DD259038A1 - MEASURING DEVICE FOR DETERMINING THE SPECTRAL DISTRIBUTION OF ELECTROMAGNETIC RADIATION - Google Patents

Abstract

The invention relates to a measuring device for determining the spectral distribution of electromagnetic radiation and is applicable in spectrometry, analytical chemistry and cosmos research. According to the invention, the absorption of electromagnetic radiation in a gas or a liquid having known absorption properties is utilized. The measuring device consists of a cuvette which allows different absorption length settings and / or different pressure settings for the contained gas or liquid and an integral photoelectric radiation detector with any but known quantum efficiency located immediately behind the cuvette.

Description

Field of application of the invention

The invention relates to a measuring device for determining the spectral distribution of electromagnetic radiation.

The device according to the invention can be used in spectrometry, analytical chemistry and cosmos research.

Characteristic of the known state of the art

In the known measuring devices for determining the spectral distribution of electromagnetic radiation, either prisms, diffraction gratings or filters with wavelength-dependent transmission are used as dispersing elements, or the Fourier spectrometer principle is used. ¹

In order to guarantee a specific spectral resolving power, the spectrometers equipped with said dispersing agents must achieve a defined linear dispersion and thus have certain, relatively large minimum dimensions.

To solve many routine spectrometric tasks in the industry, the known spectrometer are difficult to transport because of their large dimensions and masses and thus only partially operatively applicable.

Due to the use of optical and mechanical precision parts, in particular the Fourier spectrometer, the economic outlay in the production of known spectrometers is very high.

DD-WP 136075 proposes an optical spectrometer whose mass and dimensions are substantially reduced compared to conventional devices. The spectrometer has an optical filter with location-dependent spectral characteristic in the beam path in front of a self-scanning receiver matrix.

Each element of the receiver matrix is provided with an optical filter of the desired wavelength and spectral width, so that only radiation of the selected spectral element reaches this element. The production and positioning of very small pixel size optical filters is associated with major technological problems.

The optically reduced image of a large optical filter with a variable spectral characteristic proposed in said DD-WP 136075 does not lead to success either.

To achieve a significant effect, the object size (filter) of the imaging optics must be chosen comparatively large, which contradicts the task of creating a spectrometer arrangement with significantly reduced dimensions contradicts.

Laid-open specification DE 2546253 describes a spectrometer which has a plurality of photosensitive receivers. At least some of the receivers should have different spectral sensitivities. The different spectral sensitivities are realized either as a receiver property or as a combination filter plus receiver.

The receivers can be calibrated by monochromatic radiation of different wavelengths with known radiation fluxes, ie the sensitivities S _k (Aj) of the k individual receivers can be determined at different wavelengths, thus defining a sensitivity matrix.

If a radiation receiver arrangement whose sensitivity matrix has been determined in the prescribed manner is irradiated with radiation of unknown spectral distribution, then under certain conditions the signals emitted by the receivers can be converted into the actually present spectral values of the unknown radiation by means of the sensitivity matrix.

The spectrometer proposed in the published patent application DE 2546253 has a number of disadvantages. The sensitivity matrix of the receiver system must have a defined structure of the matrix elements, if a defined spectral resolution of the spectrometer is to be achieved, this requirement can be met only with great technical effort by optical filters and their exact positioning in front of the individual receivers.

A disadvantage of the proposed solution also that for calibration and recalibration a very powerful monochromator must be available, and that the image receiver characteristics of the receiver systems are completely lost.

James, I.F., Sternberg, R.S. "The design of optical spectrometers", Chapman and Hall Ltd, London 1969.

Object of the invention

The aim of the invention is to allow measurements of the spectral distribution of electromagnetic radiation in a much wider range of applications than before and to achieve a cost-effective production of the spectrometric measuring device used.

Explanation of the essence of the invention

The invention has for its object to develop a measuring device for reliable and accurate determination of the spectral distribution of electromagnetic radiation, which avoids the disadvantages of the prior art and can be realized with significantly reduced dimensions and lower material requirements and with simple technical effort with consistent performance.

According to the invention, the absorption of electromagnetic radiation in a gas or a liquid with known absorption properties is used to achieve the object.

The measuring device according to the invention consists of a special cuvette and an integral radiation detector.

The cuvette, in which various absorption length settings or different pressure settings for the contained gas or liquid can be realized, is disposed immediately before the integral photoelectric radiation detector having any but known quantum efficiency depending on the wavelength.

During the measuring process, the radiation current to be spectroscopically examined falls on the measuring device and produces at the output of the photoelectric detector a Dßtektor output voltage.

A ₂ U = κ / / τ ^ (λ) Φ ₀ (λ) θχρ [-α _ν σ (λ) π (ρ)]] αλ π)

K Transfer factor of the detector in V / W

λ wavelength nm

X ₁ Wavelength of the short-wave limit of the sensitivity range of the detector X ₂ Wavelength of the long-wave limit of the sensitivity range of the detector η (λ) Quantum efficiency of the detector as a function of the wavelength cpo (X) Unknown radiation flux in front of the measuring cuvette in W / nm as a function of the wavelength σ ( λ) absorption cross section of the gas or the liquid in the cuvette in m ² / molecule

n (p) Molecular density of the gas or liquid in molecules / m ³

(pressure dependent on gas) P Gas pressure in Pa

d _v different absorption lengths in m decomposing the integral (1) into I intervals, results

U = ΚΣ V ₁ ^ ₀₂ exp [-cly ⁰ Z ⁿ (p)] < ² >

For k different cell lengths and n (p) = η = const, it follows from (2)

U _K = ΚΣ ^ ₂ Φ _ΟΪ exp (-d _K & ₂ n) _{3)

or at i different pressure settings for gas filling and d _v = d = const.

^ ₁ ⁷ Iz V ^ex p (-ci ^ ₂ n _f ) (4)

If I = k = i different measurements are carried out, (3) and (4) represent linear systems of equations for the unknown quantities φ _{0> ζ} , which are solvable according to the general solution theory of linear equation systems, if the equations of a system (3) or ( 4) are linearly independent, that is, the coefficient determinants of the systems D Φ. From the matrix theory follows:

1.1

= Α

^r o _r 4

^? 0.2

U.

(5)

A ¹ Inverse of matrix A

In the solution it can be assumed that the quantities K, η _ζ , d *, σ _ζ , and η

or K, η _ζ , σ _ζ , ni and d are known, and the voltages U _k or Ui are determined measured values.

Thus, the determination of the unknown spectrum is possible φ ₀ , ι ··· φ _ο , ΐη / after the inverse of the matrix A has been calculated by known mathematical methods.

The matrices A and A ~ ¹ should be precomputed on a powerful computer. The matrix elements of the inverse matrix A " ¹ then belong to the device-specific data which are available in a spectrometer which operates on the basis of the proposed absorption method.

The inverse matrix A " ¹ can be determined experimentally by means of the radiation of known spectral distribution.

Ausführungsbeispiei

The invention will be explained below with reference to an embodiment of Figure 1 in more detail.

The measuring device consists of a cuvette 1, which allows, for example, five different absorption length settings and is arranged directly in front of an integral radiation detector 2.

The cuvette 1 is filled with N ₂ O 3, which is at normal temperature under normal pressure. The integral detector 2 has a constant quantum efficiency η ₂ ο in the spectral range from 185 nm to 230 nm. B. d. A. = 1. Also the transfer factor of the detector 2Ko.BdA = 1 should be set.

In known manner, the absorption cross sections for N ₂ O are obtained:

o ₂ = 3.7-1 (T ²⁴

a ₃ = 1.0-1 (T ²⁴

O ₄ = 1.7-1CT ²⁵

σ ₅ = 8.0-1 CT ²⁶

m ²

at 190nm at 200nm at 210nm at 220nm

at 225 nm

The gas density under normal conditions is

η = 2.6868-10 ²⁵ ιτΓ ³ .

During the measuring process, the radiation current 4 to be determined spectroscopically falls onto the cuvette 1. The radiation _current 4, which can be decomposed into five radiation flux _values cp _Oi1 ... (P _o , ₅₎ , generates a signal at the output of the photoelectric detector 2 an amplifier 5 is amplified and can be read as a voltage reading on the detector voltage display 6.

With five different cuvette length settings, five different voltage measured values U ₁ ,... U _{5 result} . The unknown five radiation flux values Cp ₀ J ... cp _o , _{s of} the incident radiation 4 should be represented as linear combinations of the five detector output voltage values Ui, ... U ₅ . Since each measured value Ui,... U ₅ results from five radiation flux values, the problem mathematically represents an inversion of a matrix. The original matrix A is as follows:

exp (-cL n exp (-d ₂ n

The first line results for d = ο, the next lines with increasing d or nd. The columns are arranged in such a way that the σ values decrease monotonically from left to right. The following matrix is the theoretically most favorable:

11111 \ 0 1111 »

oo ι ι r j

0 0 0 11-1 0 0 0 0 1

The inverse matrix is:

1 -1 0 0 0 0 1 -1 0 0 0 0 1 -1: 0 0 0 0 1 -1 0 0 0 0 1

For the five absorption cross sections given, the ideal matrix is best approximated by choosing the following five cell length settings:

d-i = om

d ₂ = 0.005 m

d ₃ = 0.02 m

d ₄ = 0.075 m

d ₅ = 0.2m This yields the following matrix A:

0.101898

1,32588 2,1217

0.0001078

-15

10

10 -40

0.608318 0.136937 0.0005780 2.3186.10 " ^£

0.874.293 0.584289 0.133307 0.004637

0.977421 0.912697 0.709946 0.401113

\ 0,989310;

0.957922 0.851115 0.650582

The inverse matrix is:

/ 1,24519

j -0.33998 0.12939 -0.08786 0.05324

-2,40797 3,34180

-1,27484 0,85563

-0.52461

1,60628 -5,07219

4.74363 -3.24395

1.96523

-0.59413 2.89547

-5.99005 9.50832

-5.81961

0.15988 -0.87877

2.59155 -8.84399

6.97133

So, for example:

(Po, ι = 1.24519U ₁ - 2.40797U ₂ + 1.60628 U ₃ - 0.59413U ₄ + 0.15988U ₅

Since the elements of the inverse matrix A " ^{1 are available} as device-specific data, the radiation fluxes to be determined can be determined in a simple manner.

It should be pointed out here that a monotonic increase or monotonic decrease of the values of the σ-values in the spectral region of interest is not necessary, it is sufficient if the σ-values are different.

Expedient in the sense of the embodiment of the inventive idea is the use of a mixture of several known gases or liquids, which is used in the cuvette, since in this case a greater variation margin in the task-oriented, optimal design of the absorption path arises.

The gas or fluid pressure change can be generated by an electronically controlled temperature control, so that a change in the absorption length is eliminated and thus mechanically moving precision parts are not needed.

Claims (1)

Measuring device for determining the spectral distribution of electromagnetic radiation, characterized in that a different absorption length settings and / or different pressure settings for the resulting gas or liquid or gas or liquid mixture, the absorption properties of the medium used are known, realizing cuvette (1) directly is arranged in front of an integral photoelectric radiation detector (2) with any but known quantum efficiency. For this 1 page drawing