WO2005095910A1

WO2005095910A1 - Spectrometer

Info

Publication number: WO2005095910A1
Application number: PCT/RU2005/000159
Authority: WO
Inventors: Alexandr Markovich Livshits
Original assignee: Alexandr Markovich Livshits
Priority date: 2004-04-01
Filing date: 2005-04-01
Publication date: 2005-10-13
Also published as: RU2262086C1

Abstract

A method of measuring a spectrum makes possible the recording and measuring of an extended spectrum section to be obtained by means of a concave grating, without losses at the interfaces between linear video signal shapers, in particular linear charged-coupled devices (CCD-registers). A spectrometer realizing the claimed method may be made small-size, movable and permissive to carry out spectrum measurements promptly. A small-size embodiment of the spectrometer makes possible, at the expense of a mirror to be arranged at the center of the Rowland circle, further decrease in its overall dimensions by a factor of two. The method contemplates a preliminary division of a flux of radiation to be investigated into two parts, which are directed toward a grating separately through two slits (3) being displaced with respect to each other in the direction being perpendicular to the plane of the Rowland circle (2), and then toward different linear video signal shapers (6), while forming on one linear video signal shaper, from one flux part, a spectrum section being a continuous extension of a spectrum section to be formed on the other linear video signal shaper from the other flux part.

Description

SPECTROMETER

FIELD OF THE INVENTION The present invention relates to spectrometry.

BACKGROUND OF THE INVENTION Historically, the known spectrometers have been created using optical designs of pre-existing spectrographs, in which they incorporated an entrance slit, a concave grating and a photographic film as a radiation detector. There has been known a spectrometer described in RU Patent 2,105,272 (publication date February 20, 1998) that comprises a concave grating, an entrance slit and a photodetector. To measure the spectrum, provision is made for displacing the entrance slit along the Rowland circle. Radiation from the entrance slit to the photodetector is transmitted through light pipes. The spectrometer makes possible the simultaneous measurement of spectra of three radiations directed through the entrance slit. The drawbacks to this spectrometer reside in its bulkiness brought on by considerable sizes of the Rowland circle and the availability of a scanning mechanism. There have been known methods, as described in GB Patent 631,748 (publication date November 9, 1949) and DE Patent 3,621,464 (publication date January 8, 1987), of using a mirror in the optical design comprising an entrance slit, a concave grating and a radiation detector, which enabled overall instrument dimensions to be decreased significantly. In DE Patent 3,621,464 provision is made for the arrangement of a flat mirror at the center of the Rowland circle to turn about the axis being perpendicular to the plane of the Rowland circle at its center. However, the availability of a spectrum scanning mechanism by means of turning the mirror results, in turn, in bulkiness and hence in an increase in the spectrometer overall dimensions and a decrease in its reliability. Moreover, the scanning prevents an extended spectrum from being measured simultaneously. Among the known spectrometers, the closest prior art with respect to the presently claimed spectrometer resides in a spectrometer described by A. M. Livshits, A. V. Peleznev, Y. A. Levykin in "A Mobile Automated System for Classifying Metal Alloys", Achievements of Science and Technology. VIMI Inter- Branch Collection, 1990, Issue 3. This spectrometer comprises an entrance slit, a concave grating and radiation detectors. Linear video signal shapers (LVSS), in particular linear charged-coupled devices (CCD-registers), are used, however, as radiation detectors. In so doing, not a limited set of isolated spectral lines, but rather those extended sections of the spectrum that are coincide in length with a CCD-register photosensitive part, are recorded. The drawback to the closest prior art with respect to the present invention resides in the formation of "blind regions" between CCD-registers placed in series on the Rowland circle. Even though the CCD-registers are placed immediately adjacent to each other, a "blind region", that is the absence of radiation reception, will be preserved between their photosensitive portions. The other drawbacks reside in the availability of considerable sizes to be defined by the radius of curvature of the concave grating and hence by the diameter of the Rowland circle.

SUMMARY OF THE INVENTION The claimed inventions are aimed at creating low-bulk spectrometers that make possible the measuring of extended spectra. A technical effect to be ensured by the claimed method of measuring a radiation spectrum, the claimed spectrometer and the claimed small-size spectrometer consists in the measurement of extended spectra using several LVSS without loss of information about a spectrum section placed at the LVSS interfaces. In the claimed small-size spectrometer, an additional decrease in the spectrometer overall dimensions is provided. The above technical effect is afforded in a method of measuring a radiation spectrum contemplating the directing of a radiation flux through a slit toward a concave grating and then toward, at least, two linear video signal shapers. In accordance with the present invention the radiation flux is pre-divided into two parts directed toward the said grating separately through two slits displaced from each other in the direction being perpendicular to the plane of the Rowland circle, and then toward different linear video signal shapers, while forming on one linear video signal shaper, from one flux part, a spectrum section being a continuous extension of a spectrum section to be formed on the other linear video signal shaper from the other flux part. The radiation flux parts to be directed toward the concave grating may be equal. The radiation flux parts may be directed toward the concave grating through two slits displaced from the plane of the Rowland circle by one amount but different in sign, relative to the said plane. It is possible to use different amount of linear video signal shapers (CCD- registers). In particular, it is possible to form, on two or three linear video signal shapers from one flux part, spectrum sections being a continuous extension of spectrum sections to be formed on the other two linear video signal shapers from the other flux part. It is also possible to use 2N or 2N+1 linear video signal shapers, where N is equal to 1, 2, 3, ... and limited to a reasonable amount, which may be as much as several dozens. In this case, on N or N+l linear video signal shapers there are formed spectrum sections from one flux part, which are a continuous extension of spectrum sections to be formed on N other video signal shapers from the other flux part. The above technical effect is afforded in a spectrometer that realizes the method as disclosed above. To this end, the spectrometer comprises an entrance slit, a concave grating and linear video signal shapers. Additionally, to measure a spectrum without loss of information about a spectrum section placed at the interfaces between the linear video signal shapers, the spectrometer comprises a second entrance slit arranged to be displaced from a first slit in the direction being perpendicular to the plane of the Rowland circle, an optical unit that divides the radiation flux into two parts to be directed by said unit respectively through the first and second slits toward the concave grating, whereas one of said linear video signal shapers being optically linked, by means of the concave grating, to the first entrance slit, the other - to the second entrance slit, and the both linear video signal shapers being arranged so that the spectrum sections formed on them are a continuous extension of each other. It should be noted that just a preliminary division of the radiation flux and a simultaneous separate measurement of spectra of the radiation flux parts make possible the achievement of the above technical effect. A corresponding optical system is of a radically different kind from an optical system used in spectrographs and the known spectrometers. To avoid inclination of spectral lines relative to CCD-registers, said inclination being caused by the displacement of slits from the Rowland circle, the entrance slits may be turned in their plane about the axis being perpendicular to this plane and fixed in this position. The entrance slits may be arranged with displacement along the Rowland circle. The spectrometer may comprise 2N or 2N+1 linear video signal shapers, where N = 1, 2, 3 etc. In so doing, one group of N or N+l linear video signal shapers being optically linked, by means of the concave grating, to the first entrance slit, the other group of N other linear video signal shapers - to the second entrance slit, and the both groups of linear video signal shapers being arranged so that the spectrum sections formed on linear video signal shapers from one group are a continuous extension of the spectrum sections to be formed on linear video signal shapers from the other group. The mentioned technical effects are provided in a small-size spectrometer that realizes the method as disclosed above. To this end, the small-size spectrometer comprises an entrance slit, a concave grating and linear video signal shapers. In addition, according to the present invention, in order to measure a spectrum without loss of information about a spectrum section placed at the interfaces between the linear video signal shapers and to decrease its overall dimensions, the small-size spectrometer comprises a flat mirror being arranged perpendicular to the plane of the Rowland circle at its center, a second entrance slit being arranged with displacement relative to a first slit in the direction being perpendicular to the plane of the Rowland circle, and an optical unit that divides the radiation flux into two parts to be directed by said unit respectively through the first and second slits toward the flat mirror, whereas one of said linear video signal shapers being optically linked, by means of the flat mirror and concave grating, to the first entrance slit, the other - to the second entrance slit, and the both linear video signal shapers being arranged so that the spectrum sections formed on them are a continuous extension of each other. The small-size spectrometer may comprise 2N or 2N+1 linear video signal shapers, where N = 1, 2, 3 etc. In so doing, one group of N or N+l linear video signal shapers being optically linked, by means of the flat mirror and the concave grating, to the first entrance slit, the other group of N other linear video signal shapers - to the second entrance slit, and the both groups of linear video signal shapers being arranged so that the spectrum sections formed on linear video signal shapers from one group are a continuous extension of the spectrum sections to be formed on linear video signal shapers from the other group. When using a concave grating of large curvature and a flat mirror, the region of a possible LVSS positioning is limited because of a decrease in the spectrometer overall dimensions, thus resulting in the limitation of extent of a spectrum to be measured. To preserve the possibility of measuring spectra of a large extent by sequential measurement of various extended sections of the spectrum of the same radiation using all spectrometer LVSS, the flat mirror may have several, at least two fixed positions, and be arranged to turn by corresponding angles about the axis being perpendicular to the plane of the Rowland circle at its center.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. 1 and FIG. 2 illustrate a spectrometer optical design; FIG. 3 and FIG. 4 illustrate the embodiments of placing entrance slits and LVSS relative to the plane of the Rowland circle; FIG. 5 illustrates an optical design of a small-size spectrometer.

MODES FOR CARRYING OUT THE INVENTION A method of measuring a spectrum and a corresponding spectrometer may be implemented as shown in FIG. 1. The radius of curvature of the concave grating 1 corresponds to the diameter of the Rowland circle 2 and must be minor, in order to achieve compactness of the device in accordance with the present invention. Two entrance slits 3 are positioned so that a first one is above and a second one is below the plane of the Rowland circle 2. As to the Rowland circle for concave gratings, see, for example, A. N. Zaidel, G. V. Ostrovskaya, Y. I. Ostrovsky "The Technique and Practice of Spectroscopy", Nauka, Moscow, 1976, p. 57, or M. Born and E. Volf "The Foundations of Optics", Nauka, Moscow, 1970. Illumination of the slits is carried out by dividing the luminous flux from a radiation source, using an optical unit - a divider, into two parts to be transmitted separately toward a first and a second slit respectively. In particular, said optical unit - divider may be made to the shape of a light pipe 4 having one input optically linked with a radiation source 5 and two branching outputs brought immediately adjacent to the entrance slits. In so doing, there are formed two identical spectra positioned at the same distances as their respective slits, from the plane of the Rowland circle - one is above the other is below. Radiation coming from the upper slit forms the spectrum below the plane of the Rowland circle, whereas that coming from the lower slit forms the spectrum above the plane of the Rowland circle. In points of forming these spectra (see FIG. 2, in which there is depicted a view of the entrance slit and LVSS from the center of the grating), on the Rowland circle LVSS 6 are arranged such that their photosensitive parts 7 in the sum total overlap without losses the entire spectral range to be recorded. As distinct from the design of spatial mounting of the concave grating in accordance with the Eagle mounting (see, A. N. Zaidel, G. V. Ostrovskaya, Y. I. Ostrovsky "The Technique and Practice of Spectroscopy", Nauka, Moscow, 1976, p. 61), in this mounting a spectrum to be observed is located not under the slit but with displacement along the Rowland circle. Values of the spectra themselves are calculated by means of a computer connected via an electronic unit to LVSS. This electronic unit serves to control operation of LVSS, to take signals therefrom and enter these signals to a computer for their presentation in digital and visual forms. As LVSS, use may be made, for example, of photodiode matrixes, photodiode registers or CCD. Because of displacement of entrance slits above and below the Rowland circle, spectral lines are arranged at an angle with respect to the lines of LVSS photosensitive cells (see, A. N. Zaidel, G. V. Ostrovskaya, Y. I. Ostrovsky "The Technique and Practice of Spectroscopy", Nauka, Moscow, 1976, p. 156). To compensate for this inclination, the both slits, when calibrating the device, have a chance of turning about the axis passing perpendicular to the slit planes through their center 8. There has been created a spectrometer in which the curvature of the grating amounts to 330 mm. Rulings are scribed on the surface measuring 45mm x 45 mm at a frequency of 1800 rulings/mm. Dispersion = 1.5 nm/mm. The number of CCD- registers amounts to 4 or 5 (TCD1304AP - TOSHIBA, Japan). To enable application of these registers in the ultra-violet spectrum region, glass entrance windows were replaced with quartz ones. The number of photosensitive cells in the CCD-register amounts to 3648. Each cell measures 8 x 200 μm. An operating region of the spectrum measures 180 - 350 nm or 180 - 410 nm. One entrance slit of the created spectrometer is positioned 7 mm above the Rowland circle, whereas the other - 7 mm below the Rowland circle. This makes possible, firstly, the extension of two obtained spectra below and above the plane of the Rowland circle by the same 7 mm without overlapping with each other. And, secondly, the falling two or three CCD-registers within the clearance limits above the plane of the Rowland circle, whilst two CCD-registers - below the plane of the Rowland circle. As special cases of the claimed technical solution, there are possible various embodiments of arranging the slits and LVSS. For example, the entrance slits are arranged above each other, whereas LVSS are arranged above or below the Rowland circle in staggered order (see, FIG. 3). In another example, the entrance slits are spaces apart relative to each other in the Rowland circle for such distance in which LVSS are arranged strictly one above another (see, FIG. 4). In the first embodiment, the entrance slits are arranged compactly, whilst in the second embodiment - LVSS do so. In order to implement a small-size spectrometer, the spectrometer design (see, FIG. 5) additionally comprises a flat mirror 9 being arranged perpendicular to the plane of the Rowland circle 2 with its reflecting plane being directed toward entrance slits 3 (in FIG. 5 they are merged into one image, since they are above each over) and aligned with the axis that is perpendicular to the plane of the Rowland circle and pass through its center 10. In so doing, the mirror has a possibility to turn about the said axis. The entrance slits 3, a grating 1 and a set of LVSS 6 (which are also arranged above each other in staggered order) are arranged on one side from the mirror, to allow reduction in the spectrometer overall dimensions by one half. Radiation coming out of the entrance slits 3 is reflected from the mirror 9 and falls on the grating 1 and, after having been reflected from the grating 1, it decomposes with space according to wavelengths and finds its way back to the mirror 9. After a secondary reflection from this mirror, radiation of each wavelength is focused on photosensitive parts of radiation detectors 6. Radiation coming out of the upper slit forms a spectrum below the plane of the Rowland circle, whereas radiation coming out of the lower slit forms a spectrum above the Rowland circle. By turning the mirror 9 about the axis passing through a center 10 of the Rowland circle perpendicular to the plane of this circle, it is possible, firstly, to remove the obtained spectra to the most convenient, from the technical point of view, range of the Rowland circle and, secondly, to measure, after one extended spectrum section has been measured, another extended spectrum section. Although the present invention has been described with reference to preferred embodiments, the invention is not limited to the details thereof, and various changes and modifications obvious to one skilled in the art to which the invention pertains are deemed to be within the spirit, scope and contemplation of the invention as further defined in the appended claims.

Claims

WHAT IS CLAIMED IS: 1. A method of measuring a radiation spectrum comprising the directing of a radiation flux through a slit toward a concave grating and then toward, at least, two linear video signal shapers, characterized in that the radiation flux is pre-divided into two parts directed toward the said grating separately through two slits displaced from each other in the direction being perpendicular to the plane of the Rowland circle, and then toward different linear video signal shapers, while forming on one linear video signal shaper, from one flux part, a spectrum section being a continuous extension of a spectrum section to be formed on the other linear video signal shaper from the other flux part. 2. A method as defined in claim 1, characterized in that the radiation flux parts to be directed toward the concave grating are equal to each other. 3. A method as defined in claim 1 , characterized in that the radiation flux parts are directed toward the concave grating through two slits displaced from the plane of the Rowland circle by one amount but in different directions. 4. A method as defined in claim 1, characterized in that on two or three linear video signal shapers, from one flux part, there are formed spectrum sections being a continuous extension of spectrum sections to be formed on the other two linear video signal shapers from the other flux part. 5. A method as defined in claim 1, characterized in that on N or N+l linear video signal shapers, where N = 1, 2, 3 etc., there are formed spectrum sections from one flux part, which are a continuous extension of spectrum sections to be formed on N other video signal shapers from the other flux part. 6. A spectrometer comprising an entrance slit, a concave grating, at least two linear video signal shapers, characterized in that it additionally comprises a second entrance slit arranged to be displaced from a first slit in the direction being perpendicular to the plane of the Rowland circle, and an optical unit that divides the radiation flux into two parts to be directed by said unit respectively through the first and second slits toward the concave grating, whereas one of said linear video signal shapers being optically linked, by means of the concave grating, to the first entrance slit, the other - to the second entrance slit, and the both linear video signal shapers being arranged so that the spectrum sections formed on them are a continuous extension of each other. 7. A spectrometer as defined in claim 6, characterized in that each entrance slit is arranged to turn about the axis being perpendicular to the plane of the slit and to be fixed in a turned position. 8. A spectrometer as defined in claim 6, characterized in that the entrance slits are arranged with displacement along the Rowland circle. 9. A spectrometer as defined in claim 6, characterized in that the optical unit dividing the radiation flux into two parts is constructed of pipe lines. 10. A spectrometer as defined in claim 6, characterized in that it comprises linear charged-coupled devices as said linear video signal shapers. 11. A spectrometer as defined in claim 6, characterized in that it comprises photodiode matrixes as said linear video signal shapers. 12. A spectrometer as defined in claim 6, characterized in that comprises 2N or 2N+1 linear video signal shapers, where N = 1, 2, 3 etc., whereas one group of N or N+l linear video signal shapers being optically linked, by means of the concave grating, to the first entrance slit, the other group of N other linear video signal shapers - to the second entrance slit, and the both groups of linear video signal shapers being arranged so that the spectrum sections formed on linear video signal shapers from one group are a continuous extension of the spectrum sections to be formed on linear video signal shapers from the other group. 13. A small-size spectrometer comprising an entrance slit, a concave grating, linear video signal shapers, characterized in that it additionally comprises a flat mirror being arranged perpendicular to the plane of the Rowland circle at its center, a second entrance slit being arranged with displacement relative to a first slit in the direction being perpendicular to the plane of the Rowland circle, and an optical unit that divides the radiation flux into two parts to be directed by said unit respectively through the first and second slits toward the flat mirror, whereas one of said linear video signal shapers being optically linked, by means of the flat mirror and concave grating, to the first entrance slit, the other - to the second entrance slit, and the both linear video signal shapers being arranged so that the spectrum sections formed on them are a continuous extension of each other. 14. A small-size spectrometer as defined in claim 13, characterized in that comprises 2N or 2N+1 linear video signal shapers, where N = 1, 2, 3 etc., whereas one group of N or N+l linear video signal shapers being optically linked, by means of the flat mirror and the concave grating, to the first entrance slit, the other group of N other linear video signal shapers - to the second entrance slit, and the both groups of linear video signal shapers being arranged so that the spectrum sections formed on linear video signal shapers from one group are a continuous extension of the spectrum sections to be formed on linear video signal shapers from the other group. 15. A small-size spectrometer as defined in claim 13, characterized in that the flat mirror is arranged to turn about the axis being perpendicular to the plane of the Rowland circle at its center and to be fixed, at least, in two positions on the plane of the Rowland circle.