FR2883977A1 - LASER MACHINE FOR DIRECT ANALYSIS - Google Patents

Abstract

The invention relates to a direct analysis laser machine for the elemental microanalysis of samples comprising an ablation chamber (1), laser ablation means (9), a focusing means (8), a set of analysis (12) and gas transfer means (17). According to the invention, it comprises means for moving the laser beam (18) disposed between the laser ablation means (9) and the sample holder (5) adapted to return the laser beam (10) of the laser ablation means (9) to at least one ablation zone (11) and allowing the laser beam (10) to move on the surface (7) of at least one sample (6) to be analyzed in two directions parallel to said surface (7) so as to carry out a rapid etching of at least one ablation zone (11).

Description

The present invention relates to a direct analysis laser machine for the

  elemental microanalysis of samples.

  The techniques of analysis and microanalysis of trace metals in solid samples consist for the most part of solids dissolution (chemical attacks), followed by detection by spectrometry (AAS, ICPAES, ICPMS). These techniques are used for the analysis of various metal oxide layers of wafers in the microelectronics industry, catalyst poison analysis, polymer analysis, metal alloy analysis, analysis of petroleum products (heavy fraction), analysis of environmental samples, etc.

  Another particularly sensitive analytical area relates to protein speciation analysis previously separated on 1D or 2D gel.

  The dissolution stage is on the one hand very restrictive, long, and sometimes non-quantitative (loss of certain elements during the mineralization) and on the other hand can lead to contamination of the sample.

  For these reasons, direct analysis techniques, such as that of patent WO 02068952, have been developed in the past (laser ablation, glow discharge, etc., coupled to ICPAES or ICPMS spectrometry).

  These techniques make it possible to have a very high spatial resolution (5200 μm) and seem well suited to microanalysis. However, these are relatively little used in comparison with wet digestion techniques because of the inherent problems of these techniques, particularly related to calibration and sampling. Current laser devices do not always make it possible to have a sampling perfectly representative of the sample, which is unfavorable for ICPMS analysis by what is called an "elementary fractionation". Elementary fractionation is related to ablation processes that result in phase enrichments or the production of too large particles that induce a biased elemental analysis depending on the elements and materials analyzed.

  In recent years, the trend has been towards the development of lasers operating at wavelengths in the UV (266, 213, 193 or even very recently 157 nm) allowing a much more efficient radiation material coupling, favoring explosive phenomena to the detriment thermal phenomena. The quality of the ablation has thus significantly improved. However, the thermal effects still remain, always leading to problems of elementary fractionation.

  Moreover, current laser devices are limited to a depth resolution of the order of one micron / pulse, which does not allow to consider layer analyzes as required.

  In the field of analysis, the most efficient lasers at the present time are excimer lasers of ArF type operating at 193 nm or F2 type operating at 157 nm. However, they have certain limitations in addition to those mentioned above: size, equipment can hardly be moved, need to fill the laser cavity with gaseous fluorine (very toxic compound), complex implementation, control software / user interface relatively little elaborate.

  A femtosecond laser coupling / ICPMS has been developed.

  The results show the benefits of femtosecond ablation compared to the UV laser operating in nanosecond pulse regime. This lies in the ablation regime. We then have a so-called cold ablation insofar as the temperature of the plasma formed on the surface of the sample is lower than that measured with a nanosecond laser. Moreover, the interaction time between the plasma and the material is very low. The thermal phenomena are therefore strongly attenuated and the particles produced extremely thin. The elemental fractionation is almost eliminated. In addition, the spatial resolution in depth with this type of laser is of the order of 10 nm / pulse, which makes possible the analysis of extremely thin layers.

  However, this coupling was developed from a high energy femtosecond laser (of the order of some mJ / pulse, low firing rate (about 10 Hz), very cumbersome hence a difficulty of implementation and price because femtosecond lasers are very expensive.

  Some laser sources can operate at a very high rate of fire and low energy per pulse, femtosecond or nanosecond. However, under these conditions, the craters spread over a range of 5 to 30 μm. The sensitivity of the laser / ICPMS coupling that is directly related to the etched surface remains poor and the sampling is not yet sufficiently representative.

  For these reasons, while remaining in the field of microanalysis, it would be desirable, for certain applications, to increase the size of formed craters up to 100 to 200 pm in diameter or more, while keeping the possibility of working with craters of small diameter.

  A signal-to-noise gain of the order of a factor of 40 would be possible by moving from a crater diameter of 15 to 100 μm.

  And a larger apparent beam size makes it easier to average the results of analyzes per unit area.

  Another problem arises in the isotopic dilution analysis which is a calibration analytical technique used in liquid analysis consisting in using as an internal standard an isotope of the analyte element in mass spectrometry. It is a question of mixing with a sample to be analyzed, of known isotopic composition, a minute and perfectly characterized quantity of a solution enriched in an isotope of the element to be analyzed. During sample preparation and analysis, the added isotope behaves in exactly the same way as the isotopes of the element to be analyzed in the sample, making it possible to correct all the biases very effectively. analytical work related to sample preparation and detection. Isotopic dilution therefore allows for extremely accurate and precise analyzes.

  This technique is known in mass spectrometry to be the most efficient, but is relatively tedious to implement, because excessively fine weighings and delicate manipulations must be implemented. With regard to isotopic dilution in solids, only studies consisting of reducing the powder sample and dotting it with an enriched isotope were performed because it is extremely difficult to homogeneously dope a given sample with enriched isotopes. . This procedure is long and tedious.

  To solve this problem, according to the invention, it is sought to carry out an isotopic dilution by laser ablation directly in the ablation chamber, that is to say in the chamber receiving the samples. It is thus ablater alternately and very quickly the sample to be analyzed and an isotopically enriched reference sample. The aerosols from the two samples mix directly and almost simultaneously in the volume of the chamber, swept by a carrier gas.

  Therefore, the objective of the present invention is therefore to provide a direct analysis laser machine for the elemental microanalysis of samples aimed at greatly reducing the elementary fractionation, to obtain a better detection sensitivity with a compact equipment and to offer the possibility of quantification by isotopic dilution directly in the ablation cell thus limiting the steps of preparation of the sample.

  To this end, the invention relates to a direct analysis laser machine 30 for the elemental microanalysis of samples comprising: an ablation chamber comprising: an optical window; an inlet orifice and an exit orifice; a carrier gas, - a sample holder which can contain at least one sample, said sample having a surface to be analyzed, - a laser ablation means of the sample adapted to send a laser beam through the optical window of the ablation chamber on the surface of the sample so as to etch an ablation zone to produce ablated elements to be analyzed, - a focusing means arranged between the sample holder and the laser ablation means capable of focusing accurately the laser beam on the ablation zone of the sample, said focusing means comprising at least one lens, - an analysis assembly comprising: - ablated element input, - an atomization source and ionization capable of transforming the ablated elements to be analyzed into atoms and ions to be analyzed, - a collimation interface of the atoms and ions to be analyzed, - an analysis means analyzing said atoms and ions, - a gas transfer means connecting the outlet of the ablation chamber to the input of ablated elements for transferring the ablated elements of the ablation chamber to the analysis assembly by the carrier gas flow.

  According to the invention, the direct analysis laser machine comprises a means for moving the laser beam disposed between the laser ablation means and the sample holder capable of returning the laser beam of the laser ablation means to at least one zone of the laser beam. ablation and allowing the displacement of the laser beam on the surface of at least one sample to be analyzed in two directions parallel to said surface so as to carry out a rapid etching of at least one ablation zone.

  In various possible embodiments, the present invention also relates to the features which will emerge during the following description, which should be considered in isolation or in all their technically possible combinations: the means for moving the laser beam comprises at least one galvanometric mirror, the means for moving the laser beam comprises an acousto-optic module, the means for moving the laser beam comprises at least one rotating prism, the laser beam alternately etches at least two ablation zones on the surface of the laser beam. at least one sample, the laser beam etches at least one ablation zone at the surface of at least one sample by circling, the laser beam etches at least one ablation zone at the surface of least one sample by describing concentric circles, the laser ablation means comprises a femtosecond laser, the ablative means a laser comprises a picosecond laser, - the laser ablation means comprises a nanosecond laser, the laser ablation means comprises an infrared laser, - the laser ablation means comprises a visible laser, - the laser ablation means comprises an ultraviolet laser, the direct analysis laser machine comprises an interface for controlling the interaction of the laser beam with at least one ablation zone comprising: a device for visualizing the ablation zone in interaction with the laser beam; means for motorized movement of the sample holder in the three directions able to control the position of the ablation zone with respect to the laser beam; the display device comprises a CCD camera connected to a video acquisition card; integrated in a central unit, said central unit comprising a three-dimensional representation software for displaying at least one ablation zone; the central unit comprises a software for control of the laser beam, - the analysis means is a mass spectrometer, - the analysis means is an optical analyzer.

  The invention will be described in more detail with reference to the accompanying drawings in which: - Figure 1 is a schematic representation of a laser coupled with an analysis assembly according to the prior art; - Figure 2 shows the etching of a point on the surface of a sample by the laser according to the prior art; FIG. 3 is a schematic representation of a direct analysis laser machine according to one embodiment of the invention; FIG. 4 is a representation of the different possibilities of laser ablation pickling on the surface of at least one sample; - Figure 5 shows the etching of two ablation zones on the surface of a sample according to one embodiment of the invention; FIG. 6 represents the etching of an ablation zone on the surface of two samples according to one embodiment of the invention; FIG. 7 is a more complete schematic representation of a direct analysis laser machine according to one embodiment of the invention; FIG. 1 represents a laser coupling system / analyzer according to the prior art comprising an ablation chamber 1 which comprises an optical window 2, an inlet orifice 3 and an outlet orifice 4 of a carrier gas. The volume of the ablation chamber 1 is of the order of 50 ml and the flow of carrier gas is between 0.1 I / min and 2 I / min, preferably of the order of 1 I / min. This gas is an inert gas of the Argon and Helium type.

  The ablation chamber 1 also comprises a sample holder 5 which can contain at least one sample 6. It is the surface 7 of the sample 6 which is analyzed.

  The laser coupling system / analyzer comprises a laser ablation means 9 of the sample 6 adapted to send a laser beam 10 through the optical window 2 of the ablation chamber 1 on the surface of the sample 7 of This stripping causes the ejection of ablated elements which are mixed with the carrier gas. Ablated elements are understood to mean a set of particles and vapors. This set is intended to be analyzed.

  The laser coupling system / analyzer comprises a focusing means 8 arranged between the sample holder 5 and the laser ablation means 9 able to accurately focus the laser beam 10 on the ablation zone of the sample 11. The means focusing device 8 comprising at least one lens.

  In Fig. 2 showing an ablation device according to the prior art, a single ablation zone 11 is etched, forming a crater spreading over an area of about 5 to 30 μm with a low energy laser source and at 200 pm usually with a higher energy laser source.

  The laser coupling / analyzer system comprises an analysis assembly 12 having an ablated element inlet 13 connected to the outlet port 4 of the ablation chamber 1 by a gas transfer means 17.

  The gas transfer means 17 allows the transfer of ablated elements from the ablation chamber 1 to the analysis unit 12 by the carrier gas flow.

  An atomization and ionization source 14 transforms the ablated elements to be analyzed into atoms and ions to be analyzed. The source used is usually a plasma torch that generates a high temperature plasma (4000-10000 K). The input of ablated elements 13 may be the injector of the plasma torch.

  A collimation interface 15 makes it possible to obtain a parallel beam of atoms and ions to be analyzed and to direct it towards an analysis means 16.

  According to the invention as shown in FIG. 3, the direct analysis laser machine comprises a means for moving the laser beam 18 disposed between the laser ablation means 9 and the sample holder 5. This moving means 18 enables to return the laser beam 10 of the laser ablation means 9 to at least one ablation zone 11. It allows the displacement of the laser beam 10 on the surface 7 of at least one sample 6 in two directions parallel to this surface 7 so as to perform rapid etching of at least one ablation zone 11.

  The laser beam 9 can strip the surface 7 of at least one sample 6 at a speed ranging from a few millimeters per second to more than 449 mm / s.

  The use of a means for moving the laser beam 18 makes it possible to better control the geometry of the craters and their arrangement on the sample 6.

  The means for moving the laser beam 18 has the function of modifying the direction of the emerging beam 10 from an external setpoint, analog or digital. The result is a displacement of the focused spot in the plane of the focusing lens.

  The means for moving the laser beam 18 can be produced in different ways with at least one galvanometric mirror or an acousto-optic module or a rotation of prisms, etc. The invention can be implemented with means for moving the beam 18 laser very varied.

  The advantages of the method are all the more important as the scanning speed is high. The laser ablation means 9 may comprise a pulsed laser of high frequency. The combination of the movement of the means for moving the laser beam 18 with the laser 9 is adjusted to produce contiguous spots which create craters of a desired shape on the sample. This system makes it possible to precisely delimit zones analyzed on the sample 6 and to produce ablated zones 11 in the form of perfectly defined craters, free of edges resulting from the recondensation of fused material. It is also possible to form ablation zones 11 in the form of a well with a flat bottom.

  The laser ablation means 9 may comprise a femtosecond NdYAG type laser source generating pulses of short duration (<400 fs) at a wavelength of 1030 nm and having a pulse frequency of between 1 Hz and 10 kHz , see more.

  The diameter of the laser beam 10 on the surface 7 of the sample 6 is advantageously from 15 to 40 μm. Beyond, and with a laser source of 100 pJ / pulse, the energy density is too low.

  The pulses energy of the laser ablation means 9 are of low energy, advantageously of the order of 100 pJ per pulse with little variation (<2.5% over 24 hours). This energy can be less than 100 pJ per pulse, or even higher. Low energy laser sources are smaller in size and less expensive than sources usually used at high energy. The laser ablation means 9 therefore consists of an extremely compact apparatus (1.4 m long) compared to "conventional" femtosecond lasers used in fundamental chemistry or micro-machining (approximately 5-6 m). It is mounted on wheels which allows a mobility from one position to another.

  With the use of a femtosecond laser source, the quality of ablation is significantly improved by avoiding elementary fractionation phenomena related to thermal effects.

  Indeed, with pulses of short durations, the material heats up much less.

  The laser ablation means 9 may also comprise a nanosecond or picosecond laser source.

  The laser ablation means 9 may also comprise an ultraviolet, visible and infrared laser source.

  It is possible to strip a surface 7 greater than a simple crater 5 to 30 pm in diameter, by moving the sample 6 very quickly and working at a high rate of fire. This leads to the almost simultaneous ablation of a given surface 7, which is larger than the size of the beam 10 focused on the sample 6. Since the laser source 9 makes it possible to work at very high firing rates (for example 10 kHz), the speed of movement of the sample holder 5 is too slow to satisfy conditions of almost simultaneous ablation of the surface 7 considered. The integration of a means for moving the laser beam 18 of the galvanometric scanner type in the optical path of the laser beam 10 makes it possible to move the beam 10 (at the microscopic scale of the analysis) very rapidly. The particularities of this type of moving means of the laser beam 18 actually reside in its speed of movement (for example 449 mm / s with an objective of 80 mm), its positioning accuracy (22 prad), its field (14 mm) and its resolution (1 pm) for a focal length of 80 mm.

  To obtain a better result, the frequency of the means of displacement of the laser beam 18 and the frequency of the laser ablation means 9 must be optimized.

  The vapors and aerosols of the sample 6 mix in the volume of the ablation chamber 1 through the carrier gas (Argon or Helium with a flow rate of about 0.1 to 2 L / min). The diameter of the injector of the atomization and ionization source 14 is fixed. The rate of introduction of the mixture depends essentially on the flow rate. The size of the ablation chamber 1 is advantageously the smallest possible.

  By way of example, it is thus possible to make crater-shaped ablation zones 100 μm in diameter successively ablating disks of 100 μm in diameter as shown in FIG. 4B) and of shallow depth (< at 10 nm). The ablation rate may be 71 times per second according to a given ablation direction 23. In FIG. 4C), the ablation direction 23 is rectilinear. It can be circular or other. It is also possible to obtain craters having a diameter of up to 300 μm under almost simultaneous conditions, or even several millimeters in a longer time (of the order of one second). Ablation zones can thus form craters of diameter generally between 5 and 300 pm or more to a depth of less than 10 nm. The ablated surface depth may be between 10 nm and a few millimeters.

  The laser beam 10 can therefore etch at least one ablation zone 11 at the surface 7 of at least one sample 6 by describing circles.

  It is also possible to make concentric circles as shown in Figure 4C). In this example, we begin by forming circles of larger diameter and smaller diameter circles as shown by the direction of progression of stripping 24.

  The possibilities are obviously not limited to the removal of circles to form craters. The beam 10 can etch the surface 7 of the sample 6 by progressing in successive and alternating rows on the surface 7 of the sample 6 while progressing in a direction 23 which is in this area.

linear example.

  In FIG. 4D), the laser beam 10 alternately etches two ablation zones 11 on the surface 7 of a sample 6 by sending impacts.

  The laser beam 10 can also etch alternately more than two ablation zones 11 on the surface 7 of at least one sample 6 by sending impacts.

  These examples represent other functionalities that also make it possible to increase the ablation surface.

  In FIG. 5, the laser beam 10 etches two ablation zones 11 on the surface 7 of a sample 6 by describing concentric circles 25.

  FIG. 6 represents another example of application of the invention for isotopic dilution.

  It is possible to perform isotopic dilution by laser ablation directly in the ablation chamber 1. It is thus possible to strip alternately and very quickly the surface of the sample to be analyzed 27 and the surface 28 of a sample reference 29, isotopically enriched. The vapors and aerosols of the two samples 27 and 29 mix in the volume of the ablation chamber 1 via the carrier gas (argon or helium at about 1 L / min).

  The lower the ablation frequency and the displacement of the laser beam 10, the more homogeneous the mixture. As before, the speed of displacement of the plates is insufficient. The surface of the two samples 27 and 29 can not be etched alternately fast enough for mixing to occur almost simultaneously in the carrier gas stream. The volume of the ablation chamber 1 is in fact of the order of 50 ml and the flow of carrier gas is of the order of 1 L / min. This volume needs to be optimized to minimize dead volumes. Only the integration of a means of displacement of the laser beam 18 of the galvanometric scanner type makes it possible to perform a sufficiently fast scan.

  The two samples 27 and 28 are placed side by side in the ablation chamber 1. An amplitude of displacement of the laser beam 10 of the order of 8 mm is achieved.

  The performance of the scanner makes it possible to perform a round-trip scan (1 shot per sample) of the order of 6 to 20 Hz, which is sufficient to ensure good homogeneity of the mixture. By way of example, commercial nanosecond lasers (for ICPMS coupling) operate at low frequency (5-10-20 or even 100 Hz) and ensure a good homogeneity of the flow of vapors and aerosols in the ablation chamber 1 .

  The direct analysis laser machine also comprises an interface for controlling the interaction of the laser beam 10 with at least one ablation zone 11. This control interface comprises a display device 19 of the ablation zone 11 in interaction with the laser beam 10, as shown in FIG. 7.

  It comprises a motorized movement means 20 of the sample holder in the three directions XYZ able to control the position of the ablation zone 11 with respect to the laser beam 10. This motorized displacement means 20 can be controlled by a joystick 30 allowing a microcontrol with strokes of 50 x 50 x 25 mm (in XYZ) and an accuracy of 10 pm.

  The display device 19 comprises a CCD camera connected to a video acquisition card 21 which is integrated in a central unit 22. The central unit 22 comprises a three-dimensional representation software for displaying at least one ablation zone 11 .

  According to a particular embodiment, the central unit 22 may comprise a control software for the laser beam 10.

  The assembly consisting of the ablation means 9, the control interface and the ablation chamber 1 may comprise a complete, light-tight cover with access doors, safety contacts and portholes filter.

  Different sizes of ablation chamber 1 allow to receive samples of variable size.

  The focusing of the laser beam 10 can be slaved to the display on a CCD camera.

  The different focus objectives allow control of crater sizes by adjusting the amount of energy per pulse that is variable from 100% to 0.1%. This is extremely important in order to work near the ablation threshold. This is the condition which makes it possible to obtain a depth resolution of about 10 nm.

  The analysis means 16 according to the invention may be a spectrometer of the mass spectrometer type, an optical analyzer or any other analysis device allowing elemental analysis.

  The invention can be applied to surface microanalysis of the trace metal analysis type or to speciation analysis.

  Indeed, by coupling a laser ablation means with a gel protein separation, metal speciation analyzes are possible. This speciation tool has considerable potential in the proteomics sector.

  The analyzed samples can be in solid, gel or liquid form.

  The invention thus makes it possible to greatly minimize the elemental fractionation and to obtain a better detection sensitivity thanks to a larger area directly analyzed in the analysis means.

  The invention allows deep microanalysis of thin layers of materials with a depth resolution of the order of 10 nm.

20 25 30

Claims (1)

CLAIMS,   1. Direct analysis laser machine for the elemental microanalysis of samples comprising: - an ablation chamber (1) comprising: - an optical window (2), - an inlet orifice (3) and an outlet orifice (4) a carrier gas, - a sample holder (5) which can contain at least one sample (6), said sample (6) having a surface (7) to be analyzed, - laser ablation means (9) of the sample (6) adapted to return a laser beam (10) through the optical window (2) of the ablation chamber (1) on the surface of the sample (7) so as to strip an area ablation device (11) for producing ablated elements to be analyzed; - a focusing means (8) arranged between the sample holder (5) and the laser ablation means (9) able to accurately focus the laser beam (10); ) on the ablation zone of the sample (1 1), said focusing means (8) comprising at least one lens, an analysis unit (12) comprising: - an input ablated elements (13), - a source of atomization and ionization (14) able to transform the ablated elements to be analyzed into atoms and ions to be analyzed, - a collimation interface (15) of the atoms and ions to Analyzing, - an analyzing means (16) analyzing said atoms and ions, - a gas transfer means (17) connecting the outlet (4) of the ablation chamber (1) to the input (13) of ablated elements for transferring the ablated elements of the ablation chamber (1) to the analysis assembly (12) by the vector gas flow, characterized in that it comprises a means for displacing the laser beam (18) arranged between the laser ablation means (9) and the sample holder (5) able to return the laser beam (10) of the laser ablation means (9) to on least one ablation zone (11) and allowing the laser beam (10) to be displaced on the surface (7) of at least one sample (6) to be analyzed in two directions parallel to said e surface (7) so as to carry out rapid stripping of at least one ablation zone (1 1).   2. direct analysis laser machine according to claim 1, characterized in that the means for moving the laser beam (18) comprises at least one galvanometric mirror.   3. Direct analysis laser machine according to claim 1, characterized in that the means for moving the laser beam (18) comprises an acousto optical module.   4. Direct analysis laser machine according to claim 1, characterized in that the means for moving the laser beam (18) comprises at least one rotating prism.   5. Laser direct analysis machine according to any one of claims 1 to 4, characterized in that the laser beam (10) alternately etches at least two ablation zones (11) on the surface (7) of a minus one sample (6).   6. Laser direct analysis machine according to any one of claims 1 to 4, characterized in that the laser beam (10) etches at least one ablation zone (11) on the surface (7) of at least a sample (6) by describing circles.   7. Direct analysis laser machine according to claim 6, characterized in that the laser beam (10) etches at least one ablation zone (1 1) on the surface (7) of at least one sample (6) by describing concentric circles (25).   8. direct analysis laser machine according to any one of claims 1 to 7, characterized in that the laser ablation means (9) comprises a femtosecond laser source.   9. direct analysis laser machine according to any one of claims 1 to 7, characterized in that the laser ablation means (9) comprises a picosecond laser.   10. Direct analysis laser machine according to any one of claims 1 to 7, characterized in that the laser ablation means (9) comprises a nanosecond laser.   11. direct analysis laser machine according to any one of claims 1 to 10, characterized in that the laser ablation means (9) comprises an infrared laser source.   12. direct analysis laser machine according to any one of claims 1 to 10, characterized in that the laser ablation means (9) comprises a visible laser source.   13. Direct analysis laser machine according to any one of claims 1 to 10, characterized in that the laser ablation means (9) comprises an ultraviolet laser source.   14. Laser direct analysis machine according to any one of claims 1 to 13, characterized in that it comprises an interface for controlling the interaction of the laser beam (10) with at least one ablation zone (11). ) comprising: - a display device (19) of the ablation zone (II) interacting with the laser beam (10), - a motorized movement means (20) of the sample holder in three directions capable of controlling the position of the ablation zone (1 1) with respect to the laser beam (10).   15. Direct analysis laser machine according to claim 14, characterized in that the display device (19) comprises a CCD camera connected to a video acquisition card (21) integrated in a central unit (22), said unit central station (22) comprising a three-dimensional representation software for displaying at least one ablation zone (11).   16. Direct analysis laser machine according to claim 15, characterized in that the central unit (22) comprises a control software of the laser beam (10).   17. Direct analysis laser machine according to any one of claims 1 to 16, characterized in that the analysis means (16) is a mass spectrometer.   18. Direct analysis laser machine according to any one of claims 1 to 16, characterized in that the analysis means (16) is an optical analyzer.