Digital holographic atmospheric CO2 concentration tomography method and fiber optic adjustment structure

Abstract

This invention discloses a digital holographic method for atmospheric CO2 concentration tomography, comprising the following steps: splitting a 355nm working laser into two beams using a beam splitter; one beam irradiates the near-Earth atmosphere at an altitude of 1000m, generating the Raman scattered light of the measured CO2 as the object beam; the other beam irradiates a Raman spectral enhancement emitter, generating the Raman scattered light of the detected CO2 as the reference beam; adjusting the optical path of the reference beam through an optical fiber path adjustment structure to ensure that the object beam at each altitude satisfies the coherence condition with the reference beam at different times; interfering the object beam at each altitude with the coherent reference beam to generate a hologram; recording the intensity information of the characteristic Raman scattered light of the measured CO2 at each altitude segment by segment, and then recording the intensity information of the characteristic Raman scattered light of CO2 across the entire imaging altitude, thus achieving atmospheric CO2 concentration tomography. This invention enables rapid and wide-range adjustment of the reference beam path, thereby achieving tomographic imaging of the characteristic Raman scattered light of atmospheric CO2 across all altitudes.

Description

Technical Field

[0001] This invention relates to the field of digital holographic microscopy, and particularly to a digital holographic atmospheric CO2 concentration tomographic imaging method. Background Technology

[0002] Compared to spatiotemporal resolution systems that use picosecond (or femtosecond) lasers, gated enhanced CCDs, and delay controllers, digital holographic systems are simple in structure, compact in size, and low in cost, which is conducive to the miniaturization and cost reduction of instruments and equipment, and is more suitable for tomographic imaging of characteristic Raman scattering light of atmospheric CO2 at all altitudes.

[0003] The prerequisite for achieving full-altitude atmospheric CO2 characteristic Raman scattering tomography in digital holography is that the hologram records the atmospheric CO2 characteristic Raman scattering information across the entire imaging height. However, the coherence length of lasers is limited; even single-mode lasers with good coherence have a coherence length of only about 100m. Under the condition that the optical path of the reference optical path remains unchanged, it is difficult to guarantee that the measured CO2 characteristic Raman scattering light within the entire near-Earth atmospheric imaging height (about 1000m) meets the coherence requirement with the detected CO2 characteristic Raman scattering light. Therefore, it is impossible to guarantee that the atmospheric CO2 characteristic Raman scattering light at the entire imaging height can interfere with the detected CO2 characteristic Raman scattering light and thus be recorded by the hologram.

[0004] Therefore, it is urgent to explore an adjustment structure that can quickly and over a wide range adjust the optical path of the Raman scattering light of CO2 characteristics, so that the Raman scattering light of atmospheric CO2 characteristics at various altitudes satisfies the coherence condition with the Raman scattering light of CO2 characteristics at different times and segments, thereby recording the intensity information of the Raman scattering light of CO2 characteristics at the entire imaging altitude and realizing full-altitude atmospheric CO2 concentration tomography. Summary of the Invention

[0005] This invention provides a digital holographic tomographic imaging method for atmospheric CO2 concentration. A 355nm working laser is split into two beams using a beam splitter, which respectively illuminate atmospheric CO2 and a Raman spectroscopy enhancement emitter, generating Raman scattered light from the measured CO2 and Raman scattered light from the probe CO2. The round-trip optical path of the probe CO2 Raman scattered light is adjusted using an optical fiber path adjustment structure, thereby ensuring that the probe CO2 Raman scattered light and the measured CO2 Raman scattered light at different altitudes meet the coherence condition, thus achieving tomographic imaging of atmospheric CO2 concentration.

[0006] The specific technical solution adopted in this invention is as follows:

[0007] A digital holographic method for atmospheric CO2 concentration tomography includes the following steps:

[0008] (1) The 355nm working laser is split into two beams by a beam splitter. One beam illuminates the near-ground atmosphere at a height of 1000m and the resulting CO2 Raman scattered light is used as the object light. The other beam illuminates the Raman spectral enhancement emitter and the resulting CO2 Raman scattered light is used as the reference light.

[0009] The Raman spectroscopy enhancement emitter can enhance the excitation, efficiently collect, and emit high-power Raman scattered light from the CO2 gas sample generated under the illumination of the working laser, producing high-intensity detection CO2 Raman scattered light.

[0010] (2) The reference light described in step (1) is passed into the fiber-optic optical path adjustment structure. The optical path of the reference light is adjusted through the structure so that the object light at each height satisfies the coherence condition with the reference light at different times.

[0011] The fiber optic path adjustment structure comprises 10 fiber segments, each 50m long, with a retroreflector connected to the end of the furthest segment. Two fiber segments are connected by a fiber optic coupler, and the other end of each coupler is connected to the input via an optical switch. By switching the optical switch, the optical path of the reference light is altered, thereby ensuring that the reference light satisfies the coherence condition with the object light at various altitudes.

[0012] (3) Interference between the object light at each altitude and the reference light in step (2) is generated to produce a hologram. The intensity information of the Raman scattering light of the measured CO2 at each altitude is recorded in segments over time. Then, the intensity information of the Raman scattering light of the CO2 at the entire imaging altitude is recorded to achieve atmospheric CO2 concentration tomography.

[0013] The beneficial effects of this invention are:

[0014] This invention designs an optical fiber-type optical path adjustment structure, which can quickly and widely adjust the optical path of the reference optical path by switching the optical switch, so that the reference light can meet the coherence condition with the object light at various heights.

[0015] This invention proposes an atmospheric CO2 concentration tomographic imaging method, which generates a hologram by interfering the characteristic Raman scattered light of atmospheric CO2 at various altitudes with the characteristic Raman scattered light of detected CO2 that meets the coherence condition. The intensity information of the characteristic Raman scattered light of the measured CO2 at each altitude is recorded in segments at different times, and then the intensity information of the characteristic Raman scattered light of CO2 at the entire imaging height is recorded. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a digital holographic atmospheric CO2 concentration tomographic imaging method.

[0017] Figure 2 For Raman spectroscopy enhancement emitter;

[0018] Figure 3 It is an optical fiber-type optical path adjustment structure. Detailed Implementation

[0019] The present invention will now be described in detail with reference to the embodiments and accompanying drawings, but the present invention is not limited thereto.

[0020] A schematic diagram of a digital holographic atmospheric CO2 concentration tomographic imaging method according to this embodiment is shown below. Figure 1 As shown, the feature is that it includes the following steps:

[0021] (1) The working laser (355nm) is split into two beams by a beam splitter. One beam illuminates the near-Earth atmosphere (at an altitude of 1000m) to produce the Raman scattered light of the measured CO2 (as the object beam), and the other beam illuminates a Raman spectroscopy enhancement emitter (such as...). Figure 2 As shown), it generates Raman scattered light for detecting CO2 (as a reference light);

[0022] The Raman spectroscopy-enhanced emitter includes a lens L1, spherical mirrors A, B, and C, a gas guide tube, a lens L2, and a beam-constricting structure. A background aluminum sheet is attached to the inner wall of the emitter to increase excitation efficiency. Following the trajectory of the incident laser, the optical path structure and its spatial positioning are as follows: lens L1, gas guide tube, spherical mirror B, gas guide tube, and spherical mirror A. The laser beam is reflected and focused back and forth between the two spherical mirrors. The ultraviolet laser irradiates the CO2 gas flow in the gas guide tube, generating Raman scattered light. Following the trajectory of the Raman scattered light, the optical path structure and its spatial positioning are as follows: gas guide tube, spherical mirror C, gas guide tube, lens L2, and beam-constricting structure. This device can enhance the excitation, efficiently collect, and emit high-power Raman scattered light from a CO2 gas sample generated under working laser irradiation, producing high-intensity detected CO2 Raman scattered light.

[0023] (2) Pass the reference light described in step (1) into the fiber optic optical path adjustment structure (e.g., Figure 3 As shown in the figure, the optical path of the reference light is adjusted by the structure so that the object light at each height satisfies the coherence condition with the reference light at different times.

[0024] The fiber optic path adjustment structure comprises 10 fiber segments, each 50m long, with a retroreflector connected to the end of the furthest segment. Two fiber segments are connected by a fiber optic coupler, and the other end of each coupler is connected to the input via an optical switch. By switching the optical switch, the optical path of the reference optical path is changed, thereby enabling the reference light to meet the coherence condition with the object light at various altitudes.

[0025] (3) Interference between the object light at each altitude and the reference light in step (2) is generated to produce a hologram. The intensity information of the Raman scattering light of the measured CO2 at each altitude is recorded in segments at different times. Then, the intensity information of the Raman scattering light of the CO2 at the entire imaging altitude is recorded to achieve full-altitude atmospheric CO2 concentration tomography.

[0026] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A digital holographic atmospheric CO2 concentration tomographic imaging method, characterized in that, Including the following steps: (1) The 355nm working laser is split into two beams by a beam splitter. One beam illuminates the near-ground atmosphere at a height of 1000m and the resulting CO2 Raman scattered light is used as the object light. The other beam illuminates the Raman spectral enhancement emitter and the resulting CO2 Raman scattered light is used as the reference light. (2) The reference light described in step (1) is passed into the fiber-optic optical path adjustment structure, and the optical path of the reference light is adjusted by the structure so that the object light at each height satisfies the coherence condition with the reference light at different times. (3) Interference between the object light at each altitude and the reference light in step (2) is generated to produce a hologram. The intensity information of the Raman scattering light of the measured CO2 at each altitude is recorded in segments at different times. Then, the intensity information of the Raman scattering light of the CO2 at the entire imaging altitude is recorded to achieve full-altitude atmospheric CO2 concentration tomography.

2. The digital holographic atmospheric CO2 concentration tomographic imaging method as described in claim 1, characterized in that, The Raman spectroscopy enhancement emitter described in step (1) can enhance the excitation, efficiently collect and emit high-power Raman scattered light from the CO2 gas sample generated under the illumination of the working laser, producing high-intensity detection CO2 Raman scattered light.

3. A fiber optic path adjustment structure used in the digital holographic atmospheric CO2 concentration tomography method of claim 1 or 2, comprising a total of 10 fiber segments, each fiber segment being 50m long, with a retroreflector connected to the end of the farthest fiber segment; two fiber segments are connected by a fiber optic coupler, and the other end of each fiber optic coupler is connected to the input end through an optical switch, and the optical path of the reference light is changed by switching the optical switch, so that the reference light can satisfy the coherence condition with the object light at various altitudes.

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