WO1992005412A1

WO1992005412A1 - Spectrometric construction method of light

Info

Publication number: WO1992005412A1
Application number: PCT/FI1990/000217
Authority: WO
Inventors: Pertti Puumalainen
Original assignee: Oplatek Oy
Priority date: 1990-09-14
Filing date: 1990-09-14
Publication date: 1992-04-02

Abstract

The object for the invention is a spectrometric, itself geometrically calibrating construction method of the light. The spectrometers using known methods are large to their size as well as expansive and they must be calibrated often. The movement required for the measuring of the spectrum in the method in accordance with the invention, with the help of which the intensities of the different wavelengths are measured, is obtained by moving the read head (5) of the diskette (6), which read head reads a certain data from the storage disk for the simultaneous control of the measuring geometry, the measuring is carried on by reading always a new spot on the disk and measuring the intensity, whereby the wished spectrum range is measured spot by spot.

Description

SPECTROMETRIC CONSTRUCTION METHOD OF LIGHT

The object for the invention is a spectrometric , itself geometrically calibrating construction method of light.

The measuring of the spectrum of the light within the sphere of the industry as well as the commerce has continually increased. The biggest reason for that is the increasing automatization, which makes all the measuring methods important and in particular those, in which the result is obtained without touching and without disturbing the process. The analyzing of the light, if it is understood in its widest concept ranging also into the ultraviolet and infrared areas, is usually taking place with spectrometers, in which the light is parallelled and after that dispersed into its different wavelength components with the help of a grating or a prism. In case it is wished to read the intensity values at the wavelength changing from the one edge limit of the spectrum to the other one, some part in the spectrometer, for instance just the prism or the grating is turned and an immov¬ able detecting device is measuring the intensity as a function of the wavelength. As detecting devices often are used semiconductors, the electric current intensity of which is depending on the magnitude of the intensity of the light hitting the surface. The quickest and the most sensitive detecting device in the photometry is the light multiplier tube, as long as it is suitable for the wished wavelength.

The present spectrometers are due just to their precision mechanisms rather large and expensive and they must be frequently calibrated for instance because of the warming-up of the mechanics. Also spectrometers have been developed, in which no mechanic movements whatsoever does exist. This can nowadays be achieved through two types of different means: The spectrum of the grating or the prism is divided directly to the linear camera, from the several hundreds or even thousands of elements of which the intensity of the light examined is read directly as a function of the wavelength. The method is somewhat more expensive compared with the ordinary spectrometer, but often the sensitivity there is not sufficient. The sensitivity can be increased by cooling-off the linear camera element, whereat the price, however, is rising considerably. A sencond method to make the spectrometer without any moving parts is to conduct the polarized light in a certain way through an acousto-optic crystal, by changing the in the crystal oscillating acoustic frequency the wished intensity of the wavelength range can be measured through 'the crystal as a function of the wavelength. In the method as a detecting device a light multiplier tube can be used and its measuring wavelength is easy to control, because the oscillation frequencies can be measured very accurately with cheap components. The disadvantage of this method is its expensive price. Consequently, very often from the point of view of the practical measurings there is no dependable simple way of measuring the spectrum of the light.

The aim of the invention is to bring forth a spectro- metric construction method of the light, by the help of which disadvantages connected with the present methods are removed. In particular the purpose of the invention is to bring forward a method, by means of which the determination of the wavelength favourably and easily electromechanically controlled is achieved during the measuring of the intensity of the spectrum.

The goal of the invention is reached by means of the me-thod, which mainly is characterized by that, what has been presented in the claims. When using the method in accordance with the invention the movement required for the measuring of the spectrum with the help of which the intensities of the different wavelengths are measured, is obtained in -the device by moving the read head of the diskette, which read head reads during the measuring a certain data from the storage disk for the simultaneous control of the measuring geometry, and in such a manner the measuring is carried on by always reading a new spot from the disk and measuring the intensity, whereat the wished spectrum range is measured spot by spot. The method is simple and favourable both to its production and operation costs.

In the following the invention is explained more in detail by referring to the attached drawing, which presents one application of a device, in which the method in accordance with the invention is taken advantage of.

To the device presented in the picture belong the limiters 2, the prism or grating 4, the disk unit

6, the read control unit 7, the read head 5, and the light conductors 8. The function of the spectro- meter in accordance with the picture is the following: the incoming light 1 to be analyzed is cut with the limiters 2, which are narrow slots, to a parallel light 3. The light rays are directed to the prism or the grating 4, which dissolves the light to the plane of the picture into a flabelliform spectrum.

The intensity of the light is measured with the help of the movement of the read head 5 of the disk unit of the computer. Here the reading has been performed with the help of optic fibres 8 in such a way, that the ends of the optic fibres measure the intensity, when the read head 5 is moved along the control unit 7 back and forth and when it is reading the diskette 6. The optic fibres are connected for instance with a sensitive light multiplier tube. The signal of the read head is conducted along the optic fibres from the reading unit away to be analyzed in this light multiplier tube. In a second application on the read head 5 can also be a mirror and the intensity is read from a standard spot outside the disk unit. Also other known solutions can be used. But the principle in all these solutions is the same: the read head is instructed to read some certain data and at the same time the intensity of the light is read. The simultaneous reading of the intensity and the disk can be performed several times after each other very quickly and take the average of the measurings. Here consequently the location of the data of the measuring of a certain wavelength is bound to the determination of the wavelength automatically. The part 4 dividing the light into the spectrum stays immovable on its spot during the measuring.

In accurate measurings the device must be temperature calibrated, whereat the 'temperature of the measuring system is measured and the distortion due to the thermal expansion of the device parts belonging to the method are corrected in accordance with the temperature measur.ed. The temperature measuring and its taking into account does not to a practical degree increase the price of the spectrometer at all, and at the same time it is possible to control the overheating of the device.

The method in accordance with the invention is not limited to the presented favourable applications, but it can vary within the frames of the claims.

Claims

1. A spectrometric , itself geometrically calibrating construction method of light, c h a r a c t e- r i z e d in, that the movement required for the measuring of the spectrum, with the help of which the intensities of the different wavelengths are measured, is obtained by moving the read head (5) of the diskette (6), which read head reads during the measuring a certain data from the storage disk for the simultaneous control of the measuring geometry, the measuring is carried on by reading always a new spot from the disk and measuring the intensity, whereat the wished spectrum range is measured spot by spot.

2. Method in accordance with claim 1, c h a r- a c t e r i z e d in, that the part (4) dividing the light into a spectrum is immobile on its spot and the spectrum of the light is measured with the help of optic fibres placed on an mobile read head (5).

3. A method in accordance with the claim 1 or 2, c h a r a c t e r i z e d in, that the temperature of the measuring method is measuren and the distortion caused by the thermal expansion in the devices belong¬ ing to the method is corrected in accordance with the measured temperature.