JP2014170018A - Interference spectrophotometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interference spectrophotometer which is capable of accurately calculating an absorbance or transmittance spectrum of a sample by excluding an influence of disturbance.SOLUTION: An interference spectrophotometer 101 includes: a moving mirror unit 260 having a moving mirror 262 capable of moving forward and backward; a fixed mirror 85; an infrared light source unit 10 which emits infrared light; a beam splitter 70; an interference light detector 20 which detects intensity information of light transmitted through or reflected by a sample S; a moving mirror speed information detector 30 which detects moving mirror speed information of the moving mirror 262; and a control unit 151 which acquires the light intensity information and the moving mirror speed information to calculate an absorbance or transmittance spectrum of the sample S. The interference spectrophotometer 101 further includes a storage unit 152 in which a correlation function indicative of variation of the light intensity information relative to the moving mirror speed and a target moving mirror speed are stored, and the control unit 151 corrects the light intensity information obtained by the interference light detector 20 into corrected light intensity information which is obtained when the moving mirror speed of the moving mirror 262 is the target moving mirror speed, by using the moving mirror speed information and the correlation function.

Description

  The present invention relates to an interference spectrophotometer, and more particularly to a Fourier transform infrared spectrophotometer (hereinafter abbreviated as “FTIR”).

  In the Michelson two-beam interferometer used for FTIR, infrared light emitted from an infrared light source is split into two directions, a fixed mirror and a moving mirror, by a beam splitter, reflected by the fixed mirror and returned to the infrared. It has a configuration in which the light and the infrared light reflected and returned by the moving mirror are combined by a beam splitter and sent to one optical path. At this time, if the moving mirror is moved back and forth in the direction of the incident optical axis, the difference in the optical path length of the divided two light fluxes changes, so the combined light is an interference whose light intensity changes according to the position of the moving mirror. It becomes an optical signal (interferogram).

FIG. 4 is a diagram showing a configuration of a main part of a conventional FTIR. The FTIR 201 includes a main interferometer main unit 40, an infrared light source unit 10 that emits infrared light, an infrared light detection unit 20 in which a sample S is disposed, a moving mirror speed information detection unit 30, and a computer 250. (For example, refer to Patent Document 1).
The infrared light source unit 10 includes an infrared light source that emits infrared light, a condensing mirror, and a collimator mirror. Thereby, the infrared light emitted from the infrared light source is applied to the beam splitter 70 of the main part 40 of the main interferometer via the condenser mirror and the collimator mirror.
The infrared light detection unit 20 includes a parabolic mirror, an ellipsoidal mirror, an infrared detector 21 that detects an interferogram (IFG signal), and a sample placement unit on which the sample S is placed. Thereby, the light collected by the parabolic mirror is irradiated on the sample S, and the light transmitted through (or reflected by) the sample S is condensed on the infrared detector 21 by the ellipsoidal mirror. It has become.

The main interferometer main part 40 includes a housing 42 having an internal space, the movable mirror unit 260 is arranged at the upper part of FIG. 4, the beam splitter 70 is arranged at the middle part of FIG. 4, and the fixed mirror is arranged at the lower part of FIG. A fixed mirror unit 80 having 85 is arranged.
FIG. 5 is a longitudinal sectional view of the movable mirror unit 260. The movable mirror unit 260 includes a top plate 264, a bottom plate 265, and two plates 266 and 267. The upper end of the plate 266 is connected to the left side of the lower surface of the top plate 264, and the lower end of the plate 266 is connected to the left side of the upper surface of the bottom plate 265. The upper end of the plate 267 is connected to the right side of the lower surface of the top plate 264, and the lower end of the plate 267 is connected to the right side of the upper surface of the bottom plate 265.
Accordingly, the bottom plate 265 is suspended so as to be movable in the left-right direction with respect to the top plate 264 via the plates 266 and 267.

A yoke 268 is fixed to the center of the lower surface of the top plate 264, and a magnet 269 a and a pole piece 269 b are fixed to the yoke 268 with bolts 270.
A voice coil 272 is fixed to the center portion of the upper surface of the bottom plate 265 via an equalizer 271. A conductive wire 273 is electrically connected to the voice coil 272, and the voice coil 272 moves in a magnetic field formed by the magnet 269a, the yoke 268, and the pole piece 269b.

On the left side of the upper surface of the bottom plate 265, the mirror holder 261 is fixed, and the central portion of the disc-shaped movable mirror 262 is fixed to the upper end portion of the mirror holder 261. As a result, when a current is passed through the voice coil 272 via the conductor 273, the voice coil 272 receives electromagnetic force from the magnetic field formed between the yoke 268 and the pole piece 269b, and the bottom plate 265 moves in the left-right direction. Thus, the movable mirror 262 is also moved in the left-right direction M.
The top plate 264 of the movable mirror unit 260 is attached to the housing 42 using screws and washers 263.

  According to such a main interferometer main unit 40, the infrared light emitted from the infrared light source unit 10 is applied to the beam splitter 70, and the beam splitter 70 causes the fixed mirror 85 and the movable mirror 262 to move in two directions. Divided. Then, the infrared light reflected and returned by the fixed mirror 85 and the infrared light reflected and returned by the movable mirror 262 return to the beam splitter 70 and are combined by the beam splitter 70 to be combined with the infrared light detector 20. Sent to the light path to At this time, since the movable mirror 262 reciprocates back and forth in the incident optical axis direction M, the difference in the optical path length of the divided two light beams periodically changes, and the beam splitter 70 to the infrared light detection unit 20. The light that goes is an interferogram whose amplitude varies with time. Then, the interferogram transmitted through the sample S is collected on the infrared detector 21. FIG. 6 is a diagram showing an IFG signal showing an example of the relationship between the light intensity and the movable mirror position.

  In addition, the FTIR 201 is provided with a moving mirror speed information detection unit 30 that detects moving mirror speed information. The moving mirror speed information detection unit 30 performs speed information detection using laser light, and includes a He-Ne laser light source unit 31 that emits laser light, half mirrors 32 and 33 that reflect laser light, and laser light. A laser beam detector 34 for detecting information (see, for example, Patent Document 2).

  According to such a moving mirror speed information detection unit 30, the laser light emitted from the He—Ne laser light source unit 31 is applied to the beam splitter 70, and the beam splitter 70 uses the fixed mirror 85 and the moving mirror 262. Divided in direction. Then, the laser beam reflected and returned by the fixed mirror 85 and the laser beam reflected and returned by the movable mirror 262 return to the beam splitter 70, and are combined by the beam splitter 70 and are directed to the laser beam detector 34. Sent to. At this time as well, since the movable mirror 262 reciprocates back and forth in the incident optical axis direction M, the difference in the optical path length of the divided two light beams periodically changes, and the laser beam is detected from the beam splitter 70. The light traveling toward the unit 34 becomes laser interference light whose amplitude varies with time. Then, the laser interference light is introduced into the laser light detection unit 34. The position of the movable mirror 262, the movable mirror speed Vc, and the like are calculated from the detection signal from the laser light detector, that is, the laser light interference fringe signal.

  The computer 250 includes a CPU (control unit) 251 and a memory 252, and a display device 53 and an input device 54 are connected to each other. The function processed by the CPU 251 is described as a block. The light intensity information acquisition unit 251a that acquires light intensity information from the infrared detector 21 and the moving mirror speed information (moving mirror speed Vc and the like) from the laser light detection unit 34 are described. The movable mirror speed information acquisition unit 251b to be acquired, the movable mirror control unit 251c that controls the movable mirror speed Vc in the movable mirror unit 260, and the sample measurement unit 251d that calculates the absorbance spectrum of the sample S are included.

  By the way, when a DLATGS detector is used as the infrared detector 21, the DLATGS detector 21 has frequency characteristics. For this reason, if the moving mirror speed Vc of the moving mirror 262 is not constant, the blinking frequency of the interferogram is not constant, and appears as a measurement error in the absorbance spectrum of the sample S. Specifically, if the moving mirror speed Vc of the moving mirror 262 at the time of measuring the background and the moving mirror speed Vc of the moving mirror 262 at the time of measuring the sample S are different, the baseline distortion or S / N is accompanied by deterioration. Further, during the measurement of the background or the sample S, the IFG signal is accumulated by repeating the reciprocating movement of the movable mirror 262, and the movable mirror speed Vc of the movable mirror 262 changes during the accumulation of the IFG signal. Even so, the S / N deteriorates.

  Therefore, the moving mirror control unit 251c causes the speed error (100 × (Vc−Vo) / Vo) between the current moving mirror speed Vc and the target moving mirror speed Vo so that the moving mirror speed Vc of the moving mirror 262 becomes constant. ) And is fed back to the voltage applied to the moving mirror unit 260 (moving mirror applied voltage). Thereby, the movable mirror speed Vc is set to the target movable mirror speed Vo (constant). The “target moving mirror speed Vo” is stored in the memory 252 by the measurer using the input device 54. FIG. 7 is a diagram showing a speed error signal showing an example of the relationship between the speed error and the movable mirror position.

JP 2002-148116 A JP 2009-139352 A

However, although the FTIR 201 as described above performs feedback control, the moving mirror speed Vc may fluctuate due to disturbance (vibration, noise). In addition, although FTIR201 is implementing the design which took the earthquake-resistant structure, it is impossible to prevent a disturbance completely. Therefore, in the FTIR 201 as described above, when a disturbance occurs, the absorbance spectrum of the sample S cannot be accurately calculated.
Therefore, an object of the present invention is to provide an interference spectrophotometer that can accurately calculate the absorbance or transmittance spectrum of a sample even when disturbance occurs and the moving mirror velocity Vc does not become constant.

  The interferometric spectrophotometer of the present invention made to solve the above problems includes a movable mirror unit having a movable mirror that can reciprocate, a fixed mirror, an infrared light source unit that emits infrared light, and the infrared light. Infrared light from the light source part is received and divided into two parts toward the fixed mirror and the moving mirror, and the infrared light reflected by the fixed mirror and the red reflected by the moving mirror are returned. A beam splitter that receives external light and synthesizes it with interference light, an interference light detection unit that detects light intensity information of interference light transmitted through or reflected by the sample, and the moving mirror speed of the movable mirror An interference spectrophotometer comprising: a moving mirror speed information detecting unit for detecting information; and a control unit for obtaining the light intensity information and the moving mirror speed information and calculating the absorbance or transmittance spectrum of the sample, Correlation of light intensity information change with moving mirror velocity A storage unit that stores the number and the target moving mirror speed, and the control unit uses the moving mirror speed information and a correlation function to calculate the light intensity information obtained by the interference light detection unit. Correction light intensity information obtained when the moving mirror speed is the target moving mirror speed is corrected.

  As described above, according to the interference spectrophotometer of the present invention, the moving mirror speed of the moving mirror is obtained by using the moving mirror speed information and the correlation function based on the light intensity information obtained by the interference light detecting unit. Since the corrected light intensity information obtained when the speed is obtained is corrected, the absorbance or transmittance spectrum of the sample can be accurately calculated. Further, since there is no data to be discarded for correction, the time does not increase.

(Means and effects for solving other problems)
In the above invention, the moving mirror speed information detection unit includes a laser light source unit that emits laser light, and the laser light is divided into two by a beam splitter toward the fixed mirror and the moving mirror, and then the fixed mirror A laser beam detector that detects laser interference light between the laser beam reflected back from the mirror and the laser beam reflected back from the movable mirror, and the control unit is based on the laser interference light The moving direction of the movable mirror, the position of the movable mirror, and the movable mirror speed may be calculated.

And in the said invention, the said control part shows the relationship between the said light intensity information and the position of a movable mirror based on the said light intensity information, the moving direction of the said movable mirror, the position of the said movable mirror, and a movable mirror speed. An interference light signal may be created, and the interference light signal may be integrated by the reciprocating movement of the movable mirror.
Furthermore, in the above invention, the control unit may perform feedback control of a voltage applied to the movable mirror unit so that the movable mirror speed becomes a target movable mirror speed.

The figure which shows the structure of the principal part of FTIR which concerns on this invention. The figure which shows an example of the correlation function which shows the change of the light intensity information with respect to a moving mirror speed. The flowchart explaining the acquisition method of IFG signal data. The figure which shows the structure of the principal part of the conventional FTIR. The longitudinal cross-sectional view of a movable mirror unit. The figure which shows the IFG signal which shows an example of the relationship between light intensity and a movable mirror position. The figure which shows the speed error signal which shows an example of the relationship between a speed error and a movable mirror position.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The present invention is not limited to the embodiments described below, and includes various modes without departing from the spirit of the present invention.

FIG. 1 is a diagram showing a configuration of a main part of an FTIR according to the present invention. In addition, the same code | symbol is attached | subjected about the thing similar to FTIR201.
The FTIR 101 includes a main interferometer main unit 40, an infrared light source unit 10 that emits infrared light, an infrared light detection unit 20 in which a sample S is disposed, a moving mirror speed information detection unit 30, and a computer 150. Is provided.

  The computer 150 includes a CPU (control unit) 151 and a memory 152, and a display device 53 and an input device 54 are connected to each other. The function processed by the CPU 151 will be described as a block. The light intensity information acquisition unit 151 a that acquires light intensity information from the infrared detector 21 and the moving mirror speed information (moving mirror speed Vc and the like) from the laser light detection unit 34. The moving mirror speed information acquisition unit 151b to be acquired, the moving mirror control unit 151c that controls the moving mirror speed Vc in the moving mirror unit 260, the sample measurement unit 151d that calculates the absorbance spectrum of the sample S, and the corrected IFG signal generation unit 151e. And have.

  The memory 152 also includes a correlation function indicating a change in light intensity information with respect to the moving mirror speed for converting the IFG signal to the corrected IFG signal, and a target moving mirror for avoiding inappropriate light intensity information. The speed range (Vo ± B) is stored in advance. B is an arbitrary constant. FIG. 2 is a diagram illustrating an example of a correlation function indicating a change in light intensity information with respect to the moving mirror speed. Here, a conversion method for converting an IFG signal into a corrected IFG signal will be described. For example, when the target moving mirror speed Vo is 2.0 mm / s and the target moving mirror speed range is (Vo ± 0.4 mm / s), the moving mirror speed Vc at a certain point of the IFG signal is a disturbance or the like. Is 2.5 mm / s. As shown in FIG. 2, the light intensity information obtained at 2.5 mm / s is 0.86 times the light intensity information obtained at 2.0 mm / s. Therefore, the light intensity information is divided by 0.86 for this one point. Thereby, the light intensity information obtained when it was 2.5 mm / s becomes light intensity information (corrected light intensity information) obtained when it was 2.0 mm / s. Although correction is made at one point in the IFG signal, correction may be made at all points without providing the target moving mirror speed range (Vo ± B).

The corrected IFG signal creation unit 151e uses the moving mirror speed Vc and the correlation function to obtain the light intensity information obtained when the absolute value of the moving mirror speed Vc is out of the target moving mirror speed range (Vo + B). Control to create a corrected IFG signal is performed by correcting the corrected light intensity information obtained when the moving mirror speed V of 262 is the target moving mirror speed Vo.
Here, an acquisition method for acquiring IFG signal data to be a corrected IFG signal of the number of times of integration N _max will be described. FIG. 3 is a flowchart for explaining a method for acquiring IFG signal data.
First, in the process of step S <b> 201, the measurer inputs a measurement start signal using the input device 54. At this time, the measurer inputs “the number of times of integration N _max ” and “target moving mirror speed Vo” and stores them in the memory 152.

Next, in the process of step S202, the number-of-integrations parameter N = 1 is set.
Next, in the process of step S203, when the movable mirror control unit 151c moves the movable mirror 262, the light intensity information acquisition unit 151a acquires the light intensity information, and the movable mirror speed information acquisition unit 151b moves. Mirror speed information (moving mirror speed Vc, etc.) is acquired. Then, an N-th IFG signal indicating the relationship between the light intensity and the movable mirror position is created (see FIG. 6).

  Next, in the process of step S204, the light intensity information obtained when the absolute value of the moving mirror speed Vc deviates from the target moving mirror speed range (Vo + B) in the N-th IFG signal is correlated with the moving mirror speed Vc. The correction light intensity information obtained when the moving mirror speed V of the moving mirror 262 is the target moving mirror speed Vo is corrected using the function. That is, a corrected IFG signal is created. Then, N = N + 1.

Next, in the process of step S205, it is determined whether or not N = N _max . If it is determined that N = N _max is not satisfied, the process returns to step S203. That is, the processing from step S203 to step S205 is repeated until the number of corrected IFG signals employed when calculating the absorbance spectrum of the sample S reaches N _max .
On the other hand, when it is determined that N = N _max , the measurement end signal is output because N _max correction IFG signals are acquired in the process of step S206.

  As described above, according to the FTIR 101, the light intensity information obtained when the absolute value of the moving mirror speed Vc of the moving mirror 262 deviates from the target moving mirror speed range (Vo + B) is obtained from the moving mirror speed Vc and the correlation function. Is used to correct the corrected light intensity information obtained when the moving mirror speed V of the moving mirror 262 is the target moving mirror speed Vo, so that the absorbance spectrum of the sample S can be accurately calculated. Further, since there is no data to be discarded for correction, the time does not increase.

<Other embodiments>
In the FTIR 101 described above, the light intensity information obtained when the absolute value of the moving mirror speed Vc of the moving mirror 262 deviates from the target moving mirror speed range (Vo + B) is corrected to the corrected light intensity information. When calculating the absorbance spectrum of the sample S using the IFG signal including the light intensity information obtained when the maximum absolute value of the moving mirror speed Vc of the moving mirror 262 deviates from the target moving mirror speed range (Vo + A). It is good also as a structure which is not employ | adopted. That is, when the speed error is too large, the IFG signal may be discarded.

  The present invention can be suitably used for an interference spectrophotometer such as a Fourier transform infrared spectrophotometer.

10 Infrared light source unit 20 Infrared light detection unit (interference light detection unit)
30 Moving mirror speed information detection unit 70 Beam splitter 85 Fixed mirror 101 FTIR (interference spectrophotometer)
151 CPU (control unit)
152 Memory (storage unit)
260 Moving mirror unit 262 Moving mirror

Claims (1)

A movable mirror unit having a movable mirror capable of reciprocating;
A fixed mirror,
An infrared light source that emits infrared light;
Infrared light from the infrared light source unit is received and divided into two parts toward the fixed mirror and the movable mirror, and the infrared light reflected by the fixed mirror and reflected by the movable mirror are returned. A beam splitter that receives the received infrared light and combines it with the interference light;
An interference light detection unit that detects the light intensity information of the interference light that is arranged and transmitted or reflected by the sample;
A moving mirror speed information detecting unit for detecting moving mirror speed information of the moving mirror;
An interference spectrophotometer comprising a control unit that acquires the light intensity information and moving mirror speed information and calculates the absorbance or transmittance spectrum of the sample,
A storage unit for storing a correlation function indicating a change in light intensity information with respect to the moving mirror speed and a target moving mirror speed;
The control unit corrects the light intensity information obtained by the interference light detection unit when the moving mirror speed of the moving mirror is a target moving mirror speed using the moving mirror speed information and a correlation function. An interference spectrophotometer characterized by correcting light intensity information.

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