CN112485214B - Device and method for improving laser absorption spectrum measurement sensitivity - Google Patents
Device and method for improving laser absorption spectrum measurement sensitivity Download PDFInfo
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- CN112485214B CN112485214B CN202011466140.XA CN202011466140A CN112485214B CN 112485214 B CN112485214 B CN 112485214B CN 202011466140 A CN202011466140 A CN 202011466140A CN 112485214 B CN112485214 B CN 112485214B
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- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/3103—Atomic absorption analysis
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
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- G—PHYSICS
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- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
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- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
- G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
- G01N21/3103—Atomic absorption analysis
- G01N2021/3111—Atomic absorption analysis using Zeeman split
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Abstract
The invention discloses a device and a method for improving the measurement sensitivity of laser absorption spectrum, the device comprises a laser, a wave plate and a glass optical cavity which are sequentially arranged on the optical path of the laser, wedge-shaped windows are arranged at two ends of the glass optical cavity, and two crucibles are respectively connected with the outer walls of two ends of the glass optical cavity and are communicated with the glass optical cavity; the exciting coils are arranged outside the two ends of the glass optical cavity; the method comprises (i) evaporating; (ii) laser excitation; (iii) adjusting the excitation coil to enrich the target atoms towards the middle. The invention utilizes the photoinduced drift (LID) effect to locally enrich target atoms to be detected, thereby improving the spectral absorption spectral sensitivity by improving the concentration of a substance to be detected, and being a novel method for detecting a low-concentration substance; the device can realize the enrichment of target atoms in the middle of the device, and the promotion effect can reach 2 to 3 orders of magnitude, so that the spectral detection of substances with extremely low content in a sample can be realized, and the spectral measurement sensitivity is improved.
Description
Technical Field
The invention belongs to the field of spectrum detection, and particularly relates to a device and a method for improving the measurement sensitivity of laser absorption spectrum.
Background
Absorption spectroscopy has the advantages of high sensitivity, response times on the order of microseconds, non-toxicity and limited interference from molecular species other than the species under study, and is therefore widely used to detect or identify a variety of molecular species. Absorption spectroscopy provides a general method for detecting important trace species. At present, when the absorption spectrum measurement is carried out on a sample with extremely low concentration, a method of increasing the optical path by passing through an absorption cell for many times is generally adopted. However, the sensitivity of laser absorption spectroscopy measurement is affected due to the increase in optical length.
The zeeman effect refers to a phenomenon in which an atom splits and polarizes a light emission line in an external magnetic field, and is called zeeman effect. The zeeman effect generally causes the atomic spectrum to be split into 3 (difference in the number of magnetic quanta), and the polarization characteristics of the 3 spectra are also different.
The phenomenon of photo-induced drift is an aerodynamic effect present in the optical field, whose principle is: based on the doppler effect, certain gas particles are "velocity-selectively excited" with laser light, so that some of the gas particles having a specific velocity component in the propagation direction of the laser light are populated on an excited state, while particles having other velocity components remain unchanged from a ground state. The gas particles are in the environment of the buffer gas, and due to the difference of collision transport characteristics of the particles on two energy states and the buffer gas, the gas particles generate macroscopic directional movement in the selected speed direction. The Light Induced Drift (LID) effect has been studied in relatively sophisticated theory and experiments to push/pull target atoms in a direction along a beam direction by selecting an appropriate excitation wavelength.
If the Zeeman effect is combined with the Light Induced Drift (LID) effect to be applied to the absorption spectrum measurement of a sample with extremely low concentration, a completely new method is provided for the detection of substances with low concentration.
Disclosure of Invention
The present invention is proposed to overcome the disadvantages existing in the prior art, and the purpose of the present invention is to provide a device and a method for improving the sensitivity of laser absorption spectrum measurement.
The invention is realized by the following technical scheme:
a device for improving the measurement sensitivity of laser absorption spectrum comprises a laser, a wave plate and a glass optical cavity which are sequentially arranged on an optical path of the laser, wherein wedge-shaped windows are arranged at two ends of the glass optical cavity, and two crucibles are respectively connected to the outer walls of two ends of the glass optical cavity and are communicated with the glass optical cavity; the outside of both ends of glass optical cavity all sets up excitation coil.
In the above technical solution, the laser is a tunable laser.
In the above technical solution, the wave plate is a quarter wave plate.
In the above technical solution, the two excitation coils are disposed between the two crucibles.
A method for improving the sensitivity of laser absorption spectrum measurement comprises the following steps:
evaporating
Putting the sample into a crucible for evaporation;
(ii) laser excitation
Laser enters the glass optical cavity after passing through the wave plate;
(iii) adjusting the excitation coil to enrich the target atoms towards the middle
Adjusting the current of the excitation coil to make the target atomic energy level split consistent with the corresponding detuning amount when the photoinduced drift effect is strongest; the current direction of the exciting coil is adjusted so that the left target atom is pushed to the right and the right target atom is pulled to the left, and finally enriched in the middle portion.
In the above technical solution, the frequency of the laser in the step (ii) is between the ground state and the first excited state when the target atom has no magnetic field.
In the above technical solution, the detuning amount corresponding to the maximum photoinduced drift effect is the detuning amount corresponding to the maximum photoinduced drift effect under the specific temperature and the buffer gas pressure obtained according to the spectrum of the target atom to be detected and the collision characteristics of the ground state and the excited state.
The invention has the beneficial effects that:
the invention provides a device and a method for improving the measurement sensitivity of a laser absorption spectrum, which are a novel method for detecting a low-concentration substance, wherein the photo-induced drift (LID) effect is utilized to locally enrich target atoms to be detected, so that the spectral absorption spectrum sensitivity is improved by a method for improving the concentration of the substance to be detected; the device can realize enrichment of target atoms in the middle of the device, and the promotion effect can reach 2-3 orders of magnitude, so that spectral detection of substances with extremely low content in a sample can be realized, and the spectral measurement sensitivity is improved.
Drawings
FIG. 1 is a schematic structural diagram of the device for improving the sensitivity of laser absorption spectroscopy measurement according to the present invention.
Wherein:
1. laser 2 wave plate
3. Glass optical cavity 4 wedge window
5. Crucible 6 excitation coil
7. And (5) testing the sample to be tested.
For a person skilled in the art, other relevant figures can be obtained from the above figures without inventive effort.
Detailed Description
In order to make those skilled in the art better understand the technical solution of the present invention, the technical solution of the apparatus and method for improving the sensitivity of laser absorption spectroscopy according to the present invention is further described below by referring to the drawings of the specification and the specific embodiments.
Example 1
As shown in fig. 1, a device for improving the measurement sensitivity of laser absorption spectrum comprises an adjustable laser 1, a quarter-wave plate 2 and a glass optical cavity 3 which are sequentially arranged on the optical path of the laser 1, wherein wedge-shaped windows 4 are arranged at two ends of the glass optical cavity 3, and two crucibles 5 are respectively connected to the outer walls of two ends of the glass optical cavity 3 and are communicated with the glass optical cavity 3; the outside of both ends of the glass optical cavity 3 are provided with magnet exciting coils 6.
Two of the excitation coils 6 are disposed between the two crucibles 5.
The device can realize the enrichment of target atoms in the middle of the device, and the promotion effect can reach 2-3 orders of magnitude (related to conditions such as specific optical power and the like), thereby realizing the spectral detection of substances with extremely low content in the sample and improving the spectral measurement sensitivity.
Example 2
Based on embodiment 1, a method for improving the sensitivity of laser absorption spectroscopy measurement comprises the following steps:
evaporating
During the detection process, putting a sample into a crucible for evaporation;
(ii) laser excitation
When the frequency is in a non-magnetic field, laser between the ground state and the first excited state energy stage enters the glass optical cavity through the 1/4 wave plate;
(iii) adjusting the excitation coil to enrich the target atoms towards the middle
And adjusting the current of the 2 excitation coils to ensure that the energy level split of the target atoms is consistent with the detuning amount corresponding to the LID effect when the LID effect is strongest, and adjusting the current direction to ensure that the left target atoms are pushed to the right, the right target atoms are pulled to the left, and finally the middle part of the target atoms are enriched, and then detecting the middle part of the target atoms by using a detector.
According to the method, the detuning amount (generally in a GHz level) corresponding to the strongest photoinduced drift effect under the specific temperature and the buffer gas pressure is obtained according to the spectrum of the target atom to be detected and the collision characteristics of the ground state and the excited state, so that the magnetic field intensity is adjusted to enable the frequency shift of the spectrum to be consistent with the detuning amount at the moment, namely the magnetic field intensity is related to the specific substance to be detected, the temperature and the pressure of the filled buffer gas (generally in a range of hundreds of pascals to be strongest).
The working principle of the invention is as follows:
the invention utilizes the Zeeman effect in combination with the Light Induced Drift (LID) effect to enrich the sample with low concentration in a certain area, thereby improving the spectral detection sensitivity.
The zeeman effect generally splits an atomic spectrum into 3 (difference of magnetic quantum numbers), and the polarization characteristics of the 3 spectra are different, so that the atoms can be excited by adopting circular polarization with the frequency of the central excitation frequency of the atoms when no magnetic field exists, only a certain energy level meeting the polarization condition or a certain energy level in the middle can be excited by detuning due to the doppler effect, namely the meeting atoms can be excited selectively, and the speed of the atoms which are excited selectively along the beam direction can be adjusted by changing the size of the magnetic field. If the excited spectral line is excited, the motion direction of the excited atom is opposite to the light propagation direction, for example, the motion direction of the excited atom is the same as the light propagation direction, the excited spectral line can be adjusted by changing the direction of the magnetic field through reasonably selecting the direction of the magnetic field, meanwhile, the direction of the selectively excited speed v can also be changed, meanwhile, as the collision cross section of the excited atom in the excited state and a buffer gas molecule (inert gas, alkane and the like) is different (the common excited state is slightly larger) compared with that of a ground state atom, the diffusion of the excited atom to the selectively excited motion direction is blocked, and thus, a group motion speed, namely a light-induced drift speed vdr (the light pressure can reach several meters or even more than ten meters per second) is generated, the speed is opposite to the motion direction of the selectively excited atom, and has no direct relation with the incident light direction. From the principle of LID, it is known that the excitation wavelength needs to be slightly offset from the central absorption wavelength of the atom. By adopting the device shown in fig. 1, reverse magnetic fields are added at two ends of the device, the magnitude of the magnetic fields is adjusted to enable the energy level splitting to be matched with the detuning amount corresponding to the LID effect, meanwhile, the direction of the magnetic fields is adjusted to enable atoms moving towards the left in the left half part of the device to be excited to generate a rightward drift velocity, atoms moving towards the right in the right half part of the device to be excited to generate a leftward drift velocity, and the drift velocity of the middle part without the magnetic fields is 0, so that target atoms in a sample to be detected at an evaporation position in a crucible are enriched in the middle of the device due to the LID effect, and the concentration of the target atoms can be greatly improved.
The invention provides a device and a method for improving the measurement sensitivity of laser absorption spectroscopy, which utilize the photoinduced drift (LID) effect to locally enrich atoms of a target to be detected, thereby improving the sensitivity of the spectral absorption spectroscopy by improving the concentration of a substance to be detected, and being a novel detection method of a low-concentration substance; the device can realize the enrichment of target atoms in the middle of the device, and the promotion effect can reach 2-3 orders of magnitude, thereby realizing the spectral detection of substances with extremely low content in the sample and improving the sensitivity of spectral measurement.
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.
Claims (6)
1. The utility model provides an improve device of laser absorption spectroscopy measurement sensitivity which characterized in that: the device comprises a laser (1), and a wave plate (2) and a glass optical cavity (3) which are sequentially arranged on the optical path of the laser (1), wherein wedge-shaped windows (4) are arranged at two ends of the glass optical cavity (3), and two crucibles (5) are respectively connected to the outer walls of two ends of the glass optical cavity (3) and are communicated with the glass optical cavity (3); the outside of the two ends of the glass optical cavity (3) are respectively provided with an excitation coil (6); the two magnet exciting coils (6) are arranged between the two crucibles (5).
2. The apparatus for improving the sensitivity of laser absorption spectroscopy measurement according to claim 1, wherein: the laser (1) is a tunable laser.
3. The apparatus for improving the sensitivity of laser absorption spectroscopy measurement according to claim 1, wherein: the wave plate is a quarter wave plate.
4. A method for improving the measurement sensitivity of a laser absorption spectrum by applying the device for improving the measurement sensitivity of a laser absorption spectrum according to any one of claims 1 to 3, wherein the method comprises the following steps: the method comprises the following steps:
evaporating
Putting the sample into a crucible for evaporation;
(ii) laser excitation
Laser enters the glass optical cavity after passing through the wave plate;
(iii) adjusting the excitation coil to enrich the target atoms towards the middle
Adjusting the current of the excitation coil to make the target atomic energy level split consistent with the corresponding detuning amount when the photoinduced drift effect is strongest; and adjusting the current direction of the excitation coil so that the left target atom is pushed to the right, the right target atom is pulled to the left, and finally, the target atoms are enriched in the middle part and then detected by the detector.
5. The method for improving the sensitivity of laser absorption spectroscopy measurement according to claim 4, wherein: and (ii) the frequency of the laser in the step (ii) is between the energy levels of the ground state and the first excited state when the target atom has no magnetic field.
6. The method for improving the sensitivity of laser absorption spectroscopy measurement according to claim 4, wherein: the detuning amount corresponding to the maximum photoinduced drift effect is the detuning amount corresponding to the maximum photoinduced drift effect under the specific temperature and the buffer gas pressure according to the spectrum of the target atom to be detected and the collision characteristics of the ground state and the excited state.
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Citations (2)
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| US5449535A (en) * | 1994-06-13 | 1995-09-12 | Competitive Technologies, Inc. | Light controlled vapor deposition |
| CN111060089A (en) * | 2018-10-17 | 2020-04-24 | 北京自动化控制设备研究所 | High-sensitivity nuclear spin precession detection method based on electronic spin magnetic resonance difference |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US8231707B2 (en) * | 2008-09-30 | 2012-07-31 | Los Alamos National Security, Llc | Gas separation using ultrasound and light absorption |
| US9140657B2 (en) * | 2009-04-13 | 2015-09-22 | The Regents Of The University Of California | Detection of J-coupling using atomic magnetometer |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5449535A (en) * | 1994-06-13 | 1995-09-12 | Competitive Technologies, Inc. | Light controlled vapor deposition |
| CN111060089A (en) * | 2018-10-17 | 2020-04-24 | 北京自动化控制设备研究所 | High-sensitivity nuclear spin precession detection method based on electronic spin magnetic resonance difference |
Non-Patent Citations (4)
| Title |
|---|
| Development of a stretched absolute wavelength standard using dichroic atomic vapor spectroscopy towards observation of light-induced drift;Y Kusano;《IOP Conference Series: Materials Science and Engineering》;20190328;第1-6页 * |
| 关键参数对锂原子光致漂移速率影响的数值研究;杨佳琦等;《光学学报》;20171017(第02期);第1-7页 * |
| 气相甲醇分子的核自旋变体的分离和转换机制研究进展;孙振东;《科学通报》;20160810(第22期);第2429-2440页 * |
| 混沌场近似下锂原子光致漂移过程的动力学模型;柴俊杰等;《光学学报》;20150110(第01期);第1-11页 * |
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