Optical: systems and elements – Single channel simultaneously to or from plural channels – By refraction at beam splitting or combining surface
Reexamination Certificate
2002-08-14
2003-12-16
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By refraction at beam splitting or combining surface
C359S618000, C359S629000, C359S636000, C359S583000
Reexamination Certificate
active
06665124
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
The present application claims priority from European Patent Application No. 01660154.4, filed Aug. 30, 2001.
BACKGROUND AND SUMMARY OF THE INVENTION
The invention relates to a geometrical beam splitter for transversally dividing a radiation beam into at least one reflected beam portion and at least one passing beam portion, said beam splitter being composed of a piece of rigid material having a non-transparent reflective surface at an angle in respect to the incident direction of said radiation beam, said angle substantially deviating from the right angle. The invention also relates to a sensor comprising a radiation source, a measuring chamber, at least two detectors, at least two optical filters each of which between the radiation source and one of the detectors, and a beam splitter composed of a piece of rigid material and being at least partly reflective; whereupon a radiation beam from said radiation source travels to said at least two detectors through the measuring chamber and through the respective optical filters, said beam splitter positioned between the detectors and the measuring chamber so as to allow a reflected portion and an undiverted portion of said radiation beam to reach the detectors simultaneously.
Beam splitters are used in optics for the purpose of combining two beams, and for separating one beam into two. Wavelength region or distribution and intensity ratio between the two separated beam portions depends upon the specific properties of the beam splitter. The most typical beam splitter is a thin plate of glass or plastic with one surface coated with a semi-reflecting coating or semi-transparent mirror coating. One portion of the beam is transmitted through the beam splitter and the other portion is reflected typically by 90 degrees. Possible absorption in the beam splitter materials is here ignored. The drawbacks caused by the reflection from the second glass surface can be avoided by using a beam splitter cube. It consists of two right angle prisms cemented together. The hypotenuse of one prism is coated with a semi-reflecting coating before cementing. The construction is expensive, especially if the wavelengths in use are in the infrared region with few suitable materials. Other type of prisms and combination of prisms are also known. Further a thin semi-reflecting membrane, a pellicle, is a possible solution but it may not be robust enough in many cases and it can be sensitive to temperature fluctuations, and its reliable fastening is also a problem. The beam splitters described above are called physical beam splitters because the complete beam aperture is available in both the transmitted and the reflected part. Physical beam splitters are described e.g. in publication Naumann/Schröder:
BAUELEMENTE DER OPTIK
Taschenbuch der Technische Optik; Carl Hanser Verlag 1987, pp. 186-187, and the use of a beam splitter can be found in the publication U.S. Pat. No. 5,908,789.
Another alternative of the beam splitters are so called geometrical beam splitters, in which the beam cross-section is either divided into two portions having different wavelength distribution by using a grating or metallic grid or a mesh, or divided into two portions with the same wavelength distribution both having a smaller cross-section area than the initial beam by using reflecting stripes or spots e.g. on a glass plate or a prism or by using a mirror to cover a section of the initial beam. The latter type of beam splitters are often used in the infrared region, but avoiding radiation absorption of the material requires use of special materials, which may cause problems in some applications, because the material has to be thin and a robust support with little temperature dependence is also in this case very difficult to construct. The gratings, grids and meshes are described in publication W. Driscoll, W. Vaugham:
HANDBOOK OF OPTICS
, McGraw-Hill Book Company 1978, pp. 8-106-8-109 do not suffer radiation absorption problems, but the feature that the transmitting portion and the diverted portion has different wavelength distributions is not acceptable for many purposes. The geometrical beam splitters for cross-sectional dividing are disclosed in publications Naumann/Schröder:
BAUELEMENTE DER OPTIK
Taschenbuch der Technische Optik; Carl Hanser Verlag 1987, pp. 186-187, and Module 6—6 “
FILTERS AND BEAM SPLITTERS
”, Center of Occupational Research and Development, 1987 {http://www.cord.org/cm/leot/course06}. FIG. 29 in the last mentioned publication shows a planar mirror with an aperture, the mirror being perpendicular to the radiation direction. This kind of mirror construction is used solely in high power CO
2
-lasers, in which semitransparent mirrors cannot be used because of the extremely high power of several kW's requiring cooling. In these CO
2
-lasers, utilized for welding and cutting metals, said mirror with aperture is used as one of the end mirrors, whereupon the main portion of the light is reflected directly back to the other mirror at the opposite end of the laser, and the productive laser power beam comes out through the aperture. FIG. 28 in the last mentioned publication shows a plant mirror partly protruding in the incident light beam and so dividing it into one smaller portion of reflected light and one larger portion of undiverted light. This alternative has the drawback not being robust or steady and it is also difficult to manufacture in small sizes with a precision high enough especially for modern sensors with several detectors.
Publications JP-05-215 683 discloses a device for analyzing e.g. the concentrations of gas components in a gas mixture on the basis of the absorption of infrared radiation. The device comprises a radiation source, the radiation emitted thereby being aligned to travel through a measuring cell, which contains the gas mixture to be analyzed, a first optical filter, which is positioned on the path of radiation, and a first detector, positioned in the radiating direction downstream of said first filter and used for detecting the radiation intensity falling thereon. The device further includes at least a second optical filter provided with a detector for identifying and/or measuring the concentration of at least one other gas component. In order that these at least two separate detectors simultaneously receive radiation from the measuring cell, the device is further provided with a beam splitter. According to the publication the beam splitter can be of the type of the semi-reflecting coating or semi-transparent mirror coating, as described above. Alternatively this publication suggests using a reflecting mirror, in the center of which an aperture is punched for passing a portion of the incoming radiation and followed by a gas filter and a detector. Also JP-05-215684 discloses a gas analyzer with a plurality of detectors. However, the beam splitter is composed only of reflecting parts. No transmitted portion of the beam is shown or described.
The publication U.S. Pat. No. 6,122,106 describes an opto-mechanical system to be used as a laser transmitter/receiver for measuring distances. The incoming light is actually not divided into a reflected and a passing beam portion but there is only a reflected portion. The two holes in the mirror are used for transmitting radiation in the opposite direction as compared to the incoming and reflected light. According to the publication these two holes are as small as possible, like “pencil thin”, so that the reflected portion is maximized, whereupon the area of the radiation transmitting in inverse direction is extremely small as compared to the area of the reflected radiation. The publication JP-63-107082 describes a laser mirror. It has one or a plurality of very small holes like pinholes in it, whereupon the reflective area is many orders larger than the area of the small holes. The laser light transmitted through this/these small hole(s) forms accordingly an extremely small portion of the whole radiation, which indeed is enough in this case, bec
Andrus Sceales Starke & Sawall LLP
Instrumentarium Corp.
Mack Ricky
Thomas Brandi N
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