Handheld LIBS Optical System

Abstract

The present invention relates to a handheld LIBS optical system, including a laser and a detector. The optical system further includes: a dichroic mirror, a first lens, a second lens, and a third lens. The laser emitted by the laser passes through the dichroic mirror and converges through the first lens to focus the light spot on the sample surface. The characteristic light emitted by the sample is converged by the first lens, reflected by the dichroic mirror, coupled by the second lens, transmitted by optical fiber, and converged by the third lens to reach the slit; a concave grating, the concave grating splits the characteristic light emitted from the slit, and enters the detector for detection after passing through a fourth lens; the two ends of the slit, the concave grating and the detector are located on the circumference of a Rowland circle whose diameter is equal to the curvature radius of the concave grating; and a fourth lens, the fourth lens makes the optical path of the characteristic light after the splitting from the concave grating to the detector through the fourth lens equal to the optical path from the concave grating directly to the circumference of the Rowland circle. The present invention has the advantages of small size, high resolution, and wide detection wavelength range.

Description

Technical Field

[0001] The invention relates to the field of spectral analysis, and in particular to a compact handheld LIBS optical system. Background Art

[0002] Laser induced breakdown spectrometer, referred to as LIBS, is an instrument that uses pulsed laser to generate plasma to ablate and excite the material in the sample. The spectra emitted by the atoms excited by the plasma are obtained through the spectrometer to identify the elemental composition of the sample, and then to identify, classify, qualitatively and quantitatively analyze the material. It can be used in laboratories and online detection in industrial sites. In order to facilitate on-site detection, handheld LIBS came into being. However, the current handheld LIBS has the following defects:

[0003] 1. Symmetrical or asymmetric Czerny-Turner optical systems are often used. This system requires multiple collimators and imaging lenses, which results in a complex instrument structure and a large volume; or the focal length is shortened to reduce the volume, resulting in reduced resolution;

[0004] 2. The wavelength range of the optical system is narrow, unable to cover the entire band, and the types of elements that can be detected are limited. Summary of the invention

[0005] In order to solve the deficiencies in the above-mentioned prior art solutions, the present invention provides a handheld LIBS optical system with simple structure, small size, high resolution and wide wavelength range.

[0006] The objective of the present invention is achieved through the following technical solutions:

[0007] A handheld LIBS optical system, comprising a laser, a detector, and the optical system further comprising:

[0008] A dichroic mirror, through which the laser light emitted by the laser passes;

[0009] A first lens, wherein the laser light passing through the dichroic mirror is converged by the first lens to focus the light spot on the sample surface;

[0010] The second lens is used for coupling the characteristic light emitted from the sample surface into the optical fiber after being converged by the first lens and reflected by the dichroic mirror;

[0011] A third lens, through which the characteristic light output from the optical fiber is converged to the slit;

[0012] A concave grating, wherein the concave grating splits the characteristic light emitted from the slit and enters the detector for detection after passing through a fourth lens; the slit, the concave grating and the two ends of the detector are located on the circumference of a Rowland circle whose diameter is equal to the curvature radius of the concave grating;

[0013] The fourth lens compensates for the optical path difference so that the optical path of the split characteristic light from the concave grating through the fourth lens to the detector is equal to the optical path from the concave grating directly to the circumference of the Rowland circle without passing through the fourth lens.

[0014] According to the above optical system, preferably, the fourth lens is a cylindrical lens, and both ends of the cylindrical lens are wedge-shaped.

[0015] According to the above optical system, preferably, the cylindrical lens is a plano-convex cylindrical mirror, and the side adjacent to the concave grating is a curved surface to converge the characteristic light.

[0016] According to the above optical system, optionally, the focal length of the cylindrical lens, that is, the distance from the cylindrical lens to the imaging surface of the detector, is f=R / (n-1), R is the radius of curvature of the cylindrical lens surface, and n is the refractive index of the cylindrical lens material.

[0017] According to the above optical system, preferably, the cylindrical lens is fixed on the surface of the detector.

[0018] According to the above optical system, preferably, the concave grating, the fourth lens and the detector constitute a group of measuring light paths, and the optical system includes at least two groups of measuring light paths, the incident light of the first group of measuring light paths is the characteristic light emitted by the slit, and the incident light of the other groups of measuring light paths is the 0th order light of the concave grating in the previous group of measuring light paths.

[0019] According to the above optical system, preferably, the positions of the two ends of the detector on the circumference of the Rowland circle are determined by the wavelength measurement range.

[0020] According to the above optical system, preferably, the detector is an array detector.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention adopts a Rowland circle design, does not require a collimator and an imaging mirror, has a simple structure and a small size; by adding a cylindrical lens with wedge-shaped ends in front of the detector, the spectrum after passing through the grating is imaged on the Rowland circle, increasing the detection light intensity, improving the signal-to-noise ratio of the spectrometer, and improving the resolution.

[0023] 2. The present invention adopts array detectors for detection, and spectrum information of one level can be obtained in one acquisition, and the spectrum acquisition speed is fast.

[0024] 3. The present invention realizes 170-800nm ​​full spectrum collection by superposition of multiple concave gratings, cylindrical lenses and detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The disclosure of the present invention will become easier to understand with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only used to illustrate the technical solution of the present invention and are not intended to limit the scope of protection of the present invention. In the drawings:

[0026] Figure 1 1 is a light path diagram of a handheld LIBS optical system according to embodiment 1 of the present invention. Implementation

[0027] Figure 1 The following description describes optional embodiments of the present invention to teach those skilled in the art how to implement and reproduce the present invention. In order to teach the technical solution of the present invention, some conventional aspects have been simplified or omitted. It should be understood by those skilled in the art that variations or substitutions derived from these embodiments will be within the scope of the present invention. It should be understood by those skilled in the art that the following features can be combined in various ways to form multiple variations of the present invention. Thus, the present invention is not limited to the following embodiments, but is only limited by the claims and their equivalents.

[0028] Example 1

[0029] Figure 1 The optical path diagram of the handheld LIBS optical system of this embodiment is schematically shown as follows: Figure 1 As shown, the optical system comprises:

[0030] Laser 1, the laser emits laser light to a dichroic mirror;

[0031] A dichroic mirror 2, through which the laser light passes;

[0032] A first lens 3, the laser light passing through the dichroic mirror is converged by the first lens to focus the light spot on the surface of the sample 4;

[0033] The second lens 4, the characteristic light emitted from the sample surface is converged by the first lens, reflected by the dichroic mirror, and then coupled into the optical fiber 5 through the second lens;

[0034] A third lens 6, through which the characteristic light output from the optical fiber is converged to the slit 7;

[0035] A concave grating 8, which splits the characteristic light emitted from the slit, and enters the detector 10 for detection after passing through a fourth lens 9; the slit 7, the concave grating 8 and the two ends of the detector 10 are located on the circumference of a Rowland circle whose diameter is equal to the curvature radius of the concave grating;

[0036] The fourth lens 9 is a cylindrical lens, and the two ends 91 and 92 of the cylindrical lens are wedge-shaped; the fourth lens compensates for the optical path difference, so that the optical path of the split characteristic light from the concave grating through the fourth lens to the detector is equal to the optical path from the concave grating directly to the circumference of the Rowland circle without passing through the fourth lens;

[0037] The detector 10 is an array detector, which detects characteristic light of sample elements.

[0038] The detection area of ​​the array detector is small. In order to increase the detection light intensity and improve the signal-to-noise ratio, the following are used:

[0039] Furthermore, the cylindrical lens is a plano-convex cylindrical mirror, and the side adjacent to the concave grating is a curved surface, which converges the characteristic light; the focal length of the cylindrical lens, that is, the distance from the cylindrical lens to the imaging surface of the detector, is f=R / (n-1), R is the curvature radius of the cylindrical lens curved surface, and n is the refractive index of the cylindrical lens material.

[0040] Preferably, the cylindrical lens is fixed on the surface of the detector to simplify the structure.

[0041] The wavelength of the element to be measured corresponds to its imaging position on the detector. Therefore, the positions of the two ends of the detector on the circumference of the Rowland circle are determined by the wavelength measurement range. However, due to the limitation of the detector length, the detection range that a single detector can measure is narrow, so:

[0042] Further, the concave grating, the fourth lens and the detector form a set of measuring light paths, and the optical system includes at least two sets of measuring light paths, the incident light of the first set of measuring light paths is the characteristic light emitted by the slit, and the incident light of the other sets of measuring light paths is the 0-order light of the concave grating in the previous set of measuring light paths. That is, the previous set of measuring light paths determines the position of the concave grating in the next set of measuring light paths on the circumference of the Rowland circle, and the position of the detector in the next set of measuring light paths is determined by the wavelength range to be measured, and can continue the measurable wavelength range of the previous set of measuring light paths.

[0043] The advantages of this embodiment are: the Rowland circle design is adopted, the spectrometer has a simple structure, a small volume, a high resolution, and a wide measurable wavelength range.

Claims

1. A handheld LIBS optical system without collimating mirror and imaging mirror, comprising a laser and a detector, characterized in that: The optical system further comprises: A dichroic mirror, through which the laser light emitted by the laser passes; A first lens, wherein the laser light passing through the dichroic mirror is converged by the first lens to focus the light spot on the sample surface; The second lens is used for coupling the characteristic light emitted from the sample surface into the optical fiber after being converged by the first lens and reflected by the dichroic mirror; A third lens, through which the characteristic light output from the optical fiber is converged to the slit; A concave grating, wherein the concave grating splits the characteristic light emitted from the slit and enters the detector for detection after passing through a fourth lens; the slit, the concave grating and the two ends of the detector are located on the circumference of a Rowland circle whose diameter is equal to the curvature radius of the concave grating; a fourth lens, wherein the fourth lens compensates for the optical path difference so that the optical path of the split characteristic light from the concave grating through the fourth lens to the detector is equal to the optical path from the concave grating directly to the circumference of the Rowland circle without passing through the fourth lens, so that the spectrum after passing through the concave grating is imaged on the detector; The fourth lens is a cylindrical lens, and both ends of the cylindrical lens are wedge-shaped.

2. The optical system according to claim 1, characterized in that: The cylindrical lens is a plano-convex cylindrical mirror, and the side adjacent to the concave grating is a curved surface, which converges the characteristic light.

3. The optical system according to claim 2, characterized in that: The distance f from the cylindrical lens to the imaging surface of the detector is R / (n-1), where R is the radius of curvature of the cylindrical lens surface, and n is the refractive index of the cylindrical lens material.

4. The optical system according to claim 3, characterized in that: The cylindrical lens is fixed on the surface of the detector.

5. The optical system according to claim 1, characterized in that: The concave grating, the fourth lens and the detector constitute a group of measuring light paths. The optical system includes at least two groups of measuring light paths. The incident light of the first group of measuring light paths is the characteristic light emitted by the slit, and the incident light of the other groups of measuring light paths is the 0th order light of the concave grating in the previous group of measuring light paths.

6. The optical system according to claim 5, characterized in that: The positions of the two ends of the detector on the circumference of the Rowland circle are determined by the wavelength measurement range.

7. The optical system according to any one of claims 1 to 6, characterized in that: The detector is an array detector.

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