A prism-type heterodyne spectrometer with fixed localization surface

Abstract

The present invention relates to a prism-type heterodyne spectrometer with a fixed localization surface, and belongs to the technical field of spectrometers. The present invention solves the problem that the position of the interference fringe localization surface varies with the wavelength in the prism-type spatial heterodyne spectroscopy technology in the prior art. The prism-type heterodyne spectrometer with a fixed localization surface of the present invention comprises a beam splitting optical element, a first prism, a first reflecting optical element, a first plane reflector, a first tuning axis, a second prism, a second reflecting optical element, a second plane reflector, a second tuning axis, an imaging optical element, and a first detector. The prism-type heterodyne spectrometer with a fixed localization surface adopts the form of "prism + reflecting optical element + plane reflector" to construct spatial heterodyne, so as to achieve the fixation of the interference fringe localization surface. Moreover, by rotating the optical element, the working spectrum range of the instrument can be increased, the spectrum can be tuned, and the position of the localization surface can still be kept unchanged.

Description

Technical Field

[0001] The invention belongs to the technical field of spectrometers, and in particular relates to a prism-type heterodyne spectrometer with a fixed localization surface. Background Art

[0002] A spectrum is the pattern formed by the arrangement of complex colors of light according to their wavelengths after separation. It can reveal a wide range of microscopic and macroscopic properties, including the energy levels and geometric structures of atoms and molecules, and the reaction rates of specific chemical processes. An instrument designed to analyze spectra using the principles of dispersion or interference is called a spectrometer.

[0003] Spatial heterodyne spectroscopy was born in the 1970s. Compared with traditional interferometric spectrometers, it can achieve higher spectral resolution with the same number of detector sampling points and has broad prospects. Spatial heterodyne spectrometers generally use gratings as dispersive elements for interferometric modulation. However, gratings as dispersive elements have the following problems: First, the grating has the characteristic of multi-order diffraction, which causes the energy to be distributed in different orders, not only reducing the energy of the interfering beam, but also potentially causing interference between different diffraction orders; second, for tunable spatial heterodyne spectrometers based on blazed gratings, the grating is rotated to achieve a wider spectral range, but rotating the grating causes the incident angle to deviate from the blaze angle, reducing the diffraction efficiency and limiting the spectral range of the instrument; third, compared with prisms, gratings are more prone to diffuse reflection and generate stray light.

[0004] Prism-based spatial heterodyne spectroscopy is a new technology developed in recent years. The principle of prism light splitting is that the refractive index of the prism material varies with wavelength, thus avoiding the aforementioned problems caused by diffraction. Existing prism-based spatial heterodyne spectrometers generally use a "dispersive prism + reflector" configuration. Similar to a Michelson interferometer, it replaces the plane mirrors in the two arms with dispersive prisms and plane reflectors (or prisms coated with a reflective coating).

[0005] Another problem with the "dispersion prism + reflector" spatial heterodyne spectrometer is that the position of the equivalent localization plane of the interference fringes changes with wavelength. For traditional grating-type spatial heterodyne spectrometers, since the light beams in both arms are diffracted by the reflection grating only once, the localization plane passes through the center of the grating, which is relatively intuitive. However, in the "dispersion prism + reflector" spatial heterodyne spectrometer, the light beams in both arms pass through the dispersion prism before and after reflection from the reflector, and are refracted by the dispersion prism more than once. Therefore, the position of the localization plane needs to be calculated, and the calculation results show that the position of the localization plane is a function of wavelength.

[0006] To visualize interference fringes on a detector, the localized surface must be imaged onto the detector surface via a post-imaging system. When the light source is not an ideal point source—that is, when the incident light is partially spatially coherent—if the position of the localized surface at a particular wavelength deviates from the conjugate plane of the detector surface with respect to the post-imaging system, the clarity of the interference fringes on the detector will be reduced. Therefore, this shift in the position of the localized surface reduces fringe clarity and limits the detectable spectral range. Summary of the Invention

[0007] The present invention aims to address the problem of wavelength-dependent variations in the position of the interference fringe localization plane in prior art prism-based spatial heterodyne spectroscopy. The present invention provides a prism-based heterodyne spectrometer with a fixed localization plane. The instrument employs a "prism + reflective optical element + plane reflector" structure to construct a spatial heterodyne, achieving a fixed interference fringe localization plane. Furthermore, rotating the optical element can increase the instrument's operating spectral range, achieving spectral tunability while maintaining a constant localization plane position.

[0008] The technical solutions adopted by the present invention to solve the above technical problems are as follows.

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

[0010] The beam splitting optical element splits the incident light beam into two arm light beams, which are incident on the first prism and the second prism located in the two arms respectively, and the combined light beam reflected back by the first plane reflector and the second plane reflector located in the two arms is 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 reflecting optical element transmits the incident light to the first plane reflecting mirror after reflecting the incident light twice or more. The output optical axis of the first reflecting optical element is parallel to the incident optical axis, and an additional optical axis is provided between the output optical axis and the incident optical axis.

[0013] The first plane reflector 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 reflecting mirror and drives the first reflecting optical element and the first plane reflecting mirror to rotate;

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

[0016] The second reflecting optical element transmits the incident light to the second plane reflecting mirror after reflecting the incident light twice or more. The output optical axis of the second reflecting optical element is parallel to the incident optical axis, and an additional optical axis is provided between the output optical axis and the incident optical axis.

[0017] The second plane reflector 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 reflecting mirror and drives the second reflecting optical element and the second plane reflecting 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 the interference image.

[0020] Preferably, the beam splitting optical element splits the incident light beam into two arm light beams with equal intensities.

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

[0022] Preferably, the device further comprises a collimating optical element, wherein the collimating optical element collimates the incident light beam;

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

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

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

[0026] More preferably, the angle that the first reflective optical element needs to rotate during the tuning process is twice the angle that the first plane reflector needs 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 reflector and passes through the center of the first plane reflector.

[0028] Preferably, the exit optical axes of the first plane reflector and the second plane reflector are respectively perpendicular to the surface of the beam splitting optical element.

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

[0030] More 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 reflective 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 reflector and passes through the center of the second plane reflector.

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

[0033] Preferably, it also includes a second imaging optical element and a second detector. After the beam splitting optical element combines the two arm light beams, there are two outgoing light paths. The first imaging optical element and the first detector are located in any one of the outgoing light paths, and the second imaging optical element and the second detector are located in the other outgoing light path. The second imaging optical element images the interference fringe localization surface onto the second detector, and the second detector is used to receive the interference image.

[0034] The principle of this invention is that when the wavelength of the incident light is equal to the tuned blaze wavelength, the wavefronts of the two-arm output light 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-arm light beams are deflected in opposite directions relative to the optical axis by the same angle, effectively interfering on a localized surface. The distance from the localized surface to the post-positioned first imaging optical element is equal to the length of the optical axis from the prism's refractive surface to the post-positioned first imaging optical element. This length of the optical axis remains unchanged regardless of the tuned blaze wavelength or the wavelength of the incident light. This solves the problem of wavelength-dependent variations in the position of the interference fringe localized surface, a problem that exists in current prism-based spatial heterodyne spectroscopy techniques. This improves fringe contrast and expands the operating spectral range.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] Compared with the grating-type spatial heterodyne spectrometer, the prism-type heterodyne spectrometer with a fixed localization surface of the present invention avoids the problems of multi-order diffraction of the grating and the grating being prone to diffuse reflection and generating stray light, and can have a higher signal-to-noise ratio.

[0037] Compared with the existing prism-type spatial heterodyne spectrometer, the prism-type heterodyne spectrometer with a fixed localization plane of the present invention solves the problem that the position of the interference fringe localization plane of the existing prism-type spatial heterodyne spectrometer changes with the wavelength, and realizes the fixation of the interference fringe localization plane.

[0038] When the light source is not an ideal point light source, that is, 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-arm light beams of the prism-type heterodyne spectrometer with a fixed localized surface of the present invention are not traced back to the light source after the two-arm light beams are combined by the beam-splitting optical element. The interference patterns received by the two detectors can be processed by differential amplification, etc., which is beneficial to increase the light flux and improve the signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

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

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

[0043] The present invention will be further described in detail below 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 reflector 5, a first tuning axis 6, a second prism 7, a second reflecting optical element 8, a second plane reflector 9, a second tuning axis 10, a first imaging optical element 11 and a first detector 12.

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

[0046] The incident light beam 1 should be collimated first, and the collimating optical element should be selected based on 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, such as a celestial body, an optical fiber can be used to collect a certain field of view of light from the telescope's focus and transmit it to the collimating optical element.

[0047] The collimated incident light beam 1 is vertically incident on the beam splitting optical element 2 with a splitting ratio of 1:1, and is proportionally divided into two arms of light paths. The beam splitting optical element 2 is preferably a cubic beam splitter. The placement directions of the first prism 3 and the second prism 7 are flipped upside down relative to each other, and the incident surfaces should be parallel to the exit surfaces of the reflected light and the transmitted light of the beam splitting optical element 2, respectively, so that the two arms of the light beam emitted from the beam splitting optical element 2 are vertically incident on the incident surfaces of the first prism 3 and the second prism 7, respectively. The light beams of the two arms are refracted on the exit surfaces of the first prism 3 and the second prism 7, so that the exit light beams of the two arms are tilted in opposite directions relative to the optical axis, and are 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 reflectors with a right angle and an edge connecting the two plane reflectors (the intersection of the two right-angled surfaces). The second reflecting optical element 8 preferably includes two plane reflectors with a right angle and an edge connecting the two plane reflectors. The prisms of the first reflecting optical element 4 and the second reflecting optical element 8 are respectively perpendicular to the exit optical axes of the first prism 3 and the second prism 7 (the optical axis of the spectrometer can be regarded as the path through which the light of the blazing wavelength emitted from the center of the light source passes), and are respectively parallel to the side surfaces of the first prism 3 and the second prism 7 (the side surfaces are surfaces perpendicular to both the incident surface and the exit surface of the corresponding prism). In this way, the exit optical axes of the first reflecting optical element 4 and the second reflecting optical element 8 are parallel to their own incident optical axes, and there is an extra optical axis between the exit optical axis and the incident optical axis, which staggers the incident light beam and the exit light beam, making it possible for the two-arm light beam to pass through the prism only once. Preferably, the material and the vertex 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 vertex angle is 30°, and the half width of the incident light is 20mm, it has a spectral detection range of 10,000cm -1 ~25641cm -1 The theoretical spectral resolution within the range of ) is about 1381 to 27595. The first reflecting optical element 4 and the second reflecting optical element 8 respectively reflect the incident light to the other reflecting surface, and then reflect it to the first plane reflecting mirror 5 and the second plane reflecting mirror 9.

[0048] In order to allow the light beams from the two arms to return to the beam-splitting optical element 2 for combination, a plane mirror is added behind the reflective optical element to change the direction of the optical axis. The plane mirror is tilted at an appropriate angle so that its output optical axis is perpendicular to the surface of the beam-splitting optical element, thereby combining the light beams from the two arms. The first plane mirror 5 is perpendicular to the plane formed by the incident optical axis and the output optical axis of the first prism 3. The angle formed by the first plane mirror 5 and the incident optical axis of the first prism 3 is equal to half the angle of rotation of the output optical axis of the first prism 3 relative to the incident optical axis. The first tuning axis 6 is located on the output surface of the first prism 3 and passes through the center of the output surface. It 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 reflector 5 share a first tuning axis 6, while the second reflecting optical element 8 and the second plane reflector 9 share a second tuning axis 10. By rotating about the corresponding tuning axis to tune to the desired blaze wavelength, the operating spectral range is broadened. The angle of rotation 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 reflector 5 and the second plane reflector 9 are perpendicular to the surface of the beam-splitting optical element 2, where the two beams are combined. The first imaging optical element 11 is an imaging lens or an imaging lens assembly located in one of the two output light paths after the two beams are combined. Its function is to image the interference fringe localization plane onto the first detector 12. The interference fringe localization plane passes through the center of the exit surface of the first prism 3 and the second prism 7. The distance between the interference fringe localization plane and the first imaging optical element 11 is equal to the length of the optical axis between the exit 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-space telecentric system or a double-telecentric system. During optimization, the parallel plate aberration introduced by the beam-splitting optical element 2 is preferably taken into consideration.

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

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

[0051] The optical path employed in this invention is a modification of the Michelson interferometer and represents only a preferred embodiment of the invention. The relative positions of the first prism 3, second prism 7, first reflective optical element 4, first reflective optical element 8, first plane reflector 5, and second plane reflector 9 represent only a preferred embodiment of the invention. While remaining within the principles of the present invention for constructing spatial heterodyning, various improvements and modifications to the optical path are possible and should be considered within the scope of protection of this invention.

Claims

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

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

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

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

5. The prism-type heterodyne spectrometer with a fixed localization plane according to claim 1, characterized in that: The first reflecting optical element (4) comprises two plane reflectors with a right angle, the prism connecting the two plane reflectors is perpendicular to the exit optical axis of the first prism (3) and parallel to the side surface of the first prism (3), the first plane reflector (5) is perpendicular to the plane formed by the incident optical axis and the exit 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 of the angle of rotation of the exit optical axis of the first prism (3) relative to the incident optical axis; The second reflecting optical element (8) comprises two plane reflectors with a right angle, the prism connecting the two plane reflectors is perpendicular to the exit optical axis of the second prism (7) and parallel to the side surface of the second prism (7), the second plane reflector (9) is perpendicular to the plane formed by the incident optical axis and the exit 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 of the angle of rotation of the exit optical axis of the second prism (7) relative to the incident optical axis; The exit optical axes of the first plane reflector (5) and the second plane reflector (9) are respectively perpendicular to the surface of the beam splitting optical element (2).

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

7. The prism-type heterodyne spectrometer with a fixed localization plane according to claim 1, characterized in that: The first tuning axis (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 reflector (5) and passes through the center of the first plane reflector (5); The second tuning axis (6) 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 reflector (9) and passes through the center of the second plane reflector (9).

8. The prism-type heterodyne spectrometer with a fixed localization plane according to claim 1, characterized in that: The invention also includes a second imaging optical element and a second detector. The beam splitting optical element (2) combines the two arm light beams to form two outgoing light paths. The first imaging optical element (11) and the first detector (12) are located on any one of the outgoing light paths. 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. The second detector is used to receive the interference image.

Images