An outer sphere diffuse reflectance spectrum measuring device

Abstract

The present invention discloses an outer sphere diffuse reflection spectrum measuring device, which includes a light source capable of emitting near-infrared light, a first optical system for transmitting a portion of the light emitted by the light source to a sample surface, a second optical system for transmitting a portion of the light emitted by the light source to a reference channel system and collecting diffuse reflection light from the sample surface and transmitting it to a signal channel system, an integrating sphere for receiving optical signals transmitted from the reference channel system and the signal channel system in a time domain sequence, a spectrum analyzer connected to the output end of the integrating sphere through a third optical fiber, and a set of methods for optimally calculating an optimal working distance in coordination with the device for optimal use effect, optimal signal-to-noise ratio and fastest measurement efficiency. The present invention is easy to carry, greatly reduces the time required for full spectrum acquisition and data analysis, and improves the quality of signal light, measurement accuracy and reliability of measurement results.

Description

[Technical field]

[0001] The invention belongs to the technical field of spectral information measurement, and in particular relates to an outer sphere diffuse reflection spectrum measurement device. [Background technology]

[0002] Molecules have certain discrete energy levels. In the near-infrared spectrum, molecules absorb photon energy, thereby inducing a transition from the ground state to the second excited state. This transition is called overtone. Near-infrared spectroscopy is based on molecular vibration modes. Near-infrared radiation can usually penetrate samples of considerable thickness, so near-infrared spectroscopy techniques, such as diffuse reflectance near-infrared spectroscopy, can be very useful detection tools. In addition, near-infrared spectroscopy usually does not require sample preparation and can be used for material characterization and molecular analysis applications such as pharmaceuticals, medical diagnostics, neurology, neuroimaging, neonatal research, urology, food and pesticide quality control, etc.

[0003] Near-infrared spectroscopy is a superposition of the absorption characteristics of various chemical components in a material. Different chemical bonds absorb at different wavelengths, and interactions between chemical components, multiple scattering, and differences in particle size, shape, and orientation produce multiple absorption bands in the raw spectral data.

[0004] According to the American Society for Testing and Materials (ASTM E1790-2016), the actual definition applies to the short-wave near-infrared region, which is approximately 780nm to 1100nm, and the long-wave near-infrared region, which is approximately 1100nm to 2500nm. These near-infrared absorption bands are associated with functional groups such as carbon-hydrogen (CH), hydrogen-oxygen (OH), and nitrogen-hydrogen (NH), which have higher frequencies in the mid-infrared band, so the first, second, and even third overtones can be found in the near-infrared band. Weaker absorption means that useful signals require longer optical paths, so overtones of the third overtone and above, which are usually found in the short-wave near-infrared region, are not as practical. In contrast, the long-wave near-infrared region has a large amount of information and less spectral overlap, making it more useful for near-infrared spectroscopy.

[0005] The concentrations of components such as water, proteins, fats and carbohydrates can in principle be determined using classical absorption spectroscopy. However, spectral variations caused by physical properties obscure the chemical information. This makes NIR spectroscopy a secondary method that needs to be calibrated against more precise reference methods such as classical wet chemistry. Once the calibration is in place, NIR spectroscopy can be used as a very simple and fast way to predict compositional information.

[0006] With the development of specialized near-infrared spectrometers and mathematical models for processing spectral data, multiple component information can be obtained simultaneously. However, the application of near-infrared spectroscopy in qualitative analysis is still relatively new, and related technologies are also constantly developing. Specialized near-infrared instruments are developing from fixed laboratory status to online production status and mobile status. Faced with complex environments such as dust, high temperature and humidity, and vibration, new challenges have been posed to existing technologies.

[0007] NIR spectroscopy analysis can be performed by comparing the NIR absorption spectra of unknown materials with those of known reference materials. Therefore, obtaining high-quality NIR spectra is one of the important goals of instrument manufacturers. More specifically, high-quality NIR spectra have high signal-to-noise ratio, high resolution, and spectral repeatability.

[0008] Near-infrared spectrometers usually include two main functional modules: the light emitting and collecting module and the light measuring module. Signal light is the part of light that enters the interior of the sample and returns with composition information. Part of the light that does not carry composition information, such as mirror reflection and stray light, will bring noise and errors to the system. Of course, noise also includes system noise, such as dark current noise, etc. A good signal-to-noise ratio depends mainly on a well-designed optical system, namely the light emitting and collecting module. The spectral resolution depends on the light measuring module. For grating-based modules, the slit size and the number of detectors in the detector array jointly determine the spectral resolution. For modules based on Fourier transform (FT), the moving distance of the reflector determines the resolution. Spectral repeatability is reflected by the standard error of the peak of the spectrum scanned multiple times. It is a key indicator of system stability and plays an important role in model transfer.

[0009] Light emitted from a light source to a sample surface and providing both specular and diffuse reflection. Specular reflection is the reflection from the sample surface where the angle of incidence equals the angle of reflection. It is not transmitted into the sample for interaction; therefore, it is best excluded from the optical path of the signal beam. Diffuse reflection is the result of the interaction of light with various chemical and physical factors within the sample reaction volume and is the main component of the measurement.

[0010] The light emitting and collecting module includes a first optical path for transmitting light to the sample and a second optical path for collecting light carrying useful composition information. In patent CN1079050A, light is transmitted through the light transmission port of the wheel and illuminates the sample through a window in the integrating sphere. The diffuse reflected light is collected by the sphere through the same window and detected by the light sensor. In this device, most of the specular reflection of the window is collected by the integrating sphere and is difficult to separate from the signal.

[0011] WO2010 / 029390A1 patent discloses a system and method for solving some of the above problems. In this invention, a specific reflector curvature is designed for the light collector so that when there is no sample, all light is reflected to the central area in the absence of a light-collecting optical fiber. Therefore, this arrangement ensures that all light collected when testing the sample is diffusely reflected light. Although this arrangement solves the above problems, it uses about seven optical fibers to collect signals, which increases the complexity of the system and may not be very effective. In addition, the optical fiber may not be able to collect enough signal light to form a sufficiently high signal-to-noise ratio. Therefore, the industry needs a high-performance optical structure based on spatial optical design and a new method for collecting near-infrared signals.

[0012] Therefore, it is necessary to provide a new outer sphere diffuse reflectance spectrum measuring device to solve the above problems. [Summary of the invention]

[0013] The main purpose of the present invention is to provide an outer-sphere diffuse reflectance spectrum measuring device, which is easy to carry, greatly reduces the time required for full spectrum acquisition and data analysis, and improves the quality of signal light, and improves the measurement accuracy and reliability of the measurement results.

[0014] The present invention achieves the above-mentioned purpose through the following technical scheme: an outer sphere diffuse reflectance spectrum measuring device, which includes a light source that can emit near-infrared light, a first optical system that transmits a part of the light emitted by the light source to the sample surface, a second optical system that transmits a part of the light emitted by the light source to a reference channel system and collects diffusely reflected light from the sample surface and transmits it to a signal channel system, an integrating sphere that receives optical signals transmitted from the reference channel system and the signal channel system in time domain sequence, and a spectrum analyzer connected to the output end of the integrating sphere through a third optical fiber.

[0015] Furthermore, the first optical path system includes a shell that surrounds the light source, the shell includes a light reflecting arc surface located at the top that reflects the light emitted by the light source in a cylindrical collimated manner, and a cylinder that forms a first optical channel. Part of the light emitted by the light source passes through the light reflecting arc surface to form cylindrical collimated light and is emitted through the first optical channel; a polarizing component and an exit window are sequentially arranged at the exit window of the first optical channel along the direction of the light beam.

[0016] Further, the second optical system comprises a second optical channel arranged in parallel at the center of the first optical channel and passing through the polarizing component, and a 45° reflector located above the second optical channel, the second optical channel is located directly below the light source, the 45° reflector is located between the light source and the second optical channel, and an optical busbar of the 45° reflector is located on the same optical horizontal line as the signal channel system and the reference channel system;

[0017] The signal channel system includes a second lens barrel and a second lens disposed in the second lens barrel and directly coupled to the signal port of the integrating sphere.

[0018] Furthermore, the second optical channel is extended upward from the upper surface of the exit window; the second optical channel is coaxially arranged with the first optical channel.

[0019] Furthermore, a high-reflection material coating is provided on a surface of the 45° reflector facing the light source; and an infrared reflective coating is coated on a surface of the 45° reflector facing the second optical channel.

[0020] Furthermore, the reference channel system includes a first optical fiber that receives the reference light transmitted by the 45° reflector and transmits it to the reference port of the integrating sphere, and a reference shutter that is arranged at one end of the first optical fiber and coupled to the reference port.

[0021] Furthermore, the reference channel system also includes a first lens barrel and a first lens disposed in the first lens barrel. The other end of the first optical fiber is connected to the first lens barrel and is used to receive the optical signal output by the first lens and transmit it to the integrating sphere.

[0022] Furthermore, the signal channel system includes a second optical fiber that receives the signal light transmitted from the 45° reflector and transmits it to the signal port of the integrating sphere, and a signal shutter that is arranged at one end of the second optical fiber and coupled to the signal port.

[0023] Furthermore, the signal channel system also includes a second lens barrel and a second lens disposed in the second lens barrel; the second optical fiber receives the optical fiber output by the second lens and transmits it to the integrating sphere.

[0024] Furthermore, the working distance range of the outer sphere diffuse reflectance spectrum measuring device is f to 2f, where f is the focal length of the polarizing component;

[0025] The optimal working distance range of the outer sphere diffuse reflectance spectrum measuring device is:

[0026]

[0027] Wherein, r is the cross-sectional radius of the second optical channel, R is the cross-sectional radius of the first optical channel, and f is the focal length of the polarizing component.

[0028] Compared with the prior art, the beneficial effects of the outer-sphere diffuse reflectance spectrum measuring device of the present invention are: improving the signal-to-noise ratio, and further maximizing the signal level by designing the optimal working distance, thereby greatly reducing the time required for full-spectrum acquisition and data analysis, improving the measurement efficiency, and having strong online application adaptability in a wide range of fields; and proposing the optimal working distance for use with the device, which greatly improves the use effect, achieves the optimal signal-to-noise ratio, and improves the measurement efficiency.

Brief Description of the Drawings

[0029] Figure 1 Schematic diagram of the beam that produces the diffuse reflectance spectrum for the illuminated sample;

[0030] Figure 2 It is a structural schematic diagram of an embodiment of the present invention;

[0031] Figure 3 is another structural schematic diagram of an embodiment of the present invention;

[0032] Figure 4 A schematic diagram of a structure for designing an optimal working distance according to an embodiment of the present invention;

[0033] Figure 5 A simplified schematic diagram of the optimal working distance design of an embodiment of the present invention. [Specific implementation method]

[0034] Example:

[0035] Diffuse reflectance near-infrared spectroscopy is a technique that collects and analyzes scattered near-infrared energy. Like diffuse reflectance, near-infrared light penetrates and interacts with samples at the nanometer scale. Figure 1A simplified schematic diagram is shown, assuming that the sample 14 is thick enough so that light does not penetrate the sample 14. When incident light 10 illuminates the sample 14 with a rough surface, a portion of each individual incident light follows the law of reflection to produce specular reflection 11 in the expected main reflection angle; another portion of each individual incident light is reflected at all possible angles and directions to produce diffuse reflection 12. The degree or magnitude of diffuse reflection 12 depends on the characteristics of the reflecting material and surface. Since near-infrared light (NIR for short) is very transparent to many materials, the incident light 10 will inevitably interact with the inner material of the sample 14 to produce diffuse reflection phenomenon. The general mechanism for producing diffuse reflection does not completely involve the surface. Most of the light is contributed by scattering centers below the surface. The main interactions include scattering and absorption; the scattering effect is determined by the size and direction of these scattering centers, while absorption is significantly affected by the percentage of certain components in the sample 14.

[0036] Please refer to Figure 1-Figure 5 The present embodiment is an outer-sphere diffuse reflectance spectrum measuring device, which includes a light source 20 that can emit near-infrared light, a first optical system that transmits the light emitted by the light source 20 to the sample surface 13, a second optical system that transmits the light emitted by the light source 20 to a reference channel system and collects diffusely reflected light from the sample surface 13 and transmits it to a signal channel system, an integrating sphere 30 that receives optical signals transmitted from the reference channel system and the signal channel system, and a spectrum analyzer 40 connected to the output end of the integrating sphere through a third optical fiber 34.

[0037] The first optical path system includes a housing 16 that surrounds the light source 20. The housing 16 includes a light reflecting arc surface 161 located at the top and collimating the light emitted by the light source 20 in a cylindrical shape, and a cylinder 163 formed with a first optical channel 162. Part of the light emitted by the light source 20 passes through the light reflecting arc surface 161 to form a cylindrical collimated light and then passes through the first optical channel 162. The exit window of the first optical channel 162 is sequentially provided with a polarizing component 21 and an exit window 22 along the direction of the light beam. The polarizing component 21 can be a hollow Fresnel lens or an annular optical glass lens, which is mainly used to focus the cylindrical collimated light formed by the light reflecting arc surface 161 on the sample surface 13. The exit window 22 can be an optical lens with a focusing function. The light reflecting arc surface 161 forms a reflector.

[0038] The light source 20 may be a single light source or a plurality of LED lamps having different near infrared wavelength outputs. The light source 20 may include a broad spectrum NIR light source to allow the NIR light energy output coupled to the first optical path. The wavelength of the light source 20 is in the range of 780 nm to 2500 nm, which is an effective wavelength for analysis.

[0039] The light reflecting arc surface 161 is usually realized by a parabolic reflector, which can be made of aluminum alloy or aluminum-plated material.

[0040] The cylinder 163 is preferably a metal cylindrical structure, and can be made of aluminum alloy or stainless steel, and is black oxidized, mainly used to limit light and play a role in heat dissipation.

[0041] The second optical system includes a second optical channel 17 arranged parallel to the center of the first optical channel 162 and passing through the polarizing component 21, and a 45° reflector 23 located above the second optical channel 17. The second optical channel 17 is located directly below the light source 20, and the 45° reflector 23 is located between the light source 20 and the second optical channel 17. The 45° reflector 23 is located on the same optical horizontal line as the signal channel system and the reference channel system. The second optical channel 17 extends upward from the upper surface of the exit window 22. The second optical channel 17 is coaxially arranged with the first optical channel 162.

[0042] The projection area of ​​the 45° reflector 23 matches the cross-section of the second optical channel 17. The 45° reflector 23 does not mean that it must be installed at a position that is 45° to the central axis of the second optical channel 17. It can be positioned at other angles around 45°. For ease of use, 45° is a better setting. The surface of the 45° reflector 23 facing the light source 20 is coated with a high-reflection material, such as BaSO4, Zenith Polymerand and Spectralon. These materials are ideal diffuse reflection materials that can directly reflect part of the light emitted by the light source 20 into the reference channel system. The surface of the 45° reflector 23 facing the second optical channel 17 (the back side is close to the light source 20) is coated with an infrared reflection coating to achieve mirror reflection of the signal.

[0043] Please refer to Figure 2 The polarizing component 21 is placed from the inside of the cylinder 163 directly above the exit window 22. The polarizing component 21 can adopt a Fresnel lens or an annular optical glass lens, which is mainly used to converge the exit light to illuminate the sample surface at a specific range of incident angles, and to exclude the mirror reflection light from entering the second optical channel 17 to the maximum extent. This arrangement excludes the advantage of the mirror reflection light from the second optical channel 17 being mixed with the signal light from the basic principle. Therefore, the light entering the second optical channel 17 is a very pure signal light carrying the material composition information, thereby greatly improving the signal-to-noise ratio.

[0044] The reference channel system is mainly used to measure the reference spectrum of the white standard material, and includes a first lens barrel 14 fixed on the housing 16, a first lens 24 arranged in the first lens barrel 14, a first optical fiber 26 receiving the output light of the first lens 24 and transmitting it to the reference port 32 of the integrating sphere 30, and a reference shutter 28 arranged at the other end of the first optical fiber 26 and coupled with the reference port 32. The first lens 24 is installed to transmit more light to the first optical fiber 26. When the reference light is strong enough, the first lens 24 may not be needed. One end of the first optical fiber 26 is connected to the first lens barrel 14, and if the first lens barrel 14 is not in place, it can be directly connected to the housing 16, and the other end thereof is connected to the reference shutter 28. The reference shutter 28 controls the reference input entering the integrating sphere 30 through the reference port 32 in the time domain, and provides a switch function.

[0045] The signal channel system is mainly used to measure signals, and includes a second lens barrel 15 fixed on the housing 16, a second lens 25 arranged in the second lens barrel 15, a second optical fiber 27 receiving the optical fiber output by the second lens 25 and transmitting it to the signal port 31 of the integrating sphere 30, and a signal shutter 29 arranged at the other end of the second optical fiber 27 and coupled with the signal port 31. The second lens 25 is installed to transmit more signal light to the second optical fiber 27. When the signal light is strong enough, the second lens 25 is not needed. One end of the second optical fiber 27 is connected to the second lens barrel 15. If the second lens barrel 15 is not in place, the second optical fiber 27 can be directly connected to the housing 16, and the other end is connected to the signal shutter 29. The signal shutter 29 controls the signal input to the integrating sphere 30 through the signal port 31 in the time domain, and provides a switching function. When the signal light is not strong enough, the second lens 25 helps to transmit most of the signal light to obtain a higher signal-to-noise ratio.

[0046] The integrating sphere 30 is connected to the spectrum analyzer 40 through the outlet 33 via the third optical fiber 34. The integrating sphere 30 has two inlets and one outlet, wherein the two inlets are the signal port 31 and the reference port 32, and the outlet is the outlet 33.

[0047] Please refer to Figure 3 In another embodiment, the signal channel is upgraded by directly coupling the second lens 25 in the second lens barrel 15 to the signal port 31 of the integrating sphere 30, such as Figure 3 As shown. The advantage of this device is that almost all signal light is coupled into the integrating sphere 30, so that the near infrared spectrum has a higher signal-to-noise ratio in online or offline measurement and the spectrum acquisition can become faster. The signal shutter 29 controls the signal input to the integrating sphere 30 through the signal port 31 in the time domain.

[0048] In this embodiment, a 45° reflector 23 is arranged just above the second optical channel 17, which effectively blocks the columnar collimated light reflected by the light reflecting arc surface 161 from entering the second optical channel 17, thereby improving the purity of the signal light in the second optical channel 17 and the signal-to-noise ratio. On the other hand, the 45° reflector 23 is used to receive part of the columnar collimated light reflected by the light reflecting arc surface 161, and fully reflects it to the reference channel system to provide measurement data of the reference light.

[0049] Generally speaking, for Figure 2 and Figure 3 In the two structures described above, the exposed area on the sample surface 13 can be characterized by a ring, which becomes smaller and smaller until it reaches a point where the working distance is equal to the focal length (f) of the exit window 22. The working distance of an outer sphere diffuse reflectance spectrum measurement device in this embodiment is f to 2f, that is, the distance between the sample surface and the lower surface of the polarizing component 21 is f to 2f. If the working distance is less than f, there may be specular reflection in the second optical channel 17; if the working distance is too far, greater than 2f, the light becomes too divergent, and there is not enough light to illuminate the sample surface directly below the second optical channel 17.

[0050] like Figure 4-Figure 5 As shown, it demonstrates how to set the optimal working distance to obtain a better signal-to-noise ratio. Assuming that the radius of the cross section of the second optical channel 17 is r, the radius of the cross section of the housing 16 is R, and the focal length of the polarizing component 21 is f, the optimal working distance d0 can be calculated by the following formula:

[0051]

[0052] but,

[0053]

[0054] We assume that the ideal working distance interval is [d0-Δ, d0+Δ], where Δ is between d0 and f, and

[0055]

[0056] The optimal working distance range that can be calculated is:

[0057]

[0058] like Figure 4 As shown in the middle gray shading, subtracting the upper limit from the lower limit in the above optimal working distance range gives:

[0059]

[0060] It can be seen that the size of the optimal working distance range is determined by two independent radius and focal length.

[0061] This embodiment is an outer sphere diffuse reflectance spectrum measurement device, which provides a light source 20, which emits an illumination beam through a first optical system, and is focused by an optical element to illuminate the sample surface 13. The light emitted by the light source 20 is collimated by a parabolic reflector (i.e., a light reflecting arc surface 161); the collimated light is focused by a polarizing component 21; the light source 20 is located inside the housing 16, and the second optical channel 17 is located at the central axis position of the housing 16. At a set position close to the light source 20 or the focusing polarizing component 21, a 45° reflector 23 with a high-reflection material coating is placed on the central axis at a 45-degree angle to the central axis of the first optical channel 162, and is located above the second optical channel 17. The side of the 45° reflector 23 coated with a high-reflection material coating is used to transmit part of the light from the light source 20 to the reference channel system, and then transmitted to the reference port 32 through the first optical fiber 26, and input into the integrating sphere 30. The housing 16 itself has a good heat dissipation function. When more heat needs to be released, a heat sink can be installed behind the light source 20 to dissipate excess heat.

[0062] After the collimated light is focused by the polarizing component 21 and irradiated onto the sample surface, the specular reflection and diffuse reflection light generated from the sample surface enter the second optical channel 17, and then are transmitted to the signal channel system through the 45° reflector 23 above the second optical channel 17, and are transmitted to the signal port 31 through the second optical fiber 27 and input into the integrating sphere 30.

[0063] The light source 20 emits collimated light, the first part of the light is reflected by a 45° mirror 23 to the side facing the light source and collected by an integrating sphere. The back of the 45° mirror 23 is coated with a highly reflective material. The light collected and measured through this optical path is used as white background data or the so-called reference; the second part of the light illuminates the sample and carries the signal information and enters the second optical channel 17. After the second optical channel 17, the signal light is reflected by the other side of the 45° mirror 23 and collected by the integrating sphere 30. The entrance of the signal and the reference of the integrating sphere are gated by shutters respectively, and can be measured at different times by a spectrometer optically connected to the integrating sphere when needed. Any type of spectrometer can be used to separate the light into specific wavelengths and record the spectrum, such as a grating-based system or an interferometer-based system.

[0064] In a preferred embodiment, the reference light is transmitted to the integrating sphere via an optical fiber or a fiber bundle. If the brightness is too low, a lens can be set in front of the collection end; the lens is placed at an appropriate distance from the fiber collection end so that it can focus enough light into the fiber, but not too close to the focal position, as this may cause the fiber to overheat.

[0065] In practical applications, near-infrared spectrometers need to shift from laboratory applications to production lines with more complex environments, so high-quality signal light, that is, a higher signal-to-noise ratio, is required. A high signal-to-noise ratio usually means more signal light and less noise or other irrelevant light. The present invention provides an innovative device for optimizing the optical path and a method for calculating the optimal working distance to improve the quality of the signal light. The present invention is particularly suitable for industrial online applications that require real-time monitoring.

[0066] The present embodiment provides an outer-sphere diffuse reflectance spectrum measurement device, which improves the signal-to-noise ratio and further maximizes the signal level by designing an optimal working distance, thereby greatly reducing the time required for full-spectrum acquisition and data analysis, improving measurement efficiency, and having strong online application adaptability in a wide range of fields.

[0067] 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 creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. An outer sphere diffuse reflectance spectrum measuring device, characterized in that: It includes a light source capable of emitting near-infrared light, a first optical system for transmitting a portion of the light emitted by the light source to a sample surface, a second optical system for transmitting a portion of the light emitted by the light source to a reference channel system and collecting diffusely reflected light from the sample surface and transmitting it to a signal channel system, an integrating sphere for receiving optical signals transmitted from the reference channel system and the signal channel system in a time domain sequence, and a spectrum analyzer connected to the output end of the integrating sphere via a third optical fiber. It also includes a first optical path system, which includes a shell surrounding the light source, the shell includes a light reflection arc surface located at the top and which collimates the light emitted by the light source in a cylindrical shape, and a cylinder body formed with a first optical channel, part of the light emitted by the light source passes through the light reflection arc surface to form a cylindrical collimated light and is emitted through the first optical channel; a polarizing component and an exit window are sequentially arranged at the exit window of the first optical channel along the direction of the light beam, The second optical system comprises a second optical channel arranged in parallel at the center of the first optical channel and passing through the polarizing component, and a 45° reflector located above the second optical channel, the second optical channel is located directly below the light source, the 45° reflector is located between the light source and the second optical channel, and an optical busbar of the 45° reflector is located on the same optical horizontal line as the signal channel system and the reference channel system; The signal channel system includes a second lens barrel, a second lens disposed in the second lens barrel and directly coupled to the signal port of the integrating sphere, The second optical channel extends upward from the upper surface of the exit window; the second optical channel is coaxially arranged with the first optical channel, A high-reflection material coating is provided on a side surface of the 45° reflector facing the light source; and an infrared reflective coating is coated on a side surface of the 45° reflector facing the second optical channel.

Images