Trajectory method for laser-induced breakdown spectroscopy

Abstract

A method for compositional analysis includes providing a sample having a surface and determining, with a controller, a plurality of equidistant positions along an oscillation path along the surface. The oscillation path is sinusoidal in at least one orthogonal dimension in a plane generally parallel to the surface. The method further includes, for each equidistant position of the plurality of equidistant positions, moving an ablation point along the oscillation path to each equidistant position, pulsing an energy source to provide an electromagnetic energy beam to ablate material at the ablation point, and collecting, with a spectroscopic instrument, an emission spectrum in response to pulsing the energy source. The method also includes analyzing the emission spectrum to determine a composition at the surface.

Description

Technical Field

[0001] The present disclosure generally relates to systems and methods for performing laser-induced breakdown spectroscopy.

Background Art

[0002] Elemental analysis techniques are useful for determining the elemental composition of materials in various forms. Elemental analysis techniques range from destructive (e.g., the material is destroyed in the test) to semi-destructive (e.g., the material is sampled or the surface is damaged) to more fully non-destructive (e.g., the material remains completely intact). Exemplary techniques include inductively coupled plasma-atomic emission spectroscopy (e.g., ICP-AES), ICP-mass spectrometry (e.g., ICP-MS), electrothermal atomization atomic absorption spectroscopy (e.g., ETA-AAS), X-ray fluorescence spectroscopy (e.g., XRF), X-ray diffraction (e.g., XRD), laser-induced breakdown spectroscopy (e.g., LIBS). Elemental analysis can be either qualitative or quantitative and often requires calibration against known standards.

[0003] Laser-induced breakdown spectroscopy (LIBS) is an analytical technique used to analyze a wide variety of materials, including metals, polymers, glasses, ceramics, and minerals. LIBS can detect and quantify the elements of the periodic table with great accuracy. It can analyze large and small samples, requires little or no sample preparation, and can be used for both bulk elemental analysis and microscanning for imaging. LIBS relies on pulsed energy radiation, such as pulsed laser radiation, directed at the sample to ablate, atomize, and ionize the material. The collision of each laser pulse on the surface of the sample forms a plasma plume, and the light from it can be analyzed to perform qualitative or quantitative spectroscopic measurements. Therefore, LIBS can provide in-situ chemical analysis with high precision, detection limits, and low cost, and is easy to use, rapid.

[0004] The laser interaction with matter is governed by quantum mechanics, which describes how photons are absorbed or emitted by atoms. When an atom absorbs a photon, one or more electrons transition from the ground state to a higher energy quantum state. Electrons tend to occupy the lowest possible energy levels, and in the cooling / collapse process, the atom emits photons to return to a lower energy level. The different energy levels of different atoms generate different photon energies for each atomic species, accompanied by narrow-band emissions due to their quantization. These emissions correspond to the spectral emission lines seen in the LIBS spectrum.

[0005] The plasma lifetime has three basic stages. The first stage is the ignition process that includes initial bond breaking and plasma formation during the laser pulse. This ignition process is affected by the laser type, laser power, and pulse duration. The second stage of the plasma lifetime is the most important for the optimization of LIBS spectrum acquisition and measurement because the plasma causes atomic emission during the cooling process. After ignition, the plasma continues to expand and cool. At the same time, the electron temperature and density change. This process depends on the ablated mass, spot size, energy coupled to the sample, and environmental conditions (such as the state of the sample, pressure, etc.).

[0006] The final stage of the plasma lifetime is not very useful for LIBS measurement. A certain amount of the ablated mass is not excited as vapor or plasma. Therefore, this material is ablated as particles, and these particles form condensed vapor, liquid sample emission, and solid sample exfoliation, which do not emit radiation. Furthermore, the ablated atoms cool down and generate nanoparticles in the recombination process of the plasma.

[0007] This disclosure can be better understood by referring to the accompanying drawings, and its numerous features and advantages can be made apparent to those skilled in the art.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

[0009] The use of the same reference numerals in different drawings indicates similar or identical items.

DETAILED DESCRIPTION OF THE INVENTION

[0010] In one embodiment, a system for compositional analysis includes an energy source that provides an energy beam directed at an ablation point on the surface of a sample. The energy source can be, for example, a laser. The ablation point can be sequentially moved to positions (sample points) on the surface along a vibration path. In one example, these positions can be arranged at equidistant locations along the vibration path. In one instance, the vibration path includes a sine wave pattern in at least one orthogonal dimension of the planar dimension. The system can include a controller that directs the movement of the ablation point to positions along the vibration path. The system can further include a lens and a mirror, or optionally, a linear stage platform for facilitating the movement of the ablation point. The energy beam ablates material from the surface of the sample at the ablation point. The ablated material generates an emission spectrum. The system can include a collection system for collecting the emission spectrum. In one example, the collection system includes a collection lens optically connected to a spectrometer or a spectroscope for determining the wavelengths emitted by the ablated material. The system can use the emission spectrum to determine what elements are present, and optionally, in what amounts.

[0011] In a further example, a method for compositional analysis includes providing a sample having a surface. At each position (sample point) continuously along a vibration path, material is ablated from the surface at that position, an emission spectrum is collected, and the emission spectrum is analyzed to determine the composition at the surface. Optionally, the emission spectrum is converted to a digital signal for further analysis to determine the composition. The composition can be analyzed, for example, by averaging, to determine an average surface composition. In another example, an image or map of the position-resolved composition can be formed using the composition at the positions.

[0012] It has been found that conventional scanning methods cannot provide rapid and dispersed coverage of the surface, especially when used with irregular shapes. When averaging the composition across the surface, conventional methods tend to overemphasize one region of the surface relative to another. The systems and methods described herein advantageously provide, among other advantages, uniform coverage and test speed.

[0013] FIG. 1 includes a schematic diagram of a system 1 for performing compositional analysis, for example, by laser-induced breakdown spectroscopy. A sample 2 is disposed on a platform 4. An energy source 6 directs an energy beam 8 through an optical system such as a lens 10 to an ablation point 12 disposed on the surface of the sample 2. Material is ablated from the surface of the sample 2, and at least a portion of the ablated material is atomized or ionized to obtain an emission spectrum 14 that is collected by a collection lens 16 optically connected to a spectrometer 18, for example, using an optical fiber cable.

[0014] The energy source 6 can be a laser. In one example, the energy source 6 is a pulsed laser having a wavelength in the range of 200 nm to 1100 nm, such as 1064 nm, 532 nm, or 266 nm. Further, the energy source 6 has a peak power in the range of at least 0.5 MW / cm 2 such as, 0.5 MW / cm 2 to 2 GW / cm 2 to be sufficient to ablate material from the surface of the sample and examine the elemental composition. For example, the laser pulse has an energy in the range of 100 μJ to 100 mJ and a pulse width in the femtosecond, picosecond, or nanosecond regime, and the pulse repetition rate can be up to the MHz regime. The laser can be a mode-locked laser or a Q-switched laser. For example, the laser can be a passive Q-switched laser or an active Q-switched laser.

[0015] Lens 10 can include a spherical lens, a flat-field scanning lens, for example, an F-tan(θ) scanning lens, or an F-theta scanning lens. In particular, lens 10 is an F-theta scanning lens.

[0016] The collection system can include a collection lens 16 and a spectrometer 18. In one example, the spectrometer includes an imaging device such as a charge coupled device (CCD) imaging device. In a further example, the emission spectrum can be directed to the spectrometer by one or more mirrors. In an additional example, the spectrometer can include various optical components such as one or more mirrors, lenses, apertures, gratings, prisms, and radiation collection devices. In one example, the radiation collection device is a charge coupled device (CCD) device. However, in other examples, other radiation detectors can be used.

[0017] In particular, system 1 includes a controller 20. In one example, controller 20 can control the relative movement of ablation point 12 with respect to the position on the surface of sample 2. For example, controller 20 can control a linear stage translation table such as platform 4 to move sample 2 relative to fixed beam 8. In another example, a mirror such as a galvanometer mirror, prism, or lens can be used to change the relative position of the ablation point on a fixed sample. Controller 20 can sequentially control the relative movement of ablation point 12 along the vibration path towards the position on the surface of sample 2. From the collection of the emission spectrum at each position on the surface of sample 2, it is possible to construct a composition map of the scanned surface.

[0018] Controller 20 can further control the timing of laser 6 to ablate material only at desired positions on the sample surface. Further, controller 20 can control a collection system such as spectrometer 18 to collect the emission spectrum at a time delayed from the activation of laser 6.

[0019] In one example, the controller 20 can further enable selection of a test area on the surface of sample 2. For example, the controller 20 can use a laser system to detect the edges of the surface and select the entire surface area. In another example, the controller 20 can use an optional camera 11 to detect the edges of the surface. In a further example, the controller 20 can provide the user with an interface that enables the user to select an area of the surface for testing.

[0020] As an alternative to the translation table, the system can include a set of movable positioning mirrors such as fixed mirrors and galvo mirrors for one or more samples, and can direct the electromagnetic energy beam through a lens to an ablation point on the surface. In one example, the motor-driven mirror can be automatically controlled and adjusted to direct the ablation point to positions (sample points) sequentially arranged along a vibration path on the surface of sample 2. In one example, the controller 20 controls an adjustable mirror to adjust the position (sample point) on the surface of sample 2 where the ablation point 12 is located. In particular, the controller 20 is configured to move the ablation point to positions sequentially arranged along the vibration path, for example, by controlling a motor that drives the adjustable mirror.

[0021] The controller 20 can include a computer (not shown), and for example, may include a storage medium, a memory, a processor, and one or more interfaces such as a user output interface, a user input interface, and a network interface that are linked to each other. The storage medium can be any form of non-volatile data storage device such as one or more of a hard disk drive, a magnetic disk, an optical disk, a ROM, etc. The storage medium can store one or more computer programs for causing the controller 20 to adjust the position on the surface of the sample 2 where the ablation point 12 is located. The memory can be any random access memory suitable for storing data or computer programs. The processor can be any processing unit suitable for executing one or more computer programs (such as those stored on the storage medium or in the memory, etc.). The processor can include a single processing unit, or a plurality of processing units that operate in parallel, separately, or in cooperation with each other. When executing processing operations, the processor can store data in the storage medium or the memory, or read data from the storage medium or the memory. An interface, which can be any unit, can be provided to provide an interface between the computer and the movable mirror, or between the translation platform 4 and the energy source 6. The user input interface can be configured to receive input from a user or an operator. The user can provide this input via one or more input devices of a controller such as a mouse (or other pointing device) or a keyboard that is connected to or communicates with the user input interface. However, it will be understood that the user can provide input to the computer via one or more additional or alternative input devices (such as a touch screen). The computer can store the input received from the input device via the user input interface in the memory for the processor to access and process later, or can directly pass the input to the processor so that the processor can respond to the user input accordingly.The user output interface can be configured to provide graphical / visual output to the user or operator. For example, the emission spectrum collected from the sample can be provided to the user or operator as graphical / visual output. Thus, the processor can instruct the user output interface to form an image / video signal representing the desired graphical output, and this signal can be configured to be provided to a video display unit (VDU) such as a monitor (or screen display unit) connected to the user output interface. The computer architecture described above is merely exemplary, and it will be understood that other computer systems having different architectures (e.g., having fewer components, or having additional or alternative components) can be used. By way of example, the computer can include one or more of a personal computer, a server computer, a laptop, etc.

[0022] FIG. 2 includes a diagram of a laser-induced breakdown spectroscopy (LIBS) system 100 that includes a pulsed laser 113, a beam expander 111, a two-axis scanning galvo system 110, a lens 108, a chamber 103, one or more mirrors 105, associated lenses 116, and one or more spectrometers 117. The sample 101 can be placed on a table that includes an opening or analysis aperture for exposing the surface of the sample inside the chamber 103.

[0023] The laser source 113 emits an optical pulse 112 having, for example, a wavelength or power as described above in connection with FIG. 1. The laser source 113 can have a pulse rate in the range of 1 to 1000 Hz. Each pulse 112 is directed at the surface of the sample 101, where a plasma 102 is generated. The light emitted from the plasma 102 can be collected by the mirror 105 and directed through the lens 116 to the spectrometer 117. The corresponding detection of the light intensity can be used to perform qualitative or quantitative spectroscopy, leading to the identification of elements and potential compositions on the surface.

[0024] Optionally, a beam expander 111 is disposed in the path of the laser beam 112 from the laser source 113 to increase the diameter of the laser beam 112. Increasing the diameter of the laser beam 112 reduces the power per unit area and avoids damaging optical components such as the mirrors of the galvo system 110, and then achieves a more tightly focused spot on the sample surface. Thus, when the beam 112 hits the mirror 110, it reflects in a larger area 109. In one example, the beam expander 111 includes an incident lens 111B and an exit lens 111A.

[0025] The galvo system 110 can include two galvanometric mirrors 110A and 110B. Such galvanometric mirrors 110A and 110B coupled with a lens 108 such as an F-theta lens can direct the beam according to a mapping on the surface of the sample 101. In one example, the lens 108 can focus the laser beam 112 onto a spot of about 10 μm on the sample surface. The laser intensity per unit area on the spot is sufficient to generate a plasma 102. A portion of the light 104 emitted by the plasma 102 is collected by one or more mirrors 105A, 105B, 105C, or 105D and focused onto one or more spectrometers 117 through one or more lenses 116A, 116B, 116C, or 116D. Four mirrors 105A, 105B, 105C and 105D and four corresponding lenses 116A, 116B, 116C and 116D are shown, but it will be understood that embodiments can include one or more such mirrors and one or more corresponding lenses.

[0026] The spectrometer 117 uses a slit 117A and a grating 117B to split the light 104 according to wavelength and uses a linear array sensor 117C or a single channel sensor 117D to detect the light. The sensor signal from the sensor 117C or 117D can be used to determine the elemental composition of the sample.

[0027] Sample 101 is coupled to chamber 103 such that the surface of sample 101 is exposed inside chamber 103. Otherwise, chamber 103 can be hermetically sealed. For example, lens 108 or 116 can include an O-ring 107 or 115.

[0028] Gas such as argon, nitrogen, helium, or air can be flowed into chamber 103. The interior of chamber 103 can be maintained at pressure or vacuum. The gas can be injected into chamber 103 through opening 106 and exit chamber 103 through a second opening 114. Optionally, a vacuum pump can be connected to the second opening 114 to evacuate the interior of chamber 103 as the gas moves through chamber 103. Depending on the location of opening 106 or 114, a gas flow across the chamber can be provided to reduce dead volume and discharge dust formed by plasma 102. By connecting a vacuum pump to the second opening 114, dust can be discharged through the vacuum pump. In particular, the quality and properties of plasma 102 and the resulting emission light 104 depend on the environment inside chamber 103. Therefore, an airtight chamber 103 with dust management is highly desirable.

[0029] As shown in the exemplary LIBS system of FIG. 3, a sample table 201 having an analysis aperture 202 is positioned above chamber 210. The sample can be held in place by a sample press 209. Laser system 207 is coupled to lens 205 via a galvo mirror system by a beam expander 206, and the lens directs a laser pulse onto the surface of the sample exposed through analysis aperture 202.

[0030] The light emitted from the plasma formed as a result of the laser pulse impinging on the surface of the sample through the analysis aperture 202 can be collected by mirrors held by the plasma vision mirror supports 204A and 204B. In one example, the light collected by the mirror coupled to the plasma vision mirror support 204A is directed towards the spectroscopic lens 208. In another example, the light collected by the mirror attached to the plasma vision mirror support 204B is projected onto the spectroscope 203.

[0031] Figure 4 further shows details of the LIBS system of FIG. 1. The sample press 301 can fix the sample to the sample table 303 having an analysis aperture 304 that opens towards the inside of the chamber 313. The laser pulse directed through the beam expander 309 and the F-theta lens 308 can impinge on the sample through the analysis aperture 304. The F-theta lens 308 can be supported by the F-theta lens support 310. Using a galvanometer mirror system as shown in FIG. 2, the laser pulse passing through the beam expander 309 and the F-theta lens 308 can be mapped onto the surface of the sample exposed through the analysis aperture 304.

[0032] The light emitted from the resulting plasma can be collected by the mirror 307A or 307B and directed through the spectroscopic lens 302 or towards the spectroscope 311. For example, the light collected by the mirror 307A can be redirected towards the spectroscope 311 again. In another example, the light collected by the mirror 307B can be directed towards the spectroscopic lens 302. The mirror 307A or 307B can be held in place by the plasma vision mirror supports 306A or 306B, respectively.

[0033] In a further example, the chamber 313 can be configured such that the gas flow pulls dust particles formed by the plasma away from the sample surface and the sample aperture 304. For example, the chamber 313 can have a gas inlet (not shown) disposed proximate to the bottom of the chamber near the lens 308. The gas can flow upward through the chamber 313 toward the analysis aperture 304. The chamber 313 can define a flow pipe 305 or a wall. The gas flows into an annulus connected to the outlet 312 over the wall. Optionally, the outlet 312 can be connected to a vacuum pump, and the vacuum pump sucks the gas through the chamber 313 across the flow pipe 305 into the annulus and discharges it from the outlet 312.

[0034] FIG. 5 shows an exemplary path of light extending through the system. For example, the laser beam 410 can be directed to the galvanometer system's galvanometer mirrors 409A or 409B and through the F-theta lens 408 that provides a focused laser beam onto the sample plane 401. When the laser beam impinges on the sample at the sample plane 401, the laser beam forms a plasma 404 that emits light 405. The light 405 of the plasma 404 can impinge on the mirrors 406A or 406B, which direct the collected light 405 onto the spectroscopic lens 402 or into the spectrometer through the inlet 403. In one example, a spectrometer, such as the spectrometer shown in FIGS. 1, 2, or 3, can collect the spectrum emitted by the plasma and determine the elemental composition based on the spectrum.

[0035] Each of the systems shown in FIGS. 2, 3, 4, and 5 can include each other's elements and features, or the elements and features of the system shown in FIG. 1. In one example, each of the systems of FIGS. 2, 3, 4, and 5 can further include a controller having the form and function described in connection with FIG. 1. In a further example, each of the systems of FIGS. 2, 3, 4, and 5 can have a camera as described in connection with FIG. 1.

[0036] The features of the system as shown in FIGS. 1 to 5 are the oscillatory scanning across the surface of the sample for bulk elemental analysis. In one example, the oscillatory scanning enables averaging over a number of sample points after each measurement to obtain the desired statistics. The collection of a large number of sample points across the sample surface under consideration increases the accuracy of qualitative or quantitative analysis. Collecting measurements from a large number of sample points across the entire surface better represents the sample composition as compared to a single point. For example, the system can analyze a surface area with a diameter of 1 mm to 10 mm as compared to a single point with a diameter of about 10 μm.

[0037] Without the scanning of the system described above, the laser ablates the same part of the sample in each pulse, and after each pulse, the composition of the sample is analyzed at different depths. Such measurement techniques are limited because there are depth limits beyond which further analysis becomes impossible. For example, the plasma etches into the crater until the point where the plasma is shielded by the depth of the crater or until the point where the laser focus is no longer sufficient to form a reliable plasma. In contrast, the scanning of the present system increases the number of measurements while continuously detecting the plasma at the focus of the F-theta lens.

[0038] For an accurate and representative analysis of the sample surface, it is desirable to have distributed sampling across the surface, for example, using a scanning path that provides distributed sampling of the surface and improved mirror movement with reduced acceleration jumps. In particular, the scanning path can be defined as a sine wave pattern (e.g., sine or cosine) for movement in at least one orthogonal dimension (e.g., the x or y dimension on the surface). In one example, the sine wave pattern can be a function of time. For example, the sine wave pattern can include periodic parameters. Further, the sine wave pattern can have an amplitude, which can be constant or a function of time or position. Generally, the first derivative of a sine wave pattern is also a sine wave. For example, the sine wave pattern can be a sine or cosine pattern. In one example, when the sine wave pattern is a sine pattern, the first derivative is cosine and the second derivative is sine. The sine wave pattern and the sine wave derivative are preferred to reduce acceleration jumps in the mirror movement and enable continuity at the ends of the scanning path so that the scan can be performed multiple times to increase the number of sampling points and thus the accuracy of the analysis results.

[0039] Sample points can be defined along the sample path, for example, by a sine wave pattern. The sample points can be defined equidistantly along the path. In one example, the equidistant sample points can be points that are linearly equidistant or curvilinearly equidistant. The sine wave path and the equidistant sample points along the path enable the desired movement of the mirror such that while the mirror can rapidly move the beam to the next sample point, the laser remains stationary at each sample point long enough to generate the desired plasma.

[0040] FIG. 6 includes a block diagram showing an exemplary method 600 for analyzing a sample. Method 600 includes inserting a sample, as shown at block 602. For example, the sample can be inserted into the chamber or placed on a platform within the chamber. In another example, the sample can be placed against a sample table having an analysis aperture that exposes the surface of the sample to the interior of the chamber.

[0041] As shown at block 604, the system can determine a vibration path defined across the surface of the sample. For example, the analysis aperture can define the area of the sample that is exposed for testing. The vibration path can utilize a sine wave pattern in at least one dimension across the area exposed on the surface of the sample. Alternatively, an irregular shape can be exposed on the surface or selected by the user of the instrument. The system can define a vibration path that provides a desired distribution of sample points across the surface of the irregular test area. In one example, as shown in FIG. 1, the controller of the system can utilize a camera to determine the shape of the surface and define an appropriate vibration path that provides a desired distribution of sample points across the surface.

[0042] In one example, the vibration path is a sine wave along at least one of two orthogonal dimensions along the surface of the sample. For example, the vibration path can have a sine or cosine pattern along at least one of two orthogonal dimensions. For example, the vibration path can have a sine pattern along the height dimension. The sine wave pattern can be characterized by a periodicity parameter and an amplitude. The periodicity parameter can be specified to provide multiple vibrations across the surface in one orthogonal dimension. The amplitude can be constant. In another example, the amplitude can be a function of time. In a further example, the amplitude can be a function of position.

[0043] In a further example, both orthogonal dimensions are defined by sine wave patterns. In one example, the sine wave pattern in the first orthogonal dimension can be a sine pattern, while the sine wave pattern in the second orthogonal dimension is a cosine pattern. Each pattern can be defined by a periodicity parameter. The periodicity parameters of both patterns along the two orthogonal dimensions can be the same. In another example, the periodicity parameters are different. For example, the ratio of the two periodicity parameters can be an integer. In one example, the ratio is an even integer. Alternatively, the ratio is an odd integer. The amplitudes associated with the sine wave patterns of the two orthogonal dimensions can be the same. For example, the amplitudes can be the same function of time or the same constant. In another example, the amplitudes of each of the sine wave patterns of the two orthogonal dimensions are different. Further, the amplitude of the sine wave pattern of the second dimension can be constant, and the amplitude associated with the sine wave pattern of the first orthogonal dimension can be a function of position.

[0044] In another example, an oscillation path having at least one sine wave pattern defined along at least one of the orthogonal dimensions can include a non-sine wave pattern on the second orthogonal dimension. For example, the sine wave pattern in the y dimension can be a sine wave pattern having a desired periodicity and amplitude, and the pattern in the x dimension is linear, such as a linear function of time.

[0045] Furthermore, sample points are defined along the oscillation path. For example, equidistant sample points can be continuously defined along the oscillation path. The equidistant ablation points can be linearly equidistant or curvilinearly equidistant.

[0046] As shown in block 606, the ablation point of the laser can be directed to the next sample point along the vibration path. The re-direction of the laser can be achieved by moving the mirror so as to direct the ablation point of the laser to a new position. The inertial characteristics of the galvo may not allow the mirror to completely stop their movement at each ablation point. Nevertheless, the advantage of using the oscillatory motion presented here is that the rotation of the galvo is kept constant, allowing the mirror to smoothly continue their path. Since the laser pulse is several orders of magnitude faster than the galvo motion, each pulse impinges as if the mirror were effectively stationary. As a result, each ablation point is directed to the intended position on the sample, and there is no recognizable distortion of the ablation spot.

[0047] For example, as shown in block 608, the laser is actuated. As a result of the activation of the laser, one or more pulses impinge on the surface of the sample at the ablation point, forming a plasma at that point along the surface that emits spectral characteristics of the composition of the sample.

[0048] As shown in block 610, the emission spectrum is collected. For example, the emission spectrum can be collected by a mirror that directs the collected emission spectrum to a spectroscopic lens or spectrometer. The spectrometer converts the emission spectrum into a signal, as shown in block 612.

[0049] As shown in block 614, the system can determine whether it has reached the last sample point along the vibration path. If it has not reached the last sample point, the system can repeat moving the ablation point to the next sample point along the vibration path as shown in block 606, actuating the laser as shown in block 608, collecting the emission spectrum as shown in block 610, and converting the emission spectrum into a signal as shown in block 612.

[0050] When the last sample point reaches the end of the vibration path that has been tested, the system can analyze the converted signal, as shown in block 616. For example, the system can analyze the signal to determine the composition at each point. Further, the system can average the measured values. In one example, the system can determine the average value, median value, or mode of the measurements. For example, the system can determine the average composition measurement across the tested sample points. Although the analysis is shown as being performed after the sampling process is completed, the analysis can be performed simultaneously with the testing of the sample points along the vibration path.

[0051] FIG. 7 includes a block diagram of a further method 700 for testing a sample. Method 700 is particularly useful when testing a sample having a surface that is not defined by an aperture or other regular-shaped mechanical feature associated with the device. In particular, samples that include an irregularly shaped test area benefit from the method of FIG. 7.

[0052] In one example, method 700 includes inserting the sample into the system, as shown in block 702. For example, inserting the sample can include placing the sample on a table, such as a translation table, or placing the sample above an aperture exposed in a chamber.

[0053] As shown in block 704, a test area is selected on the sample. For example, an image of the sample can be provided to the user to select the desired test area. In another example, the system can determine an edge associated with the surface of the sample and select the test area based on the edge of the sample surface. In some examples, the test area can have a regular shape, such as circular or rectangular. In other examples, the selected test area can have an irregular shape.

[0054] As shown in block 706, the system can determine a center line and boundary parameters. For example, the system can determine the width of the test area on the center line and the distance from the center line to the boundary or edge.

[0055] As shown in block 710, vibration parameters, such as periodicity parameters or amplitudes, can be determined to define a vibration path. For example, periodicity parameters related to a sine wave pattern along one or both orthogonal dimensions along the surface can be defined. Further, the amplitude parameters can be determined for one or both patterns along two orthogonal dimensions.

[0056] As shown in block 712, the system can determine equidistant points along the vibration path. For example, these points can be linearly equidistant along the vibration path. In another example, the points can be curvilinearly equidistant along the vibration path.

[0057] The system can test each of the sample points defined along the vibration path. For example, as shown in block 714, the system can move the ablation point of the laser to the next sample point along the vibration path. As shown in block 716, the laser can be pulsed one or more times to generate a plasma.

[0058] As shown in block 718, the emission spectrum emitted by the plasma can be collected. Next, as shown in block 720, the emission spectrum can be converted into a signal, for example, by a spectroscopic lens or a spectrometer.

[0059] As shown in block 722, the system can determine whether it has reached the end of the sample points along the vibration path or whether to move to the next sample point along the vibration path. When reaching the end of the vibration path, the system can analyze the converted signal as shown in block 724. For example, the system can determine the composition at each point along the surface. Further, the system can determine the average composition. In one example, the system can determine the average value, median, or mode of the measured values. The system can average the measured values of the converted signal and determine the composition based on the sum of the signals. Alternatively, the system can determine the composition at each point and average the composition across the sample points.

[0060] Using such a method, a pattern can be defined that provides a desired distribution of sample points across the surface for test regions of various shapes. For example, the test region can be circular. In another example, the test region can be rectangular. In a further example, the test region can be irregular.

[0061] For example, FIG. 8 includes a diagram of an exemplary vibration path covering a circular test region. The path follows a spiral pattern. Such a pattern can be generated using a sine wave pattern in both of two orthogonal dimensions. In one example, the sine wave pattern in the first of the two orthogonal dimensions is a sine pattern, and the sine wave pattern in the second orthogonal dimension is a cosine pattern. Each sine wave pattern is a function of time. Further, in the illustrated example, the periodicity parameters associated with each of the patterns are equal. The amplitude associated with each of the sine wave patterns is the same and is a function of time. For example, the following equation (Equation 1) can be used to generate the pattern. As described, the amplitude increases with time (t) until it reaches a maximum value, and when it reaches the maximum value, the amplitude decreases. (Equation 1) x(t)=r(t)·cos(k·t), and y(t)=r(t)·sin(k·t), where 0 < t < t rmax In this case, r(t) = k r ·t, and t rmax < t < t rzero In this case, r(t) = r max -k r ·t

[0062] Here, t rmax is the time to reach the maximum radius (r(t)), and t rzero is the time when the radius (r(t)) returns to 0. k and k r are constants. FIG. 9 shows a further example of a vibration path generated using a sine wave pattern in at least one of two orthogonal dimensions along one surface. For example, the vibration path can have a sine wave pattern in the y-dimension. The periodic parameter can be defined to provide a number of vibrations across the surface. The amplitude α of the sine wave pattern is constant, and k y is constant. (Equation 2) y(t) = α·sin(k y ·t)

[0063] The second dimension, such as the x-dimension, can be defined using a linear pattern or a sine wave pattern such as a cosine pattern. In one example, the x-dimension is defined as a linear function that increases with time until it reaches the end point or full width, and at the point when it reaches the end point or full width, the pattern reverses direction using the same velocity constant k x is used. (Equation 3) 0 < t < t xmax In this case, x(t) = k x ·t, and t xmax < t < t xzero In this case, x(t) = x max -k x ·t Here, t xmax is the time when x(t) reaches the maximum width, and t xzero is the time when x(t) returns to 0.

[0064] Alternatively, the second dimension can be defined using a sine pattern such as a cosine pattern having a periodicity different from that of the sine pattern of the first orthogonal dimension. In the illustrated example, the periodicity parameter of the sine pattern is 14 times that of the cosine pattern of the second orthogonal dimension. Thus, the vibration path vibrates 7 times between the boundaries of the y dimension for each vibration across the width of the x dimension. (Equation 4) x(t) = β·cos(k x ·t) where [Number] (For example, i = 14) Here, β is a constant, k x is a constant.

[0065] Figures 8 and 9 show a vibration path whose amplitude is constant or a function of time. Alternatively, the vibration path can be defined using a pattern in which the amplitude of at least one dimension is a function of position.

[0066] Figure 10 shows a block diagram illustrating a method 1000 for determining a sine wave pattern having an amplitude as a function of position. For example, as shown in block 1002, when a test region is selected, the system can establish a center line. For example, the center line can be defined along one of the orthogonal dimensions such as, for example, the x dimension. In particular, the center line can be selected with the maximum width along the x dimension.

[0067] As shown in block 1004, the system measures the width of the center line. Based on the width of the center line, the desired number of vibrations across the surface, and the desired number of sample points, the system can determine the periodicity parameter for the sine wave pattern of one or both orthogonal dimensions, as shown in block 1006. In one example, the ratio of the periodicity parameters is an even integer. Alternatively, the ratio of the periodicity parameters is an odd integer.

[0068] When a periodic parameter is determined, the position of each peak in the period of at least one sine wave pattern among the orthogonal dimensions can be known. For example, when a sine wave function or pattern is assigned to the y dimension, based on a linear pattern or a sine wave pattern in the x dimension, the x dimension position of the peak of the sine wave pattern in the y dimension can be determined.

[0069] As shown in block 1008, the distance from the center line to the edge of the test region can be determined at each x position of the peak of the sine wave pattern in the y dimension. In block 1010, the amplitude parameter of the sine wave pattern in the y dimension can be determined based on the measured distance from the center line at each peak. For example, each time the sine wave pattern in the y dimension passes through the center line, the system can assign a new amplitude parameter to the sine wave pattern in the y dimension.

[0070] When the oscillator path is determined, the system can determine equidistant points along the oscillation path, as shown in block 1012. Such equidistant points can be sample points.

[0071] For example, FIGS. 11 and 12 show exemplary vibration paths across a circular test region. In the illustrated example, the vibration path has a sine wave pattern such as a sine pattern in the y dimension. In a further example, the pattern can include a sine wave pattern in the x dimension such as a cosine pattern. The periodic parameter of the sine wave pattern in the y dimension is 14 times the periodic parameter of the sine wave pattern in the x dimension. The amplitude of the cosine pattern in the x dimension is constant. However, the amplitude of the sine pattern in the y dimension is a function of position. For example, each time the vibration path passes through the center line, the amplitude α of the sine function in the y dimension can be changed based on the distance to the outer edge. (Equation 5) x(t)=β·cos(k x ·t), and y(t)=α(x)·sin(k y ·t), where

Number

[0072] For example, as shown in FIG. 12, the system can determine a center line having a width W in the x dimension. The amplitude of the cosine pattern in the x dimension can be selected such that the pattern crosses the full width of each period. The periodicity of the sine pattern associated with the y dimension can be selected such that the ratio of the periodicity of the sine pattern to the periodicity parameter of the cosine pattern is an integer such as 14.

[0073] Based on a known cosine pattern extending in the x dimension, the x position of each peak of the sine pattern in the y dimension can be known. Then, the system can determine the distance from the center line to the edge at the peak of the sine pattern and determine the amplitude of the sine pattern based on the distance from the center line to the edge. For example, each time the sine pattern passes through the center line, the distance to the edge can be determined, and the amplitude of the sine pattern can be determined based on the distance H'. Similarly, when the sine pattern passes through the center line, the distance H can be determined, and based on the distance H, the amplitude of the sine pattern can be determined.

[0074] FIGS. 13 and 14 include further illustrations of applying such a methodology to an irregular test area. The center line and the width of the center line W can be determined. Based on the determined center line, a pattern related to the x dimension can be determined. In one example, the pattern can be linear (e.g., Equation 3). In another example, the pattern can be a sine wave such as a cosine pattern (e.g., Equation 4).

[0075] Based on the desired frequency across the surface during each period of the cosine pattern in the x-dimension, the periodicity parameter of the sine wave pattern in the y-dimension can be determined. In the illustrated example, the ratio of the periodicity parameter in the y-dimension to that in the x-dimension is 11. The amplitude of the sine wave pattern in the y-dimension can be a function of position (e.g., Equation 5). For example, for each peak, the distance from the center line H or H' can be determined. The amplitude can be set based on the intersection of the center line towards a given peak of the sine wave pattern in the y-dimension. Thus, an irregular pattern can be traversed from end to end to provide the distribution of the sample.

[0076] For each of the vibration paths, the system can determine equidistant sample points along that path for testing using laser ablation of the surface. For example, as shown in FIG. 15, the vibration path can include equidistant sample points. The equidistant sample points can be determined based on the linear distance (e.g., Equation 6) as shown at 1504. Alternatively, the distance can be determined based on the curvilinear distance (e.g., Equation 7) along the vibration path as shown at 1506.

Number

[0077] When a laser pulse is directed at the surface to generate plasma, the mirror that directs the laser may be stationary. When the laser is being redirected, the laser pulse can be stopped. For example, as shown in FIG. 16, the laser is actuated during a period (P) when the position of the ablation point is stationary at a sample point along the vibration path. When the pulse stops, the system can change the direction of the laser and move the ablation point during a period (M). The movement during the period (M) when viewed as a position versus time can have an s-shaped form. The first derivative of the s-shaped motion provides a velocity having a triangular shape, and the second derivative provides an acceleration shown as a square wave. Thus, a vibration path with equally spaced sample points along the path provides a rapid movement between the positions and periods when the system is stationary to test points along the vibration path.

[0078] For example, as shown in FIG. 17, after a period (P) during which one or more pulses are directed at the sample surface, a rapid movement during a period (M) continues to redirect the ablation point of the laser to the next sample point. Thus, based on the positioning of the points along the path, the kinematics between each point can be defined, and during the passage of a time long enough to enable the laser to generate multiple pulses on the same spot on the sample surface in one period, the mirror is stationary. Such a passage of time is generally on the order of milliseconds. Such stationary positioning provides a stable and reproducible plasma and improves the analysis performance. During the second part or period of the kinematic movement, the ablation point is moved to the next sample point using an s-profile (displacement as a function of time). Such a profile provides a desired velocity between points and an acceleration profile that ensures smooth mirror dynamics. By utilizing both a sine wave pattern with equally spaced sample points and a kinematics with an s-profile, a system with low scanning error and desirable analysis performance is provided. Further, the analysis can be repeated at a desired speed on the order of kilohertz and above.

[0079] In the first embodiment, the method for compositional analysis includes providing a sample having a surface and using a controller to determine a plurality of equidistant positions along a vibration path along the surface. The vibration path is sinusoidal in at least one orthogonal dimension in a plane substantially parallel to the surface. For each of the plurality of equidistant positions, the method includes moving an ablation point to each equidistant position along the vibration path and pulsing an energy source to provide an electromagnetic energy beam for ablating material at the ablation point, and in response to pulsing the energy source, collecting an emission spectrum using a spectroscopic instrument. The method further includes analyzing the emission spectrum to determine the composition at the surface.

[0080] In one example of the first embodiment, moving the ablation point includes moving the sample using a translation plate.

[0081] In another example of the first embodiment and the above example, moving the ablation point includes positioning a mirror.

[0082] In a further example of the first embodiment and the above example, the plurality of equidistant positions are linearly equidistant along the vibration path.

[0083] In a further example of the first embodiment and the above example, the plurality of equidistant positions are curvilinearly equidistant along the vibration path.

[0084] In another example of the first embodiment and the above example, in another orthogonal dimension in the plane, the vibration path changes in proportion to time.

[0085] In a further example of the first embodiment and the above examples, in another orthogonal dimension in the plane, the vibration path is a sine wave. For example, the vibration path is continuously differentiable. In another example, in at least one orthogonal dimension in the plane, the vibration path varies as one of a sine function or a cosine function of time, and in another orthogonal dimension in the plane, the vibration path varies as the other of a sine function or a cosine function of time. In a further example, in at least one orthogonal dimension in the plane, the vibration path varies with a first periodicity, and in another orthogonal dimension in the plane, the vibration path varies with a second periodicity, and the first periodicity is an integer multiple of the second periodicity. For example, the integer multiple is in the range of 1 to 100, such as in the range of 2 to 20. In a further example, the integer multiple is 1, and the amplitudes of the vibration paths in both at least one dimension and another dimension are proportional to time. In another example, the amplitude of the vibration path in at least one dimension is a function of the position in another orthogonal dimension.

[0086] In a further example of the first embodiment and the above examples, analyzing the emission spectrum includes averaging the composition for each of a plurality of equidistant positions.

[0087] In another example of the first embodiment and the above examples, the method further includes selecting a test region on the surface of the sample, and the vibration path is within the test region. For example, the method further includes determining a center line of the test region and determining a width of the center line, and the center line extends in another orthogonal dimension in the plane. In one example, the method further includes using a controller to determine a distance in at least one orthogonal dimension from the center line at the peak of the sine wave vibration to the edge of the test region, and adjusting the amplitude of the sine wave vibration based on the distance.

[0088] In a second embodiment, a system for laser-induced breakdown spectroscopy includes a table for receiving a sample, a laser source for providing a laser beam, and a mirror system for directing the laser beam onto the surface of the sample. The laser beam is for ablating a portion of the sample at an ablation point to initiate a plasma that emits an emission spectrum. The system further includes a spectroscopic instrument for receiving the spectrum and a controller in communication with the mirror system. The controller is for determining a plurality of equidistant positions along a vibration path along the surface. The vibration path is sinusoidal in at least one orthogonal dimension in a plane substantially parallel to the surface. The controller is for controlling the mirror system to move the ablation point to each equidistant position along the vibration path.

[0089] In an example of the second embodiment, the controller is in communication with the laser source, and the controller is for instructing the laser to pulse the laser beam.

[0090] In another example of the second embodiment and the above example, the controller is in communication with the spectrometer, and the controller is for instructing the spectrometer to collect the emission spectrum. For example, the controller analyzes the emission spectrum to determine the composition on the surface.

[0091] In a further example of the second embodiment and the above example, the system further includes a beam expander in the path of the laser beam in front of the mirror system.

[0092] In a further example of the second embodiment and the above example, the system further includes an F-theta lens in the path of the laser beam following the mirror system.

[0093] In another example of the second embodiment and the above example, the plurality of equidistant positions are linearly equidistant along the vibration path.

[0094] In a further example of the second embodiment and the above examples, a plurality of equidistant positions are equidistant curvilinearly along the vibration path.

[0095] In a further example of the second embodiment and the above examples, in another orthogonal dimension in the plane, the vibration path changes in proportion to time.

[0096] In another example of the second embodiment and the above examples, in another orthogonal dimension in the plane, the vibration path is a sine wave. For example, the vibration path is continuously differentiable. In another example, in at least one orthogonal dimension in the plane, the vibration path changes as one of a sine function or a cosine function of time, and in another orthogonal dimension in the plane, the vibration path changes as the other of a sine function or a cosine function of time. In a further example, in at least one orthogonal dimension in the plane, the vibration path changes with a first periodicity, and in another orthogonal dimension in the plane, it changes with a second periodicity, and the first periodicity is an integer multiple of the second periodicity. For example, the integer multiple is in the range of 1 to 100, such as in the range of 2 to 20. In one example, the integer multiple is 1, and the amplitudes of the vibration paths in both at least one dimension and another dimension are proportional to time. In a further example, the amplitude of the vibration path in at least one dimension is a function of the position in another orthogonal dimension.

[0097] In a further example of the second embodiment and the above examples, the controller analyzes the emission spectrum by averaging the composition for each of the plurality of equidistant positions.

[0098] In an additional example of the second embodiment and the above examples, the controller selects a test region on the surface of the sample, and the vibration path is within the test region. For example, the controller determines the center line of the test region and is for determining the width of the center line, and the center line extends in another orthogonal dimension in the plane. In one example, the controller determines the distance in at least one orthogonal dimension from the center line at the peak of the sine wave vibration to the edge of the test region, and adjusts the amplitude of the sine wave vibration based on that distance.

[0099] In a third embodiment, a method for compositional analysis includes providing a sample having a surface and using a controller to determine a plurality of positions along a vibration path along the surface. The vibration path is sinusoidal in two orthogonal dimensions in a plane substantially parallel to the surface. The vibration path changes with time in the two orthogonal dimensions. For each position among the plurality of positions, the method includes moving an ablation point to each position along the vibration path, pulsing an energy source to provide an electromagnetic energy beam to ablate material at the ablation point, and in response to pulsing the energy source, collecting an emission spectrum using a spectroscopic instrument. The method further includes analyzing the emission spectrum to determine the composition at the surface.

[0100] In an example of the third embodiment, the plurality of positions are a plurality of equally spaced positions arranged continuously along the vibration path.

[0101] In another example of the third embodiment and the above example, the plurality of equally spaced positions are linearly equally spaced along the vibration path.

[0102] In a further example of the third embodiment and the above example, the plurality of equally spaced positions are curvilinearly equally spaced along the vibration path.

[0103] In a further example of the third embodiment and the above example, the vibration path is continuously differentiable.

[0104] In another example of the third embodiment and the above example, in one of the two orthogonal dimensions in the plane, the vibration path changes as one of a sine function or a cosine function of time, and in the other of the two orthogonal dimensions in the plane, the vibration path changes as the other of a sine function or a cosine function of time.

[0105] In a further example of the third embodiment and the above examples, in one of the two orthogonal dimensions in the plane, the vibration path changes with a first periodicity, and in the other of the two orthogonal dimensions in the plane, the vibration path changes with a second periodicity, and the first periodicity is an integer multiple of the second periodicity. For example, the integer multiple is within the range of 1 to 100, such as the range of 2 to 20. In a further example, the integer multiple is 1, and the amplitudes of the vibration paths in both at least one dimension and another dimension are proportional to time. In a further example, the amplitude of the vibration path in at least one dimension is a function of the position in another orthogonal dimension.

[0106] In a further example of the third embodiment and the above examples, analyzing the emission spectrum includes averaging the composition for each of a plurality of equidistant positions.

[0107] In another example of the third embodiment and the above examples, the method includes selecting a test region on the surface of the sample, and the vibration path is within the test region. For example, the method further includes determining a center line of the test region and determining a width of the center line, and the center line extends in another orthogonal dimension in the plane. In one example, the method further includes using a controller to determine a distance in at least one orthogonal dimension from the center line at the peak of the sine wave vibration to the edge of the test region, and adjusting the amplitude of the sine wave vibration based on the distance.

[0108] In the fourth embodiment, a system for laser-induced breakdown spectroscopy includes a table for receiving a sample, a laser source for providing a laser beam, and a mirror system for directing the laser beam onto the surface of the sample. The laser beam is for ablating a portion of the sample at an ablation point and for initiating a plasma that emits an emission spectrum. The system further includes a spectroscopic instrument for receiving the spectrum and a controller in communication with the mirror system. The controller is for determining a plurality of positions along a vibration path along the surface. The vibration path is sinusoidal in two orthogonal dimensions in a plane substantially parallel to the surface. The vibration path changes with time in the two orthogonal dimensions. The controller is for controlling the mirror system to move the ablation point to each position along the vibration path.

[0109] In an example of the fourth embodiment, the controller is in communication with the laser source, and the controller is for instructing the laser to pulse the laser beam.

[0110] In another example of the fourth embodiment and the above example, the controller is in communication with the spectrometer, and the controller is for instructing the spectrometer to collect the emission spectrum. For example, the controller analyzes the emission spectrum to determine the composition on the surface.

[0111] In a further example of the fourth embodiment and the above example, the system further includes a beam expander in the path of the laser beam in front of the mirror system.

[0112] In a further example of the fourth embodiment and the above examples, the system further includes an f-theta lens in the path of the laser beam following the mirror system.

[0113] In another example of the fourth embodiment and the above examples, the plurality of positions are a plurality of equally spaced positions arranged sequentially along the vibration path. For example, the plurality of equally spaced positions are linearly equally spaced along the vibration path. In another example, the plurality of equally spaced positions are curvilinearly equally spaced along the vibration path.

[0114] In a further example of the fourth embodiment and the above examples, the vibration path is continuously differentiable.

[0115] In a further example of the fourth embodiment and the above examples, in one of the two orthogonal dimensions in the plane, the vibration path changes as one of a sine function or a cosine function of time, and in the other of the two orthogonal dimensions in the plane, the vibration path changes as the other of a sine function or a cosine function of time.

[0116] In another example of the fourth embodiment and the above examples, in one of the two orthogonal dimensions in the plane, the vibration path changes with a first periodicity, and in the other of the two orthogonal dimensions in the plane, the vibration path changes with a second periodicity, and the first periodicity is an integer multiple of the second periodicity. For example, the integer multiple is in the range of 1 to 100, such as in the range of 2 to 20. In another example, the integer multiple is 1, and the amplitudes of the vibration paths in both at least one dimension and the other dimension are proportional to time. In a further example, the amplitude of the vibration path in at least one dimension is a function of the position in the other orthogonal dimension.

[0117] In a further example of the fourth embodiment and the above examples, the controller analyzes the emission spectrum by averaging the composition for each of the plurality of equally spaced positions.

[0118] In a fourth embodiment and further examples of the above examples, the controller selects a test region on the surface of the sample, and the vibration path is within the test region. For example, the controller determines a center line of the test region and is for determining the width of the center line, and the center line extends in another orthogonal dimension in the plane. In one example, the controller determines a distance in at least one orthogonal dimension from the center line at the peak of the sine wave vibration to the edge of the test region, and adjusts the amplitude of the sine wave vibration based on that distance.

[0119] Note that not all of the activities described above in the general description or examples are required, and in some cases, a portion of a particular activity may not be required, and one or more additional activities may be performed in addition to those described. Further, the order in which the activities are listed is not necessarily the order in which they are performed.

[0120] In the foregoing specification, concepts have been described with reference to specific embodiments. However, those skilled in the art will understand that various modifications and changes can be made without departing from the scope of the invention as set forth in the following claims. Accordingly, the specification and drawings are to be considered in an illustrative rather than a limiting sense, and all such modifications are intended to be included within the scope of the invention.

[0121] As used herein, the terms "comprises," "comprising," "includes," "including," "has," "having," or any other variation thereof are intended to cover non-exclusive inclusion. For example, a process, method, article, or apparatus that comprises a list of features is not necessarily limited to only those features, but may include other features not expressly listed or inherent to such process, method, article, or apparatus. Further, unless expressly stated to the contrary, "or" refers to an inclusive "or" and not an exclusive "or." For example, the condition A or B is satisfied by any one of the following: A is true (or present) and B is false (or absent), A is false (or absent) and B is true (or present), and both A and B are true (or present).

[0122] Also, the use of "a" or "an" is employed to describe elements and components described herein. This is for merely convenience and to give a general sense of the scope of the invention. This description should be read to include one or at least one, and the singular also includes the plural unless it is obvious that it means otherwise.

[0123] Advantages, other benefits, and solutions to problems have been described above with respect to specific embodiments. However, advantages, benefits, solutions to problems, and any feature that may give rise to any advantage, benefit, or solution, or that may become more pronounced, should not be construed as critical, required, or essential features of any or all of the claims.

[0124] After reading this specification, those skilled in the art will understand that, for clarity, the specific features described herein in the context of separate embodiments may be provided in combination in a single embodiment. Conversely, various features described in the context of a single embodiment for brevity may be provided separately or in any sub-combination. Further, references to values described in ranges include each and every value within that range.

Claims

1. A method for compositional analysis, comprising: providing a sample having a surface; selecting a test region on the surface of the sample; using a controller to determine a plurality of equally spaced positions along a vibration path along the surface, wherein the vibration path is within the test region and the vibration path is sinusoidal in at least one orthogonal dimension in a plane substantially parallel to the surface; determining a center line of the test region extending in another orthogonal dimension in the plane and determining a width of the center line; determining a distance in the at least one orthogonal dimension from the center line to an edge of the test region at a peak of the sinusoidal vibration of the vibration path; adjusting an amplitude of the sinusoidal vibration based on the distance; for each of the plurality of equally spaced positions: moving an ablation point along the vibration path to each of the equally spaced positions; ablating material at the ablation point and pulsing a laser to provide a laser beam for generating a plasma that emits light, wherein the laser is focused on the ablation point using an F-theta lens; in response to pulsing the laser, collecting an emission spectrum of the light emitted by the plasma using a spectroscopic instrument; analyzing the emission spectrum to determine a composition on the surface.

2. The method of claim 1, wherein moving the ablation point comprises moving the sample using a translation plate.

3. The method of claim 1 or 2, wherein moving the ablation point comprises positioning a mirror.

4. The method according to any one of claims 1 to 3, wherein the plurality of equally spaced positions are linearly equally spaced along the vibration path.

5. The method according to any one of claims 1 to 4, wherein the plurality of equally spaced positions are curvilinearly equally spaced along the vibration path.

6. The method according to any one of claims 1 to 5, wherein in another orthogonal dimension in the plane, the vibration path changes in proportion to time.

7. The method according to any one of claims 1 to 6, wherein in another orthogonal dimension in the plane, the vibration path is sinusoidal. Claim 8 The method according to claim 7, wherein the vibration path is continuously differentiable. Claim 9 The method according to claim 7, wherein in the at least one orthogonal dimension in the plane, the vibration path changes as one of a sine function or a cosine function of time, and in the other orthogonal dimension in the plane, the vibration path changes as the other of a sine function or a cosine function of time. Claim 10 The method according to claim 7, wherein in the at least one orthogonal dimension in the plane, the vibration path changes with a first periodicity, and in the other orthogonal dimension in the plane, the vibration path changes with a second periodicity, and the first periodicity is an integer multiple of the second periodicity. Claim 11 The method according to claim 10, wherein the integer multiple is in the range of 1 to 100. Claim 12 The method according to claim 11, wherein the integer multiple is in the range of 2 to 20. Claim 13 The method according to claim 10, wherein the integer multiple is 1, and the amplitudes of the vibration paths in both the at least one orthogonal dimension and the other orthogonal dimension are proportional to time. Claim 14 The method according to claim 10, wherein the amplitude of the vibration path in the at least one orthogonal dimension is a function of the position in the other orthogonal dimension. Claim 15 The method according to any one of claims 1 to 14, wherein analyzing the emission spectrum includes averaging the composition for each of the plurality of equidistant positions.

Images