US3571602A - Optical system to reduce reflection losses in a photocell - Google Patents

Optical system to reduce reflection losses in a photocell Download PDF

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Publication number
US3571602A
US3571602A US787953A US3571602DA US3571602A US 3571602 A US3571602 A US 3571602A US 787953 A US787953 A US 787953A US 3571602D A US3571602D A US 3571602DA US 3571602 A US3571602 A US 3571602A
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United States
Prior art keywords
wall
prism
sides
reflected
nonparallel
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Expired - Lifetime
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US787953A
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English (en)
Inventor
Axel Erik Ludvig Ohlsson
Lars-Erik Skagerlud
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Saab Bofors AB
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Bofors AB
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J40/00—Photoelectric discharge tubes not involving the ionisation of a gas
    • H01J40/02—Details
    • H01J40/04—Electrodes
    • H01J40/06—Photo-emissive cathodes

Definitions

  • ABSTRACT A photodetector system including a photocell of ⁇ 31] 321/68 the type having a photosensitive coating on the internal surface of a plane transparent wall forming part of the envelope [54] OPTICAL SYSTEM To REDUCE REFLECTION of the cell. At least one prism whose principal section has the form of a trapezoid is attached to the wall so that the shorter g afm gg one of the two parallel sides of the prism is in contact with the exterior surface of the wall in front of a central portion of the U.S.
  • the lengths of the ides and the angles of the prin- 250/213, 3.50/286 cipal section of the prism are so chosen that a bundle of light .1 entering the longer one of the parallel sides at angles to Field Of Search 250/216, that side, is in part reflected by a first one of the nonparallel 277, 213; 350/286, 96, 171,203; 313/65, 94 sides towards the other one of the nonparallel sides and 56 R f Cm!
  • the invention relates to a photodetector system, which comprises a substantially plane wall of transparent material, for instance glass, the inside of which is coated with a material emitting electrons when exposed to light.
  • the wall may form part of a closed envelope, for instance a glass bulb.
  • a photodetector of this kind which may be in the form of an electronmultiplier photo tube, can be considered as an electron tube, in which the cathode is constituted by the light-sensitive coat- A light beam directed from the outside towards the photodetector must first pass through the transparent wall, before the light strikes the photocathode. When the light falls at right angles to the wall, a great part thereof will be reflected against the outer side of the wall and against the inner side of the wall. Thus, only a relatively small portion of the incident light is utilized for releasing electrons from the photosensitive layer, that is the efficiency becomes low.
  • the light beam can be guided to arrive at the wall in parallel with the axis of the photodetector, but the drawback of the very limited beam diameter remains.
  • At least one prism is attached to the outer side of the wall.
  • the principle section of the prism has the form of a polygon with at least two parallel sides. A first one of the parallel sides is in contact with the wall at a central portion in front of the coating.
  • Two of the nonparallel sides of the prism form such angles to the parallel sides that light entering the second one of the two parallel sides at right angles is in part reflected by one of said nonparallel sides towards the other one of the nonparallel sides and reflected towards the wall by the last-mentioned side, while another part of the light entering the second one of the parallel sides at right angles is reflected by one of the nonparallel sides directly towards the wall, so that both the light reflected by one of the nonparallel sides and the light reflected by both of the nonparallel sides enters the wall under an angle of about 45.
  • FIG. 1 shows a cross section one embodiment of the invention
  • FIG. 2 shows in cross section another embodiment of the invention.
  • FIG. 3 shows in cross section a third embodiment of the invention.
  • FIG. 1 shows in section a part of an envelope 1 of a photodetector.
  • the envelope comprises a plane wall 2 of transparent material, the inside of which is provided with'a coating 3 of a material emitting electrons when exposed to light.
  • the photodetector is of a known type, and therefore those parts of it which are not necessary for the understanding of the invention has been omitted from the drawing.
  • a prism 4 is attached to a central portion of the outer side of the wall 2.
  • This prism has a trapezoid section.
  • the two parallel sides are designated 5 and 6.
  • the prism 4 is fixed in some known manner to the outer surface of the wall 2 so that the shorter one of the two parallel sides is in contact with the wall.
  • One of the two nonparallel sides 7 is at right angles to the two parallel sides, while the other one 8 of the nonparallel sides forms an angle of 225 to the perpendicular to the wall.
  • a bundle of light 9 which falls at right angles upon the side 6 of the prism and strikes the oblique side 8 within he prism is totally reflected by the last mentioned side and proceeds in a direction fonning an angle of 45 to the perpendicular of wall 2.
  • That part of the light which is not utilized for releasing electrons is reflected by the inner side of wall 2 towards its outer side and is reflected from here back to the inner side where it strikes other points on the inside and causes additional electrons to be emitted from the coating 3. These repeated reflections proceed towards the border of the wall 2. Since the prism 4 is located centrally on wall 2, both the reflections travelling upwards (as seen in FIG. I) and those travelling downwards will be utilized for the release of electrons. If the prism 4 is placed adjacent to the border of the wall 2, only about one-half of the incident light bundle 9 would be utilized for this purpose.
  • the thickness of the wall 2 is designated by a on the FIG.
  • the side 5 of the prism 4 which is in contact with the wall 2 has a length of 2a. It is readily understood that if side 5 had a length larger than 2a, a part of the light reflected from the inside of wall 2 would again enter the prism and be lost.
  • the light bundle 9 can be given a diameter of 2a /2.
  • the thickness of the wall 2, that is the value of a is usually about 1.5 mm., and thus the light bundle 9 can be given a diameter of about 4.2 mm.
  • Such a large diameter of the light bundle is advantageous, since it can be easily produced by means of a simple optical system. Also, the mounting of the photodetector in relation to the optical system requires less accuracy than in the case when the light bundle has a smaller diameter.
  • the distance between the t vo parallel sides 5 and 6 should obviously be at least 4a +2a /2.
  • FIG. 2 shows an embodiment including two prisms which are arranged symmetrically in relation to the perpendicular of the wall 2.
  • Each of these prisms is of he same shape as prism 4 in FIG. 1.
  • the two prisms 4 and 4a in FIG. 2 are so arranged that the edge formed by sides 6 and 8 of prism 4 engages the corresponding edge formed by sides 6a and 8a of prism 4a.
  • the light beam falls centrally upon the photodetector.
  • the diameter of the light beam can obviously be increased to 4a V2.
  • FIG. 3 shows two prisms 4 and 4a which are extended by parallelepipedal parts bounded by the sides 6, 7, 11, 12 and 6a, 7a, Ila, 12, respectively.
  • the sides 11 and Ila have been indicated by dotted lines in the FIG. to indicate that the parallelepipedal parts can be integral with the other parts of the respective prisms.
  • These parallelepipedal extension parts may, however, also be separate plates. If the arrangement comprises two prisms as shown in FIG. 3, these plates may be joined into one plate (the contact surface 12 is omitted).
  • a prism of a rotationally symmetrical form that is a prism whose section in a plane parallel to the wall 2 has the form of an annulus.
  • a longitudinal section of an arrangement with a prism of this form would have the same appearance as the arrangement shown in FIG. 2 or FIG. 3
  • the prism is preferably made of the same material as the wall 2 or at least of a material having the same optic properties.
  • Photodetector system comprising a plane wall of transparent material, one side of which bears a coating of a material emitting electrons when exposed to light, at least one prism attached to the other side of said wall, the principal section of said prism having the form of a polygon with at least two parallel sides, a first one of said parallel sides being in contact with the wall at a central part thereof and in front of said coating, and two of the nonparallel sides of the prism forming such angles to said parallel sides that light entering the second one of said two parallel sides at right angles thereto is in part reflected by one of said nonparallel sides towards the other one of the nonparallel sides and reflected towards said wall by the last-mentioned side, while another part of the light entering said second one of said parallel sides at right angles thereto is reflected by one of said nonparallel sides directly towards said wall, so that both the light reflected by one of said nonparallel sides and the light reflected by both of said nonparallel sides enters said wall under an angle of about

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  • Optical Elements Other Than Lenses (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Investigating Or Analysing Materials By Optical Means (AREA)
  • Optical Radar Systems And Details Thereof (AREA)
US787953A 1968-01-10 1968-12-30 Optical system to reduce reflection losses in a photocell Expired - Lifetime US3571602A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE321/68A SE307023B (cs) 1968-01-10 1968-01-10

Publications (1)

Publication Number Publication Date
US3571602A true US3571602A (en) 1971-03-23

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US787953A Expired - Lifetime US3571602A (en) 1968-01-10 1968-12-30 Optical system to reduce reflection losses in a photocell

Country Status (7)

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US (1) US3571602A (cs)
CH (1) CH486118A (cs)
DE (1) DE1900637A1 (cs)
FR (1) FR2000116A1 (cs)
GB (1) GB1235411A (cs)
NO (1) NO121227B (cs)
SE (1) SE307023B (cs)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20020074484A1 (en) * 2000-12-15 2002-06-20 Heinz Kousek Light beam receiver for a laser positioning device
US6462862B2 (en) * 1995-03-20 2002-10-08 Fujitsu Limited Optical fiber amplifier and dispersion compensating fiber module for optical fiber amplifier

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1240905A (en) * 1917-04-09 1917-09-25 F A Hardy & Company Binocular-magnifier.
US2119544A (en) * 1937-03-22 1938-06-07 Otto K Kaspereit Prism
US2954721A (en) * 1957-10-09 1960-10-04 Austin P Voelker Optical inspection instrument
US3415990A (en) * 1966-03-21 1968-12-10 Itt Invisible light sensor tube and faceplate material
US3424516A (en) * 1964-05-28 1969-01-28 Texas Instruments Inc Prism system comprising joined pentaprisms

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1240905A (en) * 1917-04-09 1917-09-25 F A Hardy & Company Binocular-magnifier.
US2119544A (en) * 1937-03-22 1938-06-07 Otto K Kaspereit Prism
US2954721A (en) * 1957-10-09 1960-10-04 Austin P Voelker Optical inspection instrument
US3424516A (en) * 1964-05-28 1969-01-28 Texas Instruments Inc Prism system comprising joined pentaprisms
US3415990A (en) * 1966-03-21 1968-12-10 Itt Invisible light sensor tube and faceplate material

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US6462862B2 (en) * 1995-03-20 2002-10-08 Fujitsu Limited Optical fiber amplifier and dispersion compensating fiber module for optical fiber amplifier
US20020074484A1 (en) * 2000-12-15 2002-06-20 Heinz Kousek Light beam receiver for a laser positioning device
US6950250B2 (en) * 2000-12-15 2005-09-27 Hilti Ahtiengesellschaft Light beam receiver for a laser positioning device

Also Published As

Publication number Publication date
GB1235411A (en) 1971-06-16
FR2000116A1 (cs) 1969-08-29
DE1900637A1 (de) 1969-09-04
SE307023B (cs) 1968-12-16
NO121227B (cs) 1971-02-01
CH486118A (de) 1970-02-15

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