Prism-type heterodyne spectrometer with fixed localization plane

Abstract

The present invention belongs to the technical field of spectrometers, and relates to a prism-type heterodyne spectrometer with a fixed localization plane, which solves the problem in the prior art of the position of the localization plane of interference fringes varying with wavelength in prism-type spatial heterodyne spectroscopy. The prism-type heterodyne spectrometer with a fixed localization plane of the present invention comprises a beam-splitting optical element, a first prism, a first reflective optical element, a first flat reflector, a first tuning rotating shaft, a second prism, a second reflective optical element, a second flat reflector, a second tuning rotating shaft, an imaging optical element and a first detector. The prism-type heterodyne spectrometer with a fixed localization plane constructs a spatial heterodyne structure by using a configuration of "prisms + reflective optical elements + flat reflectors", thereby fixing the localization plane of interference fringes. In addition, by means of rotating optical elements, the working spectral range of the instrument can be expanded, and spectral tunability is achieved, while the position of the localization plane remains unchanged.

Description

A prism-type heterodyne spectrometer with a fixed localization surface Technical Field

[0001] This invention belongs to the field of spectrometer technology, specifically relating to a prism-type heterodyne spectrometer with a fixed localization surface. Background Technology

[0002] A spectrum is a pattern formed by arranging polychromatic light according to its wavelength after dispersion. It can reflect various microscopic and macroscopic properties of atoms and molecules, such as energy levels and geometric structures, and reaction rates of specific chemical processes. Instruments designed to analyze spectra using the principles of dispersion or interference are called spectrometers.

[0003] Spatial heterodyne spectroscopy emerged in the 1970s. Compared to traditional interferometric spectrometers, it offers higher spectral resolution with the same number of detector sampling points, showing great promise. Spatial heterodyne spectrometers typically use gratings as dispersive elements for interference modulation. However, using gratings as dispersive elements presents several problems: First, gratings exhibit multi-order diffraction, resulting in energy being distributed across different orders. This not only reduces the energy of the interference beam but may also cause interference between different diffraction orders. Second, for tunable spatial heterodyne spectrometers based on blazed gratings, rotating the grating allows for tuning to achieve a wider spectral range. However, rotating the grating causes the incident angle to deviate from the blaze angle, reducing diffraction efficiency and limiting the instrument's spectral range. Third, compared to prisms, gratings are more prone to diffuse reflection, generating stray light.

[0004] Prism-type spatial heterodyne spectroscopy is a relatively new technology that has emerged in recent years. The spectral dispersive principle of a prism is based on the fact that its material has different refractive indices for different wavelengths, thus avoiding the problems caused by diffraction. Existing prism-type spatial heterodyne spectrometers generally adopt a "dispersive prism + reflecting mirror" configuration, similar to a Michelson interferometer, replacing the plane mirrors on the two arms with a dispersive prism and a plane reflecting mirror (or a reflective coating on the prism).

[0005] A problem with spatial heterodyne spectrometers using a "dispersion prism + mirror" configuration is that the position of the equivalent localization surface of the interference fringes changes with wavelength. For traditional grating-type spatial heterodyne spectrometers, since the beams from both arms only undergo diffraction once through the reflecting grating, the localization surface passes through the grating center, making it relatively straightforward. However, in the "dispersion prism + mirror" configuration, the beams from both arms pass through the dispersion prism both before and after reflection by the mirror, resulting in multiple refractions. Therefore, the position of the localization surface needs to be calculated, and the calculation results show that the position of the localization surface is a function of wavelength.

[0006] To visualize interference fringes on the detector, a localization surface needs to be imaged onto the detector surface using a post-imaging system. When the light source is not an ideal point source, i.e., the incident light is partially spatially coherent, the sharpness of the interference fringes on the detector will decrease if the position of the localization surface at a certain wavelength deviates from the conjugate surface of the detector surface with respect to the post-imaging system. Therefore, the phenomenon of changing position of the localization surface reduces fringe sharpness and limits the detectable spectral range. Summary of the Invention

[0007] The purpose of this invention is to solve the problem of the interference fringe localization plane position changing with wavelength in existing prism-type spatial heterodyne spectroscopy. This invention provides a prism-type heterodyne spectrometer with a fixed localization plane, which uses a "prism + reflecting optical element + plane mirror" configuration to construct the spatial heterodyne, thus achieving a fixed interference fringe localization plane. Furthermore, rotating the optical element can increase the instrument's operating spectral range, enabling spectral tunability while maintaining the unchanged localization plane position.

[0008] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows.

[0009] The prism-type heterodyne spectrometer with a fixed localization surface of the present invention includes a beam-splitting optical element, a first prism, a first reflecting optical element, a first plane mirror, a first tuning axis, a second prism, a second reflecting optical element, a second plane mirror, a second tuning axis, a first imaging optical element, and a first detector.

[0010] The beam splitting optical element splits the incident beam into two arm beams, which are respectively incident on the first prism and the second prism located in the two arms, and the combined beams reflected back by the first plane mirror and the second plane mirror located in the two arms are incident on the first imaging optical element.

[0011] The first prism refracts the incident light at the exit surface to the first reflective optical element;

[0012] The first reflective optical element transmits the incident light to the first planar reflector after being reflected more than twice. The outgoing optical axis of the first reflective optical element is parallel to its incident optical axis, and there is an additional optical axis between the outgoing optical axis and the incident optical axis.

[0013] The first planar mirror reflects the incident light back to the beam-splitting optical element;

[0014] The first tuning shaft is fixedly connected to the first reflecting optical element and the first plane mirror and drives the first reflecting optical element and the first plane mirror to rotate;

[0015] The second prism refracts the incident light at the exit surface to the second reflective optical element;

[0016] The second reflective optical element transmits the incident light to the second plane mirror after being reflected more than twice. The outgoing optical axis of the second reflective optical element is parallel to its incident optical axis, and there is an additional optical axis between the outgoing optical axis and the incident optical axis.

[0017] The second plane mirror reflects the incident light to the beam-splitting optical element;

[0018] The second tuning shaft is fixedly connected to the second reflecting optical element and the second plane mirror and drives the second reflecting optical element and the second plane mirror to rotate; the first imaging optical element images the interference fringe localization surface onto the first detector;

[0019] The first detector is used to receive interferometric images.

[0020] Preferably, the beam-splitting optical element splits the incident beam into two arms of equal intensity.

[0021] Preferably, the beam-splitting optical element is a cubic beam splitter.

[0022] Preferably, it also includes a collimating optical element that collimates the incident beam.

[0023] Preferably, the first prism and the second prism are dispersive prisms.

[0024] Preferably, the first prism and the second prism are both right-angle prisms, and their incident surfaces are both right-angled surfaces. The incident surfaces of the first prism and the second prism are parallel to the exit surfaces of the reflected light and transmitted light of the beam-splitting optical element, respectively.

[0025] Preferably, the first reflective optical element includes two plane mirrors with a right angle between them. The edge connecting the two plane mirrors is perpendicular to the outgoing optical axis of the first prism and parallel to the side surface of the first prism. The first plane mirror is perpendicular to the plane formed by the incident optical axis and the outgoing optical axis of the first prism, and the angle formed between the first plane mirror and the incident optical axis of the first prism is equal to half the angle of rotation of the outgoing optical axis of the first prism relative to the incident optical axis.

[0026] Preferably, the angle required for the first reflective optical element to rotate during the tuning process is twice the angle required for the first planar reflector to rotate.

[0027] Preferably, the first tuning axis is located on the exit surface of the first prism and passes through the center of the exit surface, and is also located on the first plane mirror and passes through the center of the first plane mirror.

[0028] Preferably, the outgoing optical axes of the first and second planar reflectors are perpendicular to the surface of the beam-splitting optical element.

[0029] Preferably, the second reflective optical element includes two plane mirrors with a right angle between them. The edge connecting the two plane mirrors is perpendicular to the outgoing optical axis of the second prism and parallel to the side surface of the second prism. The second plane mirror is perpendicular to the plane formed by the incident optical axis and the outgoing optical axis of the second prism, and the angle formed between the second plane mirror and the incident optical axis of the second prism is equal to half the angle of rotation of the outgoing optical axis of the second prism relative to the incident optical axis.

[0030] Preferably, the angle required for the second reflective optical element to rotate during the tuning process is twice the angle required for the second plane mirror to rotate.

[0031] Preferably, the second tuning axis is located on the exit surface of the second prism and passes through the center of the exit surface, and is also located on the second plane mirror and passes through the center of the second plane mirror.

[0032] Preferably, the first imaging optical element is an imaging lens or an imaging lens group.

[0033] Preferably, it further includes a second imaging optical element and a second detector. The beam splitting optical element combines the two arm beams into two outgoing light paths. The first imaging optical element and the first detector are located on either outgoing light path, while the second imaging optical element and the second detector are located on the other outgoing light path. The second imaging optical element images the interference fringe localization surface onto the second detector, which is used to receive the interference image.

[0034] The principle of this invention is as follows: when the wavelength of the incident light is equal to the tuned blaze wavelength, the wavefronts of the two outgoing beams are perpendicular to the optical axis, and no interference fringes are generated; when the wavelength of the incident light is not equal to the tuned blaze wavelength, the two beams are deflected by the same angle in opposite directions relative to the optical axis, which is equivalent to interference occurring on the localization surface. The distance from the localization surface to the rear first imaging optical element is equal to the length of the optical axis from the refractive surface of the prism to the rear first imaging optical element, and the length of this optical axis will not change regardless of the tuned blaze wavelength or the wavelength of the incident light. This solves the problem of the interference fringe localization surface position changing with wavelength in current prism-type spatial heterodyne spectroscopy, thus improving fringe contrast and increasing the working spectral range.

[0035] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0036] Compared to grating-type spatial heterodyne spectrometers, the prism-type heterodyne spectrometer with a fixed localization surface of the present invention avoids problems such as multi-level diffraction of gratings and the tendency of gratings to generate stray light through diffuse reflection, and can achieve a higher signal-to-noise ratio.

[0037] Compared to existing prism-type spatial heterodyne spectrometers, the prism-type heterodyne spectrometer with fixed localization surface of the present invention solves the problem that the position of the localization surface of the interference fringes changes with wavelength in existing prism-type spatial heterodyne spectrometers, and realizes the fixation of the localization surface of the interference fringes.

[0038] When the light source is not an ideal point source, i.e. the incident light is partially spatially coherent, the prism-type heterodyne spectrometer with a fixed localization surface of the present invention can improve the clarity of the interference fringes received by the detector and increase the spectral range.

[0039] In addition, the two beams emitted from the two arms of the prism-type heterodyne spectrometer with a fixed localization surface of the present invention are not backlights returning to the source direction after being combined by the beam-returning optical elements of the two arms. They can be received by two different detectors. The interferograms received by the two detectors can be processed by differential amplification, which is beneficial to improve the light throughput and enhance the signal-to-noise ratio. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 is an optical path diagram of the prism-type heterodyne spectrometer with a fixed localization surface according to the present invention;

[0042] In the figure, 1 is the incident light, 2 is the beam splitting optical element, 3 is the first prism, 4 is the first reflecting optical element, 5 is the first plane mirror, 6 is the first tuning axis, 7 is the second prism, 8 is the second reflecting optical element, 9 is the second plane mirror, 10 is the second tuning axis, 11 is the first imaging optical element, and 12 is the first detector. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings.

[0044] The prism-type heterodyne spectrometer with a fixed localization surface of the present invention includes a beam-splitting optical element 2, a first prism 3, a first reflecting optical element 4, a first plane mirror 5, a first tuning shaft 6, a second prism 7, a second reflecting optical element 8, a second plane mirror 9, a second tuning shaft 10, a first imaging optical element 11, and a first detector 12.

[0045] As shown in Figure 1, the optical path of the prism-type heterodyne spectrometer with a fixed localization surface of the present invention is as follows.

[0046] The incident beam 1 should be collimated first, and the collimating optical element should be selected according to the specific light source. For example, for a light source that can be approximated as a point, a collimating lens can be selected, or an off-axis parabolic mirror can be selected to eliminate chromatic aberration; for an extended light source, taking celestial objects as an example, optical fibers can be used to collect light of a certain field of view from the focal point of the telescope and transmit it to the collimating optical element.

[0047] The collimated incident beam 1 is perpendicularly incident on the beam-splitting optical element 2 with a splitting ratio of 1:1, and is proportionally split into two arm beam paths. The beam-splitting optical element 2 is preferably a cubic beam splitter. The first prism 3 and the second prism 7 are positioned with their orientations reversed relative to each other, and their incident surfaces are parallel to the exit surfaces of the reflected and transmitted light from the beam-splitting optical element 2, respectively, so that the two arm beams exiting the beam-splitting optical element 2 are perpendicularly incident on the incident surfaces of the first prism 3 and the second prism 7. The beams of the two arms are refracted on the exit surfaces of the first prism 3 and the second prism 7, causing the exit beams of the two arms to be tilted in opposite directions relative to the optical axis, and respectively incident on one of the reflecting surfaces of the first reflecting optical element 4 and the second reflecting optical element 8. The first reflecting optical element 4 preferably includes two plane mirrors with a right angle and an edge (the intersection of the two right-angled surfaces) connecting the two plane mirrors. The second reflecting optical element 8 preferably includes two plane mirrors with a right angle and an edge connecting the two plane mirrors. The edges of the first reflecting optical element 4 and the second reflecting optical element 8 are perpendicular to the output optical axes of the first prism 3 and the second prism 7, respectively (the optical axis of the spectrometer can be considered as the path of the blaze wavelength light emitted from the center of the light source), and parallel to the sides of the first prism 3 and the second prism 7, respectively (the sides are the surfaces perpendicular to both the incident and output surfaces of the corresponding prisms). This results in the output optical axes of the first reflecting optical element 4 and the second reflecting optical element 8 being parallel to their own incident optical axes, and creating an additional optical axis segment between the output and incident optical axes, thus offsetting the incident and output beams and making it possible for the two beams to pass through only one prism. Preferably, the material and apex angle of the first prism 3 and the second prism 7 should be selected according to the required spectral range and spectral resolution. For example, when the material is set to N-LASF9, the apex angle is 30°, and the half-width of the incident light is 20mm, it has a spectral detection range (10000cm). -1 ~25641cm -1 The theoretical spectral resolution within the range is approximately 1381~27595. The first reflecting optical element 4 and the second reflecting optical element 8 reflect the incident light to another reflecting surface, and then reflect it to the first plane mirror 5 and the second plane mirror 9, respectively.

[0048] To allow the beams from both arms to return to the beam-splitting optical element 2 and be combined, a plane mirror is added behind the reflecting optical element to change the direction of the optical axis. The plane mirror is tilted at an appropriate angle so that its outgoing optical axis is perpendicular to the surface of the beam-splitting optical element, thus achieving beam combining of the two arms. The first plane mirror 5 is perpendicular to the plane formed by the incident and outgoing optical axes of the first prism 3, and the angle formed between it and the incident optical axis of the first prism 3 is equal to half the angle of rotation of the outgoing optical axis of the first prism 3 relative to the incident optical axis. The first tuning axis 6 is located on the outgoing surface of the first prism 3 and passes through the center of the outgoing surface, and is also located on the first plane mirror 5 and passes through the center of the first plane mirror 5. The positions of the second plane mirror 9 and the second tuning axis 10 relative to the second prism 7 are similar. The first reflecting optical element 4 and the first plane mirror 5 share the first tuning axis 6, and the second reflecting optical element 8 and the second plane mirror 9 share the second tuning axis 10. The working spectral range is broadened by rotating around the corresponding tuning axes to tune to various blaze wavelengths. The rotation angle is determined by the direction of the output optical axis of the first prism 3 or the second prism 7 at the desired blaze wavelength. The output optical axes of the first plane mirror 5 and the second plane mirror 9 are perpendicular to the surface of the beam-splitting optical element 2, and the beams from both arms are combined within the beam-splitting optical element 2. The first imaging optical element 11 is an imaging lens or imaging lens group, located in one of the two output light paths after the beams from both arms are combined. Its function is to image the interference fringe localization surface onto the first detector 12. The interference fringe localization surface passes through the center of the output surfaces of the first prism 3 and the second prism 7, and the distance between it and the first imaging optical element 11 is equal to the length of the optical axis between the output surface of the first prism 3 or the second prism 7 and the first imaging optical element 11. The first imaging optical element 11 can be designed as an object-side telecentric system or a dual telecentric system. In the optimization, it is best to take into account the parallel plate aberration introduced by the beam-splitting optical element 2.

[0049] According to the above optical path design, when the wavelength of the incident beam 1 is equal to the tuned blaze wavelength, the beams combined and emitted from the beam-splitting optical element 2 are parallel to the optical axis, and the frequency of the interference fringes on the first detector 12 is zero. When the wavelength of the incident beam 1 is not equal to the blaze wavelength, the beams of the two arms, after being combined and emitted from the beam-splitting optical element 2, deflect by the same angle in opposite directions relative to the optical axis, and the frequency of the interference fringes on the first detector 12 is not zero. A Fourier transform of the interference image received by the first detector 12 can be performed to obtain its spectrum. From the spectrum, the angle between the beams of the two arms and the optical axis after passing through the exit surfaces of the first prism 3 and the second prism 7 can be deduced. Based on this angle and combined with Snell's law, the wavelength of the incident beam 1 can be deduced.

[0050] The present invention uses a "prism + reflective optical element + plane mirror" to construct spatial heterodyne, which is only a preferred embodiment of the present invention. The first reflective optical element 4 and the first reflective optical element 8 can be replaced by optical elements with two or more reflective surfaces, such as a roof prism, or by two or more reflective elements.

[0051] The optical path used in this invention is a modification of the Michelson interferometer and is only a preferred embodiment of the invention. The relative positions of the first prism 3, the second prism 7, the first reflecting optical element 4, the first reflecting optical element 8, the first plane mirror 5, and the second plane mirror 9 in this invention are only preferred embodiments. Without departing from the principle of constructing spatial heterodyne in this invention, several improvements and modifications can be made to the optical path, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A prism-type heterodyne spectrometer with a fixed localization surface, characterized in that, It includes a beam splitting optical element (2), a first prism (3), a first reflecting optical element (4), a first plane mirror (5), a first tuning axis (6), a second prism (7), a second reflecting optical element (8), a second plane mirror (9), a second tuning axis (10), a first imaging optical element (11), and a first detector (12). The beam splitting optical element (2) splits the incident beam (1) into two arm beams, which are respectively incident on the first prism (3) and the second prism (7) located on the two arms, and the combined beams reflected back by the first plane mirror (5) and the second plane mirror (9) located on the two arms are incident on the first imaging optical element (11). The first prism (3) refracts the incident light at the exit surface to the first reflective optical element (4). The first reflective optical element (4) transmits the incident light to the first plane reflector (5) after being reflected more than twice. The outgoing optical axis of the first reflective optical element (4) is parallel to its incident optical axis, and there is an additional optical axis between the outgoing optical axis and the incident optical axis. The first planar reflector (5) reflects the incident light back to the beam splitter optical element (2); The first tuning shaft (6) is fixedly connected to the first reflective optical element (4) and the first plane mirror (5) and drives the first reflective optical element (4) and the first plane mirror (5) to rotate; The second prism (7) refracts the incident light at the exit surface to the second reflective optical element (8); The second reflective optical element (8) transmits the incident light to the second plane mirror (9) after being reflected more than twice. The outgoing optical axis of the second reflective optical element (8) is parallel to its incident optical axis, and there is an additional optical axis between the outgoing optical axis and the incident optical axis. The second plane mirror (9) reflects the incident light to the beam splitting optical element (2); The second tuning shaft (10) is fixedly connected to the second reflective optical element (8) and the second plane mirror (9) and drives the second reflective optical element (8) and the second plane mirror (9) to rotate; The first imaging optical element (11) images the interference fringe localization surface onto the first detector (12); The first detector (12) is used to receive interference images.

2. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, The beam splitting optical element (2) splits the incident beam (1) into two beams of equal intensity; And / or, the beam-splitting optical element (2) is a cube beam splitter.

3. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, It also includes a collimating optical element that collimates the incident beam (1).

4. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, The first prism (3) and the second prism (7) are dispersive prisms, respectively; And / or, the first prism (3) and the second prism (7) are right-angle prisms, and the incident surfaces are both right-angle surfaces. The incident surfaces of the first prism (3) and the second prism (7) are parallel to the exit surfaces of the reflected light and the transmitted light of the beam splitting optical element (2), respectively.

5. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, The first reflective optical element (4) includes two plane mirrors with a right angle between them. The edge connecting the two plane mirrors is perpendicular to the outgoing optical axis of the first prism (3) and parallel to the side surface of the first prism (3). The first plane mirror (5) is perpendicular to the plane formed by the incident optical axis and the outgoing optical axis of the first prism (3), and the angle formed with the incident optical axis of the first prism (3) is equal to half the angle of rotation of the outgoing optical axis of the first prism (3) relative to the incident optical axis. The second reflective optical element (8) includes two plane mirrors with a right angle between them. The edge connecting the two plane mirrors is perpendicular to the outgoing optical axis of the second prism (7) and parallel to the side surface of the second prism (7). The second plane mirror (9) is perpendicular to the plane formed by the incident optical axis and the outgoing optical axis of the second prism (7), and the angle formed with the incident optical axis of the second prism (7) is equal to half the angle of rotation of the outgoing optical axis of the second prism (7) relative to the incident optical axis. The outgoing optical axes of the first plane mirror (5) and the second plane mirror (9) are perpendicular to the surface of the beam splitting optical element (2).

6. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, The angle required for the first reflective optical element (4) to rotate during the tuning process is twice the angle required for the first plane mirror (5) to rotate; The angle required for the second reflective optical element (8) to rotate during the tuning process is twice the angle required for the second plane mirror (9) to rotate.

7. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, The first tuning shaft (6) is located on the exit surface of the first prism (3) and passes through the center of the exit surface, and is also located on the first plane mirror (5) and passes through the center of the first plane mirror (5); The second tuning axis (10) is located on the exit surface of the second prism (7) and passes through the center of the exit surface, and is also located on the second plane mirror (9) and passes through the center of the second plane mirror (9).

8. The prism-type heterodyne spectrometer with a fixed localization surface according to claim 1, characterized in that, It also includes a second imaging optical element and a second detector. The beam splitting optical element (2) combines the two arm beams into two outgoing light paths. The first imaging optical element (11) and the first detector (12) are located on any one outgoing light path, while the second imaging optical element and the second detector are located on the other outgoing light path. The second imaging optical element images the interference fringe localization surface onto the second detector, which is used to receive the interference image.

Images