CN104374698B - Sample table for laser-induced breakdown spectroscopy detection - Google Patents

Abstract

The invention discloses a sample stage for laser-induced breakdown spectrum detection, which includes an electric shift stage with at least one-dimensional degree of freedom, and a movable lifting plate is installed on the electric shift stage, and is slidably fitted with a The object stage of the sample, the lifting plate is provided with a transparent confinement window, and the laser hits the sample after passing through the confinement window; Confinement cavities are distributed on the plate, and the confinement cavities are used to confine the plasma excited by the sample. The invention constrains the plasma horizontally and vertically, and adjusts the size of the confinement space according to different sample requirements to adjust the spectral line intensity, and the spectral line intensity enhancement range is 2-10 times.

Description

A sample stage for laser-induced breakdown spectroscopy detection

technical field

The invention relates to laser-induced breakdown spectrum detection technology, in particular to a sample stage for laser-induced breakdown spectrum detection.

Background technique

Laser-Induced Breakdown Spectroscopy (LIBS) uses the plasma generated by the pulsed laser to ablate and excite the material in the sample (usually solid), and obtain the spectrum emitted by the excited plasma atoms through the spectrometer to This is used to identify the elemental composition in the sample, and then the identification, classification, qualitative and quantitative analysis of materials can be carried out. This technology does not require sample pretreatment, and can quickly realize remote and micro-destructive detection of sample elements (especially metal elements), and can be used for the detection of solid, gas, and liquid samples. Laser-induced breakdown spectroscopy is also used in a wide range of applications, such as biomedicine, archaeology, environmental monitoring, detection of heavy metals in water, and detection of explosives.

However, the laser-induced breakdown spectroscopy analysis and detection technology also has corresponding limitations: 1. The detection limit is relatively high. Usually the detection limit of LIBS is greater than μg/g. 2. Poor repeatability. Since LIBS detection and analysis are easily affected by energy, objective lens distance, sample matrix, etc., the relative standard deviation of the detection results is generally around 10%. Therefore, improving the detection ability and repeatability of LIBS technology is an important content in the development of LIBS technology.

Spatial confinement is an effective method to increase the signal intensity of laser-induced breakdown spectroscopy and reduce the detection limit. For example, the patent application CN 103543131A proposes a method for improving the measurement accuracy of elements based on double pulses and space confinement. In this method, pits or cavities are first made above the surface of the sample to be tested, and then the sample is hit with a double pulse laser. The first pulse creates a low-pressure environment inside the pit or chamber, and the second pulse excites the sample to create a plasma. The plasma is limited by space during the expansion process, which makes the plasma temperature and electron density significantly increased, and the plasma is more uniform, which is conducive to increasing the stability of the measurement signal, improving the signal-to-noise ratio, and reducing the detection of trace elements in the sample. limit. The patent points out that space constraints can improve the strength and stability of LIBS measurement signals, which is conducive to the improvement of element measurement accuracy.

Contents of the invention

The invention provides a sample stage for laser-induced breakdown spectrum detection, which adopts spatial transverse and longitudinal confinement methods to enhance spectral line intensity, the plasma confinement plate adopts a chrome-plated aluminum plate, the confinement cavity adopts a conical structure, and the sample adopts a V-shaped slider The rail structure moves.

Concrete technical scheme of the present invention is as follows:

A sample stage for laser-induced breakdown spectroscopy detection, including an electric shift stage with at least one-dimensional degree of freedom, a movable lifting plate is installed on the electric shift stage, and a load for placing samples is slidably matched tower,

The lifting plate is provided with a transparent confinement window, and the laser hits the sample after passing through the confinement window;

A confinement plate is arranged under the lifting plate, and the confinement plate is placed directly above the sample. Confinement cavities are distributed on the confinement plate, and the confinement cavity is used to confine the plasma excited by the sample.

The present invention provides a sample stage based on spatial limitation to enhance the spectral line intensity, which can constrain the plasma horizontally and vertically, and adjust the size of the confined space to adjust the spectral line intensity according to different sample requirements. The spectral line intensity enhancement range is 2-10 times. The confinement window is mainly used to confine the plasma longitudinally, and has a good transmittance to the characteristic spectral lines generated by the incident laser and the plasma. The confinement cavity on the confinement plate is mainly used to confine the plasma laterally, and to confine the characteristic spectral lines to propagate, so as to improve the spectral line collection efficiency and spectral line intensity, and the spectral line intensity enhancement range is 2-10 times.

The electric moving table is provided with a lifting mechanism for driving the lifting plate, including a lifting rod with a rack and a slide block sliding along the lifting rod, the slide block is provided with a gear meshed with the rack, and the The lifting plate is fixed on the slide block. Utilizing the meshing of the rack and the gear to drive the sliding block up and down, the structure is simple and easy to operate.

The lifting plate is an L-shaped right-angle adapter plate. The lifting plate is provided with a light-transmitting port, and the light-transmitting port is covered with a light-transmitting plate, and the light-transmitting port and the light-transmitting plate form the constraint window. The inner edge of the light-transmitting opening is provided with supporting steps, and the light-transmitting plate is directly placed in the light-transmitting opening and fixed by the supporting steps.

In the present invention, the transparent plate is a plexiglass plate, the material is N-BK7, the thickness is 1-5mm, the transmittance is greater than 90%, and the energy threshold is greater than 10J/cm ² . The line enhancement effect is affected by the distance between the confinement window and the sample. Since the properties of samples and the intensity of spectral lines of elements to be detected are different, the confinement window of the present invention can be moved in the vertical direction to adjust the intensity of spectral lines as required. In order to ensure effective laser excitation and effective collection of characteristic spectral lines, the transmittance of the light-transmitting plate to the laser wavelength and characteristic spectral lines should be greater than 90%. At the same time, in order to prevent the laser from damaging the plexiglass plate, its energy threshold should be greater than 10J/cm ² .

Preferably, the constraining plate is a chrome-plated aluminum plate with a thickness of 1-3mm. Chromium plating is carried out in the confined cavity of the aluminum plate, so that the inner cavity has a high reflectivity, the characteristic spectral lines are constrained to propagate, and the collection efficiency of the spectral lines is improved.

The confinement cavity is conical, the diameter of the upper cone is 2-8 mm, and the diameter of the lower cone is 1-3 mm larger than that of the upper cone. The diameter of the conical surface adopting this size can effectively confine the plasma of different samples. In addition, the confinement cavity adopts a conical structure, which can confine the plasma better than a cylindrical structure due to its small top and bottom large structure. In addition, when the plasma is ejected from the conical confinement cavity, its electron density and motion speed will be enhanced due to its increased spatial confinement, which is more conducive to the enhancement of spectral line signals.

In order to facilitate the placement of the sample to be tested, a sliding guide groove is provided on the electric shift table, and the described object stage has a guide block matched with the sliding guide groove, and adopts a slider guide rail structure, and the object stage can be flexibly pushed in Or pull out just below the constraint window to avoid cumbersome operations such as raising the constraint window and the constraint plate.

Two guide columns are installed on the electric moving table, and the constraint plate is sleeved on the guide columns. Move the restraint plate up and down along the guide column to adjust the height of the restraint plate. The restraint plate covers the surface of the sample, which is beneficial to smooth the surface of the sample and improve the repeatability of the test, while avoiding the contamination of other areas to be tested by excited particles. When the sample to be tested is a sample with an uneven surface such as a fresh leaf, there is a difference in the distance between the area to be tested and the lens, which in turn affects the laser parameters of the laser reaching the sample. The detection stability of laser-induced breakdown spectroscopy is closely related to the laser parameters of the area to be detected, so flattening the sample surface is conducive to fixing the laser parameters and improving the repeatability of detection. In addition, the upper conical structure of the confinement plate is small and the bottom is large, which is beneficial to avoid particle pollution excited by the previous detection area to the greatest extent, ensuring that the detected object is an element in the area to be detected.

The beneficial effects that the present invention has are:

1) It can effectively enhance the LIBS spectral line signal, and the spectral line intensity enhancement range is 2-10 times;

2) It can prevent the excited particles from re-covering the surface of the sample, which will affect the subsequent detection and analysis of the sample;

3) It can level the surface of the sample (especially for uneven samples such as fresh leaves), so that the distance from the sample to the focusing lens remains constant, thereby improving the detection repeatability;

4) It has the characteristics of simple adjustment, low cost, and convenient disassembly.

Description of drawings

Figure 1 is a structural diagram of a sample stage for laser-induced breakdown spectroscopy detection;

Fig. 2 is the top view of sample stage in Fig. 1;

Fig. 3 is the right view of the sample stage in Fig. 1;

Fig. 4 is the schematic diagram that the sample on the sample stage is hit;

Figure 5 is an unconfined plasma diagram;

Fig. 6 is a diagram of confinement of plasma by confinement window and confinement cavity.

detailed description

As shown in Figures 1-3, a sample stage for laser-induced breakdown spectroscopy detection includes a rack lifter 1, a gear slider 2, a right-angle adapter plate 3, a plasma confinement window 4, and a cylindrical guide rail 5. Plasma confinement plate 6 , V-shaped slider 7 , combined electric shift stage 9 , and tie rod 10 .

The combined electric translation stage 9 adopts a four-degree-of-freedom (x, y, z, w) combined electric translation stage, including three single-degree-of-freedom (x, y, and z) pulse electric translation stages and one rotational degree of freedom (w) electric rotation tower.

The rack elevating rod 1 is vertically installed on the combined electric moving platform 9, and the gear slide block 2 is engaged with the rack elevating rod 1, and can move up and down along the vertical direction. The right-angle adapter plate 3 is fixed on the gear slider 3 by bolts, a rectangular light-transmitting opening is provided on the plane, supporting steps are provided on the edge of the light-transmitting opening, and a light-transmitting plate is arranged inside the light-transmitting opening to form a plasma confinement window 4 .

The cylindrical guide rail 5 is fixed on the combined electric shift stage 9, and the plasma confinement plate 6 can slide up and down along the cylindrical guide rail 5. Both the cylindrical guide rail 5 and the rack lifting rod 1 are connected to the combined electric moving table 9 by bolts. The combined electric moving table 9 has a V-shaped groove, and the V-shaped slider 7 can slide left and right along the V-shaped groove under the action of the pull rod 10, and the pull rod 10 is fixed in the V-shaped slider 7 by threads. The sample 8 is placed on the V-shaped slider 7 (equivalent to the stage), and the laser strikes from above downwards, passes through the plasma confinement window 4, and passes through the plasma confinement plate 6, and hits the surface of the sample to excite the plasma. The characteristic spectral lines emitted by the cooling are collected by the optical fiber.

In this embodiment, the material of the plasma confinement window 4 is N-BK7, the thickness is 1-3mm, the transmittance is greater than 90%, and the energy threshold is greater than 10J/cm ² . The plasma confinement window 4 is mainly used to confine the plasma longitudinally, and has a good transmittance to the characteristic spectral lines generated by the incident laser and the plasma. N-BK7 is a common optical glass that can transmit light in the 350nm-2000nm band, its laser transmittance is greater than 90%, and its energy threshold is greater than 10J/cm ² . Therefore, the constrained window 4 is made of N-BK7 with a thickness of 1-3m.

The plasma confinement window 4 can move vertically under the action of the gear slider 2 . The line enhancement effect is affected by the distance between the confinement window and the sample. Due to the different properties of the samples and the intensity of the spectral lines of the elements to be detected, the plasma confinement window 4 of the present invention can be moved in the vertical direction to adjust the spectral line intensity as required.

In this embodiment, the material of the plasma confinement plate 6 is a chrome-plated aluminum plate with a thickness of 1 mm, and a conical confinement cavity 11 is evenly distributed in the middle, and the diameters of the upper and lower cones are 2 mm and 3 mm, respectively. The distance between the confinement cavities 11 should be consistent with the planned displacement of the combined electric shift stage 9 . The plasma confinement plate 6 is mainly used to confine the lateral direction of the plasma, and confine the propagation of the characteristic spectral lines, so as to improve the collection efficiency of the spectral lines and the intensity of the spectral lines. Chromium plating is carried out in the confined cavity 11 of the aluminum plate, so that the inner cavity has a higher reflectivity, the characteristic spectral lines are constrained to propagate, and the collection efficiency of the spectral lines is improved. The confinement cavity adopts a conical structure. Due to its small top and bottom large structure, it can better confine the plasma than the cylindrical structure. In addition, when the plasma is ejected from the conical confinement cavity, its electron density and motion speed will be enhanced due to its increased spatial confinement, which is more conducive to the enhancement of spectral line signals. The distance between the confinement cavities of the plasma confinement plate 6 of the present invention is consistent with the planned displacement of the combined electric shift stage 9, and can be applied to the working mode of laser-induced breakdown spectrum surface scanning. In the present invention, the plasma confinement plate 6 is used to cover the surface of the sample, which is beneficial to leveling the surface of the sample and improving the repeatability of detection, while avoiding contamination of other regions to be measured by excited particles. When the sample to be tested is a sample with an uneven surface such as a fresh leaf, there is a difference in the distance between the area to be tested and the lens, which in turn affects the laser parameters of the laser reaching the sample. The detection stability of laser-induced breakdown spectroscopy is closely related to the laser parameters of the area to be detected, so flattening the sample surface is conducive to fixing the laser parameters and improving the repeatability of detection. In addition, the upper and lower conical structures of the plasma confinement plate 6 are beneficial to avoid particle contamination from the previous detection area to the greatest extent, ensuring that the detected object is an element in the area to be detected.

The V-shaped slider 7 can move along the V-shaped groove under the action of the pull rod 10. The V-shaped slider guide rail structure is used to avoid cumbersome operations such as raising the plasma confinement window and the plasma confinement plate. The connection between the plasma confinement plate 6 and the cylindrical guide rail 5 is a tight connection, and the plasma confinement plate 6 cannot slide freely under the action of gravity.

When assembling the present invention, the gear lifting rod 1 and the cylindrical guide rail 5 are first fixed with the combined electric moving table 9 through bolts, and then the V-shaped slider 7 and the pull rod 10 are fixed through internal and external threads, and the V-shaped slider 7 and the combined electric moving table are fixed together. The V-shaped groove of moving platform 9 cooperates so that it can slide freely along the V-shaped groove. Pass the matching holes of the plasma confinement plate 6 through the two cylindrical guide rails 5, so that it cannot slide down freely under the action of gravity. The gear slider 2 cooperates with the gear lifting rod 1 through the rack and pinion, and the right-angle adapter plate 3 is connected to the gear slider 2 through screws. The plasma confinement window 4 on the right-angle adapter plate 3 is under the action of the rack and pinion. Can move vertically.

As shown in Figure 4, the present invention is applicable to multiple working modes of laser-induced breakdown spectroscopy, which can realize both collinear excitation and vertical excitation; it can be applied to single-pulse laser-induced breakdown spectroscopy, Also applicable to double-pulse laser-induced breakdown spectroscopy. The invention is especially suitable for biological samples such as fresh leaves of plants, and can effectively improve the signal intensity. Taking the double-pulse vertical laser-induced breakdown spectroscopy system as an example, when the present invention works, the V-shaped slider 7 is moved out from the working position through the pull rod 10, the sample 8 to be tested is placed on the V-shaped slider 7, and then the V-shaped slider 7 is placed Type slide block 7 is pushed into working position. The plasma confinement plate 6 is moved to press it against the sample 8, and then the upper and lower positions of the plasma confinement window 4 are adjusted to confine the excited plasma. The combined electric shift stage 9 is controlled to make the conical confinement cavity 11 of the plasma confinement plate 6 correspond to the position of the upper laser, and the working step of the combined electric shift stage 9 is set to be the adjacent distance or a multiple of the conical confinement cavity. The first laser beam B passes through the optical path system, propagates downward through the focusing lens, passes through the plasma confinement window 4, and hits the sample through the conical confinement cavity. The laser transmittance of the plasma confinement window 4 is greater than 90%, and the energy threshold is greater than 10J/cm ² . The second laser beam A is focused and hits the excited plasma through the focusing lens along the vertical direction to enhance the spectral line signal. The characteristic spectral line C emitted by plasma cooling is collected by the optical fiber collection system above. Each position can select the required number of hits according to actual requirements, and after a position is completed, the electric shift table 9 is moved to perform multiple position spectrum acquisitions. As shown in Figures 5 and 6, when there is no plasma confinement window 4 and plasma confinement plate 6, the excited plasma D is in a free excitation state; when the excited plasma D is confined, the plasma D As the density increases, the temperature of the plasma increases, which enhances the intensity of the spectral lines of the excited atoms.

The working principle of the present invention:

Spatial confinement is an effective method to increase the signal intensity of laser-induced breakdown spectroscopy and reduce the detection limit. First, when the expansion of the plasma is spatially constrained, both the temperature and the electron density of the plasma increase. Secondly, due to the secondary pressure wave and reflected shock wave generated by space constraints, the primary plasma is reheated, so the temperature and electron density of the plasma are further increased. Therefore, when the excited plasma is space-confined, the plasma temperature and electron density are greatly increased, which is conducive to the realization of thermal equilibrium conditions, enhanced spectral line intensity, and reduced detection limit.

Claims (7)

1. A sample stage for laser-induced breakdown spectroscopy detection, comprising an electric shift stage with at least one-dimensional degree of freedom, characterized in that a movable lifting plate is installed on the electric shift stage, which is useful for sliding cooperation on the stage where the sample is placed, The lifting plate is provided with a transparent confinement window, and the laser hits the sample after passing through the confinement window; A confinement plate is provided below the lifting plate, the confinement plate covers the surface of the sample, and confinement cavities are distributed on the confinement plate, and the confinement cavity is used to confine the plasma excited by the sample; The electric moving table is provided with a lifting mechanism for driving the lifting plate, including a lifting rod with a rack and a slide block sliding along the lifting rod, the slide block is provided with a gear meshed with the rack, and the The lifting plate is fixed on the slider; The lifting plate is provided with a light-transmitting port, and the light-transmitting port is covered with a light-transmitting plate, and the light-transmitting port and the light-transmitting plate form the constraint window; The confinement cavity is conical, the diameter of the upper cone is 2-8 mm, and the diameter of the lower cone is 1-3 mm larger than that of the upper cone. 2. The sample stage for laser-induced breakdown spectroscopy detection according to claim 1, wherein the lifting plate is an L-shaped right-angle adapter plate. 3. The sample stage for laser-induced breakdown spectroscopy detection according to claim 1, wherein a supporting step is provided on the inner edge of the light-transmitting opening, and the light-transmitting plate is placed on the supporting step. 4. The sample stage for laser-induced breakdown spectroscopy detection as claimed in claim 3, wherein the light-transmitting plate is a plexiglass plate with a thickness of 1-5 mm, a transmittance greater than 90%, and an energy The threshold is greater than 10 J/cm ² . 5 . The sample stage for laser-induced breakdown spectroscopy detection according to claim 1 , wherein the constraining plate is a chrome-plated aluminum plate with a thickness of 1-3 mm. 6. The sample stage for laser-induced breakdown spectroscopy detection as claimed in claim 1, wherein a sliding guide groove is provided on the described electric shift stage, and the described object stage has a guide block. 7 . The sample stage for laser-induced breakdown spectroscopy detection according to claim 6 , wherein two guide posts are installed on the electric shift stage, and the constraining plate is sleeved on the guide posts. 7 .