JPH01253620A - Double-luminous-flux interferometer - Google Patents

Abstract

PURPOSE:To stabilize the movement of a moving mirror, by adopting a flexure pivot for a sliding support mechanism for moving the moving mirror, and making a current which is obtained by adding an error voltage to a driving voltage flow through the support mechanism. CONSTITUTION:A flexure pivot is adopted for a sliding support mechanism 8 which moves a moving mirror 6 in a double-luminous-flux interferometer. When a current is made to flow through a coil 39, the coil 39 receives Lorentz force by the magnetic fields of a magnet 36 and a pole piece 37. The moving mirror 6 is moved to the right and left through a base 31. A driving voltage is proportional to the displacement of the support mechanism 8 and outputted from driving voltage generating circuits 15, 16, 17 and 18. An error voltage is proportional to the speed difference of the moving mirror 6 and outputted from error-voltage generating circuits 19 and 20. The error voltage is added to the driving voltage. A current corresponding to the added voltage is made to flow through the support mechanism 8 so as to drive the mechanism. As a result, the moving mirror can be remarkably stabilized.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention provides a beam splitter that splits an incident light beam from a laser into two, and a movable mirror and a fixed mirror that return each of the two split beams to the beam splitter. This relates to a beam interferometer.

Such a three-beam interferometer can be used, for example, as a control interferometer for collecting interferogram data in a Fourier transform infrared spectrophotometer.

(Prior Art) As a sliding support mechanism for moving a movable mirror, there are two types: one using an air bearing and the other using a mechanical bearing.

(Problems to be Solved by the Invention) A sliding support mechanism using an air bearing can perform highly accurate control, but it is expensive, requires an intake system, and has the problems of being large.

A sliding support mechanism using mechanical bearings is inexpensive and can be made compact, but it is difficult to maintain the normal direction of the movable mirror while sliding it. Even in the case of the most accurate cross roller bearing, spike-like nonlinearity occurs depending on the surface roughness of the raceway surface.

SUMMARY OF THE INVENTION An object of the present invention is to provide a three-beam interferometer equipped with a sliding support mechanism that can control the movement of a movable mirror with high precision and that can be manufactured inexpensively and compactly. be.

(Means for Solving the Problems) To explain with reference to FIG. 1 showing an embodiment, the three-beam interferometer of the present invention includes a linearly polarized laser 1 and a beam splitter that divides the incident light beam 2 from the laser 1 into two. 5, a movable mirror 6 and a fixed mirror 7 that return each of the split lights to the beam splitter 5, a sliding support mechanism 8 having a flexure pivot that supports and moves the movable mirror 6, and a beam splitter 5 that splits the light into two parts. a phase plate 9 provided on one side of the optical path, a polarizing beam splitter 10 that splits the interference light 4 from the beam splitter 5 into two, and two light receiving detectors 11 that detect the light split into two by the polarizing beam splitter 10. 12 and the interference signal outputs with different phases from the light receiving detectors 11 and 12 are input, and the displacement and moving direction of the sliding support mechanism 8 from its natural position (the position when no driving current is applied) are input. drive voltage generation circuits 15.16 and 17.18 that recognize the displacement and generate a drive voltage proportional to the displacement, and a light receiving detector 11.1.
Error voltage generation circuits 19 and 20 generate an error voltage proportional to the moving speed error of the movable mirror 6 from the frequency of the interference signal output of one of the two interference signals, and add the drive voltage and the error voltage to supply a current to the sliding support mechanism 8. It is equipped with drive circuits 21 and 22 for causing the current to flow.

(Function) Among the reflected light from the movable mirror 6 and the reflected light from the fixed mirror 7,
The polarized light of the reflected light on the optical path where the phase plate 9 is provided becomes circularly polarized light, and the reflected light on the other optical path remains linearly polarized light.

The output waveform from one light receiving detector 11.12 obtained by separating the interference light of those reflected lights by the polarizing beam splitter 10 is the waveform of the output from the phase plate 9.
If this is a 1/8-wave plate, the signals will be 90 degrees out of phase with each other, as shown by A and B in Figure 2. The interference signals A and B become sine waves determined by the wavelength of the laser beam 2 and the moving speed of the movable mirror 6.

Two interference signals A are generated depending on whether the movable mirror 6 moves toward or away from the beam splitter 5.
, B are reversed.

The drive voltage generating circuits 15, 1.6, 17.18 detect the moving direction of the movable mirror 6 from the phase relationship between the two detection signals A and B, and detect the moving direction of the movable mirror 6 from the peak number of either of the detection signals A and B.
detects the amount of displacement and generates a drive voltage proportional to the amount of displacement.

The error voltage generation circuits 19 and 20 receive either of the detection signals A,
When it is detected that the frequency of B deviates from the reference value Vr, an error voltage is generated.

The drive voltage and the error voltage are added by the drive circuits 21 and 22, a current is passed through the voice coil of the sliding support mechanism 8, and a thrust is exerted on the movable mirror 6 by a Lorentz force proportional to the current.

-4 = flexure pivot
It will be explained next that the drive current of the sliding support mechanism 8 with the rotation center (T rotation center) is a current proportional to the displacement X from the natural position.

The support mechanism part of the sliding support mechanism with a flexure pivot can be treated as a copper body, and can be considered as a mass point at the center of gravity. The support mechanism moves like a simple pendulum with its orbital surface constrained.

The Lorentz force applied to move the movable mirror 6 at a constant speed on the X-axis must be a force in the opposite direction equal to the tangential component of gravity, as shown in FIG. Furthermore, since it is a constrained motion, there is no need to consider centripetal force and centrifugal force components.

From this relationship, PcosO=mgsinθ P=mgtanO (1) On the other hand, the relationship between displacement angle 0 and time t is expressed as (3
= c t, so equation (1) can be expressed as P=mgt, a
It can be rewritten as n(at) −・−・−(1′).

Also, as in the later verification, tan(at) = c
Since it may be transformed to t, P = cm g t −““−m−(2). In the end, the thrust P to be applied has a magnitude proportional to the time t, but since there is a constraint that movement is performed at a constant speed, it can be said to have a magnitude proportional to the displacement X. That is, P=c'mgx...
...(2').

Straight line C in Figure 6 is the thrust given by this proportional relationship,
D is the relationship expressed by equation (1').

The fact that θ=ct can be established will be verified using FIGS. 7 and 8.

From FIG. 7, the amount of movement X when tilted by an angle of 0 is x=IlsinO. Since it is necessary to move at a constant speed, d x/
d t == Qcosθ・dθ/dt:C0n5t Therefore, sin 6 = (const/Q)・tθ(t)
= arcsin (ct) Here, since the maximum value fj max of the displacement angle θ is about 14°, it can be set as follows: 0(t)=ct.

The deviation from the calculated value at this time will be discussed with reference to FIG.

θ(t) = arcsin (ct) to t = (
1/c) sj, no.

The slope of θ(t) = arcsin (ct) is θ=
(Omax/t max) The slope of t is equal to: dt/clθ= (1/c) cos O= t m
From ax/θmax, θ2 = arccos(c 0t max/θmax)
(3) Therefore, t 2 : (1/c) sin(arccos(c
0t max/θmax)) Also, θ1=(θ+nax/t+nax)(1/c)
sin(arccos(c ・t max/ Omax
))-(4) The maximum value of uncertainty ΔO is Δ0=02-01 = arccos(c 1t max/θ+nax)-(
θl1laXmax) (1/c) sin (a
rccos (c- is vessel X/θjunX))...(5). Applying the actual values, θmax=arcsin(12mm152mm)=13
．． If 34°=0.2329rad C=1, then the maximum value of uncertainty is 0.01°.

The error at that time is about 0.1%, which is sufficient for practical use.

(Example) FIG. 1 represents one embodiment.

1 is an H e -N e laser that outputs a linearly polarized laser beam, and 2 is an incident light beam from the laser 1 . 5 is a piece splitter that divides the incident light beam into two; 6 is a movable mirror that reflects one of the light beams that has been split into two by the beam splitter 5 and returns it to the beam splitter 5; and 7 is a fixed mirror that returns the other light beam that has been split in half to the beam splitter 5. It is. 8 is a sliding support mechanism that has a flexure pivot and supports and moves the movable mirror 6.

A 1/8 wavelength plate 9 is provided as a phase plate in the optical path between the beam splitter 5 and the fixed mirror 7.

4 is an interference signal of the bidirectionally emitted light beams 3a and 3b. Reference numeral 10 denotes a polarizing beam splitter, which splits the interference light 4 into two light in the vertical axis direction and light in the horizontal axis direction. 11 and 12 are detectors that detect the interference light split into two by the polarization beam splitter 10, and 13 and 14 are amplifiers that amplify the respective signals of the detectors 11 and 12. Let the output signals of amplifiers 13 and 14 be A and B, respectively.

15 is an up/down counter, and amplifiers 13, .
14, the traveling direction of the movable mirror 6 is detected from the phase difference relationship of the surface input signals, and the displacement amount of the movable mirror 6 is detected from the peak number.

The up/down counter 15 is also reset to make the count value O when the sliding support mechanism 8 is in the natural position (the position when Ov is applied to the power amplifier 22, which will be described later). In order to obtain the reset signal, for example, a photocoupler may be provided in the sliding support mechanism 8 to detect the natural position, and the reset signal may be set to reset 1 when the interferometer is started.

16 is a D/A converter with a multiplication function, which multiplies the output signal of the up/down counter 15 corresponding to the amount of displacement of the movable mirror 6 by a coefficient and outputs a driving voltage. The coefficient is C
The signal is output from the PU 1.7 via the D/A converter 18.

Up/down counter 5, D/A converter 16, 18, and CPU 17 constitute a drive voltage generation circuit.

In order to stabilize the sliding movement of the movable mirror 6, a frequency-voltage converter 19 is provided, and the output of one amplifier 13 is inputted thereto. A speed error generating amplifier 20 compares the output voltage of the frequency-voltage converter 19 with a reference voltage Vr and generates a voltage proportional to the error.

The frequency-voltage converter 19 and the speed error generation amplifier 20 constitute an error voltage generation circuit.

A summing amplifier 21 is provided to add the drive voltage output from the D/A converter 6 and the error voltage output from the speed error generation amplifier 20. The power amplifier 22 is used to supply the drive current to the
is provided and amplified to the output necessary for driving.

The sliding support mechanism 8 is specifically shown in FIGS. 3 and 4. FIG. 3 is a longitudinal sectional view, and FIG. 4 is a left side view of FIG. 3.

30 is a body, 31 is a base, and the base 31 is rotatably suspended from the body 30 via plates 32 and 33. Between the body 30 and the plates 1-32, 33, and between the base 31 and the plates 32, 33, there is a film 4.
], , 42 and can rotate freely.

A movable mirror 6 is fixed to the base 31 via a mirror holder 34.

Inside the body 30 are magnets 1-36 and pole piece 3.
7 is fixed to the plays 1 to 35 by bolts 38.

A coil 39 is also connected to the base 3J via a tombstone 40.
is fixed, and the coil 39 is positioned so as to move in the magnetic field formed by the magnet 36 and the pole piece 37.

In this sliding support mechanism 8, when a current is passed through the coil 39,
The coil 39 receives a Lorentz force due to the magnetic field of the magnet 36 and the pole piece 37, and moves the movable mirror 6 in the horizontal direction in the figure via the base 31.

Next, the operation of this embodiment will be explained.

Applying 0 volts to the power amplifier 22, the sliding support mechanism 8
is the natural position and the up/down counter 1 is set in that state.
Reset 5 to O.

When the movable mirror 6 is moved at a constant speed, the detector 11, j2
Interference signals A and B as shown in FIG. 2 are detected. These interference signals A and T3 are input to the amplifier down counter 15. For example, when the movable mirror 6 moves from left to right, the count is added by 1 for each peak of interference signal A or B, and vice versa. The count is 1 in the direction
Subtracted.

The D/A converter 16 outputs a driving voltage based on the count value of the up/down counter 5 and the coefficient from the D/A converter 18, and the sliding support mechanism 8 receives a signal from a power amplifier 22 based on the displacement of the movable mirror 6. A proportional drive current is provided.

When the moving speed of the movable mirror 6 deviates from the constant speed, the output voltage of the frequency-voltage converter 19 deviates from the reference value Vr, and an error voltage corresponding to the deviation is output, and the power amplifier 2
2 gives an error current to correct the speed error,
The speed of the movable mirror 6 is returned to a constant value.

In the embodiment, the D/A converter 16 performs multiplication processing with a coefficient to convert the count value into a drive voltage, but the count value output of the up-down counter 15 is once input to the CPU, and the count value is After converting the voltage into a driving voltage, the driving voltage may be outputted via a D/A converter.

A phase shift plate 9 is provided in the optical path on the fixed mirror 7 side, but the movable mirror 6
It may be provided in the side optical path.

In addition, in order to correct the speed error of the movable mirror 6, the amplifier 1
Although the output A of the amplifier 3 is used, the output B of the amplifier] 4 may also be used.

(Effects of the Invention) In the present invention, a sliding support mechanism for moving a movable mirror is provided with a flexure pivot, and a drive current proportional to the amount of displacement of the movable mirror is used as a drive current for driving the movement of the movable mirror.
Since the error current for making the speed of the movable mirror constant is applied to the sliding support mechanism, the movement of the movable mirror can be stabilized.

Furthermore, the sliding support mechanism with the flexure pivot can be constructed at low cost.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram showing one embodiment, and Figure 2 is a second diagram of the same embodiment.
FIG. 3 is a vertical sectional view showing an example of the sliding support mechanism used in the same embodiment, FIG. 4 is a left side view of FIG. 3, and FIG. 5 is a waveform diagram of the same embodiment. FIG. 6 is a diagram showing the relationship between the displacement and thrust of the movable mirror in the same embodiment; FIG. 7 is a diagram showing the relationship between the angle and displacement of the sliding support mechanism; FIG. The figure shows the error when the drive current is made proportional to the displacement. 1... Laser, 2... Incident light flux, 5
...Beam splitter, 6...Moving mirror, 8...Sliding support mechanism, 9...
・1/8 wavelength plate, 10...Polarizing beam splitter, 11.12...Photodetector, 15...Up/down counter, 16.18.
...D/A converter, 17...CPU, 19...
... Frequency-voltage converter, 20 ... Speed error generation amplifier, 21 ...
・Summing amplifier, 22...Power amplifier. Patent applicant: Shimadzu Corporation

Claims (1)

[Claims] (1) A linearly polarized laser, a beam splitter that splits the incident light beam from the laser into two, a moving mirror and a fixed mirror that return each of the split lights to the beam splitter, and a flexure pivot that supports the moving mirror. a sliding support mechanism for moving the optical path; a phase plate provided on one side of the optical path divided into two by the beam splitter; a polarizing beam splitter for dividing the interference light from the beam splitter into two; By inputting the two light receiving detectors that detect light and the interference signal outputs of these light receiving detectors that have different phases from each other, the displacement and movement direction of the sliding support mechanism from its natural position are recognized, and the a drive voltage generation circuit that generates a proportional drive voltage; an error voltage generation circuit that generates an error voltage proportional to the moving speed error of the moving mirror from the frequency of the interference signal output of one of the light receiving detectors; A two-beam interferometer equipped with a drive circuit that adds voltage and causes current to flow through the sliding support mechanism.