CN100371770C

CN100371770C - Focusing device for laser ablation microarea analysis

Info

Publication number: CN100371770C
Application number: CNB2006100575409A
Authority: CN
Inventors: 姚宁娟; 陈吉文; 杨志军; 沈学静; 王海舟
Original assignee: Central Iron and Steel Research Institute
Current assignee: Detection Technology Of Ncs Ltd By Share Ltd
Priority date: 2006-03-14
Filing date: 2006-03-14
Publication date: 2008-02-27
Anticipated expiration: 2026-03-14
Also published as: CN1815295A

Abstract

The present invention relates to a focusing device provided for laser ablation micro-zone analysis, and the focusing device is composed of a laser trigonometrical measuring system, a signal acquiring and processing system, and a sample moving and positioning system. A laser trigonometrical measuring principle is adopted by the present invention, a semiconductor laser is used as a light emission source, and a CCD sensor is used as a light receiving element. The relative position of an analyzed sample and a laser focusing lens used for ablation is obtained by analyzing and processing trigonometrical measuring results, and the relative position is compared with the specified focusing position. In this way, a step motor is controlled to drive a sample working table to complete automatic and accurate focusing on the surface of the analyzed sample with a laser used for ablation by utilizing the compared result.

Description

Focusing device in laser ablation micro-area analysis

Technical Field

The device provides a simple and accurate focusing device for laser ablation micro-area analysis, and mainly relates to the field of material component analysis.

Background

In recent decades, laser ablation has been widely applied in the field of material composition analysis, and is now widely applied in the fields of mining and metallurgy, geology, archaeology, environment, chemical industry, biomedicine, and the like. The analysis object can be a solid phase sample micro-selection area and a particle sample, can also be a gas phase sample and a liquid phase sample, and can also be used for analyzing a conductor, a non-conductor or a high-temperature melting sample, the sample does not need to be pretreated or only needs to be simply treated, the spatial resolution is 5-10 um, and the detection limit is in ppt magnitude.

In laser ablation micro-area analysis, laser can be directly used as an analysis instrument of a sample atom/ionization source, such as LA-OES/MS, or used as a sample evaporation source, and Inductively Coupled Plasma (ICP), microwave Induced Plasma (MIP) or empty cathode discharge (HCD) is used as an instrument of an atom/ionization source, such as LA-ICP/MIP/HCD-MS. In these instruments, the purpose of laser ablation is to focus the laser on the sample surface, to couple the laser energy efficiently into the sample, and to generate a stable and sensitive emission spectrum or a stable and uniform sample volume for quantitative analysis.

Laser parameters such as laser mode, laser energy and repetition rate, which affect the quantitative analysis result, can be optimized to obtain relatively good reproducibility. The focus position of the laser on the sample surface directly affects the energy coupled into the sample, and it is difficult to ensure the accuracy of the focus position of the laser on the sample surface in the existing commercial instruments or other focusing devices disclosed in laser ablation devices, because in the existing focusing methods, the focus position is usually adjusted by observing the clarity of the sample in the micro-imaging CCD through the human eye, see the documents laser ablation in analytical chemistry-a review, richard e.russo, xiaolei mao, haiche liu ect, talanta,57 (2002) 427. The problems with this focusing method are:

1) The CCD microscopic imaging light path and the laser output light path are the same light path, the laser focal length depends on the laser wavelength, and the focusing point of the laser beam and the optical imaging focusing point are not at the same position;

2) The method is suitable for samples with smooth surfaces and is not suitable for samples with uneven surfaces.

Disclosure of Invention

The invention aims to provide a distance measuring automatic focusing device for solving the problem of the insufficient focusing method in laser ablation micro-area analysis.

The main technical scheme of the invention is to adopt a laser triangulation principle, a semiconductor laser is used as a light source, a CCD sensor is used as a light receiving detector, and a stepping motor drives an automatic focusing device of a sample worktable.

The technical scheme of the invention is that the focusing device comprises a laser triangulation system, a data acquisition and processing system and a sample moving and positioning system:

the laser triangulation system consists of a laser, a transmitting lens, a receiving lens and a detector, light emitted by the laser is converged by the transmitting lens and then irradiates the surface of an analyzed sample, light reflected by the surface of the analyzed sample is imaged on the detector through the receiving lens, and displacement X is generated from a reference surface to the surface of the analyzed sample along the direction of incident light, so that the displacement X' is generated on an image spot of the detector, and further the change of an output signal of the detector is generated. The displacement X of the sample to be analyzed and the displacement X' of the image spot of the detector meet the principle of triangular measurement, and the calculation formula of the relative distance S between the sample to be analyzed and the laser lens for ablation is as follows:

S＝S0±X

if the surface of the sample to be analyzed moves downwards from the position of the reference surface, taking "-, and otherwise, taking the" + "sign, L, L' -respectively representing the object distance and the image distance at the reference surface, wherein alpha is the structural parameter of the system, and S0 is the distance from the laser focusing lens to the reference surface;

the signal acquisition and processing system consists of a detector driving and acquisition circuit and a computer, wherein the detector driving and acquisition circuit acquires the change of the output signal of the detector, the computer processes the signal output by the detector driving and acquisition circuit, calculates the relative distance between the sample to be analyzed and the laser lens for ablation according to the formula, and compares the relative distance with a given focusing position;

the sample moving and positioning system is composed of a sample workbench, and the sample moving and positioning system adjusts the position of the sample workbench to realize the moving and positioning of the analyzed sample according to the comparison result of the computer.

Another technical solution of the present invention is that, in the above-mentioned sample moving and positioning system, in addition to the sample stage, the system further includes a motion control card, a stepping motor and a driving circuit, the comparison result of the computer is transmitted to the motion control card, and the motion control card controls the stepping motor and the driving circuit to drive the sample stage to move to a given focusing position, so as to realize automatic focusing of the sample to be analyzed.

In still another aspect of the present invention, the laser is a semiconductor laser.

In another embodiment of the present invention, the detector is a CCD sensor.

In still another aspect of the present invention, the emitting lens and the focusing lens of the laser for ablation are the same lens.

Compared with the prior art, the invention has the following advantages:

1) The whole focusing process is automatically completed by the focusing device without manual participation, and the method is accurate and high in efficiency.

2) The semiconductor laser has good directionality, high optical power, high measurement resolution and high measurement precision, so that the focusing precision is high, and the reproducibility of the laser ablation micro-area analysis result is improved.

3) The laser ablation micro-area analysis method can be suitable for focusing of uneven samples and can be used for on-line focusing, and the application range of laser ablation micro-area analysis is widened.

Drawings

FIG. 1 is a schematic view of a focusing device in laser ablation micro-area analysis according to the present invention.

Detailed Description

The following is a further detailed description with reference to the accompanying drawings.

As can be seen from the attached figure 1, the invention comprises a laser triangulation system, a signal acquisition and processing system and a sample moving and positioning system.

The laser triangulation system consists of a semiconductor laser 1, an emitting lens 2, a receiving lens 4 and a CCD sensor 5, light emitted by the semiconductor laser 1 is converged by the emitting lens 2 and then irradiates the surface of an analyzed sample 3, and light reflected by the analyzed sample 3 is focused on the CCD sensor 5 through the receiving lens 4. The distance measurement principle is as follows:

the semiconductor laser 1 is converged and irradiated on a 0 point (hereinafter referred to as an object light point) of a reference surface, and is imaged on a 5 photoelectric center 0' point (hereinafter referred to as an image light point) of a CCD sensor through a receiving lens group 4. The output of the CCD sensor 5 is zero at this time. When the laser beam is irradiated on the sample 3 to be analyzed, the object light spot will be displaced X in the incident light direction, causing the image light spot to be displaced X', which in turn causes a change in the output signal of the CCD sensor 5. The displacement X of the sample to be analyzed and the displacement X' of the image spot of the detector meet the principle of triangulation, and the calculation formula of the relative distance S between the sample to be analyzed 3 and the laser lens for ablation is as follows:

S＝S0±X

if the surface of the analyzed sample 3 moves downwards from the position of the reference surface, taking "-"; otherwise take the "+" sign. L, L' — the object and image distances at the reference plane, respectively. α is a structural parameter of the system. And S0 is the distance from the laser focusing lens to the reference surface. Therefore, the displacement X of the sample to be analyzed can be obtained by accurately measuring X', and the distance S between the sample to be analyzed and the laser focusing lens for ablation can be obtained.

The signal acquisition processing system consists of a CCD sensor driving and acquisition circuit 6 and a computer 7, wherein the computer 7 processes signals output by the CCD sensor driving and acquisition circuit 6, calculates the relative distance between the sample 3 to be analyzed and the laser lens for ablation, and compares the relative distance with a given focusing position.

The sample moving and positioning system consists of a motion control card 8, a stepping motor and drive circuit 9 and a sample worktable 10, the comparison result obtained by the computer is transmitted to the motion control card 8, and the motion control card 8 controls the stepping motor and drive circuit 9 to drive the sample worktable 10 to move to a given focusing position.

Claims

1. A focusing device in laser ablation micro-area analysis is characterized by comprising:

laser triangulation system, by laser instrument (1), transmitting lens (2), receiving lens (4), and detector (5) are constituteed, the light that laser instrument (1) sent shines in by transmitting lens (2) convergence back at the sample analyzed (3) surface department, the light that is reflected by the sample analyzed (3) surface is formed images in detector (5) through receiving lens (4), from the reference surface to sample analyzed (3) surface along incident light direction displacement X, thereby arouse detector (5) image spot to take place displacement X ', and then arouse the change of detector (5) output signal, sample analyzed displacement X and detector image spot displacement X' satisfy the triangulation theory, the formula of calculating relative distance S of sample analyzed (3) and transmitting lens (2) is:

S＝S0±X

if the surface of the analyzed sample (3) moves downwards from the position of the reference surface, taking "-", otherwise taking a "+" sign, L, L' -respectively representing the object distance and the image distance at the reference surface, alpha representing the structural parameter of the system, and S0 representing the distance from the transmitting lens (2) to the reference surface;

the signal acquisition processing system consists of a detector driving and acquisition circuit (6) and a computer (7), wherein the detector driving and acquisition circuit (6) acquires the change of the output signal of the detector (5), and the computer (7) processes the signal output by the detector driving and acquisition circuit (6), calculates the relative distance between the sample (3) to be analyzed and the laser lens for ablation, and compares the relative distance with a given focusing position;

the sample moving and positioning system consists of a sample workbench (10), and the position of the sample workbench (10) is adjusted according to the comparison result of the computer (7) to realize the moving and positioning of the analyzed sample (3).

2. The focusing device in the laser ablation micro-area analysis as claimed in claim 1, wherein the sample moving and positioning system further comprises a motion control card (8) and a stepping motor and driving circuit (9), the comparison result of the computer (7) is transmitted to the motion control card (8), and the motion control card (8) controls the stepping motor and driving circuit (9) to drive the sample stage (10) to move to a given focusing position, thereby realizing the automatic focusing of the analyzed sample.

3. A focusing arrangement in laser ablation micro-area analysis according to claim 1 or 2, characterized in that said laser (1) is a semiconductor laser.

4. A focusing device in the analysis of laser ablation micro-areas according to claim 1 or 2, characterized in that the detector (5) is a CCD sensor.

5. A focusing device in laser ablation micro-area analysis according to claim 3, characterized in that said detector (5) is a CCD sensor.