Laser ablation system

Abstract

To provide a laser ablation system that allows for flexible and highly accurate setting of the optimal focusing diameter and laser output according to the material, shape, and purpose of analysis of the object being analyzed. [Solution] A variable magnification beam expander capable of continuously varying the beam diameter of the laser light is placed in the optical path leading to a focusing lens that concentrates the laser light, enabling the setting of any focal diameter according to the sample. In addition, an optical modulator capable of rapidly modulating the output of the laser light is provided, allowing for optimal control of the output for each irradiation position and material.

Description

Technical Field

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[0001] The present invention relates to a laser ablation system.

Background Art

[0002] Laser ablation systems are widely used as sample introduction means for introducing ablation products generated from a sample by laser ablation into an analytical device such as ICP-MS (Inductively Coupled Plasma Mass Spectrometry) or ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry).

[0003] In the laser ablation system, since the condensing diameter of the irradiated laser light affects the size of the ablation region, the removal amount, the spatial resolution of analysis, etc., a configuration that can change the condensing diameter according to the analysis target has been desired. For example, in Patent Document 1, a technique for obtaining different condensing diameters by selectively switching a plurality of condensing lenses is disclosed.

[0004] Also, in Non-Patent Document 1, by combining a laser oscillator having a repetition frequency of 1 kHz or more and a galvanometer scanner, a plurality of different types of samples are irradiated alternately at high speed, and the ablation products obtained from each are mixed to average the differences between the samples and improve the quantitative accuracy. A multi-point irradiation method has been reported.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Non-Patent Documents

[0006]

Non-Patent Document 1

[0007] However, conventional laser ablation systems have proposed configurations that involve switching between multiple focusing lenses to change the focusing diameter. In this configuration, the usable focusing diameter depends on the type of lens that has been prepared in advance. Therefore, there is a problem in that it is difficult to continuously and flexibly adjust the focusing diameter according to the shape, material, or purpose of the object to be analyzed.

[0008] Furthermore, in multi-point irradiation techniques that improve quantitative accuracy by mixing multiple types of samples by irradiating them alternately at high speed, the configuration generally uses a constant laser output during irradiation. This can lead to uneven distribution of ablation products due to differences in ablation efficiency among samples. Consequently, the homogeneity of the mixed ablation products is compromised, resulting in a decrease in the accuracy of quantitative analysis.

[0009] Therefore, we provide a laser ablation system that allows for flexible and highly accurate setting of the optimal focusing diameter and laser output according to the material, shape, and purpose of analysis of the object being analyzed. [Means for solving the problem]

[0010] The present invention has a configuration in which laser light emitted from a laser oscillator passes through an electrically driven variable magnification beam expander arranged in the optical path leading to a focusing lens, and the diameter of the incident beam to the focusing lens is continuously varied, thereby enabling the focusing diameter to be continuously set. Furthermore, it has a high-speed output modulation device that enables high-speed modulation of the laser output (intensity or power) using an optical modulator (AOM (acousto-optic modulator), EOM (electro-optic modulator), or similar optical modulation means) placed between the laser light source and the focusing lens. This eliminates the need to switch between multiple focusing lenses as in conventional methods, allowing for flexible focusing diameter settings according to the sample material, shape, and analytical purpose. In both cases, even when rapidly switching the laser irradiation position using a laser light scanning device such as a galvanometer scanner, it becomes possible to set the optimal output according to the material and characteristics of each irradiation point, thereby achieving appropriate ablation even for materials with different ablation characteristics. [Effects of the Invention]

[0011] According to the present invention, the variable magnification beam expander allows for setting the optimal focusing diameter according to the material and shape of the sample, without being limited by the lens switching required in conventional methods. Furthermore, the high-speed power modulation device enables uniform ablation by individually controlling the laser output when ablating composite materials made of different materials or when irradiating samples of different materials together, thereby improving the reliability of the analysis. [Brief explanation of the drawing]

[0012] [Figure 1] This figure shows a schematic configuration example of the laser ablation system of the present invention. [Modes for carrying out the invention]

[0013] The laser ablation system according to an embodiment will be described in detail below with reference to the drawings.

[0014] Figure 1 shows the configuration of a laser ablation system 1 according to one exemplary embodiment of the present invention. The laser ablation system 1 is a device that performs ablation on a sample 21 by irradiating it with laser light L, and comprises a laser oscillator 10, a laser light scanning device 17, a focusing lens 18a, a variable magnification beam expander 12, an imaging optical system 15, and a control unit 24.

[0015] The laser oscillator 10 can be selected to be optimal for the analysis content and target sample, regardless of pulse width (femtosecond to millisecond), wavelength (infrared to ultraviolet), or oscillation mode (continuous oscillation and pulsed oscillation). For example, in applications requiring high-resolution surface analysis, it is preferable to use a femtosecond pulse deep ultraviolet wavelength laser.

[0016] The laser beam scanning device 17 may be configured using a mechanical scanning mechanism such as a galvanometer scanner, an optical MEMS scanner, a resonant scanner, a polygon scanner, a piezo scanner, or an optical deflection element such as an AOD (acousto-optic deflector), an EOD (electro-optic deflector), or a KTN (potassium tantalum niobate) crystal.

[0017] When performing a wide range of scanning, it is preferable to use an fθ lens for the condenser lens 18a in order to obtain a flat condensing surface over the entire scanning range. On the other hand, in high-resolution analysis applications that require a spatial resolution of 2 μm or less, it is preferable to use a high-NA objective lens for laser processing.

[0018] The laser beam L is continuously changed in its beam diameter by the variable magnification beam expander 12 and is incident on the condenser lens 18a. As a result, the condensing diameter can be continuously set without physically switching the condenser lens as in the prior art, and optimal ablation according to the analysis sample is realized.

[0019] The variable magnification beam expander 12 is electrically driven and is configured to expand or contract the beam diameter incident on the condenser lens 18a to a beam diameter corresponding to a specified condensing diameter based on a control signal from the control unit.

[0020] The zoom ratio (the ratio of the maximum magnification to the minimum magnification) of the variable magnification beam expander 12 is preferably at least 5 times. For example, under the conditions where the wavelength of the laser beam L is 256 nm, the focal length of the condenser lens is 100 mm, the M2 value representing the beam quality is 1.2, and the beam diameter incident on the variable magnification beam expander 12 is 2.6 mm, when the variable range is from 1 time to 5 times, the condensing diameter can be set within the range of 3 μm to 15 μm.

[0021] In this embodiment, in order to obtain a condensing diameter exceeding the variable range of the variable magnification beam expander 12, a plurality of condensing lenses 18a to 18c and a condensing lens switching stage 19 which is a mechanism for switching them may be further provided. Thereby, a wide range of condensing diameters can be selected stepwise or continuously.

[0022] In this embodiment, a high-speed output modulation device 11 capable of modulating the laser output at high speed may be further provided. The high-speed output modulation device 11 preferably has a modulation frequency corresponding to the repetition frequency of the laser oscillator 10. For this reason, it is preferable to use an AOM (acousto-optic modulator), an EOM (electro-optic modulator), or a SOM (semiconductor optical modulator) having a high-speed responsiveness exceeding 10 MHz for this device. <{

[0023] The high-speed output modulation device 11 may be provided outside the laser oscillator 10, or may be integrated inside the laser oscillator 10. The high-speed output modulation device 11 is synchronously controlled with the laser oscillator 10 and the laser beam scanning device 17, and by controlling the output according to the irradiation position and the material region, the uniformity of the amount of ablation products is realized.

[0024] In this embodiment, a focus variable device 14 may be further provided. The focus variable device 14 is arranged in front of the condensing lens 18a, and by dynamically changing the divergence angle of the incident beam to the condensing lens 18a, it is configured to vary the focal position of the beam after passing through the condensing lens 18a. Thereby, the focal position can be adjusted at high speed during scanning according to the height difference and gradient of the sample surface, and ablation can always be performed at an optimal focus.

[0025] In this embodiment, a polarization control device 13 for variably controlling the polarization state of the laser beam L may be further provided. The polarization control device 13 can switch between linearly polarized light, circularly polarized light, and elliptically polarized light, and adjust the polarization direction of linearly polarized light using a λ / 4 wavelength plate and a λ / 2 wavelength plate. Thereby, optimal irradiation conditions can be given even to a sample having polarization dependence, and improvement in ablation efficiency and selective ablation become possible.

[0026] In this embodiment, a triaxial (XYZ) sample stage 22 on which the sample cell 20 is placed may be further provided. The control unit 24 enables so-called on-the-fly control by synchronously controlling the movement of the laser beam scanning device 17 and the sample stage 22. This makes it possible to complete wide-area scanning quickly and precisely by feeding back the amount of movement of the sample stage 22 to the laser beam scanning device 17 via the control unit 24 and correcting its scanning trajectory, in addition to the conventional step-and-scan method.

[0027] In this embodiment, a surface shape measuring device 23 may be further provided. The surface shape measuring device 23 uses a laser displacement meter, a laser confocal measuring device, and a white light interferometer to measure the shape of the sample surface in three dimensions with high precision. This makes it possible to accurately calculate the ablation volume based on the difference in surface shape before and after ablation, thereby improving the accuracy of the analysis. Furthermore, the surface shape profile obtained by measurement is fed back to the control unit 24 and used to control the irradiation coordinates of the focus variable device 14, the sample stage 22, and the laser light scanning device 17, thereby realizing three-dimensional laser ablation control.

[0028] The control unit 24 calculates the irradiation coordinates on the sample surface in three dimensions based on information obtained from the imaging optical system 15 or the surface shape measuring device 23, and converts this into control signals for each component such as the laser light scanning device 17, laser oscillator 10, and variable focus device 14 to set appropriate scanning trajectories and output settings.

[0029] The control unit 24 provides a reference clock to the laser oscillator 10 and the laser light scanning device 17, and performs synchronization control to ensure that laser irradiation is performed accurately at specified positions and at specified intervals according to the irradiation program. The reference clock may be based on the oscillation period of the laser oscillator 10 or on an external clock.

[0030] The ablation product is transported from the sample cell 20 to the analyzer 2 by a transport gas supplied from the transport gas supply unit 3, where elemental analysis, emission spectroscopy, etc., are performed. The control unit 24 is also equipped with an interface function with the analyzer 2, enabling synchronous control of the laser ablation system 1 and the analyzer 2.

[0031] The analytical instrument 2 may be a mass spectrometer such as ICP-MS (inductively coupled plasma mass spectrometry) or an emission spectrometer such as ICP-OES (inductively coupled plasma emission spectrometry). [Industrial applicability]

[0032] The laser ablation system according to the present invention integrates various functions such as variable control of the focusing diameter and output modulation, enabling flexible irradiation condition settings and achieving precise and highly reliable analysis. This makes it useful in various fields, including semiconductors, materials development, life sciences, earth sciences, and environmental analysis. [Explanation of Symbols]

[0033] 1. Laser Ablation System 2 Analyzer 3. Conveyor gas supply machine 10. Laser Oscillator 11. High-speed output modulation device 12 Variable Magnification Beam Expander 13 Polarization control device 14. Variable focus device 15. Imaging optical system 16 Laser Reflecting Mirrors 17. Laser scanning device 18a, 18b, 18c Focusing lenses 19. Focusing lens switching stage 20 sample cells 21 samples 22 Sample Stage 23 Surface profile measuring device 24 Control Unit L laser light Ga, Gb conveying gas line

Claims

1. A system that performs ablation by irradiating a sample with laser light, A laser oscillator that emits laser light, A laser beam scanning device that scans the laser beam from the aforementioned laser oscillator in two dimensions, A focusing lens for focusing the aforementioned laser light, A motor-driven variable magnification beam expander that continuously varies the beam diameter of the laser light incident on the focusing lens, A high-speed output modulation device capable of rapidly modulating the output of the laser light, An imaging optical system for observing the aforementioned sample and determining the laser irradiation position, A control unit that synchronously controls the laser oscillator, the laser light scanning device, the high-speed output modulation device, and the imaging optical system, Equipped with, The variable magnification beam expander allows for continuous changes in the focusing diameter according to the sample without physically switching multiple focusing lenses, The laser ablation system is characterized in that the high-speed output modulator has a responsiveness capable of modulating the laser output according to the irradiation position, and regardless of whether it is continuous oscillation or pulsed oscillation, it controls the output for each irradiation position or material region by synchronous control with the laser light scanning device, thereby achieving uniformity of the ablation product.

2. The system according to claim 1, In order to obtain a focusing diameter exceeding the variable range of the aforementioned variable magnification beam expander, the system further comprises multiple focusing lenses and a mechanism for switching between them. A laser ablation system characterized by enabling a wider range of focusing diameter selection by combining the aforementioned variable magnification beam expander with multiple focusing lenses.

3. The system according to claim 1, A laser ablation system characterized by further comprising a variable focus device that adjusts the focal position during scanning according to the height difference and gradient of the sample surface, in order to perform uniform ablation even on sample surfaces with different heights or gradients.

4. The system according to claim 1, A laser ablation system characterized by having a polarization control device that variably controls the polarization state of laser light, thereby providing optimal irradiation conditions for polarization-dependent samples.

5. The system according to claim 1, It further includes a stage for placing sample cells, A laser ablation system characterized in that the control unit synchronously controls the movement of the laser light scanning device and the stage, thereby enabling efficient irradiation of a wide area of ​​the sample surface.

6. The system according to claim 1, A laser ablation system characterized by further comprising a surface shape measuring device that measures the surface shape of a sample before and after ablation, calculates the volume removed from the sample by laser ablation, acquires height difference and gradient information of the sample surface, and reflects this information in the focusing unit and three-dimensional scanning.

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