A compact near-infrared online detection system with a built-in integrating sphere

Abstract

The present invention discloses a compact near-infrared online detection system with a built-in integrating sphere. The system comprises a light source, a reflector that reflects the light emitted by the light source into a cylindrical beam with a set diffusion angle, an integrating sphere positioned in the path of the cylindrical beam, a light collector located directly below the integrating sphere, and a spectral detector connected to the integrating sphere via an optical fiber. The cylindrical beam passes through a light exit window and strikes the surface of a sample. Diffusely reflected light from the sample surface passes through the light collector and enters the integrating sphere. The system effectively avoids specular reflections, adaptively adjusts the effective illumination range, and maximizes the extraction of effective light intensity, thereby significantly improving system sensitivity and signal-to-noise ratio.

Description

Technical field

[0001] The present invention belongs to the technical field of spectral information measurement, and in particular relates to a compact near-infrared online detection system with a built-in integrating sphere. [Background Technology]

[0002] Near-infrared spectroscopy is widely used, but its absorption is weak and its sensitivity is low. Therefore, various methods have been invented in the prior art to improve the signal-to-noise ratio and increase the sensitivity of the measurement.

[0003] Invention patent application CN201910503942.4 discloses an active, non-contact, high-throughput diffuse reflectance fiber optic probe device for measuring near-infrared spectra. While it boasts a large area for collecting reflected light, high throughput, and strong spectral signals, its light-guiding path is based on a fiber optic design. Typical fiber diameters are 200 to 300 microns, and quartz fiber can reach diameters as low as 10 mm. However, even with quartz glass fiber, the light flux is two orders of magnitude lower than that of a light engine based on 100 mm spatial optics. Ordinary optical fiber is two orders of magnitude lower, resulting in a relatively low light flux. This impact on the signal-to-noise ratio is also at least an order of magnitude higher, due to the potential for uneven light intensity distribution or varying optical divergence angles. In this case, as the authors describe, the larger the area of the collimated light spot, the weaker the light intensity. Furthermore, the light engine includes a movable device to provide a calibration path for background reference light, making the instrument's stability, accuracy, and inter-instrument variability unreliable.

[0004] Patent US5406084A designs a spatial optics-based light engine with a built-in high-speed rotating wheel and Blisch sphere (integrating photometer). The sample window is affixed to the bottom of the integrating sphere, directly isolating the instrument from the sample. This allows some specularly reflected light to enter the integrating sphere and mix with the effective signal, affecting the signal-to-noise ratio. The presence of the moving wheel also reduces the instrument's stability over long-term use, extending the time required for a single sampling.

[0005] Patent CN206601328 employs a probe design in which a central transmitting fiber is surrounded by five collection fibers, each surrounded by a hexagonal ring of transmitting fibers. This compact probe structure, unless the probe is submerged or placed in close proximity to the sample, allows a significant amount of specularly reflected light to enter the collection fiber bundle, limiting the application range of near-infrared spectrometers.

[0006] Therefore, it is necessary to provide a new compact near-infrared online detection system with built-in integrating sphere to solve the above problems. [Summary of the invention]

[0007] The main purpose of the present invention is to provide a compact near-infrared online detection system with a built-in integrating sphere. The system has a compact structure, can effectively avoid mirror-reflected light, adaptively adjust the effective illumination range, and extract the effective light intensity to the greatest extent, thereby achieving significantly improved system sensitivity and signal-to-noise ratio.

[0008] The present invention achieves the above-mentioned purpose through the following technical solution: a compact near-infrared online detection system with a built-in integrating sphere, which includes a light source, a reflective cover that reflects the light emitted by the light source into a columnar beam with a set diffusion angle, an integrating sphere arranged in the path of the columnar beam, a light collector located directly below the integrating sphere, and a spectral detector connected to the integrating sphere via an optical fiber. The columnar beam passes through a light exit window and hits the sample surface, and the diffusely reflected light generated on the sample surface passes through the light collector and enters the integrating sphere.

[0009] Furthermore, it also includes a shell that surrounds the reflector to form a hollow cavity, the integrating sphere and the light collector are arranged in the hollow cavity, and the light exit window is arranged at one end of the shell.

[0010] Furthermore, the integrating sphere is provided with a first opening for the diffusely reflected light to enter to form signal light, a second opening for part of the columnar light beam to enter to form reference light, a third opening for connecting to a calibration light source inside the spectral detector, and a fourth opening for connecting to the spectral detector.

[0011] Furthermore, the fourth opening is an SMA95 optical fiber interface, which is connected to the spectrum detector via an optical fiber.

[0012] Furthermore, the third opening is an SMA95 optical fiber interface, which is connected to a calibration light source via an optical fiber.

[0013] Furthermore, the first opening, the second opening, and the third opening are respectively equipped with a first shutter, a second shutter, and a third shutter.

[0014] Furthermore, the light collector is a concave-convex mirror and is located directly below the first opening.

[0015] Furthermore, the signal-to-noise ratio can be improved by at least one order of magnitude by adjusting the working distance or focal length, and the spot diameter D formed on the sample surface is:

[0016]

[0017] Where: μ is the object distance, that is, the distance from the light collector to the signal collection port of the integrating sphere, W d is the working distance, and f is the focal length of the light collector and is a negative number.

[0018] Compared with the prior art, the advantageous effects of the compact near-infrared online detection system with a built-in integrating sphere of the present invention are as follows: providing a compact design, cleverly placing the integrating sphere directly below the light source, and effectively avoiding the specular reflected light through the small diffusion angle design, effectively expanding the effective light spot range, so that the effective light spot basically coincides with the visible light spot, thereby increasing the effective light intensity by at least one order of magnitude, thereby improving the system sensitivity and the signal-to-noise ratio; the overall structure of the scheme is compact, the space occupied is small, and online near-infrared spectrum detection can be realized, which greatly expands the scope of application; the scheme also provides an irradiation area according to actual needs, by adjusting the working distance W d Or the focal length f method is used to transmit the effective diffuse reflected light to the system with maximum efficiency. Therefore, this method adaptively solves the problems of poor signal-to-noise ratio, strong light intensity but weak effective light intensity, and poor sensitivity in the existing technology.

Brief Description of the Drawings

[0019] Figure 1 Schematic diagram of the structure of an embodiment of the present invention. [Specific implementation method]

[0020] Example:

[0021] Please refer to Figure 1 The present embodiment provides a compact near-infrared online detection system 100 with a built-in integrating sphere, which includes a light source 10, a reflector 11, a housing 16 surrounding the reflector 11 to form a hollow cavity 15, an integrating sphere 20 and a light collector 14 disposed in the hollow cavity 15, and a light exit window 13 formed at one end of the housing 16. The integrating sphere 20 is provided with four openings, namely a first opening 21, a second opening 23, a third opening 25, and a fourth opening 27. The first opening 21, the second opening 23, and the third opening 25 are respectively equipped with respective shutters, namely a first shutter 22, a second shutter 24, and a third shutter 26. The first opening 21 is arranged toward the light exit window 13, and the third opening 25 is arranged horizontally outward. The light collector 14 is located directly below the first opening 21.

[0022] Fourth opening 27 can be an SMA95 fiber optic interface and is connected to a spectrum detector 30 via an optical fiber 31 to measure spectral data. Third opening 25 is opened and closed by a third shutter 26, which is connected to a calibration light source 33, such as a xenon lamp or other type of calibration light source, via an optical fiber 32 connected to the SMA95 fiber optic interface to perform necessary calibration of wavelength or spectral line shape.

[0023] The second opening 23 forms a closable opening through the second shutter 24, allowing part of the light from the light source 10 to enter the integrating sphere 20 to provide reference light measurement data. The first opening 21 forms a closable opening in combination with the first shutter 22 to receive the signal light.

[0024] We know that a large part of the stray light that affects the signal in the signal path is caused by mirror reflection, so this embodiment provides a small diffusion angle of about 6 degrees through the reflector 11, such as Figure 1 As shown, since the middle of the light path is blocked by the integrating sphere 20, the light can only be emitted from the periphery, and the direction of emission is slightly divergent outward. This ensures that the mirror-reflected light irradiated on the surface of the sample will not enter the signal channel, that is, the mirror-reflected light cannot enter the first opening 21. This embodiment provides a light-collecting method that also achieves such an effect. This embodiment uses a new diffusion method, combined with the light collector 14, to expand the effective area to the entire visible light spot area PQ. Different from the existing solution, although the visible light spot may be made large enough, the area that can actually enter the signal collection area is actually very limited. This example achieves the perfect fusion of the visible light spot and the effective light spot, greatly improving the effective signal strength.

[0025] The light collector 14 is an optical device that diffuses light, such as a single concave lens or a double concave lens. Figure 1 The light collector 14 can also be a set of optical components to achieve the purpose of guiding the light in the PQ area into the first opening 21.

[0026] The focal length of the concave lens collector 14 is a negative number f, and the virtual image formed is negative. Assuming that the object distance is μ, the following relationship is satisfied:

[0027]

[0028] Where ν is the image distance. Figure 1 The relationship between similar triangles in

[0029]

[0030]

[0031] Where W d is the working distance, d is the diameter of the area blocked by the integrating sphere in the spot area on the working surface, and D is the diameter of the spot on the working surface. Combining equations (2) and (3), we can deduce:

[0032]

[0033] The object distance μ is a fixed value, that is, the distance from the first opening 21 of the integrating sphere 20 to the center point of the light collector 14. If the working distance Wd It is also determined, usually the working distance W is recommended by the manufacturer d , the ratio d / D is only a function of the image distance ν, and according to formula (1), the ratio d / D is only a function of the focal length f. d represents the size of the shadow covered by the integrating sphere, W d If f is determined, then d is a fixed value. Therefore, the effective irradiation range is a function of the focal length. From the above deduction, we can deduce that we can adjust the size of the effective spot by selecting the focal length. Note that f is a negative value, and the spot diameter D is:

[0034]

[0035] In practical applications, we determine D based on the surface area of the sample to be irradiated, and inversely deduce the required f. Or if f is fixed in the instrument, we can adjust the working distance W d Get the desired ideal irradiation range D.

[0036] For example, if a user is measuring an apple, they can estimate the required illumination range based on the average size of the apple and configure the system to effectively measure the desired internal components. If measuring a watermelon, the illumination area may be several times larger than that of an apple, so system parameters such as working distance and focal length can be adjusted accordingly to achieve effective measurement.

[0037] The working principle of the compact near-infrared online detection system 100 with a built-in integrating sphere in this embodiment is as follows: the light emitted by the light source 10 is reflected by the reflector 11 into a circularly distributed diffused light with a set diffusion angle, and then emitted through the light outlet window 13 to hit the sample surface; a portion of the diffused light will enter the integrating sphere 20 from the second opening 23 to provide measurement data of the reference light; the light hitting the sample surface is diffusely reflected, converged at the first opening 21 through the light collector 14, and connected to the integrating sphere 20 to provide signal light for measurement.

[0038] The beneficial effects of a compact near-infrared online detection system 100 with a built-in integrating sphere in this embodiment are as follows: the integrating sphere is built into a shell, and a light source and a reflector are arranged in the shell, the reflector is used to reflect the light from the light source into a light beam with a set diffusion angle, and the light beam is allowed to hit the sample surface after passing through the integrating sphere, and then a light collector is arranged below the signal light inlet of the integrating sphere to converge the diffused light generated on the sample surface at the signal light inlet, and then connected to the integrating sphere to form signal light, and at the same time, the diffuse light beam is used to pass through the integrating sphere, and the reference light is collected through the reference light inlet of the integrating sphere, and then the spectrum measurement and analysis is performed using a spectrum detector connected to the integrating sphere through an optical fiber; the overall structure of this solution is compact, the space occupation is small, and online near-infrared spectrum detection can be realized, which greatly improves the scope of application; this solution exponentially increases the effective irradiation area, thereby improving the signal-to-noise ratio and sensitivity; and this solution also provides an irradiation area according to actual needs, by adjusting the working distance W d Or the focal length f method is used to transmit the effective diffuse reflected light to the system with maximum efficiency. Therefore, this method adaptively solves the problems of poor signal-to-noise ratio, strong light intensity but weak effective light intensity, and poor sensitivity in the existing technology.

[0039] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A compact near-infrared online detection system with a built-in integrating sphere, characterized by: It includes a light source, a reflector that reflects the light emitted by the light source into a columnar beam with a set diffusion angle, an integrating sphere arranged in the path of the columnar beam, a light collector located directly below the integrating sphere, and a spectrum detector connected to the integrating sphere via an optical fiber. The columnar beam passes through a light exit window and hits the sample surface. The diffusely reflected light generated on the sample surface passes through the light collector and enters the integrating sphere. It also includes a shell that surrounds the reflector to form a hollow cavity, the integrating sphere and the light collector are arranged in the hollow cavity, and the light exit window is arranged at one end of the shell. The integrating sphere is provided with a first opening for the diffusely reflected light to enter to form signal light, a second opening for part of the columnar light beam to enter to form reference light, a third opening for connecting to the calibration light source inside the spectral detector, and a fourth opening for connecting to the spectral detector.

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