JPH0723856B2 - Two-beam interferometer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a two-beam interferometer used for a Fourier transform infrared spectrophotometer (FTIR) and the like.

(Prior Art) As a two-beam interferometer of a Fourier transform infrared spectrophotometer, a Michelson interferometer composed of two plane mirrors and a beam splitter is used. One of the two plane mirrors is a fixed mirror and the other is a movable mirror, and the movable mirror is continuously slid.

Such a two-beam interferometer is particularly sensitive to changes in environmental temperature and vibrations. Therefore, stabilize the interference condition 1
As one means, a dynamic alignment method using laser light is adopted.

The dynamic alignment method is described in, for example, US Pat. No. 405323.
It is described in Japanese Patent Publication No. 1 and will be outlined with reference to FIG. The light from the laser 100 is converted into a plurality of laser light fluxes by a lens or other optical system 102 and is incident on a plurality of places of a beam splitter 104 to be split.
The lights respectively reflected at are returned to the beam splitter 104 to meet and enter the detector 110. The detector 110 is a detector in which a plurality of photodiodes and a plurality of light receiving elements are arranged. The fixed mirror 108 can be adjusted in the normal direction by electrostrictive elements 112a and 112b. If the phases of the photocurrents from the light receiving elements R, H, and V of the respective values of the detector 110 are different, the electrostrictive elements 112a and 112 are arranged so that the phases become the same.
The voltage applied to b is changed to adjust the normal direction of the fixed mirror 108. However, the dynamic alignment method has a drawback that the apparatus becomes complicated.

As an optical system that is strong against vibration, there is a system that uses a corner cube instead of a mirror. As a two-beam interferometer using a corner cube, there is one in which a corner cube is used as a movable mirror of a Michelson interferometer, and the corner cube is supported by a mechanical bearing and slid in the front-back direction.

As another two-beam interferometer using a corner cube,
There is one in which two corner cubes are attached to a metal support rod so as to face each other in an oblique direction, and the corner cubes are rotated in a reciprocating direction in a plane with the corner cubes facing each other.

Fig. 13 shows an interferometer using two corner cubes. The corner cubes 80 and 82 are arranged diagonally opposite to each other, and a beam splitter 84 and a compensator 86 are arranged in front of them. The beam from the He-Ne laser 88 as the light source is divided into two beams by the beam splitter 84, and the transmitted light and the reflected light from the beam splitter 84 are reflected by the corner cubes 80 and 82, respectively, and are again reflected by the beam splitter 84.
Is incident on the detector 90 and becomes an interference signal, which is received and detected by the detector 90.

There is also an interferometer in which one of the corner cubes 80 and 82 is a moving mirror and the other is a fixed mirror, and the corner cubes 80 and 82 are integrated by a metal supporting rod 81 as shown by a chain line, and the supporting rod 81 is There is also an interferometer that moves in the reciprocating direction as indicated by arrow 83.

The interference signal of the interferometer of Figure 13 is
An interference signal that repeats the same phase every 0.6328 μm is given.
When such an interferometer is used in FTIR, the stabilization of its sliding speed is determined by the fixed phase of the interference signal (for example, only the zero-cross point that changes from negative to positive or the zero-cross point that changes from positive to negative). Each)) is compared with the clock signal corresponding to the reference speed. In addition, a method called quadrature control is also used to detect the position of the moving mirror with a two-beam interferometer. FIG. 16 shows an example thereof. 104 is a beam splitter, 106 is a moving mirror,
Reference numeral 108 denotes a fixed mirror, which includes the beam splitter 104 and the fixed mirror 108.
A λ / 8 plate (λ is a wavelength) 114 is provided between the two, and a polarization beam splitter 116 is provided to separate the interference signal associated by the beam splitter 104 into a P wave and an S wave. Are detected by the detectors 118a and 118b. At this time, if the sliding direction of the movable mirror 106 is away from the beam splitter 104, the phase of the detection signal of the detector 118b leads the phase of the detection signal of the detector 118a by 90 degrees, and conversely the sliding direction of the movable mirror 106. If the moving direction is the direction approaching the beam splitter 104, the phase of the detection signal of the detector 118b is the detector 11b.
90 degrees behind the phase of the detection signal of 8a. As a result, from the phase relationship and the wave number of the detection signals of both detectors 118a and 118b, the moving mirror 1
The position of 06 can be detected.

(Problems to be Solved by the Invention) In an interferometer such as that shown in FIG. 13, when sampling is performed at the zero-cross position of the same phase of the primary interference signal, the interference signal that gives the carrier frequency is low when the sliding speed is low. Since it becomes a frequency signal, the stability is poor.

If sampling is performed at both zero-cross positions that change from positive to negative and twice from negative to positive that occur twice in one cycle of the interference signal, the measurement accuracy in the near-infrared region deteriorates. . The reason for this is due to the interference signal generation process. That is, a method is adopted in which this interference signal is detected by a light receiving element such as a photodiode, then amplified by using an appropriate amplifier circuit, the modulation component is extracted, and the zero-cross position of the modulation signal is used as the sampling point. The interval between both zero-cross positions changes with time due to the bias voltage of the photodiode, the bias point of the modulation component extraction circuit, the bias voltage of the comparator circuit that determines the zero-cross point, and the like. Furthermore, the sampling interval deviates from a certain amount even when the operation of the comparator circuit changes from positive to negative and when the operation changes from negative to positive. For these reasons, the measurement accuracy becomes poor. Especially, the influence becomes remarkable in the near infrared region having a wavelength closer to that of the He-Ne laser used for sampling.

An object of the present invention is to provide a two-beam interferometer capable of performing stable sampling even when sliding an FTIR or the like at a low speed.

Another object of the present invention is to provide a two-beam interferometer capable of stably performing measurement in the near infrared region and not causing oversampling in the measurement in the mid infrared region.

It is another object of the present invention to provide a two-beam interferometer capable of performing quadrature control capable of detecting the absolute position of a corner cube.

Another object of the present invention is to provide a two-beam interferometer that is provided with two corner cubes, facilitates assembly and adjustment, and is stable against disturbances such as temperature changes and vibrations. Is.

(Means for Solving the Problem) According to the present invention, a plane mirror in which one or two plane mirrors of two corner cubes each including three plane mirrors are present in a common plane and are not in the common plane The two corner cubes are integrally configured so as to correspond to each other between the two corner cubes, and a part of the incident light is reflected in front of the common 1 or 2 plane mirror and guided to one of the corner cubes. A beam splitter positioned to transmit the remaining light and guide it to the other corner cube and to interfere with the reflected light from both corner cubes is provided, and the distance between at least one of the two corner cubes and the beam splitter is The interferometer that can be changed and the primary interference light emitted from this interferometer are placed on the optical path. A plane mirror returning to the interferometer is provided, and the two-light interference light emitted from the interferometer is used as a distance measurement signal.

In order to be able to extract not only the two-light interference light but also the primary interference light, a half mirror should be placed instead of the above-mentioned plane mirror, and the primary interference light should be extracted from the transmitted light from the half mirror. Good.

In order to realize the quadrature control function, a 1/8 wavelength plate is placed on the optical path from the beam splitter to one of the corner cubes, and the primary interference light or the secondary interference light emitted from the interferometer is placed. A polarization beam splitter may be arranged on the exit optical path of the above, and the P wave and the S wave split by this polarization beam splitter may be used as the distance measurement signals.

The interferometer using the two corner cubes may be a Michelson interferometer that supports the corner cube on the moving mirror side with mechanical bearings to slide.
Attach the two corner cubes to the metal support bar and
It is also possible to rotate two corner cubes in a reciprocating direction in a plane in a state where they are diagonally opposed to each other.
In order to facilitate the assembly and adjustment and to make the interferometer stable against disturbances such as temperature changes and vibrations, two corner cubes should be integrally configured so that one or two mirror surfaces become a common plane. Good.

(Operation) When the primary interference light emitted from the interferometer is reflected by the plane mirror and returned to the interferometer again, the secondary interference light is obtained. With the secondary interference light, a signal having a frequency twice that of the primary interference light can be obtained, and stable sampling can be performed even when the interferometer slides at a low speed.

If a half mirror is arranged instead of the plane mirror that returns the primary interference light to the interferometer, the reflected light from the half mirror becomes the secondary interference light, while the light transmitted through the half mirror is received as the primary interference light.

If a 1/8 wavelength plate is placed on the optical path between one of the corner cubes and the beam splitter, interference light split into P and S waves will be obtained by the polarization beam splitter placed in the optical path of the secondary interference light. Therefore, by using these two interference signals, it is possible to create a signal having a frequency twice that of one interference signal. Also, from the phase relationship of the P wave and the S wave and the wave number, the corner is controlled by the quadrature control technique. The absolute position of the cube can be detected.

(Embodiment) FIG. 1 shows a first embodiment.

Reference numerals 4 and 8 respectively denote two corner cubes that are diagonally opposed to each other, and are integrally configured with one mirror surface 6 in common to form a double corner cube 2. A beam splitter 26 and a compensator 28 are provided in front of the corner cubes 4 and 8, and two corner cubes 2 are provided.
Is rotated in the reciprocating direction by a connecting rod 16 on the back side of the common mirror surface 6. This interferometer will be specifically described later with reference to FIGS. 5 to 8.

A He-Ne laser 60 is used as a light source, and a laser beam 62 is incident on the interferometer. A plane mirror 66 is arranged on the optical path of the primary interference light emitted from this interferometer. The interference light reflected by the plane mirror 66 enters the interferometer again,
The secondary interference light is emitted from the interferometer.

Between one corner cube, for example, the corner cube 4 and the beam splitter 26, the laser beams are directed in opposite directions to each other.
The 1/8 wave plate 64 is arranged at a position where the wave passes once.

On the optical path of the secondary interference light emitted from the interferometer, a polarization beam splitter 68 is arranged in front of the light receiver, and the interference light separated into the P wave and the S wave by the polarization beam splitter 68 is independently detected. Therefore, PIN photodiodes 70 and 72 are arranged as detectors.

In the embodiment shown in FIG. 1, the detectors 70 and 72 obtain the A'phase and B'phase interference signals shown in FIG. 2, respectively. These interference signals are two types of secondary interference signals whose phases differ from each other by approximately 90 degrees. When each of the secondary interference signals is used as the velocity-stabilized carrier, it is possible to obtain twice the frequency of the primary interference signal by itself.

Further, it is also possible to implement quadrature control capable of recognizing the current sliding position from two interference signals of A'phase and B'phase.

In the embodiment of FIG. 1, if only the secondary interference signal is used without separating into P wave and S wave, the 1/8 wave plate 64 and the deflecting beam splitter 68 are omitted and one detector is used. Then, the secondary interference light may be received.

FIG. 3 shows the second embodiment.

Compared to Fig. 1, a plane mirror that returns the primary interference light to the interferometer
A half mirror 74 is arranged in place of 66. In order to receive the primary interference light transmitted through the half mirror 74, a PIN photodiode 76 is arranged as a detector on the optical path of the transmitted light.

According to the embodiment of FIG. 3, as shown in FIG. 4, the secondary interference light is split into the P wave and the S wave by the polarization beam splitter 68, and the detectors 70 and 72 respectively detect the A ′ phase and the B wave. The primary interference light detected as the'phase and passing through the half mirror 74 is detected by the detector.
At 76, it is detected as phase C. The A'-phase and B'-phase interference signals are interference signals each having an optical path difference of 0.3164 μm, and are suitable for near-infrared region measurement with a measurement wave number of 15802 to ⁰ cm ^-1.
The phase interference signal has an optical path difference of 0.6328 μm and a measured wave number of 7901
The spectrum of ~ ⁰ cm ^-1 can be recovered, and this C
The phase interference signal is convenient for measurement in the mid-infrared region of wave numbers of 4000 to 400 cm ^-1 .

If you want to measure the mid-infrared region with the secondary interference signal, for example, use the A'phase only as a trigger signal to activate the A / D converter at each instant when it changes from negative to positive. Sampling theorem is 1580
Since the spectrum of 2 to ⁰ cm ^-1 is restored, both the memory capacity and the calculation time become uneconomical. Therefore, if the zero-cross position of the A'phase signal is taken in once every two times as a trigger signal, the spectrum of 7901 to 0 cm ^-1 can be recovered, which is convenient, but the secondary interference signals are adjacent to each other. Which of the same phase points is adopted is arbitrarily changed for each series of measurements. That is, the quantized and stored infrared interferogram may change from one measurement to another. This gives the result that the Gram-Schmidt calculation, which directly displays the infrared chromatographic signal from the time change of the interferogram when combining the chromatographic equipment and FTIR, such as GC / FTIR or GPC / FTIR, cannot be performed accurately. .

According to the embodiment shown in FIG. 3, when the C-phase detection signal which is the primary interference signal is used and the A / D converter is started at the zero-cross point of the same phase indicated by the arrow in FIG. 4, the Gram-Schmidt calculation is performed. Can be performed accurately.

As a preferred example of an interferometer provided with two corner cubes, one configured such that one mirror surface is a common plane is shown in FIGS. 5 to 8. 5 is a perspective view showing the interferometer, FIG. 6 is a plan view of a partial cross section showing the mirror portion of the interferometer together with a driving mechanism, FIG. 7 is a left side view of FIG. 6, and FIG. It is a front view of FIG.

This two-beam interferometer is an interferometer using a double corner cube 2 unlike a normal Michelson interferometer.

The double-corner cube 2 is assembled by five cutting plane mirrors for convenience. The plane mirrors 4a, 4b, 6 constitute one corner cube 4, and the plane mirrors 8a, 8b, 6 constitute the other corner cube 8. The plane mirror 6 is common to both corner cubes 4 and 8.

In the corner cubes 4 and 8, the adjacent surfaces form a right angle, and the deviation of the assembly accuracy from the right angle is within about 2 to 5 seconds (angle). Processing with such high precision is easy with the current technology.

A ridge 10 formed by the two mirror surfaces 4a and 4b of one corner cube 4 and a ridge 12 formed by the two mirror surfaces 8a and 8b of the other corner cube 8 are parallel to each other. A connecting rod 16 is screwed to the back surface side of the common mirror surface 6 of the two corner cubes 4 and 8 in the plane 14 including. The connecting rod 16 has a flat surface 14 including two ridges 10 and 12.
The bearing 18 is embedded so that it can rotate in one direction (horizontal direction in this example), and the two corner cubes 4 and 8 rotate freely while keeping the plane 14 in one direction. be able to.

A movable part 20 of the linear motor is screwed to the end of the connecting rod 16, and a coil 22 is wound around the movable part 20. The movable part 20 is combined with the stator 24 of the linear motor, and by passing an electric current through the coil 22, the stator
A reciprocating motion is carried out in a limited range by the Lorentz force generated between the connecting rod 16 and 24, and the reciprocating motion causes the connecting rod 16 to make a reciprocating motion as indicated by an arrow in FIG. .

As shown in FIG. 5, a beam splitter 26 and a compensator 28 are installed near the center front of the two-corner cubes 4 and 8 to configure an interferometer. A part of the incident light ray 30 is reflected by the beam splitter 26, reflected by one corner cube, and is incident on the beam splitter 26 again. A ray 34 of the incident ray 30 that has passed through the beam splitter 26 is reflected by the other corner cube 8 and is incident on the beam splitter 26 again. Both corner cubes 4,
The reflected light from 8 becomes the interference light 36 at the beam splitter 26.

As an example of a preferable interferometer having two corner cubes, an example in which two mirror surfaces are integrally configured so as to be a common plane is shown in FIGS. 9 to 12. 9 is a plan view showing the interferometer, FIG. 10 is a plan view showing a mirror portion of the interferometer, FIG. 11 is a front view of the mirror portion, and FIG.
The drawing is a left side view of FIG.

Reference numeral 42 is a double-corner cube, which is assembled by four cutting plane mirrors for convenience. One corner cube 44 is configured by the plane mirrors 45, 46, 47, and the plane mirrors 46, 47,
The other corner cube 49 is constituted by 48.
The plane mirrors 46 and 47 are common to both corner cubes 44 and 49 and are orthogonal to each other. Both plane mirrors 45 and 48 are orthogonal to both common plane mirrors 46 and 47. 2 in the vertical symmetry plane 54 including the ridge 50 formed by the two common plane mirrors 46, 47.
A connecting rod 56 is attached to the back side of the two plane mirrors 46 and 47. A rotating bearing 58 is embedded in the connecting rod 6 so that the connecting rod 5 can rotate while keeping the symmetry plane 54 in one direction (horizontal direction in this example). , 49 can rotate freely while keeping the plane 54 in one direction.

At the other end of the connecting rod 56, the same rotary drive mechanism as shown in FIGS. 6 and 7 is provided.

The 9th corner is located near the center of the two-corner cubes 44,49.
As shown in the figure, a beam splitter 26 and a compensator 28 are installed to configure an interferometer.

The operation of the interferometer in the embodiment of FIG. 9 is the same as that of the interferometer of FIG.

In the interferometer of FIG. 5, two corner cubes 4 and 8 are constructed by assembling five cutting plane mirrors, and in the interferometer of FIG. 9, two corner cubes 44 and 49 are four cutting machining. Although the flat mirror is assembled and configured, it is also possible to cut out one base material to manufacture an integrated double corner cube.

These interferometers are also installed so that the plane containing the opposite edges of the two corner cubes or the plane of symmetry containing the edges of the two common mirror surfaces is horizontal, but these planes are always kept horizontal. It is not necessary and may be any direction such as a vertical direction.

Further, the connecting rod 16 or 56 is a flat surface 14 including the opposite edges 10 and 12.
A connecting rod, which is provided inside or in a plane 54 including the ridge 50.
16 may be provided in a plane parallel to the plane 14 or 54.

(Effect of the invention) In the present invention, since the primary interference light emitted from the interferometer is reflected by the plane mirror or the half mirror and returned to the interferometer again,
Secondary interference light is obtained. For the secondary interference light, two of the primary interference light
Since a signal with double the frequency can be obtained, a stable sliding speed can be achieved even when the interferometer slides at a low speed, accurate sampling can be performed, and an accurate near-infrared spectrum can be obtained. Can be recovered.

If a half mirror is placed instead of the plane mirror that returns the primary interference light to the interferometer, the transmitted light from the half mirror is received as the primary interference light, so the memory capacity of the chromatocoupler for the mid-infrared spectrum Good Gram-Schmidt calculation can be performed without degrading the economic efficiency of calculation time.

If a 1/8 wavelength plate is placed in the optical path between one of the corner cubes and the beam splitter, and a polarization beam splitter is placed in the exit optical path of the primary interference light or the secondary interference light, it will be split into P and S waves. Since it is possible to obtain the generated interference light, it is possible to create a signal having a frequency twice as high as these two interference signals. Further, the quadrature control technique can be obtained from the phase relationship between the P wave and the S wave and the wave number. Can detect the absolute position of the corner cube.

Two corner cubes, one for each mirror or two
Two sets of mirror groups are integrally formed by facing each other in an oblique direction so that two mirror surfaces are common, and reciprocating rotary motion is performed in an open surface including two opposing edges or a plane including two common mirror surfaces. By doing so, only reciprocating rotary motion having one rotation center is performed, and adjustment at the time of assembly is extremely simple and easy, and can be manufactured at low cost. Since the dual corner cube can be made of the same material, it is stable against temperature changes. It is also stable against disturbances such as vibration.

[Brief description of drawings]

FIG. 1 is a plan view showing the first embodiment, FIG. 2 is a waveform diagram showing a detection signal of the same embodiment, FIG. 3 is a plan view showing the second embodiment, and FIG. 4 is the same embodiment. 5 is a waveform diagram showing a detection signal of the interferometer, FIG. 5 is a perspective view showing a preferred specific example of the interferometer, FIG. 6 is a partial cross-sectional plan view showing a mirror portion of the interferometer together with a driving mechanism, and FIG. 6 is a left side view of FIG. 6 and FIG.
The front view of the figure, FIG. 9 is a perspective view showing another preferred embodiment of the interferometer, FIG. 10 is a plan view showing the mirror portion of the interferometer, FIG. 11 is a front view of the mirror portion, and FIG. The drawing is a left side view of FIG. FIG. 13 is a plan view showing a conventional interferometer, and FIG. 14 is a waveform diagram showing a detection signal of the interferometer of FIG. FIG. 15 is a plan view showing an optical system of the dynamic alignment method, and FIG. 16 is a plan view showing an optical system of the quadrature control method. 2,42 …… Double corner cube, 4,8,44,49 …… Corner cube, 4a, 4b, 6,8a, 8b, 45,46,47,48 …… Plane mirrors that make up the corner cube, 10, 12 …… The opposite ridges of two corner cubes, 14 …… The plane containing the two opposite ridges, 16,56 …… Support rods, 18,58 …… Rotary bearings, 20
...... Movable parts of linear motor, 24 ...... Stator of linear motor, 50 ...... Ridge formed by two common mirror surfaces, 54 …… Symmetric surface, 64 …… 1/8 wavelength plate, 66 …… Plane mirror, 68 …… Deflection beam splitter, 70, 72, 76 …… Photo diode, 74 ……
Half mirror.

Claims (4)

[Claims] 1. One or two plane mirrors of two corner cubes each consisting of three plane mirrors are in a common plane, and plane mirrors not in the common plane correspond between both corner cubes. The two corner cubes are integrally formed with each other, and a part of the incident light is reflected in front of the common plane mirror 1 or 2 to be guided to one corner cube and the remaining part of the incident light is transmitted to the other corner cube. An interferometer that is provided with a beam splitter positioned so as to guide light to the corner cubes and interfere with reflected light from both corner cubes, and change the distance between at least one of the two corner cubes and the beam splitter. , A plane mirror that is placed on the optical path of the primary interference light emitted from this interferometer and returns the primary interference light to this interferometer again. Comprising, two-beam interferometer for distance measurement signal two light interference light emitted from the interferometer. 2. One or two plane mirrors of two corner cubes each consisting of three plane mirrors exist in a common plane, and plane mirrors not in the common plane correspond between both corner cubes. The two corner cubes are integrally formed with each other, and a part of the incident light is reflected in front of the common plane mirror 1 or 2 to be guided to one corner cube and the remaining part of the incident light is transmitted to the other corner cube. An interferometer that is provided with a beam splitter positioned so as to guide light to the corner cubes and interfere with reflected light from both corner cubes, and change the distance between at least one of the two corner cubes and the beam splitter. , Is placed on the optical path of the primary interference light emitted from this interferometer, and if a part of the primary interference light is returned to this interferometer again, Moni, and a half mirror that transmits the remainder, the primary interference light transmitted through the half mirror and / or two-beam interferometer for distance measurement signal two light interference light emitted from the interferometer. 3. A 1/8 wavelength plate is arranged on the optical path from the beam splitter to one of the corner cubes in the interferometer, and the primary interference light or the secondary interference light emitted from the interferometer is output on the optical path. The two-beam interferometer according to claim 1 or 2, wherein a polarization beam splitter is disposed, and the P wave and the S wave split by the polarization beam splitter are used as distance measurement signals. 4. The two corner cubes of the interferometer are integrally configured so that one or two mirror surfaces of each of them are common planes, and the two integrated corner cubes are the two corner cubes of the two corner cubes. The two light fluxes according to claim 1, 2 or 3, which are rotationally driven in a reciprocating direction in a state where a plane including opposing edges or a symmetry plane including two shared mirror surfaces is maintained in one direction. Interferometer.