A method of collimating light for a transmissive optical system in an imaging infrared spectrometer

Abstract

The application discloses a light calibration method for a transmission optical system of a Fourier transform imaging type infrared spectrometer, which utilizes a reflection auxiliary adjustment element to solve the wavelength constraint problem of adjusting and assembling the transmission infrared optical system on a testing instrument. Meanwhile, the interference testing method is utilized, and the reflection element with low price and easy-to-control machining precision is cooperated with light calibration, so that the simultaneous testing and assembly of multiple parameters such as inclination, eccentricity and element spacing can be realized, and the light calibration efficiency and light calibration precision are improved.

Description

Technical Field

[0001] This invention belongs to the field of optical testing and optical assembly, specifically referring to an optical calibration method for a transmission optical system in an imaging infrared spectrometer. Technical Background

[0002] Fourier transform spectroscopy boasts numerous advantages, including multi-channel operation, high optical throughput, and high spectral resolution, making it one of the main development directions in space remote sensing and atmospheric detection technologies. In Fourier transform imaging infrared spectrometers, the imaging optical path plays a crucial role in the spectrometer's spectral resolution.

[0003] In infrared imaging optical paths, the infrared lenses in the system cannot transmit visible light due to the limitations of optical component materials and the wavelength band used by the system. Common assembly and adjustment instruments that use visible light for testing, such as autocollimators, cannot be used in the optical calibration of this system. The assembly and adjustment equipment is limited by the transmission wavelength of the system, resulting in fewer options. Furthermore, the infrared wavelength cannot be directly observed by the human eye, which increases the difficulty of optical calibration.

[0004] Therefore, how to assemble and adjust the infrared imaging optical system of a Fourier spectrometer with high precision becomes a problem to be considered. Summary of the Invention

[0005] The purpose of this invention is to provide an optical calibration method for a transmission optical system in an imaging infrared spectrometer. This method utilizes commonly used visible light optical calibration equipment to assemble and adjust the infrared transmission optical system, solving the problem of the limitation on the wavelength range of the instrument used in the infrared imaging system. The equipment and devices used in the assembly and adjustment process are all commonly used optical calibration tools. The auxiliary plano-concave double-sided reflector is technologically mature and has a wide range of material options. By employing interferometric high-precision testing, the assembly and testing accuracy of the imaging system is improved, and multiple parameters such as the eccentricity, tilt, and element spacing of the infrared lens can be simultaneously calibrated. This achieves the goals of easy operation, high precision, and high efficiency in optical calibration.

[0006] The technical solution of this invention is as follows: The optical calibration system consists of an interferometer, an autocollimator, a double-sided reflector, a two-dimensional angle adjustment mechanism, a first auxiliary reflector, a first lens mount, a high-precision readable five-dimensional adjustment mechanism, an adapter plate, a second auxiliary reflector, and a second lens mount. The specific method steps are as follows:

[0007] Step 1: Install the plane lens on the interferometer, fix the double-sided mirror on the two-dimensional angle adjustment mechanism and place it between the interferometer and the autocollimator. Adjust the two-dimensional angle adjustment mechanism in conjunction with the interferometer to make the normal of the double-sided mirror's reflecting surface parallel to the interferometer's optical axis. Adjust the autocollimator so that its optical axis is parallel to the normal of the double-sided mirror's reflecting surface.

[0008] Step Two: Install the spherical lens on the interferometer. Mount the first auxiliary reflector in the first lens mount. The first lens mount is connected and fixed to the high-precision, readable five-dimensional adjustment mechanism via an adapter plate and placed in the optical path between the interferometer and the autocollimator. Adjust the high-precision, readable five-dimensional adjustment mechanism to control the first auxiliary reflector so that its planar reflecting surface normal is parallel to the autocollimator, and the center of its concave reflecting surface coincides with the convergence point of the spherical waves in the interferometer. This ensures that the spherical waves emitted by the interferometer return to the interferometer via the concave reflection of the first auxiliary reflector, resulting in the minimum RMS value of the interferogram displayed in the interferometer. Secure the first lens mount.

[0009] Step 3: Remove the first auxiliary reflector, install the second auxiliary reflector in the second lens mount, and mount it on the high-precision readable five-dimensional adjustment mechanism via an adapter plate. Place it in the optical path of the interferometer and autocollimator. Adjust the high-precision readable five-dimensional adjustment mechanism to control the second auxiliary reflector so that the normal of its planar reflection surface is parallel to the autocollimator, and the center of its concave reflection surface coincides with the convergence point of the spherical waves of the interferometer. This allows the spherical waves emitted by the interferometer to return to the interferometer through the concave reflection of the second auxiliary reflector. Then, fix the second lens mount in place.

[0010] Step 4: Replace the auxiliary reflector with an infrared imaging system lens to complete the optical calibration of the relative angles and positions between the lenses in the imaging system. This invention takes an imaging system containing two lenses as an example. If the system contains more lenses, simply repeat step 3 to install and adjust the other lenses in sequence.

[0011] In the method of the present invention, the installation direction of the lens frame to be optically corrected is determined by the planar reflecting surface of the auxiliary reflector, and the position of the lens frame to be optically corrected is determined by the center of the concave reflecting surface of the auxiliary reflector and the focal point of the interferometer.

[0012] The beneficial effects of this invention are as follows: This invention proposes a method for assembling and testing a coaxial infrared transmission optical system, solving the problem that common assembly and adjustment instruments cannot be directly used for assembly and adjustment due to the limitation of the transmission wavelength of the infrared system. Applying interferometric testing technology to the system assembly and adjustment improves the system's assembly and testing accuracy. The assembly and adjustment process is simple; the auxiliary components used are made from a wide range of inexpensive and readily available materials, with mature processing technology and low processing costs. This method can simultaneously correct multiple parameters of the lens elements in a coaxial infrared transmission system, such as tilt, eccentricity, and element spacing, thus improving optical assembly and adjustment efficiency. This invention can be extended as a mature assembly and adjustment process to the assembly and adjustment of coaxial transmission optical systems in other wavelength bands. Attached Figure Description

[0013] Figure 1 To align the optical axis of the interferometer with the optical axis of the autocollimator

[0014] Figure 2Schematic diagram of the position and angle of the first lens mount in the imaging system.

[0015] Figure 3 Schematic diagram of the method for controlling the lens spacing.

[0016] Figure 4 Schematic diagram of the position and angle of the second lens mount in the imaging system. Detailed Implementation

[0017] The following describes in detail, with reference to the accompanying drawings, examples of implementation of the method of the present invention.

[0018] like Figure 1-4 The following describes the equipment and components used in this invention:

[0019] The optical calibration system in the optical system includes: an interferometer 1, an autocollimator 2, a double-sided mirror 3, a two-dimensional angle adjustment mechanism 4, a first auxiliary mirror 5, a first lens mount 6, a high-precision readable five-dimensional adjustment mechanism 7, an adapter plate 8, a second auxiliary mirror 9, and a second lens mount 10.

[0020] The autocollimator model 2 is TA300-57, with a resolution of 0.01″ and an accuracy of 0.75″.

[0021] The RMS of the three-sided double-sided reflector is better than 1 / 40λ, where λ = 632.8 nm. The parallelism of the front and rear reflecting surfaces is better than 2″.

[0022] The two-dimensional angle adjustment mechanism 4 is a mechanism that allows for fine adjustment of pitch and azimuth angles via a knob. The loading surface is a flat surface that can accommodate a double-sided reflector 3.

[0023] The first auxiliary reflector 5 is an auxiliary leveling concave reflector for the first infrared lens in the imaging optical system, and the second auxiliary reflector 9 is an auxiliary leveling concave reflector for the second infrared lens in the imaging optical system. The auxiliary reflectors are manufactured according to the lens aperture and spacing required for the optical system to be optically calibrated. Their materials can be metals such as aluminum. The aperture is consistent with the lens aperture in the system to be optically calibrated. The RMS of the planar surface type is better than 1 / 20λ, λ = 632.8nm, and the RMS of the concave surface type is better than 1 / 20λ, λ = 632.8nm. The concave radius is determined according to the spacing between the lenses in the optical system to be optically calibrated. For example, if the spacing between the two lenses in the optical system to be optically calibrated is d, and the center thicknesses of the two auxiliary reflectors are t1 and t2 respectively, if the concave radius R1 of the first auxiliary reflector is d1, then the concave reflective surface radius R2 of the second auxiliary reflector 9 is d2 = d1 + t1 - d - t2, and so on.

[0024] The first lens mount 6 and the second lens mount 10 are the mounting brackets for the two lenses in the infrared imaging system to be optically corrected.

[0025] The high-precision, readable five-dimensional adjustment mechanism 7 allows for fine-tuning of translation, pitch, and azimuth in the x, y, and z directions, and can record readings.

[0026] The adapter plate 8 is a mechanical plate that can connect the first lens frame 6 to the high-precision readable five-dimensional adjustment mechanism 7.

[0027] Both the first lens mount 6 and the second lens mount 10 are fixed on the same substrate. After adjusting the mounts using a high-precision, readable five-dimensional adjustment mechanism, the mounts are connected to the substrate using screws and suitable shims. The first auxiliary reflector 5 and the second auxiliary reflector 9 are then removed, and the lenses at the corresponding positions in the infrared imaging system are installed in the lens mounts, thus completing the assembly and adjustment of the infrared transmission system.

Claims

1. A method for optical calibration of a transmission optical system in an imaging infrared spectrometer, wherein the optical calibration system in the optical system comprises: An interferometer (1), an autocollimator (2), a double-sided mirror (3), a two-dimensional angle adjustment mechanism (4), a first auxiliary mirror (5), a first lens mount (6), a high-precision readable five-dimensional adjustment mechanism (7), an adapter plate (8), a second auxiliary mirror (9), and a second lens mount (10), characterized in that the method includes the following steps: Step 1: Install the double-sided mirror (3) on the two-dimensional angle adjustment mechanism (4) and place it between the interferometer (1) and the autocollimator (2). The interferometer (1) uses a plane lens to emit parallel light. Adjust the two-dimensional angle adjustment mechanism (4) to make the normal of the reflecting surface of the double-sided mirror (3) parallel to the optical axis of the interferometer (1). Adjust the autocollimator (2) to make the optical axis of the autocollimator (2) parallel to the normal of the reflecting surface of the double-sided mirror (3). Remove the double-sided mirror (3) and the two-dimensional angle adjustment mechanism (4). With the assistance of the double-sided mirror (3), the optical axis of the interferometer (1) and the optical axis of the autocollimator (2) are adjusted to be parallel. Step 2: Install the first auxiliary mirror (5) in the first lens frame (6) of the optical system, and install the second auxiliary mirror (9) in the second lens frame (10) of the optical system; Step 3: Install the structure from Step 2 onto the high-precision readable five-dimensional adjustment mechanism (7) via the adapter plate (8) and place it in the optical path of the interferometer (1) and the autocollimator (2). Adjust the pitch and azimuth angle of the first lens mount (6) through the high-precision readable five-dimensional adjustment mechanism (7) so that the normal of the plane reflecting surface of the first auxiliary reflector (5) is parallel to the optical axis of the autocollimator (2). Replace the lens of the interferometer (1) with a spherical lens to emit spherical waves, which are reflected back to the interferometer (1) by the concave surface of the first auxiliary reflector (5). Adjust the position and angle of the first lens mount (6) through the high-precision readable five-dimensional adjustment mechanism (7) so that the spherical waves emitted by the interferometer (1) are reflected back to the interferometer (1) by the concave surface of the first auxiliary reflector (5). The concave reflection of the auxiliary reflector (5) returns to the interferometer (1) along the original path, and the planar reflection surface of the first auxiliary reflector (5) is autocollimated with the autocollimator (2). The center of the concave spherical reflection surface of the first auxiliary reflector (5) coincides with the convergence point of the spherical wave emitted by the interferometer (1). The normal of the planar reflection surface of the first auxiliary reflector (5) is parallel to the optical axis of the interferometer (1) and the autocollimator (2). The optical axis of the first auxiliary reflector (5) passes through the convergence point of the interferometer (1) and is in the direction of the optical axis of the autocollimator, which is the axis of the first lens mount (6). Fix the first lens mount (6), remove the first auxiliary reflector (5), and repeat step three to install the other lens mounts in the system.

2. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The interferometer (1) is a Zygo interferometer.

3. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The autocollimator (2) mentioned above is model TA300-57, with a resolution of 0.01″ and an accuracy of 0.75″.

4. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The surface profile RMS of the double-sided reflector (3) is better than 1 / 40λ, λ = 632.8nm, and the parallelism of the front and rear reflective surfaces is better than 2″.

5. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The two-dimensional angle adjustment mechanism (4) is a mechanism that can finely adjust the pitch and azimuth angles, and the loading surface is a plane on which a double-sided reflector (3) can be placed.

6. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The first auxiliary reflector (5) is a plano-concave reflector used for auxiliary adjustment of the infrared first lens in the transmission optical system of the spectrometer. It is made of metal and has the same aperture as the infrared first lens in the optical calibration system. The RMS of the planar surface type is better than 1 / 20λ, λ = 632.8nm, and the RMS of the concave surface type is better than 1 / 20λ, λ = 632.8nm. The radius R1 of the concave spherical surface is determined according to the F number of the interferometer spherical lens and the aperture D of the infrared first lens.

7. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The first lens mount (6) is the mounting mount for the infrared first lens in the optical calibration system.

8. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The high-precision, readable five-dimensional adjustment mechanism (7) is used for fine-tuning translation in the horizontal, vertical, and forward / backward directions, pitch, and azimuth, and records the readings.

9. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The adapter plate (8) is a mechanical plate that connects the first lens frame (6) to the high-precision readable five-dimensional adjustment mechanism (7).

10. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The second auxiliary reflector (9) is an auxiliary adjustment reflector for the infrared second lens in the optical system of the spectrometer. It is a plano-concave double-sided reflector made of metal. Its aperture is the same as that of the infrared second lens. The RMS of the planar surface is better than 1 / 20λ, λ = 632.8nm, and the RMS of the concave surface is better than 1 / 20λ, λ = 632.8nm. The radius of the concave surface is determined according to the spacing between the lenses of the optical calibration system.

11. The optical calibration method for a transmission optical system in an imaging infrared spectrometer according to claim 1, characterized in that: The second lens mount (10) is the mounting mount for the infrared second lens in the imaging optical system.

Images