CA1232469A - Method of laser emission spectroscopical analysis and apparatus therefor - Google Patents
Method of laser emission spectroscopical analysis and apparatus thereforInfo
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- CA1232469A CA1232469A CA000470412A CA470412A CA1232469A CA 1232469 A CA1232469 A CA 1232469A CA 000470412 A CA000470412 A CA 000470412A CA 470412 A CA470412 A CA 470412A CA 1232469 A CA1232469 A CA 1232469A
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- spectral line
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Abstract
ABSTRACT OF THE DISCLOSURE
In a method of laser emission spectroscopically analysis, wherein a light emitted from the surface of a sample when a laser beam is irradiated onto the surface of the sample is spectroscopically analyzed, an emission mode of the laser beam is fixed to a gauss distribution type Temoo mode to avoid variations in an intensity distribution due to a change in mode, and an analyzed value is obtained from an intensity of a spectral line of an element to be measured when an intensity of a preset spectral line or an intensity ratio between a pair of preset spectral lines is within a predetermined range, so that the influence of wide fluctuations in an evaporation and an excitation processes occurring on the surface of the sample can be eliminated, thereby improving the accuracy of analysis.
In a method of laser emission spectroscopically analysis, wherein a light emitted from the surface of a sample when a laser beam is irradiated onto the surface of the sample is spectroscopically analyzed, an emission mode of the laser beam is fixed to a gauss distribution type Temoo mode to avoid variations in an intensity distribution due to a change in mode, and an analyzed value is obtained from an intensity of a spectral line of an element to be measured when an intensity of a preset spectral line or an intensity ratio between a pair of preset spectral lines is within a predetermined range, so that the influence of wide fluctuations in an evaporation and an excitation processes occurring on the surface of the sample can be eliminated, thereby improving the accuracy of analysis.
Description
:~32~
Method OF LASER EMISSION SPECTROSCOPICALLY ANALYSIS
AND APPARATUS THEREFORE
BACKGROUND OF THE INVENTION
_ _ _ _ 1. Field of the Invention This invention relates to a method of laser emission spectroscopically analysis and an apparatus therefore and more particularly to improvements in a method of laser emission spectroscopically analysis and an apparatus therefore wherein a light emitted from the surface of a sample when a laser beam irradiates the surface of the sample is spectroscopically analyzed, and which are suitable for use in direct analysis of hot metal, molten steel, slag and the like.
Method OF LASER EMISSION SPECTROSCOPICALLY ANALYSIS
AND APPARATUS THEREFORE
BACKGROUND OF THE INVENTION
_ _ _ _ 1. Field of the Invention This invention relates to a method of laser emission spectroscopically analysis and an apparatus therefore and more particularly to improvements in a method of laser emission spectroscopically analysis and an apparatus therefore wherein a light emitted from the surface of a sample when a laser beam irradiates the surface of the sample is spectroscopically analyzed, and which are suitable for use in direct analysis of hot metal, molten steel, slag and the like.
2. Description of the Prior Art With the progress of the laser technique, in various fields, there have been seen such an attempt that the laser may be utilized as a source of excitation to conduct an emission spectroscopically analysis. More specifically, when a powerful laser beam adapted to take the focus on the surface of a sample by a focusing lens having a suitable focal length irradiates the surface of the sample, a surface layer is rapidly heated.
Particularly, if the laser beam is formed into pulse shapes of several ten nanosecond, then such conditions occur that energy is locally poured into the sample before heat is diffused in the sample, whereby melting and evaporation occur. Vapor is further excited by the laser beam to be formed into plasma which emits a light. According to the method of laser emission -- .,~, j ,.
spectroscopically analysis, this light is transmitted to a spectroscopes by means of a suitable light introducing system, spectrally separated by a diffraction grating and the like and formed into spectra, and thereafter, detected by a photographic film, a ph~tomultiplier tube; a photo-diode and the like, whereby contents of aimed elements are determined. This method has such outstanding characteristic features that this method is also applicable to non-electrically conductive materials, can make analysis in atmosphere and so on. However, this method has been disadvantageous in that variations in data are high and the accuracy of analysis is unsatisfactory. The major cause is generally considered to reside in the variations in the output intensity of the laser, with the result that such a method has been normally adopted that the intensity of laser is constantly monitored by a suitable method and data are normally collected only within a predetermined range. However, this method has been disadvantageous in that it is impossible to cope up with changes in the distribution of the intensities of laser beams and the adverse influence of the variations in the evaporation and excitation processes due to the contour of the surface of the sample and also due to the presence of contaminations, an oxide layer and the like cannot be removed.
SUMMARY OF TOE INVENTION
._ The present invention has been developed to obviate the above-described disadvantages of the prior art and has as its object the provision of a method of laser emission spectroscopically analysis and an apparatus therefore wherein an analysis can be conducted with high accuracy irrespective of variations in the output intensity of laser and the like.
According to the present invention, there is pro-voided a method of laser emission spectroscopically analysis, wherein light emitted from a surface of a sample when a pulsed laser beam irradiates the surface of the sample is spectra-scopically analyzed, characterized in that said method in-eludes the steps of:
(i) fixing the emission mode of the laser beam to lo a gauss distribution type Tempo mode; and (ii) measuring the spectral line intensity of a sample element only when the intensity ratio between a pair of preset spectral lines in the light emitted from the sample is within a preset range.
The present invention has been achieved on the basis of the results of survey made by the present inventors on variations in intensity of spectral line, which variations are regarded as a drawback in the laser emission spectra-scopical analysis. More specifically, the followings were clearly known by the survey made by the present inventors.
(1) If an output from a laser oscillator is increased, then the coefficient of variation (one obtained by dividing a standard deviation by a mean value) of the intensity of a spectral line decreases. However, if an amplifier is positioned in a stage posterior to the laser oscillator and the output is further increased, then the coefficient of variation of the intensity of the spectral line increases, to the contrary.
(2) When the amplifier is not used and a laser beam is obtained only by a laser oscillator, the variations of the intensity of spectral line is higher than the variations of the output of laser.
According to the present invention, there is also :~23'~
provided an apparatus for 'maser emission spectroscopically analysis, comprising:
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type O O;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally sepal rating light emitted from the surface of said sample;
a monitoring light detecting means for measuring the intensity of a preset spectral line in the light emit-ted from the sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
: 20 a spectral line intensity monitor for determine in whether the intensity of the preset spectral line in the light emitted from said sample is within a preset range in accordance with an output from said monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity of the preset spectral line in the light from said sample is within the preset range; and an indicating means for obtaining and indicating a measurement of the output of said measuring light detect tying means, when said gate means is opened.
According to the invention, there is also pro-voided an apparatus for laser emission spectroscopically analysis, comprising:
. . .
..... Jo I
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto the surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
dual monitoring light detecting means for measuring the intensities of a pair of preset spectral lines in the light emitted from the sample a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determine in whether the intensity ratio between the preset spectral lines in the light emitted from said sample is within a preset range in accordance with the output of the monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity ratio between . the pair of preset spectral lines in the light from said sample is within the preset range; and an indicating means for measuring and indicating the output of said measuring light detecting means, when said gate means is opened.
BRIEF DESCRIPTION OF THE DRAWINGS
The exact nature of this invention, as well as other objects and advantages thereof, will be readily apparent from consideration of the following specification -pa-.....
I, .~: , ,.
~23~
relating to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof and wherein:
Fig. 1 is a chart showing the relationship between the laser output and 271.4 nanometer wavelength Fe spectral line intensity;
Fig. 2 is a chart showing a comparison between the laser output, the coefficient of variation of the laser out-put and the coefficient of variation of 271.4 nanometer wavelength Fe spectral line intensity;
Fig. 3 is a block diagram showing the arrangement of one embodiment of the laser emission spectroscopically analysis, in which is adopted the method of laser emission spectroscopically analysis according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Figs. 1 and 2 show the results of experiments.
The sample used in the experiments was an Fe alloy. As the laser beam, an infrared laser having a wavelength of 1.06 micrometer and a pulse width of 15 nanosecond was used. As apparent from Fig. 1, when the output of laser exceeds an output 2 joule obtained through the utilization of an amply-lien, the coefficient of variation suddenly increases. The cause is considered to reside in the intensity distribution of laser pulses. More specifically, in general, in the intensity distribution (mode) of a laser beam emitted from a laser oscillator in the direction of vertical section, there are various symmetries. When such a high output as used in the emission spectroscopically analysis is required, there is adopted a multi-mode oscillation in which modes are changed over from one to another per pulse. However, if an amplifier is actuated when peaks of several intensity distributions are present in a beam as described above, then - 4b -"
UP
a specified peak becomes amplified preferentially. In consequence, if the laser beam having the above-described intensity distributions is converged onto the surface of the sample, then, in the spot caliber thereon, a zone of a high irradiation density occurs locally. Since such wide flue-tuitions in the irradiation density are varied from a pulse to another, the intensities of emission spectra are varied.
Then, the present inventors thought of also fixing the laser beam used in the emission spectroscopically analysis to the ox I/
- 4c -:~32~
mode in which the gauss distribution type output is obtainable through the utilization of a mode lock method used in the holography and the like. Although Timely mode and the like in which an annular distribution is obtainable may be utilized as such a mode described above, it is considered that the gauss distribution is most suitable for the emission spectroscopically analysis. Additionally, if the mode lock is adopted, the laser output decreases. However, an output of the laser oscillator is increased and another amplifier is added for use, so that this decrease in the laser output can be made up for. Needless to say, when the laser beam is fixed to Tempo mode, even if the amplifier is utilized, the mode is not changed.
On the other hand, Fig. 2 shows a comparison between the coefficient of variation (solid line A) of 271.4 nanometer wavelength Fe spectral line intensity and the coefficient of variation (solid line B) of the laser output when a laser beam identical with that shown in Fig. l irradiates an Fe alloy. In spite of non-use of the amplifier, the variations in intensity of spectral line are larger than the width of variation of the laser output. The above-described variation in intensity of emission spectra can ye improved by the aforesaid mode lock. In addition to this, the influences of wide fluctuations in an evaporation and an excitation processes occurring on the surface of the sample during the irradiation of laser cannot be disregarded. Since the latter cannot be removed only by controlling the laser output and the mode, it has been thought of that, in the case of a predetermined spectral line such as an 1 I.
Fe alloy which is obtainable during the irradiation of laser, one or two of Fe spectral lines each having a suitable wavelength are selected, the intensity or the intensity ratio thereof is constantly monitored, and the spectral line intensity of an aimed element to be measured is read only within the preset variation range. Particularly, the letter method of regulating the intensity ratio can restrict the temperature of the plasma produced by the irradiation of laser, thus being effective in improving the accuracy of analysis.
The present invention has been attained on the basis of the above-described knowledge.
According to the present invention, an analysis with high accuracy can be conducted irrespective of the variations in the laser output intensity and the like.
While 13.0 % was obtained when the coefficient of variation of the spectral line intensity measured according to the conventional method in measuring So spectral line intensity of 288.2 nanometer wavelength in an Fe alloy, the coefficient of variation was improved to 9.0 % when the laser output was fixed to Tempo mode. Further, according to the present invention, the laser output was fixed to Tempo mode, and only when the 271.4 nanometer wavelength Fe spectral line intensity being monitored was within the range of plus-minus 5 % of a predetermined value, 288.2 nanometer wavelength So spectral line intensity was read, then 7.3 % was obtained. Furthermore, also, according to the present invention, the laser output was fixed to Tempo mode, two Fe spectral lines of 271.4 nanometer wavelength and 273.1 ~3;2 nanometer wavelength were monitored, and So spectral line intensity was read when the intensity ratio thereof was within the range of plus-minus 5 of a predetermined value, then 5.9 was obtained. It was ascertained that, in the cases of the both methods as described above, the coefficient of variation in the spectral line intensity became small as compared with the case of the conventional method or the case of only fixing the laser output to Tempo mode.
/
/
.'~71 .~, owe Detailed description will hereunder be given of one embodiment of the apparatus of laser emission spectroscopically analysis, in which is adopted the method of laser emission spectroscopically analysis according to the present invention with reference to the drawings.
As shown in Fig 3, this embodiment comprises:
a laser oscillator 10 assembled whereinto with a mechanism for the mode lock, not shown, for oscillating a laser beam;
an oscillator power source 11 for driving the laser oscillator 10;
a power source 12 of a high speed switching element, for actuating a high speed switching element not shown, assembled into the laser oscillator 10;
an up collimator 13 for expanding a beam caliber of a laser beam oscillated from the laser oscillator 10;
an amplifier 14 for amplifying the laser beam emitted from the up collimator 13;
an amplifier power source 15 for driving the amplifier 14;
a rectangular prism 16 for changing a direction of irradiation of the laser beam emitted from the amplifier 14;
a focusing lens 18 for converging the laser beam onto the surface of a sample 20;
a spectroscopes optical system 24 formed of a concave mirror for example, for forming an image of a light emitted by the irradiation of laser from the surface of the sample 20 directed in a predetermined direction relative to the laser beam at an inlet slit 26 of a spectroscopes 22;
~3~รง9 the electroscope 22 for separating the light emitted from the sample 20 whose image is formed Nat the inlet slit 26 into spectral lines by a diffraction grating and the like;
one or two monitoring light detectors 28 for detecting the intensity of a spectral line having a wavelength for monitoring out of the spectral lines separated by the spectroscopes 22 to convert the same into an electric signal;
a measuring light detector 30 for detecting the intensity of a spectral line of an element to be measured to convert the same into an electric signal;
a spectral line intensity monitor 32 for detecting whether an intensity of a preset spectral line or an intensity ratio : between a pair of preset spectral lines in the light emitted from the sample is within a preset range in accordance with an ; 15 output from the light detector 28 for monitoring;
a gate circuit 34 to be opened by the spectral line intensity monitor 32 when the intensity of the preset spectral line or the intensity ratio between the pair of preset spectral lines in the light emitted from the sample is within the preset range; and an indication section 36 for obtaining a measured value from an output of the light detector 30 for measuring, when the gate circuit 34 is opened, to indicate the same.
As the laser oscillator 10, a ruby laser having a wavelength of 0.69 micrometer or an infrared laser having a wavelength of 1.05 to 1.06 micrometer, for example.
To control the density of laser so as to less than a ~2~4~P~
predetermined value, a laser substance used in the amplifier 14 is larger in caliber than that of the laser oscillator 10. The up collimator 13 is used to offset the differences in caliber of these laser substances.
The rectangular prism 16 is used to cause the laser to irradiate the surface of the sample 20 at an angle of a predetermined value, and, when a laser emission section including a laser oscillator 10 is provided in a predetermined direction from the beginning, the rectangular prism 16 can be dispensed with.
Description will now be given of action.
Firstly, electric energy accumulated in the power source 11 for the oscillator and a power source 15 for the amplifier is transmitted to the laser substances in the laser oscillator 10 and the amplifier 14 to excite the both laser substances. When the energy of a predetermined value is accumulated in the laser substance of the laser oscillator 10, a signal is delivered to the power source 12 for the high speed switching element to actuate the same, and the energy accumulated in the laser oscillator 10 is released at once. The mode lock mechanism is assembled into the laser oscillator 10, and the released pulse-shaped laser beam is formed into the gauss distribution type Tempo mode. The laser beam oscillated from the laser oscillator 10 falls into the amplifier 14 through the up collimator 13. Then, the energy accumulated in this amplifier 14 is also released in a moment, whereby the laser beam is further intensified. The powerful laser pulses thus obtained so . I-:~3~4~
are converged onto the surface of the sample 20 through the rectangular prism 16 and the focusing lens I Then, the surface of the sample 20 is locally heated for a short period of time to thereby be formed into a plasma. At this time, the light emitted from the plasma is led to the spectroscopes 22 by the spectroscopes optical system 24, and dispersed by the diffraction grating and the like of the spectroscopes 22. Out of dispersed lights, a spectral line having a specified wavelength for monitoring is detected by the monitoring light detector 28, and in the spectra] line intensity monitor 32, it is detected whether the intensity of the preset spectral line or the intensity ratio of the pair of preset spectral lines is within the preset range or not. Only when the intensity of the spectral line or the intensity ratio is within the preset range, the gate circuit 34 is opened, and an output from the measuring light detector 30 which has received the spectral line of the ; element to be measured is delivered to the indication section 36, where the result of measurement is indicated. The intensity of the spectral line of the element to be measured thus obtained is data processed by an ordinary method.
Particularly, if the laser beam is formed into pulse shapes of several ten nanosecond, then such conditions occur that energy is locally poured into the sample before heat is diffused in the sample, whereby melting and evaporation occur. Vapor is further excited by the laser beam to be formed into plasma which emits a light. According to the method of laser emission -- .,~, j ,.
spectroscopically analysis, this light is transmitted to a spectroscopes by means of a suitable light introducing system, spectrally separated by a diffraction grating and the like and formed into spectra, and thereafter, detected by a photographic film, a ph~tomultiplier tube; a photo-diode and the like, whereby contents of aimed elements are determined. This method has such outstanding characteristic features that this method is also applicable to non-electrically conductive materials, can make analysis in atmosphere and so on. However, this method has been disadvantageous in that variations in data are high and the accuracy of analysis is unsatisfactory. The major cause is generally considered to reside in the variations in the output intensity of the laser, with the result that such a method has been normally adopted that the intensity of laser is constantly monitored by a suitable method and data are normally collected only within a predetermined range. However, this method has been disadvantageous in that it is impossible to cope up with changes in the distribution of the intensities of laser beams and the adverse influence of the variations in the evaporation and excitation processes due to the contour of the surface of the sample and also due to the presence of contaminations, an oxide layer and the like cannot be removed.
SUMMARY OF TOE INVENTION
._ The present invention has been developed to obviate the above-described disadvantages of the prior art and has as its object the provision of a method of laser emission spectroscopically analysis and an apparatus therefore wherein an analysis can be conducted with high accuracy irrespective of variations in the output intensity of laser and the like.
According to the present invention, there is pro-voided a method of laser emission spectroscopically analysis, wherein light emitted from a surface of a sample when a pulsed laser beam irradiates the surface of the sample is spectra-scopically analyzed, characterized in that said method in-eludes the steps of:
(i) fixing the emission mode of the laser beam to lo a gauss distribution type Tempo mode; and (ii) measuring the spectral line intensity of a sample element only when the intensity ratio between a pair of preset spectral lines in the light emitted from the sample is within a preset range.
The present invention has been achieved on the basis of the results of survey made by the present inventors on variations in intensity of spectral line, which variations are regarded as a drawback in the laser emission spectra-scopical analysis. More specifically, the followings were clearly known by the survey made by the present inventors.
(1) If an output from a laser oscillator is increased, then the coefficient of variation (one obtained by dividing a standard deviation by a mean value) of the intensity of a spectral line decreases. However, if an amplifier is positioned in a stage posterior to the laser oscillator and the output is further increased, then the coefficient of variation of the intensity of the spectral line increases, to the contrary.
(2) When the amplifier is not used and a laser beam is obtained only by a laser oscillator, the variations of the intensity of spectral line is higher than the variations of the output of laser.
According to the present invention, there is also :~23'~
provided an apparatus for 'maser emission spectroscopically analysis, comprising:
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type O O;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally sepal rating light emitted from the surface of said sample;
a monitoring light detecting means for measuring the intensity of a preset spectral line in the light emit-ted from the sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
: 20 a spectral line intensity monitor for determine in whether the intensity of the preset spectral line in the light emitted from said sample is within a preset range in accordance with an output from said monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity of the preset spectral line in the light from said sample is within the preset range; and an indicating means for obtaining and indicating a measurement of the output of said measuring light detect tying means, when said gate means is opened.
According to the invention, there is also pro-voided an apparatus for laser emission spectroscopically analysis, comprising:
. . .
..... Jo I
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto the surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
dual monitoring light detecting means for measuring the intensities of a pair of preset spectral lines in the light emitted from the sample a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determine in whether the intensity ratio between the preset spectral lines in the light emitted from said sample is within a preset range in accordance with the output of the monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity ratio between . the pair of preset spectral lines in the light from said sample is within the preset range; and an indicating means for measuring and indicating the output of said measuring light detecting means, when said gate means is opened.
BRIEF DESCRIPTION OF THE DRAWINGS
The exact nature of this invention, as well as other objects and advantages thereof, will be readily apparent from consideration of the following specification -pa-.....
I, .~: , ,.
~23~
relating to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof and wherein:
Fig. 1 is a chart showing the relationship between the laser output and 271.4 nanometer wavelength Fe spectral line intensity;
Fig. 2 is a chart showing a comparison between the laser output, the coefficient of variation of the laser out-put and the coefficient of variation of 271.4 nanometer wavelength Fe spectral line intensity;
Fig. 3 is a block diagram showing the arrangement of one embodiment of the laser emission spectroscopically analysis, in which is adopted the method of laser emission spectroscopically analysis according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Figs. 1 and 2 show the results of experiments.
The sample used in the experiments was an Fe alloy. As the laser beam, an infrared laser having a wavelength of 1.06 micrometer and a pulse width of 15 nanosecond was used. As apparent from Fig. 1, when the output of laser exceeds an output 2 joule obtained through the utilization of an amply-lien, the coefficient of variation suddenly increases. The cause is considered to reside in the intensity distribution of laser pulses. More specifically, in general, in the intensity distribution (mode) of a laser beam emitted from a laser oscillator in the direction of vertical section, there are various symmetries. When such a high output as used in the emission spectroscopically analysis is required, there is adopted a multi-mode oscillation in which modes are changed over from one to another per pulse. However, if an amplifier is actuated when peaks of several intensity distributions are present in a beam as described above, then - 4b -"
UP
a specified peak becomes amplified preferentially. In consequence, if the laser beam having the above-described intensity distributions is converged onto the surface of the sample, then, in the spot caliber thereon, a zone of a high irradiation density occurs locally. Since such wide flue-tuitions in the irradiation density are varied from a pulse to another, the intensities of emission spectra are varied.
Then, the present inventors thought of also fixing the laser beam used in the emission spectroscopically analysis to the ox I/
- 4c -:~32~
mode in which the gauss distribution type output is obtainable through the utilization of a mode lock method used in the holography and the like. Although Timely mode and the like in which an annular distribution is obtainable may be utilized as such a mode described above, it is considered that the gauss distribution is most suitable for the emission spectroscopically analysis. Additionally, if the mode lock is adopted, the laser output decreases. However, an output of the laser oscillator is increased and another amplifier is added for use, so that this decrease in the laser output can be made up for. Needless to say, when the laser beam is fixed to Tempo mode, even if the amplifier is utilized, the mode is not changed.
On the other hand, Fig. 2 shows a comparison between the coefficient of variation (solid line A) of 271.4 nanometer wavelength Fe spectral line intensity and the coefficient of variation (solid line B) of the laser output when a laser beam identical with that shown in Fig. l irradiates an Fe alloy. In spite of non-use of the amplifier, the variations in intensity of spectral line are larger than the width of variation of the laser output. The above-described variation in intensity of emission spectra can ye improved by the aforesaid mode lock. In addition to this, the influences of wide fluctuations in an evaporation and an excitation processes occurring on the surface of the sample during the irradiation of laser cannot be disregarded. Since the latter cannot be removed only by controlling the laser output and the mode, it has been thought of that, in the case of a predetermined spectral line such as an 1 I.
Fe alloy which is obtainable during the irradiation of laser, one or two of Fe spectral lines each having a suitable wavelength are selected, the intensity or the intensity ratio thereof is constantly monitored, and the spectral line intensity of an aimed element to be measured is read only within the preset variation range. Particularly, the letter method of regulating the intensity ratio can restrict the temperature of the plasma produced by the irradiation of laser, thus being effective in improving the accuracy of analysis.
The present invention has been attained on the basis of the above-described knowledge.
According to the present invention, an analysis with high accuracy can be conducted irrespective of the variations in the laser output intensity and the like.
While 13.0 % was obtained when the coefficient of variation of the spectral line intensity measured according to the conventional method in measuring So spectral line intensity of 288.2 nanometer wavelength in an Fe alloy, the coefficient of variation was improved to 9.0 % when the laser output was fixed to Tempo mode. Further, according to the present invention, the laser output was fixed to Tempo mode, and only when the 271.4 nanometer wavelength Fe spectral line intensity being monitored was within the range of plus-minus 5 % of a predetermined value, 288.2 nanometer wavelength So spectral line intensity was read, then 7.3 % was obtained. Furthermore, also, according to the present invention, the laser output was fixed to Tempo mode, two Fe spectral lines of 271.4 nanometer wavelength and 273.1 ~3;2 nanometer wavelength were monitored, and So spectral line intensity was read when the intensity ratio thereof was within the range of plus-minus 5 of a predetermined value, then 5.9 was obtained. It was ascertained that, in the cases of the both methods as described above, the coefficient of variation in the spectral line intensity became small as compared with the case of the conventional method or the case of only fixing the laser output to Tempo mode.
/
/
.'~71 .~, owe Detailed description will hereunder be given of one embodiment of the apparatus of laser emission spectroscopically analysis, in which is adopted the method of laser emission spectroscopically analysis according to the present invention with reference to the drawings.
As shown in Fig 3, this embodiment comprises:
a laser oscillator 10 assembled whereinto with a mechanism for the mode lock, not shown, for oscillating a laser beam;
an oscillator power source 11 for driving the laser oscillator 10;
a power source 12 of a high speed switching element, for actuating a high speed switching element not shown, assembled into the laser oscillator 10;
an up collimator 13 for expanding a beam caliber of a laser beam oscillated from the laser oscillator 10;
an amplifier 14 for amplifying the laser beam emitted from the up collimator 13;
an amplifier power source 15 for driving the amplifier 14;
a rectangular prism 16 for changing a direction of irradiation of the laser beam emitted from the amplifier 14;
a focusing lens 18 for converging the laser beam onto the surface of a sample 20;
a spectroscopes optical system 24 formed of a concave mirror for example, for forming an image of a light emitted by the irradiation of laser from the surface of the sample 20 directed in a predetermined direction relative to the laser beam at an inlet slit 26 of a spectroscopes 22;
~3~รง9 the electroscope 22 for separating the light emitted from the sample 20 whose image is formed Nat the inlet slit 26 into spectral lines by a diffraction grating and the like;
one or two monitoring light detectors 28 for detecting the intensity of a spectral line having a wavelength for monitoring out of the spectral lines separated by the spectroscopes 22 to convert the same into an electric signal;
a measuring light detector 30 for detecting the intensity of a spectral line of an element to be measured to convert the same into an electric signal;
a spectral line intensity monitor 32 for detecting whether an intensity of a preset spectral line or an intensity ratio : between a pair of preset spectral lines in the light emitted from the sample is within a preset range in accordance with an ; 15 output from the light detector 28 for monitoring;
a gate circuit 34 to be opened by the spectral line intensity monitor 32 when the intensity of the preset spectral line or the intensity ratio between the pair of preset spectral lines in the light emitted from the sample is within the preset range; and an indication section 36 for obtaining a measured value from an output of the light detector 30 for measuring, when the gate circuit 34 is opened, to indicate the same.
As the laser oscillator 10, a ruby laser having a wavelength of 0.69 micrometer or an infrared laser having a wavelength of 1.05 to 1.06 micrometer, for example.
To control the density of laser so as to less than a ~2~4~P~
predetermined value, a laser substance used in the amplifier 14 is larger in caliber than that of the laser oscillator 10. The up collimator 13 is used to offset the differences in caliber of these laser substances.
The rectangular prism 16 is used to cause the laser to irradiate the surface of the sample 20 at an angle of a predetermined value, and, when a laser emission section including a laser oscillator 10 is provided in a predetermined direction from the beginning, the rectangular prism 16 can be dispensed with.
Description will now be given of action.
Firstly, electric energy accumulated in the power source 11 for the oscillator and a power source 15 for the amplifier is transmitted to the laser substances in the laser oscillator 10 and the amplifier 14 to excite the both laser substances. When the energy of a predetermined value is accumulated in the laser substance of the laser oscillator 10, a signal is delivered to the power source 12 for the high speed switching element to actuate the same, and the energy accumulated in the laser oscillator 10 is released at once. The mode lock mechanism is assembled into the laser oscillator 10, and the released pulse-shaped laser beam is formed into the gauss distribution type Tempo mode. The laser beam oscillated from the laser oscillator 10 falls into the amplifier 14 through the up collimator 13. Then, the energy accumulated in this amplifier 14 is also released in a moment, whereby the laser beam is further intensified. The powerful laser pulses thus obtained so . I-:~3~4~
are converged onto the surface of the sample 20 through the rectangular prism 16 and the focusing lens I Then, the surface of the sample 20 is locally heated for a short period of time to thereby be formed into a plasma. At this time, the light emitted from the plasma is led to the spectroscopes 22 by the spectroscopes optical system 24, and dispersed by the diffraction grating and the like of the spectroscopes 22. Out of dispersed lights, a spectral line having a specified wavelength for monitoring is detected by the monitoring light detector 28, and in the spectra] line intensity monitor 32, it is detected whether the intensity of the preset spectral line or the intensity ratio of the pair of preset spectral lines is within the preset range or not. Only when the intensity of the spectral line or the intensity ratio is within the preset range, the gate circuit 34 is opened, and an output from the measuring light detector 30 which has received the spectral line of the ; element to be measured is delivered to the indication section 36, where the result of measurement is indicated. The intensity of the spectral line of the element to be measured thus obtained is data processed by an ordinary method.
Claims (7)
1. A method of laser emission spectroscopical analysis, wherein light emitted from a surface of a sample when a pulsed laser beam irradiates the surface of the sample is spectroscopically analyzed, characterized in that the said method includes the steps of:
fixing the emission mode of the laser beam to a gauss distribution type TEM00 mode; and measuring the spectral line intensity of a sample element only when the intensity ratio between a pair of preset spectral lines in the light emitted from the sample is within a preset range.
fixing the emission mode of the laser beam to a gauss distribution type TEM00 mode; and measuring the spectral line intensity of a sample element only when the intensity ratio between a pair of preset spectral lines in the light emitted from the sample is within a preset range.
2. A method of laser emission spectroscopical analysis as set forth in claim 1, wherein said preset spec-tral line is a 271.4 nanometer wavelength Fe spectral line.
3. A method of laser emission spectroscopical analysis as set forth in claim 1, wherein said pair of preset spectral lines are two Fe spectral lines of 271.4 nanometer and 273.1 nanometer wavelengths.
4. An apparatus for laser emission spectro-scopical analysis, comprising:
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type TEM00;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
a monitoring light detecting means for measuring the intensity of a preset spectral line in the light emitt-ed from said sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determi-ning whether the intensity of the preset spectral line in the light emitted from said sample is within a preset range in accordance with an output from said monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity of the preset spectral line in the light from said sample is within the preset range; and an indicating means for obtaining and indicating a measurement of the output of said measuring light detec-ting means, when said gate means is opened.
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type TEM00;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
a monitoring light detecting means for measuring the intensity of a preset spectral line in the light emitt-ed from said sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determi-ning whether the intensity of the preset spectral line in the light emitted from said sample is within a preset range in accordance with an output from said monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity of the preset spectral line in the light from said sample is within the preset range; and an indicating means for obtaining and indicating a measurement of the output of said measuring light detec-ting means, when said gate means is opened.
5. An apparatus for laser emission spectrosco-pical analysis as set forth in claim 4, wherein said laser oscillating means is a ruby laser or an infrared, into which a mechanism for mode lock is assembled.
6. An apparatus for laser emission spectrosco-pical analysis as set forth in claim 4, wherein a laser substance used in said amplifying means is larger in caliber than that used in the said laser oscillating means, and an up collimator for offsetting said difference in caliber between the laser substances is used.
7. An apparatus for laser emission spectrosco-pical analysis, comprising:
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type TEM00;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
dual monitoring light detecting means for mea-suring the intensities of a pair of preset spectral lines in the light emitted from said sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determin-ing whether the intensity ratio between the preset spectral lines in the light emitted from said sample is within a preset range in accordance with the output of the monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity ratio between the pair of preset spectral lines in the light from said sample is within the preset range; and an indicating means for measuring and indicating the output of said measuring light detecting means, when said gate means is opened.
a laser oscillating means for oscillating a pulsed laser beam, wherein the emission mode of said laser oscillating means is fixed to a gauss distribution type TEM00;
an amplifying means for amplifying the laser beam oscillated from said laser oscillating means;
a focusing lens for focusing the laser beam emitted from said amplifying means onto a surface of a sample;
a spectral separating means for spectrally separating light emitted from the surface of said sample;
dual monitoring light detecting means for mea-suring the intensities of a pair of preset spectral lines in the light emitted from said sample;
a measuring light detecting means for measuring the intensity of a spectral line of a sample element and converting the spectral line into an electric signal;
a spectral line intensity monitor for determin-ing whether the intensity ratio between the preset spectral lines in the light emitted from said sample is within a preset range in accordance with the output of the monitoring light detecting means;
a gate means to be opened by said spectral line intensity monitor when the intensity ratio between the pair of preset spectral lines in the light from said sample is within the preset range; and an indicating means for measuring and indicating the output of said measuring light detecting means, when said gate means is opened.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000470412A CA1232469A (en) | 1984-12-18 | 1984-12-18 | Method of laser emission spectroscopical analysis and apparatus therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000470412A CA1232469A (en) | 1984-12-18 | 1984-12-18 | Method of laser emission spectroscopical analysis and apparatus therefor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1232469A true CA1232469A (en) | 1988-02-09 |
Family
ID=4129400
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000470412A Expired CA1232469A (en) | 1984-12-18 | 1984-12-18 | Method of laser emission spectroscopical analysis and apparatus therefor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1232469A (en) |
-
1984
- 1984-12-18 CA CA000470412A patent/CA1232469A/en not_active Expired
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