JP2858630B2 - FTIR moving mirror controller - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a moving mirror control apparatus for controlling a moving mirror using a quadrature control in a Fourier transform infrared spectrophotometer (FTIR). FTIR is used for qualitative analysis and quantitative analysis of substances, and can be used for a wide range of substances irrespective of polymer materials, semiconductors, organic substances and inorganic substances.

[0002]

2. Description of the Related Art In addition to a main interferometer for measuring a sample, the FTIR is provided with a control interferometer for activating data collection and stabilizing a sliding speed of a movable mirror with respect to the main interferometer. The control interferometer employs a technique called quadrature control to detect the position of the movable mirror. In the quadrature control, a phase shift plate such as a λ / 8 plate is provided between a beam splitter and a fixed mirror, and an interference signal associated with the beam splitter is separated into a P wave and an S wave by a polarization beam splitter. The separated polarization components are detected by the respective detectors, and the position of the movable mirror is detected from the phase relationship between the detection signals of the two detectors and the wave number.

[0003] Prior to the start of measurement, the center burst position is determined. The center burst position can be detected as the position where the interferogram takes the maximum value when the movable mirror is moved. In the measurement, the movable mirror is moved in a range that can be measured by the specified wave number resolution in the + direction and the − direction with the determined center burst position as the center.

FIG. 1 shows an operation for determining a center burst position in FTIR using a movable mirror whose gravity direction is a balanced position. The position shown by the broken line is the center burst position. First, reset at the gravity balance position,
Distance corresponding to wave number resolution of 2 cm ^-1 from the movement start position to the position (approximately -2.5 mm, 8192 minutes in measurement points)
Then, the sliding direction is turned back and the section (about 5 mm, 16384 points) for obtaining the wave number resolution of 2 cm ^-1 is moved, and data collection is performed during that time. The position at which the maximum value of the interferogram obtained during the movement of the movable mirror in that section is calculated at the time point and that position is set as the center burst position, and at that time the specified wave number decomposition centered on the center burst position The measurement start position is calculated so as to perform the measurement in step (1), the sliding direction is turned back using the position as the measurement start position, and the first data collection is performed. The time required to move the moving mirror to obtain a wavenumber resolution of 2 cm ^-1 is about 2 seconds.

[0005]

In order to determine the center burst position, the movable mirror is moved by a predetermined range around the initial position (gravity balance position), and the position where the interferogram becomes maximum in that range is determined. The center burst position is determined. However, if the movable mirror is displaced or the surface of the table on which the FTIR is placed is greatly inclined, the center burst position will be largely displaced from the initial position. Therefore, the center burst position may not be accurately determined. In order to avoid such a situation, it is necessary to set a large moving range of the movable mirror for determining the center burst position, but the movable mirror for determining the center burst position is moved for each measurement. Therefore, there arises a problem that the measurement requires wasted time.

Further, the adjustment of the movable mirror requires that the distance from the fixed mirror to the beam splitter be equal to the distance from the movable mirror to the beam splitter, and that the interference matching needs to be performed in the same manner. The error of the degree is inevitable,
For example, considering the moving mirror sliding mechanism 6 of the embodiment shown in FIG. 7, the length of the plates 132 and 133 is set to 100 m.
If m, the allowable amount of inclination becomes only about ± 0.5 °. An object of the present invention is to enable a center burst position to be determined at the time of measurement in a short time and accurately.

[0007]

FIG. 2 shows the present invention. The main interferometer 202 and the control interferometer 204 use a fixed mirror and a movable mirror in common.
00. Center burst position detector 2
06 inputs the interference signal from the control interferometer and the interferogram data from the main interferometer at the time of adjustment,
The center burst position where the interferogram takes the maximum value is detected. The detected center burst position is stored in a center burst position storage unit 208 including a nonvolatile memory device. At the time of measurement, the movable mirror control unit 20
0 determines the measurement start point based on the center burst position stored in the center burst position storage unit 208.

[0008]

FIG. 3 and FIG. 5A show the operation of determining the center burst position at the time of adjustment and storing the center burst position. Reset at the gravity balance position, and move the movable mirror from the gravity balance position over a predetermined range (→). At the time of adjustment, it is moved over a wider range than at the time of measurement. For example, in the range of 1 cm ^-1 minute (approximately ± 5 mm) in wave number resolution, that is, as shown by → from the gravity balance position, move about 5 mm in the (−) direction, and move 16384 points in the number of measurement points, and slide in the position Is returned, 1 cm ^-1 (approximately 10 mm, data for 32,768 points are collected (), and after the data is collected, the sliding direction is turned back. The position (center burst position) at which the maximum value of the interferogram is obtained at the time is calculated. At that time, the center burst position is stored in a nonvolatile memory device, for example, EEP.
It is stored in ROM (PROM which can be electrically erased).

At the time of adjustment, the wave number resolution is 1 cm ^-1 minute (about 10 m
The time required to move the movable mirror to collect data (m, 32768 points) is about 4 seconds, but this is not a problem because the movement is performed only during adjustment. Assuming that the error of the beam splitter adjustment is ± 1.5 mm, the allowable amount of the inclination is widened to about ± 2 °.

The operation at the time of measurement will be described with reference to FIGS. 4 and 5B. Reset at the gravity balance position and recall the center burst position from the EEPROM. Let L be the distance to the called center burst position.
It slides in the (-) direction (→), calculates a measurement start point so as to measure at a wavenumber resolution of 2 cm ⁻¹ around the center burst position, and moves to the measurement start point. The sliding direction is turned back at the measurement start point, and 2 cm ^-1 (about 5 mm, 163
Data collection (for 84 points) is performed (section), and after the data collection, a position (center burst position) where the interferogram takes the maximum value at the time is calculated, and the sliding direction is turned back. At that time, the measurement start position is calculated so that the measurement is performed with the specified wave number resolution centering on the obtained center burst position, and after sliding to the calculated measurement start position, the sliding direction is turned back and the first time Data collection (section). Thereafter, data collection is repeated for the second and third times.

Each time the sample changes, the movable mirror is first moved to accurately determine the center burst position as shown in FIGS. 4 and 5B prior to the start of the measurement. Since the center burst position determined at the time is stored in the center burst position storage unit, the movement of the movable mirror for confirming the stored center burst position is the same or shorter than that at the time of measurement. The center burst position can be accurately determined even in the range movement. Therefore, the time required for determining the center burst position during measurement is reduced. Further, at the time of moving mirror adjustment, the center burst position determined at the time of device adjustment and stored in the center burst position storage unit can be used. Can be reduced.

[0012]

FIG. 6 shows an example of FTIR to which the present invention is applied. 2 is a beam splitter and compensator (hereinafter simply referred to as a beam splitter), 4 is a fixed mirror, 6 is a movable mirror, and the beam splitter 2 is 30 ° with respect to the normal direction of the fixed mirror 4 and the normal direction of the movable mirror 6. They are arranged with an inclination. The fixed mirror 4 is mounted on a fixed mirror support block 8, and the movable mirror 6 is supported by a sliding mechanism 14.
Moves the movable mirror 6 by a linear motor 16 in a direction approaching the beam splitter 2 and in a direction away from the beam splitter 2. Reference numeral 18 denotes a power amplifier that supplies a current to the linear motor 16, and reference numeral 20 denotes a sliding controller that controls the linear motor 16 via the power amplifier 18.

An infrared light source 22 is provided to constitute a main interferometer together with the beam splitter 2, the fixed mirror 4, and the movable mirror 6 to provide an infrared spectroscopic measurement system. , Aperture 26, collimator mirror 28
, And is incident on the beam splitter 2 and modulated by this interferometer. The modulated light passes through the sample chamber 34 from the mirror 30 and the condenser mirror 32 and then passes through the ellipsoidal mirror 36 to the infrared detector 38.
And is converted into an electric signal. 40 is a detector 38
, A preamplifier for amplifying the detection signal of
4 is an auto gain amplifier, 46 is a sample hold amplifier, and 48 is an A / D converter for converting a sampled signal into a digital signal.

In order to form a control interferometer together with the beam splitter 2, the fixed mirror 4, and the movable mirror 6, a He-Ne laser 50 is provided as a light source. Reference numeral 54 denotes a half mirror that causes a laser beam to enter the beam splitter 2. A λ / 8 plate 56 is provided between the beam splitter 2 and the fixed mirror 4 for changing the laser beam reflected by the beam splitter 2 and reflected by the fixed mirror 4 and returned to the beam splitter 2 from linearly polarized light to circularly polarized light. Have been. The λ / 8 plate 56 is installed such that its polarization axis is inclined by 45 degrees from the plane of polarization of the incident laser beam. A polarization beam splitter 60 is provided to divide the interference light modulated by the interferometer and reflected by the half mirror 58 into P-wave and S-wave polarization components. Reference numeral 62 denotes a photodiode serving as a detector that receives one polarized component transmitted through the polarizing beam splitter 60, and reference numeral 64 denotes a photodiode serving as a detector that receives the other polarized component reflected by the polarizing beam splitter 60. . The photodiode 62 is connected to a preamplifier 66, and the photodiode 64 is connected to a preamplifier 68. Reference numerals 78 and 80 denote waveform shapers for converting an input signal into a pulse train, and reference numeral 82 denotes an up / down counter for inputting two pulse signals a and b whose waveforms are shaped. The up / down counter 82 determines the up / down mode from the phase relationship between the two input signals, counts the number of pulses of the input signal,
The data is transmitted to the CPU bus line 84.

The waveform a of the signal of the photodiode 62 is also sent to the sliding controller 20, the sample and hold amplifier 46, and the A / D converter 48. C
The PU bus line 84 includes an MPU 86, a program storage memory 88, a data storage memory 90, an external storage device 92,
CRT94, plotter 96 and auto gain amplifier 4
4. The A / D converter 48 and the up / down counter 82 are connected. The center burst position detection unit 206 in the present invention is realized by the MPU 86, and the center burst position storage unit 208 is realized by connecting an EEPROM separately or by the external storage device 92.

FIG. 6 shows the operation of FTIR in the embodiment of FIG. (A) Operation of control interferometer The laser interference lights having different phases from each other split by the polarization beam splitter 60 are output from the photodiodes 62 and 6 respectively.
4 and the respective photodiodes 62 and 64
Of the detection signal is shaped as a pulse signal and taken in as two inputs a and b of the up / down counter 82. The up / down counter 82 uses the up /
The down mode is determined from the phase relationship between both input signals. That is, if the moving mirror 6 approaches the beam splitter 2, one signal a has a phase of 9 with respect to the other signal b.
This is because the phase of the signal a is delayed by 90 degrees with respect to b if the moving mirror 6 moves away from the beam splitter 2 by 0 degrees. The number of pulses of the input signal counted by the up / down counter 82 is a signal depending on the position of the movable mirror 6. The output signal of the up / down counter 82 is taken into the MPU 86 via the bus line 84, and is used as a signal for detecting abnormal sliding of the moving mirror and for integrating the interferogram of infrared spectroscopy. Can be

The sliding controller 20 controls the voltage applied to the linear motor 16 via the power amplifier 18 so that the frequency of the detection signal of the photodiode 62 becomes constant. The signal (a signal) obtained by shaping the detection output of the photodiode 62 is supplied to the sample-and-hold amplifier 46.
And the conversion start signal of the A / D converter 48.

(B) Operation of Infrared Data Collection The signal emitted from the infrared light source 22, modulated by the interferometer, and converted into an electric signal by the infrared detector 38 through the sample chamber 34 is filtered from the preamplifier 40 by the filter. 42, the signal is sampled by a sample hold amplifier 46 via an auto gain amplifier 44, converted into a digital signal by an A / D converter 48, and taken into a bus line 84. An interferogram is generated as the movable mirror 6 moves. A / D conversion of the A / D converter 48 is started using the signal a which is an interference signal of the control interferometer. The current position of the movable mirror 6 is detected in real time by the quadrature control. This current position signal is generated by an up / down counter 82, and is used to know the start and end points of data collection of a series of interferograms. Successive MPU
Recognition is performed by 86 and data collection is performed in the reciprocating direction of the movable mirror 6.

FIG. 7 shows an example of the movable mirror sliding mechanism 14 in which the initial position of the movable mirror 6 is the gravity balance position.
(A) is a vertical sectional view, and (B) is a left side view of (A). 130 is a body, 131 is a base, and the base 131 is rotatably suspended from the body 130 via plates 132 and 133. The films 141 and 142 are fixed between the body 130 and the plates 132 and 133 and between the base 131 and the plates 132 and 133 and can rotate freely. Base 131
The movable mirror 6 is fixed via a mirror holder 134. In the body 130, a magnet 136 and a pole piece 137 are fixed to a plate 135 by bolts 138.
It is fixed to. The base 131 also includes
40, the coil 139 is fixed.
Reference numeral 39 is positioned so as to move in a magnetic field formed by the magnet 136 and the pole piece 137.
In this sliding support mechanism, when an electric current is applied to the coil 139, the coil 139 receives Lorentz force due to the magnetic field of the magnet 136 and the pole piece 137, and moves the movable mirror 6 via the base 131 in the left and right direction in FIG. Let it.

[0020]

According to the present invention, the moving range of the movable mirror for determining the center burst position can be adjusted over a large range at the time of adjustment, and only a narrow range can be moved based on the result at the time of measurement. Is larger than the gravity balance position.
As a result, in the conventional case, for example, ± 2.5 mm for each measurement
In the present invention, the measurement time does not become longer even if the range of ± 5 mm is moved.
For example, the adjustment foot for adjusting the inclination of FTIR may be omitted, or F
This has the effect of increasing the allowable amount of inclination of the table on which the TIR is installed. Despite the increase in the adjustment range of the center burst position determination, the time required for the center burst position determination during measurement does not change or is shortened. Since the center burst position is stored in advance, the setting state of the movable mirror can be monitored during adjustment.

[Brief description of the drawings]

FIG. 1 is a diagram showing a conventional center burst position determination operation.

FIG. 2 is a block diagram illustrating the present invention.

FIG. 3 is a flowchart showing a center burst position determining operation at the time of adjustment.

FIG. 4 is a flowchart showing an operation at the time of measurement.

FIGS. 5A and 5B are diagrams showing operations at the time of adjustment and at the time of measurement, respectively.

FIG. 6 is a schematic configuration diagram illustrating an example of an FTIR to which the present invention is applied.

7A and 7B are diagrams showing an example of the moving mirror sliding mechanism in FIG. 6, wherein FIG. 7A is a vertical sectional view, and FIG. 7B is a left side view of FIG.

[Explanation of symbols]

 Reference Signs List 200 Moving mirror control unit 202 Main interferometer 204 Control interferometer 206 Center burst position detection unit 208 Center burst position storage unit

Claims (1)

(57) [Claims] 1. A phase plate is arranged between a beam splitter of a main interferometer for measuring a sample and a fixed mirror or a movable mirror,
A quadrature that separates and detects two polarization components from the interference signal multiplexed by the beam splitter, and detects a moving direction and a position of a movable mirror from a phase relationship and a wave number of the two detection signals that are out of phase with each other. In a moving mirror control device provided with a control interferometer of a true control type, the moving mirror is of a type suspended so that an initial balance position thereof is in the direction of gravity, and the control interferometer is used at the time of adjustment. Center burst position detector that detects the center burst position where the interferogram takes the maximum value from the gravity balance position, and stores the center burst position A center burst position storage unit comprising a non-volatile memory device for storing data. An FTIR moving mirror control device, wherein a measurement start point is determined based on a center burst position stored in a tarburst position storage unit.