JPS63212827A - Fourier transform spectrophotometer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a spectrophotometer that measures spectral characteristics by Fourier transformation.

(Prior Art) Spectrophotometers are usually 2fl of dispersion type and Fourier transform type.
The former is a method that irradiates the sample with light emitted from a light source, and the light from the sample is separated using a prism or interference filter to detect the light intensity of each wavelength. The sample is irradiated with light from a Niko East type optical interferometer, and the interferogram is reciprocated by moving the interferometer a back and forth (Fig. 3), which is then Fourier transformed to calculate the light intensity for each wavelength. It is then analyzed by converting it into .

The major feature of this Fourier transform type is that it not only simplifies the optical system by eliminating the need for a spectroscopic optical mechanism, but also improves measurement sensitivity by increasing the number of measurements. It is equipped with

However, if you perform multiple measurements to increase measurement sensitivity, the amount of distortion of the mirrors that make up the three-beam optical interferometer and the brightness characteristics of the light source may change as time passes from the start of the measurement, resulting in changes in the measurement results. There is a problem in that errors occur.

(Purpose) The present invention was made in view of these problems, and its purpose is to provide a new Fourier spectrophotometer that can correct changes over time and perform stable measurements over a long period of time. It is about providing.

(Summary of the Invention) The feature of the present invention is that the light on the optical path from the optical interference means to the sample is detected, converted into a digital signal with a resolution lower than that of the measurement system, and subjected to Fourier transformation. The main feature is that the measurement results are corrected by reliably detecting the tendency of changes over time in the optical interference system.

(Example) The details of the present invention will be described below based on illustrated examples.

FIG. 1 shows an embodiment of the present invention, in which reference numeral 1 denotes a two-beam optical interferometer, which emits a light beam B from a light source 2.
O is split by a beam splitter 1a, one is made incident on a fixed mirror]b, and the other is made incident on a movable mirror 1C that reciprocates in the optical axis direction, and the two light beams BL and B3 reflected from each weight 1b and 1C are It is configured to interfere and emit light.

3 is a first photodetector which collects the light beam B4 from the interferometer 1 using a condensing optical system 4 and receives the light transmitted through the sample S; It receives light from the neon laser 7. A portion of the light beam B3, for example 1
A mesh type mirror 8 that reflects 0% is disposed, and the light from this is configured to be incident on a second photodetector 9 having a low wavelength resolution.

10 is an analog-to-digital conversion circuit that converts the signal from the first photodetector 3 into a digital signal with a high resolution of, for example, 16 hits, and 11 converts the signal from the second photodetector 9 into a digital signal with a low resolution, such as 10 hits. An analog-to-digital conversion circuit for converting into digital signals; 12 is a sampling signal generation circuit for extracting interference fringe signals of laser light; the circuit is configured to convert signals from photodetectors 3 and 9 into digital signals at interference wave number intervals; has been done. 14 is a fast Fourier transform circuit that converts the signal from the analog-digital converter 10.11 input via the changeover switch 13 into a power spectrum. Reference numeral 15 denotes a ratio spectrum calculation circuit that calculates the ratio of power spectra based on the outputs of the first photodetector 3 and the second photodetector 9 output from the fast Fourier transform circuit 14. Reference numeral 16 denotes a division circuit, which is configured to store the reference ratio spectrum and execute division with the ratio spectrum at the time of sample measurement.

Next, the operation of the apparatus configured as described above will be explained.

When the device M is activated without setting a sample, the light source 2
The light beam Bt from the three-beam optical interference 1 receives optical interference and then directly enters the first photodetector 3. At the same time, a portion of the light B3 exiting the optical interferometer 1 is split by a mirror 8 and enters a second photodetector 9.

On the other hand, the laser beam B4 similarly receives optical interference in the interferometer 1 and enters the first photodetector 3. The interference fringe signal based on this laser beam is converted into a sampling signal by the sampling signal extraction circuit 12 and input to the analog-to-digital conversion circuit 10.11, and the wavelength interval of the interference fringe ( 3), the signals from the first and second photodetectors 3.9 are sampled and input to the fast Fourier transform circuit 14. Fast Fourier calculation time lol! J14 executes Fourier transform based on the signals from the first and second photodetectors 3.9 to calculate the power spectra P*, Pz'l of the signals from each detector. These power spectra Pi and P2 are input to the ratio spectrum calculation circuit 15 to calculate the ratio of the two, but at this time, the power spectrum Pr2 is based on a detection signal with low resolution, so the power spectrum Pr2 is light B3
Since only the rough tendency of is shown, this calculation result shows the background ratio spectrum Pr (Fig. 2).

Next, when the sample S is set and the same measurement as described above is performed, the signals from these two photodetectors 3.9 are transformed into power spectra P′ and P2° by the fast Fourier transform circuit 4, respectively. ylt, and then the ratio spectrum Pr' of both is calculated by the ratio spectrum calculation circuit 15 (
Figure 2 ■).

By the way, in this measurement, the light incident on the first photodetector 3 is the one that has passed through the sample S, so this power spectrum p% detects not only the absorption characteristic of the sample S but also the reference ratio spectrum Pr. Although the power spectrum P2' includes a fluctuation component of the optical system of the interferometer 1 caused by the passage of time from the point in time, the power spectrum P2' is equal to the reference ratio spectrum Pr.
Interferometer 1 caused by the passage of time from the time of t detection
Since it reflects only the alignment information of optical system fluctuations and is based on a detection signal with low resolution, the ratio spectrum Pr'', which is the ratio of both,
alignment fluctuations will be canceled out. Therefore, by calculating the ratio between the reference ratio spectrum Pr and the measurement ratio spectrum P'r using the division circuit 16, the true transmittance spectrum of the sample S, in which alignment fluctuations of the interference system 1 have been removed, is obtained. In other words, the absorption characteristics of the sample S can be determined.

In the above embodiment, the light for monitoring changes over time in the optical system is taken from the focusing optical system, but the same can be done if the light on the optical path from the optical interferometer 1 to the sample S is detected. It is clear that this effect is achieved.

In addition, in the above embodiment, the light for monitoring changes over time in the optical system is received by a photodetector with a low wavelength resolution, and analog-to-digital conversion is performed at a low resolution. Alignment spectra can be obtained by simply lowering the value.

Roughly speaking, in the above-mentioned embodiments, the explanation was given by taking an example of measuring an absorption spectrum, but it is clear that the present invention can be similarly applied to measuring a reflection spectrum from a sample.

(Effects) As described above, according to the present invention, the light on the optical path from the optical interference system to the sample is detected, this is Fourier transformed with low resolution, and the measurement result is based on this. By correcting for The combination of sharing the calculation means and the possibility of using low-resolution, inexpensive correction detectors and analog-to-digital converters makes it possible to realize highly accurate inferences at the lowest possible cost. can.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an apparatus showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the operation of the same apparatus, and FIG. 3 is an explanatory diagram showing the principle of a Fourier spectrophotometer. 1...Two-beam optical interferometer 2...Light source 3...
...First photodetector 4...Condensing optical system 6...
... Half mirror 7 ... Laser light source 8 ... Half mirror 9 ... Second photodetector S ... Sample

Claims (1)

[Claims] a first light receiving means that irradiates the sample with light from the light interference means and receives the light; a first digital-to-analog conversion means that converts the signal from the light interference means into a digital signal; a second light receiving means for receiving light on the optical path leading to the second light receiving means; and a second analog-to-digital converting means for converting the signal from the second light receiving means into a digital signal with a resolution lower than that of the first analog-to-digital converting means. , a Fourier transform type spectrophotometer comprising means for Fourier transforming signals from the first and second analog-to-digital converting means to calculate a power spectrum and calculating a ratio of each power spectrum.