JP2018156904A - Mass spectrometer and mass spectrometry method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mass spectrometer and a mass spectrometry method, in which ionization probability of atoms ejected from a solid sample is improved.SOLUTION: A mass spectrometry method 20 includes: a vacuum chamber 22; a sample state 24 arranged in the vacuum chamber 22; an ion beam source 26 for discharging atoms by irradiating a solid sample X arranged on the sample stage 24 with an ion beam B; a laser light source 28 for passing laser light L1 over the irradiation region of the ion beam B of the solid sample X; a reflection mirror 30 which is arranged in the vacuum chamber 22, reflects the laser light L1 and overlaps the laser light L1 and reflection light L2 in the upper side of the irradiation region; and an analyzer 32 capable of analyzing the mass of atoms ionized by the laser light L1 and the reflection light L2.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a mass spectrometer and a mass spectrometry method.

  As an analysis method of trace elements, mass spectrometry (see, for example, Patent Document 1) is known. Since mass spectrometry measures the weight of atoms (atomic mass), it has the feature that isotope analysis is possible. As an application of this mass spectrometry, there is radioisotope analysis of nuclear fuel and nuclear waste.

  In general, since a radioactive element has a different half-life for each isotope, when the isotope ratio of the radioactive element contained in a sample is measured, it is possible to determine when it was generated. For example, in the case of radioactive material contamination caused by the accident at the Fukushima Daiichi nuclear power plant, there is no confirmation that the radioactive material originated from the nuclear accident just because the radioactive material was detected. This is because various radioactive elements exist thinly and widely due to fallout caused by past nuclear accidents and nuclear tests. However, even in the same radioisotope, the isotope ratio varies depending on the generation time. This is because the half-life is different for each isotope, and by using this fact, it is possible to determine when the radioactive substance was generated. However, it is actually difficult to distinguish from the fallout mentioned above.

  In view of this, the present inventors have developed an imaging mass spectrometer that can analyze components for each microparticle of several micrometers or less. Although an imaging mass spectrometer can perform isotope ratio analysis of individual particles, radioactive materials generally have a small abundance, and further enhancement of sensitivity is required.

  In conventional imaging mass spectrometers, atoms are released from the sample surface and ionized only by ion beam irradiation. In this case, the probability of ionization is at most several percent, and high sensitivity is required. There is a limit. Therefore, a method has been developed in which atoms emitted from the sample surface are irradiated with high-density laser light to be photoionized. This method is called sputtering neutral particle mass spectrometry (SNMS). However, in sputter neutral particle mass spectrometry, a low repetition pulsed laser is used to achieve a sufficient light density, and a laser having a high repetition rate (approximately 10 kHz) necessary for imaging has low pulse energy. There was a problem that a sufficient ionization probability could not be obtained.

JP 2001-108657 A

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a mass spectrometer and a mass spectrometry method that improve the ionization probability of atoms emitted from a solid sample.

  A mass spectrometer according to a first aspect of the present invention includes a vacuum chamber, a sample stage disposed in the vacuum chamber, and ions that emit an atom by irradiating a solid sample disposed on the sample stage with an ion beam. A beam source, a laser light source that allows laser light to pass above the ion beam irradiation region of the solid sample, and a laser light source that is disposed in the vacuum chamber, reflects the laser light, and is above the irradiation region. And a reflecting mirror that superimposes the reflected light and the reflected light, and an analysis unit that analyzes the mass of the atoms ionized by the laser light and the reflected light.

  In the mass spectrometer of the first aspect, atoms emitted from the solid sample by laser light and reflected light (hereinafter referred to as “sputtered atoms” as appropriate) are ionized. Here, since the laser beam and the reflected beam are superimposed above the ion beam irradiation region of the solid sample (hereinafter, referred to as “ionization space” as appropriate), for example, the laser beam and the reflected beam are superimposed in the ionization space. Compared to a mode in which the laser light and the reflected light in the ionization space overlap, the photon density increases, and the probability that the photons collide with the sputtered atoms increases. That is, the ionization probability of sputtered atoms is improved. The increase in the number of sputtered atoms that are ionized in this way improves the mass analysis accuracy of the analysis unit.

  The mass spectrometer of the second aspect of the present invention is the mass spectrometer of the first aspect, wherein the reflecting mirror is attached to the sample stage so that the optical axis of the laser beam and the optical axis of the reflected light are coaxial. ing.

In the mass spectrometer of the second aspect, since the optical axis of the laser light and the optical axis of the reflected light are coaxial, the area where the laser light and the reflected light overlap in the ionization space increases, and the ionization probability is further improved.
Moreover, in the said analyzer, since a reflecting mirror is attached to a sample stand, compared with the aspect which attaches a reflecting mirror away from a sample stand, for example, the operation | work which matches the optical axis of a laser beam and a reflecting mirror coaxially becomes easy.

  A mass spectrometer according to a third aspect of the present invention is the mass spectrometer according to the first aspect, wherein the plurality of reflecting mirrors are attached to the sample stage so that the reflected lights overlap each other a plurality of times above the irradiation region. Yes.

  In the mass spectrometer of the third aspect, since the reflected light is relayed by a plurality of reflecting mirrors, at least the reflected lights overlap each other multiple times in the ionization space, so that the region where the reflected light in the ionization space overlaps increases, and the ionization probability Is further improved.

  A mass spectrometer according to a fourth aspect of the present invention includes a vacuum chamber, a sample stage disposed in the vacuum chamber, and ions that emit an atom by irradiating a solid sample disposed on the sample stage with an ion beam. A plurality of beam sources, a laser light source that irradiates laser light in parallel with the surface of the sample stage, and a plurality of laser light sources that are arranged in the vacuum chamber, reflect the laser light, and irradiate the reflected light to the ion beam of the solid sample. A reflecting mirror that overlaps above the region; and an analyzer that analyzes the mass of the atoms ionized by the reflected light.

  In the mass spectrometer of the fourth aspect, atoms emitted from the solid sample are reflected by the reflected light. Here, since the reflected lights reflected by the plurality of reflecting mirrors are superimposed above the irradiation region of the ion beam of the solid sample, for example, the reflected lights in the ionization space are compared with each other in a mode in which the reflected lights are not superimposed. The photon density increases in the overlapping region, and the probability of photons colliding with the sputtered atoms increases. That is, the ionization probability of sputtered atoms is improved. The increase in the number of sputtered atoms that are ionized in this way improves the mass analysis accuracy of the analysis unit.

  The mass spectrometer of the fifth aspect of the present invention is the mass spectrometer according to any one of the first to fourth aspects, wherein the laser light source is the laser according to the type of atoms contained in the solid sample. The wavelength of light can be changed.

  In the mass spectrometer of the fifth aspect, sputtered atoms can be resonantly ionized by changing the wavelength of the laser beam according to the type of atoms contained in the solid sample. This further improves the ionization probability of the sputtered atoms.

  A mass spectrometer according to a sixth aspect of the present invention is the mass spectrometer according to any one of the first to fifth aspects, wherein the sample stage is detachably attached to the vacuum chamber, and the vacuum chamber Is provided with an outlet for taking out the sample stage.

  In the mass spectrometer of the sixth aspect, the solid sample can be exchanged by removing the sample stage from the vacuum chamber and taking it out from the outlet. In addition, when the sample stage is detached, the reflecting mirror can be cleaned or replaced.

  The mass spectrometric method of the seventh aspect of the present invention includes a step of placing a sample stage on which a solid sample is placed in a vacuum chamber, evacuating the inside of the vacuum chamber, A step of emitting atoms from the solid sample; a step of ionizing the atoms by passing a laser beam above the ion beam irradiation region of the solid sample; and a reflected light reflected so as to overlap the laser beam To ionize the atoms that have not been ionized by the laser beam, and to analyze the mass of the ionized atoms.

  The mass spectrometric method of the seventh aspect of the present invention has the same effects as the mass spectroscope of the first aspect described above.

  ADVANTAGE OF THE INVENTION According to this invention, the mass spectrometer and the mass spectrometry method which improved the ionization probability of the atom discharge | released from the solid sample can be provided.

It is the schematic which shows the structure of the mass spectrometer which concerns on 1st Embodiment. It is the enlarged view to which the principal part of the mass spectrometer of FIG. 1 was expanded. It is the enlarged view to which the principal part of the mass spectrometer of FIG. 1 was expanded, and has shown the state in which the pulse laser was reflected with the reflective mirror. It is the top view which looked at the principal part of the mass spectrometer of FIG. 1 from upper direction. It is the top view which looked at the principal part of the mass spectrometer which concerns on 2nd Embodiment from upper direction, and is a top view which shows the outward path | route of a pulse laser. It is the top view which looked at the principal part of the mass spectrometer of FIG. 5 from upper direction, and is a top view which shows the return path | route of a pulse laser. It is a mass spectrum obtained by non-resonant ionization with a single reflection of a pulsed laser. It is explanatory drawing which shows the ionization process by non-resonant two-photon absorption of a sputtered atom. It is explanatory drawing which shows the ionization process by the resonance two-photon absorption of a sputter atom. It is a graph which shows the relationship between the wavelength of a pulse laser, and the number of detected ions of zirconium (Zr). It is a graph which shows the relationship between the outgoing path wavelength of a pulse laser, a return path wavelength, and the number of detected ions of zirconium (Zr). It is explanatory drawing which shows the ionization range of a sputter | spatter atom group when a pulse laser is passed once. It is explanatory drawing which shows the ionization range of a sputter | spatter atom group when a pulse laser passes once and it reflects once.

[First Embodiment]
Hereinafter, the mass spectrometer and the mass spectrometry method according to the first embodiment of the present invention will be described with reference to FIGS.

<Mass spectrometer>
FIG. 1 is a schematic diagram showing a configuration of a mass spectrometer 20 of the present embodiment.
The mass spectrometer 20 releases the atoms (neutral particles) contained in the solid sample X, and ionizes the emitted atoms (hereinafter referred to as “sputtered atoms S” as appropriate) by laser light. It is a device for analyzing the mass of atoms.

  As shown in FIG. 1, the mass spectrometer 20 includes a vacuum chamber 22, a sample stage 24, an ion beam source 26, a laser light source 28, a reflecting mirror 30, and an analysis unit 32.

(Vacuum chamber)
As shown in FIG. 1, the vacuum chamber 22 accommodates a sample stage 24, an ion beam source 26, a reflecting mirror 30, and an analysis unit 32 inside. A negative pressure circuit (not shown) is connected to the vacuum chamber 22. By operating the negative pressure circuit, the vacuum chamber 22 is evacuated.

  The vacuum chamber 22 is provided with an outlet 34 for the sample stage 24. The outlet 34 is opened and closed by an open / close door 36 provided in the vacuum chamber 22. In the present embodiment, the open / close door 36 is a single door, but the present invention is not limited to this configuration. For example, the open / close door may be a double door or a sliding door. Further, the opening direction of the opening / closing door is not particularly limited.

  Further, a transmissive glass 38 is fitted on the side wall of the vacuum chamber 22 on the optical axis of the laser light L1 emitted from the laser light source 28. The laser light L 1 from the laser light source 28 passes through the transmission glass 38 and enters the vacuum chamber 22.

(Sample stage)
As shown in FIG. 1, the sample stage 24 is detachably attached to a pedestal 40 provided at the lower part of the vacuum chamber 22. The surface 24A of the sample stage 24 is a flat surface, and the solid sample X is disposed thereon. Note that the sample stage 24 has a manipulator capable of appropriately adjusting the position of the solid sample X serving as a target in order to adjust the irradiation position of the ion beam B.

(Ion beam source)
The ion beam source 26 is a beam source for irradiating the solid sample X disposed on the sample stage 24 with the ion beam B to emit atoms contained in the solid sample X. As the ion beam source 26, for example, a generally available device such as a focused ion beam (FIB) device may be used. When irradiating the solid sample X with the ion beam, for example, the ion beam may be taken out from a liquid metal gallium ion source and focused, and then the solid sample X may be irradiated in a pulse shape with nanoscale accuracy.

  Alternatively, the ion beam source 26 may be configured to be movable, and the surface of the solid sample X may be scanned with the ion beam B by moving the ion beam source 26. With such a configuration, it is possible to perform imaging on a micro scale by recording the signal amount of the sputtered atoms S in the irradiation region of the ion beam B. The pedestal 40 may be configured to be movable, and the surface of the solid sample X may be scanned with the ion beam B by moving the pedestal 40.

(Laser light source)
As shown in FIGS. 1, 2, and 4, the laser light source 28 is a pulse laser (pulse-like) above the irradiation region of the ion beam B of the solid sample X (hereinafter referred to as “ionization space” as appropriate). This is a device that irradiates a pulsed laser so that the laser passes through. Hereinafter, the incident light of the pulse laser is described as laser light L1. The laser light source 28 is installed outside the vacuum chamber 22 and irradiates the laser beam L1 parallel to the surface 24A of the sample table 24.

  The laser light source 28 ionizes the sputtered atoms S by irradiating the sputtered atoms S (atom group) emitted from the solid sample X with a pulse laser having a predetermined wavelength and a predetermined laser intensity.

  Although it does not specifically limit as a wavelength of the pulse laser irradiated from the laser light source 28, For example, you may be 266 mm.

  The atoms emitted from the solid sample X by the ion beam B are not isotropic, but dissipate and fly, so the laser light L1 emitted from the laser light source 28 is emitted near the surface 24A of the sample stage 24. It is preferable to install the laser light source 28 in such a manner. Thereby, the released sputtered atoms S can be efficiently ionized. When the laser beam L1 is irradiated in parallel to the surface 24A of the sample table 24, for example, the gap between the laser beam L1 and the surface 24A of the sample table 24 is preferably about 1 mm.

  As the laser light source 28, for example, a wavelength tunable laser such as a commercially available ultraviolet laser generator may be used.

(Reflector)
As shown in FIGS. 1 and 3, the reflecting mirror 30 is attached to the surface 24 </ b> A of the sample table 24. The reflecting mirror 30 is disposed within 10 mm from the center of the solid sample X. In addition, the reflecting mirror 30 is configured so that the optical axis of the laser light L1 (indicated by a black arrow in FIGS. 1 and 2) and the optical axis of the reflected light L2 (indicated by a white arrow in FIG. 3) are coaxial. Is attached to the surface 24A. For this reason, the laser light L1 and the reflected light L2 overlap in the ionization space. In the present embodiment, the reflecting mirror 30 is fitted in a recess (not shown) provided on the surface 24A of the sample stage 24.

  The reflectance of the reflecting mirror 30 is preferably closer to 100%, but is not particularly limited.

(Analysis Department)
The analysis unit 32 is for mass analysis of ionized atoms. As the analysis unit 32, various devices such as a sector magnetic field mass spectrometer, a time-of-flight mass spectrometer (TOF-MS), and a quadrupole mass spectrometer (QMS) can be applied.

(Control part)
The control unit 42 controls each component included in the mass spectrometer 20. Specifically, the control unit 42 controls the irradiation timing of the ion beam B irradiated from the ion beam source 26 and the laser light source 28. The irradiation timing control of the laser beam L1 is performed. Next, a method for controlling each component by the control unit 42 will be described.

  The control unit 42 controls the laser light source 28 so that the laser beam L1 is irradiated to the ionization space where the sputtered atoms S are emitted after a predetermined time has elapsed since the solid sample X was irradiated with the ion beam B. . By irradiating the ionization space with the laser beam L1, the sputtered atoms S in the ionization space are ionized. Further, since the reflected light L2 reflected by the reflecting mirror 30 also passes through the ionization space, the sputtered atoms S are ionized. Thereby, the ionization probability is improved.

<Mass spectrometry method>
The mass spectrometry method of this embodiment will be described. In the mass spectrometry method of the present embodiment, the mass spectrometer 20 is used.

  First, the solid sample X is placed on the surface 24 </ b> A of the sample stage 24, and the sample stage 24 is attached to the base 40 through the outlet 34 of the vacuum chamber 22. Thereafter, the open / close door 36 is closed and the above-described negative pressure circuit is operated to bring the vacuum chamber 22 into a vacuum state.

  Next, the solid sample X is irradiated with the ion beam B, and atoms are emitted from the solid sample X.

  Next, the laser beam L1 is passed through the ionization space above the irradiation region of the ion beam B of the solid sample X. Thereby, the sputtered atoms S in the ionization space are ionized.

  The laser light L1 that has passed through the ionization space is reflected by the reflecting mirror 30. The reflected light L2 reflected ionizes the sputtered atoms S that have not been ionized by the laser light L1. Here, since the wavelength of the pulse laser is long and the distance D from the center of the solid sample X to the reflecting mirror 30 is 10 mm or less, the front part of the reflected light L2 (the front part in the laser reflection direction) is the rear part of the laser light L1 ( It overlaps with the rear part of the laser incident direction.

  Thereafter, the ionized atoms are drawn into the analysis unit 32, and mass analysis of the atoms is performed.

Next, the effect of this embodiment is demonstrated.
In the mass spectrometer 20, the sputtered atoms S emitted from the solid sample X are ionized by the laser light L1 and the reflected light L2. Here, since the laser light L1 and the reflected light L2 are superimposed in the ionization space above the irradiation region of the ion beam B of the solid sample X (in FIG. 3, the range of the laser light L1 is indicated by a two-dot chain line, and the reflected light The range of L2 is indicated by a solid line.) For example, the photon density is increased in the region where the laser light L1 and the reflected light L2 in the ionization space overlap as compared with the case where the laser light L1 and the reflected light L2 are not superimposed in the ionization space. In addition, the probability that a photon collides with the sputtered atoms S increases. That is, the ionization probability is improved. As the number of atoms ionized in this way increases, the mass analysis accuracy by the analysis unit 32 is improved.

Further, in the mass spectrometer 20, since the optical axis of the laser light L1 and the optical axis of the reflected light L2 are coaxial, the region where the laser light and the reflected light overlap in the ionization space is increased, and the ionization probability of the sputtered atoms S is further increased. improves.
In addition, since the reflecting mirror 30 is attached to the sample stage 24, for example, the operation of aligning the optical axes of the laser light L1 and the reflected light L2 on the same axis can be facilitated as compared with a configuration in which the reflecting mirror 30 is attached away from the sample stage 24. .

  Further, in the mass spectrometer 20, the solid sample X can be exchanged by removing the sample stage 24 from the vacuum chamber 22 and taking it out from the outlet 34. Further, when the sample stage 24 is detached, the reflecting mirror 30 can be cleaned or replaced.

[Second Embodiment]
Next, a mass spectrometer and a mass spectrometry method according to the second embodiment of the present invention will be described with reference to FIGS.

  As shown in FIGS. 5 and 6, the mass spectrometer 50 of the present embodiment has the same configuration as that of the first embodiment except for the configuration of the sample stage 52. For this reason, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In the sample stage 52, a plurality of (four in this embodiment) groove portions 54 are formed on the surface 52A. These groove portions 54 extend from the outer peripheral edge portion of the sample stage 52. Further, the reflecting mirror 30 is fitted in these groove portions 54. By fitting the reflecting mirrors 30 into the grooves 54, the laser light L1 emitted from the laser light source 28 is reflected by the plurality of reflecting mirrors 30, and the reflected light L2 is reflected as shown in FIGS. The ionization space is configured to be superimposed a plurality of times.

Next, the effect of this embodiment is demonstrated.
In the mass spectrometer 50, the sputtered atoms S emitted from the solid sample X are ionized by the reflected light L2. Here, since the reflected lights L2 reflected by the plurality of reflecting mirrors 30 are superimposed in the ionization space above the irradiation region of the ion beam B of the solid sample X, for example, the reflected lights L2 are not superimposed on each other. In comparison, the photon density increases in the region where the reflected lights L2 in the ionization space overlap each other, and the probability that the photons collide with the sputtered atoms S increases. That is, the ionization probability is improved. As the number of atoms ionized in this way increases, the mass analysis accuracy by the analysis unit is improved.

  In the mass spectrometer 50 of the second embodiment, as shown in FIG. 5, the laser light L1 emitted from the laser light source 28 is configured not to pass through the ionization space, but the present invention is limited to this configuration. Not. The configuration of the sample stage 52 to which a plurality of reflecting mirrors 30 are attached may be applied to the mass spectrometer 20 of the first embodiment. In this configuration, since the laser light L1 emitted from the laser light source 28 also passes through the ionization space, the ionization probability of the sputtered atoms S is improved.

  Moreover, in the mass spectrometer 20 of 1st Embodiment, although the wavelength of the pulse laser (laser beam L1) irradiated from the laser light source 28 is fixed, this invention is not limited to this structure. For example, the laser light source 28 may be configured such that the wavelength of the laser light L1 can be changed according to the type of atoms contained in the solid sample X. In this configuration, since the wavelength of the laser beam can be changed according to the type of atoms contained in the solid sample X, the sputtered atoms S can be resonantly ionized. Thereby, the ionization probability of the sputtered atoms S can be further improved. In addition, you may apply the structure which changes the wavelength of the said laser beam L1 to the mass spectrometer 50 of 2nd Embodiment.

<Experiment>
(Confirmation of the effect of the present invention)
Hereinafter, the effect of improving the ionization probability according to the present invention will be described. Since the ionization probability improvement effect according to the present invention has two mechanisms having different principles, each will be described.

(1) Effect of increased photon density due to overlap of incident light and reflected light of pulsed laser (non-resonant ionization)

FIG. 7 shows a mass spectrum of an experiment in which one reflection mirror is used and an increase effect by a single reflection is obtained. The solid sample used was an indium (In) plate. The laser light source used had a laser wavelength of 266 nm, a repetition rate of 2 kHz, a pulse width of about 7 ns, and the reflecting mirror was a mirror-polished silicon wafer. Note that the reflectance of the laser beam from the silicon wafer is determined to be 63% by a prior measurement. As a result, the peak area intensity of 115In + ions increased 1.8 times compared to the case of no reflection. Since the reflectivity of the reflector is 63%, it is possible to expect an increase effect of 1.63 times by combining the laser forward and return paths (laser incident light and reflected light). ing.
This can be explained as shown in FIGS. 8A and 8B. The pulse width of the laser used is 7 ns, which exceeds 2 meters as the pulse length.
On the other hand, the distance from the center of the solid sample to the reflecting mirror is close to 10 mm or less, and the reflected light and the incident light overlap above the sample stage. The ionization of indium atoms at a laser wavelength of 266 nm is non-resonant two-photon absorption ionization, and theoretically the ionization probability is proportional to the square of the photon density.
According to theory, (1 + 0.63) 2 = 2.66 times of the effect should be obtained, but in reality, a slight deviation of the optical axis and atoms already ionized by incident light are effective in this effect. Considering that they are not added, it can be explained that the increase rate in the experiment does not reach 2.66 times, but is larger than 1.63 times that is a simple sum.
Therefore, in a single reflection, it was shown that, under the condition where the optical axis overlaps between the laser forward path and the return path, an ionization probability improvement effect exceeding the simple sum of the laser forward path and the return path assumed from the reflectance can be obtained. .
As shown in FIG. 2, the installation accuracy of the reflecting mirror is as follows. When the distance D between the center of the solid sample and the reflecting mirror is about 10 mm and the thickness of the optical axis of the laser is about 0.2 mm, As estimated from geometric calculation, the effect can be obtained by adjusting the angle to within 1 degree and ensuring the coaxiality with the incident light.

(2) Increase effect (resonance ionization) by passing laser (incident light and reflected light) twice from different directions

  In the method using single reflection, a case with a higher increase rate was discovered. As shown in FIGS. 8A and 8B, processes in which atoms absorb light and ionize include “non-resonant ionization” and “resonance ionization”.

  Non-resonant ionization corresponds to the above-described experiment with indium. That is, this is a case where two photons of a laser beam having a certain wavelength are simultaneously absorbed to reach the ionization potential. In this case, as described above, since the probability is that the first photon is absorbed and the second photon is absorbed, the ionization probability is proportional to the square of the photon density.

On the other hand, when light having a wavelength tuned to the internal level (excitation level) of the atom is used, as shown in FIG. 8A, the first photon is excited and the excited state is maintained for about several ns. If the second photon is absorbed during that time, ionization will occur.
That is, in the resonance process, there is a time delay of several ns for the absorption of the second photon, so that the ionization probability increases rapidly when the laser light is adjusted to the resonance wavelength. This is called resonance ionization. The laser light source used for resonance ionization must be variable in wavelength, and the laser system that can withstand practical use, such as the repetition rate and energy of the laser, is even more severe than in the case of non-resonance. Therefore, even in the case of laser resonance ionization, a method that uses a wavelength variable laser with a certain repetition rate and energy to obtain the maximum effect (ionization probability) is desired.

FIG. 9 shows the result of using zirconium (Zr) as a solid sample.
The horizontal axis represents the wavelength of the laser, and an effect of increasing the number of ions by resonance is observed in the region of 737.69 nm to 737.72 nm centered on the fundamental wavelength of 737.705 nm (because the second harmonic of the fundamental wave was used, The wavelength of the laser beam is half of these).

  In the experiment, signals were separated into the laser incident direction and the reflected direction (referred to as the forward path and the return path, respectively) and plotted in FIG. The reflection mirror used is an Al coat mirror, and the reflectance is 90%.

As shown in FIG. 9, the number of ions almost the same as that in the forward path is detected in the return path, and if the ratio to the total value of the forward path and the return path is defined as an increase rate, the effect is about twice at the resonance center wavelength (737.705 nm). was gotten.
In the resonance ionization process, as described above, since the excitation level is once passed, the relationship between the ionization probability and the photon density is not a square but a square (linear). Since the reflectance was 90% this time, the simple sum of the forward and return paths is 1.9 times.
Actually, the effect was twice as much as the simple sum, although it was a little. This is interpreted as follows. In the resonance ionization process, the first photon is absorbed and becomes an excited state. This excited state differs depending on the element and the excited level, but generally has a lifetime of about nanoseconds.
Therefore, even if excited by the forward laser and subsequently does not absorb the second photon, a process of absorbing the second photon by the backward laser can occur. That is, it was proved that the increase rate of the overlap of the incident light and the reflected light by the single reflection in the resonance ionization is increased by this effect rather than the simple sum.

In addition, a Doppler effect may be observed in the resonance ionization process.
From the ion beam irradiation point, atoms are emitted in various directions with various kinetic energies to form sputtered atoms. When a laser is incident on this sputtered atom group from one direction, there are atoms flying away from and in the direction away from the laser incident direction, and the frequency of the laser viewed from each atom changes. . This is the so-called Doppler effect. Since the sputtered atom group is a group having various motion directions and energies, the wavelength at which the resonance effect appears is broadened. This is called Doppler spread below. If the wavelength width of the Doppler broadening is wider than the line width of the laser, only atoms within the sputter atom group whose Doppler shift is within the laser line width will be resonantly ionized. This leads to a decrease in ionization probability. The best method is to make the laser line width variable and make this line width coincide with the Doppler broadening, but it is generally difficult to make the laser line width variable on the spot.

  It will be shown below that resonance ionization by single reflection in the present invention is also effective in the Doppler broadening. FIG. 10 shows the same data as FIG. 9, but shows only the signal intensity of laser incident light (outward path) and reflected light (return path) in a simplified manner. Referring to FIG. 10, it can be seen that the resonance peak wavelength is slightly shifted between the laser forward path and the return path (the laser forward path is shifted to the short wavelength side and the laser return path is shifted to the long wavelength side).

  The laser light source used this time has a line width of about 0.005 nm, and the line width is not so thin with respect to the Doppler broadening, but the resonance wavelength still depends on the laser forward and backward paths, that is, the laser passing direction. A shift is shown, and it can be seen that the laser travels to different Doppler shift zones on the forward and return paths. From this, as shown in FIGS. 11A and 11B, it is possible to expect an increase effect especially under the condition that the line width of the laser can be set only within a narrow range with respect to the Doppler broadening. For example, in FIG. 11A, when the laser is incident from the left side, if the center wavelength of the laser is tuned to a sputtered atomic group having a vertical component without Doppler shift, atoms within the range indicated by the bold line are ionized. In other words, the other range (the range indicated by the thin line) has a large amount of Doppler shift and falls outside the resonance condition.

On the other hand, as shown in FIG. 11B, it is assumed that ionization is performed after using reflected light and setting the center wavelength of the laser to the shorter wavelength side by about half the line width. In this case, the atom group emitted toward the left side of the vertical direction at the time of incidence (pulse laser forward path) is resonantly ionized, and the direction changes at the time of reflection (laser return path), so the atoms emitted toward the right side. The group is resonantly ionized.
That is, it is possible to cause resonance ionization with respect to a broader Doppler spread than a single pass. Although the experimental results shown in FIG. 9 and FIG. 10 include the effects described here, since the laser line width is not so narrow with respect to the Doppler broadening, the optical axes in the laser forward path and the return path as described above. The experimental results could be interpreted only by the overlap effect. Note that. When the laser line width is narrower, the technique shown in FIG. 11B is more effective.

  Although one embodiment of the present invention has been described above, the present invention is not limited to the above, and various modifications other than the above can be implemented without departing from the spirit of the present invention. Of course.

DESCRIPTION OF SYMBOLS 20 Mass spectrometer 22 Vacuum chamber 24 Sample stand 24A Surface 26 Ion beam source 28 Laser light source 30 Reflector 32 Analyzing part 34 Outlet 36 Opening and closing door 38 Transmission glass 40 Base 42 Control part 50 Mass spectrometer 52 Sample stage 52A Surface L1 Laser Light L2 Reflected light X Solid sample

Claims (7)

A vacuum chamber;
A sample stage disposed in the vacuum chamber;
An ion beam source for emitting an atom by irradiating a solid sample disposed on the sample stage with an ion beam;
A laser light source that allows a laser beam to pass above the irradiation region of the ion beam of the solid sample;
A reflecting mirror that is disposed in the vacuum chamber, reflects the laser light, and superimposes the laser light and the reflected light above the irradiation region;
An analysis unit for analyzing the mass of the atoms ionized by the laser light and the reflected light;
Having a mass spectrometer.   The mass spectrometer according to claim 1, wherein the reflecting mirror is attached to the sample stage so that an optical axis of the laser light and an optical axis of the reflected light are coaxial.   The mass spectrometer according to claim 1, wherein the plurality of reflecting mirrors are attached to the sample stage so that the reflected lights overlap each other a plurality of times above the irradiation region. A vacuum chamber;
A sample stage disposed in the vacuum chamber;
An ion beam source for emitting an atom by irradiating a solid sample disposed on the sample stage with an ion beam;
A laser light source for irradiating a laser beam parallel to the surface of the sample table;
A plurality of reflectors arranged in the vacuum chamber, reflecting the laser light, and superimposing the reflected lights on an irradiation area of the ion beam of the solid sample;
An analysis unit for analyzing a mass of the atom ionized by at least the reflected light;
Having a mass spectrometer.   The mass spectrometer according to any one of claims 1 to 4, wherein the laser light source is capable of changing a wavelength of the laser light according to a kind of atoms contained in the solid sample. The sample stage is detachably attached to the vacuum chamber,
The mass spectrometer according to any one of claims 1 to 5, wherein the vacuum chamber is provided with an outlet for taking out the sample stage. Placing a sample stage on which a solid sample is placed in a vacuum chamber, and evacuating the vacuum chamber;
Irradiating the solid sample with an ion beam to release atoms from the solid sample;
Passing the laser beam above the ion beam irradiation region of the solid sample to ionize the atoms;
Ionizing the atoms that have not been ionized with the laser light by the reflected light reflected so as to overlap the laser light;
Analyzing the mass of the ionized atoms;
A mass spectrometric method.