GB2192274A - Optical arrangement for simultaneous spectrometers - Google Patents

Description

1 GB2192274A 1 SPECIFICATION ments are dispensed with, guarantees a high

degree of geometric accuracy of adjustment Optical arrangement for simultaneous spec- and consistency with respect to time. Dis trometers pensing with a reference signal (improved utili 70 sation of measuring time), together with the The invention relates to an optical arrangerelatively low number of reflecting surfaces, ment for simultaneous spectrometers, in which also ensures a favourable signal-to-noise ratio.

radiation emitted by light sources in spectral The disadvantages with respect to a double subranges is split at a first common intersec- beam spectrometer are to be, found in the tion point by optical deflection units, which 75 greater drift and the impossibility of simulta have light-transmitting and reflecting regions, neous measurement of a sample against a ref into a measurement beam and a reference erenoe sample.

beam, recombined at a second common inter- In another technical solution dislosed in USA section point and, separated according to Patent Specification No. 4227079, a spectro wavelengths, fed to a detector, 80 meter having a reference beam path is de The detectors are line detectors, such as scribed. If required, several samples can be photodiode arrays or CCD lines, which allow measured simultaneously against a reference simultaneous investigations to be carried out sample. This is made possible by a computer throughout the entire spectral range provided. controlled "beam director" with a feedback When compared with. UV/VIS scanning 85 system for optical beam positioning. Such "si spectrometers, the following technical prob- multaneous measurement" of several samples lems are found in sumultaneously operating against a reference sample requires, however, UV/VIS spectrometers based on line detec- a longer measurement period if the signal-to tors: noise ratio is constant, or, if the measurement 1. The individual detector elements are 90 period is constant, the signal- to-noise ratio is smaller than the conventional photomultipliers poorer.

of scanning spectrometers by several orders For the majority of applications, in which of magnitude, and this has two consequences. only one sample is measured against a refer Firstly, the system components of a simulta- ence sample, this technical solution represents neous spectrometer must guarantee a high de- 95 an expensive and, moreover, slow arrange gree of geometric accuracy of adjustment and ment.

consistency with respect to time. Secondly, As far as lamps are concerned, the problem the geometric light guide value of the simulta- of combining the UV and VIS subregions is neous spectrometers, which is approximately solved in that VIS radiation from a halogen one order of magnitude smaller, means an in- 100 lamp is radiated into a deuterium lamp from crease in expenditure in order to achieve a one side, so that the radiation portions of good signal-to-noise ratio. both lamps are radiated beyond the opposite 2. The UV/VIS spectral range represents a side.

conventional application-oriented unit. How- Separation of the spectral subregions on the ever, there are no light sources or gratings 105 grafting or detector side is effected by a spe which possess sufficiently good properties for cial grating and two separate line detectors in the entire spectral range. In scanning spectro- the polychromator, which is disposed beyond meters, the instrumental UV subrange and the the sample. This special grating comprises instrumental VIS subrange are:-used in succes- one partial grating each for the UV and VIS sion. This is not possible in a'simultaneous 110 subranges, which are disposed on the same spectrometer. Thus, the object is to combine grating support, the grating grooves of the the two subranges in front of the sample and two partial gratings being inclined with respect to separate them again beyond the sample, to one another. In this way, two mutually in that is, on the grating or detector side. - clined partial spectrums are formed in the fo3. The third technical problem relates to re- 115 cal plane of the polychromator and arrive at ducing stray light or suppressing radiation of a the detectors.

higher order. In scanning spectrometers, this It is disadvantageous that, using this grating, object can be satisfactorily achieved by the only half the aperture.and half the light guide use of stray light and order filters which are value can be used for each spectral subrange.

placed in the beam path in succession in the 120 Manufacturing a special grating requires special individual spectral subranges. This solution technology and hence also the associated ex cannot be used in simultaneous spectromet- penditure.

ers. The problem is particularly relevant when It is the-object of the present invention to UV and VIS radiation arrives simultaneously in reduce expenditure on simultaneous measure a common polychromator. 125 ments in the entire UV/VIS range in the - Some of the known technical solutions opknown technical solutions, to ensure a high erate according to the single-beam principle. light guide value and to improve stray light The more compact optical-geometrical con- conditions.

struction of the single-beam spectrometer, to- In accordance with the present invention, gether with the fact that movable reflector eletwo light sources, each emitting radiation in a 2 GB2192274A 2 respective spectral subrange, are each associ- radiation and there are favourable prerequisites ated with a respective polychromator, the light with regard to stray light.

sources and polychromators being disposed Thus, by use of the present invention, in an symmetrically with respect to the straight line arrangement for simultaneous measurement in connecting the intersection points, the light- 70 the UV/VIS range working on the double reflecting regions of the deflection units being beam principle, and given functional separation bilaterally reflecting regions, and the deflection of the spectral subranges and alternating use units functioning in phase synchronism with of the light sources, it is possible to allow the respect to one another. radiant power of each light source throughout Advantageously, in order to reduce the influ- 75 the entire measurement period and the avail- ence of the thickness of the deflection ele- able aperture for both subranges to become ments, one reflection position of one deflec- effective, and to prevent superimposition of tion unit is always associated with a transmis- UV spectrums of a higher order with VIS sion position of the other deflection unit (both spectrums.

deflection units operate at a phase shift of 80 The invention is described further herein 1800 with respect to one another). If the after, by way of example only, with reference thickness influences are negligible, that is, if to the accompanying schematic drawings, in the entrance slits of the polychromators are which:

fully illuminated despite error in alignment of Figure 1 shows the guidance of a beam in the beam, it is also possible for the deflection 85 an apparatus according to the present inven units to operate in such a way that the reflec- tion; tion position or transmission positions are asFigure 2 illustrates the use of rotating reflec sociated with one another (the two deflection tors as deflection units; and units operate without phase shift in parallel Figure 3 illustrates the use of pivotal reflec with one another). 90 tors as deflection units.

Advantageously, the optical deflection units In the optical arrangement shown in Fig. 1, are rotating sector reflectors or pivotal reflec- which comprises a lamp section 1, a sample tors, whose phase synchronism is effected by section 2 and a polychromator section 3, a means of stepping drives. UV and a VIS light source 6, 7 and elliptic The line detectors, which serve as detec- 95 imaging reflectors 8, 9 are disposed symmetritors, are connected in series so that all the cally with respect to the straight line G con following electrical equipment (control circuit, necting the intersection points 4, 5. The UV amplifier, A-D converter) is only required once. light source 6 is a deuterium lamp, and the - The solution according to the invention VIS light source 7 is a halogen lamp.

combines two partial Spectrometers into one 100 Elliptic imaging reflectors 10, 11 and poly spectrometer for the entire spectral range by chromators 12, 13, which comprise entrance keeping an optical-geometrical: symmetry and slits 14, 15, imaging gratings 16, 17 and line using common functional elements, the func- detectors 18, 19, are also provided symmetri tional separation of the UWand VIS spectral cally with respect to the straight line G. The ranges iri the device being ensured. 105 gratings 16, 17 have been optimised for the The disadvantages which result from a con- relevant spectral subrange (UV or VIS).

sistent instrumental separation of the two A measurement beam path 20 and a refer spectral ranges (such as a large expenditure ence beam path 21 run through the sample on apparatus, two separate measuring posi- section 2.

tions for the sample, etc) are obviated by the 110 Deflection units 22, 23 are disposed in the proposed solution. intersection points 4, 5 and are in the form of As a result of the bilateral and phase-syn- rotating or pivotal reflectors (Fig. 2 and Fig. 3) chronous anti-parallel or parallel operation of and are driven in phase synchronism by the deflection units, the radiation issuing from means of stepping motors 24, 25. The deflec the light sources is interlaced and guided alter- 115 tion units 22, 23 have bilaterally reflecting re nately through the measurement sample and gions 26 and light-transmitting regions 27, reference sample onto the polychromator as- and operate in an anti- parallel manner, that is, sociated with the light source, which polychro- when the deflection unit 22 is in the reflection mator comprises an entrance slit, imaging position, the other deflection unit 23 is in the grating and -line detector. In the UV partial 120 transmission position.

spectrometer, the radiation arrives at the poly- The light sources 6, 7 are imaged in a ratio chromator by way of the measurement beam of 1: 1 onto the entrance slits 14, 15 of the path at thd same time as it does in the VIS polychromators 12, 13. Intermediate images, partial spectrometer by way of the reference that is locations of the narrowest bundle con beam path and vice: versa. 125 striction, occur at the two intersection points - The use of two polychromates for the two 4, 5 and in the two beam paths 20, 21. The UV and VIS partial regions ensures utilisation samples are disposed at the locations of nar of the whole aperture for each of the poly- rowest bundle constriction in the beam paths, chromators. The UV spectrums of higher or- 20, 21 (not shown).

der cannot reach the line detector for the VIS 130 The alternating of the deflection units 22, 3 GB2192274A 3 23, which are provided in the intersection with a transmission position of the other points 4, 5, between the reflection and deflection unit.

transmission positions causes an interlacing of 3. An optical arrangement as claimed in the portions of radiation emitted by the light claim 1, wherein, given negligible effects of sources 6, 7. When the deflection unit 22 is 70 the thickness of the deflection units, each in the reflection position, both the UV and VIS reflection position and transmission position of radiation is reflected. The UV radiation enters one deflection unit is associated with a reflec the measurement beam path 20 and the VIS tion position and a transmission position of radiation enters the reference beam path 21. the other deflection unit.

The UV radiation then reaches the polychro- 75 4. An optical arrangement as claimed in mator 12, which has been optimised therefor, claim 2 or 3, wherein the optical deflection and the VIS radiation reaches the optimised units, are rotating sector reflectors or pivotal polychromator 13 by way of the associated reflectors, whose phase synchronism is ef transmission position of the other deflection fected by means of stepping drives.

element 23. 80 5. An optical arrangement for simultaneous If the deflection units 22, 23 are associated spectrometers, substantially as hereinbefore with one another in reverse, that is, if the described, with reference to and as illustrated deflection unit 22 is in the transmission posi- in the accompanying drawings.

tion and the deflection unit 23 in the reflection Printed for Her Majesty's Stationery Office position, the UV radiation passes through the by Burgess & Son (Abingdon) Ltd, Dd 8991685, 1988.

reference beam path 21 and the VIS radiation Published at The Patent Office, 25 Southampton Buildings, passes through the measurement beam path London, WC2A 1 AY, from which copies may be obtained.

22 before both types of radiation arrive in the associated optimised polychromators 12, 13.

The beam path can be optically modulated either by a separate interrupter or by an interrupter which is combined with the optical deflection units 22, 23.

The line detectors 18, 19 are advantage- ously connected in series electrically (not shown), so that all the following electrical equipment is only required once.

It is also possible to allow the deflection units 22, 23 to function in parallel, that is, that both are in the reflection position or in the transmission position. This requires the deflection elements 22, 23 to have a sufficiently small thickness so that, despite an error in beam alignment, complete illumination of the entrance slits 14, 15 is ensured.

Claims (2)

1. CLAIMS 7

   V 1. An optical arrangement for simultaneous spectrometers, in which radiation emitted by - light -sources in spectral subranges is split at a first common intersection point by optical deflection units, which have light-emitting and reflecting regions, into a measurement beam and a reference beam, recombined at a sec- ond common intersection point and, separated according to wavelengths fed to a detector, and wherein two said ligt sources, each emitting radiation in a respective spectral subrange, are each associated' with a respective polychromator, the light sources and polychromators are'disposed symmetrically with respect to the straight line connecting the intersection points, the light-reflecfing regions of the deflection unit are in the form of bilaterally reflecting regions, and the deflection units function in phase synchronism with respect to one another.
2. 2. I'An: optical arrangement as claimed in claim 1, wherein the reflection position of one of the deflection units is always associated