WO1998013857A1 - Transducteurs de rayonnement - Google Patents

Transducteurs de rayonnement Download PDF

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Publication number
WO1998013857A1
WO1998013857A1 PCT/GB1997/002650 GB9702650W WO9813857A1 WO 1998013857 A1 WO1998013857 A1 WO 1998013857A1 GB 9702650 W GB9702650 W GB 9702650W WO 9813857 A1 WO9813857 A1 WO 9813857A1
Authority
WO
WIPO (PCT)
Prior art keywords
radiation
arrangement
absorption
enhanced absorption
trap regions
Prior art date
Application number
PCT/GB1997/002650
Other languages
English (en)
Inventor
Peter David Townsend
Original Assignee
Btg International Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Btg International Limited filed Critical Btg International Limited
Publication of WO1998013857A1 publication Critical patent/WO1998013857A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B1/00—Optical elements characterised by the material of which they are made; Optical coatings for optical elements
    • G02B1/10—Optical coatings produced by application to, or surface treatment of, optical elements
    • G02B1/12—Optical coatings produced by application to, or surface treatment of, optical elements by surface treatment, e.g. by irradiation
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J1/00—Details of electrodes, of magnetic control means, of screens, or of the mounting or spacing thereof, common to two or more basic types of discharge tubes or lamps
    • H01J1/02—Main electrodes
    • H01J1/34—Photo-emissive cathodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/06—Electrode arrangements
    • H01J43/08—Cathode arrangements
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J43/00—Secondary-emission tubes; Electron-multiplier tubes
    • H01J43/04—Electron multipliers
    • H01J43/28—Vessels, e.g. wall of the tube; Windows; Screens; Suppressing undesired discharges or currents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J49/00—Particle spectrometers or separator tubes
    • H01J49/02—Details
    • H01J49/025—Detectors specially adapted to particle spectrometers

Definitions

  • This invention relates to radiation transducers and finds particular application in photomultiplier tubes for detection of optical radiation.
  • Photomultiplier detection of light is a preferred method when the requirements include (a) a wide wavelength coverage, from less than 200 nm and through the visible spectrum; (b) high signal gain, of >10 6 ; (c) rapid response, of the order of nanoseconds; (d) a wide and linear dynamic range and (e) high quantum efficiency, which reaches ⁇ 25% for photoelectron production with blue light.
  • a serious weakness of current photomultiplier photocathodes is that the quantum efficiency falls rapidly for longer wavelengths with all standard coating layers.
  • a variety of ways may be used to extend the long wavelength performance and the tail of useable sensitivity extends to about 950nm for trialkali photocathodes (extended S20 or S25), or to -1.1 micron for SI coatings (but with efficiencies as low as 0.01%).
  • Gallium arsenide-based layers have been marketed with better red performance to -900 nm, but reduced ultra violet/blue performance.
  • Commercially quoted S 1 or S20 long wavelength limits do not define an absolute long wavelength cutoff, but rather a practical limit where the efficiency has fallen below 0.1%.
  • Condition (2) for electron escape imposes a thickness limitation which is incompatible with (1) for total light absorption, and indeed most photocathodes are semitransparent and from their colour it is visually apparent that they are prtmarily blue absorbing, and transmit red light.
  • cathodes have been made which are within the photomultiplier tube and are operating in a reflective mode. In this case the light may be absorbed either on entry or on reflection. This doubling of the thickness gives a gain in the fraction of red photons which are absorbed in a thin layer.
  • Data published by photomultiplier tube manufacturers for semitransparent and reflective mode photocathodes show that, in the blue, the gains are very small, but by
  • Gallium arsenide-based layers have the advantage that the small band gap of the material offers strong absorption coefficients, even for thin layers of photocathode, however they tend to have a sharp wavelength cutoff and may not operate as far into the infra red as trialkali cathodes.
  • US patent 3873829 proposes a solution to this problem in which an array of prisms is mounted on a plane support for the absorbing layer in order to produce repeated total reflection of incident radiation.
  • an arrangement is both costly and difficult to produce.
  • an arrangement for enhanced absorption of radiation comprising a radiation receiving surface having an abutting array of substantially contiguous protruding surfaces each having a surface remote from said radiation receiving surface for the absorption of radiation wherein the surface for the absorption of radiation is not substantially parallel to said radiation receiving surface and wherein the surface for the absorption of radiation includes a plurality of trap regions of lateral dimensions less than the wavelength of the radiation.
  • Figure 1 shows in diagrammatic form the structure of a prior art photocathode
  • Figure 2 is a diagram illustrating a feature of a specific embodiment of the invention
  • Figure 3 is a diagram showing cathode material response
  • FIGS 4a to 4d illustrate an alternative embodiment of the invention
  • FIG. 1 In a prior art cathode for a photomultiplier tube ( Figure 1 ) radiation enters the tube through a transparent window, as indicated by the arrows, and impinges on a photoemissive film 2 where it releases electrons which are accelerated toward the photomultiplier electrodes (not shown).
  • the basis of the improvements is to design a total light trap on the inner (vacuum) side of the photomultiplier window beneath, but coupled, to the photocathode material.
  • Figure 1 This uses an array of small cones 3 to cancel all reflection and act as a perfect black body absorber.
  • the array of cones is provided with a surface layer 4 of a material, such as zinc, which will absorb the radiation.
  • An alternative embodiment uses an array of ridges.
  • trapping is dependent on the aspect ratio and angle which defines a trap region of lateral dimensions less than the wavelength of the light, rather than any intrinsic absorption coefficient of the cone material.
  • the light trap is non-reflecting because the forward scattered beam within the inner coned window surface is internally reflected into regions which are small, or less than, the optical wavelength in the glass.
  • evanescent energy interacts progressively with the thin coating layer on the cone surface, and thus will absorb the light.
  • the overall efficiency will depend on the cone angle, the thickness, refractive indices and absorption coefficients of the total cone design, but the effectiveness of the cones will increase with longer wavelengths.
  • a further advantage is that, whilst the thickness of the emissive layer has not been increased, so electron escape efficiency is unchanged, the effective distance over which absorption can be considered has been extended from a few tens of nanometres to about a micron.
  • Manufacturers' catalogue data for transmissive and reflective photocathodes suggests that even at 900nm the absorption coefficient of the emissive layer is still quite high, at -10 3 c ⁇ _ " '. It is estimated that a photocathode in accordance with a particular aspect of the present invention employing a cone version of the emissive layer should approach 100% absorption. In an ideal situation the proposed method could raise the efficiency near the end of the current long wavelength range of an S20/25 or S 1 photocathodes from 0.1 or 0.25% towards 25%, where the upper limit is set by electron extraction.
  • the best tube performance is between 25 to 30% efficient in terms of electron extraction per incident photon.
  • this may be achieved with a reduced thickness photocathode layer.
  • the resulting improved electron extraction could raise the overall efficiency to around 50% across the entire spectral range of the tube.
  • Photomultiplier tube data are normally plotted as a function of wavelength on diagrams of radiant sensitivity (mA/W) together with contour lines of selected quantum efficiency.
  • Figure 3 gives the quantum efficiency in terms of photon energy.
  • a comparison between transmissive and reflective cathode data indicates an energy shift in the limit of the operating range. Cone structures for the electron emissive cathode surface both increase the efficiency and extend the infra red operating range.
  • Figure 2 shows that currently the additional absorption from reflective coatings extends the S20 coating limits by some 0. leV. Initial indications of the much higher absorption from a light trap lead to a further extension towards the infra red by an additional 0.1 or 0.2eV. For SI layers this is equivalent extending the operating range to include signals at 1.3 micron (at photon counting intensities, not just for laser power levels, as is the current situation). Further, photomultiplier operation at even longer wavelengths, down to 1.54 micron, are feasible and can be assessed if the cone systems are effective for shorter wavelengths.
  • Figure 3 indicates that an energy displacement is possible, and although the movements of the lower limit are only on the scale of tenths of an eV, this is all that is required to open up a much wider spectral coverage.
  • the electric fields between the photocathode and the first dynode is, typically, around 100 V/cm, but this will not be altered by a coned surface geometry since there will be a high density of cones and the cone heights will be only a few microns. This should not perturb the existing field imaging, nor lead to enhanced electron emission.
  • Capacitance and conductivity control of the photocathode are currently less than ideal, but clearly operational.
  • the larger volume of coating material on the cones, albeit normal to the window surface, will reduce the present charge depletion problems.
  • Possible methods of enhancing the conductivity are ion implantation, buried metal ions, or variants of indium tin oxide. Such conductivity increases may be gained at the expense of ultra violet performance, but if the infra red region can be accessed then this would be an acceptable compromise.
  • Cone structures may be formed by ion beam sputtering, laser ablation, and thin film deposition, but for most examples these were unwanted and uncontrolled features.
  • Cone shapes are variable and range from beehive, to obelisk to column features and are generally brittle and larger than required for the light trap. Brittleness is unimportant as in this application the cones would be within the vacuum tube, so would not be subject to mechanical abrasion. However, size and shape control are significant as these will define the wavelength dependence of the process, and in extreme cases might influence the photoelectron extraction and conductivity.
  • cone generation examples include (I) lithography and chemical etching; (ii) formation of stable surface precipitates such as ion implanted colloids, followed by preferential chemical or ion beam etching to leave shielded cones; (iii) metal evaporation and holographic laser patterning, prior to an etching phase; (iv) inclusions within the glass that automatically define preferential etch rates; (v) excimer laser ablation where local coherence results in cone generation or surface structure, and (vi) holographic laser ablation.
  • Ion beam sputtering either directly, or by defining etchable patterns, is an attractive option since this will allow some control over the cone angles and hence can be tailored for specific wavelengths.
  • holographically defined patterns may be used as an initial processing step. Ion beam sputtering of this initial structure could be used to convert the cosine surface into more triangular patterns.
  • the level to which the patterning is critical will determine how sophisticated an industrial process needs to be, compared with the laboratory experiments. For example a commercial process might use a laser ablation route to generate a non-uniform set of cones and surface features, since this processing step might be performed within the vacuum chamber in which the emissive coatings are deposited. It would be less than optimum, but simple and direct.
  • a further method, illustrated in Figures 4a-4d, provides an alternative way of making cathode structures. It is based on the use of a fibre optic face plate, a device which consists of a plurality of optical fibre light guides mounted parallel to one another to conduct optical radiation between two surfaces, which are usually planar, but may have some other topography if it is desired to modify the characteristics of an incident wavefront.
  • a typical face plate is shown in perspective view in Figure 4a. It comprises a plurality of optical fibre light guides LG mounted in juxtaposition. Surfaces SI , S2 are ground in planes orthogonal to the axes of the light guides.
  • the light guides from which the face plate is formed are usually fabricated from glass.
  • Figures 4b-d typically, they comprise a central core 1 1 which may be a few micrometres in diameter, surrounded by a sheath of a glass 13 having a lower refractive index than that of the core to restrict optical radiation to the core by a process of internal reflection.
  • the sheath may be surrounded by a further layer 15 of opaque glass to absorb any radiation which is evanescent from the sheath.
  • Interstices 17 between light guides in the face plate are typically filled by a solder glass 19. Normally the glasses are of different chemical composition. When subjected to an etchant, they will Iherefore be dissolved at a different rate.
  • FIGs 4b and 4c illustrate ends of different fibres which have been etched in this way. With fibres illustrated in figure 4b, trap regions are in the form of conical ends 21. In the fibres illustrated in Figure 4c, the cones 21 are re-entrant.
  • the process may be used to produce a photomultiplier cathode with properties suitable for the present invention.
  • the principle may be further adapted by fabricating a face plate from fibres the chemical composition of which has been selected so that, in conjunction with a predetermined etchant, a desired surface profile may be obtained. Fibres may also be fabricated to have desired optical characteristics. For example, the refractive index profile may be chosen to shape the wavelength transmission characteristic of the face plate.

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)

Abstract

Cette invention se rapporte à un agencement assurant une absorption de rayonnement améliorée. Ledit agencement comprend une surface de réception du rayonnement aboutant un ensemble de surfaces en saillie sensiblement continues, possédant chacune une surface éloignée de ladite surface de réception du rayonnement, qui comporte une pluralité de régions piège sensiblement coniques de dimensions latérales inférieures à la longueur d'onde du rayonnement, destinées à l'absorption du rayonnement. Le piège à rayonnement est non réfléchissant du fait que le faisceau diffusé vers l'avant à l'intérieur de la surface interne de la fenêtre à cônes est réfléchi intérieurement dans des régions qui sont de petite taille, ou de dimension inférieure à la longueur d'onde optique dans le verre. De ce fait, l'énergie évanescente interagit progressivement avec la fine couche de revêtement sur la surface des cônes, et absorbe ainsi la lumière. Le rendement global dudit agencement dépend de l'angle des cônes, de l'épaisseur, des indices de réfraction et des coefficients d'absorption de la structure à cônes dans son ensemble, mais l'efficacité des cônes augmente avec des longueurs d'ondes supérieures.
PCT/GB1997/002650 1996-09-26 1997-09-26 Transducteurs de rayonnement WO1998013857A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9620037.3 1996-09-26
GBGB9620037.3A GB9620037D0 (en) 1996-09-26 1996-09-26 Radiation transducers

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WO1998013857A1 true WO1998013857A1 (fr) 1998-04-02

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1444718A2 (fr) * 2001-11-13 2004-08-11 Nanosciences Corporation Photocathode
JP2012516023A (ja) * 2009-01-22 2012-07-12 ビーエイイー・システムズ・インフォメーション・アンド・エレクトロニック・システムズ・インテグレイション・インコーポレーテッド コーナーキューブにより改善された光電陰極
US8507785B2 (en) 2007-11-06 2013-08-13 Pacific Integrated Energy, Inc. Photo induced enhanced field electron emission collector
JP2015536522A (ja) * 2012-10-12 2015-12-21 フォトニ フランス 吸収率を改善した半透明光電陰極
US9348078B2 (en) 2010-06-08 2016-05-24 Pacific Integrated Energy, Inc. Optical antennas with enhanced fields and electron emission
US10782014B2 (en) 2016-11-11 2020-09-22 Habib Technologies LLC Plasmonic energy conversion device for vapor generation

Citations (14)

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Publication number Priority date Publication date Assignee Title
FR685296A (fr) * 1928-12-01 1930-07-08 Perfectionnements aux dispositifs sensibles à la lumière
GB984936A (en) * 1960-10-12 1965-03-03 Fernseh Gmbh Electron discharge device including a photoemissive layer
US3243626A (en) * 1962-07-17 1966-03-29 Rca Corp Photosensitive cathode with closely adjacent light-diffusing layer
GB1181231A (en) * 1966-02-16 1970-02-11 Emi Ltd Improvements relating to Photo-Electrical Sensitive Devices
US3586895A (en) * 1968-05-08 1971-06-22 Optics Technology Inc Photocathode of light fibers having ends terminating in truncated corner cubes
US3700947A (en) * 1971-04-08 1972-10-24 Bendix Corp Increased sensitivity photocathode structure
US3809941A (en) * 1971-01-27 1974-05-07 Westinghouse Electric Corp Photoemitter structure including porous layer of photoemissive material
US3867662A (en) * 1973-10-15 1975-02-18 Rca Corp Grating tuned photoemitter
US4013465A (en) * 1973-05-10 1977-03-22 Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Reducing the reflectance of surfaces to radiation
EP0029914A1 (fr) * 1979-11-05 1981-06-10 International Business Machines Corporation Procédé de réduction de la réflection optique de surfaces
EP0068776A1 (fr) * 1981-06-29 1983-01-05 Minnesota Mining And Manufacturing Company Surfaces absorbantes de radiations
US4591717A (en) * 1983-05-03 1986-05-27 Dornier System Gmbh Infrared detection
DE3736185A1 (de) * 1986-10-27 1988-04-28 Hamamatsu Photonics Kk Photoelektrische wandlerroehre
EP0437242A2 (fr) * 1990-01-08 1991-07-17 Hamamatsu Photonics K.K. Procédé de fabrication d'un dispositif émettant des photoélectrons, dispositif émettant des photoélectrons et photomultiplicateur

Patent Citations (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR685296A (fr) * 1928-12-01 1930-07-08 Perfectionnements aux dispositifs sensibles à la lumière
GB984936A (en) * 1960-10-12 1965-03-03 Fernseh Gmbh Electron discharge device including a photoemissive layer
US3243626A (en) * 1962-07-17 1966-03-29 Rca Corp Photosensitive cathode with closely adjacent light-diffusing layer
GB1181231A (en) * 1966-02-16 1970-02-11 Emi Ltd Improvements relating to Photo-Electrical Sensitive Devices
US3586895A (en) * 1968-05-08 1971-06-22 Optics Technology Inc Photocathode of light fibers having ends terminating in truncated corner cubes
US3809941A (en) * 1971-01-27 1974-05-07 Westinghouse Electric Corp Photoemitter structure including porous layer of photoemissive material
US3700947A (en) * 1971-04-08 1972-10-24 Bendix Corp Increased sensitivity photocathode structure
US4013465A (en) * 1973-05-10 1977-03-22 Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland Reducing the reflectance of surfaces to radiation
US3867662A (en) * 1973-10-15 1975-02-18 Rca Corp Grating tuned photoemitter
EP0029914A1 (fr) * 1979-11-05 1981-06-10 International Business Machines Corporation Procédé de réduction de la réflection optique de surfaces
EP0068776A1 (fr) * 1981-06-29 1983-01-05 Minnesota Mining And Manufacturing Company Surfaces absorbantes de radiations
US4591717A (en) * 1983-05-03 1986-05-27 Dornier System Gmbh Infrared detection
DE3736185A1 (de) * 1986-10-27 1988-04-28 Hamamatsu Photonics Kk Photoelektrische wandlerroehre
EP0437242A2 (fr) * 1990-01-08 1991-07-17 Hamamatsu Photonics K.K. Procédé de fabrication d'un dispositif émettant des photoélectrons, dispositif émettant des photoélectrons et photomultiplicateur

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* Cited by examiner, † Cited by third party
Title
"semi-transparent cathode PMT having enhanced sensitivity", RESEARCH DISCLOSURE, no. 244, August 1984 (1984-08-01), pages 369, XP002027688 *

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1444718A2 (fr) * 2001-11-13 2004-08-11 Nanosciences Corporation Photocathode
EP1444718A4 (fr) * 2001-11-13 2005-11-23 Nanosciences Corp Photocathode
US8507785B2 (en) 2007-11-06 2013-08-13 Pacific Integrated Energy, Inc. Photo induced enhanced field electron emission collector
US8969710B2 (en) 2007-11-06 2015-03-03 Pacific Integrated Energy, Inc. Photon induced enhanced field electron emission collector
JP2012516023A (ja) * 2009-01-22 2012-07-12 ビーエイイー・システムズ・インフォメーション・アンド・エレクトロニック・システムズ・インテグレイション・インコーポレーテッド コーナーキューブにより改善された光電陰極
US8581228B2 (en) 2009-01-22 2013-11-12 Bae Systems Information And Electronic Systems Integration Inc. Corner cube enhanced photocathode
US8900890B2 (en) 2009-01-22 2014-12-02 Bae Systems Information And Electronic Systems Integration Inc. Corner cube enhanced photocathode
EP2380047B1 (fr) * 2009-01-22 2018-07-11 BAE Systems Information and Electronic Systems Integration Inc. Photocathode améliorée à sommets de cube
US9348078B2 (en) 2010-06-08 2016-05-24 Pacific Integrated Energy, Inc. Optical antennas with enhanced fields and electron emission
JP2015536522A (ja) * 2012-10-12 2015-12-21 フォトニ フランス 吸収率を改善した半透明光電陰極
US10782014B2 (en) 2016-11-11 2020-09-22 Habib Technologies LLC Plasmonic energy conversion device for vapor generation

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Publication number Publication date
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