embodiment of the present invention will be described in detail as methods , devices and apparatus for transmitting light into or receiving light exiting a vessel . embodiments have particular application in situations in which the vessel contains fluid under high pressure . optical fibers are difficult to secure and maintain optical transparency . individuals skilled in the art will readily appreciate that the present invention has broad applications to situations where it is desirable to secure optical fibers for other purposes as well . turning first to fig1 , an apparatus , in the form of a flow cell , that embodies features of the present invention , is depicted generally designated by the numeral 11 . the apparatus 11 has the following major elements : a vessel 13 , vessel wall 17 , first gasket 19 a , second gasket 19 b , and a first connector device 21 a and a second connector device 21 b . the vessel wall 17 defines a chamber 25 for containing fluid , such as sample , under pressure . embodiments of the present invention can withstand pressures greater than 4 , 000 psi and up to 15 , 000 psi . light and sample are introduced into and taken out of the chamber 25 through at least one of the first connector device 21 a and second connector device 21 b . first connector device 21 a and second connector device 21 b are identical to facilitate the manufacture of the flow cell 11 . first connector device 21 a and second connector device 21 b are for connecting optical fibers 29 a and 29 b respectively to vessel 13 . each first connector device 21 a and second connector device 21 b has a connector housing 31 having an exterior surface 33 and an optical fiber bore 35 . this discussion will describe first connector 29 a in detail for the purpose of clarity with the understanding the discussion applies to second connector 29 b as well . turning now to fig2 , first connector device 21 a has a housing 31 shown in cross section . housing 31 has an optical fiber bore 35 having a first opening 37 and a second opening 39 . the first opening 35 is for receiving and substantially engaging in sealing relationship one end of optical fiber 29 a . a fiber optic coupling surface 41 is formed on the exterior surface 33 of said housing 31 . there are well - known techniques such as optical polishing for producing a high quality optical finishes on the fiber coupling surface 41 . preferably , the housing 31 is made of metal or rigid plastics . a preferred material is stainless steel . the dimensions will be influenced by the size of the vessel 15 . a typical size is approximately 0 . 3 to 0 . 6 inches in diameter and similar dimensions in depth . the housing 31 fits to a vessel 13 appropriately sized in diameter and approximately 10 mm in length . returning now to fig1 , the second opening 39 is for receiving the optical fiber 29 a extending from said first opening 37 . a potting material 45 in optical fiber bore 35 secures the optical fiber 29 a . receiving and substantially engaging in sealing relationship , with respect to the optical fiber 29 a in first opening 37 means that the potting material 45 does not leak excessively during the potting operation . preferably , during the potting operation , the potting material 45 is placed around the optical fiber 29 a . the optical fiber 29 a is in place or is placed in the first opening 37 with the potting material 45 and the housing heated to a temperature that allows the potting material 45 to flow and occupy optical fiber bore 35 . preferably , the connector device 21 a has an optical fiber sleeve 47 as best seen in fig2 . optical fiber sleeve 47 has a cylindrical shape with an exterior diameter less than the optical fiber bore 35 and greater than the diameter of the optical fiber 29 a . optical fiber sleeve 47 is placed into said optical fiber bore 35 and receives optical fiber 29 a and potting material 45 to align , position and protect the optical fiber 29 a . the connector device 21 a has at least one capillary bore 51 . capillary bore 51 has a first capillary opening 53 and a second capillary opening 55 . first capillary opening 53 is for receiving and substantially engaging in sealing relationship one end of a capillary 57 to form a capillary coupling surface 59 on the exterior surface 33 of housing 31 . the second capillary opening 55 is for receiving capillary 57 extending from said first capillary opening 53 . capillary 57 can be sized to tightly fit the capillary bore 51 and be able to withstand pressures of greater than 4 , 000 psi and up to 15 , 000 psi . for some applications it may be useful to increase the size of capillary bore 51 and second capillary opening 55 for receiving a potting material [ not shown ] in the manner described with respect to the optical fiber bore 35 , to secure the capillary 55 in the capillary bore 51 . and , for some applications , it is useful to use a capillary sleeve [ not shown ] in the manner of the optical fiber sleeve 47 . the capillary sleeve is a cylindrical form sized with an exterior diameter less than the capillary bore 51 and an interior diameter greater than the diameter of the capillary 57 , the capillary sleeve extending into the capillary bore to align , position and protect the capillary . housing 31 has a flow cell receiving surface 61 about the capillary first opening 53 and said optical fiber first opening 37 for affixing to a flow cell vessel 15 . turning now to fig1 , flow cell 15 has a corresponding housing receiving surface 63 a and 63 b for connector device 21 a and 21 b respectively . the optical fiber 29 a has a light path on axis ( illustrated with arrows ) and optical fiber 29 b receives light along a light path after such light has traversed chamber 25 . sample in the chamber 25 will alter the nature of the light received by optical fiber 29 b . chamber 25 is in fluid communication with capillaries 57 a and 57 b of the first connector device 21 a and second connector device 21 b to receive and discharge sample fluid . first gasket 19 a is interposed between the vessel 15 at housing receiving surface 63 a and flow cell receiving surface 61 a . similarly second gasket 19 b is interposed between the vessel 15 at housing receiving surface 63 b and flow cell receiving surface 61 b . first gasket 19 a and second gasket 19 b convey fluids and seal gaps between the housings 31 of connector devices 21 a and 21 b and the flow cell . at least one of the first gasket 19 a , second gasket 19 b , flow cell receiving surface 61 and housing receiving surface 63 have channel means to convey fluid between the respective capillary 57 a or 57 b and chamber 25 . a preferred channel means is a channel 67 a and 67 b in first gasket 19 a and second gasket 19 b respectively . turning now to fig3 , gasket 19 a has a light opening 71 and a channel 67 a . the groove 67 a extends to a position in communication with capillary opening . gasket 19 a is intended to be positioned with the channel 67 a against the flow cell receiving surface 61 of the connector housing 31 . however , in the event it is desired to place channel 67 a against the housing receiving surface 63 or the vessel 15 , a sample opening [ not shown ] is provided in gasket 19 a . in order to align the channel 67 a and opening 71 , gasket 19 a has keying means in the nature of holes 73 . holes 73 cooperate with pins 79 as best seen in fig1 . in the alternative , channel means in the form of a groove [ not shown ] can be provided in the flow cell receiving surface 61 , or the housing receiving surface 63 in which case the gasket 19 a can omit the channel 67 a . thus , the vessel 15 receives light and sample through a single entrance , and discharges light and sample through a single exit . the chamber 25 of vessel 15 has a wall 17 of cylindrical form in which the cylinder axis is aligned with the light path . the wall 17 has a composition having a lower refractive index than aqueous solutions . one such material is an amorphous fluorocarbon polymer . one such material is sold under the trademark teflon af ( dupont ). the wall having a low refractive index reflects light impinging on the wall 17 back into the chamber 25 . the wall 17 extends the length of the vessel 15 and forms a first rim 75 a and a second rim 75 b at the edges . light entering the first rim 75 a can interfere with the signal generated by the flow cell 11 . light exiting the second rim 75 b also interferes with the signal . first gasket 19 a and second gasket 19 b are comprised of an opaque material . a preferred material is a metal capable of being readily etched to provide a channel . first gasket 19 a is positioned along the light path to block the light from traveling from said optical fiber 29 a from entering material of which wall 17 is made . second gasket 19 b is positioned along the light path to block light traveling through the material from entering the optical fiber 29 b . optical fiber 29 b would normally in communication with a photon detector [ not shown ]. the flow cell 11 further comprises a pressure assembly 81 . pressure assembly 81 has base 83 having a hollow 85 having an abutment ridge 87 for receiving second connector 21 . second gasket 19 b , vessel 17 , first gasket 19 a , and first connector 19 a are stacked within the hollow 85 . affixing means in the form of a nut 89 compresses the elements held in hollow 85 to affect sealing . the flow cell 11 can receive sample at pressures of 4 , 000 psi and up to 15 , 000 psi . thus , we have described an apparatus for placing light into a sample . the apparatus has a vessel 15 having a chamber 25 for containing sample and receiving light traveling a light path . the chamber 25 has at least one wall 17 parallel to said light path having a layer of a material having a refractive index less than water to form a light guide . the chamber 25 has a light entrance in the form of optical fiber 29 a for receiving light at the entrance having a rim 75 of the material . a first gasket 19 a , opaque or reflective to the light , covers the rim 75 a to prevent light from entering said material . a second gasket 19 b , opaque or reflective to light , covers the rim 75 b to prevent light from entering second optical fiber 29 b . the flow cell 11 has a chamber 25 in which sample and light have a common entrance through first gasket 19 a having a channel 67 a for transporting sample to the chamber 25 . similarly the flow cell 11 has a chamber 25 in which sample and light have a common exit through a second gasket 19 b having a channel 67 b for transporting sample from the chamber 25 . thus , we have disclosed a method of making a first connector 21 a and second connector 21 b for optical fiber 29 a and 29 b respectively . the method comprises the steps of providing a housing 31 having an exterior surface 33 and an optical fiber bore 35 . the optical fiber bore 35 has a first opening 37 and a second opening 39 . the first opening 37 is for receiving and substantially engaging in sealing relationship one end of an optical fiber 29 a to form a fiber optic coupling surface 41 on the exterior surface 33 of the housing 31 . the second opening 39 is for receiving the optical fiber extending from said first opening 37 and for receiving a potting material 45 to secure said optical fiber 29 in the optical fiber bore 35 . the method further comprises the step of placing an optical fiber 29 in the first opening 37 and extending through said second opening 39 and placing a potting material 45 in the second opening 39 and allowing the potting material 45 to substantially fill the optical fiber bore 35 to secure the optical fiber 29 . the method may be extended to capillaries wherein said housing 31 has a least one capillary bore 51 . the capillary bore 51 has a first capillary opening 53 and a second capillary opening 55 . the method further comprising the steps of placing a capillary 57 in the first capillary opening 53 and extending through the second opening 55 and placing a potting material 45 in the second capillary opening 55 to secure the capillary 57 . thus , we have disclosed a method of preventing stray light from entering a chamber 25 of a flow cell 11 or from being discharged from a chamber 25 of a flow cell 11 . the method comprises the steps of fitting a first gasket 19 a or a second gasket 19 b to cover a rim 75 a or 75 b respectively . we have disclosed preferred embodiment of the present invention which embodiments are capable of modification and alteration without departing from the teaching and spirit of the invention . thus , the present invention should not be limited to the precise detail herein but should encompass the subject matter of the following claims and their equivalents .