JP3160622B2 - Plasma temperature distribution measuring method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma temperature distribution measuring method and apparatus. More specifically, the invention of this application is to measure the two-dimensional or three-dimensional temperature distribution of plasma in a very short time, which is useful for high precision and high performance such as processing technology using a high power laser and plasma processing. And a new method and apparatus for measuring plasma temperature distribution.

[0002]

2. Description of the Related Art In recent years, processing techniques such as steel welding using a high-power laser have been actively studied and developed in order to realize new structural materials having high performance and high functionality.
However, as illustrated in FIG.
When the material (12) such as steel is irradiated with the (1), a plasma (10) is generated in an irradiated portion on the material (12). The generation of the laser-induced plasma (10) depends on the laser (1) used.
It has become very remarkable with the large output of 1),
The laser (11) is absorbed in the plasma (10),
There are problems that the penetration depth is extremely reduced, and various defects are induced by a severe fluctuation of the plasma (10).

[0003] Therefore, it is very important to measure the state of the plasma, to understand the influence on the welding phenomenon and the like, and to improve the processing quality. In particular, the plasma temperature distribution has a great influence on the processing quality and processing phenomena.
As a method for measuring the temperature of plasma, a probe method, a spectroscopic method, a scattering method, a propagation method, and the like are generally well known.

[0004] However, any of these methods is useful as a simple temperature measurement of plasma, but in order to obtain a two-dimensional and three-dimensional distribution of the temperature, the measurement position must be manipulated in a two-dimensional and three-dimensional manner. Since this operation requires a long time, it has been very difficult to obtain the temperature distribution of the plasma, which has a large time variation. Therefore, the invention of this application has been made in view of the circumstances described above, and solves the problems of the prior art. It is an object of the present invention to provide a new plasma temperature distribution measuring method and apparatus capable of performing accurate measurement in a short time.

[0005]

Means for Solving the Problems The present invention is directed to a method for measuring the temperature distribution of plasma, which solves the above-mentioned problems. Extract emission line spectra emitted by excited atoms or ions using a spectrometer
And, imaging the bright line spectrum image composed only this bright line spectrum, a plasma temperature distribution measurement method characterized by calculating a plasma temperature distribution from the intensity distribution of the bright line spectrum image (claim 1) In this method, the temperature distribution is calculated from the intensity distribution of the emission line spectrum image using the absolute intensity method (Claim 2), or the parallel component light emitted from the plasma is divided into a plurality of pieces, and Among them, simultaneously obtain emission line spectrum images composed of emission line spectra of different wavelengths emitted by excited atoms or ions of the plasma constituent elements, and obtain the plasma from the relative ratio of the intensity of each position in each of these emission line spectrum images. Calculating the temperature distribution (claim 3) or using the relative intensity method to calculate the temperature from the relative ratio of the intensity. Calculating the distribution (claim 4)
Alternatively, using a chromatic aberration correcting lens and a set of slit slits or pinholes orthogonal to each other, the plasma image incident on the chromatic aberration correcting lens is converted to a set of orthogonal slits or pinholes arranged at the focal point of the chromatic aberration correcting lens. The present invention provides, as its modes, taking out parallel component light emitted from the plasma by injecting the light into the plasma (Claim 5), and capturing a bright line spectrum image (Claim 6 ).

Further, the invention of this application is an apparatus for measuring the temperature distribution of plasma, comprising a parallel component light extracting means, a spectroscope as a bright line spectrum extracting means, a bright line spectrum image acquiring means, and a calculating means. Parallel component light emitted from the plasma is extracted by the parallel component light extraction means, and the emission line spectrum emitted by the excited atoms or ions of the plasma constituent elements is extracted from the parallel component light by the spectroscope, and the emission line spectrum image acquisition means A plasma temperature distribution measuring device (claim 7 ) is also provided, wherein a bright line spectrum image composed only of the bright line spectrum is obtained by the calculation, and a plasma temperature distribution is calculated from the intensity distribution of the bright line spectrum image by the calculating means. In this device, the intensity distribution of the emission line spectrum image is calculated using the absolute intensity method. (Claim 8 ), and a splitting means is provided. The splitting means splits the parallel component light emitted from the plasma into a plurality of pieces, and outputs one or a plurality of bright line spectrum extracting means. Emission line spectra of different wavelengths emitted by excited atoms or ions of plasma constituent elements are separately extracted from each parallel component light, and emission line spectrums constituted by each emission line spectrum by one or more emission line spectrum image acquisition means. The images are obtained simultaneously, and the temperature distribution of the plasma is calculated from the relative ratio of the intensity at each position in each of the bright line spectral images by the arithmetic means (Claim 9 ), or from the relative ratio of the intensity using the relative intensity method. the temperature distribution is calculated (claim 10) and the chromatic aberration correction les as parallel component light extraction means And a pair of slits or pinholes orthogonal to each other are provided, and the plasma image incident on the chromatic aberration correction lens is incident on a pair of orthogonal slits or pinholes disposed at the focal point of the chromatic aberration correction lens. In this case, the parallel component light of the plasma image is extracted (claim 11 ), and an imaging means for capturing a bright line spectrum image is provided (claim 12 ).

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, the invention of this application provides a bright line spectrum image composed only of bright line spectra emitted by excited atoms or ions of plasma constituent elements among parallel component light emitted from plasma. An image is formed, and the temperature distribution of the plasma is calculated from the intensity portion of the bright line spectrum image.

More specifically, for example, parallel component light emitted from plasma is extracted, and from this parallel component light,
The emission line spectrum emitted by the excited atoms or ions of the plasma constituent elements is taken out, an emission line spectrum image drawn only with the emission line spectrum is formed, and the intensity distribution of the emission line spectrum is obtained from the luminance distribution in the emission line spectrum image. From the intensity distribution, for example, a two-dimensional or three-dimensional temperature distribution of the plasma can be calculated with high accuracy and high speed by a computer or the like using a known absolute intensity method.

Further, for example, the parallel component light emitted from the plasma is divided into a plurality of parts, and the emission line spectra of different wavelengths emitted by the excited atoms or ions of the plasma constituent elements are separately extracted from each of the parallel component lights. A bright line spectrum image composed of each bright line spectrum may be obtained at the same time, and the plasma temperature distribution may be calculated from the relative ratio of the intensity at each position in each of the bright line spectrum images. In this case, for example, The plasma temperature distribution can be calculated in a two-dimensional or three-dimensional manner with excellent accuracy and in a very short time by a computer or the like using a known relative intensity method.

FIG. 1 is a main configuration diagram showing an example of a measurement configuration or a measurement apparatus according to the present invention when a plasma image is divided into two. For example, in the measuring apparatus shown in FIG. 1, a plasma image (1) is incident on a chromatic aberration correcting lens (2) as a parallel component extracting means, and is then transmitted in two directions by a beam splitter (3) provided as a dividing means. Divided.

Each of the divided plasma images (1) is incident on each of the entrance slits (51) of the two spectroscopes (5) via the reflection mirrors (4) arranged on each optical path. The entrance slit (51) is composed of a set of slits orthogonal to each other, and constitutes a parallel component extracting means together with the chromatic aberration correction lens (2). Since the entrance slit (51) is arranged at the focal point of the chromatic aberration correction lens (2), Plasma image (1)
, It is possible to extract only the parallel component light emitted from.
It should be noted that only the parallel component light can be extracted by using, for example, a pinhole instead of the incident slit (51).

Next, each parallel component light is guided into a spectroscope (5), which is an emission line spectrum extracting means, and is emitted by one of the spectroscopes (5) by excited atoms or ions which are plasma constituent elements. And the other spectroscope (5) takes out a bright line spectrum having a specific wavelength emitted by excited atoms or ions that are plasma constituent elements. These emission line spectra have different wavelengths due to the energy levels of the excited atoms and ions, respectively.

The spectroscope (5) may have, for example, a structure as illustrated in FIG. That is, in the example of FIG. 2, the parallel plasma component light incident through the entrance slit (51) is converted into parallel light by the concave mirror (53) provided in the spectroscope (5), and the plane mirror (54) The light is applied to the grating (55) through the light source. The grating (55) disperses the parallel light according to the wavelength, and by adjusting the angle thereof, it is possible to select only light having a specific wavelength. That is, it is possible to select the emission line spectra having different unique wavelengths emitted by the excited atoms or ions of the plasma constituent elements. Then, the selected bright line spectrum is condensed by the concave mirror (54) to the exit slit (52) and exits.

Of course, the structure of the spectroscope (5) is not limited to the example shown in FIG. 2 as long as it can realize the function of extracting the emission line spectrum from the excited atoms or ions of the plasma constituent elements. Good. Although two spectrometers (5) are used in the example shown in FIG. 1, only one spectrometer (5) capable of separately decomposing each emission line spectrum from the parallel component light and emitting the same is provided. It can also be used. Further, three or more spectroscopes (5) are used in some cases such as selecting three or more bright line spectra having different wavelengths.

The emission line spectra having the specific wavelengths extracted as described above pass through an exit lens (6) disposed on the exit side of each spectroscope (5) as an emission line spectrum image acquiring means, and the image intensity is increased. Fire (7)
An image is formed on the light receiving surface, the light intensity is amplified, and a two-dimensional bright line spectrum image drawn by each is simultaneously obtained.

Here, in the example shown in FIG. 1, each bright line spectrum image is picked up by a CCD camera (8). This two-dimensional bright line spectrum image can be stored in the computer (9) or a separate storage medium. As the imaging means, not only a CCD camera (8) but also a video camera or a film camera is used. Then, for example, a two-dimensional intensity distribution is obtained from the two-dimensional luminance distribution of each bright-line spectrum image by the computer (9) as the calculating means. If it can be assumed, the three-dimensional intensity distribution is analyzed using the Abel transform or the CT method if it cannot be assumed to be axisymmetric,
This three-dimensional plasma intensity distribution is converted into a three-dimensional plasma temperature distribution by a known method. In the example of FIG. 1 in which the plasma image (1) is divided, for example, the three-dimensional temperature distribution of the plasma is calculated from the relative ratio of the intensity at each position in the three-dimensional intensity distribution of each bright line spectrum image according to a known method. Is done. This calculation can be performed using, for example, a known relative intensity method.

When the plasma image (1) is not divided, the spectroscope (5), the exit lens (6), and the image intensity do not need the beam splitter (3) in the measuring apparatus illustrated in FIG. Fire (7), CCD
Only one camera (8) is required. FIG.
FIG. 2 is a main part configuration diagram showing an example of the present invention when the plasma image (1) is not divided, that is, when the parallel component light emitted from the plasma is not divided into a plurality.

In the measuring device illustrated in FIG. 3, a known chromatic aberration correcting lens (14) and a pinhole (15) are used instead of the chromatic aberration correcting lens (2) in the measuring device of FIG. The telecentric optical system (13) is provided, and parallel component light is extracted by the telecentric optical system (13). Then, the extracted parallel component light is condensed on the entrance slit (51) by the field lens (16) and is incident on the spectroscope (5). In the spectroscope (5), an emission line spectrum by one of the excited atoms or ions, which are plasma constituent elements, is taken out. Then, an emission line spectrum image constituted by this emission line spectrum is obtained in the same manner as in the above-described measuring apparatus of FIG. And an exit lens (6) and an image intensifier (7).

From the intensity distribution of the bright line spectrum image, a plasma temperature distribution is calculated two-dimensionally or three-dimensionally according to a known method. Here, the conversion from the three-dimensional intensity distribution to the three-dimensional temperature distribution uses an absolute intensity method. Note that a two-dimensional temperature distribution can be obtained by taking a cross section of the three-dimensional intensity distribution obtained as described above, or a two-dimensional temperature distribution can be directly obtained from the two-dimensional intensity distribution.

According to the present invention, the two-dimensional emission line spectrum intensity is obtained by acquiring, as a two-dimensional image, the emission line spectrum emitted by the excited atoms or ions of the plasma constituent elements from the parallel component light emitted from the plasma. Since the distribution can be easily obtained, only the calculation according to the above-mentioned various known calculation methods is performed by a computer or the like using the two-dimensional distribution of the intensity. It is possible to measure a two-dimensional or three-dimensional temperature distribution of a plasma with a large fluctuation in time and with excellent accuracy. Furthermore, by photographing this temperature distribution at a high speed, it is possible to know a change in the temperature distribution with high time resolution.

The parallel component light extracting means, the bright line spectrum extracting means, and the bright line spectrum image acquiring means are not limited to the above examples as long as they can fulfill their respective functions. Hereinafter, embodiments will be described with reference to the accompanying drawings, and embodiments of the present invention will be described in further detail.

[0022]

(Example 1) Steel SM490 for general welding structure
Under the conditions of a laser output of 5 kW, a welding speed of 50 cm / min, and an assist gas flow rate of 40 L / min (Ar).
The temperature distribution of the plasma formed when performing the _two laser welding was measured according to the present invention illustrated in FIG.

From each of the parallel component lights emitted from the divided plasma, emission line spectra of different wavelengths emitted by the excited atoms (ArI) and ions (ArII) of the plasma constituent element Ar are extracted, and the respective emission line spectra are obtained. The drawn two-dimensional emission line spectrum image,
Images were taken and recorded simultaneously by a high-sensitivity CCD camera (8). The wavelength of the emission line spectrum from the excited atom (ArI) is 696.5 nm, and the wavelength of the emission line spectrum from the ion (ArII) is 480.7 nm. In this embodiment, the wavelength resolution of these emission line spectra by the spectroscope (5) is used. Was 1 nm or less.

Then, a computer (9) calculates a three-dimensional intensity distribution from the two-dimensional intensity distribution of each emission line spectral image using Abel transform, and, based on the three-dimensional intensity distribution, an ArII / The two-dimensional temperature distribution of the plasma was calculated using the ArI two-line intensity ratio method. On the other hand, when the parallel component light emitted from the plasma was not split, the plasma temperature distribution was measured as described above. An emission line spectrum image composed of emission line spectra by excited atoms (ArI) is imaged, a three-dimensional intensity distribution is calculated from the two-dimensional intensity distribution of this emission line spectrum image by Abel transform, and further, an absolute value is calculated from the three-dimensional intensity distribution. The three-dimensional temperature distribution of the plasma was calculated using the off-axis maximum radiation counting method, which is a kind of intensity method.

[0025] As a result, divides the parallel component light emitted from the plasma, in the case of using the ARII / ArI 2-wire intensity ratio method, and without dividing the parallel component light emitted from the plasma, the off-axis maximum radiation counting method When used together,
A high-precision three-dimensional temperature distribution that matched well with each other was obtained in an extremely short time. (Embodiment 2) In Embodiment 2, an example in which the temperature distribution of plasma is measured using the measuring apparatus illustrated in FIG. 3 will be described.

In the measuring apparatus shown in FIG. 3, the pinhole (15) constituting the telecentric optical system (13) has a diameter of 3 mm, the spectroscope (5) has a focal length of 277 nm, and emits plasma with a wavelength resolution of about 1 nm. Only a specific bright line spectrum in it can be selected. The CCD camera (8) has 1280 × 1024 pixels. Using such a device, a laser output of 5 kW, a welding speed of 8.3 mm / s, and an Ar shielding gas flow rate of 40 L / min.
The material (12) was subjected to CO ₂ laser welding under the conditions described above, and a bright line spectrum image of the plasma generated at this time was captured at a high speed of 10 ms, and the temperature distribution of the plasma was measured.

FIG. 4A is a photograph instead of a drawing showing an example of a plasma image formed during laser welding. In the parallel component light from the plasma image as exemplified in FIG. 4A, the excited atoms (ArI
), A bright line spectrum having a wavelength of 696.5 nm was extracted, and a two-dimensional image of the bright line spectrum was formed. FIG. 4B is a photograph replacing a drawing showing an example of the bright line spectrum image.

In the second embodiment, the temperature distribution of the plasma is obtained from the intensity distribution of the emission line spectrum image by using the off-axis maximum radiation counting method. In this case,
First, as illustrated in FIG. 5, it is necessary to evaluate the spectrum intensity based on the integrated value of the ArI emission line spectrum intensity (the shaded portion in the diagram). Therefore, first, as illustrated in FIG. 6, the slit width of the entrance slit (51) of the spectroscope (5) is set to 0.
The slit width of the exit slit (52) is fixed at 0.3 mm, which is fixed at 1 mm, and the increase rate of the spectral intensity of the ArI emission line with respect to the slit width of the exit slit (52) is constant. The integrated intensity was determined by subtracting the intensity. FIG. 7 shows the material (1) obtained from the emission spectrum image of FIG.
FIG. 2 illustrates a two-dimensional intensity distribution of an ArI emission line spectrum at a position 6 mm in height from 2). Next, this two-dimensional intensity distribution is converted into a local intensity distribution by performing an Abel transform, and further, a two-dimensional temperature distribution is obtained assuming that the plasma is in a local thermal equilibrium state. Three-dimensional temperature distribution was analyzed by performing at each position in the beam axis direction. The time required for this analysis was about 10 ms. FIGS. 8 and 9 show examples of the obtained two-dimensional temperature distribution and three-dimensional temperature distribution, respectively.
A very accurate two-dimensional or three-dimensional temperature distribution can be obtained even in an extremely short time of 0 ms.

By photographing such a temperature distribution at a high speed at intervals of about 10 ms, it is possible to obtain a temporal variation of the plasma temperature distribution with a high temporal resolution.
Of course, the present invention is not limited to the above-described example, and it goes without saying that various aspects are possible in detail.

[0030]

As described in detail above, the present invention provides
It is possible to measure the temperature distribution of the plasma with rapid time variation two-dimensionally and three-dimensionally, in a very short time and accurately, and it is very useful for basic analysis of plasma formation phenomena, Since the temperature distribution can be monitored with high time resolution, it can be effectively used as a control signal for positively controlling the plasma.

[Brief description of the drawings]

FIG. 1 is a main part configuration diagram showing an example of a measurement configuration according to a plasma temperature distribution measurement method of the present invention or a measuring apparatus of the present invention.

FIG. 2 is a main configuration diagram showing an example of a spectroscope.

FIG. 3 is a main part configuration diagram showing another example of a measurement configuration according to the plasma temperature distribution measurement method of the present invention or a measuring apparatus of the present invention.

FIGS. 4 (a) and 4 (b) are photographs instead of drawings showing examples of a plasma image and a bright line spectrum image, respectively.

FIG. 5 is a diagram illustrating a relationship between a wavelength and a relative intensity of a bright line spectrum;

FIG. 6 is a diagram illustrating the relationship between the exit slit width and the relative intensity of the ArI emission line spectrum.

FIG. 7 is a diagram showing an example of a two-dimensional intensity distribution of an ArI emission line spectrum.

FIG. 8 is a diagram showing an example of a two-dimensional temperature distribution of plasma.

FIG. 9 is a diagram showing an example of a three-dimensional temperature distribution of plasma.

FIG. 10 is a conceptual diagram showing an example of generation of plasma by laser irradiation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma image 2 Chromatic aberration correction lens 3 Beam splitter 4 Reflecting mirror 5 Spectroscope 51 Incident slit 52 Exit slit 53 Concave mirror 54 Planar mirror 55 Grating 56 Concave mirror 6 Ejection lens 7 Image intensifier 8 CCD camera 9 Computer 10 Plasma 11 Laser 12 Material 13 Electric lens system 14 Chromatic aberration correction lens 15 Pinhole 16 Field lens

Claims (12)

(57) [Claims] 1. A method for measuring a temperature distribution of a plasma, wherein, among parallel component lights emitted from the plasma, an emission line spectrum emitted by excited atoms or ions of a plasma constituent element is taken out using a spectroscope, and Bright line spec
Imaging the bright line spectrum image composed only vector,
A plasma temperature distribution measuring method, wherein a plasma temperature distribution is calculated from the intensity distribution of the bright line spectrum image. 2. The plasma temperature distribution measuring method according to claim 1, wherein the temperature distribution is calculated from the intensity distribution of the emission line spectrum image using an absolute intensity method. 3. The parallel component light emitted from the plasma is divided into a plurality of parallel component lights, and among these parallel component lights, emission lines composed of emission line spectra having different wavelengths emitted by excited atoms or ions of the plasma constituent elements. 2. The plasma temperature distribution measuring method according to claim 1, wherein a spectrum image is simultaneously obtained, and a plasma temperature distribution is calculated from a relative ratio of the intensity at each position in each of these bright line spectrum images. 4. The plasma temperature distribution measuring method according to claim 3, wherein a temperature distribution is calculated from a relative ratio of intensity using a relative intensity method. 5. Using a chromatic aberration correcting lens and a set of slits or pinholes orthogonal to each other, a plasma image incident on the chromatic aberration correcting lens is converted to a set of orthogonal slits or a pair of slits arranged at the focal point of the chromatic aberration correcting lens. 5. The method of measuring a plasma temperature distribution according to claim 1, wherein parallel component light emitted from the plasma is extracted by being incident on a pinhole. 6. The method according to claim 1, wherein a bright line spectrum image is taken.
Any one of the plasma temperature distribution measuring methods according to any one of the first to fifth aspects. 7. An apparatus for measuring a temperature distribution of plasma, comprising: a parallel component light extracting means, an emission line spectrum extracting means .
Spectrometer and, bright line spectrum image acquiring means, and calculating means are provided, parallel component light is taken out of the light emitting from the plasma by parallel component light extraction means, a plasma constituent elements than <br/> spectroscope The emission line spectrum emitted by the excited atoms or ions is extracted from the parallel component light,
A plasma temperature distribution measuring apparatus characterized in that a bright line spectrum image composed of only a bright line spectrum is obtained by a bright line spectrum image acquiring means and a plasma temperature distribution is calculated from an intensity distribution of the bright line spectrum image by an arithmetic means. 8. The plasma temperature distribution measuring apparatus according to claim 7 , wherein the temperature distribution is calculated from the intensity distribution of the emission line spectrum image using an absolute intensity method. 9. A splitting means is provided, the splitting means splits parallel component light emitted from plasma into a plurality of pieces, and radiates by one or more emission line spectrum extracting means by excited atoms or ions of plasma constituent elements. Each of the emission line spectra having different wavelengths is separately extracted from each parallel component light, and an emission line spectrum image composed of each emission line spectrum is obtained at the same time by one or more emission line spectrum image obtaining means. 8. The plasma temperature distribution measuring apparatus according to claim 7 , wherein the temperature distribution of the plasma is calculated from the relative ratio of the intensity at each position in each of the bright line spectrum images. 10. The plasma temperature distribution measuring apparatus according to claim 9 , wherein a temperature distribution is calculated from a relative ratio of intensity using a relative intensity method. 11. A chromatic aberration correcting lens and a pair of slits or pinholes orthogonal to each other are provided as parallel component light extracting means, and a plasma image incident on the chromatic aberration correcting lens is arranged at a focal point of the chromatic aberration correcting lens. The plasma temperature distribution measuring apparatus according to any one of claims 7 to 10 , wherein the laser beam is incident on a pair of slits or pinholes orthogonal to each other and a parallel component light of the plasma image is extracted. 12. Any of the plasma temperature distribution measurement apparatus of claims 7 imaging means is provided for imaging a line spectrum image 11.