Temperature measurement method and system based on structured light-thermal auxiliary fluorescence

Abstract

The invention discloses a temperature measurement method and system based on structured light-thermal auxiliary fluorescence, and the method combines structured light modulation with thermal auxiliary fluorescence temperature measurement, thereby greatly simplifying the architecture of the measurement system while guaranteeing the temperature measurement precision. The temperature measurement system is composed of a laser module, a reflection assembly, a refraction assembly, a structured light modulation module, a single-camera double-light-path signal acquisition module and a signal processing module, a single-wavelength ultraviolet light source emitted by the laser module is used for driving OH free radical thermal power to assist fluorescence response, and structured light modulation and single-camera double-light-path time-space synchronous acquisition are combined. On the premise that the number of lasers and optical channels are not increased, optical layer filtering of scattering noise and accuracy of dual-band fluorescence are achieved, and stable operation of the system under severe working conditions of high temperature, vibration, limited installation space and the like is ensured.

Description

Technical Field

[0001] This invention relates to the field of fluorescence thermometry, and in particular to a thermometry method and system based on structured light-thermal-assisted fluorescence. Background Technology

[0002] Research on combustion temperature measurement is of great significance for exploring the combustion process and mechanism, and plays a key role in realizing low-pollution, low-energy combustion technologies. Non-contact laser diagnostic methods, due to their minimal interference with the flow field, high measurement frequency, and flexible measurement point arrangement, have become important research tools in complex combustion environments. Among various non-contact laser diagnostic techniques, two-dimensional laser-induced fluorescence (PLIF) can obtain information such as the transient two-dimensional structure and temperature field of a flame by analyzing the fluorescence emitted by specific components during energy level transitions.

[0003] Two-dimensional laser-induced fluorescence technology mainly includes excitation wavelength scanning laser-induced fluorescence method, double-line method and thermo-assisted fluorescence thermometry method. Thermo-assisted fluorescence thermometry uses a single-wavelength laser to excite molecules to a high energy state. The molecules transfer to neighboring energy levels through thermal motion. This process is temperature-dependent. The temperature can be inverted by analyzing the fluorescence spectra of different vibrational energy levels.

[0004] Furthermore, structured light illumination planar imaging technology, by replacing uniform sheet light with spatially modulated structured light, can effectively distinguish between directly scattered photons carrying sample information and disordered multiple scattering noise. With the aid of phase-shifting algorithms and frequency-domain demodulation, high signal-to-noise ratio two-dimensional quantitative images can be extracted from aliased signals.

[0005] However, when performing two-dimensional temperature field measurements in strong scattering environments such as closed combustion chambers, multiple scattering noise and effective signals are severely mixed, limiting the accuracy of temperature inversion. To achieve high-precision measurements, existing technologies often require increasing the number of lasers and equipping them with complex synchronous control systems, which increases the complexity and cost of the system. Summary of the Invention

[0006] In view of the shortcomings of the prior art, the purpose of this invention is to provide a temperature measurement method and system based on structured light-thermal-assisted fluorescence, which aims to solve the problem that it is difficult to construct a high signal-to-noise ratio and high contrast two-dimensional quantitative image in a two-dimensional temperature field using simplified equipment.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A thermometry method based on structured light-thermal-assisted fluorescence includes the following steps:

[0009] S1. Laser Output and Shaping: After the laser module outputs green laser, it converts the green laser into ultraviolet light and uses the ultraviolet light as a light source. Then, the incident direction and position of the ultraviolet light are adjusted by the reflection component, and the ultraviolet light is shaped into a sheet-like beam that matches the preset height by the refraction component.

[0010] S2. Structured light modulation: Using a prism element to modulate a sheet beam into interference fringes with spatial phase information, and the modulation characteristics of the interference fringes can be fluorescence preserved;

[0011] S3. Signal Acquisition: The structured light fluorescence signal is acquired by using a single-camera dual-optical-path signal acquisition module. The fluorescence spectra of OH radicals (A²Σ⁺→X²Π) in the (0,0) and (1,0) bands are captured simultaneously using a framing filter, and the signal is synchronized through a photoelectric detection module.

[0012] S4. Signal Processing: The acquired fluorescence spectrum is processed, and the fluorescence signal is decomposed into sine and cosine components. A reference signal containing the modulation frequency is created to upconvert the stray light signal. The stray light signal is filtered out by a filter, and the demodulated fluorescence signal is extracted.

[0013] S5. Temperature Field Inversion: Based on thermo-assisted fluorescence technology, the relationship between fluorescence intensity ratio and temperature is obtained through the VET model. The two-dimensional temperature field is then inverted using the following formula to obtain the two-dimensional local temperature field.

[0014]

[0015] Where, ΔE 10 The fluorescence signals represent the vibrational energy levels 1 and 0 of excited state A to ground state 0, k is the Boltzmann constant, T is the absolute temperature, Q1 represents the rate of quenching and all other energy losses, and V... 10 It is the rate of downward vibrational transmission between vibrational energy level 1 and vibrational energy level 0 in excited state A. , These are the fluorescence signals from vibrational energy levels 1 and 0 of excited state A to ground state energy level 0 of ground state X after demodulation. 00 A represents the spontaneous emission Einstein coefficient for the 0→0 energy level transition. 10 The Einstein coefficient for spontaneous emission during the 1→0 energy level transition.

[0016] Furthermore, in step S2, when the prism element modulates the sheet beam with structured light, a formula is introduced to relate the height of the structured light spatial center, the distance between the structured light center and the incident surface of the prism element, and the base angle of the prism element:

[0017]

[0018]

[0019] Where H represents the height of the structured light space center, L represents the distance between the structured light center and the incident surface of the prism element, θ represents the base angle of the prism, n1 represents the refractive index of the prism element material at a specific light source wavelength, and n2 represents the refractive index of air. At this time, n1 / n2 = 1.485.

[0020] Furthermore, in step S3, in order to shorten the exposure time of the single-camera dual-optical-path signal acquisition module, a timing adjustment module is introduced, and the fluorescence spectrum acquired by the single-camera dual-optical-path signal acquisition module after being adjusted by the timing adjustment module is sent to the photoelectric detection module.

[0021] Furthermore, the photodetector module includes an image intensifier and a camera. The image intensifier enhances the intensity of the fluorescence signal, and the camera converts the fluorescence signal into digital image data.

[0022] Furthermore, before performing step S4, a signal correction step is required for the fluorescence signal. The signal correction step includes correcting the geometric distortion of the fluorescence signal using a calibrated checkerboard image and correcting the camera response using a standard light-emitting plate, so as to ensure that a consistent signal intensity distribution is obtained.

[0023] Furthermore, step S4 includes the following steps:

[0024] S41. Signal Reception: Receives the fluorescence signal transmitted from the single-camera dual-optical-path signal acquisition module. The fluorescence signal includes stray light signals and valid signals. The relationship between the valid signal and the stray light signal is expressed as follows:

[0025]

[0026] Among them, F X For fluorescence signal, F S For a valid signal, F MS Here, υ represents the stray optical signal, Φ represents the modulation frequency, and Φ represents the modulation spatial phase.

[0027] S42. Signal demodulation is used to extract the effective signal. A phase demodulation algorithm is applied, utilizing the Pythagorean trigonometric identities to decompose the fluorescence signal into sine and cosine components. The effective signal is then obtained by calculating the square root of the sum of their squares. The amplitude is used to filter out stray light signals.

[0028] ;

[0029] S43. Match the effective signals of the (0,0) band obtained by demodulation in step S42 with those of the (1,0) band.

[0030] A temperature measurement system based on structured light-thermal-assisted fluorescence, applicable to any of the aforementioned temperature measurement methods based on structured light-thermal-assisted fluorescence, comprising:

[0031] The laser module includes a solid-state laser and a dye laser. The solid-state laser outputs green laser light, which is then converted into ultraviolet light by the dye laser, and the ultraviolet light serves as the light source.

[0032] The reflective component includes a first reflector and a second reflector arranged in sequence, which can change the incident direction and position of the light source;

[0033] The refractive assembly includes a concave lens and a convex lens arranged in sequence. The concave lens and the convex lens work together to shape the light source from a cylindrical state into a sheet-like beam.

[0034] Structured light modulation module, the structured light modulation module is a prism element;

[0035] The single-camera dual-optical-path signal acquisition module includes a framing filter and a photoelectric detection module; and a signal processing module, which includes a computer.

[0036] Furthermore, the cross-section of the prism element is an isosceles triangle. The sheet-like beam enters perpendicularly from the base of the isosceles triangle, and after refraction at the waist of the isosceles triangle, it forms two sheet-like beams. After crossing and merging, they form structured light with varying intensity and brightness.

[0037] Furthermore, the structured light space formed by the intersection and fusion of the two sheet-like beams has a rhomboid structure, with the center of the structured light space located in the flame measurement area above the combustion chamber.

[0038] Furthermore, the framing filter includes a rectangular filter and a neutral density filter. The rectangular filter can only transmit fluorescence signals in the (0,0) and (1,0) bands, and the filtering areas of the (0,0) and (1,0) bands each occupy half of the rectangular filter.

[0039] The beneficial effects of this invention are:

[0040] 1. The present invention proposes a temperature measurement method based on structured light-thermal-assisted fluorescence, which includes using a prism element to modulate a sheet beam into structured light with spatial phase information, processing the acquired fluorescence spectrum, and combining it with thermal-assisted fluorescence temperature measurement technology, which greatly simplifies the architecture of the measurement system while ensuring temperature measurement accuracy.

[0041] 2. The present invention proposes a temperature measurement method based on structured light-thermal-assisted fluorescence. In step S2, a formula relating the spatial center height of the structured light, the distance between the structured light center and the incident surface of the prism element, and the base angle of the prism element is introduced. Based on this formula, quantitative modeling and precise control of the spatial geometric parameters of the structured light are achieved, avoiding the problem of structured light coverage deviation. This ensures that the structured light region can stably fall on the core position of the combustion chamber flame measurement area, so that the fluorescence signals of OH free radicals in the (0,0) band and the (1,0) band have spatial and temporal consistency, providing a high-fidelity original data foundation for subsequent phase demodulation and thermal-assisted fluorescence temperature inversion.

[0042] 3. The present invention proposes a temperature measurement method based on structured light-thermal-assisted fluorescence. In step S3, a timing adjustment module is introduced. The timing adjustment module can transmit the fluorescence spectrum acquired by the single-camera dual-optical-path signal acquisition module to the photoelectric detection module. The timing adjustment module can ensure that the dual-band signals are captured simultaneously, thereby avoiding the calculation error of the dual-band intensity ratio caused by time asynchrony. This provides a high-fidelity original data basis for subsequent temperature field inversion based on the thermal-assisted fluorescence temperature measurement method.

[0043] 4. The present invention proposes a temperature measurement method based on structured light-thermal-assisted fluorescence. Before performing step S4, geometric distortion correction of the fluorescence signal is performed using a calibration checkerboard image, and camera response is corrected using a standard light-emitting plate. Geometric correction can solve the problem of spatial coordinate inaccuracy, and corresponding correction can solve the problem of fluorescence signal intensity inaccuracy, so as to ensure a consistent signal intensity distribution between the flame and the camera.

[0044] 5. The present invention proposes a temperature measurement method based on structured light-thermal-assisted fluorescence. In step S4, a phase demodulation algorithm is applied, and the fluorescence signal is decomposed into sine and cosine components using the Pythagorean trigonometric identity. This filters out stray light signals and eliminates demodulation errors caused by laser power fluctuations, image intensifier gain drift, or local spatial phase mismatch, thus ensuring amplitude stability.

[0045] 6. The present invention proposes a temperature measurement system based on structured light-thermal-assisted fluorescence, which uses a single-wavelength ultraviolet light source to drive the thermo-assisted fluorescence response of OH radicals. Combined with structured light modulation and single-camera dual-optical-path spatiotemporal synchronous acquisition, it achieves optical-level filtering of scattering noise and accuracy of dual-band fluorescence without increasing the number of lasers or optical channels, ensuring stable operation of the system under harsh conditions such as high temperature, vibration, and limited installation space.

[0046] 7. The present invention proposes a temperature measurement system based on structured light-thermal-assisted fluorescence, including a structured light modulation module, which is a prism element with an isosceles triangle cross-section. A sheet-like beam is perpendicularly incident from the base of the isosceles triangle and refracted through the waist of the isosceles triangle to form two sheet-like beams. After crossing and merging, they form structured light with varying intensity and brightness. Geometric symmetry ensures strict consistency of the two refracted beams in propagation direction, optical path difference, and deflection angle, thereby generating high-contrast, periodically stable, and phase-continuous interference fringes in the subsequent spatial superposition process. This structure does not rely on external phase compensation devices and has the characteristics of large assembly tolerance and high thermal stability.

[0047] 8. The present invention proposes a temperature measurement system based on structured light-thermal-assisted fluorescence, which has a framing filter. The framing filter includes a rectangular filter and a neutral density filter. The rectangular filter can only transmit fluorescence signals in the (0,0) and (1,0) bands, and the filtering areas of the (0,0) band and the (1,0) band each occupy half of the rectangular filter. The two OH radical fluorescence channels with very close center wavelengths and high risk of spectral overlap are forcibly separated by physical spatial segmentation, ensuring that the two signals are strictly isolated in the image plane space, the spectral responses do not interfere with each other, and the dynamic range of light intensity is controllable. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of a temperature measurement method based on structured light-thermal-assisted fluorescence according to the present invention;

[0050] Figure 2 This is a schematic diagram of a temperature measurement system based on structured light-thermal-assisted fluorescence according to the present invention;

[0051] Figure 3 This is a schematic diagram of a prism element in a temperature measurement system based on structured light-thermal-assisted fluorescence according to the present invention.

[0052] In the diagram, 10 is the laser module; 101 is the solid-state laser; 102 is the dye laser; 20 is the reflective component; 201 is the first reflecting mirror; 202 is the second reflecting mirror; 30 is the refractive component; 301 is the concave lens; 302 is the convex lens; 40 is the structured light modulation module; 401 is the prism element; 50 is the single-camera dual-optical-path signal acquisition module; 60 is the signal processing module; and 601 is the computer. Detailed Implementation

[0053] The following is combined Figures 1-3 The present invention will be described in detail below.

[0054] A thermometry method based on structured light-thermal-assisted fluorescence includes the following steps:

[0055] S1. Laser output and shaping: After the laser module 10 outputs laser, it converts the laser into ultraviolet light and uses the ultraviolet light as a light source. Then, the incident direction and position of the ultraviolet light are adjusted by the reflection component 20, and the ultraviolet light is shaped into a sheet-like beam that matches the preset height by the refraction component 30.

[0056] S2. Structured light modulation: The sheet beam is modulated into interference fringes with spatial phase information using a prism element 401. The modulation characteristics of the interference fringes can be retained by fluorescence, while the modulation depth of multiple scattering noise approaches zero, thereby achieving background filtering at the optical level.

[0057] S3. Signal acquisition: The structured light fluorescence signal is obtained by using a single-camera dual-optical-path signal acquisition module 50. The fluorescence spectrum of OH free radical (A²Σ⁺→X²Π) in the (0,0) band and (1,0) band is captured synchronously using a framing filter, and the signal is synchronized through a photoelectric detection module.

[0058] S4. Signal Processing: The acquired fluorescence spectrum is processed, and the fluorescence signal is decomposed into sine and cosine components. A reference signal containing the modulation frequency is created to upconvert the stray light signal. The stray light signal is filtered out by a filter, and the demodulated fluorescence signal is extracted.

[0059] S5. Temperature Field Inversion: Based on thermo-assisted fluorescence technology, the relationship between fluorescence intensity ratio and temperature is obtained through the VET model. The two-dimensional temperature field is then inverted using the following formula to obtain the two-dimensional local temperature field.

[0060]

[0061] Where, ΔE 10 Let V be the energy difference between vibrational energy level 1 and vibrational energy level 0 in excited state A, k be the Boltzmann constant, T be the absolute temperature, Q1 represent the rate of quenching and all other energy losses, and V be the energy difference between excited state A and excited state B. 10 It is the rate of downward vibrational transmission between vibrational energy level 1 and vibrational energy level 0 in excited state A. , These are the fluorescence signals from vibrational energy levels 1 and 0 of excited state A to ground state energy level 0 of ground state X after demodulation. 00 A represents the spontaneous emission Einstein coefficient for the 0→0 energy level transition. 10The Einstein coefficient for spontaneous emission during the 1→0 energy level transition.

[0062] Through the above methods and steps, the sheet beam is modulated into structured light with spatial phase information using the prism element 401, and the acquired fluorescence spectrum is processed. Combined with thermo-assisted fluorescence thermometry, the architecture of the measurement system is greatly simplified while ensuring the accuracy of temperature measurement.

[0063] In step S1, a green laser with a wavelength of 532 nm is output at an emission frequency of 10 Hz. The beam is then converted into ultraviolet light with a wavelength of 308.983 nm by a frequency conversion unit and grating inside the laser module 10. The energy of this ultraviolet light is approximately 2.5 mJ. This ultraviolet light serves as a pump source for the electron transition of OH radicals (A²Σ⁺→X²Π). The refractive component 30 can shape the cylindrical laser into a sheet-like beam with a thickness of 0.5 mm and a length of 40 mm, matching the flame measurement area of ​​the combustion chamber.

[0064] In step S5, the state of the OH radical is described using the VET model, reflecting the energy change between vibrational energy levels 1 and 0 of the A-excited state pumped by ultraviolet light. This model can capture and express the instantaneous changes in the fluorescence signal within a very short time, ensuring the accuracy of the temperature retrieved by measuring the fluorescence intensity ratio in the (0,0) and (1,0) bands. During the inversion, the demodulated (0,0) and (1,0) fluorescence images are pixel-level registered and intensity normalized. The ratio of each pixel is calculated, and by substituting the corresponding values, the ratio of each pixel in the image can be calculated to obtain the two-dimensional temperature distribution map of the combustion chamber.

[0065] This method outputs single-wavelength ultraviolet light, which is then adjusted in direction by the reflector 20 and shaped by the refraction 30 to form a highly controllable sheet-like beam. This provides a stable input for structured light modulation. The beam is then generated by the prism element 401, producing spatially phase-defined structured light. This modulation characteristic is directly inherited by the OH radical fluorescence signal, while multiple scattering noise loses its modulation capability due to spatial incoherence, thus achieving optical background suppression. The single-camera dual-path signal acquisition module 50 uses a framing filter to simultaneously capture OH radicals (A²Σ⁺→X²Π) in the (0,0) band and (1,0) band. The fluorescence spectrum in the 0-band is used to reduce time error interference. The phase demodulation algorithm accurately separates the effective signal from the modulated fluorescence through orthogonal reference signal and low-pass filtering, and further suppresses residual stray light. The VET model inversion formula establishes a quantitative analytical relationship between fluorescence intensity ratio and temperature, and finally outputs a two-dimensional local temperature field with high spatial resolution, high signal-to-noise ratio and high temperature accuracy. This scheme solves the core problems of low signal-to-noise ratio, system complexity and synchronization difficulty in the quantitative measurement of two-dimensional temperature field in a closed high scattering environment without increasing hardware complexity, and provides a reliable technical path for combustion diagnosis.

[0066] In step S2, the relationship between the height of the structured light space center, the distance between the structured light center and the incident surface of the prism element 401, and the base angle of the prism element 401 when the prism element 401 modulates the sheet beam is as follows:

[0067]

[0068]

[0069] Where H represents the height of the structured light space center, L represents the distance between the structured light center and the incident surface of the prism element 401, θ represents the base angle of the prism, n1 represents the refractive index of the prism element 401 material at a specific light source wavelength, the prism element 401 material is JGS1 material (i.e., far-ultraviolet grade synthetic fused silica glass), at this time n1=1.485, n2 represents the refractive index of air, n2 can be approximated as 1, therefore n1 / n2=1.485.

[0070] The height H of the structured light spatial center refers to the vertical height of the rhomboid structured light formed by the cross-fusion of two segments refracted by the waist surface of the prism. In this embodiment, the theoretical design value of H is 20mm, corresponding to the midpoint of the original height of the sheet beam (40mm), ensuring that the effective area of ​​the structured light completely encloses the main generation and quenching range of OH free radicals. The height of the sheet laser is constrained by the size of the frame, so the height of the sheet laser is set to 40mm, and the theoretical value of H is set to 20mm. This is because the modulation principle of the prism element 401 limits the sheet laser to be divided into two segments, which cross-fuse to form the structured light region. The height of this structured light region can be close to half the height of the sheet laser, i.e., 20mm.

[0071] The distance L between the center of the structured light and the incident surface of the prism element 401 refers to the projection distance along the optical axis from the bottom edge of the prism to the geometric center of the rhomboid region in the structured light space. This distance determines the positioning accuracy of the structured light in the combustion chamber axis and its matching with the camera's field of view. If L is too short, the structured light cannot cover the combustion chamber flame area; if L is too long, it exceeds the combustion chamber flame area, resulting in a decrease in the utilization efficiency of the structured light. In this embodiment, the design target for L is 350mm, which is greater than the axial distance from the last reflector to the center of the sealed combustion chamber flame in a conventional optical testing system. Therefore, the prism element 401 can be placed in front of the last reflector to ensure sufficient space.

[0072] The base angle θ of the prism element 401 is a core control parameter connecting optical design and mechanical processing. It directly determines the incident angle, refraction angle and outgoing direction angle of the light on the two waist surfaces, and thus dominates the spatial phase distribution of the structured light.

[0073] In step S2, a formula relating the height of the structured light spatial center, the distance between the structured light center and the incident surface of the prism element 401, and the base angle of the prism element 401 is introduced. Based on this formula, quantitative modeling and precise control of the structured light spatial geometric parameters are achieved, avoiding the problem of structured light coverage deviation. This ensures that the structured light region can stably fall on the core position of the combustion chamber flame measurement area, so that the fluorescence signals of OH free radicals in the (0,0) band and (1,0) band have spatial and temporal consistency, providing a high-fidelity original data basis for subsequent phase demodulation and thermo-assisted fluorescence temperature inversion.

[0074] In step S3, because the fluorescence lifetime of OH radicals is extremely short and the emission process is a linear response, the sheet-like beam forms interference fringes with spatial phase information after reflection by the prism element 401, and the fluorescence signal can directly inherit the modulation characteristics of this phase information, thus forming "structured fluorescence".

[0075] To shorten the exposure time of the single-camera dual-optical-path signal acquisition module 50, a timing adjustment module is introduced. The fluorescence spectrum acquired by the single-camera dual-optical-path signal acquisition module 50, adjusted by the timing adjustment module, is then transmitted to the photodetector module. The timing adjustment module ensures that the dual-band signals are captured simultaneously, thus avoiding calculation errors in the intensity ratio of the two bands due to time asynchrony. This provides a high-fidelity raw data foundation for subsequent temperature field inversion based on the thermo-assisted fluorescence thermometry method. Furthermore, the photodetector module includes an image intensifier and a camera. The image intensifier enhances the intensity of the fluorescence signal, and the camera converts the fluorescence signal into digital image data.

[0076] The timing adjustment module is an electronic synchronization control unit with time resolution capability. Its input terminal is connected to the signal output terminal of the laser module 10, the image intensifier gating signal, and the camera exposure trigger signal. The output terminal of the timing adjustment module sends a precise delay and pulse width adjustable synchronization command to the camera and the image intensifier, which can realize the time alignment between the laser pulse leading edge, the image intensifier gain activation time, and the effective integration window of the camera photosensitive array.

[0077] In the single-camera dual-path signal acquisition module 50, the "exposure time" specifically refers to the effective time interval during which the camera image sensor actually responds and accumulates fluorescence signals within one trigger cycle. Its value is directly set by the width of the exposure enable pulse output by the timing adjustment module.

[0078] Before performing step S4, a signal correction step is performed on the fluorescence signal. The signal correction step includes correcting the geometric distortion of the fluorescence signal using a calibrated checkerboard image and correcting the camera response using a standard light-emitting plate to ensure a consistent signal intensity distribution between the flame and the camera.

[0079] The calibration checkerboard image is a standard two-dimensional planar calibration target with a high-contrast black and white square array. This checkerboard can establish a mapping relationship between the image pixel coordinates and the real physical coordinates of the optical imaging system. Through a calibration procedure, distortion correction parameters are generated to map the distorted image to a distortion-free image, thus solving the problem of spatial coordinate inaccuracy. The standard light-emitting plate is a uniform surface light source, which can eliminate the influence of pixel sensitivity differences on the intensity distribution of fluorescence signals in the image at the same wavelength, thereby truly reflecting the true distribution of fluorescence signals at the same wavelength in the image.

[0080] Step S4 includes the following steps:

[0081] S41. Signal Reception: Receives the fluorescence signal transmitted from the single-camera dual-optical-path signal acquisition module 50. The fluorescence signal includes stray light signal and valid signal, wherein the relationship between the valid signal and stray light signal is expressed as follows:

[0082]

[0083] Among them, F X For fluorescence signal, F S For a valid signal, F MS Here, υ represents the stray optical signal, Φ represents the modulation frequency, and Φ represents the modulation spatial phase.

[0084] S42. Signal demodulation is used to extract the effective signal. A phase demodulation algorithm is applied, utilizing the Pythagorean trigonometric identities to decompose the fluorescence signal into sine and cosine components. The effective signal is then obtained by calculating the square root of the sum of their squares. The amplitude is used to filter out stray light signals:

[0085] ;

[0086] S43. Match the effective signals in the (0,0) and (1,0) bands obtained by demodulation in step S42, i.e., the fluorescence signals from the A excited state vibrational energy level 1 to the X ground state energy level 0 after demodulation. (corresponding to the (1,0) band of the OH radical), and the fluorescence signal from the A excited state vibrational level 0 to the X ground state level 0. (corresponding to the (0,0) band of OH radicals), ensuring that the two signals correspond perfectly in time and space.

[0087] In step S4, a phase demodulation algorithm is applied, which uses the Pythagorean trigonometric identity to decompose the fluorescence signal into sine and cosine components, thereby filtering out stray light signals. The calculation eliminates demodulation errors caused by laser power fluctuations, image intensifier gain drift, or local spatial phase mismatch, ensuring amplitude stability.

[0088] The VET model in step S5 focuses on the VET process between various vibration levels, which can connect the fluorescence intensity ratio with temperature through a reliable and deterministic functional relationship, providing a model basis for inversion. Based on the VET model, a two-dimensional local temperature field with physical meaning and engineering accuracy can finally be inverted from the captured images.

[0089] A temperature measurement system based on structured light-thermal-assisted fluorescence, applicable to the aforementioned structured light-single-wavelength thermal-assisted fluorescence temperature measurement method, includes:

[0090] Laser module 10 includes a solid-state laser 101 and a dye laser 102. The solid-state laser 101 outputs green laser light, which is then converted into ultraviolet light by the dye laser 102. The ultraviolet light serves as the light source.

[0091] The reflective component 20 includes a first reflector 201 and a second reflector 202 arranged sequentially. The first reflector 201 and the second reflector 202 can change the incident direction and position of the light source.

[0092] The refractive assembly 30 includes a concave lens 301 and a convex lens 302 arranged sequentially. The concave lens 301 and the convex lens 302 work together to shape the light source from a cylindrical state into a sheet-like beam.

[0093] Structured light modulation module 40, the structured light modulation module 40 is a prism element 401;

[0094] The single-camera dual-optical-path signal acquisition module 50 includes a frame-splitting filter and a photoelectric detection module; and the signal processing module 60 includes a computer 601.

[0095] The system uses the five-step process defined by the above method as its functional framework. Through the precise mapping and collaborative integration of physical modules, it constructs a full-chain measurement platform with high spatial resolution, strong background suppression capability, and compact layout characteristics.

[0096] The laser module 10 provides a single-wavelength, high-energy, narrow-linewidth ultraviolet pump source. The solid-state laser 101 can be an Nd:Yag frequency-doubled green laser with an emission frequency of 10Hz. The dye laser 102 can be a Sirah dye laser. Fluorescence is generated by the reaction in the internal dye pool of the Sirah dye laser and converted into ultraviolet light with a wavelength of 308.983nm by its internal frequency conversion unit and grating.

[0097] The reflector 20 is used to achieve spatial guidance and precise positioning of the columnar laser beam. The first reflector 201 and the second reflector 202 are arranged collinearly, and both the first reflector 201 and the second reflector 202 can be installed on a precision adjustment frame to support three-dimensional fine adjustment of pitch, yaw and translation to adapt to the position of different combustion chamber observation windows and the requirements of optical path reversal.

[0098] The refractive assembly 30 is used to shape the cylindrical laser into a thin and uniform sheet-like beam. The concave lens 301 is a cylindrical lens with a focal length of f1 = −100 mm, and the convex lens 302 is a spherical lens with a focal length of f2 = 400 mm. In other embodiments, the focal lengths of the convex lens 302 and the concave lens 301 can be interchanged while maintaining the same magnification ratio.

[0099] The structured light modulation module 40 is a prism element 401, whose function is to convert uniform sheet light into a spatially periodically intensity-modulated interference fringe field. This modulation characteristic can be directly inherited by the fluorescence process, while the multiple scattering noise, due to phase randomization, causes the modulation depth to approach zero. The prism element 401 is made of JGS1 (i.e., far-ultraviolet grade synthetic fused silica glass) and coated with a UVAR coating (i.e., ultraviolet antireflection coating) to ensure that the transmittance to the ultraviolet pump light source is above 95%, while simultaneously meeting a damage threshold greater than 10 J / cm. 2 Surface flatness (PV): λ / 10 (308nm), surface quality is 10-5, dimensional error is less than 0.1mm, the height of the prism element 401 is set to 50mm, and the height of the sheet laser is 40mm.

[0100] Among them, "surface quality 10-5" refers to the degree of scratches visible on the surface of the prism element 401 under standard test light. 10 means that the significance of the scratches should not be worse than the standard "10-level scratch template", and 5 means that the diameter of any single pit on the surface of the prism element 401 should not exceed 127 micrometers. Surface quality 10-5 restricts the state of the surface of the prism element 401.

[0101] Furthermore, the prism element 401 has an isosceles triangular cross-section. A sheet-like beam enters perpendicularly from the base of the isosceles triangle, and after refraction at the waist of the triangle, forms two sheet-like beams. These beams intersect and merge to form structured light with varying intensity. As the core optical element of the structured light modulation module 40, the cross-sectional geometry of the prism element 401 directly determines the spatial distribution characteristics and modulation fidelity of the structured light. The isosceles triangular cross-section ensures strict consistency in the propagation direction, optical path difference, and deflection angle of the two refracted beams through geometric symmetry, thereby generating high-contrast, periodically stable, and phase-continuous interference fringes during subsequent spatial superposition. This process features large assembly tolerance and high thermal stability. This process requires no dynamic scanning, no multi-frame acquisition, and no digital image processing compensation; it is all completed in one go within the optical domain. This is the physical basis for achieving the differentiated response mechanism of "fluorescence-preserved modulation characteristics" and "multiple scattering noise modulation depth approaching zero."

[0102] Let the height of the prism element 401 be denoted as H1, and the height of the sheet laser be denoted as H2. To ensure the finest sheet laser and the largest area of ​​structured light above the burner, the distance between the prism element 401 and the spherical convex lens 302 is set to 50 mm. Based on the formula relating the center height of the structured light space, the distance between the structured light and the incident surface of the prism element 401, and the base angle of the prism element 401, the base angle θ of the prism element 401 is calculated to be 3.37°, and the apex angle is 173.26°. At this point, the center height H of the structured light area is 19.97 mm, which meets the requirement of being at the center of the laser sheet height. The sheet laser enters at an angle perpendicular to the base surface of the prism element 401, propagates along the center of the prism element 401, and is refracted by the inclined plane and divided into two equal segments. The two segments of sheet light intersect and merge to form a rhomboid structured light area with varying intensity. The rhombus is formed by two rectangular light spots on the cross section of two sheet-like lights overlapping obliquely at a certain angle. Its four vertices are the intersection points of the four sides of the two light spots, and the length of the diagonals respectively characterizes the effective measurement scale of the structured light in the horizontal and vertical directions.

[0103] Specifically, there are definite geometric and physical constraints between the parameters: the base angle θ of the prism directly determines the angle between the two light beams, thus controlling the size of the acute angle of the rhombus; the distance L from the incident surface of the prism to the imaging plane determines the horizontal span of the rhombus; and the center height H is modulated by the height of the light beams, the angle between them, and the propagation distance. The three work together to ensure that the light region of the rhombus structure can cover the high-density area of ​​OH free radicals, thereby enhancing the accuracy of the measurement.

[0104] Preferably, the value of H1 is 50mm, the value of H2 is 40mm, and the distance L from the incident surface of the prism element 401 to the center of the structured light space is set to 350mm.

[0105] The single-camera dual-optical-path signal acquisition module 50 is used to simultaneously capture OH radical (0,0) and (1,0) dual-band fluorescence images. The frame-splitting filter in the single-camera dual-optical-path signal acquisition module 50 includes a rectangular filter and a neutral density filter. The rectangular filter can only transmit fluorescence signals in the (0,0) and (1,0) bands, and the filtering areas of the (0,0) band and the (1,0) band each occupy half of the rectangular filter. The two OH radical fluorescence channels with very close center wavelengths and high risk of spectral overlap are forcibly separated by physical spatial segmentation, ensuring that the two signals are strictly isolated in the image plane space, the spectral responses do not interfere with each other, and the dynamic range of light intensity is controllable. Since the fluorescence signal in the (0,0) band is much stronger than that in the (1,0) band, in order to obtain a sufficiently strong fluorescence signal in the (1,0) band while ensuring that the fluorescence signal in the (0,0) band is within the camera's threshold, a neutral density filter is added to the side of the fluorescence signal in the (0,0) band to reduce the signal intensity across the entire band. The signal intensity is then restored to its original strength during post-processing.

[0106] The signal processing module 60 includes a computer 601, which runs signal demodulation algorithms and temperature inversion models. It is pre-installed with customized image processing software and supports real-time phase demodulation, dual-band image geometric registration, fluorescence intensity ratio calculation, and VET model temperature inversion. The key algorithms are embedded in the hardware logic unit, which can reduce the operation latency and achieve low power consumption operation.

[0107] The working principle of the temperature measurement system based on structured light-thermal-assisted fluorescence provided in this embodiment is as follows:

[0108] First, a solid-state laser 101 outputs 532nm green light at a frequency of 10Hz, which is then input into a dye laser 102. Through the combined action of the dye pool, frequency conversion unit, and grating within the dye laser 102, it is converted into ultraviolet light with a wavelength of 308.983nm and an energy of approximately 2.5mJ. This ultraviolet light is then guided by the first and second reflecting mirrors 201 and 202 to a refractive assembly 30 composed of a concave lens 301 and a convex lens 302, and shaped into a shape with a length of 40mm and a thickness of approximately 0.5mm. The sheet-like beam then passes through the prism element 401, forming two segments of sheet light. These two segments intersect and merge to form structured light with varying intensity and brightness. The position of the prism element 401 is adjusted so that the center of the structured light space is above the combustion chamber. After the structured light excites the fluorescence signal, the signal is acquired by the single-camera dual-path signal acquisition module 50. At the same time, the fluorescence signals with wavelengths of (0,0) and (1,0) are filtered out by a rectangular filter. During this process, the timing is adjusted by the computer 601 to achieve signal synchronization, ensuring that the corresponding fluorescence signal can be captured after the laser is triggered. The computer 601 also undertakes the signal post-processing task, demodulating and inverting the structured light fluorescence signal, and finally completing the quantitative measurement of the two-dimensional temperature field.

[0109] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand and implement the present invention. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A temperature measurement method based on structured light-thermodynamically assisted fluorescence, characterized in that, Includes the following steps: S1. Laser output and shaping: After the laser module outputs green laser, it converts the green laser into ultraviolet light and uses the ultraviolet light as a light source. Then, the incident direction and position of the ultraviolet light are adjusted by the reflection component, and the ultraviolet light is shaped into a sheet-like beam that matches the preset height by the refraction component. S2, Structured light modulation: The sheet-like light beam is modulated into interference fringes with spatial phase information using a prism element, and the modulation characteristics of the interference fringes can be fluorescence preserved; S3. Signal Acquisition: The structured light fluorescence signal is acquired by using a single-camera dual-optical-path signal acquisition module. The fluorescence spectra of OH radicals (A²Σ⁺→X²Π) in the (0,0) and (1,0) bands are captured simultaneously using a framing filter, and the signal is synchronized through a photoelectric detection module. S4. Signal Processing: The acquired fluorescence spectrum is processed by decomposing the fluorescence signal into sine and cosine components, creating a reference signal containing the modulation frequency to upconvert the stray light signal, filtering out the stray light signal through a filter, and extracting the demodulated fluorescence signal. S5. Temperature Field Inversion: Based on thermo-assisted fluorescence technology, the relationship between fluorescence intensity ratio and temperature is obtained through the VET model. The two-dimensional temperature field is then inverted using the following formula to obtain the two-dimensional local temperature field. Where, ΔE 10 Let V be the energy difference between vibrational energy level 1 and vibrational energy level 0 in excited state A, k be the Boltzmann constant, T be the absolute temperature, Q1 represent the rate of quenching and all other energy losses, and V be the energy difference between excited state A and excited state B. 10 It is the rate of downward vibrational transmission between vibrational energy level 1 and vibrational energy level 0 in excited state A. , These are the fluorescence signals from vibrational energy levels 1 and 0 of excited state A to ground state energy level 0 of ground state X after demodulation. 00 A represents the spontaneous emission Einstein coefficient for the 0→0 energy level transition. 10 The Einstein coefficient for spontaneous emission during the 1→0 energy level transition.

2. The temperature measurement method based on structured light-thermodynamically assisted fluorescence as described in claim 1, characterized in that, In step S2, when the prism element modulates the sheet-like beam with structured light, the following formula is introduced to relate the height of the structured light spatial center, the distance between the structured light center and the incident surface of the prism element, and the base angle of the prism element: Where H represents the height of the structured light space center, L represents the distance between the structured light center and the incident surface of the prism element, θ represents the base angle of the prism element, n1 represents the refractive index of the prism element material at a specific light source wavelength, and n2 represents the refractive index of air. At this time, n1 / n2 = 1.

485.

3. The temperature measurement method based on structured light-thermodynamically assisted fluorescence as described in claim 1, characterized in that, In step S3, in order to shorten the exposure time of the single-camera dual-optical-path signal acquisition module, a timing adjustment module is introduced, and the fluorescence spectrum acquired by the single-camera dual-optical-path signal acquisition module after being adjusted by the timing adjustment module is transmitted to the photoelectric detection module.

4. The temperature measurement method based on structured light-thermodynamically assisted fluorescence as described in claim 3, characterized in that, The photoelectric detection module includes an image intensifier and a camera. The image intensifier can enhance the intensity of the fluorescence signal, and the camera can convert the fluorescence signal into digital image data.

5. The temperature measurement method based on structured light-thermodynamically assisted fluorescence as described in claim 4, characterized in that, Before performing step S4, a signal correction step is required for the fluorescence signal. The signal correction step includes correcting the geometric distortion of the fluorescence signal using a calibrated checkerboard image and correcting the camera response using a standard light-emitting plate, so as to ensure that a consistent signal intensity distribution is obtained.

6. The temperature measurement method based on structured light-thermodynamically assisted fluorescence as described in claim 1, characterized in that, Step S4 includes the following steps: S41. Signal Reception: Receive the fluorescence signal transmitted from the single-camera dual-optical-path signal acquisition module, wherein the fluorescence signal includes the stray light signal and the effective signal, and the relationship between the effective signal and the stray light signal is expressed as: Among them, F X For the fluorescence signal, F S For the valid signal, F MS The stray light signal is υ, where υ is the modulation frequency and Φ is the modulation spatial phase. S42. Signal demodulation to extract the effective signal: Applying a phase demodulation algorithm and using the Pythagorean trigonometric identities, the fluorescence signal is decomposed into sine and cosine components. Then, the effective signal is obtained by calculating the square root of the sum of their squares. The amplitude is used to filter out the stray light signal. ； S43. Match the effective signal of the (0,0) band obtained by demodulation in step S42 with the (1,0) band.

7. A temperature measurement system based on structured light-thermal-assisted fluorescence, wherein the temperature measurement system can be applied to the temperature measurement method based on structured light-thermal-assisted fluorescence as described in any one of claims 1-6, characterized in that, include: A laser module, comprising a solid-state laser and a dye laser, wherein the solid-state laser outputs green laser light, which is then converted into ultraviolet light by the dye laser, and the ultraviolet light serves as a light source; A reflective assembly, comprising a first reflector and a second reflector arranged sequentially, wherein the first reflector and the second reflector can change the incident direction and position of the light source; A refractive assembly, comprising a concave lens and a convex lens arranged in sequence, wherein the concave lens and the convex lens cooperate to shape the light source from a cylindrical state into a sheet-like beam; A structured light modulation module, wherein the structured light modulation module is a prism element; A single-camera dual-optical-path signal acquisition module, comprising a frame-splitting filter and a photoelectric detection module; And a signal processing module, which includes a computer.

8. The temperature measurement system based on structured light-thermal-assisted fluorescence as described in claim 7, characterized in that, The cross-section of the prism element is an isosceles triangle. The sheet-like beam enters perpendicularly from the base of the isosceles triangle and is refracted at the waist of the isosceles triangle to form two sheet-like beams. After they cross and merge, they form structured light with varying intensity and brightness.

9. A temperature measurement system based on structured light-thermal-assisted fluorescence as described in claim 8, characterized in that, The structured light space formed by the intersection and fusion of the two sheet-like beams has a rhomboid structure, and the center of the structured light space is located in the flame measurement area above the combustion chamber.

10. A temperature measurement system based on structured light-thermal-assisted fluorescence as described in claim 7, characterized in that, The framing filter includes a rectangular filter and a neutral density filter. The rectangular filter can only transmit fluorescence signals in the (0,0) and (1,0) bands, and the filtering areas of the (0,0) band and the (1,0) band each occupy half of the rectangular filter.

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