Prism type heterodyne spectrometer with fixed localization plane

Abstract

The invention relates to a prism type heterodyne spectrometer with a fixed localization plane, and belongs to the technical field of spectrometers. The problem that the position of an interference fringe localization plane changes along with the wavelength in the prism type spatial heterodyne spectrum technology in the prior art is solved. The invention discloses a prism type heterodyne spectrometer with a fixed localization plane. The prism type heterodyne spectrometer comprises a beam splitting optical element, a first prism, a first reflection optical element, a first plane mirror, a first tuning rotating shaft, a second prism, a second reflection optical element, a second plane mirror, a second tuning rotating shaft, an imaging optical element and a first detector. According to the prism type heterodyne spectrometer with the fixed localized plane, spatial heterodyne is constructed in a form of a prism, a reflection optical element and a plane mirror, and the localized plane of interference fringes is fixed. And the working spectral range of the instrument can be enlarged by rotating the optical element, so that the spectrum can be tuned, and the position of the localized 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] Spectrum refers to the pattern formed by the arrangement of complex colored light according to its wavelength after being split. It can reflect the energy level and geometric structure of atoms and molecules, the reaction rate of specific chemical processes and many other microscopic and macroscopic properties. An instrument designed based on the principle of dispersion or interference to analyze the spectrum is called a spectrometer.

[0003] Spatial heterodyne spectroscopy was born in the 1970s. Compared with traditional interference spectrometers, it can have higher spectral resolution under the same number of detector sampling points and has broad prospects. Spatial heterodyne spectrometers generally use gratings as dispersive elements for interference modulation, and there are several problems with gratings as dispersive elements: First, the grating has the characteristics of multi-order diffraction, which causes the energy to be distributed in different orders, which not only reduces the energy of the interference beam, but also may cause 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 the rotation of the grating will cause the incident angle to deviate from the blazed 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 stray light.

[0004] Prism-type spatial heterodyne spectroscopy is a new technology developed in recent years. The principle of prism light splitting is that the refractive index of its material is different for different wavelengths, so the above-mentioned problems caused by diffraction are avoided. Existing prism-type spatial heterodyne spectrometers generally adopt the form of "dispersion prism + reflector", which is similar to the Michelson interferometer, using dispersion prisms and plane reflectors (or coating the prism with a reflective film) instead of the plane mirrors on the two arms.

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

[0006] In order to see interference fringes on the detector, the localized surface needs to be imaged onto the detector surface through a post-imaging system. When the light source is not an ideal point light source, that is, the incident light is partially spatially coherent, if the position of the localized surface of a certain 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, the phenomenon of the change in the position of the localized surface will reduce the clarity of the fringes and limit the detectable spectral range. Summary of the invention

[0007] The purpose of the present invention is to solve 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, and to provide a prism-type heterodyne spectrometer with a fixed localization surface, which adopts the form of "prism + reflective optical element + plane reflector" to construct a spatial heterodyne to achieve the fixed interference fringe localization surface. And by rotating the optical element, the working spectrum range of the instrument can be increased, the spectrum can be tunable, and the position of the localization surface can still be kept unchanged.

[0008] The technical solution adopted by the present invention to solve the above technical problems is 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 rotating shaft, a second prism, a second reflecting optical element, a second plane reflecting mirror, a second tuning rotating shaft, 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 photosynthetic 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 for more than two times, the outgoing optical axis of the first reflecting optical element is parallel to the incident optical axis thereof, and an additional optical axis is provided between the outgoing 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 for more than two times, the exit optical axis of the second reflecting optical element is parallel to the incident optical axis thereof, and an additional optical axis is provided between the exit 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 cubic beam splitter.

[0022] Preferably, it 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-angle 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 reflectors with a right angle, the edge connecting the two plane reflectors is perpendicular to the output optical axis of the first prism and parallel to the side of the first prism, the first plane reflector 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 required for the first reflective optical element to rotate during the tuning process is twice the angle required for the first plane 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 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 reflector 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, the beam splitting optical element has two outgoing light paths after combining the two arm light beams, the first imaging optical element and the first detector 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, and the second detector is used to receive the interference image.

[0034] The principle of the present invention is: when the wavelength of the incident light is equal to the tuned blaze wavelength, the wavefronts of the two-arm outgoing 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 deflect the same angle in opposite directions relative to the optical axis, and are equivalent to interference on the localized surface. The distance from the localized 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 no matter what the tuned blaze wavelength is or what the wavelength of the incident light is, the length of this section of the optical axis will not change, solving the problem of the interference fringes localized surface position changing with the wavelength existing in the current prism-type spatial heterodyne spectroscopy technology, thereby improving the fringes contrast and increasing the working spectrum range.

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

[0036] Compared with a 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, the grating being more 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 drawings required for use in the embodiments will be briefly introduced below. 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 creative work.

[0041] Figure 1 The optical path diagram of the prism-type heterodyne spectrometer with fixed localization plane of 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 is 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 reflecting mirror 5, a first tuning shaft 6, a second prism 7, a second reflecting optical element 8, a second plane reflecting mirror 9, a second tuning shaft 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 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 bodies as an example, an optical fiber can be used to collect a certain field of view from the focus of the telescope 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 divided into two arm optical paths in equal proportion. 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 arm light beams 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 reflection 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 outgoing optical axes of the first prism 3 and the second prism 7 (the optical axis of the spectrometer can be regarded as the path of the light of the blazing wavelength emitted from the center of the light source), and are respectively parallel to the side surfaces of the first prism 3 and the second prism 7 (the side surfaces are the surfaces perpendicular to both the incident surface and the exit surface of the corresponding prism), so that the outgoing 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 section of optical axis between the exit optical axis and the incident optical axis, which staggers the incident light beam and the outgoing 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 high resolution in the spectral detection range (10000cm -1 ~25641cm -1 ) within a theoretical spectral resolution range of about 1381 to 27595. The first reflecting optical element 4 and the second reflecting optical element 8 respectively reflect the incident light to another 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 of the two arms to return to the beam splitting optical element 2 for beam combination, a plane reflector is added behind the reflective optical element to change the direction of the optical axis. The plane reflector is tilted at an appropriate angle so that its output optical axis is perpendicular to the surface of the beam splitting optical element, thereby achieving beam combination of the two arms. The first plane reflector 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 reflector 5 and the incident optical axis of the first prism 3 is equal to half of 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, and is also located on the first plane reflector 5 and passes through the center of the first plane reflector 5. The positions of the second plane reflector 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 reflecting mirror 5 use the first tuning axis 6 together, and the second reflecting optical element 8 and the second plane reflecting mirror 9 use the second tuning axis 10 together. The widening of the working spectrum range is achieved by rotating around the corresponding tuning axis to tune to each blazing wavelength. The rotation angle is determined by the direction of the exit optical axis of the first prism 3 or the second prism 7 at the required blazing wavelength. The exit optical axes of the first plane reflecting mirror 5 and the second plane reflecting mirror 9 are respectively perpendicular to the surface of the beam splitting optical element 2, and the light beams of the two arms are combined in the beam splitting optical element 2. The first imaging optical element 11 is an imaging lens or an imaging lens group, which is located in one of the two exit light paths after the two-arm light beams are combined, and 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, and the distance between it 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 may be designed as an object-space telecentric system or a double-telecentric system. In the 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 light beam combined and 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 light beams of the two arms are deflected by the same angle in opposite directions 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 not zero. The frequency spectrum of the interference image received by the first detector 12 can be obtained by Fourier transforming. The angle between the light 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 inferred from the frequency spectrum. The wavelength of the incident light beam 1 can be inferred from the angle and combined with Snell's law.

[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 optical elements with two or more reflective surfaces such as roof prisms, or by two or more reflective elements.

[0051] The optical path adopted by the present invention is a deformation based on the Michelson interferometer, which is only a preferred embodiment of the present invention. The relative positions of the first prism 3, the second prism 7, the first reflective optical element 4, the first reflective optical element 8, the first plane reflector 5 and the second plane reflector 9 in the present invention are only preferred embodiments of the present invention. Without departing from the principle of constructing spatial heterodyne of the present invention, several improvements and modifications can be made to the optical path, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A prism-type heterodyne spectrometer with a fixed localization plane, characterized in that: It 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 exit 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 exit 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 exit 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 exit 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 the 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 cubic beam splitter.

3. The prism-type heterodyne spectrometer with a fixed localization plane according to claim 1, characterized in that: It also comprises 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-angle surfaces, and the incident surfaces of the first prism (3) and the second prism (7) are respectively parallel to the exit surfaces of the reflected light and the exit surfaces of the transmitted light of the beam splitting optical element (2).

5. The prism-type heterodyne spectrometer with fixed localization plane according to claim 1, characterized in that: The first reflecting optical element (4) comprises two plane reflecting mirrors with a right angle, the edge connecting the two plane reflecting mirrors is perpendicular to the output optical axis of the first prism (3) and parallel to the side surface of the first prism (3), the first plane reflecting mirror (5) is perpendicular to the plane formed by the incident optical axis and the output 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 output optical axis of the first prism (3) relative to the incident optical axis; The second reflecting optical element (8) comprises two plane reflecting mirrors with a right angle, the edge connecting the two plane reflecting mirrors is perpendicular to the output optical axis of the second prism (7) and parallel to the side surface of the second prism (7), the second plane reflecting mirror (9) is perpendicular to the plane formed by the incident optical axis and the output 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 output 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 reflective optical element (4) to rotate during the tuning process is twice the angle required for the first plane reflective mirror (5) to rotate; The angle at which the second reflecting optical element (8) needs to rotate during the tuning process is twice the angle at which the second plane reflecting mirror (9) needs 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: It also includes a second imaging optical element and a second detector. The beam splitting optical element (2) combines the two arm light beams to have 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