Patent Description:
Laser-induced breakdown spectroscopy (LIBS) is a well-known technique to retrieve elemental information from a given sample. A typical LIBS measurement is performed as follows: a short laser pulse is sent and focused onto a sample surface; the surface is rapidly heated by the laser pulse, part of the material is vaporized, and the gas is transformed into plasma, the plasma composition being representative of the sample's elemental content; excited electrons in the plasma eventually return to the ground state of their associated atoms as the plasma cools, and the radiative electron recombination emits photons with discrete energies allowed by their associated atoms energy levels; and the emitted photons are collected and sent in a spectrometer to produce optical emission spectra. The spectral distribution of the spectra (intensity versus wavelength) is linked to the elemental composition of the plasma, hence to the elemental composition of the sample. For example, see <CIT> and references cited therein.

LIBS systems known in the art typically fall within one of three types:.

Document "<NPL> discloses using the first laser-induced breakdown spectrometer (LIBS) on a planetary mission, and provides sample texture and morphology data using a remote micro-imager (RMI) for finding quantitative elemental compositions including light elements like hydrogen and some elements to which LIBS is uniquely sensitive (e.g., Li, Be, Rb, Sr, Ba); remote removal of surface dust and depth profiling through surface coatings; context imaging; and passive spectroscopy over the <NUM>-<NUM> range. ChemCam comprises an optical demultiplexer, three spectrometers, detectors, their coolers, and associated electronics and data handling logic. Additional instrument components include a <NUM> optical fiber which transfers the LIBS light from the telescope to the body unit, and a set of onboard calibration targets.

Document <CIT> discloses a handheld LIBS spectrometer that includes an optics stage movably mounted to a housing and including a laser focusing lens and a detection lens. A laser source in the housing is oriented to direct a laser beam to the laser focusing lens. A spectrometer subsystem in the housing is configured to receive electromagnetic radiation from the detection lens and to provide an output.

Document <CIT> discloses systems, methods, compositions, and apparatus for laser induced ablation spectroscopy are disclosed. Light emitted from a plasma plume produced with laser ablation can be gathered into a lightguide fiber bundle that is subdivided into branches. One branch can convey a first portion of the light to a broadband spectrometer operable to analyze a relatively wide spectral segment, and a different branch can convey a second portion of the light to a high dispersion spectrometer operable to measure minor concentrations and/or trace elements. Emissions from a plasma plume can be simultaneously analyzed in various ways using a plurality of spectrometers having distinct and/or complementary capabilities.

Document "<NPL>, discloses an experiment to perform laser induced breakdown spectroscopy, using minor modifications of our existing laser blow-off impurity injection system. The radiation produced by the laser pulse focused at the TJ-II wall evaporates a surface layer of deposited impurities and the subsequent radiation produced by the laser-produced plasma is collected by two separate lens and fiber combinations into two spectrometers. The first spectrometer, with low spectral resolution, records a spectrum from <NUM> to <NUM> to give a survey of impurities present in the wall. The second one, with high resolution, is tuned to the wavelengths of the Hα and Dα lines in order to resolve them and quantify the hydrogen isotopic ratio present on the surface of the wall.

There remains a need in the field for a LIBS system that could combine higher sensitivity comparable to laboratory or industrial systems, with the portability of handheld systems.

In accordance with one aspect, there is provided a Laser-Induced Breakdown Spectroscopy (LIBS) system to detect a constituent element of interest within a sample.

The LIBS system is disclosed in independent claim <NUM>.

In some implementations, the probe optics include an upstream dichroic filter centered on a wavelength of the light pulses, the upstream dichroic filter being positioned to respectively direct:.

In some implementations, the probe optics further include a scanning mirror assembly provided between the upstream dichroic filter and the probing interface.

In some implementations, the probing interface comprises a transparent window. In some implementations, the pulsed laser source is mounted within the probe head.

In some implementations, the downstream dichroic filter is centered on the spectral feature of the constituent element of interest and disposed to separate the plasma light into said narrowband and broadband spectral portions. In some implementations, the probe optics are mounted within the probe head.

In some implementations, the LIBS system further includes a first optical fiber link having a fiber input disposed to receive the narrowband spectral portion of the plasma light from the probe optics and a fiber output connected to the high-resolution spectrometer, and a second optical fiber link having a fiber input disposed to receive the broadband spectral portion of the plasma light from the probe optics and a fiber output connected to the low-resolution spectrometer.

In some implementations, the element detection assembly may include a photomultiplier detector or an avalanche photodiode coupled to an output of the high-resolution spectrometer.

In some implementations, the broadband detection assembly may include a CCD camera coupled to an output of the low-resolution spectrometer.

In some implementations, the high-resolution spectrometer is based on a Czerny-Turner configuration using cascaded primary and secondary gratings without intervening optics therebetween.

In some implementations, the low-resolution spectrometer is based on a folded or unfolded Czerny-Turner configuration comprising a planar grating.

In some implementations, the low-resolution spectrometer comprises a concave grating.

In some implementations, the LIBS system, further includes a mobile housing enclosing therein the element detection assembly and the broadband detection assembly, a power supply unit enclosed within said mobile housing, and wire connectors providing electrical and optical communication between the mobile housing and the probe head.

Other features and advantages of the invention will be better understood upon reading of embodiments thereof with reference to the appended drawings.

Embodiments described herein generally concern a LIBS system to detect a constituent element of interest within a sample.

As readily understood by those skilled in the art, LIBS generally relies on the use of a repetitively-fired laser source to emit intense and short pulses of light that are used to ablate/vaporize matter from a sample target. The interaction of the light pulses with the vaporized matter creates a plasma plume, which in turn radiates light. The analysis of the plasma-emitted light brings qualitative and quantitative information on the nature and concentration of the constituent elemental components of the target. More specifically, the qualitative and quantitative data related to the elemental components of the target is obtained from the processing and analysis of the spectral signature of the plasma-emitted light.

In a typical LIBS configuration, the light emitted by the plasma is optically collected and brought into a spectrometer, whose function is to extract the spectral information contained in the plasma-emitted light. The output of the spectrometer consists of a spectrum (in the form of a two-dimensional profile representing the light intensity vs. optical wavelength), which is characteristic of the collected light. The spectral distribution is recorded by means of a detector (often a line or <NUM>-D camera).

The spectral profile provided by the spectrometer is made up of a collection of spectral lines. Each of these lines is related to an element present in the plasma plume. The elements found in the plasma come from the ablated/vaporized matter from the target and from the ambient gas, if any. The analysis of the spectral lines provides information on the nature of the elements in the plasma as well as their concentration.

In some implementations, the LIBS systems presented herein have a hybrid configuration which provides both a low-resolution spectrum of the plasma light covering a broad spectral range, and a high-resolution spectrum of the same plasma light over a narrow spectral range centered on a spectral line or feature of a constituent element of interest of the sample.

LIBS systems according to the present description may be useful in a variety of context where an elemental analysis of a sample is desired, such as soils or organic products analysis, the evaluation of minerals and other samples from the mining industry, material science and thin-film analysis, pharmaceutical products monitoring, material sorting and recycling, archeology and cultural artifacts studies, etc..

In some implementations, the present LIBS system may be of use in the context of mining, in particular gold mining. Gold mines are very important economic assets for many countries in the world. However, mining industries are facing increasing decisional challenges associated with lower grade ore and complexity of mineralization with higher impurity levels, which imply more frequent sample analyses in the production process. Mining sample analyses performed using conventional techniques typically involve wait times of at least <NUM> hours, causing production delays on the mining or exploration sites and thus increasing the operating and production costs.

In order to address these issues, the mining industry would benefit from the measure of precious metal concentration in real time and on site during the different exploration and mining production stages. In the case of gold, the ability to measure an average concentration down to about <NUM> ppm is desired. Existing technology, such as infrared spectroscopy, allows determining the mineralogy of the rock samples (quartz, pyrite, chalcopyrite, sphalerite, arsenopyrite, etc.), but the elemental composition is out of reach with this technique. Furthermore, X-ray fluorescence has been used successfully for determining the concentration of some basic metals such as copper, zinc and nickel; it is however inadequate for quantifying gold concentration, because of the low sensitivity and poor limits of detection. Additionally, the gold spectral line used in x-ray fluorescence suffers from interference with a strong zinc line which compromises the sensitivity of this technique for the determination of gold concentration.

LIBS technology is a suitable candidate for providing the desired analysis of gold samples. However, the detection of gold in rocks by prior art LIBS setups or instrumentation at such low concentration levels requires the use of high resolution spectrometer and highly sensitive ICCD detector which are bulky, costly and not robust; as a result of these drawbacks, the prior art LIBS instrumentation is not well adapted for onsite and harsh mining environment.

Advantageously, embodiments of LIBS systems described herein can provide a fast method for measuring the content of gold, and identifying the matrix in which gold is embedded. In addition, such embodiments provide a portable instrument that can be brought onsite for fast analysis without sample preparation.

Referring to <FIG>, there is schematically illustrated a LIBS system <NUM> according to one embodiment. It will be readily understood that the configuration illustrated and described herein is shown by way of example only and is in no way meant as limitative to the invention.

In some implementations, the illustrated LIBS system can be designed in a compact portable arrangement and can be brought to a sample <NUM> for analysis. Features of such an arrangement are described and explained further below.

The LIBS system <NUM> includes a pulsed laser source <NUM> generating light pulses <NUM> apt to create a plasma <NUM> upon irradiating the sample <NUM>, according to the LIBS process described above. As well known in the art, the measurement sensitivity depends on the laser beam fluence (defined as the ratio corresponding to the laser pulse energy divided by the area of the beam spot) at the target surface. For instance, to achieve the ablation of the target material and create a plasma, a minimum (threshold) value of the fluence must be reached. Furthermore, the sensitivity is a function of the radiant flux emitted by the plasma; for a given fluence, the larger the plasma size (that is, the larger the beam spot size), the higher the total radiant flux which can be collected by the system. By way of example, the pulsed laser source <NUM> may be embodied by a flash lamp-pumped (FP) or diode-pumped solid-state (DPSS) laser source with active Q-switching, or the like. The light pulses may having a pulse energy from a few mJ to a few hundreds of mJ; a spot size (diameter) from a few <NUM> µm to <NUM>; and a repetition rate from a few Hz to <NUM>. In accordance with some implementations, the duration of the laser pulses is short, for example in the nanosecond regime. The full width at half-maximum (FWHM) of the pulses may for example be within the range of a few nanoseconds. Therefore, in this regime, the plasma light emission begins just after the laser pulse firing; it then grows, decays and finally disappears after a certain period of time, referred to as the plasma lifetime.

According to the invention, the LIBS system <NUM> has a hybrid configuration including two different detection schemes, enabled by two separate detection assemblies: an element detection assembly <NUM>, and a broadband detection assembly <NUM>. The element detection assembly <NUM> includes a high-resolution spectrometer <NUM> having a narrowband spectral range covering a spectral feature of the constituent element of interest, whereas the broadband detection assembly <NUM> includes a low-resolution spectrometer <NUM> having a broadband spectral range.

In the context of the present description, the term "resolution" in meant to refer to the spectral resolution of the corresponding spectrometer, typically defined as the minimum wavelength difference between two wavelengths that can be resolved unambiguously. The expression "high-resolution" is meant to refer to a resolution sufficient to allow the identification of a spectral feature of the constituent element of interest for a given application. The expression "narrowband" is meant to refer to a spectral bandwidth broad enough to cover the spectral feature of interest while being small enough to distinguish this spectral feature. By contrast, the expression "low-resolution" and "broadband" are meant to refer to a resolution and spectral range allowing an overview of the spectral contents of the plasma light without necessarily permitting identification of all individual lines. Furthermore, it will be readily understood that the terminology explained above is used herein in relatively, that is, to distinguish the different components of the LIBS system from each other without imparting limits on the scope of protection.

In some embodiments the high-resolution spectrometer <NUM> of the element detection assembly <NUM> may be based on the so-called Czerny-Turner configuration or Czerny-Turner spectrometer, a dominant design of spectrometers used in LIBS analysis. In such a configuration, the received plasma light is transferred to an array detector via an optical path that involves one or more dispersing elements. In other variants, the high-resolution spectrometer may be based on other designs known in the art, such as for example an echelle spectrometer.

Referring to <FIG>, there is shown an exemplary design for the element detection assembly <NUM>. In this example, the high-resolution spectrometer <NUM> is based on a Czerny-Turner design using cascaded gratings. Such a design is shown in provisional patent application number <CIT> and entitled "High resolution and high throughput spectrometer", the entire contents of which is incorporated herein by reference.

In the particular implementation of <FIG>, the spectrometer <NUM> includes an input slit <NUM> through which a light beam <NUM> to be analyzed is received, followed by one or more collimating lenses <NUM>. The input slit <NUM> creates a point-type source from the incoming light, and the light beam <NUM> is therefore spatially divergent upon entering the spectrometer. The collimating lens <NUM> is disposed across the path of the diverging light beam <NUM> and aligns its composing beamlets along a parallel direction, thereby collimating the light beam <NUM>. Each collimating lens <NUM> may be embodied by a cylindrical lens or by a spherical singlet lens, a multi-element spherical lens assembly (such as a combination of plano-convex and meniscus lenses, or an achromatic doublet), by a non-spherical singlet lens (such as a best-form or aspheric lens), or the like.

The spectrometer <NUM> further includes a primary diffraction grating <NUM> on which the light beam <NUM> impinges. In the illustrated variant, the primary diffraction grating <NUM> is disposed immediately downstream the collimating lens <NUM>, without intervening optics. In the illustrated implementation, the light beam <NUM> impinges on the primary diffraction grating <NUM> at normal incidence.

As known in the art, light at normal incidence on the primary diffraction grating <NUM> will be diffracted according to the so-called basic grating equation. Preferably, the primary diffraction grating <NUM> is designed such that light at wavelength of interest is diffracted within the -<NUM> and +<NUM> diffraction orders of the grating, defining two primary diffracted beams <NUM> and <NUM>'.

The spectrometer <NUM> further includes two planar secondary diffraction grating <NUM> and <NUM>' positioned in a path of the primary diffracted beams <NUM> and <NUM>', preferably at normal incidence. Each secondary diffraction grating <NUM> and <NUM>' diffracts the corresponding primary diffracted light beam <NUM> and <NUM>' into a twice diffracted beam <NUM>, <NUM>'. In this embodiment, the primary and secondary diffraction gratings <NUM> and <NUM>, <NUM>' are disposed in a cascade without intervening optics therebetween. The provision of a pair of secondary diffraction gratings <NUM>, <NUM>' and corresponding branches can advantageously provide the parallel and simultaneous analysis of two different spectral features within a same spectral band of the light beam <NUM>.

The spectrometer may further include one or more imaging lens <NUM>, <NUM>' disposed in the path of each twice diffracted beam <NUM>, <NUM>'. The spectrometer <NUM> therefore provides as output two focused light beams of limited spectral bandwidth in which different wavelengths are spatially separated. As will be noticed, in the illustrated variant the secondary diffraction gratings <NUM>, <NUM>' <NUM> are positioned so as to reflect the corresponding twice diffracted beam <NUM>, <NUM>' rearwardly of the primary grating <NUM>, in a cross-beam configuration. Such a configuration can provide a long focal length within an optimized compact form factor.

The element detection assembly <NUM> further includes a photodetector <NUM>, <NUM>' apt to provide a spectrogram of the output light of both branches of the spectrometer <NUM>. Each photodetector <NUM> may for example be embodied by an avalanche photodiode, a photomultiplier tube, a single-photon avalanche diode (SPAD), a Silicon photomultiplier detector (SiPM). The photodetector may also consist in a linear or two-dimensional array of individually addressable SPADs or SiPMs; such a combination of detectors would allow to record a portion of the spectral light distribution found in the spectrometer image plane. The photodetector <NUM>, <NUM>' may be spectrally resolved. In the illustrated variant, mechanisms providing a fine tuning of the wavelength on each photodetector <NUM>, <NUM> may be provided. Such a mechanism may for example be embodied by a wavelength tuning refractive plate <NUM>,<NUM>' used in transmission, whose angular position may be accurately controlled using miniature stepping motors with encoders (not shown).

Characteristics and relative positions of optical components of the spectrometer <NUM>, define the range of wavelengths the spectrometer <NUM> is able to consider in the analysis. While such spectrometer can be applied for high-quality analysis, due to physical characteristics of the optical components of the spectrometer required to reach a sufficient range of wavelengths, the optical path defined by the optical components of the spectrometer <NUM> cannot be made arbitrarily short. In particular, the operation of the diffraction element <NUM> typically requires a certain minimum length for the optical path. In other words, the minimum size of the portable analyser employing the spectrometer <NUM> is limited due to the length of the optical path. On the other hand, having a portable analyser device of as small size as possible would be preferred to make the handling of the analyser device more convenient for the user and also to enable using the analyser device in narrow spaces. The configuration described above and other equivalents design can advantageously be helpful in minimizing the footprint of the spectrometer <NUM>, favoring portability.

Referring to <FIG>, there is shown an example of a broadband detection assembly <NUM>, including the low-resolution spectrometer <NUM> and a detector, for example a CCD line camera <NUM> as known in the art. In some embodiments the low-resolution spectrometer may also be based on a Czerny-Turner configuration, for example a single-grating design such as known in the art. By way of example, such a Czerny-Turner configuration may be of the unfolded type such as shown in <FIG>, and may include an input slit <NUM>, a plane grating <NUM>, a collimating spherical mirror <NUM> and a focusing spherical mirror <NUM>. Referring to <FIG>, the Czerny-Turner configuration may also be of the folded/crossed type, in which the light paths intersect; this design allows a more compact form factor than its unfolded counterpart. Such a configuration includes an input slit <NUM>, a plane grating <NUM>, a collimating spherical mirror <NUM> and a focusing spherical mirror <NUM>. In other embodiments, the low-resolution spectrometer may be based on the use of a concave grating. This design relies on a fewer number of optical components than the Czerny-Turner approach, since the beam collimating and imaging functionalities are both performed by the grating itself, owing to its concaveness. Referring to <FIG>, there is shown a typical basic concave grating design comprises an input slit <NUM> and a concave grating <NUM>.

In accordance with some implementations, the high-resolution spectrometer <NUM>, the low-resolution spectrometer <NUM> or both are operated in a time-gated regime. As is known to those skilled in the art, the temporal behaviour of the LIBS plasma-emitted light is correlated to the evolution of the plasma temperature and the electronic density. In an initial phase of the plasma lifetime, the plasma light is dominated by a "white light" continuum that has little intensity variation as a function of wavelength. This light is caused by bremsstrahlung and recombination radiation from the plasma, as free electrons and ions recombine in the cooling plasma. If the plasma light is integrated over the entire life-time of the plasma, this continuum light can seriously interfere with the detection of weaker emissions from minor and trace elements in the plasma. For this reason, LIBS measurements are usually carried out using time-resolved detection. In this way the strong background light from the initial phase can be removed from the measurements by turning the detector on after this background light has significantly subsided in intensity, but atomic emissions are still present. Relevant parameters for time-resolved detection generally include td, the time between plasma formation and the start of the observation of the plasma light, and tb, the time period over which the light is recorded.

By selecting a proper time delay td between the onset of the light pulse and the signal acquisition window, the optimum contrast between the intensity the spectral lines of interest and the signal background can be achieved. This increases the dynamic range of the measurement, which in turn contributes to maximize the sensitivity of the technique and to achieve lower values for the limit of detection (LOD).

When performing time-resolved measurements, the gated spectral signal is acquired at each laser shot (or laser pulse). To achieve time-resolved measurements, a CCD camera equipped with an image intensifier (ICCD) is used as detector. In this configuration, the image intensifier has two functions: it acts as a very fast optical shutter (typically with sub-ns rise and fall times), therefore allowing the selection of relevant gating parameters td and tb with high accuracy and shot-to-shot reproducibility; and owing to its adjustable internal gain, it allows matching/optimizing the dynamic range of the input signal intensity with the camera's CCD sensor.

In some implementations, delayed signal acquisition (td) may also be performed using low cost line cameras such as those equipping some compact spectrometers. However, these detectors have substantial limitations related to the acquisition gate width (tb), which in some cases cannot be set below a given value (e.g. the ms range).

Referring back to <FIG> and with additional reference to <FIG>, as will be readily understood by one skilled in the art, the LIBS system <NUM> comprises probe optics <NUM> directing, shaping, focussing, collecting or otherwise acting on light travelling within the system.

The probe optics defines a probing light path <NUM> generally directing the light pulses <NUM> from the pulsed light source <NUM> to the sample <NUM> and collecting the resulting plasma light <NUM>. A transparent window or equivalent structure can define a probing interface <NUM> through which light exists and enters the LIBS system <NUM>. The probe optics <NUM> may further define a first output light path <NUM> directing a narrowband spectral portion <NUM> of the plasma light <NUM> encompassing the spectral feature of the constituent element of interest to the high-resolution spectrometer <NUM>, and a second output light path <NUM> directing a broadband spectral portion <NUM> of the plasma light <NUM> to the low-resolution spectrometer <NUM>. The probe optics <NUM> therefore optically couples the probing interface <NUM> with the pulsed laser source <NUM>, the low-resolution spectrometer <NUM> and the high-resolution spectrometer <NUM>. In the illustrated embodiment, the probe optics <NUM> include, along the probing light path, a laser beam attenuator <NUM> positioned downstream the output of the pulsed laser source <NUM>, for example embodied by a polarizer <NUM> at a <NUM> degrees angle with respect to the propagation direction of the light pulses <NUM> and positioned between a halfwave plate <NUM> and a quarterwave plate <NUM>. The probe optics <NUM> next include a laser beam expander <NUM>, here illustrated as lenses <NUM>. The probe optics <NUM> may further include a focussing and imaging lens <NUM>, and a scanning mirror assembly <NUM>. The scanning mirror assembly <NUM> is for example embodied by a pair of pivoting mirrors 48a, 48b which can be jointly operated to spatially scan the light pulses <NUM> over the sample <NUM> through the transparent window <NUM>, as is well known in the art. It will be readily understood that the laser beam attenuator <NUM>, laser beam expander <NUM> focussing and imaging lens <NUM> and scanning mirror assembly <NUM> are typical components well known in the art of optics and that a variety of different components or configurations could alternatively be used, as well known to those skilled in this art.

Still referring to the configuration of <FIG>, the probe optics <NUM> include an upstream dichroic filter <NUM> provided in the path of the light pulses <NUM>, for example positioned between laser beam expander <NUM> and the focussing imaging lens <NUM>. As known to those skilled in the art, dichroic filters are optical components having a birefringence designed to split incoming light according to spectral content. In the illustrated example, the upstream dichroic filter <NUM> is a bandpass filter centered on the wavelength of the light pulses <NUM>; accordingly, the light pulses <NUM> are transmitted through the upstream dichroic filter <NUM>, whereas the plasma light <NUM> at other wavelengths incident thereon is reflected. The upstream dichroic filter <NUM> is positioned to respectively direct the light pulses <NUM> from the laser source <NUM> towards the probing interface <NUM>, and the plasma light <NUM> from the probing interface <NUM> towards the element detection assembly <NUM> and broadband detection assembly <NUM>. By way of example, the upstream dichroic filter <NUM> may be disposed at a <NUM>° angle with respect to the common propagation axis of the light pulses <NUM> and plasma light <NUM>. Of course, in other configurations a notch filter could be used and/or the upstream dichroic filter <NUM> may be arranged to transmit the plasma light <NUM> and reflect the laser pulses <NUM>.

The probe optics <NUM> next include a downstream dichroic filter <NUM> centered on the spectral feature of the constituent element of interest. The downstream dichroic filter is disposed to separate the plasma light <NUM> into the narrowband and broadband spectral portions <NUM> and <NUM>. According to the invention, the downstream dichroic filter <NUM> is a notch filter reflecting the narrowband spectral portion <NUM> and transmitting through the broadband spectral portion <NUM>. Of course, in other configurations a bandpass filter could be used and/or the downstream dichroic filter <NUM> may be arranged to transmit the narrowband spectral portion <NUM> and reflect the broadband spectral portion <NUM>.

Along the first output light path <NUM>, the LIBS system <NUM> may include a first optical fiber link <NUM> having a fiber input <NUM> disposed to receive the narrowband spectral portion <NUM> of the plasma light from the probe optics <NUM>, and a fiber output <NUM> connected to the high-resolution spectrometer <NUM>. A first focussing lens <NUM> may be provided upstream the first optical fiber link <NUM> to focus the narrowband spectral portion <NUM> of the plasma light onto the fiber input <NUM>. Of course, numerous other configurations are possible using any number of optical components as well known in the art.

Along the second output light path <NUM>, the LIBS system <NUM> may further include a second optical fiber link <NUM> having a fiber input <NUM> disposed to receive the broadband spectral portion <NUM> of the plasma light from the probe optics <NUM>, and a fiber output <NUM> connected to the low-resolution spectrometer <NUM>. In the illustrated configuration, a wideband mirror <NUM> redirects the broadband spectral portion <NUM> in a direction parallel to the propagation direction of the narrowband spectral portion <NUM> and a second focussing lens <NUM> may be provided upstream the second optical fiber link <NUM> to focus the broadband spectral portion <NUM> of the plasma light onto the fiber input <NUM>. Again, numerous other configurations are possible using any number of optical components as well known in the art.

Referring to <FIG>, <FIG>, in some implementation the LIBS system <NUM> described herein may be embodied in a portable design. By "portable" it is understood that an operator or user may carry all the components of the system to a site of a sample to perform the LIBS analysis on-site. It will be further understood that the portable design of the present LIBS system <NUM> does not necessarily involve that the system can be handheld, i.e. fit in an operator's hand, although in some implementations at least some components of the LIBS system <NUM> may be small enough to be handheld.

According to the invention, the LIBS system includes probe head <NUM> transportable by a user or operator to a sample site. The probe head <NUM> includes a probing interface as defined above, i.e. configured to irradiate the sample with the light pulses and collect resulting plasma light. The pulsed laser source may be mounted within the probe head <NUM>, although in some embodiment it may be part of a separate structure optically connected to the probe head via optical fiber. The probe optics, or at least some components thereof, may also be mounted within the probe head <NUM>.

Referring more particularly to <FIG>, an example conceptual design of a probe head <NUM> is illustrated. In this design, the probe head houses all of the components of the probe optics <NUM> as described above. Of course, other configurations could be implemented. In some variants, the probe head <NUM> may be mounted on a swivelling base pod <NUM> or similar structure facilitating its handling. Referring back to <FIG>, the LIBS system <NUM> further includes a mobile housing <NUM> in which are enclosed the element detection assembly and the broadband detection assembly. Other components may also be provided in the mobile housing <NUM>, such as for example a power supply unit <NUM> for providing electrical power to active components of the system. Wire connectors <NUM> can provide electrical and optical communication between the mobile housing <NUM> and the probe head <NUM>. In the illustrated embodiment, the mobile housing <NUM> is the size of a suitcase, although different form factors and sizes may be considered depending on the nature of the components housed therein. Depending on the intended context of use, the probe head <NUM> and mobile unit <NUM> may be made of rugged materials suitable to the environment of the sample site and apt to protect the components therein.

Referring to <FIG>, examples of data that can be obtained using LIBS systems such as described herein are presented.

<FIG> and <FIG> illustrate the spectra obtained on a quartz chlorite matrix. The full spectrum obtained through the broadband detection assembly is shown, and a window illustrates the high-resolution spectrum obtained through the element detection assembly, showing the dependence of gold versus concentration. Furthermore, the full spectrum allows to draw quantitative information on the concentration of several elements contained in the matrix, such as Si, Mg, Ca, Na, etc., which may be present at the % level. This can be achieved by performing univariate analysis of the spectral data, using appropriate spectral lines found in the full spectrum. One can also deploy chemometric (multivariate) analysis methods and algorithms, such as the Principal Components Analysis PCA, and apply them to the spectral data extracted from the full spectrum. Such methods can be used to draw information pertaining to the mineralogy of the sample being probed, as known in the art.

<FIG> shows the narrowband spectrum obtained through the high-resolution spectrometer, centered on the <NUM> gold spectral line. As already mentioned above, univariate analysis can also be performed using the <NUM> line in order to obtain the trace concentrations of gold in the matrix. Moreover, information contained in the full spectrum, such as selected spectral background data or the energy density measured within a given spectral range, can be used to determine the proper univariate calibration parameters to be applied to the high-resolution data, as a function of the actual mineralogical matrix encountered.

<FIG> illustrates a calibration curve obtained with the high-resolution spectrometer described herein, again using univariate processing of the data obtained from the quartz chlorite reference gold samples.

Claim 1:
A Laser-Induced Breakdown Spectroscopy (LIBS) system to detect a constituent element of interest within a sample (<NUM>) having a target spectral feature, said LIBS system (<NUM>) comprising:
- a pulsed laser source (<NUM>) generating light pulses (<NUM>) apt to create a plasma (<NUM>) upon irradiating said sample (<NUM>);
- an element detection assembly (<NUM>) comprising a high-resolution spectrometer (<NUM>) having a narrowband spectral range covering the spectral feature of the constituent element of interest and a resolution sufficient to distinguish the spectral feature of the constituent element of interest;
- a broadband detection assembly (<NUM>) comprising a low-resolution spectrometer (<NUM>) having a broadband spectral range;
- a probe head (<NUM>) transportable by a user to a sample site and having a probing interface (<NUM>) configured to irradiate the sample (<NUM>) with the light pulses (<NUM>) and collect resulting plasma light (<NUM>);
- probe optics (<NUM>) optically coupling the probing interface (<NUM>) with the pulsed laser source (<NUM>), the low-resolution spectrometer (<NUM>) and the high-resolution spectrometer (<NUM>), the probe optics (<NUM>) comprising a dichroic notch filter (<NUM>) or a bandpass filter (<NUM>) for:
directing a narrowband spectral portion (<NUM>) of the plasma light (<NUM>) encompassing said spectral feature of the constituent element of interest to the high-resolution spectrometer (<NUM>) on a first output light path (<NUM>); and
directing a broadband spectral portion (<NUM>) of said plasma light (<NUM>) to the low-resolution spectrometer (<NUM>) on a second output light path (<NUM>),
wherein a dichroic notch filter (<NUM>) reflects the narrowband spectral portion (<NUM>) and transmits the broadband spectral portion (<NUM>) and a bandpass filter (<NUM>) transmits the narrowband spectral portion (<NUM>) and reflects the broadband spectral portion (<NUM>).