A compact, in-folding long optical path cavity device

Abstract

The application belongs to the technical field of optical detection, and discloses a compact inner folding long optical path cavity device, which comprises an outer reflection unit, an inner reflection unit and a detection reflection unit; the outer reflection unit is used for coupling the light beam emitted by a laser unit into the inner reflection unit and can couple the light beam reflected by the inner reflection unit back to the detection reflection unit; the inner reflection unit is used for reflecting the light beam entering its interior multiple times and reflecting the light beam reflected multiple times back to the outer reflection unit; and the detection reflection unit is used for coupling the light beam reflected multiple times to a receiving unit; the application adopts the inner folding plane mirror technology, significantly reduces the physical size of the cavity, greatly extends the effective optical path by increasing the number of reciprocating reflections of the light beam, solves the technical pain point of the traditional long optical path cavity that the longer the optical path is, the larger the volume is, and provides a lightweight optical cavity solution for portable detection equipment.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology, and in particular to a compact, internally folded, long-path optical cavity device. Background Technology

[0002] With the increasing demand for portable, on-site, and high-precision detection equipment in fields such as environmental monitoring and industrial process control, higher requirements are being placed on the structural design of optical cavities. These cavities must ensure a sufficiently long effective optical path while minimizing physical volume, and simultaneously consider optical path stability and ease of assembly. Currently, the industry mainly uses two types of optical cavity structures to achieve long optical paths: the Herriott cell and the White cell. Both have significant technical limitations in optical design and practical applications.

[0003] Herriott cell: It uses two opposing concave mirrors, and the light beam is reflected between these mirrors, thereby increasing the optical path. The Herriott cell has a relatively simple design and can achieve efficient optical path extension, but its physical size is usually large, especially when a longer optical path is required, the length of the cell will increase accordingly.

[0004] White Pool: Employs a three-mirror design, where two smaller concave mirrors and one larger concave mirror form a reflective optical path. The reflection path of the beam between these mirrors forms a "V" shape. Compared to the Herriott Pool, the White Pool is more suitable for using incoherent light sources (such as thermal radiation sources), but its design is more complex, and it is more difficult to manufacture and adjust.

[0005] Although these cell types perform well in many applications, their large physical size and high precision requirements for mirror adjustment limit their application in certain situations, especially those requiring compact design and high sensitivity.

[0006] To address this, a compact, internally folded, long-path optical cavity device is proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a compact, inwardly folded, long-path optical cavity device, thereby solving or at least alleviating one or more of the aforementioned and other problems existing in the prior art.

[0008] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] A compact, inwardly folded, long-path optical cavity device includes an external reflection unit, an internal reflection unit, and a reflection detection unit;

[0010] The external reflection unit is used to couple the light beam emitted by the laser unit into the internal reflection unit, and can couple the light beam reflected back by the internal reflection unit into the detection reflection unit;

[0011] The inner reflection unit is used to reflect the light beam entering its interior multiple times, and then reflect the light beam after multiple reflections back to the outer reflection unit.

[0012] The detection reflection unit is used to couple the light beam after multiple reflections to the receiving unit.

[0013] According to a compact, inwardly folded, long-path optical cavity device of the present invention, the internal reflection unit includes a first large flat plate reflector and a second large flat plate reflector. The first large flat plate reflector and the second large flat plate reflector are arranged parallel to each other, and a beam multiple-folding reflection zone is formed between the first large flat plate reflector and the second large flat plate reflector, such that the beam is reflected in a zigzag pattern within the beam multiple-folding reflection zone, and the normal of the first large flat plate reflector is not parallel to the horizontal direction.

[0014] In a compact, inwardly folded, long-path optical cavity device according to the present invention, the first large flat plate reflector and the second large flat plate reflector are arranged in an alternating vertical arrangement.

[0015] In a compact, inwardly folded long-path optical cavity device according to the present invention, the inner reflection unit further includes a first concave reflector and a second concave reflector. The first concave reflector is disposed below the first large flat plate reflector, and the second concave reflector is disposed above the second large flat plate reflector. The first concave reflector is used to reflect the light beam emitted from the multiple-fold reflection region back into the multiple-fold reflection region. The second concave reflector is capable of coupling the incident light beam reflected by the outer reflection unit into the multiple-fold reflection region, and is capable of coupling the light beam reflected back from the multiple-fold reflection region into the outer reflection unit.

[0016] In a compact, inwardly folded, long-path optical cavity device according to the present invention, the second concave mirror is a perforated concave mirror.

[0017] In a compact, inwardly folded, long-path optical cavity device according to the present invention, the first concave mirror and the second concave mirror are arranged parallel to each other, and the normal of the first concave mirror is parallel to the horizontal direction.

[0018] In a compact, inwardly folded long-path optical cavity device according to the present invention, the external reflection unit is disposed on one side of the internal reflection unit, the external reflection unit includes a first folded circular plane mirror and a second folded circular plane mirror, the first folded circular plane mirror being located above the second folded circular plane mirror;

[0019] The second folded circular plane mirror is used to receive the light beam emitted by the laser unit and reflect the light beam back to the first folded circular plane mirror, and can also reflect the light beam reflected back by the first folded circular plane mirror back to the detection reflection unit;

[0020] The first folded circular plane mirror is used to receive the light beam reflected by the second folded circular plane mirror and reflect the light beam to the inner reflection unit, and is also able to reflect the light beam reflected back by the inner reflection unit to the second folded circular plane mirror.

[0021] In a compact, inwardly folded long-path optical cavity device according to the present invention, the normal of the first folded circular plane mirror is perpendicular to the normal of the second folded circular plane mirror.

[0022] In a compact, inwardly folded, long-path optical cavity device according to the present invention, the detection and reflection unit includes a folded detector plane mirror disposed below the inner reflection unit, the folded detector plane mirror being used to reflect the light beam reflected back by the second folded circular plane mirror to the receiving unit.

[0023] In a compact, internally folded, long-path optical cavity device according to the present invention, the laser unit is one of a gas laser, a solid-state laser, or a semiconductor laser, and the receiving unit is one of a photodiode, a charge-coupled device, or a photomultiplier tube.

[0024] The present invention has at least the following beneficial effects:

[0025] By employing an inward-folding plane mirror technology, the effective optical path is significantly extended by increasing the number of beam reflections while significantly reducing the physical size of the cavity. This solves the technical pain point of traditional long-path optical cavities where "the longer the optical path, the larger the volume," and provides a lightweight optical cavity solution for portable detection equipment.

[0026] Folding the optical path effectively extends the interaction optical path between the beam and the sample being measured. Based on Beer-Lambert's law, this can significantly enhance the absorption signal response to trace and minute substances, thereby improving detection accuracy and sensitivity.

[0027] Adopting a modular design, the external reflection unit, internal reflection unit, and detection reflection unit have clearly defined functions. The positions and angles of each reflector are precisely matched, making assembly and debugging difficult and eliminating the need for complex adjustment mechanisms. This significantly reduces manufacturing and maintenance costs. It also boasts high three-dimensional space utilization and a small planar footprint, perfectly meeting the compact design requirements of portable testing equipment. Attached Figure Description

[0028] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings:

[0029] Figure 1 This is a schematic diagram of the structure of the present invention;

[0030] Figure 2 The pattern of multiple reflected light spots formed by optical cavities in existing technologies;

[0031] Figure 3 This is a pattern of multiple reflected light spots formed by the internally folded optical cavity of the present invention.

[0032] Explanation of icon numbers:

[0033] 1. First concave reflector; 2. Second concave reflector; 3. First large flat reflector; 4. Second large flat reflector; 5. First folded circular plane reflector; 6. Second folded circular plane reflector; 7. Folded detector plane reflector. Detailed Implementation

[0034] The following will describe in detail the implementation of this application with reference to the accompanying drawings and embodiments, so that the implementation process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0035] Please refer to Figures 1 to 3 As shown, an embodiment of the present invention provides a compact, inwardly folded, long-path optical cavity device, including an external reflection unit, an internal reflection unit, and a reflection detection unit;

[0036] The external reflection unit is used to couple the beam emitted by the laser unit into the internal reflection unit, and can couple the beam reflected back from the internal reflection unit into the detection reflection unit;

[0037] The internal reflection unit is used to reflect the light beam entering its interior multiple times, and then reflect the light beam after multiple reflections back to the external reflection unit.

[0038] The reflection detection unit is used to couple the beam after multiple reflections to the receiving unit.

[0039] By adopting the above technical solution, a three-level optical reflection coupling structure is constructed, consisting of an external reflection unit, an internal reflection unit, and a detection reflection unit. The external reflection unit serves as the relay hub for the beam entering and exiting the cavity, realizing the precise coupling input of the laser beam from the laser unit to the internal reflection unit, as well as the coupling transmission of the beam reflected by the internal reflection unit to the detection reflection unit. The internal reflection unit, as the core unit for optical path extension, effectively extends the optical path through multiple reflections of the beam. The detection reflection unit, as the final beam refraction unit, realizes the coupling guidance of the beam transmitted by the external reflection unit to the receiving unit. The three units form a coordinated optical path transmission closed loop, ensuring stable propagation of the beam from emission to detection.

[0040] In this embodiment, the external reflection unit, the internal reflection unit, and the detection reflection unit are all integrated into a sealed aluminum alloy cavity body. The interior of the cavity body is treated with an anti-light treatment to avoid stray light interference. Each unit is installed in the cavity body through a high-precision optical mounting bracket.

[0041] In this embodiment, the internal reflection unit includes a first large flat plate reflector 3 and a second large flat plate reflector 4. The first large flat plate reflector 3 and the second large flat plate reflector 4 are arranged parallel to each other. A beam multiple folding reflection zone is formed between the first large flat plate reflector 3 and the second large flat plate reflector 4, so that the beam is reflected in a zigzag pattern within the beam multiple folding reflection zone. The normal of the first large flat plate reflector 3 is not parallel to the horizontal direction.

[0042] By adopting the above technical solution, the first large flat plate reflector 3 and the second large flat plate reflector 4 are set parallel to each other, ensuring that the reflection direction of the light beam between the two mirrors is stable and preventing the light beam from being deflected and escaping due to the non-parallelism of the mirrors. The multiple folding reflection zone formed between the two reflectors provides a dedicated reflection space for the light beam. The normal of the first large flat plate reflector 3 is not parallel to the horizontal direction. Combined with the parallel relationship between the two mirrors, the normal of the second large flat plate reflector 4 is also not parallel to the horizontal direction, so that the light beam incident on the reflection zone cannot propagate in a straight line, and thus forms a zigzag reciprocating reflection in the reflection zone, completing the extension of the optical path.

[0043] In this embodiment, both the first large flat plate reflector 3 and the second large flat plate reflector 4 are made of K9 optical glass substrate with a thickness of 10mm. The reflective surface is coated with a silver metal high-reflectivity film with a thickness of 200nm and a high reflectivity of ≥99.5%. The angle between the normal of the first large flat plate reflector 3 and the horizontal direction is set to 6.6°, and the second large flat plate reflector 4 is tilted at a 6.6° angle to it. This ensures that the light beam has sufficient space for reciprocating reflection within the reflection area, and that the light spot does not touch the edge of the mirror surface, thus preventing energy loss.

[0044] In this embodiment, the first large flat panel reflector 3 and the second large flat panel reflector 4 are arranged in an alternating vertical arrangement.

[0045] By adopting the above technical solution, the first large flat plate reflector 3 and the second large flat plate reflector 4 are arranged in an alternating vertical arrangement. Combined with their parallel structure and non-horizontal normals, the zigzag reciprocating reflection path of the light beam in the multiple folding reflection area does not overlap, avoiding self-interference of the light beam during reflection and ensuring the propagation stability of the light beam. At the same time, the alternating vertical structure further increases the optical path length of a single reflection of the light beam, improves the optical path extension efficiency, and achieves a longer effective optical path within the same cavity space.

[0046] In this embodiment, the inner reflection unit further includes a first concave reflector 1 and a second concave reflector 2. The first concave reflector 1 is disposed below the first large flat reflector 3, and the second concave reflector 2 is disposed above the second large flat reflector 4. The first concave reflector 1 is used to reflect the light beam emitted from the multiple-fold reflection zone back into the multiple-fold reflection zone. The second concave reflector 2 can couple the incident light beam reflected by the outer reflection unit into the multiple-fold reflection zone, and can couple the light beam reflected back from the multiple-fold reflection zone into the outer reflection unit.

[0047] By adopting the above technical solution, a first concave reflector 1 and a second concave reflector 2 are added to the inner reflection unit. The first concave reflector 1 is located below the first large flat reflector 3, which can accurately receive the light beam emitted from the multiple folding reflection area and reflect it back into the reflection area, so that the light beam continues to participate in the zigzag reciprocating reflection, greatly increasing the number of reflections of the light beam in the reflection area and further extending the optical path. The second concave reflector 2 is located above the second large flat reflector 4, serving as the light beam inlet and outlet of the inner reflection unit. It realizes the accurate coupling input of the incident light beam reflected by the outer reflection unit to the multiple folding reflection area, and can also couple the light beam that has completed multiple reflections in the reflection area back to the outer reflection unit, forming a closed-loop reflection structure of the inner reflection unit.

[0048] The second concave reflector 2 is a concave reflector with a hole.

[0049] By adopting the above technical solution, the second concave reflector 2 is set as a concave reflector with a hole. The through hole in the center provides a precise light transmission channel for the incident beam of the outer reflector unit, allowing the beam to pass through the through hole and directly couple into the beam multiple folding reflection area, avoiding unnecessary reflection of the beam during incident and causing energy loss. At the same time, the concave reflector structure can focus the beam, suppress the divergence trend of the beam during propagation, ensure the stability of the beam spot size in the beam multiple folding reflection area, and improve the reflection efficiency of the beam.

[0050] In this embodiment, the first concave mirror 1 and the second concave mirror 2 are arranged parallel to each other, and the normal of the first concave mirror 1 is parallel to the horizontal direction.

[0051] By adopting the above technical solution, the first concave reflector 1 and the second concave reflector 2 are arranged parallel to each other, and the normal of the first concave reflector 1 is parallel to the horizontal direction, so that the normal of the second concave reflector 2 is also parallel to the horizontal direction. The horizontal normal keeps the reflection direction of the light beam by the two concave reflectors horizontal, which can accurately reflect the light beam to the beam multiple folding reflection area or the external reflection unit, avoiding the optical path offset caused by the tilt of the normal. The parallel arrangement of the two ensures that the reflected light path direction is consistent, realizing the accurate reflection and coupling of the light beam between the first concave reflector 1 and the beam multiple folding reflection area, and between the second concave reflector 2 and the external reflection unit.

[0052] In this embodiment, the external reflection unit is disposed on one side of the internal reflection unit. The external reflection unit includes a first folded circular plane mirror 5 and a second folded circular plane mirror 6. The first folded circular plane mirror 5 is located above the second folded circular plane mirror 6.

[0053] The second folded circular plane mirror 6 is used to receive the light beam emitted by the laser unit and reflect the light beam back to the first folded circular plane mirror 5, and can also reflect the light beam reflected back by the first folded circular plane mirror 5 back to the detection reflection unit.

[0054] The first folding circular plane mirror 5 is used to receive the light beam reflected by the second folding circular plane mirror 6 and reflect the light beam to the inner reflection unit, and can also reflect the light beam reflected back by the inner reflection unit to the second folding circular plane mirror 6.

[0055] By adopting the above technical solution, the external reflection unit is set on one side of the internal reflection unit, realizing the side entry of the optical path into the cavity and effectively reducing the overall volume of the device. The external reflection unit consists of a first folded circular plane mirror 5 and a second folded circular plane mirror 6 arranged vertically. The second folded circular plane mirror 6 serves as the first receiving end of the laser beam, completing the reception of the laser beam and the folding of the laser beam to the first folded circular plane mirror 5. It also serves as the relay end of the return beam from the internal reflection unit, folding the return beam from the first folded circular plane mirror 5 to the detection reflection unit. The first folded circular plane mirror 5 completes the precise folding of the beam from the second folded circular plane mirror 6 to the internal reflection unit, and the folding of the return beam from the internal reflection unit to the second folded circular plane mirror 6. The two work together to realize the two foldings of the beam entering and exiting the cavity, ensuring that the beam propagation direction is precisely matched with the optical path of the internal reflection unit and the detection reflection unit.

[0056] Among them, the first folding circular plane mirror 5 and the second folding circular plane mirror 6 both have a mirror diameter of 4cm, use fused silica glass substrate, and have a multi-layer dielectric high-reflection film on the reflective surface to match the working wavelength of the laser unit, with a reflectivity ≥99.5%.

[0057] In this embodiment, the normal of the first folded circular plane mirror 5 is perpendicular to the normal of the second folded circular plane mirror 6.

[0058] By adopting the above technical solution, the normal of the first folding circular plane mirror 5 and the normal of the second folding circular plane mirror 6 are set perpendicular to each other, so that the two mirrors form a standard folding optical path of 90°, realizing the optical path conversion between the horizontal and vertical directions of the beam. This allows the horizontal incident beam of the laser unit to be accurately folded into a vertical direction and incident on the inner reflection unit. At the same time, it can also accurately fold the vertical return beam of the inner reflection unit into a horizontal direction and incident on the detection reflection unit, avoiding optical path offset caused by normal angle deviation and ensuring the accuracy of beam folding.

[0059] In this embodiment, the detection reflection unit includes a folding detector plane reflector 7, which is disposed below the inner reflection unit. The folding detector plane reflector 7 is used to reflect the light beam reflected back by the second folding circular plane reflector 6 to the receiving unit.

[0060] By adopting the above technical solution, the detection and reflection unit is equipped with a folding detector plane reflector 7 and is placed below the inner reflection unit. It can accurately receive the horizontal light beam reflected back by the second folding circular plane reflector 6, and fold the light beam into a vertical direction through mirror reflection, realizing the last folding of the optical path, so that the light beam can be accurately coupled to the light-transmitting detection surface of the receiving unit, ensuring the light signal acquisition efficiency of the receiving unit. At the same time, placing the detection and reflection unit below the inner reflection unit makes full use of the three-dimensional space of the device and further reduces the planar area occupied by the device.

[0061] In this embodiment, the laser unit is one of a gas laser, a solid-state laser, or a semiconductor laser, and the receiving unit is one of a photodiode, a charge-coupled device, or a photomultiplier tube.

[0062] By adopting the above technical solution, the laser unit is limited to one of gas lasers, solid-state lasers, and semiconductor lasers. The three types of lasers are adapted to different detection wavelengths, powers, and application scenarios, enabling the device to adapt to the wavelength of different detection objects. The receiving unit is limited to one of photodiodes, charge-coupled devices, and photomultiplier tubes. The three types of detection elements are adapted to the detection of light signals of different intensities, enabling accurate detection of conventional light signals, weak light signals, and imaging light signals. This allows for precise matching between laser emission and light signal detection, improving the versatility and detection adaptability of the device.

[0063] When applied to online environmental gas detection scenarios, the laser unit uses a semiconductor laser with an emission wavelength of 1653.7nm, adapted to the characteristic absorption peak of methane gas, and an output power of 5mW. It features small size and low power consumption. The receiving unit uses a photodiode with a response speed of ≥1ns, and the detection band covers the laser emission wavelength, enabling rapid optical signal acquisition and conversion. When applied to trace chemical component detection scenarios, the laser unit uses a solid-state laser with an emission wavelength of 532nm and an output power of 20mW. It has high beam stability, and the receiving unit uses a photomultiplier tube with a gain of ≥10^6, enabling amplification and accurate detection of weak optical signals. When applied to optical imaging detection scenarios, the laser unit uses a gas laser with an emission wavelength of 632.8nm. It has good beam uniformity, and the receiving unit uses a charge-coupled device with a pixel resolution of 2048×2048, enabling imaging detection and analysis of optical signals.

[0064] Working principle:

[0065] The laser unit emits a detection beam, which is horizontally incident on the second folded circular plane mirror 6 of the outer reflection unit. After being reflected by the second folded circular plane mirror 6, the light path is folded 90° and vertically incident on the first folded circular plane mirror 5.

[0066] After being reflected by the first folding circular plane mirror 5, the light beam is folded 90° again and horizontally incident on the second concave mirror 2 of the inner reflection unit. After passing through the through hole in the center of the second concave mirror 2, it is coupled to the beam multiple folding reflection area between the first large flat plate mirror 3 and the second large flat plate mirror 4.

[0067] After the beam enters the beam folding reflection zone, due to the parallel, non-horizontal and staggered structure of the first large flat plate mirror 3 and the second large flat plate mirror 4, a zigzag reciprocating reflection is formed. When the beam exits from the beam folding reflection zone to the first concave mirror 1, it is reflected by the first concave mirror 1 and then folded back to the beam folding reflection zone to continue the zigzag reciprocating reflection, thus completing the optical path extension after multiple reflections.

[0068] The beam that has undergone multiple reflections is coupled from the beam multiple folding reflection area to the second concave reflector 2, and then horizontally incident on the first folded circular plane reflector 5 of the outer reflection unit through the through hole of the second concave reflector 2.

[0069] After being reflected by the first folding circular plane mirror 5, the light beam is vertically incident on the second folding circular plane mirror 6, and then reflected by the second folding circular plane mirror 6 before being horizontally incident on the folding detector plane mirror 7 of the detection reflection unit.

[0070] After the light beam is reflected by the plane mirror 7 of the folding detector, the light path is folded and precisely coupled to the receiving unit. The receiving unit converts the optical signal into an electrical signal, completing the signal transmission and acquisition of the entire detection optical path.

[0071] The foregoing description illustrates and describes several preferred embodiments of the present invention. However, as previously stated, it should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the inventive concept by means of the foregoing teachings or techniques or knowledge in related fields. Any modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A compact, in-folding long optical path cavity device, characterized by, It includes an external reflection unit, an internal reflection unit, and a reflection detection unit; The external reflection unit is used to couple the light beam emitted by the laser unit into the internal reflection unit, and can couple the light beam reflected back by the internal reflection unit into the detection reflection unit; The inner reflection unit is used to reflect the light beam entering its interior multiple times, and then reflect the light beam after multiple reflections back to the outer reflection unit. The detection reflection unit is used to couple the beam after multiple reflections to the receiving unit; The internal reflection unit includes a first large flat plate reflector (3) and a second large flat plate reflector (4). The first large flat plate reflector (3) and the second large flat plate reflector (4) are arranged parallel to each other. A beam multiple folding reflection zone is formed between the first large flat plate reflector (3) and the second large flat plate reflector (4), so that the beam is reflected in a zigzag pattern within the beam multiple folding reflection zone. The normal of the first large flat plate reflector (3) is not parallel to the horizontal direction. The first large flat plate reflector (3) and the second large flat plate reflector (4) are arranged in an alternating vertical arrangement.

2. A compact, in-folding long optical path cavity device according to claim 1, wherein, The inner reflection unit further includes a first concave reflector (1) and a second concave reflector (2). The first concave reflector (1) is disposed below the first large flat reflector (3), and the second concave reflector (2) is disposed above the second large flat reflector (4). The first concave reflector (1) is used to reflect the light beam emitted from the multiple-fold reflection zone back into the multiple-fold reflection zone. The second concave reflector (2) is able to couple the incident light beam reflected by the outer reflection unit into the multiple-fold reflection zone, and is able to couple the light beam reflected back from the multiple-fold reflection zone into the outer reflection unit.

3. A compact, in-folding long optical path cavity device according to claim 2, wherein, The second concave reflector (2) is a concave reflector with a hole.

4. A compact, inwardly folded, long-path optical cavity device according to claim 3, characterized in that, The first concave mirror (1) and the second concave mirror (2) are arranged parallel to each other, and the normal of the first concave mirror (1) is parallel to the horizontal direction.

5. A compact, inwardly folded, long-path optical cavity device according to claim 1, characterized in that, The external reflection unit is disposed on one side of the internal reflection unit. The external reflection unit includes a first folded circular plane mirror (5) and a second folded circular plane mirror (6). The first folded circular plane mirror (5) is located above the second folded circular plane mirror (6). The second folded circular plane mirror (6) is used to receive the light beam emitted by the laser unit and reflect the light beam to the first folded circular plane mirror (5), and can reflect the light beam reflected back by the first folded circular plane mirror (5) to the detection reflection unit; The first folded circular plane mirror (5) is used to receive the light beam reflected by the second folded circular plane mirror (6) and reflect the light beam to the inner reflection unit, and is also able to reflect the light beam reflected back by the inner reflection unit to the second folded circular plane mirror (6).

6. A compact, inwardly folded, long-path optical cavity device according to claim 5, characterized in that, The normal of the first folded circular plane mirror (5) is perpendicular to the normal of the second folded circular plane mirror (6).

7. A compact, inwardly folded, long-path optical cavity device according to claim 6, characterized in that, The detection reflection unit includes a folding detector plane reflector (7), which is disposed below the inner reflection unit. The folding detector plane reflector (7) is used to reflect the light beam reflected back by the second folding circular plane reflector (6) to the receiving unit.

8. A compact, inwardly folded, long-path optical cavity device according to claim 1, characterized in that, The laser unit is one of a gas laser, a solid-state laser, or a semiconductor laser, and the receiving unit is one of a photodiode, a charge-coupled device, or a photomultiplier tube.

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