JPH1062250A - Fourier transform infrared spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable proper adjustment of a positional relationship of a corner cube and a beam splitter by generating an interferrogram for each value of a control signal to a beam splitter adjusting means to use the control signal value at which a center burst reaches the maximum peak height. SOLUTION: For example, when a controller 22 outputs a control signal to an actuator 34 utilizing a piezo-electric element, a mobile part 35 is displaced according to the signal so that the position and angle of a splitter holder 28 can be controlled freely. In the adjustment of the apparatus, the controller 22 changes a control signal to corner cubes 12 and 13 varying the value of the control signal to a beam splitter 24 by stages to generate an interferrogram at each signal to the actuator 34. A relationship of the control signal with the peak height of the center burst is determined to define the control signal for maximizing the peak height as adjustment value. In a measurement after such an adjustment, the control signal of the controller 22 is always held to the adjustment value, thereby accomplishing a measurement with a beam splitter holder 28 always kept in correct condition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer used for a Fourier transform infrared spectrophotometer.

[0002]

2. Description of the Related Art Fourier transform infrared spectrophotometer (FT-I)
In the interferometer R), the infrared light, which is the measuring light, is split into two by a beam splitter. After traveling along different optical paths, the two infrared lights are combined again on the beam splitter and interfere with each other. The interferometer is provided with a mechanism for changing the positional relationship of the optical elements included therein, and when this mechanism is driven to change the optical path difference between the two infrared lights, the interference light is changed according to the optical path difference. Changes in intensity. By performing a Fourier transform on the interferogram representing the intensity change of the interference light, a power spectrum representing the intensity for each wavelength is obtained.

As a mechanism for changing the positional relationship between the optical elements, for example, a moving mirror arranged on one of the optical paths of the infrared light is driven by a linear motor or the like to change the optical path length of the infrared light. Configurations are generally known. In the interferometer having such a configuration, when driving the movable mirror, it is necessary to maintain the mirror surface of the movable mirror in a constant direction with high accuracy and maintain the parallel relationship between the incident optical path and the reflected optical path. Therefore, if the measurement is performed in an environment in which the FT-IR is subject to vibration, the direction of the mirror surface of the moving mirror changes due to the vibration, and the above-described parallel relationship may be lost, and a correct measurement result may not be obtained. .

On the other hand, interferometers having a configuration in which the optical path difference is changed by another mechanism have been proposed. One of such interferometers is an interferometer using a corner cube. The corner cube has three reflecting surfaces that intersect at right angles to each other. Light incident on the three surfaces is sequentially reflected by the three reflecting surfaces and then emitted in parallel with the incident direction. The parallel relationship between the incident light path and the output light path is maintained even if the corner cube slightly changes. If such a corner cube is used, the above-mentioned parallel relationship is favorably maintained even under vibration.

FIG. 3A is a diagram showing an example of the configuration of a conventional interferometer using a corner cube. In the figure,
On the optical path of the infrared light emitted from the light source 10, a beam splitter 24 including a semi-transparent mirror and the like, and a beam splitter 24
The compensator 26 for correcting a change in the optical path and the optical path difference caused by the above is integrally held and fixed by a beam splitter fixing base 31 at the peripheral portion. Light source 10
Is incident on the compensator 26 and then split by the beam splitter 24 into infrared light L1 and L2. Corner cubes 12 and 13 are disposed on the optical paths of the infrared lights L1 and L2, and are fixed to the arms of the T-shaped member 14 so as to face each other. The T-shaped member 14 rotates around the rotation shaft 16 by operating the voice coil motor 18. When the infrared light from the light source 10 is split into infrared lights L1 and L2 by the beam splitter 24, the infrared light L1 is reflected by the corner cube 12, and then passes through an optical path parallel to the incident optical path again to the beam splitter. Head to 24. Similarly, after the infrared light L2 is reflected by the corner cube 13, the beam splitter 24
Head to. Thus, the two infrared lights L1 and L2 are combined again on the beam splitter 24, and then detected by the detector 20. Here, when the T-shaped member 14 is rotated by the voice coil motor 18, the positions of the corner cubes 12 and 13 with respect to the beam splitter 24 change, so that the optical path difference between the infrared light L1 and the infrared light L2 is reduced. The intensity of the interference light detected by the detector 20 changes accordingly (see FIG. 3B), and an interferogram is obtained.

[0006]

As described above, in the interferometer using the pair of corner cubes and the beam splitter, when the positional relationship between the corner cube and the beam splitter changes due to disturbance such as temperature change, it is detected. Since the interference pattern of the interference light also changes and the output signal of the detector changes accordingly, there is a problem that correct measurement cannot be performed. Particularly in the above example, the beam splitter fixing base 31 is easily affected by the temperature change. The beam splitter fixing base 31 is made of, for example, a metal such as aluminum, but its size and shape slightly change due to temperature change.
However, since the phenomenon of light interference is an extremely delicate phenomenon, even if the position of the beam splitter 24 changes only on the order of several tens of μm due to deformation of the beam splitter fixing base 31, for example, the interference pattern greatly changes, and the measurement result may vary. It has an effect.

The present invention has been made to solve such a problem, and an object of the present invention is to change the positional relationship between a pair of corner cubes and a beam splitter due to disturbance such as temperature change. Another object of the present invention is to provide a Fourier transform infrared spectrophotometer capable of appropriately correcting a change in the positional relationship and performing a correct measurement.

[0008]

SUMMARY OF THE INVENTION The Fourier transform infrared spectrophotometer according to the present invention, which has been made to solve the above problems, comprises: a) a beam splitter for bisecting infrared light; and b) the beam splitter. A pair of opposing corner cubes for reflecting infrared light bisected by the splitter; c) corner cube driving means for changing a position of the corner cube with respect to the beam splitter; A Fourier transform infrared spectrophotometer comprising: a detector that detects interference light generated when external light is recombined and outputs a signal corresponding to the intensity thereof; e) the position of the beam splitter and Beam splitter adjusting means for adjusting the angle; andf) optical system control means for controlling the operations of the corner cube driving means and the beam splitter adjusting means. g) monitoring the output signal from the detector and the control signal output by the optical system control means to the beam splitter adjustment means, analyzing the intensity data of the output signal from the detector by a predetermined method, And a data processing unit for obtaining an adjustment value of a control signal to the beam splitter adjustment unit based on the analysis result.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS At the time of adjusting the apparatus, the optical system control means controls the operations of the corner cube drive means and the beam splitter adjustment means in a predetermined manner by outputting control signals as appropriate. At this time, a control signal output from the optical system control unit to the beam splitter adjustment unit and an output signal output by the detector according to the intensity of the interference light are monitored by the data processing unit. The data processing means analyzes the intensity data of the output signal of the detector by a predetermined method, obtains an adjustment value of the control signal of the beam splitter adjustment means based on the analysis result, and stores the adjustment value. Next, when the spectrum of the sample is actually measured, the data processing means reads the adjustment value and sends it to the optical system control means. Upon receiving this, the optical system control means always maintains the control signal to the beam splitter adjustment means through the measurement at the above-mentioned adjustment value.

The beam splitter adjusting means can be constituted by an actuator comprising a piezo element or the like and a voltage application circuit for applying a voltage to the piezo element. That is, when the optical system control means outputs a control signal to the voltage application circuit, the voltage application circuit applies a voltage to the piezo element according to the value of the control signal, and the shape of the piezo element changes according to the applied voltage. , The position and angle of the beam splitter change in accordance with the shape change. In this way, the position and angle of the beam splitter can be controlled with sufficiently high accuracy.

The method of controlling the operations of the corner cube driving means and the beam splitter adjusting means for adjusting the apparatus is described, for example, by changing the value of a control signal to the beam splitter adjusting means stepwise within a predetermined range. Means that the control signal to the corner cube driving means is changed over a predetermined range at each stage. According to this method, an interferogram can be generated for each value of the control signal to the beam splitter adjusting unit.

Analyzing the intensity data of the output signal of the detector,
As a method of obtaining the adjustment value of the control signal to the beam splitter adjustment unit based on the analysis result, for example, an interferogram is generated for each value of the control signal to the beam splitter adjustment unit, and the control signal value and the There is a method in which a relationship with the peak height of the center burst is obtained, the value of the control signal that maximizes the value of the peak height is checked, and this is used as an adjustment value. Further, the power at a predetermined wavelength of the power spectrum obtained by further Fourier transforming the interferogram may be obtained, and the value of the control signal that maximizes the power may be used as the adjustment value. According to the latter method, the time required for data processing is longer than that of the former method, but adjustment with higher accuracy is possible.

[0013]

According to the present invention, even if the positional relationship between the corner cube and the beam splitter changes due to a disturbance such as a temperature change, the change in the positional relationship can be properly corrected and correct measurement can be performed. Become like Further, in the manufacturing stage of the apparatus, the adjustment work for determining the positional relationship between the corner cube and the beam splitter can be simplified, so that the production efficiency is improved.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an FT-IR according to the present invention will be described with reference to FIG. FIG. 1A shows F of the present embodiment.
FIG. 1 is a plan view showing a configuration of a T-IR interferometer, and FIG.
(B) is a partially cutaway view of the interferometer viewed from the side.

First, in FIGS. 1A and 1B, a light source 10, corner cubes 12 and 13, a T-shaped member 14, a rotating shaft 16, a voice coil motor 18, a detector 20, a beam splitter 24, and a compensator 26
Can be used for the conventional FT-IR shown in FIG. Voice coil motor 18 and detector 2
0 is connected to the control device 22. The periphery of the beam splitter 24 and the compensator 26 is integrally held and fixed by a beam splitter holder 28. The beam splitter holder 28 is disposed in the opening 32 of the beam splitter support 30. On one side surface of the beam splitter support 30, three elastic members 36 made of a leaf spring or the like are provided at three positions on the peripheral edge of the opening 32. On the other side surface, three actuators 34 are provided with the beam splitter support 30 interposed therebetween.
The two elastic members 36 are disposed at positions facing each other. The beam splitter holder 28 is movably supported from both side surfaces within the opening 32 of the beam splitter support base 30 by these three pairs of actuators 34 and elastic members 36.

The operation of the actuator 34 is controlled by the controller 22. That is, when the control device 22 outputs a control signal to each actuator 34, the movable part 35 of each actuator 34 is displaced in accordance with each control signal. Thus, the position and angle of the beam splitter holder 28 (that is, the position and angle of the beam splitter 24) can be freely controlled. Here, the actuator 34 is required to operate with extremely high accuracy. As such an actuator, for example, an actuator using a piezo element can be suitably used.

In the interferometer having the above configuration, control signals output from the control device 22 to the three actuators 34 (for example, voltage values applied to the actuators 34)
, X, Y, and Z, the value of each control signal can take n values. That is, X = Xi (i = 1, 2,..., N) Y = Yj (j = 1, 2,..., N) Z = Zk (k = 1, 2,..., N) Here, n is a positive integer. Under these assumptions,
A procedure for obtaining the adjustment values Xc, Yc and Zc of the control signals X, Y and Z will be described.

The control unit 22 controls each of the control signals X, Y and Z
(Hereinafter referred to as “points (X, Y, Z)”) is stepwise changed by a predetermined method within a range defined by the above equation, and the center at each point (Xi, Yj, Zk) is changed. The burst peak height Hijk is checked as follows. First, the control device 22 compares the value of each control signal with a point (X
i, Yj, Zk) and the beam splitter holder 2
With the position and angle of 8 kept constant, the positions of the corner cubes 12 and 13 are changed within a predetermined range using the voice coil motor 18. When a detection signal of the interference light obtained at this time is input from the detector 20 to the control device 22, the control device 22 converts the intensity of the detection signal into digital data and sequentially stores the digital data in a memory (not shown). When the process of changing the positions of the corner cubes 12 and 13 is completed, the control device 22 reads out the intensity data stored in the memory, forms an interferogram, obtains the peak height Hijk of the center burst, and stores the value in the memory. To be stored. The above processing is performed at each point (Xi,
Yj, Zk), and Hijk corresponding to each point
Is obtained. When a maximum value is specified from the n ³ pieces of Hijk data thus obtained and is set as Hmax, a point corresponding to the Hmax is adjusted to the control signal adjustment value (Xc,
Yc, Zc).

When the sample is measured after the adjustment as described above, the control device 22 always keeps the value of the control signal at the above-mentioned adjustment value (Xc, Yc, Zc) through the measurement. Thus, the measurement is performed in a state where the position and the angle of the beam splitter holder 28 are always kept correctly.

FIG. 2 is a flowchart showing an example of a procedure for obtaining Hmax. First, Hmax = 0, i = 1, j = 1, and k = 1 are set by initialization at the start of adjustment (steps S12 to S16). Then, the control signals (X, Y,
Z) is set to a point (Xi, Yj, Zk) (step S1).
8), and find a corresponding Hijk (step S2)
0). Next, the calculated Hijk is compared with Hmax (step S22). If Hijk is greater than Hmax, Hma
x is updated by Hijk, and i, j, and k at that time are updated.
Are stored as imax, jmax and kmax, respectively (step S24). On the other hand, if Hijk is equal to or smaller than Hmax, Hmax is not updated. The above processing (steps S18 to S24) is repeated while sequentially changing the values of k, j, and i from 1 to n (steps S14 to S36). In step S36, i ≧
When n + 1 is reached, the above-mentioned imax, jmax and kmax are read out and the corresponding points (Ximax, Yjmax, Zkma
x) is stored as an adjustment value (Xc, Yc, Zc) of the control signal (step S38).

In the above embodiment, the control signal is adjusted so that the peak height of the center burst becomes the maximum. Of course, the adjustment is performed by examining the physical quantity other than the peak height of the center burst. It may be performed. For example, when an interferogram corresponding to a point (Xi, Yj, Zk) is obtained, it is sequentially Fourier transformed to calculate a power spectrum, and a predetermined wave number (a point on a relatively short wavelength side is desirable, for example, 3000 cm). ⁻¹ ), and the point (Ximax, Yj) at which the value of Pijk becomes the maximum is obtained in the same procedure as in FIG.
max, Zkmax), the time required for the adjustment becomes longer, but the adjustment can be performed with higher accuracy.

[Brief description of the drawings]

FIG. 1A is a plan view showing the configuration of an FT-IR interferometer according to one embodiment of the present invention, and FIG. 1B is a partially cutaway view of the interferometer viewed from a side.

FIG. 2 is a flowchart illustrating an example of a procedure for obtaining a maximum value of a peak height of a center burst.

3A is a plan view showing a configuration of a conventionally used interferometer, and FIG. 3B is a view showing a state where an optical path difference has changed in the interferometer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Light source 12, 13 ... Corner cube 18 ... Voice coil motor 20 ... Detector 22 ... Control device 24 ... Beam splitter 26 ... Compensator 28 ... Beam splitter holder 30 ... Beam splitter support 32 ... Opening 34 ... Actuator 36 ... Elasticity Element

Claims (1)

[Claims] A) a beam splitter for bisecting infrared light; b) a pair of opposing corner cubes for reflecting infrared light bisected by the beam splitter; A corner cube driving means for changing a position with respect to the beam splitter; d) a detector for detecting interference light generated when the bisected infrared light is recombined and outputting a signal corresponding to the intensity thereof And e) beam splitter adjusting means for adjusting the position and angle of the beam splitter; andf) operation of the corner cube driving means and the beam splitter adjusting means. G) an output signal from the detector, and the optical system control means outputs the signal to the beam splitter adjustment means. Monitoring the control signal, analyzing the intensity data of the output signal from the detector by a predetermined method, based on the analysis result, a data processing means for obtaining an adjustment value of the control signal to the beam splitter adjustment means, A Fourier transform infrared spectrophotometer, comprising: