JPS6347625A - Interferogram measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve Fourier transform within a short time, by subtracting the background component stored in a memory means from the output signal of an image sensor and outputting only the AC component of an interferogram. CONSTITUTION:A signal is sent to a drive circuit 13 by the operation of a key input terminal 15 and the angle theta of inclination of the reflecting mirror 5 of a Michelson luminous flux interferometer M is changed to set the reflecting mirror 5 to a state of light path difference of zero allowing the interferogram interference fringe on an image sensor 7 to disappear and the min. visible degree is confirmed on a display part 12. Next, the serial signal from a photoelectric converting part is stored in a memory means 10a and the angle theta of inclination is varied to set the visible degree to the max. value and a control part 11 reads the background component of the means 10 corresponding to said control part 11 from the serial signal in synchronous relation to the scanning of the sensor 7 and the AC component being the difference from the serial signal is calculated by a removal operation means 10b to be collected at an output terminal 11a in a real time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an interferogram measurement device used in a Fourier spectrometer or the like, and particularly relates to an interferogram collection technique.

[Archived technology] For example, as shown in FIG. 3, a Fourier spectrometer using a Michelson interferometer includes a white light source 1, a collimator lens 2. Beam splitter 3° reflector 4. A Michelson interferometer M consisting of a reflecting mirror 5 tilted by an inclination angle θ and an imaging lens 6, and an image sensor 7 having a large number of photoelectric conversion units in the transverse direction of the interferogram spatially created by this interferometer M. The configuration has the following. The interferogram is scanned by an image sensor 7,
The signal is sequentially output as a serial signal, and then subjected to Fourier transformation in a subsequent processing device (not shown) to obtain information such as the spectrum of the white light source.

By the way, the interferogram on the image sensor 7 is given by the following equation.

I(x)=fS(σ) (1+cos(2w(f
θx))da' where 5(d) is the spectrum of the white light source l, d is the wave number, θ is the inclination angle of the reflecting mirror 5, and X is the distance above the image sensor 7.

Therefore, the output of the image sensor 7 includes a DC component S.
In the post-processing Fourier transform, the DC component is identified from the output data of the image sensor 7 collected, and the AC component of the interferogram is subtracted from the output data. (fsc) co
It is first necessary to perform data processing to extract s (2π by θX)cj/.

[Problems to be Solved] However, the above conventional interferogram measurement technology has the following problems.

(2) The alternating current component of the interferogram can only be obtained through data processing after the output data of the image sensor 7 has been collected in the interferogram measurement, so it takes time and effort to obtain it.

■Data processing is a method of extracting the DC component from the entire waveform, and depending on the waveform of the interferogram, it may be difficult to extract it.Also, if there is eclipse in the optical system, it may be difficult to extract it from the output data. Identifying the DC component of the interferogram is a cumbersome task that inevitably involves errors, and the sensitivity of each photoelectric conversion section of the image sensor 7 is different, so the AC component of the interferogram can be accurately obtained through post-processing. That is difficult.

An object of the present invention is to solve the above-mentioned problems, and to provide an interferogram measuring device that can collect AC components of an interferogram necessary for Fourier transform with high precision in a short time. .

[Means for Solving the Problems] In order to solve the above problems, the interferogram measuring device according to the present invention consists of the following four constituent elements.

■There must be a white light source.

■There is a two-beam interferometer that receives the white light and creates an interferogram spatially on the image plane.

The "two-beam interferometer" includes a Michelson interferometer with an inclined reflecting mirror, a triangular optical path common path interferometer, a square optical path common bus interferometer, and the like.

(2) There must be a means for varying the optical element that provides the optical path difference in advance and storing the output signal of the image sensor in a state where the visibility of the interferogram is minimized as a background component.

``variable the optical element'' refers to changing the angle of the optical element, moving the optical element, etc.

(2) There is a calculation means for subtracting the corresponding background component from the output signal of the image sensor in regular interferogram measurement and sequentially outputting the difference.

(Function) According to the interferogram measurement device having such a configuration,
The image sensor receives the DC component of the interferogram in a state in which the optical element that provides the optical path difference is varied in advance so that the visibility of the interferogram is minimized, that is, in a state in which the stripes disappear. do,
This is output as a serial signal, and the storage means stores this as a background component.Next, in the measurement of a regular interferogram, the calculation means stores the output signal of the image sensor in the corresponding storage means. Subtract the background component and output the difference sequentially. That is, only the alternating current components of the interferogram useful for Fourier transform are output in real time.

[Example 1 Next, embodiments of the present invention will be described based on the drawings.

FIG. 1 is a block diagram showing an embodiment of an interferogram measuring device according to the present invention.

1 is a white light source, such as a small light bulb or light emitting diode, which has a continuous spectrum in a specific wavelength range. 0M is a Michelson interferometer with a tilted reflecting mirror, and 2 is a parallel light beam from the incident light beam. It is a collimator lens. 3
is a beam splitter that divides the amplitude of a parallel light beam and separates it into two light beams. 4 is a reflecting mirror provided on one optical path.

Reference numeral 5 denotes a reflecting mirror provided on the other optical path at an angle of inclination θ. Reference numeral 6 denotes an imaging lens that forms an image of the light beam using both light beams. Reference numeral 7 denotes an image sensor having a large number of photoelectric conversion units in the transverse direction of the interferogram, which scans the interferogram at predetermined intervals and sequentially outputs serial signals.1 For example, a self-scanning photodiode array etc. are used. 8 is a preamplifier that outputs the output signal of the image sensor 7 to #! It is something that resonates. Reference numeral 9 denotes an analog/digital converter, which converts the amplified serial signal of the interferogram into a digital signal and outputs the digital signal.The configuration of 0 and above is the same as in the conventional one.

Next, lO is a signal processing unit, which mainly consists of background component storage means IQa and background component removal calculation means 1.
0b. The background component storage means 10a stores the output of the image sensor 7 in a state where the visibility of the interferogram is minimum, that is, the background component including the DC component of the interferogram is stored. The background component removal calculation means tab is sequentially inputted to the image sensor 7.
The corresponding background component is subtracted from the output of , and the difference is output. In other words, only the AC component of the interferogram is sequentially output. Reference numeral 11 denotes a control unit that controls the entire system. In particular, under the control of the control unit 11, an interferogram is displayed on a display unit 12 such as a CRT, and the drive circuit 3 is controlled to control the electrostrictive element, etc. The driving element 14 increases or decreases the inclination angle 0 of the reflecting mirror 5. Reference numeral 15 denotes a key input terminal for transmitting a drive signal to the drive circuit 13 and controlling the inclination angle 0 of the reflecting mirror 5 from the outside. Note that the signal processing section 10 and the like can be configured with a microcomputer.

Next, to explain the operation of the above embodiment, first, by operating the key input terminal 15, the inclination angle θ is changed, and the inclination angle θ=O
That is, the optical path difference is set to zero. When the optical path difference is zero, the interference fringes of the interferogram on the image sensor 7 have disappeared, and the visibility of the interferogram is V.
is the minimum, and this is confirmed by the display unit 12. That is, as shown in FIG. ff12 (A), only a DC component (background component) twice as large as the interferogram appears on the display section 12.

Here, the DC component of the interferogram is expressed as l5(()
If the sensitivity of the i-th photoelectric conversion unit is Ti, then the i-th photoelectric conversion unit is Ti 112 f 5Cd)tl(
Outputs a serial signal that is compatible with the Generally sensitivity Ti
is different for each photoelectric conversion unit, so the waveform appearing on the display unit 12 is not a straight line.The serial signal from each photoelectric conversion unit is stored at the corresponding address of the background component storage means 10a.

Next, the inclination angle θ is varied and set to an angle at which the visibility ■ of the interferogram on the display unit 12 is maximized. In such a state, the waveform of the interferogram appearing on the display unit 12 is, as shown in FIG. 2(B), the above-mentioned DC component l−fS(f)clf weighted with an AC component (interference fringes). However, the background component element 1-fS(do)d is removed by the background component removal calculation means Job, and as shown in FIG. 2(C), the AC component of the interferogram is output to the output terminal 11a. only are retrieved sequentially. That is, in synchronization with the scanning of the image sensor 7, the control unit 11 extracts the background component element i 2 r which is the content of the address of the background component storage means 10a corresponding to the serial signal of the i-th photoelectric conversion unit. s (tt)dtr is read out, and the background component removal calculation means 10b calculates the alternating current component of the interferogram, which is the difference between the serial signal and Ti.f S Cet)clf.

According to the above embodiment, only the alternating current components of the interferogram necessary for Fourier transform can be collected at the output terminal 11a in real time. , there is no need for data processing to extract the components, and what is collected is only the AC component of the interferogram from which the DC component of the interferogram, which is affected by the uneven sensitivity of the photoelectric conversion section of the image sensor 7, has been removed. can be,
Highly accurate interferograms can be collected and Fourier transform processing can be performed as is. Another advantage is that the analog/digital converter 9 can have a wide dynamic range.

In the above embodiments, the method for determining whether the visibility of the interferogram is the minimum is to visually check the interferogram displayed on the display unit 12; Needless to say, it is possible to perform statistical processing to automatically determine the state with the minimum visibility.

Further, in the above embodiment, the drive circuit 13 and the drive element 14 are provided, but these may not be provided and the reflecting mirror 5 may be slightly moved manually.

Furthermore, if we also take into account the sensitivity sensitivity of the photoelectric conversion section of the image sensor 7, which affects the alternating current component of the interferogram, the alternating current component of the interferogram obtained from the background component removal calculation means 10b is stored as a background component. The correction may be applied based on the distribution curve of the background component of the means 10a.

As the two-beam interferometer used in the present invention, in addition to the Michelson interferometer in which the reflecting mirror is tilted in the above embodiment, a triangular optical path common bus interferometer, a square optical path common bus interferometer, etc. may be used, for example, When using a triangular optical path common bus interferometer, the state where the visibility of the interferogram is minimum is set by moving the optical element that provides the optical path difference.

[Effects of the Invention] As explained above, the interferogram measuring device according to the present invention measures the DC component (background component) of the interferogram in advance, and in regular measurements, the interferogram measurement device that is obtained sequentially Since the present invention is characterized in that the corresponding DC component (background component) is subtracted from the serial signal and output, the following effects are achieved.

■The alternating current component of the interferogram can be measured in real time, and Fourier transform can be performed directly in a short period of time without the need for post-processing.

■It is possible to suppress the effects of uneven sensitivity of the image sensor and obtain only the alternating current component of the interferogram from which background components have been removed, making highly accurate measurements possible.

■Enables wide dynamic range of analog/digital converters, etc.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an interferogram measuring device according to the present invention. FIG. 2(A) is a waveform diagram showing the DC component of the interferogram in the same example. FIG. 2(B) is a waveform diagram showing an interferogram in the same example. FIG. 2(C) is a waveform diagram showing the alternating current component of the interferogram in the same example. FIG. 3 is a block diagram showing an example of a Fourier spectrometer using a conventional Michelson interferometer. 1... White light source, M-... Michelson interferometer with tilted reflecting mirror, γφ image sensor, 8Φ... Preamplifier, 9... Analog/digital converter, 10...
Signal processing section, lOa... Background component storage means, IQb --- Background component removal calculation means, 11... Control section, 11a*... Output terminal, 12.
Fist - display section, 13...drive circuit, 14...Φ drive element, ! 5...Key input terminal.

Claims (1)

[Claims] A white light source, a two-beam interferometer that receives the white light and spatially creates an interferogram on an image plane, an image sensor that has a large number of photoelectric conversion units in the transverse direction of the interferogram, and an optical path difference that is determined in advance. means for storing an output signal of the image sensor in a state where the visibility of the interferogram is minimized by varying an optical element to provide the image sensor as a background component, and an output signal of the image sensor in measuring a regular interferogram An interferogram measurement device comprising: arithmetic means for subtracting the corresponding background component from the background component and sequentially outputting the difference.