. A vapour containment structure as claimed in any one of the preceding claims, further comprising: a vacuum pump configured to evacuate the first vapour reservoir, first vapour containment structure segment, and second vapour containment structure segment.

10. A vapour containment structure as claimed in Claim 9 when dependent on Claim 2, wherein the vacuum pump is configured to evacuate the second vapour reservoir and third vapour containment structure segment.

11. A vapour containment structure as claimed in any one of the preceding claims, wherein the first vapour containment structure segment comprises a first end and a second end, and the second vapour containment structure segment comprises a first end and a second end, the first interface of the first portion of the first connector is configured to configured to connect to the second end of the first vapour containment structure segment and the second interface of the first portion of the first connector is configured to connect to the first end of the second vapour containment structure segment, the vapour containment structure further comprising: a first termination segment comprising a first interface configured to connect to a first end of the first vapour containment structure segment; anda second termination segment comprising a first interface configured to connect to a second end of the second vapour containment structure segment.

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