Focal length detection device and method for adjustment process of long-focal-length optical system

Abstract

The invention discloses a focal length detection device and a focal length detection method for a long-focal-length optical system installation and adjustment process, and solves the problems of low detection precision and low repeatability of a large-aperture long-focal-length optical system in the prior art. The focal length detection device specifically comprises a plane mirror arranged at the emergent end of the to-be-detected optical system, an interferometer lens and an interferometer body which are arranged at the incident end of the to-be-detected optical system and are mounted on a one-dimensional translation table, and a length measurement mechanism and a diameter measurement mechanism; the interferometer body is used for emitting a measuring light beam to an incident end of a to-be-measured optical system, the aperture of the plane mirror is greater than the effective clear aperture D of the to-be-measured optical system, and the one-dimensional translation stage is used for controlling the interferometer lens and the interferometer body to translate along the optical axis direction of the measuring light beam; when the interferometer detects the optical system to be detected, the relation between the actual displacement before and after the dynamic interferometer and the wavefront power component of the system is established, and the focal length of the optical system is calculated by using the least square fitting method.

Description

Technical Field

[0001] The present invention relates to a focal length detection device and method, and particularly to a focal length detection device and method for the alignment process of a long focal length optical system. Background Art

[0002] Large-aperture long focal length optical systems are widely used in fields such as earth observation and astronomical technology research, and their detection and alignment are one of the current frontiers of hard technology. These long focal length optical systems have important commercial value in multiple applications such as space long-distance imaging and laser weapon focusing. With the increase in the aperture of long focal length optical systems, the requirements for their optical detection and assembly also increase.

[0003] As an important physical quantity of an optical system, the high-precision measurement of focal length is a key link in the system development stage. At present, common focal length detection methods for long focal length optical systems include the detection method combining a theodolite and a glass scale plate, and the precision angle measurement method, etc.

[0004] The basic steps of the glass scale plate detection method are to install the glass scale plate on the focal plane of the optical system, illuminate it with a light source, and measure the angle between the scale lines of the glass scale plate through a theodolite, so as to calculate the focal length of the optical system. However, in actual operation, the glass scale plate detection method requires a high-precision theodolite to aim at the image point on the focal plane of the optical system. Due to the large focal length of the optical system, the image point size is extremely small, and affected by air flow and the resolution of the human eye, large errors are likely to occur during observation. Therefore, the focal length detection accuracy and repeatability of this method are relatively low, and it is difficult to meet the requirements of image quality detection and alignment of modern optical systems.

[0005] The precision angle measurement method usually requires placing the optical system on a turntable for rotation, and providing an infinitely distant target image through a large-aperture collimator, which poses high requirements for hardware equipment.

[0006] Therefore, there is an urgent need for a high-precision, convenient and low-cost detection method and device to achieve precise detection of the focal length of a large-aperture long focal length optical system during the alignment process. Summary of the Invention

[0007] In order to solve the technical problems of the low detection accuracy and repeatability of the existing technology for large-aperture long focal length optical systems, or the high detection cost, the present invention provides a focal length detection device and method for the alignment process of a long focal length optical system.

[0008] The inventive concept of the present invention is:

[0009] When the interferometer detects the optical system to be measured, the present invention establishes the relationship between the actual displacement amount before and after the dynamic interferometer and the system wavefront power (defocus) component, and uses the least square fitting method to calculate and obtain the focal length of the optical system.

[0010] To achieve the above object and complete the above inventive concept, the present invention adopts the following technical solutions:

[0011] A focal length detection device for the alignment process of a long focal length optical system, characterized in that it includes a plane mirror disposed at the exit end of the optical system to be measured, an interferometer lens and an interferometer body disposed at the entrance end of the optical system to be measured and mounted on a one-dimensional translation stage, as well as a length measuring mechanism and a diameter measuring mechanism;

[0012] The interferometer body is used to emit a measurement beam to the entrance end of the optical system to be measured and measure the defocus wavefront PV value or power value Δw of the optical system to be measured;

[0013] The interferometer lens is used to converge the measurement beam into the optical system to be measured and then convert it into parallel light through the optical system to be measured;

[0014] The aperture of the plane mirror is larger than the effective clear aperture D of the optical system to be measured, and is used to reflect the parallel light emitted by the optical system to be measured back into the optical system to be measured, and then enter the interferometer body through the interferometer lens;

[0015] The one-dimensional translation stage is used to control the translation of the interferometer lens and the interferometer body along the optical axis direction of the measurement beam;

[0016] The length measuring mechanism is used to monitor the displacement Δz of the one-dimensional translation stage;

[0017] The diameter measuring mechanism is used to measure the effective clear aperture D of the optical system to be measured.

[0018] Further, the F-number of the interferometer lens is less than the F-number of the optical system to be measured.

[0019] Further, the interferometer body is a dynamic interferometer.

[0020] Further, the length measuring mechanism is a length measuring interferometer.

[0021] Further, the diameter measuring mechanism is a three-coordinate device.

[0022] A focal length detection method for the alignment process of a long focal length optical system, characterized in that it includes the following steps:

[0023] Step 1, set up the focal length detection device for the alignment process of the long focal length optical system as described above;

[0024] Step 2, start the interferometer body to emit a measurement beam to the entrance end of the optical system to be measured and measure the defocus wavefront PV value or power value Δw of the optical system to be measured;

[0025] Step 3: Drive the interferometer lens and the interferometer body to move along the optical axis of the measurement beam by a one-dimensional translation stage, so that the PV value or power value Δw of the defocused wavefront measured by the interferometer body meets the preset requirements, and record the position where the interferometer body is located at this time as the stepping zero position;

[0026] Step 4: Drive the interferometer lens and the interferometer body to move back and forth along the optical axis of the measurement beam multiple times starting from the stepping zero position by a one-dimensional translation stage, monitor the displacement Δz of the one-dimensional translation stage through a length measuring mechanism, and record the PV value or power value Δw of the defocused wavefront corresponding to each displacement of the interferometer body at the same time;

[0027] Step 5: Calculate the focal length value of the optical system to be measured corresponding to each displacement amount

[0028] Step 6: Fit the calculated multiple focal length values f to obtain the actual focal length value of the optical system to be measured, and complete the focal length detection.

[0029] Further, step 4 is specifically:

[0030] Drive the interferometer lens and the interferometer body to move back and forth along the optical axis of the measurement beam multiple times starting from the stepping zero position by a one-dimensional translation stage, monitor the displacement Δz of the one-dimensional translation stage through a length measuring mechanism, and at the same time, after each displacement, measure the PV value or power value of the defocused wavefront multiple times by the interferometer body and take the average value to obtain Δw.

[0031] Further, in step 4:

[0032] When moving the interferometer lens and the interferometer body, it is necessary to monitor that the interference fringes obtained by the interferometer body are always in the center of the image.

[0033] Further, step 6 is specifically:

[0034] Fit the calculated multiple focal length values f by the least squares method to obtain the actual focal length value of the optical system to be measured, and complete the focal length detection.

[0035] Further, in step 5:

[0036] The effective clear aperture D of the optical system to be measured is measured by a three-coordinate device.

[0037] Advantages of the present invention:

[0038] 1. A focal length detection device and method for the alignment process of a long focal length optical system provided by the present invention. Compared with the detection method using a Burch plate, the present invention uses the PV value or power value of the defocused wavefront recorded by an interferometer and the displacement measured by a length measuring mechanism to fit and obtain the actual focal length of the optical system to be measured, greatly reducing the detection error caused by human eye aiming and the image point position drift caused by air flow disturbance, improving the detection efficiency and accuracy, and having a high repeatability.

[0039] 2. A focal length detection device and method for the alignment process of a long focal length optical system provided by the present invention can achieve the quantitative measurement of the focal length of the long focal length optical system. By combining the calculation and processing of the measurement data, the focal length offset of the long focal length optical system can be quantitatively given, accurately guiding the system alignment and detection.

[0040] 3. A focal length detection device for the alignment process of a long focal length optical system provided by the present invention has a simple structure and a short detection time, and can preferably solve the problem of high-precision and rapid quantitative measurement of the focal length of the long focal length optical system in the use posture. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 FIG. is a schematic structural diagram of an embodiment of a focal length detection device for the alignment process of a long focal length optical system of the present invention.

[0042] Reference Signs in the Drawings:

[0043] 1 - plane mirror, 2 - optical system to be measured, 3 - focal plane, 4 - interferometer lens, 5 - interferometer body, 6 - one-dimensional translation stage, 7 - length measuring mechanism. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0044] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the drawings and embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0045] A focal length detection device for the alignment process of a long focal length optical system provided in this embodiment is as Figure 1As shown in the figure, the detection device includes a plane mirror 1 disposed at the exit end of the optical system 2 to be measured, an interferometer lens 4 disposed at the entrance end of the optical system 2 to be measured and mounted on a one-dimensional translation stage 6, an interferometer body 5, a length measuring mechanism 7 and a diameter measuring mechanism; the interferometer body 5 is used to emit a measurement beam to the entrance end of the optical system 2 to be measured and measure the defocus wavefront PV value or power value Δw of the optical system 2 to be measured; the interferometer lens 4 is used to converge the measurement beam at the focal plane 3, and the optical system 2 to be measured then converts the converged beam into parallel light; the aperture of the plane mirror 1 is larger than the effective light passing aperture D of the optical system 2 to be measured, and is used to reflect the parallel light emitted by the optical system 2 to be measured back to the optical system 2 to be measured, converge again at the focal plane 3 and then enter the interferometer body 5 through the interferometer lens 4; adjust the postures of the plane mirror 1 and the interferometer body 5 to test the field position concerned by the optical system 2 to be measured. In this embodiment, the interferometer body 5 is a dynamic interferometer; the F number of the interferometer lens 4 is less than the F number of the optical system 2 to be measured. The one-dimensional translation stage 6 is used to control the translation of the interferometer lens 4 and the interferometer body 5 along the optical axis direction of the measurement beam; the length measuring mechanism 7 is used to monitor the displacement amount Δz of the one-dimensional translation stage 6; in this embodiment, the length measuring mechanism 7 is a length measuring interferometer. The diameter measuring mechanism is used to measure the effective light passing aperture D of the optical system 2 to be measured. In this embodiment, the diameter measuring mechanism is a three-coordinate device.

[0046] The specific measurement steps are as follows:

[0047] Step 1. Set up the focal length detection device for the alignment process of the long focal length optical system as described above;

[0048] 1.1 Select an interferometer lens 4 with an F number less than that of the optical system 2 to be measured, install it on the interferometer body 5, and place it at the position of the focal plane 3;

[0049] 1.2 Fix a one-dimensional translation stage 6 that moves along the optical axis direction below the interferometer body 5;

[0050] 1.3 Place a length measuring interferometer in the moving direction of the one-dimensional translation stage 6 to monitor the displacement amount of the interferometer body 5;

[0051] 1.4 Place a plane mirror 1 at the light exit of the optical system 2 to be measured (the aperture of the plane mirror 1 should be larger than the effective light passing aperture D of the optical system 2 to be measured);

[0052] Step 2. Start the interferometer body 5 to emit a measurement beam to the entrance end of the optical system 2 to be measured, and measure the defocus wavefront PV value or power value Δw of the optical system 2 to be measured;

[0053] Step 3: Drive the interferometer lens 4 and the interferometer body 5 along the optical axis of the measurement beam by the one-dimensional translation stage 6, so that the defocus wavefront PV value or power value Δw measured by the interferometer body 5 meets the preset requirements, and record the position where the interferometer body 5 is located at this time as the stepping zero position;

[0054] Step 4: Drive the interferometer lens 4 and the interferometer body 5 to move back and forth along the optical axis of the measurement beam multiple times starting from the stepping zero position by the one-dimensional translation stage 6, and monitor the displacement Δz of the one-dimensional translation stage 6 through the length measuring mechanism 7. At the same time, after each displacement, measure the defocus wavefront PV value or power value multiple times by the interferometer body 5 and take the average value to obtain Δw; when moving the interferometer lens 4 and the interferometer body 5, it is necessary to monitor that the interference fringes obtained by the interferometer body 5 are always in the center of the image.

[0055] Step 5: Calculate the focal length value of the optical system 2 to be measured corresponding to each displacement The effective clear aperture D of the optical system 2 to be measured is measured by a three-coordinate device and can be measured before Step 1.

[0056] Step 6: Fit the calculated multiple focal length values f by the least squares method to obtain the actual focal length value of the optical system 2 to be measured, and complete the focal length detection.

[0057] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any change or replacement within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A focal length detection device for a long focal length optical system during assembly and adjustment, characterized in that: It comprises a plane reflector (1) arranged at the output end of the optical system to be measured (2), an interferometer lens (4) and an interferometer body (5) arranged at the incident end of the optical system to be measured (2) and mounted on a one-dimensional translation stage (6), as well as a length measuring mechanism (7) and a diameter measuring mechanism; The interferometer body (5) is used to emit a measuring light beam to the incident end of the optical system (2) to be measured, and to measure the defocused wavefront PV value or power value Δw of the optical system (2) to be measured; The interferometer lens (4) is used to converge the measuring light beam into the optical system to be measured (2), and then convert it into parallel light through the optical system to be measured (2); The plane reflector (1) has an aperture greater than the effective aperture D of the optical system to be measured (2), and is used to reflect parallel light emitted by the optical system to be measured (2) back to the optical system to be measured (2), and then enter the interferometer body (5) through the interferometer lens (4); The one-dimensional translation stage (6) is used to control the translation of the interferometer lens (4) and the interferometer body (5) along the optical axis direction of the measuring light beam; The length measuring mechanism (7) is used to monitor the displacement Δz of the one-dimensional translation stage (6); The diameter measuring mechanism is used to measure the effective light aperture D of the optical system (2) to be measured.

2. The focal length detection device for the long focal length optical system assembly and adjustment process according to claim 1, characterized in that: The F number of the interferometer lens (4) is smaller than the F number of the optical system (2) to be measured.

3. The focal length detection device for the long focal length optical system assembly and adjustment process according to claim 1 or 2, characterized in that: The interferometer body (5) is a dynamic interferometer.

4. The focal length detection device for the long focal length optical system assembly and adjustment process according to claim 3, characterized in that: The length measuring mechanism (7) is a length measuring interferometer.

5. The focal length detection device for the long focal length optical system assembly and adjustment process according to claim 4, characterized in that: The diameter measuring mechanism is a three-coordinate device.

6. A focal length detection method for a long focal length optical system during assembly and adjustment, characterized in that: The following steps are involved: Step 1: constructing a focal length detection device for a long focal length optical system assembly and adjustment process as described in any one of claims 1 to 5; Step 2, starting the interferometer body (5) to emit a measuring beam to the incident end of the optical system (2) to be measured, and measuring the defocused wavefront PV value or power value △w of the optical system (2) to be measured; Step 3, driving the interferometer lens (4) and the interferometer body (5) to move along the optical axis of the measuring light beam by a one-dimensional translation stage (6), so that the defocused wavefront PV value or the power value △w measured by the interferometer body (5) meets the preset requirements, and the position of the interferometer body (5) at this time is recorded as the step zero position; Step 4, driving the interferometer lens (4) and the interferometer body (5) to move forward and backward multiple times along the optical axis of the measurement light beam from the stepping zero position by means of a one-dimensional translation stage (6), and monitoring the displacement Δz of the one-dimensional translation stage (6) by means of a length measuring mechanism (7), while recording the defocused wavefront PV value or power value Δw corresponding to each displacement of the interferometer body (5); Step 5: Calculate the focal length value of the optical system (2) to be measured corresponding to each displacement Step 6: Fit the calculated multiple focal length values ​​f to obtain the actual focal length value of the optical system (2) to be tested, and complete the focal length detection.

7. The focal length detection method for the long focal length optical system assembly and adjustment process according to claim 6, characterized in that: Step 4 is as follows: The interferometer lens (4) and the interferometer body (5) are driven by a one-dimensional translation stage (6) to move forward and backward multiple times along the optical axis of the measurement light beam from the stepping zero position, and the displacement Δz of the one-dimensional translation stage (6) is monitored by a length measuring mechanism (7). At the same time, after each displacement, the defocused wavefront PV value or power value is measured multiple times by the interferometer body (5) and the average value is taken to obtain Δw.

8. The focal length detection method for the long focal length optical system assembly and adjustment process according to claim 7, characterized in that: In step 4: When the interferometer lens (4) and the interferometer body (5) are moved, it is necessary to monitor that the interference ring obtained by the interferometer body (5) is always in the center of the image.

9. The focal length detection method for a long focal length optical system assembly and adjustment process according to claim 8, characterized in that: Step 6 is as follows: The calculated multiple focal length values ​​f are fitted by the least square method to obtain the actual focal length value of the optical system (2) to be tested, thereby completing the focal length detection.

10. The focal length detection method for a long focal length optical system assembly and adjustment process according to claim 9, characterized in that: In step 5: The effective aperture D of the optical system (2) to be measured is measured by a three-coordinate device.

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