JPS63284429A - Spectro-photometer - Google Patents

Abstract

PURPOSE:To accurately measure absolute wavelength by diffracting light for calibration and light to be measured spectrally by the same spectroscope and photodetecting them by respective photodetecting means respectively. CONSTITUTION:The light to be measured and the light from a light source 10 for calibration are incident on the spectroscope (Czerny-Turner diffraction spectroscope) through upper and lower fibers 4 and 6 and reflected by a collimator mirror 2 to become parallel light beams, which are incident on a diffraction grating 1. The diffracted light beams are reflected by a camera mirror 3, converged on a projection slit 8, and incident on photodetecting elements 5 and 7 respectively. Their spectra are compared with each other to perform high- accuracy calibration which is not affected by the play, etc., of a driving system. Further, when a spectrum measurement is taken, the spectrum of the light to be measured and the high-order spectrum are cut off by a degree cut filter and the high-order spectrum of the calibration light can be utilized for wavelength calibration.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spectrophotometer having a wavelength calibration function. More specifically, the objective is to provide a novel spectrophotometric device that can measure absolute wavelengths with extremely high accuracy.

[Prior Art] In an optical wavelength measuring instrument such as an optical spectrum analyzer, a dispersive element such as a diffraction grating is used in the spectroscopic section. The situation will be explained using FIG. 5. The diffraction grating 1 has an angle of incidence α
, between the diffraction angle β (sin α+sin β)=mλ
There is the relationship (1). Here, d is the number of grooves in the diffraction grating, λ is the wavelength of the light incident on the diffraction grating, and m is the order of diffraction and is an arbitrary integer.

A spectroscopic optical system using such a diffraction grating 1 is shown in FIG. The wavelength λ1 incident from the slit 16. The measured light of λ2 becomes parallel light by the collimator mirror 2 and enters the diffraction grating 1. Since the diffraction angle β (see FIG. 5) from the diffraction grating 1 follows equation (1), the diffraction angles β for the lights of wavelengths λ1 and λ2 are different from each other. Diffraction grating 1 is point G. When the light is focused by the camera mirror 3 and detected by the light receiving element 5 such as a foot diode placed after the slit 8, the light to be measured is determined from the relationship between this rotation angle and the detected light intensity. wavelength components can be measured, making photometry possible.

In a spectroscopic optical system that rotates the diffraction grating 1 made of such a dispersive element, when determining the absolute wavelength, a light source whose wavelength components are known in advance, such as the 8th light source, is used before photometry.
The light from the mercury lamp whose spectral distribution is shown in the figure is slit 1.
6, the rotation angle at which the light is detected is memorized, and wavelength calibration is performed by determining the relationship between the rotation angle and the wavelength.Next, the light to be measured is input through the slit 16, and the wavelength calibration is performed. From the relationship between the rotation angle and wavelength obtained, the
Photometry was carried out to determine the absolute wavelength.

The configuration shown in FIG. 7 has a movable mirror 18 inserted between the input slit 16 and the collimator mirror 2.
For example, wavelength calibration is performed by inputting light from a calibration light source 10, which is a mercury lamp, through the input slit 17, and then by removing the movable mirror 18, the light to be measured from the input slit 16 is photometered. Ta.

[Problems to be solved by the invention] For example, because wavelength calibration is performed using a mercury lamp and then photometry is performed, wavelength calibration and photometry cannot be performed at the same time, and due to play in the drive unit that rotates the diffraction grating, etc. There is a problem in that an error occurs in the rotation angle during wavelength calibration and photometry, and this results in an error in photometry of the absolute wavelength.

Furthermore, if there is a large time difference between wavelength calibration and photometry, there is a problem in that an error occurs in the rotation angle due to deterioration of the parts of the rotation drive unit, resulting in an error in photometry of the absolute wavelength.

Roughly speaking, as shown in Fig. 7, even in a spectrometer that has a built-in calibration light source 10 and a mechanism for automatically switching between photometry and wavelength calibration using a movable mirror 18, there may be problems due to play in the drive section of the diffraction grating. The above-mentioned problems that arise are not resolved,
Also, the accuracy of the movable mirror 18, the calibration light source 10. There is a problem in that the adjustment error of the slit 17 results in an error in photometry of the absolute wavelength.

[Means for Solving the Problems] In order to solve these drawbacks, the present invention realizes two optical systems for photometry and wavelength calibration using the same dispersion element, and uses the same dispersion element to separate the light to be measured and the light for calibration. By measuring light simultaneously,
It measures absolute wavelength with high precision.

For this purpose, an optical means is provided that inputs the light to be measured and the light for calibration into the spectrometer in parallel, and receives the output light based on the light to be measured and the output light based on the calibration light from the spectrometer, respectively. A light receiving means was provided.

[Operation] With this configuration, the calibration light and the measurement light are simultaneously separated by the same spectrometer and received by the respective light receiving means simultaneously.

Therefore, the calibration light and the measurement light can be measured simultaneously by rotating the diffraction grating once, and the spectrum data obtained here does not have errors caused by play in the drive system, etc., as in conventional devices. It has now become possible to determine the absolute wavelength with extremely high accuracy without the occurrence of any abnormality. It is also possible to perform only wavelength calibration using light for wavelength calibration, and it can also be used as a conventional spectroscopic optical system with a built-in light source for wavelength calibration.

[Embodiment] The configuration of an embodiment of the present invention is shown in FIG. 1 and will be described below.

Figure 1 shows the present invention applied to a Czerny-Turner type spectroscopic optical system, in which a diffraction grating 1 has grooves in the Z'' axis direction. 4 is a fiber for inputting the light to be measured, and 6 is a wavelength calibration A fiber guides light for use from, for example, a mercury lamp 10, and the light enters the spectroscopic system with a certain spread, forming a line 3.
As shown by 1 to 34, the light passes through the collimator mirror 21 and the diffraction grating 1, is focused on the slit 8 by the camera mirror 3, and is transmitted to the light receiving element 5.
incident on . Each of these lines 31-34 corresponds to the collimator mirror 21 diffraction grating 1. It passes through the optical axis of camera mirror 3. The incident points of the light to be measured and the light for wavelength calibration are shifted only in the Z-axis direction, so above the slit 8, the incident points are shifted in the wavelength scanning direction (Y
The light does not deviate in the Z'-axis direction, but is focused at a point distant in the Z'-axis direction. Therefore, the light to be measured can be measured by the light receiving element 5, and the light for calibration can be measured by the light receiving element 7, separately and simultaneously. In this case, since the relationship between the wavelength of light and the rotation angle of the diffraction grating 1 is common to both the photometric optical system and the wavelength calibration optical system, it is possible to measure the absolute wavelength with high precision.

In the example shown in FIG. 1, the photometric optical system is aligned with the optical axis, but the calibration optical system may be aligned with the optical axis and the photometric optical system is shifted in the Z-axis direction. Even if both optical systems are slightly shifted from the optical axis, the absolute wavelength can be measured with high precision in the same way.

In the system shown in Figure 1, the absolute wavelength was determined from the relationship between the rotation angle of the diffraction grating 1 and the wavelength. It can be similarly applied to a method of determining the absolute wavelength from a relationship (sine bar one method).

In FIG. 1, the light-receiving portion has a simple structure of a slit and a light-receiving element, but a lens or the like may be attached to increase the light collection efficiency.

The present invention can determine the absolute wavelength with high precision based on the same principle even if it is configured with a Littrow type spectroscopic optical system, or by using a Monk-Gilson type, Ebert type, or Saya-Namioka type spectroscopic optical system.

In Figure 2, a gas laser 12 with good wavelength stability is incorporated into a Czerny-Turner type spectroscopic optical system, and a diffraction grating 1 for measuring light 35 shown by a solid line and wavelength calibration light 36 shown by a dashed line. This shows a spectrometer that detects each type of light using an optical system that changes the angle of incidence on the light and shifts it only in the Z-axis direction.

The light to be measured 35 enters through the fiber 4 and enters the light receiving element 5 .

On the other hand, the light 36 of the gas laser 12 for calibration is transmitted through the lens 13.
．． The light becomes parallel light at 14, is diffracted at the diffraction grating 1, is focused onto the slit 8 by the mirror 3, and reaches the light receiving element 7. At this time, the parallel light emitted from the calibration input optical system 15 needs to be shifted by a small angle from the optical axis in the Z-axis direction.
By adjusting this angle, the position of the focal point on the output slit 8 on the Z-axis coordinate can be arbitrarily determined. In the case of Figure 2, unlike the one shown in Figure 1, the relationship between the wavelength and the rotation angle of the diffraction grating 1 in the photometric optical system and the wavelength calibration optical system is not the same, and correction is made between the two optical systems. Requires.

Correction is performed as follows.

・Incidence angles α, α′ and diffraction angles β, β in the two optical systems
The relationship between d (sin
α+sinβ)=mλ (2)d(sin
a' + sin β') = m' λ (3) β - α = 2
K (4) β'-α' = 2
1 (5) α+θ=β'
The relational expression (6) holds true. Here, d is the number of grooves in the diffraction grating, m and m' are the diffraction orders, λ is one of the wavelength components of the measured light, λ0 is the wavelength component of the calibration light source, and 2K and 2L are the respective optical systems. The angle between the incident light on the diffraction grating 1 and the diffracted light is a constant.

Also, θ is λ and λ for both optical systems. This is due to the difference in rotation angle when detected. Substituting equations (4) and (5) into equations (2> and (3)), λ-2dsin (β-K) cos K/m(a) λo=2dsin(β'-L)CO3l-/m' Next, from equations (4) and (6), β'-β=θ-2K
We obtain (9). Here, from equation (8), β
′ and substitute it into equation (9) to obtain β, and then convert that β into (7)
By substituting into the equation, the wavelength component λ of the light to be measured can be obtained.

In addition, if the angles 2K and 2L are selected so that θ=0 at an arbitrary order m' in equation (3), the correction calculation can be simplified. Also in the configuration example shown in FIG. Two optical systems are configured to use one diffraction grating 1,
The absolute wavelength can be determined with higher precision than in the past.

In the configuration shown in FIG. 2, the same effect can be obtained by replacing the gas laser 12 with another stabilized light source.

As another embodiment of the present invention, spectrophotometry determines the absolute wavelength by measuring a mercury lamp with a relatively large number of spectral lines and many points including its high-order diffracted light using a wavelength calibration optical system. Explain the equipment.

A mercury lamp with a spectrum as shown in Figure 8 has a spectrum of about 3
It has spectral lines in a wide range from 00 to 2000 (nm> (3000 to 20000 angstroms),
At 10,000 angstroms or more, the intensity of the spectral lines becomes weaker, and it becomes difficult to accurately measure the absolute wavelength because there is no highly sensitive light-receiving element in relatively long regions on both sides of the 10,000 angstroms. . Therefore, the wavelength calibration optical system is used to calculate the first-order diffracted light, second-order diffracted light (<2) in Fig. 8>, and third-order diffracted light ((3) in Fig. 8) of the spectral line of 5790.65 angstroms or less in Fig. 8. A case will be explained in which the absolute wavelength is determined by measuring. Generally, the m-th order diffracted light of the wavelength λ of the spectral line to be measured is λ/, = m
It is diffracted at the same angle of the diffraction grating 1 as the wavelength λ' that satisfies λ. Therefore, for example, the second-order diffracted light and the third-order diffracted light of 5790.65 angstroms are each 1158 angstroms.
This is equivalent to the existence of first-order diffracted lights of 1.30 angstroms and 17371.95 angstroms.

In this way, when the high-order diffraction light of the calibration mercury spectral line is used in the wavelength calibration optical system, even in the wavelength region of 10,000 angstroms or more, where the mercury spectral line intensity is relatively weak, it is possible to receive light with high sensitivity at 100()O angstroms or less. It is possible to accurately measure absolute wavelength using only the element.

On the other hand, in a photometric optical system that handles the light to be measured, the higher-order diffracted light generated in the light to be measured becomes noise, so the higher-order diffracted light is cut off before the photodetector 5 as shown in Figure 4. A filter 11 inserted behind the slit 8 must be used for the calibration shown in FIG.

Therefore, in the case of FIG. 6 or FIG. 7, where the wavelength calibration light receiving element and the photometry light receiving element are not independent, it is difficult to realize this embodiment.

Using the mercury spectrum in Figure 8 as a reference light source, in the measurement wavelength range of 3,500 to 17,500 angstroms
A case will be described in which the light receiving system shown in FIG. 4 is applied to the configuration shown in the figure.

The main reference spectrum and its second-order and third-order diffracted lights are applied to the calibration optical system, and all of them can be applied as reference wavelengths. In the photometric optical system, a measurement area of the light to be measured (dotted line) is shown, and a corresponding area (solid line) in which higher-order light of the light to be measured needs to be cut by a filter is shown.

FIG. 8 shows the respective cut areas (solid lines) for the three measurement areas.

In the example in which FIG. 4 is applied to FIG. 1, the light to be measured is measured using a light receiving system with a filter separate from the light for wavelength calibration, so many spectral lines including even higher-order diffracted light are detected. This is particularly effective for wavelength calibration using Furthermore, by measuring these spectral lines simultaneously with the light to be measured, the absolute wavelength can be determined with high precision. 1st
Although a mercury lamp is used as a light source for calibration in the configuration example shown in the figure and the combination of FIGS. 1 and 4, other light sources can be used in the same manner.

[Effects of the Invention] As explained above, according to the present invention, the light for wavelength calibration and the light to be measured can be measured at the same time, which eliminates rotational errors and calibration errors in the drive system, which were problems in conventional absolute wavelength determination. Errors caused by temperature differences between measurements are completely eliminated, making it possible to determine absolute wavelengths with higher precision than before. Therefore, the effects of the present invention are extremely large.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing one embodiment of the present invention, Fig. 2 is a block diagram showing another embodiment of the present invention, and Fig. 3 is a diagram showing the relationship between the incident angle and the diffraction angle of the two optical systems. , Fig. 4 is a block diagram of a light receiving system in which a wavelength selection filter is inserted in front of a light receiving element for another embodiment of the present invention, and Fig. 5 is a diagram for explaining the principle of a conventional diffraction grating. Figures 6 and 7 are block diagrams for explaining the conventional determination of absolute wavelength, and Figure 8 shows an example of the spectrum line of a conventional mercury lamp and the selection of filter characteristics shown in Figure 4. FIG. 3 is a spectrum diagram showing the relationship. 1... Diffraction grating 2... Collimator mirror 3.
...Camera mirror 4...Fiber 5...Light receiving element 6...Fiber 7...Light receiving element
8... Output slit 9... Light shielding plate
10... Calibration light source 11... Wavelength selection filter 12... Gas laser 13.14... Lens 1
5... Calibration input optical system 16.17... Input slit 18... Movable mirror 31-34... Line 35.
...Measurement light 36...Light for wavelength calibration.

Claims (4)

[Claims] (1) a first incident optical means for making the light to be measured enter; a spectroscopic means for separating the light to be measured from the first incident optical means into its wavelength components; a first light receiving means for receiving each wavelength component of the light to be measured and converting it into an electrical signal; and a second light receiving means for causing a calibration light source with a known wavelength to enter the spectroscopic means for determining the absolute wavelength. A spectrophotometer comprising: an optical means; and a second light-receiving means for converting each wavelength component of light from the calibration light source separated by the spectroscopic means into an electrical signal. (2) When the first light receiving means spectrally spectrally measures the light to be measured having a wavelength λ, an order cut filter is used to remove λ' where λ' = λ/m in the diffraction order where the integer m is the diffraction order. A spectrophotometric device according to claim 1, which comprises: (3) The spectroscopic means includes a rotatable spectroscopic element for separating light into wavelength components, and the spectral wavelength of the light to be measured and the light from the calibration light source is determined by a rotation angle of the spectroscopic element. The spectrophotometric device according to claim 1, wherein the correspondence relationship is equal. (4) The spectroscopic means includes a rotatable spectroscopic element for separating light into wavelength components, and the spectral wavelength of the light to be measured and the light from the calibration light source is determined for any rotation angle of the spectroscopic element. The spectrophotometric device according to claim 1, wherein the spectrophotometric device has different predetermined correspondence relationships.