JPS62288536A - Spectrophotometor - Google Patents

Abstract

PURPOSE:To increase the quantity of beam and to reduce noise, by making it possible to emit zero-order light from one of two monochromators. CONSTITUTION:The light emitted from a light source 1 passes through a slit 2 to be incident to a first monochromator 101 and is dispersed by a first diffraction lattice 3 to form a spectrum on a slit 4. The monochromatic light issued from the slit 4 enters a second monochrometor 102 to be dispersed by a second diffraction lattice 5 and monochromatic light reduced in stray light is emitted from a slit 6. This monochromatic light is reflected by a mirror 7 to be separated into specimen side luminous flux and reference side luminous flux by a chopper 8 and the specimen side luminous flux reaches a light detector 16 through mirrors 10, 11, 13, 15 while the reference side luminous flux reaches said detector 16 through mirrors 9, 12, 14. By this constitution, both of the measurement of low stray light and measurement at a low noise level can be performed corresponding to a measuring object.

Description

Detailed Description of the Invention 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a double monochrome spectrophotometer, and particularly to a spectrophotometer with low noise.

[Conventional technology]

In a spectrophotometer, white light from a light source is converted into monochromatic light by a spectrometer. This monochromatic light is applied to the sample, and the energy of the transmitted or reflected monochromatic light is measured.

Spectrometers used in spectrophotometers are generally classified into single monochromators and double monochromators. A single monochromator uses one dispersion element to obtain monochromatic light, but since there is only one monochromator, there is a lot of stray light. Stray light is light with a wavelength other than the one you want, so it interferes with measurements. In particular, if there is a lot of stray light, measurement errors will become large when measuring a highly concentrated sample.

On the other hand, a double monochromator has two monochromators arranged in series. By separating the light emitted from the first monochromator once again using the monochromator, it is possible to obtain a spectrometer for low stray light. However, since the double monochromator separates the light twice, the intensity of the light becomes weaker, and the signal after converting the light into an electrical signal contains a lot of noise.

Previously, it was necessary to prepare two spectrophotometers, one with a single monochromator and one with a double monochromator, and use them depending on the sample to be measured.For example, when measuring a low concentration sample, A spectrophotometer with a single monochromator was used to reduce noise, and when measuring a highly concentrated sample, a spectrophotometer with a double monochromator had to be used to reduce the error.

The present invention is a means for enabling one spectrophotometer to be used by switching between a single monochromator and a double monochromator.

[Purpose of the invention]

In general, a monochromator in a spectrophotometer disperses light using a diffraction grating and passes a portion of the dispersed light through a slit to obtain monochromatic light.

In a double monochrome spectrophotometer, these monochromators are arranged in series to reduce stray light.

However, depending on the object to be measured, it may be desirable to give priority to reducing noise rather than reducing stray light.

An object of the present invention is to provide a spectrophotometer that can increase the amount of light and perform measurements with low noise when it is desired to reduce the noise as described above.

[Summary of the invention]

The reason for the increase in noise in a double monochrome spectrophotometer is
This is because arranging monochromators in series as described above reduces the amount of light and generates noise when converting light into electrical signals.

Incidentally, undispersed light is reflected from the diffraction grating as zero-order light. The intensity of this light is stronger than that of dispersed monochromatic light.

The present invention allows this zero-order light to be emitted from one of two monochromators to increase the amount of light and reduce noise.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows an optical system diagram of an embodiment of the present invention.

Light emitted from the light source 1 passes through the slit 2 and enters the first monochromator 101. This light is dispersed by the first diffraction grating 3 and forms a spectrum on the slit 4. The monochromatic light emitted from the slit 4 enters the second monochromator 102, is dispersed by the second diffraction grating 5, and monochromatic light with less stray light comes out from the slit 6. After this monochromatic light is reflected by 1li7, it is separated by a chopper 8 into a sample-side light beam and a contrast-side light beam, and the sample-side light beam is
, the contrast side light beam reaches the photodetector 16 via the mirrors 9, 12, 14.

Here, the first diffraction grating is rotationally driven by a mechanism as shown in FIG. In normal operation, the arm 201 fixed to the rotation axis of the first diffraction grating 3 is in the position shown by the solid line. This arm 201 is pressed against a slider 203 by a spring 202.

The slider 203 is moved by a feed screw 205 rotated by a motor 204 to rotate the first diffraction grating 3 . By the angle of the first diffraction grating 3.

The wavelength of the monochromatic light emitted from the first monochromator changes.

Now, the above is the operation of the double monochrome spectrophotometer, but since the amount of light coming out from the first monochromator is small, there is a lot of noise. Therefore, samples with low transmittance,
When measuring a sample that must be measured with small noise, the first monochromator emits zero-order light that has not been spectrally separated as follows.

Zero-order light is unsplit light that is reflected from the diffraction grating. FIG. 3 shows the relationship between incident light and reflected light on the diffraction grating. The general formula of the diffraction grating is given by the following equation.

mλ=d(sinθ±sinψ) where m: diffraction order ±1. ±2. ±3...λ
: Wavelength d: Grid spacing θ: Incident angle ψ: Output angle As can be seen from this equation, a specific wavelength can be obtained depending on the output angle.

By the way, when the reflection angle ψ is the same as θ, undispersed light is reflected. This light is generally called zero-order light, and its intensity is stronger than that of dispersed light. The example of the present invention utilizes this zero-order light.

An example for emitting zero-order light will be explained with reference to FIG. 2. When emitting zero-order light, the arm 2 is
01 to move it to the stopper 212 and rotate the first diffraction grating 3. The stopper 212 is fixed to a device constituted by the slit 4 so that when the arm 201 hits the stopper 212, the zero-order light is emitted. When zero-order light is emitted from the first monochromator, the amount of light is large, so measurement results with less noise can be obtained.

If the feed screw 205 in FIG. 2 is made longer, the motor can be rotated an extra predetermined number of revolutions to obtain zero-order light.

〔Effect of the invention〕

According to the present invention, it is possible to perform both low stray light measurement and low noise measurement depending on the object to be measured.

[Brief explanation of the drawing]

FIG. 1 is an optical system diagram of an embodiment of the present invention, FIG. 2 is a detailed diagram of a rotation driving section of a first diffraction grating, and FIG. 3 is a diagram showing the relationship between incident light and reflected light. DESCRIPTION OF SYMBOLS 1... Light source, 2... Slit, 3... First diffraction grating, 4... Slit, 5... Second diffraction grating, 6...
・Slit, 7.9, 10, 11, 12, 13, 14.
15...Mirror, 8...Chopper, 16...Detector,
1o1...First monochromator, 102...Second monochromator, 201...Arm, 202...Spring, 203...Slider, 204...Motor, 205
...Feed screw, 211...Electromagnet, 212...Stopper. ,,,□I, -741,1,□: Ichiya 1I2]

Claims (1)

[Claims] 1. A double monochromator that uses a diffraction grating to disperse light and obtains monochromatic light through slits placed on the spectrum created by this dispersed light, and another monochromator arranged in series. A spectrophotometer, characterized in that zero-order light of a diffraction grating is emitted from a slit of a monochromator using the diffraction grating for measurement.