Stray light detector based on metal tube end face coupling structure

Abstract

The invention belongs to the technical field of stray light detection, and discloses a stray light detector based on a metal tube end face coupling structure. The light source is arranged on one side of the straight capillary tube and used for emitting exciting light; the first reflecting mirror is obliquely arranged above the edge of the tube wall on one side of the inlet end of the straight capillary tube and is used for reflecting the exciting light, so that the exciting light enters the straight capillary tube from the inlet end of the straight capillary tube; the first optical filter is arranged between the light source and the first reflecting mirror; the photoelectric detector is positioned above the inlet end of the straight capillary tube, and a second optical filter and an optical lens are sequentially arranged between the photoelectric detector and the straight capillary tube; a to-be-detected sample is placed at the outlet end of the straight capillary tube or inside the straight capillary tube, the to-be-detected sample is irradiated by the exciting light to emit stray light, and the stray light is transmitted towards the inlet end of the straight capillary tube in the straight capillary tube, sequentially passes through the second optical filter and the optical lens and then is received by the photoelectric detector. According to the stray light detector, the detection sensitivity can be improved, and the instrument size can be reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of stray light detection, and relates to a stray light detector based on a metal tube end face coupling structure. Background Art

[0002] When the excitation light encounters the object to be measured, reflection, scattering (such as Raman scattering), absorption, or fluorescence effect will occur, thereby generating stray light (i.e., light with a chaotic propagation direction). By analyzing the stray light, the composition of the object to be measured can be obtained.

[0003] Detection principle of fluorescence and Raman spectrometers: Use "excitation light" to irradiate the object to be measured, so that the object to be measured emits fluorescence or Raman scattered light (the fluorescence wavelength and Raman frequency shift are related to the composition of the object to be measured); among them, the fluorescence or Raman scattered light as the signal is a kind of stray light. Hereinafter, the light with a chaotic propagation direction such as reflected light, fluorescence, and scattered light is collectively referred to as stray light.

[0004] For turbidimeters, fluorimeters, and Raman spectrometers, since the power of the excitation light is very large (greater than milliwatts), while the power of the stray light is very weak (femto tile ~nano tile ). Therefore, the interference of the excitation light on the stray light becomes the main factor restricting the detection accuracy.

[0005] In order to reduce the interference of the excitation light, a vertical excitation mode is usually adopted - using a transparent capillary as the sample cell, the incident direction of the excitation light is perpendicular to the axial direction of the capillary (i.e., the excitation light is perpendicularly incident on the side wall of the capillary), and the stray light is detected in another perpendicular direction (perpendicular to both the excitation light and the axial direction of the capillary). At this time, the detection direction of the stray light, the incident direction of the excitation light, and the axial direction of the capillary are perpendicular to each other, so as to reduce the interference of the excitation light on the stray light. However, the transmission optical path of the excitation light in the sample to be measured is very short (the optical path is equal to the inner diameter of the capillary, and the excitation efficiency is proportional to the optical path), so the excitation efficiency is very low, and the collection efficiency of the stray light is also relatively low, not exceeding 5%.

[0006] To improve the excitation and collection efficiency, a coaxial excitation mode is adopted - using a straight metal tube as the sample cell, as disclosed in Optics and Lasers in Engineering, 2021, 139, 106488. Both the excitation light and the stray light are confined within the capillary and transmitted along the capillary axis. Since the metal capillary can confine and guide light, both the excitation efficiency (the optical path is equal to the capillary length) and the collection efficiency (stray light is generated and confined within the tube) are greatly improved. However, the transmission direction of the excitation light is the same as the collection direction of the stray light, and at this time, the excitation light interferes with the stray light the most. In addition, the excitation light source and the stray light detector of this mode are located at both ends of the metal tube respectively. Therefore, both ends of the metal tube need to be sealed to prevent the liquid sample in the tube from contaminating the light source or the detector and to avoid the light leakage problem at both ends. But this will cause air bubbles to easily accumulate in the tube and be difficult to discharge, affecting the test accuracy. In addition, in this mode with both ends sealed, it is impossible to test solid samples because it is difficult to put solids into the tube. It should be noted that: when the propagation direction of the excitation light and the detection direction of the stray light are the same, the interference is the greatest; when they are perpendicular, the interference is medium; when they are opposite, the interference is the smallest.

[0007] In addition, there is also a Y-type excitation mode, including a Y-type metal tube and a Y-type optical fiber. (1) For the Y-type metal tube probe, the two bifurcated metal tubes respectively transmit the excitation light and detect the stray light, and the merged main metal tube is used to place the sample to be tested. Therefore, the light needs to be transmitted along the bend of the metal tube, which will cause the light to be obliquely incident on the metal tube wall, making the light experience multiple wall reflections and transmissions. Therefore, the transmission loss is very large, as Figure 1 shown. As disclosed in the invention patent ZL 202111440339.X, although a mirror is added in the tube to avoid oblique incidence, the preparation process is complex, and the mirror will block the stray light, bringing additional losses. As Figure 1 shown, due to the curved tube wall causing the light to experience multiple reflections, the transmission loss is as high as 10 6 times. For specific details, reference can be made to the content disclosed in Analytical Chemistry, 56(8), 1401-1403 (1984).

[0008] (2) For a Y-shaped optical fiber probe, due to the small numerical aperture of the optical fiber, the range of light angles that can be received is very small, that is, the light collection ability is limited, and the beam confinement ability is weak. In addition, since the object to be measured is difficult to enter the interior of the optical fiber and is located outside the end face of the optical fiber, the interaction distance between the excitation light and the object to be measured is very short, and the excitation efficiency of the corresponding stray light is very low. At the same time, since the object to be measured is located outside the end face of the optical fiber, the stray light generated by it is also located outside the optical fiber, resulting in a very low efficiency of the stray light being collected by the optical fiber. Therefore, for a Y-shaped optical fiber probe, both the excitation efficiency and the collection efficiency of the stray light are very low. It should be noted that for special optical fibers, such as microstructured optical fibers, there are pores inside, and the object to be measured can enter the pores, but the pores are too small, with a pore diameter of no more than a few micrometers, and a high-pressure pump is required for the liquid object to be measured to enter and exit the interior of the optical fiber; in addition, its numerical aperture is still very small, and the ability to collect stray light is still limited.

[0009] Based on the above problems, exploring new structures to improve the excitation and collection efficiency of stray light and reduce the interference of excitation light, so as to improve the detection sensitivity and reduce the volume of the instrument, is the current problem faced. Summary of the Invention

[0010] The object of the present invention is to propose a stray light detector based on a metal tube end face coupling structure, which improves the excitation efficiency and collection efficiency of stray light, reduces the interference of excitation light, thereby improving the detection sensitivity and reducing the volume of the instrument at the same time.

[0011] The technical solution of the present invention:

[0012] A stray light detector based on a metal tube end face coupling structure includes a straight capillary, a light source, a filter, a reflector, an optical lens and a photodetector;

[0013] The straight capillary is used to reduce the transmission loss of light, that is, to reduce the number of reflections on the inner wall of the capillary. The inner diameter of the straight capillary is greater than 0.1 mm, the length is greater than 2 mm, and the bending angle in the axial direction of the capillary is required to be less than 15 degrees. Preferably, the straight capillary can be a straight metal tube, or a straight plastic tube, ceramic tube or glass tube with a metal film plated on the inner wall, because the metal inner wall of these tubes has a high reflectivity for obliquely incident light and can be used for low-loss transmission of excitation light and stray light.

[0014] The light source is an LED light source (beam diameter greater than 3 mm) or a laser, which is arranged on one side of the straight capillary and is used to emit excitation light;

[0015] The filter includes a first filter and a second filter. Among them, the first filter is disposed between the light source and the first mirror, and is a narrow-bandpass filter for filtering and obtaining excitation light of a specific wavelength, which is perpendicular to the excitation light emitted by the light source. The second filter is located between the straight capillary and the optical lens, and can be a long-pass filter, a linear gradient filter, a grating or other spectroscopic devices for filtering out excitation light with wavelengths different from the stray light to avoid interference. When detecting turbidity, the second filter can be removed.

[0016] The mirror includes a first mirror and a second mirror. Both the first mirror and the second mirror are metal film mirrors or dielectric film mirrors. It should be noted that the shapes of the first mirror and the second mirror can both be planar or concave. When the first mirror and the second mirror are concave mirrors, they can converge the light beam.

[0017] Among them, the first mirror includes a mirror surface and a bent edge. The mirror surface of the first mirror is inclinedly disposed above the edge of the tube wall on the light source side at the inlet end of the straight capillary. The inclination angle between the mirror surface of the first mirror and the axis of the straight capillary ranges from 90° to 160°, preferably 110° to 130°. At the same time, the first mirror cannot block (or block as little as possible) the light transmitted in the straight capillary, that is, the first mirror does not cover the inner hole of the straight capillary, or the proportion of the light transmitted in the straight capillary blocked by the first mirror is less than 50%, that is, the coverage degree of the inner hole of the straight capillary by the first mirror is less than 50%. The mirror surface of the first mirror is used to reflect the excitation light so that the excitation light enters the straight capillary from the inlet end of the straight capillary, or is reflected into the straight capillary through the semi-through hole formed by thinning the side wall as shown in Figure 3 shown. Preferably, the distance from the lowest end of the first reflection to the inlet end of the straight capillary is less than 10 mm, and the overlapping width of the first mirror in the axial direction of the straight capillary and the inner hole of the straight capillary is less than 5 mm (such as the overlapping width D in Figure 5 is less than 5 mm). Preferably, a thinning treatment is performed at the position on the side wall of the end face of the straight capillary corresponding to the first mirror so that when the excitation light is reflected into the interior of the straight capillary, the tube wall blocks the excitation light the least. Among them, the thickness of the thinnest part of the tube wall on the side close to the first mirror after thinning is less than 5 mm, and more preferably, the thickness of the thinnest part of the tube wall on the side close to the first mirror after thinning is less than 0.5 mm. Specifically, as shown in Figure 3 shown, the tube wall on the side close to the first mirror is thinned until it penetrates the tube wall, that is, a semi-circular through hole is formed by thinning, and the aperture of the through hole ranges from 0.1 mm to 6 mm.

[0018] Preferably, a curved mirror flange is introduced at the edge of the first mirror. The flange is arranged along the axial direction of the straight capillary, extends into the straight capillary, and divides the inner hole of the straight capillary into two halves, which are respectively used to transmit the excitation light and the stray light, so as to further isolate the excitation light and the stray light, thereby avoiding the excitation light interfering with the stray light, and the flange does not affect the passage of the stray light. The thickness of the flange can be as thin as 0.01 mm, and the shielding ratio for a straight capillary with an inner diameter of 5 mm is only 0.25%; at the same time, the left surface of the flange can efficiently reflect the stray light (i.e., the left surface is a mirror with a high reflectivity) to reduce the transmission loss of the stray light; the right surface of the flange can absorb the excitation light (i.e., the right surface is a rough black with a low reflectivity, such as a black anodized aluminum surface) to reduce the interference caused by the leakage of the excitation light. It should be noted that when using an LED as the excitation light source, since the LED beam diameter is relatively thick and the area of the first mirror is limited and cannot cover the orifice of the straight capillary (it is necessary to reduce the shielding of the first mirror on the stray light), it is impossible to reflect all the LED beams, and part of the LED beams will leak past the edge of the first mirror, as shown in Figure 6 (a); by introducing the flange, the present invention can avoid the leakage of the excitation light from the edge of the first mirror without increasing the shielding of the stray light. It should be noted that when using a metal film as the flange, assuming the thickness H of the metal film is 0.01 mm (the stainless steel film can be as thin as 0.002 mm), for a straight capillary with an inner diameter R of 5 mm, the shielding ratio = (H×R) / (πR 2 / 4)=0.25%. In addition, preferably, semi-cylindrical quartz rods can be placed in the left and right inner holes on both sides of the flange, which are respectively used to transmit the stray light and the excitation light to reduce the transmission loss of the straight capillary. At this time, the two quartz rods are located between the inlet end of the straight capillary and the object to be measured, and respectively play the role of transmitting the excitation light from the capillary inlet to the object to be measured and transmitting the stray light from the object to be measured to the capillary inlet end; the introduction of the quartz rods also enables the object to be measured to be far away from the capillary inlet end, facilitating the replacement and cleaning of the object to be measured.

[0019] Preferably, a second mirror is disposed at the outlet end of the straight capillary or inside the straight capillary for reflecting the excitation light transmitted in the straight capillary back to the inlet end for signal calibration. At the same time, the stray light signal can also be reflected back to the inlet end to enhance the signal. By adjusting the shape (such as flat, curved or conical), size (such as diameter) and surface reflectivity (such as surface coating) of the second mirror, an appropriate reflectivity along the capillary axis can be obtained. It can be understood that there is a gap between the second mirror and the wall of the straight capillary, which does not play a sealing role. It should be further noted that for the excitation light reflected by the second mirror in the straight capillary, the change in its power can reflect the power fluctuation of the light source, and the changes of the two are consistent; moreover, the transmission route of this part of the excitation light propagates along the set optical path, that is, through the analyte in the tube and the transmission direction is fixed. Therefore, this part of the excitation light is transmitted along the straight capillary and carries the information of the analyte. For example, the liquid level height and bubbles will also affect the power of this part of the excitation light, so it can be used for signal calibration, such as compensating for the fluctuations of the light source power and the analyte. The signal calibration refers to the power fluctuations of the light source, such as environmental temperature changes or light source aging, or the analyte fluctuations, such as inconsistent liquid level heights of liquid analytes or the introduction of bubbles into the liquid, which cause fluctuations in the excitation light power and stray light power, resulting in test errors. It should be noted that for the excitation light transmitted outside the tube, its propagation path and direction are chaotic. Therefore, if this part of the excitation light is mixed into the stray light, it is difficult to distinguish, resulting in an increase in noise. This is because existing spectral splitting devices (such as filter or grating) need to limit the beam incident angle to play a spectral splitting role. For example, the transmittance and transmission wavelength of a filter are related to the beam incident angle, and the incident beam of a grating needs to be parallel light with a consistent direction. Therefore, it is difficult for spectral splitting devices to distinguish the excitation light with chaotic directions.

[0020] The optical lens is located between the second filter and the photodetector for focusing the stray light signal on the photodetector, and its optical axis direction is parallel to the axis of the straight capillary;

[0021] The photodetector is located directly above the straight capillary for detecting the stray light signal;

[0022] Preferably, a quartz sheet is disposed at the inlet end of the straight capillary for sealing the inlet end of the straight capillary to prevent leakage of the liquid sample and not block the passage of the excitation light and the stray light; and because the straight capillary is very thin, even if one end is sealed, the liquid sample will not flow out of the straight capillary. When the bent edge of the first mirror extends into the tube, two semi-circular quartz sheets are also selected for sealing. This structure of the straight capillary with one end sealed and the other end open in the present invention can effectively prevent bubbles from accumulating in the tube.

[0023] The analyte is a liquid or a solid. When the analyte is a liquid, it is placed at the inlet end of the straight capillary or inside the straight capillary. Under the illumination of the excitation light, stray light is emitted. The stray light travels towards the inlet end inside the straight capillary and is received by the photodetector after passing through the second filter and the optical lens in sequence. Since the analyte is placed inside the straight capillary, the stray light emitted by the analyte is also confined inside the straight capillary, thereby greatly improving the collection efficiency of the stray light. The collection efficiency can be as high as 50%. Specifically, all the stray light emitted upwards can be collected, and only the stray light emitted downwards cannot be collected. Therefore, up to half of the stray light can be collected. When the analyte is a solid, such as Figure 4 as shown, the analyte is located at the outlet of the straight capillary. The stray light emitted by the analyte also propagates upwards through the straight capillary and is received by the photodetector. At this time, the optical path is short and the excitation efficiency is low, but the straight capillary can still improve the collection efficiency of the stray light. It should be noted that if the solid analyte can be put into the tube, such as the powdered analyte, the excitation efficiency can be improved at this time. Figure 4 The structure shown can also be used to detect the reflection spectrum of the analyte (at this time, the reflected light can be regarded as stray light regardless of whether its propagation direction is chaotic). The reflection spectrum is related to the absorption spectrum of the analyte (reflection spectrum = light source emission spectrum - absorption spectrum of the analyte), and the absorption spectrum is related to the composition of the analyte. Therefore, detecting the reflection spectrum can obtain the composition of the analyte.

[0024] In the present invention, when the analyte is a transparent liquid, such as Figure 2 as shown, the analyte is placed inside the straight capillary, and the excitation light can propagate inside the analyte. At this time, all the stray light excited during the entire propagation path of the excitation light in the analyte is confined inside the straight capillary, so as to be collected and detected, and thus the collection efficiency is greatly improved. In contrast, the existing turbidimeters adopt a structure where the "propagation direction of the excitation light and the detection direction of the stray light" are perpendicular to each other, and only a small part of the stray light can be collected, that is, only the stray light perpendicular to the excitation light direction can be collected. Moreover, in the present invention, the propagation path (i.e., the optical path) of the excitation light in the analyte is the distance between the liquid surface and the inlet end (top port) of the straight capillary, that is Figure 2 the h in, as the analyte increases, the liquid surface drops, and the optical path can approach the length of the straight capillary (more than 10 cm long), so the excitation efficiency can be greatly improved.

[0025] In one embodiment, a bent edge is provided on the first mirror, and the bent edge is arranged along the axial direction of the straight capillary.

[0026] In one embodiment, the bent edge can extend into the inside of the straight capillary and divide the inner hole of the straight capillary into two halves ( Figure 7), which are respectively used to transmit the excitation light and the stray light, thereby further isolating the excitation light and the stray light. Among them, on both sides of the inner hole separated by the bent edge, quartz semi-cylinders can be placed to transmit the excitation light and the stray light respectively, so as to reduce the transmission loss.

[0027] In one embodiment, a quartz sheet is provided at the inlet end of the straight capillary.

[0028] In one embodiment, the edge of the side wall of the straight capillary at the position corresponding to the first mirror is thinned, so that the thickness of the thinned edge of the side wall of the straight capillary is less than 5 mm.

[0029] In one embodiment, the edge of the side wall of the straight capillary at the position corresponding to the first mirror is thinned to a semi-circular through hole, and the aperture of the through hole is 0.1-6 mm.

[0030] In one embodiment, the distance from the lowest end of the first mirror to the inlet end of the straight capillary is less than 10 mm, and the overlapping width of the first mirror and the inner hole of the straight capillary in the axial direction of the straight capillary is less than 5 mm.

[0031] In one embodiment, the inner diameter of the straight capillary is greater than 0.1 mm and the length is greater than 2 mm. The cross-section of the capillary can be circular, elliptical, triangular, rectangular, or polygonal.

[0032] In one embodiment, a second mirror is provided inside the straight capillary or at the outlet end of the straight capillary. The second mirror can obtain a suitable axial reflectivity of the capillary by adjusting its shape (such as plane, curved surface or cone), size and reflectivity.

[0033] Advantages of the present invention:

[0034] (1) The excitation light and the stray light are transmitted in the same capillary, and optical elements such as the light source and the mirror are all located on the same side of the straight capillary, making its structure simpler and more compact, easier to align and excite the object to be measured, and improving the excitation efficiency and collection efficiency of the stray light;

[0035] (2) The transmission directions of the excitation light and the stray light in the capillary are opposite, which can minimize the interference of the excitation light on the stray light and reduce the background noise;

[0036] (3) Since both the excitation light and the stray light of the present invention need to pass through the inlet end of the capillary, it is necessary to solve the interference problem caused by the mutual squeezing of the two beams at the same port. The present invention designs the position of the first mirror, the inclination angle of the first mirror, the bent edge of the first mirror, and the thinning treatment of the capillary wall, so that both the excitation light and the stray light can pass through the capillary inlet to the maximum extent, that is, the shielding caused by the tube wall and the first mirror is minimized, and the interference of the excitation light on the stray light can be avoided, that is, the bent edge of the first mirror is used to prevent the leakage of the excitation light, so as to ensure the maximum excitation light coupling efficiency, the maximum stray light collection efficiency, and the minimum background noise;

[0037] (4) Using a straight capillary can avoid the reflection loss of the tube wall caused by bending and minimize the transmission loss of light in the capillary to the greatest extent; at the same time, the straight capillary has a strong constraint on the light transmitted in the tube. Since the light is reflected by the tube wall and cannot penetrate, the collection efficiency of the stray light can be enhanced and the signal intensity can be increased.

[0038] (5) The optical components (such as light sources, photodetectors, and optical lenses, etc.) are all located on one side of the inlet end of the straight capillary. The advantage of this structure is that only by sealing the inlet end of the straight capillary can the optical components be avoided from being contaminated by the sample to be measured in the tube; at the same time, the outlet end of the capillary is open, which can avoid the problem of air bubble accumulation in the liquid sample, and at the same time, solid samples can also be tested. In contrast, for a capillary with both ends closed, the air bubbles generated when the liquid flows into the tube are difficult to discharge, which will cause disturbances to the transmission of the excitation light and the stray light.

[0039] In addition, compared with optical fiber light guiding, a metal tube or a capillary with a metal film on the inner wall has a higher collection efficiency for stray light. This is because the collection efficiency of the optical fiber is limited by the numerical aperture, while the metal tube has no such limitation, and the sample to be measured can easily enter the metal tube to increase the optical path and improve the excitation efficiency; compared with the Y-shaped tube, the straight tube is simpler and more compact (only one tube is needed), and has lower transmission loss (the number of reflections and reflection losses on the side wall are the least).

[0040] In summary, the present invention has the advantages of simple and compact structure, small interference of excitation light, and high excitation efficiency and collection efficiency of stray light. Description of the Drawings

[0041] Figure 1 It is a schematic diagram of the light transmission trajectory in metal tubes of different shapes. Among them, (a) is a straight tube and (b) is a bent tube.

[0042] Figure 2 It is a schematic diagram of the structure of the stray light detector based on the end-face coupling structure of the metal tube of the present invention, where the object to be measured is a liquid.

[0043] Figure 3Schematic diagram of the structure where the side wall of a metal tube is thinned to a small hole. Among them, (a) is the front view and (b) is the side view.

[0044] Figure 4 Schematic diagram of the structure of the stray light detector based on the end-face coupling structure of a metal tube according to the present invention. Among them, the object to be measured is a solid.

[0045] Figure 5 Schematic diagram of the relative position of the capillary tube and the mirror (top view).

[0046] Figure 6 Comparison diagram of the structure of the first mirror in the stray light detector based on the end-face coupling structure of a metal tube according to the present invention. Among them, (a) is the case without a bent edge and (b) is the case with a bent edge.

[0047] Figure 7 Schematic diagram of the structure with the bent edge of the mirror lengthened according to the present invention. Among them, (a) is the case without a quartz rod and (b) is the case with a quartz rod.

[0048] In the figure, 1 - straight capillary tube; 2 - light source; 3 - excitation light; 4 - first filter; 5 - first mirror; 6 - second filter; 7 - optical lens; 8 - photodetector; 9 - object to be measured; 10 - liquid level; 11 - stray light; 12 - semi-through hole; 13 - leaked excitation light; 14 - bent edge; 15 - mirror inclination angle; 16 - quartz sheet; 17 - second mirror; 18 - quartz rod. Specific embodiments

[0049] The present invention will be described in detail below in conjunction with embodiments and the accompanying drawings. It should be noted that the described embodiments are only intended to facilitate the understanding of the present invention and do not limit it in any way.

[0050] A stray light detector based on the end-face coupling structure of a metal tube provided by the present invention, as Figure 2 shown, includes:

[0051] Embodiment 1

[0052] As Figure 2 shown, the straight capillary tube 1 is a silver tube with a length of 7 cm, an inner diameter of 5 mm, and a wall thickness of 3 mm. The thickness of the right side wall at the upper end opening of the straight capillary tube 1 is thinned to 0.5 mm, and the metal first mirror 5 is placed above the thinned part, and the mirror inclination angle 15 is 120°. The liquid object to be measured 9 (rhodamine B solution) is placed inside the straight capillary tube 1, and the distance h from the liquid level to the upper end face of the straight capillary tube is 5 cm;

[0053] (2)The light source 2 (ultraviolet LED) emits an ultraviolet light beam of 310 nm as the excitation light 3. The excitation light 3 passes through the first filter 4 (the optical axis direction is the same as the light emitted from the light source) to filter out stray light of other wavelengths, obtaining a pure excitation light with a wavelength of 310 nm. Then it is reflected by the first mirror 5 and enters the inside of the straight capillary 1 (entering from the upper inlet end). At this time, the shielding of the excitation light 3 by the tube wall is the least, the number of reflections of the excitation light 3 on the inner wall of the straight capillary 1 is zero, and the loss of the excitation light is the smallest.

[0054] (3)The excitation light 3 is transmitted downward along the inner hole of the straight capillary 1 and irradiates the analyte 9. The analyte 9 is located at the inlet end of the straight capillary 1 or inside the straight capillary 1. The distance from the liquid surface to the inlet end of the straight capillary 1 is h, and h is also the interaction distance between the excitation light 3 and the analyte 9 - that is, the optical path. As the liquid level of the liquid analyte 9 in the straight capillary 1 rises, the liquid level is closer to the outlet end, the optical path h is longer, the corresponding excitation efficiency is higher, and the generated stray light is also stronger. The excitation light 3 causes the analyte 9 to emit stray light 11.

[0055] (4)The stray light 11 is transmitted upward along the inner hole of the straight capillary 1 and passes through the second filter 6 and the lens 7 located above the straight capillary. Among them, the second filter 6 is a linear gradient filter, which is used to separate the excitation light of different wavelengths and the stray light 11 to avoid the excitation light interfering with the collected stray light signal. The filter 6 is perpendicular to the axial direction of the straight capillary; the lens 7 is used to focus the stray light on the photodetector 8, and its optical axis is the same as the axial direction of the straight capillary. Finally, the stray light signal is received by the photodetector 8, and the collection efficiency of the stray light can be as high as 50%.

[0056] It should be noted that the liquid surface of the liquid analyte will reflect a part of the excitation light 3 back to the inlet end of the straight capillary 1 and thus be received by the photodetector 8, which will increase the background signal and noise; however, the optical reflectivity of the liquid surface is generally only about 2%, and the influence on the noise is relatively small.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than limiting the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present disclosure.

Claims

1. A stray light detector based on a metal tube end face coupling structure, characterized in that The stray light detector includes a straight capillary, a light source, a filter, a mirror, an optical lens, and a photodetector; The light source is arranged on one side of the straight capillary and is used to emit excitation light; The filter includes a first filter and a second filter; wherein, the first filter is arranged between the light source and the mirror and is perpendicular to the excitation light emitted by the light source; the second filter is located between the straight capillary and the optical lens, and its optical axis direction is the same as the axis direction of the straight capillary; The mirror is inclinedly arranged above the tube wall edge on the light source side at the inlet end of the straight capillary; The optical lens is located between the second filter and the photodetector and is used to focus the stray light signal on the photodetector, and its optical axis is parallel to the axis of the straight capillary; The photodetector is located directly above the straight capillary and is used to detect the stray light signal; The sample to be measured is placed at the outlet end of the straight capillary or inside the straight capillary. It is irradiated by the excitation beam and emits stray light. The stray light is transmitted in the straight capillary towards the inlet end direction of the straight capillary, and is sequentially received by the photodetector after passing through the second filter and the optical lens.

2. The stray light detector based on the metal tube end face coupling structure according to claim 1, wherein, A bent edge is provided on the first mirror. The bent edge extends into the straight capillary along the axial direction of the straight capillary and divides the inner hole of the straight capillary into two halves, which are respectively used to transmit the excitation light and the stray light.

3. The stray light detector based on the metal tube end face coupling structure according to claim 2, wherein, Semicylindrical quartz rods are placed in the inner holes on the left and right sides of the bent edge, which are respectively used to transmit the stray light and the excitation light to reduce the transmission loss of the straight capillary.

4. The stray light detector based on the metal tube end face coupling structure according to claim 3, wherein, The position area of the side wall edge of the straight capillary corresponding to the first mirror is thinned, so that the thickness of this area is less than 5 mm.

5. The stray light detector based on the metal tube end face coupling structure according to claim 4, wherein, The position of the side wall edge of the straight capillary corresponding to the first mirror is thinned to a semicircular through hole, and the aperture of the through hole is 0.1 - 6 mm.

6. The stray light detector based on the metal tube end face coupling structure according to claim 5, wherein, A quartz sheet is provided at the inlet end of the straight capillary to seal the inlet end of the straight capillary.

7. The stray light detector based on the metal tube end face coupling structure according to claim 6, wherein, The inclination angle range between the mirror surface of the first mirror and the axis of the straight capillary is between 90° and 160°; the distance between the lowest end of the first mirror and the end face of the straight capillary is less than 10 mm; the coverage degree of the first mirror on the inner hole of the straight capillary is less than 50%.

8. The stray light detector based on the metal tube end face coupling structure according to claim 7, wherein, Another mirror is provided at the outlet end of the straight capillary or inside the straight capillary, which is used to reflect the excitation light transmitted in the straight capillary back to the inlet end for signal calibration, and at the same time reflect the stray light signal back to the inlet end to enhance the signal.

9. The stray light detector based on the metal tube end face coupling structure according to claim 8, wherein the straight capillary is a straight metal tube, or a straight plastic tube, ceramic tube or glass tube with a metal film plated on the inner wall; the inner diameter of the straight capillary is greater than 0.1 mm and the length is greater than 2 mm.

10. The stray light detector based on the metal tube end face coupling structure according to claim 9, wherein the first filter is a narrow band-pass filter, and the second filter is a long wave-pass filter.

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