Refraction-reflection type volume phase holographic grating transmission spectrometer

Abstract

The invention discloses a catadioptric volume phase holographic grating transmission spectrometer, and belongs to the technical field of spectral analysis. The spectrometer comprises an incidence module, a collimating lens, a wide-spectrum plane mirror, a volume phase holographic grating, an imaging lens and a detector which are sequentially arranged along a light path, the incident module limits the luminous flux and the spectral resolution of the spectrograph; the collimating lens converts incident light into parallel light beams; the plane mirror and the volume phase holographic grating are fixedly connected to form a grating assembly with an included angle of 90 degrees; the volume phase holographic grating diffracts the incident parallel light; the grating assembly rotates to change the incident angle of the light beam entering the volume phase holographic grating; the imaging lens optical axis is parallel to the collimating lens optical axis; an emergent central light beam of the grating assembly is parallel to an incident light beam to form a Z-shaped light path; and the imaging lens converges the emergent light beam to the detector to form a spectral image of the incident module, and a target spectrogram is obtained. According to the invention, the transverse size of the volume phase holographic grating transmission spectrometer is reduced, and the wide spectrum adjustment effect of the spectrometer is realized.

Description

Technical Field

[0001] This invention belongs to the field of spectral analysis technology, and more specifically, relates to a refracting-reflection bulk holographic grating transmission spectrometer. Background Technology

[0002] A bulk holographic grating transmission spectrometer is a spectral analysis instrument with high imaging quality, high resolution, and high sensitivity. Originally developed by an American company and applied in the aerospace field, it combines a mature consumer-grade SLR camera lens with a transmission bulk holographic grating (hereinafter referred to as a bulk grating) to create a spectrometer with a large relative aperture, high diffraction efficiency, and high imaging quality. Although the spectral analysis range of a transmission lens is generally narrower than that of a reflective optical system due to limitations in material transmission characteristics and dispersion, it is still suitable for specific analytical scenarios. For example, in Raman scattering analysis, the Raman shift of the highest fundamental vibration of the hydrogen molecule, which has the highest vibrational frequency, is approximately 4163 cm⁻¹. -1 If a 532 nm laser is used for excitation, the corresponding Stokes spontaneous Raman scattering wavelength range is between 532 nm and 683 nm, and the transmission lens can fully meet the spectral analysis requirements in this range.

[0003] The structure of a bulk grating transmission spectrometer is closely related to its selected Bragg wavelength (or spectral analysis range). Due to the specific angular relationship between the diffracted beam and the incident beam of the transmission grating, the instrument's shape is usually close to V-shaped or L-shaped, resulting in a large overall size and low integration, making it difficult to meet current demands for miniaturization and portability. Once the Bragg wavelength is determined, its structure is fixed and difficult to adjust. In fact, the bulk grating Bragg wavelength can be adjusted with the incident angle, exhibiting high diffraction efficiency over a wide spectral range centered on the Bragg wavelength within a wide range of incident angle adjustments, but existing structures fail to leverage this advantage. Although a proposal in 1998 to achieve "tunability" of the spectrometer by simultaneously adjusting the angles of the grating, imaging camera, and collimating lens was made, such methods often require changes to the overall structure of the spectrometer or occupy a large space, making practical operation complex and thus not widely adopted.

[0004] In existing technologies, one Raman scattering detection system using a transmission bulk holographic grating has an incident beam at a 90° angle to the exit center beam, requiring grating replacement to adapt to different excitation wavelengths. A bulk holographic transmission grating spectrometer (patent number CN220853866U) uses short-wavelength near-infrared light in the 800 nm-890 nm range as the light source. After collimation by a lens, the parallel beam is dispersed by a bulk holographic transmission grating, then focused by another lens, and finally acquired by a CCD positioned on the focal plane. The incident angle of the bulk grating is set to 30.464° based on the selection of the light source wavelength and grating line density. Once this incident angle is determined, it cannot be adjusted, making it unsuitable for Raman scattering spectroscopy applications requiring different excitation laser wavelengths or high resolution. Early full transmission spectrometers, as well as current Raman spectrometers and high-flux transmission spectrometers, all employ a fixed grating and an angled intersection of the incident beam and the outgoing center beam, making them difficult to adapt to changes in excitation wavelength or the range of the acquired spectrum.

[0005] In summary, while bulk grating transmission spectrometers exhibit excellent performance in specific wavelength ranges, the limitations of their fixed structure and adjustable capabilities, as well as the space requirements of traditional optical paths, remain key issues that need to be addressed to further realize flexible applications, integration, and functional expansion. Therefore, how to achieve a compact, easily adjustable, and stable spectrometer design while maintaining high performance is an important current challenge. Summary of the Invention

[0006] To address the shortcomings of related technologies, the present invention aims to provide a refracting-type bulk holographic grating transmission spectrometer, which solves the problem that existing solutions cannot adjust the incident angle after fixing the bulk grating, making them unsuitable for spectral analysis of different laser wavelengths.

[0007] To achieve the above objectives, the present invention provides a catadioptric volumetric holographic grating transmission spectrometer, comprising: an incident module, a collimating lens, a broadband plane mirror, a volumetric holographic grating, an imaging lens, and a detector arranged sequentially along the optical path; The incident module serves as the light inlet of the spectrometer, limiting the light flux entering the spectrometer and the resolution of the obtained spectrum; The collimating lens is used to convert the incident divergent beam into a parallel beam. The broadband plane mirror and the volumetric holographic grating are fixedly connected to form a grating assembly with an included angle of 90°; the broadband plane mirror is used to redirect the parallel light output from the collimating lens so that it is incident on the volumetric holographic grating and dispersed; the volumetric holographic grating is used to diffract the incident parallel light according to the wavelength and the corresponding exit angle, and the exit light of the same wavelength is parallel to each other. The optical axis of the imaging lens is parallel to the optical axis of the collimating lens; When the grating assembly rotates synchronously around the same axis, the incident angle of the parallel beam entering the volumetric holographic grating is changed so that the wavelength of the outgoing center beam is the Bragg wavelength corresponding to the incident angle, and the outgoing center beam of the grating assembly is parallel to the incident beam, forming a Z-shaped optical path; wherein, the axis of rotation is located on the intersection line of the plane of the reflecting mirror and the central plane of the volumetric holographic grating, and is equidistant from the optical axis of the collimating lens and the optical axis of the imaging lens; the central plane of the volumetric holographic grating is always located on the angle bisector of the angle formed by the incident beam of the volumetric holographic grating and the outgoing center beam determined by the optical axis of the imaging lens; The imaging lens is used to focus the parallel light containing different wavelengths emitted from the grating assembly to different positions on its focal plane and form a spectral image of the incident module on the detector. The detector is located on the focal plane of the imaging lens and converts the received light signal into an electrical signal to obtain the target spectrum.

[0008] Optionally, the incident module is an incident slit or an optical fiber interface.

[0009] Optionally, the relationship between the incident angle of the incident light of the grating assembly and the Bragg wavelength is: d(sinα+sinβ)=mλ, where α is the incident angle, β is the diffraction angle, β=α, and m=1.

[0010] Optionally, the grating assembly further includes a sine wave driver; The sine driver is used to drive the grating assembly to rotate around the rotating shaft at a preset speed, so that the incident angle of the grating assembly changes uniformly in a sinusoidal form, thereby realizing the electronically controlled adjustment and uniform scanning of the Bragg wavelength.

[0011] Optionally, the sine drive includes a motor, a lead screw, a slider, and a sine bar connected in sequence; The motor serves as a power source to drive the lead screw to move in the horizontal direction; The slider is provided with a guide groove, and the slider is used to move on a preset horizontal guide rail under the drive of the lead screw; One end of the sine bar is connected to one end of the rotating shaft, and the other end of the sine bar is disposed in the guide groove, which is used to slide vertically under the action of the slider to drive the rotating shaft to rotate.

[0012] Optionally, the detector is one of a unit detector, a linear array detector, or a surface array detector for the front exit slit.

[0013] Optionally, the incident module uses an optical fiber interface, the optical fiber interface is a multimode optical fiber, and the collimating lens uses an achromatic lens.

[0014] Compared with the prior art, the above-described technical solutions conceived in this invention can achieve the following beneficial effects: 1. This invention provides a catadioptric volumetric holographic grating transmission spectrometer. A broadband plane mirror and a volumetric holographic grating are combined to form a grating assembly that can rotate synchronously around a fixed axis. Within the grating assembly, the central plane of the volumetric holographic grating is always located on the angle bisector of the angle between the incident beam of the volumetric holographic grating and the exit center beam determined by the optical axis of the imaging lens. By rotating the grating assembly to change the incident angle of the parallel light entering the volumetric holographic grating, the wavelength of the exit center beam can be made to match the Bragg wavelength corresponding to the incident angle. Simultaneously, the exit center beam is parallel to the incident beam, thus allowing flexible adjustment of the Bragg wavelength and spectral detection range. This solves the problem in existing solutions where the incident angle cannot be adjusted after the volumetric holographic grating is fixed, making it unsuitable for spectral analysis of different wavelength ranges. It also reduces the angle accuracy requirements and adjustment difficulty during spectrometer fabrication. Furthermore, by constructing a catadioptric optical system using the grating assembly, the traditional V-shaped or L-shaped optical path is transformed into a Z-shaped optical path, with the imaging lens and collimating lens axes parallel, reducing the lateral size of the spectrometer and facilitating integration and portability.

[0015] 2. This invention provides a refracting-reflection bulk holographic grating transmission spectrometer. By using a sinusoidal driver to drive the grating assembly to rotate, the uniform linear motion driven by the sinusoidal driver motor is transformed into a uniform change of the incident angle of the planar diffraction grating. This enables the electronic control setting and uniform scanning of the Bragg wavelength of the spectrometer. It can be used as a spectrometer with a fixed wavelength band, or it can realize the function of a monochromator through continuous scanning, thus expanding the application range of the instrument. Attached Figure Description

[0016] Figure 1 This is an optical path diagram of a refracting bulk holographic grating transmission spectrometer provided in an embodiment of the present invention.

[0017] Figure 2 This refers to the angular relationship between the incident light beam and the broadband plane mirror and the bulk holographic grating in the grating assembly provided in this embodiment of the invention.

[0018] Figure 3 This is a schematic diagram of the connection between the grating assembly and the sine drive provided in an embodiment of the present invention.

[0019] Figure 4 This is a top view of the structure of a refracting bulk holographic grating transmission spectrometer provided in an embodiment of the present invention.

[0020] Figure 5 This is a top view of another refracting-type bulk holographic grating transmission spectrometer provided in an embodiment of the present invention.

[0021] Figure 6 This is a neon lamp spectrum obtained by a catadioptric bulk holographic grating transmission spectrometer provided in an embodiment of the present invention, wherein the Bragg angle... 36.5°, with a center wavelength of 496 nm.

[0022] Figure 7 This is another neon lamp spectrum obtained by a refracting bulk holographic grating transmission spectrometer provided in this embodiment of the invention, wherein the Bragg angle The angle is 50.0° and the center wavelength is 638 nm.

[0023] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1. Incident module, 2. Collimating lens, 21. F-mount, 3. Broadband plane mirror, 4. Volumetric holographic grating, 41. Grating assembly shaft, 42. Sine bar, 43. Slider, 44. Lead screw, 45. Motor, 5. Imaging lens, 6. Detector, 72. Front mounting plate, 71. Rear mounting plate, 8. Metal connecting rod, 9. Base plate, 91. Angle adjustment scribe line. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The following description, in conjunction with a preferred embodiment, illustrates the content involved in the above embodiments.

[0026] Example 1 In existing technologies, the incident and exit paths of the central beam (the beam traveling along the optical axis of the optical system) in a typical Czerny-Turner (CT) architecture planar grating reflectance spectrometer are determined (assuming their included angle is...). ), by rotating the grating relative to the spectrometer's axis of symmetry The wavelength of the central beam can be adjusted. The grating equation for a CT-structured planar grating reflectance spectrometer can be expressed as:

[0027] In the formula, For the grating period, This represents the interference order. Therefore, the rate of change of the central beam wavelength of the CT-architecture planar grating reflectance spectrometer with respect to the grating rotation angle is:

[0028] Central beam wavelength Rotation angle with grating Sensitive changes ( (Close to 0).

[0029] For a bulk grating transmission spectrometer with an existing structure, the directions of the incident and outgoing central beams (determined by the centerlines of the incident and outgoing optical systems, respectively) are fixed. Let the incident angle be denoted as follows: [Insert angle here]. Rotate the volume grating around the grating scribe line direction so that the angle between the grating center plane and the angle bisector is . At this point, the grating equation corresponding to the emitted central beam can be written as:

[0030] The rate of change of the central beam wavelength with adjustment of the grating angle can be expressed as:

[0031] exist When the wavelength approaches zero, the change in the central beam wavelength with adjustment angle is minimal. Existing bulk grating transmission spectrometers struggle to achieve high-precision, uniform wavelength scanning, limiting their application in scenarios such as continuous spectral measurements or tunable monochromators.

[0032] like Figure 1 As shown, the present invention provides a catadioptric volumetric holographic grating transmission spectrometer, comprising: an incident module 1, a collimating lens 2, a broadband plane mirror 3, a volumetric holographic grating 4, an imaging lens 5, and a detector 6 arranged sequentially along the optical path; The incident module 1 serves as the light inlet of the spectrometer, limiting the light flux entering the spectrometer and the resolution of the obtained spectrum; The collimating lens 2 is used to convert the incident divergent beam into a parallel beam. The broadband plane mirror 3 and the volumetric holographic grating 4 are fixedly connected to form a grating assembly with an included angle of 90°; the broadband plane mirror 3 is used to redirect the parallel light output from the collimating lens 2 so that it is incident on the volumetric holographic grating 4 and dispersed; the volumetric holographic grating 4 is used to diffract the incident parallel light according to the wavelength and the corresponding exit angle, and the exit light of the same wavelength is parallel to each other. The optical axis of the imaging lens 5 is parallel to the optical axis of the collimating lens 2; When the grating assembly rotates synchronously around the same axis, the incident angle of the parallel beam entering the volumetric holographic grating 4 is changed so that the wavelength of the outgoing center beam is the Bragg wavelength corresponding to the incident angle, and the outgoing center beam of the grating assembly 4 is parallel to the incident beam, forming a Z-shaped optical path; wherein, the axis of rotation is located on the intersection line of the plane of the reflecting mirror and the central plane of the volumetric holographic grating, and is equidistant from the optical axis of the collimating lens 2 and the optical axis of the imaging lens 5; the central plane of the volumetric holographic grating 4 is always located on the angle bisector of the angle formed by the incident beam of the volumetric holographic grating and the outgoing center beam determined by the optical axis of the imaging lens 5; The imaging lens 5 is used to focus the parallel light containing different wavelengths emitted from the grating assembly to different positions on its focal plane and form a spectral image of the incident module on the detector 6. The detector 6 is located on the focal plane of the imaging lens, and converts the received light signal into an electrical signal to obtain the target spectrum.

[0033] The grating assembly, consisting of the broadband plane mirror 3 and the bulk holographic grating 4, is the core of this solution. The two are connected at a specific angle (typically 90°) via a rigid base, forming a single module. This module is mounted on a fixed, rotatable axis and can rotate perpendicular to the image plane around this axis. The bulk holographic grating 4, as the core dispersive element, utilizes its internal periodic refractive index modulation to diffract incident parallel light at wavelength-selective exit angles. It exhibits higher diffraction efficiency and narrower bandwidth, making it particularly suitable for high-resolution, high-sensitivity applications. The broadband plane mirror 3, rotating along with the grating assembly, can change the incident angle of the bulk holographic grating 4, ensuring that the grating's central plane remains constantly located on the angle bisector of the incident and exit central beams, with the wavelength of the exit central beam being the Bragg wavelength corresponding to the changed incident angle.

[0034] In the visible light band, imaging lens 5 can be a mature consumer-grade SLR camera lens to construct a spectrometer with a large relative aperture and high imaging quality. Detector 6 is located at the focal plane of imaging lens 5, such as a CCD or CMOS linear or area array detector, and is used to receive spectral signals.

[0035] Furthermore, when the grating assembly is rotated to change the grating incident angle, the position of the imaging lens 5 does not need to be changed. Figure 2 Let UC represent the angular relationship between the incident beam and the broadband plane mirror 3 and the bulk holographic grating 4 in the grating assembly. UC is the plane containing the broadband plane mirror 3, and VC is the position of the central plane of the bulk holographic grating 4. The two are perpendicular and intersect at point C, which is the location of the rotation axis 41. The parallel beam is incident from point S to point A of the broadband plane mirror 3, and then reflected to point B of the bulk holographic grating 4. Assume the angle between the incident beam SA and the broadband plane mirror is... Then the angle of incidence of the plane reflected beam AB onto the volume holographic grating VC is also... ,by The Bragg diffracted beam BT emitted at an angle is parallel to the incident beam SA. This occurs when the broadband plane mirror 3 and the bulk holographic grating 4 remain perpendicular, and are simultaneously rotated at a certain angle... Figure 2 The parallel light beam emitted from point S, as shown by the dashed line, is incident on mirror 3. The beam is reflected to point B' of the volumetric holographic grating 4. However, regardless of the angle at which the two beams rotate, the distance between the parallel beam SA and the horizontal line passing through point C remains constant. Remaining constant, according to geometric relationships, the length of AC is... Then the length of BC is That is Then the distance BQ between point B and the horizontal line passing through point C is That is Therefore, regardless of how the broadband plane mirror 3 and the volumetric holographic grating 4 rotate, the distance between the Bragg diffracted beam BT and the incident beam SA remains unchanged. Thus, with the imaging lens 5 in a fixed position, the beam can be received at the incident angle following the volumetric holographic grating 4. A diffracted beam with a varying Bragg wavelength as its center wavelength.

[0036] The relationship between the incident angle of the incident light of the grating component and the Bragg wavelength is: d(sinα+sinβ)=mλ, where α is the incident angle, β is the diffraction angle, β=α, and m=1.

[0037] For example, polychromatic light enters from the incident module 1, is collimated into parallel light by the collimating lens 2, and then enters the broadband plane mirror 3. After being reflected, the light enters the bulk holographic grating 4 on the same component at a specific Bragg angle, resulting in dispersion. The beam dispersed by the bulk holographic grating 4 is focused by the imaging lens 5, forming a spectral image of the incident slit on the detector 6. When it is necessary to change the central detection wavelength, the grating assembly can be manually adjusted to rotate around its axis to a suitable angle, thereby changing the incident angle of the bulk holographic grating 4 and thus changing the Bragg wavelength to adapt to high-resolution analysis of a specific Raman scattering spectrum range, or to change the wavelength range corresponding to different excitation wavelengths.

[0038] Optionally, the incident module can be an incident slit or an optical fiber interface. When the incident module is an incident slit, it is suitable for conventional spectral analysis; when the incident module is an optical fiber interface, it is particularly suitable for Raman spectroscopy analysis of hollow-core optical fibers with small numerical apertures for collecting light beams.

[0039] In this embodiment of the invention, a broadband plane mirror and a bulk holographic grating are combined to form a grating assembly that can rotate synchronously around a fixed axis. Within the grating assembly, the central plane of the bulk holographic grating is always located on the angle bisector of the angle between the incident beam and the outgoing central beam. By rotating the grating assembly to change the incident angle of the parallel light entering the bulk holographic grating, the wavelength of the outgoing central beam can be made to match the Bragg wavelength corresponding to the incident angle. Simultaneously, the outgoing central beam is parallel to the incident beam, thus allowing for flexible adjustment of the Bragg wavelength and spectral detection range. This solves the problem in existing solutions where the bulk holographic grating is fixed, difficult to adjust, and unsuitable for different wavelengths of laser light. It reduces the angular accuracy requirements and adjustment difficulty during spectrometer fabrication. Furthermore, by constructing a catadioptric optical system using the grating assembly, the traditional V-shaped or L-shaped optical path is transformed into a Z-shaped optical path, with the collimating lens and imaging lens axes parallel, reducing the lateral size of the spectrometer and facilitating integration and portability.

[0040] Example 2 Based on the above embodiments, such as Figure 3 As shown, optionally, the grating assembly further includes a sine wave driver; The sine driver is used to drive the grating assembly to rotate around the rotating shaft at a preset speed, so that the incident angle of the grating assembly changes uniformly in a sinusoidal form, thereby realizing the electronically controlled adjustment and uniform scanning of the Bragg wavelength.

[0041] Optionally, the sine drive includes a motor 45, a lead screw 44, a slider 43, and a sine bar 42 connected in sequence; The motor 45 serves as a power source to drive the lead screw 44 to move in the horizontal direction; The slider 43 is provided with a guide groove, and the slider 43 is used to move on a preset horizontal guide rail under the drive of the lead screw 44; One end of the sine bar 42 is connected to one end of the rotating shaft 41, and the other end of the sine bar 42 is disposed in the guide groove, which is used to slide in the vertical direction under the action of the slider 43 to drive the rotating shaft 41 to rotate.

[0042] Furthermore, optionally, the detector is one of a unit detector, a linear array detector, or a surface array detector for the front exit slit.

[0043] When this spectrometer is to be used for spectral analysis or monochromatic applications at a specific wavelength, the fixed array detector 6 should be removed, the unit detector of the front exit slit should be placed on the imaging surface, and the grating assembly should be driven to rotate around the axis using a sine driver.

[0044] Motor 45 is the power source of the entire drive system. It receives commands from the controller and outputs controllable uniform linear motion, serving as the starting point for automated scanning. Slider 43 is constrained to the guide rail and can only perform precise left and right horizontal linear movements. Its guide groove provides a sliding fulcrum for the end of the sine bar 42. The sine bar 42 achieves a sinusoidal conversion from linear to rotational motion. One end (point C) is fixed to the grating assembly shaft 41, while the other end is freely placed in the vertical guide groove of slider 43. The left and right movement of slider 43 pushes or pulls one end of the sine bar 42 to slide within the guide groove. Due to the fixed length of the bar, the linear displacement of the slider (i.e.,...) Figure 3 The length of CE will drive the sine bar 42 to rotate the grating assembly around the axis 41, and its geometric relationship follows: ,in, The effective length of the sine bar. The angle between the sine bar and the vertical direction is also the Bragg angle of the grating, thus ensuring that the slider displacement is proportional to the sine value of the Bragg angle.

[0045] In the grating equation, the wavelength is also related to... The wavelength is directly proportional to the slider displacement, thus achieving a linear relationship between the slider displacement and the wavelength, which is the key to achieving uniform wavelength scanning.

[0046] The rotation axis 41 is the common rotation axis of the broadband plane mirror 3 of the grating assembly and the bulk holographic grating 4. It is connected to both the grating assembly and the sine bar 42, and its rotation angle is controlled by the sine bar. The grating assembly can rotate about this rotation axis 41 perpendicular to the paper surface and change the Bragg wavelength of the bulk holographic grating 4, thereby changing the center wavelength of the spectrometer.

[0047] This embodiment can replace the manual rotation in Embodiment 1, transforming the uniform linear motion of the motor screw of the sine drive into a uniform change of the sine angle of the grating incident angle, thereby realizing the electronic control adjustment and uniform scanning of the Bragg wavelength. When the detector 6 is set as a unit detector with a front slit, the detector 6 will receive the light radiation corresponding to the Bragg wavelength, and the Bragg wavelength will change linearly with time, thereby realizing the linear scanning function of the monochromator.

[0048] In this embodiment of the invention, the grating assembly is rotated by a sine driver, which transforms the uniform linear motion driven by the sine driver motor into a uniform change of the incident angle of the planar diffraction grating. This enables the electronic control setting and uniform scanning of the Bragg wavelength of the spectrometer, allowing it to be used as a spectrometer with a fixed wavelength band or as a monochromator through continuous scanning, thus expanding the application range of the instrument.

[0049] Example 3 like Figure 4The image shows a top view of a specific implementation structure of a refracting volumetric holographic grating transmission spectrometer. The spectrometer includes an incident module 1, a collimating lens 2, a broadband plane mirror 3, a volumetric holographic grating 4, an imaging lens 5, a detector 6, a front mounting plate 72, a rear mounting plate 71, a metal connecting rod 8, a base plate 9, and angle adjustment lines 91.

[0050] In this embodiment, the incident module 1 is an incident slit, specifically an SMA905 fiber optic interface with a slit width of 10. Its function is to confine the incident light and form a linear light source for the spectrometer; its width directly affects the resolution of the spectrometer.

[0051] Collimating lens 2 is a 25 mm focal length, F# 1.8 C-thread camera lens that can be directly screwed onto the front mounting plate 72. Collimating lens 2 is located behind the entrance slit 1 and collimates the diverging beam emitted from the entrance slit 1 into a parallel beam.

[0052] The broadband plane mirror 3 is a dielectric film mirror with a diameter of 35 mm, which can provide a reflectivity of >98% in the 400~750 nm (0 - 45°) band. The broadband plane mirror 3 is located behind the collimating lens 2, and deflects the parallel light beam from the collimating lens 2 at a certain angle so that it is incident on the bulk holographic grating 4.

[0053] The bulk holographic grating 4 is the core dispersive element in this embodiment. It, along with the broadband plane mirror 3, forms a grating assembly. The two are connected at 90° via a rigid base and mounted on a rotating axis. The grating can rotate perpendicularly to the base plate 9 around this axis, synchronously changing the angles of the grating and the mirror, thereby systematically altering the system's operating wavelength range. A bulk holographic grating is a grating with a periodic structure etched inside a transparent medium. It possesses advantages such as high diffraction efficiency, low polarization sensitivity, and a high laser damage threshold. Its function is to spatially disperse incident polychromatic parallel light according to different wavelengths. In this embodiment, a square bulk holographic grating with a side length of 25.4 mm is selected (a circular grating can also be used).

[0054] The imaging lens 5 is a 35 mm focal length, F# 1.4 C-thread mount camera lens, which can be directly mounted on the rear mounting plate 71 via threads to receive the light beam dispersed by the volumetric holographic grating 4. Its function is to converge parallel light of different wavelengths to different positions on its focal plane to form a series of slit images.

[0055] Detector 6 is a self-assembling area array sensor, using a Hamamatsu S16011-1006 TEC-cooled CCD chip with a pixel size of 14. The photosensitive surface of detector 6 is mounted on the focal plane of imaging lens 5 to receive the converged spectral signal, convert it into an electrical signal, and then process it through subsequent circuitry to obtain a spectral image.

[0056] The front mounting plate 72 and the rear mounting plate 71 are vertically fixed to the base plate 9 for precise mounting and fixing of various optical components. The front mounting plate 72 is provided with threaded holes for connecting and fixing the entrance slit 1 and the collimating lens 2, and the rear mounting plate 71 is also provided with threaded holes for connecting and fixing the imaging lens 5 and the detector 6.

[0057] Metal rod 8 consists of four Invar steel rods with low thermal expansion coefficients, which pass through and connect the front and rear mounting plates 72 and 71 and other main support structures. Its main function is to provide strong axial tension force, forming a high-rigidity spatial frame together with the base plate 9, improving the bending and torsional resistance of the entire module, and ensuring that the relative positions of the optical elements remain stable under mechanical vibration.

[0058] The base plate 9 serves as the mechanical reference and mounting foundation for the entire spectrometer module. All core support structures and some optical components are directly or indirectly fixed on it. It is made of rigid materials to ensure the flatness and stability of the overall structure.

[0059] The angle adjustment scale 91 is a scale machined on the base plate 9 for angle adjustment. During assembly and calibration, it is used to adjust the rotation angle of the grating assembly around the axis 41 to achieve the required incident angle, suitable for high-resolution analysis of a specific Raman scattering spectrum range. After adjustment, the base can be fixed in place by tightening the set screws.

[0060] Furthermore, the selection of the broadband plane mirror 3 needs to consider the applicable spectral analysis band and the size of the light spot after collimation by the collimating lens 3. In the visible light band, a dielectric film mirror or a protective aluminum film mirror can be selected, which can typically provide >98% reflectivity in the 400~750 nm band. The size of the light spot after collimation by the collimating lens 2 is also considered. At Bragg's Corner At an angle of 36.5°, the size of the parallel beam incident on the broadband plane mirror is: The diameter is 23.2 mm. The 35 mm diameter reflector 3 selected in this embodiment is suitable for a camera lens with a focal length of 25 mm and an F# 1.8, and meets the spectral analysis requirements in the visible light band.

[0061] Furthermore, the selection of the bulk holographic grating 4 also needs to consider the size of the light spot incident on the grating. In this embodiment, the beam with a diameter of 13.8 mm reflected by the mirror 3 is at a Bragg angle. If a beam of light is incident on a grating at an angle of 36.5°, then the size of the beam on the grating plane is... The side length is 17.2 mm. The 25.4 mm volume holographic grating selected in this embodiment can completely receive the incident light beam without causing any loss of light energy.

[0062] Furthermore, to achieve good resolution, the size of the image formed by the entrance slit 1 on the detector 6 should be consistent with the pixel size. In this embodiment, the collimating lens 2 has a focal length of 25 mm, the imaging lens has a focal length of 35 mm, and the imaging magnification ratio is 1.4. For 10 The slit width has an image size of 14. It is exactly the pixel size of the detector, which meets the usage requirements.

[0063] This embodiment of a catadioptric bulk holographic grating transmission spectrometer achieves compactness and integration by folding the optical path within a limited space while maintaining core functionality. This reduces the overall size of the instrument, making it easy to carry, move, and deploy, and suitable for various scenarios where device size is limited. However, due to the limitations on detector size in the compact optical layout, the spectrometer's sensitivity is relatively low. Therefore, this system is more suitable for applications with lower sensitivity requirements (such as Raman detection of various condensed matter samples) but higher demands for instrument portability, integration, and environmental adaptability.

[0064] Example 4 Based on the above embodiments, optionally, the incident module adopts an optical fiber interface, the optical fiber interface is a multimode optical fiber, the collimating lens adopts an achromatic lens, and the spectrometer is used for hollow fiber gas Raman analysis.

[0065] To be suitable for spectral analysis of incident beams with small numerical apertures, especially for Raman analysis of gases in hollow fiber optics, Figure 5 This is a top view of a specific implementation structure of a catadioptric volume holographic grating transmission spectrometer with an achromatic collimating lens.

[0066] The spectrometer includes an incident module 1, an F-mount 21, a collimating lens 2, a broadband plane mirror 3, a volumetric holographic grating 4, an imaging lens 5, a detector 6, a front mounting plate 72, a rear mounting plate 71, a metal connecting rod 8, a base plate 9, and angle adjustment lines 91.

[0067] The incident module 1 is a simple SMA905 fiber optic interface, without any slit components. Its function is to fix the multimode fiber with an SMA905 connector that transmits the light radiation to be detected (input beam). In this embodiment, the fiber optic interface is directly connected to a 25mm core diameter fiber. A small-diameter multimode fiber with a numerical aperture of NA 0.1 is used. The diameter of the multimode fiber replaces the slit width, which controls the incident light radiation width at the focal plane of the collimating lens 2.

[0068] F-mount mount 21 provides the option for collimating lens 2 to retain an F-mount lens and is used to fix the collimating lens.

[0069] For the specific application of gas Raman analysis in hollow fiber optics, the collimating lens 2 is an achromatic lens with a focal length of 100 mm, which is directly fixed to the front mounting plate 72 via an SM1 threaded lens barrel, collimating the divergent beam emitted from the entrance port 1 into a parallel beam.

[0070] The broadband plane mirror 3 is a 75 mm diameter dielectric-coated silver mirror, which provides >98% reflectivity in the 450~10000 nm wavelength range and is suitable for Raman scattering corresponding to excitation wavelengths of 532 nm and longer. The broadband plane mirror 3 is located behind the collimating lens 2, deflecting the parallel light beam from the collimating lens 2 at a certain angle so that it is incident on the bulk holographic grating 4.

[0071] The bulk holographic grating 4 and the broadband planar reflector 3 together form a grating assembly. They are connected at 90° via a rigid base and mounted on a rotating axis, allowing rotation about this axis perpendicular to the base plate 9. This synchronously changes the angles of the grating and the reflector, thereby systematically altering the system's operating wavelength range. In this embodiment, a bulk holographic grating with a diameter of 50.8 mm is selected.

[0072] The imaging lens 5 is a Nikkor camera lens with a focal length of 85 mm and an f# 1.4. It receives the light beam after dispersion by the volume holographic grating 4 and focuses parallel light of different wavelengths to different positions on its focal plane.

[0073] Detector 6 is an area array detector, specifically a Princeton Instruments PIXIS-100B camera with a pixel size of 20. The photosensitive surface of detector 6 is mounted on the focal plane of imaging lens 5 to receive the converged spectral signal, convert it into an electrical signal, and then process it through subsequent circuitry to obtain a spectral image.

[0074] The front and rear mounting plates 72 and 71 are vertically fixed to the base plate 9 for precise installation and fixation of various optical components. The front mounting plate has an SM1 threaded hole and an F bayonet 21 for connecting and fixing the entrance port 1 and the collimating lens 2. The rear mounting plate 71 has a threaded hole for connecting and fixing the imaging lens 5 and the detector 6.

[0075] Metal rod 8 consists of four Invar steel rods that pass through and connect the front mounting plate 72, the rear mounting plate 71, and other main support structures. Its main function is to provide strong axial tension force, forming a high-rigidity spatial frame together with the base plate 9, improving the bending and torsional resistance of the entire module, and ensuring that the relative positions of the optical elements remain stable under mechanical vibration.

[0076] The base plate 9 serves as the mechanical reference and mounting foundation for the entire spectrometer module. All core support structures and some optical components are directly or indirectly fixed on it. It is made of rigid materials to ensure the flatness and stability of the overall structure.

[0077] The angle adjustment scale 91 is a scale machined on the base plate 9 for angle adjustment. During assembly and calibration, it is used to adjust the rotation angle of the grating assembly around the axis 41 to achieve the required incident angle, suitable for high-resolution analysis of a specific Raman scattering spectrum range. After adjustment, the base can be fixed in place by tightening the set screws.

[0078] The catadioptric bulk holographic grating transmission spectrometer constructed in this embodiment is larger in size than the spectral structure in Embodiment 2, but simultaneously achieves higher sensitivity and higher spectral resolution. In application, it can meet the analytical requirements of small aperture, low light flux signals, especially in the detection of trace gas Raman spectroscopy in hollow fiber optics, where its ability to detect trace gas components and resolve spectral details is significantly improved. Although some portability is sacrificed, this embodiment provides a solution for high-sensitivity, high-precision spectral analysis.

[0079] Example 5 Based on the above embodiments, a spectrometer equipped with a 2400 g / mm bulk holographic grating was used to detect the neon lamp spectrum.

[0080] First, the spectral range to be measured needs to be confirmed. For example, if the emission spectrum of a Ne lamp with a center wavelength around 496 nm needs to be measured (e.g.,...),... Figure 6 As shown, the grating assembly needs to be rotated beforehand, and the Bragg angle of the bulk holographic grating should be set to the optimal angle of 36.5° corresponding to this wavelength according to the diffraction efficiency curve of the bulk holographic grating. At this time, the component acts as a whole, and the reflecting mirror reflects the collimated beam to the bulk holographic grating, and the grating has the highest diffraction efficiency for wavelengths around 496nm.

[0081] Polychromatic light emitted by the Ne lamp enters the spectrometer through the entrance slit and is collimated into parallel light by the collimating lens. The parallel light is incident on the plane reflector 3 and, after reflection, is directed towards the volumetric holographic grating 4. The volumetric holographic grating 4 disperses the incident parallel polychromatic light, which then enters the imaging lens. The imaging lens converges parallel light from different angles to different positions on the focal plane, thus unfolding the image of the entrance slit in wavelength order to form a sequentially changing spectral band. The detector's photosensitive surface is precisely located on this focal plane, and each pixel on it receives a light intensity signal of a specific wavelength and converts it into an electrical signal.

[0082] When it is necessary to measure another wavelength band, such as the Ne lamp spectral line with a center wavelength around 638 nm (e.g.) Figure 7 When (as shown), the grating assembly needs to be rotated to simultaneously change the angle of the mirror and the incident angle of the bulk holographic grating. The Bragg condition of the grating changes accordingly, shifting its high diffraction efficiency band (i.e., the center wavelength of the spectrometer) from around 496 nm to around 638 nm, corresponding to a Bragg angle of 50.0°. The optical path structure itself remains unchanged, but the response band of the spectrometer shifts. Re-acquiring data yields the desired results. Figure 7 The spectrum shown is illustrated. If a sine wave driver is used to drive the grating assembly consisting of a broadband plane mirror 3 and a bulk holographic grating 4, the detector can continuously acquire the spectrum, and its center wavelength will change linearly with time.

[0083] Figure 6 (Bragg's angle) =36.5°, center wavelength is 496 nm;) and Figure 7 (Bragg's angle) =50.0°, center wavelength 638 nm) demonstrates that a wide range of continuous tuning of the spectrometer's operating wavelength band can be achieved through the rotating grating assembly. The range exceeds 140 nm from 496 nm to 638 nm, exhibiting a certain wavelength tuning capability. The characteristic spectral lines of the two spectra are well separated, indicating that the Z-shaped reflective optical path design of this invention has good aberration control. The imaging lens can image the dispersed light, and the spectrometer possesses high spectral resolution. The optical path remains aligned after rotational adjustment, ensuring the accuracy and reliability of wavelength readings.

[0084] The catadioptric bulk holographic grating transmission spectrometer described in this invention not only achieves miniaturization of the spectrometer structure through a Z-shaped optical path, but also realizes the core wavelength tuning function through a rotatable grating assembly. Experimental Ne lamp spectra demonstrate the feasibility of this design, achieving a wavelength tuning range exceeding 140 nm while maintaining excellent spectral resolution, wavelength accuracy, and system stability within this range. This fully meets the design goals of a compact, multifunctional spectrometer.

[0085] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A refracting-type bulk holographic grating transmission spectrometer, characterized in that, include: The incident module, collimating lens, broadband plane mirror, volume holographic grating, imaging lens and detector are arranged sequentially along the optical path; The incident module serves as the light inlet of the spectrometer, used to limit the light flux entering the spectrometer and to obtain the resolution of the spectrum; The collimating lens is used to convert the incident divergent beam into a parallel beam. The broadband plane mirror and the volumetric holographic grating are fixedly connected to form a grating assembly with an included angle of 90°; the broadband plane mirror is used to redirect the parallel light output from the collimating lens so that it is incident on the volumetric holographic grating and dispersed; the volumetric holographic grating is used to diffract the incident parallel light according to the wavelength and the corresponding exit angle, and the exit light of the same wavelength is parallel to each other. The optical axis of the imaging lens is parallel to the optical axis of the collimating lens; When the grating assembly rotates synchronously around the same axis, the incident angle of the parallel beam entering the volumetric holographic grating is changed so that the wavelength of the outgoing center beam is the Bragg wavelength corresponding to the incident angle, and the outgoing center beam of the grating assembly is parallel to the incident beam, forming a Z-shaped optical path; wherein, the axis of rotation is located on the intersection line of the plane of the reflecting mirror and the central plane of the volumetric holographic grating, and is equidistant from the optical axis of the collimating lens and the optical axis of the imaging lens; the central plane of the volumetric holographic grating is always located on the angle bisector of the angle formed by the incident beam of the volumetric holographic grating and the outgoing center beam determined by the optical axis of the imaging lens; The imaging lens is used to focus the parallel light containing different wavelengths emitted from the grating assembly to different positions on its focal plane and form a spectral image of the incident module on the detector. The detector is located on the focal plane of the imaging lens and converts the received light signal into an electrical signal to obtain the target spectrum.

2. The spectrometer as described in claim 1, characterized in that, The incident module is an incident slit or an optical fiber interface.

3. The spectrometer as described in claim 1, characterized in that, The relationship between the incident angle of the incident light of the grating assembly and the Bragg wavelength is: d(sinα+sinβ)=mλ, where α is the incident angle, β is the diffraction angle, β=α, and m=1.

4. The spectrometer as described in claim 1, characterized in that, The grating assembly also includes a sine wave driver; The sine driver is used to drive the grating assembly to rotate around the rotating shaft at a preset speed, so that the incident angle of the grating assembly changes uniformly in a sinusoidal form, thereby realizing the electronically controlled adjustment and uniform scanning of the Bragg wavelength.

5. The spectrometer as described in claim 4, characterized in that, The sine drive includes a motor, a lead screw, a slider, and a sine bar connected in sequence; The motor serves as a power source to drive the lead screw to move in the horizontal direction; The slider is provided with a guide groove, and the slider is used to move on a preset horizontal guide rail under the drive of the lead screw; One end of the sine bar is connected to one end of the rotating shaft, and the other end of the sine bar is disposed in the guide groove, which is used to slide vertically under the action of the slider to drive the rotating shaft to rotate.

6. The spectrometer as described in claim 1, characterized in that, The detector is one of the following: a unit detector, a linear array detector, or a surface array detector for the front exit slit.

7. The spectrometer as described in claim 2, characterized in that, The incident module uses an optical fiber interface, which is a multimode optical fiber, and the collimating lens uses an achromatic lens.

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