Abstract
An ion detection system for a detecting a quantity of ions exiting from a mass analyzer of a mass spectrometer comprises: (a) photon generating means configured to receive the quantity of ions and to generate a quantity of photons that is proportional to the quantity of ions; (b) a linear array of photo-detectors configured along a line for detecting a variation of a portion of the quantity of generated photons along the line; and (c) an optical system for directing the portion of the quantity of photons from the photon generating means to the linear array of photo-detectors comprising: (c1) a first cylindrical lens having a first lens axis disposed parallel to the line; (c2) a second cylindrical lens or rod lens having a second lens axis disposed parallel to the line; and a doublet lens.
Claims
1. An ion detection system for a detecting a quantity of ions exiting from a mass analyzer of a mass spectrometer, the ion detection system comprising: (a) photon generating means configured to receive the quantity of ions and to generate a quantity of photons that is proportional to the quantity of ions; (b) a linear array of photo-detectors configured along a line for detecting a variation of a portion of the quantity of generated photons along the line; and (c) an optical system for directing the portion of the quantity of photons from the photon generating means to the linear array of photo-detectors comprising: (c1) a first cylindrical lens disposed between the photon generating means and the linear array of photo-detectors and having a first lens axis that is disposed parallel to the line; (c2) a second cylindrical lens or a rod lens disposed between the first cylindrical lens and the linear array of photo-detectors and having a second lens axis that is disposed parallel to the line; and (c3) a doublet lens disposed between the photon generating means and the first cylindrical lens.
2. An ion detection system as recited in claim 1, wherein the photon generating means comprises: (a1) electron generating means configured to receive the quantity of ions and to generate a quantity of electrons that is proportional to the quantity of ions; and (a2) a phosphor screen disposed on a surface of a substrate and configured to receive the quantity of generated electrons and to generate the quantity of photons in proportion to the quantity of generated electrons.
3. An ion detection system as recited in claim 2, wherein the electron generating means comprises: an assembly of one or more microchannel plates (MCPs), the assembly comprising a first end facing the mass analyzer and a second end facing the phosphor screen; and an electrode disposed at the first end and an electrode disposed at the second end of the assembly.
4. An ion detection system as recited in claim 2, wherein the electron generating means comprises: an assembly of one or more metal channel dynodes, the assembly comprising a first end facing the mass analyzer and a second end facing the phosphor screen.
5. An ion detection system for a detecting a quantity of ions exiting from a mass analyzer of a mass spectrometer, the ion detection system comprising: (a) photon generating means configured to receive the quantity of ions and to generate a quantity of photons that is proportional to the quantity of ions; (b) a linear array of photo-detectors configured along a line for detecting a variation of a portion of the quantity of generated photons along the line; and (c) an optical system for collecting the portion of the quantity of photons from an area of the photon generating means and transferring the portion of the quantity of photons from the area of the photon generating means to the linear array of photo-detectors, said optical system comprising: (c1) a first cylindrical lens disposed between the photon generating means and the linear array of photo-detectors and having a first lens axis that is disposed perpendicular to the line; (c2) a second cylindrical lens disposed between the first cylindrical lens and the linear array of photo-detectors and having a second lens axis that is disposed parallel to the line; and (c3) a plano-convex lens disposed between the photon generating means and the first cylindrical lens.
6. An ion detection system as recited in claim 5, wherein the photon generating means comprises: (a1) electron generating means configured to receive the quantity of ions and to generate a quantity of electrons that is proportional to the quantity of ions; and (a2) a phosphor screen disposed on a surface of a substrate and configured to receive the quantity of generated electrons and to generate the quantity of photons in proportion to the quantity of generated electrons.
7. An ion detection system as recited in claim 6, wherein the electron generating means comprises: an assembly of one or more microchannel plates (MCPs), the assembly comprising a first end facing the mass analyzer and a second end facing the phosphor screen; and an electrode disposed at the first end and an electrode disposed at the second end of the assembly.
8. An ion detection system as recited in claim 6, wherein the electron generating means comprises: an assembly of one or more metal channel dynodes, the assembly comprising a first end facing the mass analyzer and a second end facing the phosphor screen.
9. An ion detection system as recited in claim 5, wherein the linear array of photo-detectors comprises a linear array of discrete silicon photomultipliers.
10. An ion detection system for a detecting a quantity of ions exiting from a mass analyzer of a mass spectrometer, the ion detection system comprising: an assembly of one or more microchannel plates disposed at an ion exit end of the mass analyzer, the assembly having a front end disposed so as to receive the quantity of ions and a back end; a first and a second electrode disposed at the front and back ends, respectively, of the assembly of microchannel plates; at least one voltage source electrically coupled to the first, second and third electrodes; a substrate plate comprising a front face disposed facing the microchannel plate assembly and a back face and having a phosphorescent material disposed on the front face; a third electrode disposed in contact with the front face of the substrate plate; a linear array of photo-detectors configured along a line; and an optical system optically coupled between the back face of the substrate plate and the linear array of photo-detectors, said optical system comprising: a first cylindrical lens disposed having a first lens axis that is disposed parallel to the line; a second cylindrical lens or a rod lens disposed between the first cylindrical lens and the linear array of photo-detectors and having a second lens axis that is disposed parallel to the line; and a doublet lens disposed between the back face of the substrate plate and the first cylindrical lens.
11. An ion detection system as recited in claim 10, further comprising: an additional photodetector optically coupled to the back face of the substrate plate.
12. An ion detection system as recited in claim 11, wherein the additional photodetector system comprises a photomultiplier tube.
13. An ion detection system as recited in claim 10, further comprising: a fourth electrode disposed in contact with the front face of the substrate plate; and an electrometer electrically coupled to the fourth electrode.
14. An ion detection system for a detecting a quantity of ions exiting from a mass analyzer of a mass spectrometer, the ion detection system comprising: an assembly of one or more microchannel plates disposed at an ion exit end of the mass analyzer, the assembly having a front end disposed so as to receive the quantity of ions and a back end; a first and a second electrode disposed at the front and back ends, respectively, of the assembly of microchannel plates; at least one voltage source electrically coupled to the first, second and third electrodes; a substrate plate comprising a front face disposed facing the microchannel plate assembly and a back face and having a phosphorescent material disposed on the front face; a third electrode disposed in contact with the front face of the substrate plate; a linear array of photo-detectors configured along a line; and an optical system optically coupled between the back face of the substrate plate and the linear array of photo-detectors, said optical system comprising: a first cylindrical lens having a first lens axis that is disposed perpendicular to the line; a second cylindrical lens disposed between the first cylindrical lens and the linear array of photo-detectors and having a second lens axis that is disposed parallel to the line; and a plano-convex lens disposed between the back face of the substrate plate and the first cylindrical lens.
15. An ion detection system as recited in claim 14, further comprising: an additional photodetector optically coupled to the back face of the substrate plate.
16. An ion detection system as recited in claim 15, wherein the additional photodetector system comprises a photomultiplier tube.
17. An ion detection system as recited in claim 14, further comprising: a fourth electrode disposed in contact with the front face of the substrate plate; and an electrometer electrically coupled to the fourth electrode.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The above noted and various other aspects of the present invention will become further apparent from the following description which is given by way of example only and with reference to the accompanying drawings, not drawn to scale, in which:
(2) FIG. 1A is a schematic example configuration of a triple stage mass spectrometer system;
(3) FIG. 1B is a simulated recorded image of a multiple distinct species of ions as collected at the exit aperture of a quadrupole at a particular instant in time;
(4) FIG. 1C is an example embodiment of a time and position ion detector system configured with a linear array of read-out anodes;
(5) FIG. 2A is a schematic depiction of an embodiment of a time and position ion detector system in accordance with the present teachings that employs two linear photo-detector arrays;
(6) FIG. 2B is a schematic depiction of a second embodiment of a time and position ion detector system in accordance with the present teachings that employs two linear photo-detector arrays;
(7) FIG. 3A is a schematic depiction of a first embodiment of a time and position ion detector system in accordance with the present teachings that employs a single linear photo-detector array and a non-imaging detector;
(8) FIG. 3B is a schematic depiction of a second embodiment of a time and position ion detector system in accordance with the present teachings that employs a single linear photo-detector array and a non-imaging detector;
(9) FIG. 3C is a schematic depiction of a third embodiment of a time and position ion detector system in accordance with the present teachings that employs a single linear photo-detector array and a one-dimensional detector;
(10) FIG. 4A is a schematic depiction of a two-dimensional to one-dimensional optical compressor device as may be employed in conjunction with various embodiments in accordance with the present teachings;
(11) FIG. 4B is an exploded view of the two-dimensional to one-dimensional optical compressor device illustrated in FIG. 4A;
(12) FIG. 4C is another view of the two-dimensional to one-dimensional optical compressor device illustrated in FIG. 4A, as disposed in an alternative orientation;
(13) FIG. 4D is a schematic depiction of a second two-dimensional to one-dimensional optical compressor device;
(14) FIG. 5 is a schematic illustration of a photo-detector array;
(15) FIG. 6A is a schematic depiction of an optics sub-system that may be employed in various embodiments of a time and position ion detector system in accordance with the present teachings, wherein an image of a phosphor screen is strongly compressed parallel to one dimension and less strongly compressed or uncompressed parallel to a second, orthogonal dimension; and
(16) FIG. 6B is a schematic depiction of another optics sub-system that may be employed in various embodiments of a time and position ion detector system in accordance with the present teachings, wherein an image of a phosphor screen is strongly compressed parallel to one dimension and is magnified parallel to a second, orthogonal dimension.
DETAILED DESCRIPTION
(17) The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art and the generic principles herein may be applied to other embodiments. Thus, the present invention is not intended to be limited to the embodiments and examples shown but is to be accorded the widest possible scope in accordance with the features and principles shown and described. The particular features and advantages of the invention will become more apparent with reference to the appended FIGS. 2, 3A, 3B, 3C, 4A and 4B, taken in conjunction with the following description.
(18) FIG. 2A schematically depicts a first embodiment of a time and position ion detector system in accordance with the present teachings, which is shown generally as detector system 100. The ions I exiting from an ion occupation between quadrupole rod electrodes 101 are converted to electrons and the electron current is amplified by microchannel plate assembly or stack 102 comprising one or a plurality of microchannel plates as previously described with reference to FIG. 1C. It is preferable to generate photons, within the system 100, using a substrate plate 109 comprising a single-piece or integral component (such as a plate of glass, mica or plastic) that is coated with a transparent material, such as indium tin oxide, comprising a biasing electrode 106 and further coated with a phosphor material comprising a phosphorescent screen 107. A phosphor-coated plate comprising a bundle of fibers (such as plate 15 employed in the system 20 illustrated in FIG. 1C) may alternatively be employed as the substrate plate 109. Voltages V.sub.1 and V.sub.2 are applied to electrodes at opposite ends of the MCP stack 102 so as to draw ions I onto the stack and to accelerate generated electrons (denoted as e.sup.) through the stack. A voltage V.sub.3 is applied to the transparent electrode 106 to draw the electrons onto the phosphorescent screen 107 at which photons (denoted as p) are generated.
(19) Components shown on the right hand side of the substrate plate 109 in FIG. 2A serve to replace the two-dimensional camera 25 that is depicted in FIG. 1C. The replacement components comprise two separate linear photo-detector arrays 132a, 132b and associated optics. In operation, the phosphorescent screen 107 radiantly glows with a spatially-non-uniform intensity as it is impacted by electrons e.sup. that are generated as a result of impingement of ions I onto the microchannel plate assembly or stack 102. The pattern of this spatially-non-uniform glow at any time corresponds to the spatial distribution of the number of ions emitted from between the quadrupole rods 101 at such time. Lenses 112 and 120a serve to transfer an image of the glowing phosphorescent screen onto an entrance face 81 of a novel image compressor 71a (described in greater detail below). Likewise, the pair of lenses 112 and 120b serve to transfer a duplicate image of the glowing phosphorescent screen onto an entrance face 81 of a second image compressor 71b. Light comprising photons that are generated by the phosphorescent screen 107 and that pass through the substrate plate 109 is collected and partially collimated into a light beam by a light collection lens 112. The partially collimated light beam is then split into two light-beam portions along two respective pathways by a beam splitter 116. A first such pathwaytraversed by a first light beam portionis indicated in FIG. 2A by arrows 117 and a second such pathwaytraversed by the second light beam portionis indicated by arrows 118. These light beam portions thus transfer two copies of the image information. Each of these light beam portions may then comprise about half the intensity of the original light source. Alternatively, the beam splitter 116 may be configured such that the ratio between the intensities of the transmitted and reflected light beam portions is other than one-to-one (1:1), such as, for example, nine-to-one (9:1), four-to-one (4:1), one-to-four (1:4), one-to-nine (1:9), etc. Such beam splitters are commercially available as either off-the-shelf stock items or can be custom fabricated in almost any desired transmitted-to-reflected ratio. A beam splitter in which the transmitted-to-reflected ratio is other than 1:1 may be employed, for example, to deliver a greater proportion of the light beam intensity to a detector having less sensitivity or to deliver a lesser proportion to a detector which might be easily saturated.
(20) Each of the two light beam portions is refracted by a respective lens or lens system 120a, 120b so as to project a two-dimensional image of the phosphor screen onto a face of a respective image compressor device 71a, 71b (discussed in greater detail below). Two such image planes are depicted as image planes 129 in FIG. 2A. Each image compressor device 71a, 71b compresses the projected two-dimensional image into a line that is focused onto a respective linear (one-dimensional or 1-D) photo-detector array (PDA) 132a, 132b. Optionally, a reflecting device 123 comprising, such as a flat mirror or a prism, may be employed within one of the beam pathways to cause both beams to be parallel. The deflection of one of the beams by the reflecting device 123 may be used to decrease the size of the system 100 or possibly to facilitate mechanical mounting of the two photo-detector arrays 132a, 132b to a common circuit board and drive electronics.
(21) According to the configuration illustrated in FIG. 2A, the two-dimensional image of phosphorescent screen that is projected onto the image compressor device 71a is compressed within the x-dimension by the compressor device 71a so as to be focused to a line (a line parallel to the y-dimension, perpendicular to the plane of the drawing of FIG. 2A) that is coincident with the position of a first linear photo-detector array 132a. Similarly, the two-dimensional image of the phosphorescent screen that is projected onto the image compressor device 71b is compressed within the y-dimension by the compressor device 71b so as to be focused to a line that is parallel to the x-dimension and that is coincident with the position of a second linear photo-detector array 132b. The first and second linear photo-detector arrays 132a, 132b may comprise, without limitation, two line cameras. The lenses may 120a, 120b comprise spherical or aspherical lenses or may comprise any lens systems capable of image projection. Although drawn differently in FIG. 2A, the first and second beam or image compressors 71a, 71b are considered to be identical. Also, the first and second photo-detector arrays 132a, 132b are considered to be identical. The illustrated difference in shape between the first and second image compressors 71a, 71b as well as the illustrated difference in shape between the first and second photo-detector arrays 132a, 132b, are employed so as to indicate that the second set of components is rotated about an axis within the plane of the drawing so as to be orthogonal to the first set.
(22) FIG. 2B illustrates another ion detector system which is a modified version of the ion detector system shown in FIG. 2A. In the system 105 of FIG. 2B, the previously described lenses or lens systems 120a, 120b and the image compressors 71a, 71b are replaced by first and second cylindrical lenses 121a, 121b. In the example shown, the two cylindrical lenses 121a, 121b are considered to be (but are not necessarily) identical. The illustrated difference in shape between the first and second cylindrical lenses 121a, 121b is employed so as to indicate that the second cylindrical lens is rotated about an axis within the plane of the drawing so as to be orthogonal to the first cylindrical lens. In the system 105, the light-sensitive regions of the photo-detector arrays 132a, 132b are disposed at the foci of the cylindrical lenses 121a, 121b such that each of the light beam portions 117, 118 is focused to a line on the light sensitive region of the respective photo-detector array 132a, 132b.
(23) FIG. 5 is a schematic depiction of light receiving face of a general photo-detector array 132. The array comprises a plurality of individual, independent light-sensitive elements 133, which may be referred to as pixels. In the system 100 illustrated in FIG. 2A (as well as in other system embodiments taught herein), an instance of the array 132 may be interfaced to either a cylindrical lens 120a, 120b; a beam or image compressor 71a, 71b; or, a combination of a cylindrical lens and a beam/image compressor, as shown, with the linearly disposed plurality of pixels oriented so as to be coincident with a line focus produced by the cylindrical lens, beam/image compressor of lens-compressor combination.
(24) As illustrated in FIG. 2A, each linear photo-detector array retains image variation along the dimension parallel to the array and sums (or bins) image information orthogonal to the array. Because two mutually orthogonal arrays are employed, image variation parallel to both the x-direction and the y-direction (as defined above for quadrupole apparatuses) is retained. Binning the information is a very useful method of data compression without losing much information. As referred to in the aforementioned U.S. Pat. No. 8,389,929, this binning data compression can be implemented on a single, square imager with each photo-site having two outputs; one going to an x bin and one to a y bin as explained in detail in U.S. Pat. No. 8,829,409 in the name of inventor Wadsworth. For the case in which 64 bins are employed in each dimension, the full number of photo-sites with dual outputs is 6464=4096. The alternative method depicted in FIG. 2A employs optics to enable the use of two separate, simpler, photo-detector arrays, such as line cameras, to provide the same orthogonal information as the previously-described two-dimensional camera.
(25) Assuming each linear photo-detector array comprises 64 pixels, the configuration illustrated in FIG. 2A reduces the number of photo-sites needed for ion spatial and temporal imaging from 4096 pixels to 64+64=128 pixels. Such a configuration provides multiple benefits for cost since there is much less silicon used for a pair of line cameras compared to a single monolithic two-dimensional camera. Furthermore, in the case of a single or dual line camera, it is possible to orient all of the non-photo-sensitive electronics off to the side on an area of silicon not used for detecting photons. This allows line cameras to routinely have near 100% fill factor, (i.e., the amount of active photo area over the region that will be illuminated). Another important benefit is that the fabrication of relatively high speed line cameras is well known and line cameras that operate between 56 kHz and 140 kHz with resolutions of 1024 pixels or greater are commercially available. Despite the availability of commercially available line cameras, it is still desirable to produce a custom IC chip specifically designed for ion spatial and temporal imaging. Such a line camera may preferably include sub-RF cycle specificity and a microchannel analyzer per pixel, thereby allowing for substantially greater information content when using this detector design in the specific quadrupole mass analyzer imaging system. Additionally, custom linear arrays of sensors may be readily employed, such as photo diode arrays or arrays of silicon photomultipliers.
(26) FIGS. 4A-4C illustrate a specific example of a beam or image compressor device as may be employed in embodiments in accordance with the present teachings. FIG. 4D illustrates a second example of a beam or image compressor device that is a variation of the device shown in FIGS. 4A-4C. Such devices are described in greater detail in a co-pending United States Patent application titled Optical Compression Device, and application Ser. No. 14/561,158, which is filed on even date herewith and is assigned to the assignee of this application and which is incorporated by reference herein in its entirety. In accordance with the illustrated example, the compressor device 71.1 (FIGS. 4A-4C) comprises a triangular prismatic optical compression device having a triangular prism base 78 and three rectangular side faces 79. The alternative device 71.2 illustrated in FIG. 4D is formed as a truncated triangular prismatic device one in which one of the edges between side faces 79 of the device 71.1 is replaced by an additional face 76. Either of the devices 71.1-71.2 may be used to flatten a light beam having a 2D cross-section to form a beam having a substantially 1D cross section (this beam flattening operation is sometimes referred to herein as 2D to 1D light compression).
(27) FIGS. 4A-4D illustrate the compressor devices 71.1-71.2 oriented with regard to a Cartesian coordinate system, in which the x-, y- and z-axes correspond to the x-, y- and z-dimensions as defined above for a quadrupole apparatus. The term correspond to in the above sentence means that the x-, and y-axes defined for the compressor 71.1-71.2 are parallel to the projected images (as possibly reflected or rotated by various optical components) of the x- and y-dimensions of the associated quadrupole device and that the z-axis defined for the compressor is the direction of light propagation through the compressor. Thus, one rectangular side face of the prismatic compressor device is parallel to the x-y plane and is a light entrance face. FIG. 4A and FIG. 4C provide two views of the compressor device 71.1 in two different orientations. In the orientation of FIG. 4A, the linear edge 77 is parallel to the y-axis, whereas, in the orientation shown in FIG. 4C, the linear edge 77 is parallel to the x-axis. These different orientations generally correspond to the different orientations indicated for image compressor 71a and image compressor 71b, respectively, in FIG. 2A. (However, note that the image compressors 71a and 71b are shown in FIG. 2A in the truncated prismatic form, as in FIG. 4D.) The entrance face is not visible (i.e., is hidden) in FIGS. 4A-4D; however, entrance faces 81 of the image compressors 71a, 71b are noted in FIG. 2A. The light propagates through the device 71.1 or 71.2 and exits at a linear edge 77 (in the device 71.1) or at the exit face 76 (in the device 71.2) along exit trajectories 67. The light entrance and light exit faces may be referred to as light gating faces. Some or all of the non-light-gating faces of the compressor device 71 are coated by internally light reflecting coatings 73 in order to minimize any loss of scattered or internally reflected light from within each waveguide of the device.
(28) FIG. 4B provides an exploded view of the device 71.1 in which the reflective coatings 73 are shown detached from a core section 72. The coatings are applied onto at least the two side faces 79 that are parallel to the y-axis and that intersect at the edge 77 and, optionally, also to the two basal faces 78. As shown in FIG. 4B, the core section 72 of the compressor device 71 may be constructed from a plurality of generally planar waveguide layers 74 formed of a light transmissive polymer or glass or glass-like material and arranged in a stacked relationship to each other having a width that tapers from the light entrance face (i.e., the rectangular base) to the light exit face 77. Such tapering could be essentially linear or could exhibit a curved convex or concave tapering progression from the light entrance face of the device to the light exit face of the device. Such tapering can also be in the form of a parabolic concentrator in one dimension.
(29) Each waveguide 74 of the compressor device 71 may be optically coupled to a single pixel 133 of a photo-detector array 132 (see FIG. 5). To prevent significant scrambling of linear data, it is desirable that light entering any particular waveguide should exit from the same waveguide at its light exit face wherein light cross over to an adjacent waveguide or the loss of light from either of the side faces is minimized. There are a number of ways to approach this problem; a second layer 75 may be disposed between adjacent waveguides 74 that minimizes light cross-talk by having an appropriate refractive index between the waveguide and the second interposed light refracting layer that prevents light escaping from the waveguide. Alternatively, waveguides may be used that have been modified to restrict light passage from their top and bottom surfaces. Multiple types of waveguides could be used, for example, in an ABABAB type repeating pattern where light cross-talk between the layers is inherently minimized due to differences in their refractive indices.
(30) FIG. 3A is a schematic depiction of a time and position ion detector system in accordance with the present teachings that employs a single linear photo-detector array and a non-imaging detector. The system 200 depicted in FIG. 3A comprises many of the same components previously described with reference to FIG. 2A and numbered similarly to identical components shown in FIG. 2A. The system 200 differs from the system 100 in that one of the linear photo-detector arrays and its associated focusing optics (cylindrical lens or image compressor or both) is removed and is replaced with a conventional high-bandwidth non-imaging light detector, such as a photo-multiplier tube 236 as shown. The configuration of the detector system 200 enables spatial-temporal imaging detection in addition to conventional (non-imaging) detection.
(31) In the system 200, the beam splitter 116 divides a light beam generated at the phosphor-coated screen 107 into first and second light beam portions, as previously described with reference to the system 100 depicted in FIG. 2A. Also, as previously described, the first light beam portion exits from the beam splitter 116 in the direction of photo-detector array 132a and is focused onto the photo-detector array by light focusing optics. The focusing optics in the path of the first light beam portion may include a focusing lens or lens assembly 120a and image compressor 71a as shown, or, alternatively, may comprise a cylindrical lens disposed such that its focus occurs essentially at the light-sensitive region of the PDA 132a, similar to the configuration shown in FIG. 2B. The second light beam portion is directed from beam splitter to the photo-multiplier tube. Preferably, the second light beam is concentrated onto the internal phosphor screen of the photomultiplier tube by a two-dimensional parabolic concentrator device 224, which is well known in the art. A lens could be used in place of the parabolic concentrator.
(32) The beam splitter may, in some embodiments, divide the light into roughly first and second light beam portions of approximately equal intensity. However, the intensities of the first and second light beam portions may, in other embodiments, be configured to be unequal. For example, if the two detection systems are found to have unequal gain or sensitivity, then the beam splitter may be configured to direct a greater proportion of the light beam to the less-sensitive detector. Also, although the photo-multiplier tube is shown as receiving a reflected light beam portion from the beam splitter 116 in FIG. 3A, the positions of the two detectors (and their associated optics) could be interchanged from the positions shown such that the photo-detector array 132a receives the reflected light beam portion.
(33) Although a photomultiplier tube 236 is shown as a non-imaging detector in FIG. 3A, other photo-detector types, such as photodiode or photo transistor based detectors or a silicon-based photomultiplier, may alternatively be used. As is known in the art, photomultiplier tubes employ a series of dynodes which operate, electrically, very similarly to the dynode series of electron multiplier detectors, which are employed in many conventional mass spectrometer systems. Thus, the use of the photomultiplier tube 236 as the second detector can advantageously facilitate the use of existing mass spectrometer current-detection circuitry with little or no modification. This would allow a mass spectrometer having the detector system 200, when used in non-imaging detection mode, to exhibit performance and features (such as pulse counting) that are similar to those of existing electron multiplier based mass spectrometer systems, while also adding image detection capability.
(34) Some ion cloud imaging information may be lost in the system 200, relative to the system 100 (FIG. 2A) or the system 105 (FIG. 2B), as a result of the elimination of the second photo-detector array. Nonetheless, a sufficient quantity of time and position data may be obtained, in many circumstances, by only employing the single one-dimensional photo detector array 132a. The detector array 132a in the system 200 may be configured to detect ion cloud density variation in either the x-direction or the y-direction.
(35) FIG. 3B schematically depicts another time and position ion detector system in accordance with the present teachings. The system 300 shown in FIG. 3B represents a variation of the system 200 in which the beam splitter is eliminated and the second, non-imaging detector (e.g., photo-multiplier tube 236, as shown) is simply aimed in the general direction of the phosphor coated substrate plate 109 and light collection lens system 112 so as to collect photons that are scattered from lens and plate surfaces. The inventors have determined that the configuration shown in FIG. 3B not only increases the intensity of light directed to the photo-detector array 132a but also does not seriously degrade the signal since the intensity of scattered light is sufficient to be detected by a detector having high light sensitivity, such as a photomultiplier system. The focusing optics in the path of the main light beam portion may include a focusing lens or lens assembly 120a and image compressor 71a as shown, or, alternatively, may comprise a cylindrical lens disposed such that its focus occurs essentially at the light-sensitive region of the PDA 132a, similar to the configuration shown in FIG. 2B.
(36) FIG. 3C schematically depicts another time and position ion detector system, in accordance with the present teachings, that employs both an imaging detector (photo-detector array 132a) in addition to a non-imaging detector. The non-imaging detector of the system 400 shown in FIG. 3C is an electrometer which measures the image current that is collected on the phosphor screen 107. The electrons that impinge upon the electrode V.sub.3 are directed to an amplifier (shown as differential amplifier 440) and the amplified signal is directed to the electrometer 442. A capacitor could optionally be included between the electrode V.sub.3 and the amplifier 440 to facilitate pulse counting. Although only a single photo-detector array 132a is illustrated in FIG. 3C, a second photodetector array could be added (for example, according to the configuration shown in FIG. 2A) if adequate space is available. The focusing optics in the path of the main light beam portion may include a focusing lens or lens assembly 120a and image compressor 71a as shown, or, alternatively, may comprise a cylindrical lens disposed such that its focus occurs essentially at the light-sensitive region of the PDA 132a, similar to the configuration shown in FIG. 2B.
(37) In the case of embodiments that employ a linear array of photodetectors, an image of a phosphor-bearing surface must be compressed into a line, the compression being along a dimension that is orthogonal to the length of the array. However, depending on the relative sizes of the phosphor screen and the detector, it may be necessary to either compress or magnify the image along a direction parallel to the linear array. (Note that the dimensions of a phosphor screen, as used herein, will generally be approximately equivalent to the dimensions of a mass analyzer from which ions are emitted.) Conventional line cameras based on charge-coupled-device (CCD) technology generally comprise approximately two-thousand pixels where each such pixel is approximately 10-20 m in size. When such line cameras are employed, for instance, to detect phosphorescence generated from ions emitted from a quadrupole device having dimensions of 12 mm12 mm, essentially no magnification or compression is required parallel to the length of the photo-detector array.
(38) In light of the above considerations, simple optical configurations employing a cylindrical lens such as shown in FIG. 2B work well under conditions in which little or no image compression is required along a direction parallel to the photo-detector array. FIG. 6A shows a slightly more complex version of an optical system which may be employed to transfer light from a phosphorescent screen 107 onto a photo-detector array 132a with improved spatial resolution. As previously described with reference to FIG. 2B, a cylindrical lens 273 is employed to focus light emanating from phosphorescent screen 107 to a line. Additionally, a smaller cylindrical lens 275, having a long axis (cylindrical axis) parallel to the long axis of the cylindrical lens 273, is employed to provide a small beam waist at the surface of the detector array 132a. A rod lens may be used in place of the small cylindrical lens 275, without significant loss of spatial resolution. Further, an image correcting doublet 271 comprising a plano-convex and a concavo-convex lens, is employed to preserve image resolution along the dimension parallel to the detector array.
(39) The optics configuration shown in FIG. 6A may be used in a system employing only a single photo-detector array (cf., FIGS. 3A-3C) or in a system employing two photo-detector arrays (cf FIGS. 2A-2B). In the latter instance, a beam splitter (not shown in FIG. 6A) may be employed between the phosphor screen 107 and the lens doublet 271 so as to split off a second light beam portion from the optical pathway shown in FIG. 6A. A second instance of the set of lens elements 271, 273 and 275 would then be disposed along the path of the second light beam portion.
(40) Recently, a new type of line camera comprising an array of discrete silicon photomultipliers has become available. Such line cameras may be constructed, for example, from silicon photomultipliers provided commercially by SensL of Cork, Ireland. The pixels in such a line camera are significantly larger than those in line cameras employing CCD technology. For example, a sixty-four-element row of 1-mm active area SensL devices requires space between individual photo-detector sensors such that the center to center spacing is 1.7 mm. Thus, a sixty-four-element array of such devices requires an optics configuration that generates an image that is magnified to a size of over 100 mm in one dimension while being compressed to 1 mm in the orthogonal dimension.
(41) FIG. 6B illustrates an optics configuration that may be employed under in a system in which a silicon photomultiplier array detector, as described above, is employed. The optics configuration shown in FIG. 6B comprises a first cylindrical lens 283 disposed with its long axis (cylindrical axis) orthogonal to the long dimension of the discrete silicon photomultiplier array 134 and several focal lengths distant from the silicon photomultiplier array 134. Taken together with a plano-convex lens 281 adjacent to the phosphor light source, the cylindrical lens 283 functions as an optical projector so as to project a image of the phosphor screen 107 that is magnified parallel to the length of line of pixels. The optics configuration of FIG. 6B further comprises a second cylindrical lens 285 having its long axis disposed orthogonal to the long axis of the first cylindrical lens, such that the image is compressed to a line along a dimension orthogonal to the line of pixels. The effective numerical aperture of the lens system of FIG. 6B may be increased by optionally incorporating mirrors 287 disposed above and below (in accordance with the elevation views) the lens system so as to capture additional light that may not be intercepted by the lens 285. Although planar mirrors are illustrated in FIG. 6B, concave mirrors (such as sections of parabolic mirrors) may be employed so the detector 134 may capture light that diverges at a range of angles.
(42) The optics configuration shown in FIG. 6B may be used in a system employing only a single photo-detector array (cf., FIGS. 3A-3C) or in a system employing two photo-detector arrays (cf. FIGS. 2A-2B). In the latter instance, a beam splitter (not shown in FIG. 6B) may be employed between the phosphor screen 107 and the first cylindrical lens 283 so as to split off a second light beam portion from the optical pathway shown in FIG. 6B. A second instance of the set of lens elements 283 and 285 would then be disposed along the path of the second light beam portion.
(43) One of ordinary skill in the optics arts would readily understand how to construct alternative optical systems for transforming a two-dimensional image (e.g., of a phosphor screen) into a focused or nearly focused line that is transferred onto a linear detector system. For example, U.S. Pat. No. 5,513,201, in the name of inventors Yamaguchi et al. and hereby incorporated by reference herein in its entirety, teaches a large number of image rotation designs that are relevant for transferring each one-dimensional compressed image to a linear sensor.
(44) In the description of the invention herein, it is understood that a word appearing in the singular encompasses its plural counterpart, and a word appearing in the plural encompasses its singular counterpart, unless implicitly or explicitly understood or stated otherwise. Furthermore, it is understood that for any given component or embodiment described herein, any of the possible candidates or alternatives listed for that component may generally be used individually or in combination with one another, unless implicitly or explicitly understood or stated otherwise. Moreover, it is to be appreciated that the figures, as shown herein, are not necessarily drawn to scale, wherein some of the elements may be drawn merely for clarity of the invention. Also, reference numerals may be repeated among the various figures to show corresponding or analogous elements. Additionally, it will be understood that any list of such candidates or alternatives is merely illustrative, not limiting, unless implicitly or explicitly understood or stated otherwise. In addition, unless otherwise indicated, numbers expressing quantities of ingredients, constituents, reaction conditions and so forth used in the specification and claims are to be understood as being modified by the term about.
(45) The discussion included in this application is intended to serve as a basic description. The present invention is not to be limited in scope by the specific embodiments described herein, which are intended as single illustrations of individual aspects of the invention, and functionally equivalent methods and components are within the scope of the invention. For example, according to some embodiments, the electron-generating means, shown as microchannel plates (MCPs) in the drawings, may be replaced by a set of one or more metal channel dynodes. Each such metal channel dynode (MCD) may comprise a metal electrode plate having a plurality of perforations or channels therethrough. At the first MCD, ions emitted from the mass analyzer are neutralized by impact with the metal plate or with the interior walls of the perforations or channels and at least a portion of their kinetic energy is released as kinetic energy of ejected secondary electrons. Subsequent MCD plates of a stack of such plates may similarly further amplify the quantity of secondary electrons. If the metal channel dynodes are coated with an appropriate enhancer substance such as magnesium oxide or any other enhancer (generally, a metal oxide), the conversion efficiency should be as good as the input surface of an MCP. Indeed, various modifications of the invention, in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and accompanying drawings. Such modifications are intended to fall within the scope of the appended claims. Any patents, patent applications, patent application publications or other literature mentioned herein are hereby incorporated by reference herein in their respective entirety as if fully set forth herein, except that, in the event of any conflict between the incorporated reference and the present specification, the language of the present specification will control.
