Multi-grating space notch filtering spectrometer

Abstract

The invention belongs to the field of plasma physics and spectroscopy diagnosis, and relates to a multi-grating space notch filtering spectrometer which comprises a slit, a semi-reflecting and semi-transmitting mirror, a lens, gratings, a notch reflector, a displacement platform, a total reflector and a detector. The gap width is adjusted through the displacement platform, continuous adjustment of the notch filtering range can be achieved, a user can freely select to filter out a single wavelength or a section of spectrum, and the device is suitable for different application scenes. The gap position accurately corresponds to the spectral space distribution after light splitting, and the filtering pertinence is very strong. Compared with a three-grating spectrometer, only two three-gratings are needed, the gratings are high-cost elements, the manufacturing cost is lower, meanwhile, the beam combining precision can be kept, and the three-grating spectrometer is compact in structure, small in size and easy to build. According to the multi-grating space notch filtering spectrometer, interference signals are accurately filtered out, the detector only receives effective spectrums, the signal-to-noise ratio is remarkably increased, and the multi-grating space notch filtering spectrometer is very beneficial to the field of weak signal detection.

Description

Technical Field

[0001] The invention belongs to the field of plasma physics and spectroscopy diagnosis, and relates to a multi-grating spatial notch filter spectrometer. Background Art

[0002] Laser Thomson scattering (LTS) is widely recognized as one of the most accurate plasma diagnostic methods. It offers numerous advantages, including non-invasiveness, high spatial and temporal resolution, and independence from the plasma's thermal equilibrium state. LTS has been widely used to diagnose plasmas generated by various discharge methods. However, one challenge facing LTS is reducing the impact of central wavelength stray light on the LTS signal. Therefore, filtering out central wavelength stray light is a crucial component of Thomson scattering.

[0003] Because the filter's bandwidth is too wide and would filter out Thomson scattering signals, it is not used in Thomson scattering diagnostics. Spatial notch filtering can be achieved using a conventional single-grating spectrometer with a wire barrier structure, but it cannot effectively separate the broadened light of the target band from the non-stray signal, resulting in the potential for effective information to be obscured or interfered with by stray signals. While triple-grating spectrometers can also achieve spatial notching, they also suffer from complex structures, large size, and poor practicality.

[0004] Based on the above reasons, developing a suitable filtering technology is an important way to improve the accuracy of laser Thomson scattering diagnosis. Summary of the Invention

[0005] The present invention aims to provide a multi-grating spatial notch filtering spectrometer method. This method addresses existing Thomson scattering techniques, which suffer from poor filtering of central stray light signals, low Thomson scattering spectrum accuracy, and complex spectrometer structures and bulk, making them difficult to operate in confined spaces. Based on a dual-grating structure, the present invention performs wavelength-specific filtering and spectral analysis on the Thomson scattering signal, thereby obtaining a more accurate Thomson scattering signal that can also be used for spectroscopy analysis requiring filtering.

[0006] The technical solution of the present invention:

[0007] A multi-grating spatial notch filter spectrometer, comprising a slit, a half-reflective half-mirror, a lens, a grating, a notch reflector, a displacement platform, a total reflection mirror and a detector;

[0008] The slit is used to adjust the width of the incident light, with the width ranging from 0 microns to 400 microns;

[0009] The semi-reflective half-mirror has a surface perpendicular to the horizontal plane and a normal line that forms a 45° angle with the incident light, and is used to transmit the light signal emitted through the slit and reflect the filtered light signal;

[0010] The lens comprises a first lens, a second lens, a third lens and a fourth lens; wherein the first lens is located between the half-reflecting half-mirror and the first grating, and is used to direct the light signal emitted from the half-reflecting half-mirror to be parallel to the first grating; the optical axis direction of the first lens is parallel to the horizontal plane; the second lens is located between the first grating and the notch reflector, and is used to focus the light beam from the first grating onto the notch reflector; the optical axis of the second lens is parallel to the horizontal plane, and the angle formed with the direction of the incident light is in the range of 0° to 90°; the third lens is located between the total reflection mirror and the second grating, and is used to collimate the filtered light signal reflected by the total reflection mirror onto the second grating; the optical axis direction of the third lens is parallel to the horizontal plane; the fourth lens is located between the second grating and the detector, and is used to focus the light beam from the second grating onto the detector; the optical axis of the fourth lens is parallel to the horizontal plane, and the angle formed with the incident light is in the range of 0° to 90°.

[0011] The grating includes a first grating and a second grating, and is used to split light to generate a spectrum and combine the split spectrum; wherein the angle between the normal direction of the first grating and the optical axis direction of the first lens is in the range of -90° to 90°; the angle between the normal direction of the second grating and the optical axis direction of the third lens is in the range of 90° to -90°;

[0012] The notch reflector is mounted on a displacement platform and includes two plane mirrors. A gap is left between the two plane mirrors. The gap is adjusted by the displacement platform, so that the light signal at the gap is not reflected, and the light at other positions is reflected back to the semi-reflective half-mirror by the original path. The notch reflector is used to filter the light beam from the second lens and reflect the unfiltered portion back to the original path, passing through the second lens, the first grating, the first lens, and the semi-reflective half-mirror in sequence. Due to the reversible optical path, the unfiltered light is recombined to cancel the dispersion, but does not include the signal filtered at the notch reflector, thereby achieving the filtering function of the specific wavelength signal. The optical axis direction of the notch reflector completely coincides with the optical axis direction of the second lens.

[0013] The total reflection mirror is used to adjust the optical path of the light beam reflected from the half-reflecting half-mirror, that is, the light after filtering and beam combining, and the angle between its normal direction and the normal direction of the half-reflecting half-mirror is in the range of 45° to 90°.

[0014] The detector is used to detect the filtered spectral signal. The optical path of the subsequent filtered signal is as follows: the filter reflector reflects the dispersed light to the second lens. Since the optical path is reversible, the light is collimated by the second lens. After passing through the first grating, the previous dispersion is canceled and the dispersed light is combined. The combined light is refocused by the first lens and reaches the half-reflecting half-mirror lens; then the light path is adjusted by the total reflection mirror to reach the third lens, dispersed again by the second grating, focused by the fourth lens, and finally imaged on the detector.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] By adjusting the slit width through the displacement platform, the notch filter range can be continuously adjusted. Users can freely choose to filter out a single wavelength (narrow slit) or a spectrum (wide slit) to adapt to different application scenarios (such as laser line filtering or broadband background noise suppression).

[0017] The position of the slits precisely corresponds to the spatial distribution of the spectrum after splitting, and the filtering is highly targeted.

[0018] Compared with a three-grating spectrometer, the present invention only requires two three-gratings. Gratings are high-cost components and have lower manufacturing costs while maintaining beam combining accuracy. In addition, the present invention has a compact structure, a small size, and is easy to build.

[0019] By accurately filtering out interference signals, the detector only receives the effective spectrum, significantly improving the signal-to-noise ratio, which is very beneficial in the field of weak signal detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the optical system structure.

[0021] In the figure: 1. Slit; 2. Half-reflecting half-mirror; 3. First lens; 4. First grating; 5. Second lens; 6. Notch mirror; 7. Displacement platform; 8. Total reflection mirror; 9. Third lens; 10. Second grating; 11. Fourth lens; 12. Detector. DETAILED DESCRIPTION

[0022] The specific implementation of the present invention is described below in conjunction with the accompanying drawings and technical solutions.

[0023] A multi-grating spatial notch filter spectrometer performs spectral filtering, comprising:

[0024] Example 1:

[0025] (1) Incident light control: The slit width is adjusted to 60 microns to control the width and flux of the incident light. The surface of the semi-reflective and semi-mirror lens is adjusted to be perpendicular to the horizontal plane, and the optical axis direction forms a 45° angle with the incident light. The ratio of transmitted light to reflected light is 1:1.

[0026] (2) Primary Collimation and Spectroscopy: Adjust the first lens (focal length 75 mm). The first lens acts as a collimating lens, converting the transmitted light from the half-reflecting half-mirror lens into parallel light, which is then irradiated onto the first grating (line density 1800 Gr / mm). The line direction of the first grating is perpendicular to the horizontal plane, and the grating normal forms a 45° angle with the incident light. After grating spectroscopic analysis, the light reaches the second lens. The optical axis of the second lens forms a 30° angle with the incident light from the slit. The second lens acts as a focusing lens, with the focus on the reflector plane. The distance between the filter reflector and the second lens is 75 mm.

[0027] (3) Filter adjustment: Adjust the gap in the middle of the filter reflector until the appropriate filter width is reached. The filtered light beam is reflected back to the half-reflecting half-mirror mirror along the original path, and passes through the second lens, the first grating, the first lens and the half-reflecting half-mirror mirror in sequence. The second lens and the first lens serve as the collimating lens and the focusing lens respectively.

[0028] (4) Secondary optical path guidance: The filtered signal reflected by the half-reflecting half-mirror reaches the total reflector, which is at an angle of 120° to the horizontal plane. The third lens acts as a collimating lens with a focal length of 75 mm, which directs the filtered light signal parallel to the second grating. The second grating (line density 1800 Gr / mm) has lines perpendicular to the horizontal plane, and the grating normal forms a 45° angle with the optical axis of the third lens. After the second grating splits the light, the signal is focused on the detector by the fourth lens. The focal length of the fourth lens is 75 mm, and its optical axis forms a 30° angle with the optical axis of the third lens. After computer processing, the filtered spectrum is formed.

[0029] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A multi-grating spatial notch filter spectrometer, characterized in that: The multi-grating spatial notch filter spectrometer comprises a slit, a half-reflective half-mirror, a lens, a grating, a notch reflector, a displacement platform, a total reflection mirror and a detector; The slit is used to adjust the width of the incident light; The half-reflecting half-mirror is used for transmitting the light signal emitted through the slit and reflecting the filtered light signal; The lens comprises a first lens, a second lens, a third lens and a fourth lens; wherein the first lens is located between the half-reflecting half-mirror and the first grating, and is used to parallelize the light signal emitted from the half-reflecting half-mirror to the first grating; the second lens is located between the first grating and the notch reflector, and is used to focus the light beam from the first grating on the notch reflector; the third lens is located between the total reflection mirror and the second grating, and is used to collimate the filtered light signal reflected by the total reflection mirror onto the second grating; the fourth lens is located between the second grating and the detector, and is used to focus the light beam from the second grating on the detector; The grating includes a first grating and a second grating, and is used to split light to generate a spectrum and combine the split spectrum; The notch reflector is arranged on a displacement platform and includes two plane mirrors; a gap is left between the two plane mirrors, and the gap is adjusted by the displacement platform. The light signal at the gap is not reflected, and the light at other positions is reflected back to the half-reflecting half-mirror by the original path; the notch reflector is used to filter the light beam from the second lens and reflect the unfiltered portion along the original path, passing through the second lens, the first grating, the first lens, and the half-reflecting half-mirror in sequence; The total reflection mirror is used to adjust the optical path of the light beam reflected from the half-reflecting half-mirror, that is, the light after filtering and beam combining; The detector is used to detect the filtered spectral signal. The optical path of the subsequent filtered signal is as follows: the filter reflector reflects the dispersed light to the second lens. Since the optical path is reversible, the light is collimated by the second lens. After passing through the first grating, the previous dispersion is canceled and the dispersed light is combined. The combined light is refocused by the first lens and reaches the half-reflecting half-mirror lens; then the light path is adjusted by the total reflection mirror to reach the third lens, dispersed again by the second grating, focused by the fourth lens, and finally imaged on the detector.

2. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The width of the slit ranges from 0 micrometers to 400 micrometers.

3. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The surface of the semi-reflective and semi-mirror lens is perpendicular to the horizontal plane, and the normal line forms an angle of 45° with the incident light.

4. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The optical axis of the first lens is parallel to the horizontal plane; the optical axis of the second lens is parallel to the horizontal plane, and the angle between the second lens and the incident light direction is in the range of 0° to 90°; the optical axis of the third lens is parallel to the horizontal plane; the optical axis of the fourth lens is parallel to the horizontal plane, and the angle between the second lens and the incident light direction is in the range of 0° to 90°.

5. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The angle formed between the normal direction of the first grating and the optical axis direction of the first lens is in the range of -90° to 90°; the angle formed between the normal direction of the second grating and the optical axis direction of the third lens is in the range of 90° to -90°.

6. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The optical axis direction of the notch reflector completely coincides with the optical axis direction of the second lens.

7. The multi-grating spatial notch filter spectrometer according to claim 1, characterized in that: The angle between the normal direction of the total reflection mirror and the normal direction of the half-reflecting half-mirror lens is in the range of 45° to 90°.

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