CN115773724A - Low-noise Fizeau interference testing device and method based on all-solid-state random phase annular light source - Google Patents
Low-noise Fizeau interference testing device and method based on all-solid-state random phase annular light source Download PDFInfo
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Abstract
The invention discloses a low-noise Fizeau interference testing device and method based on an all-solid-state random phase annular light source. According to the device and the method, the influence of coherent noise generated by surface defects of the optical element, dust particles and the like in a Fizeau interference test can be reduced through the all-solid-state random phase annular light source module, the medium-frequency transmission capability of the interferometer is improved, low-noise and high-precision measurement of the surface shape of the planar optical element is realized, and the device and the method can be adapted to spherical surface measurement; meanwhile, the device has a point light source working mode, and can be adapted to spherical surface measurement, aspheric surface measurement, free-form surface measurement and transient measurement; the device also avoids the use of mechanical motion components and improves reliability and stability.
Description
Technical Field
The invention belongs to the technical field of optical precision detection, and particularly relates to a low-noise Fizeau interference testing device and method based on an all-solid-state random phase annular light source.
Background
The interference detection technology is the optical surface shape detection technology with highest precision and the widest application at present, the detection precision of the interference detection technology limits the highest precision of optical processing, and the interference detection technology is a foundation stone of modern optical industry. To improve the brightness and contrast of the interference image, modern interferometers typically use a laser as the light source. However, the coherence of the laser light causes diffraction and scattering at surface defects and dust of the optical elements, and causes coherent superposition of the reference and detection beams with various stray light, resulting in a large amount of ring and stripe-like coherent noise, reducing image quality and reducing the transfer function of the system. In a large-aperture interferometer for extreme detection tasks such as an ultra-high power laser system, an extreme ultraviolet lithography system and the like, coherent noise is mixed with required intermediate frequency information, and the detection precision is severely restricted.
The existing low-coherence light source and the existing extended light source can achieve a good coherent noise suppression effect in some systems, but due to the reduction of temporal coherence or spatial coherence, in a long-cavity long Fizeau interferometer commonly used for interference detection, the contrast of interference fringes is reduced to be almost zero and cannot be used. The method of placing rotating ground glass in the imaging part of the interferometer has limited capability of suppressing coherent noise, and can cause blurring of interference fringes and reduce the transfer function of the system.
Virtual annular light sources such as a rotary lens, a grating, a wedge-shaped flat plate and the like are proved to be capable of effectively inhibiting coherent noise in an interferometer, but the installation and adjustment difficulty is high and the stability is poor. A real annular light source is considered to be a simple and effective coherent noise suppression method, which has been used by ZYGO, etc., but still relies on the use of mechanical moving elements such as rotating ground glass. And the introduction of the motion elements inevitably introduces additional errors, and reduces the reliability and stability of the system. The coherent noise suppression method of the Fizeau interferometer without mechanical motion elements and the corresponding all-solid-state low-coherent noise Fizeau interference testing device are rarely reported at home and abroad.
Disclosure of Invention
The invention provides a low-noise Fizeau interference testing device and method based on an all-solid-state random phase annular light source, which are used for low-noise measurement of a plane optical element surface shape, and also provide a point light source working mode which is adaptive to spherical surface, aspheric surface, free-form surface measurement and transient measurement.
A low-noise Fizeau interference testing device based on an all-solid-state random phase annular light source comprises an all-solid-state random phase annular light source module and a Fizeau interference testing module;
the all-solid-state random phase annular light source module comprises: the device comprises a laser, a microscope objective, a pinhole filter, a first collimating lens group, an axicon, a guide rail, a focusing lens group, a first beam splitter, a spatial light modulator, a neutral density filter and an alignment camera; laser is emitted from a laser and is focused on a pinhole filter through a microscope objective to complete spatial filtering; the point light source formed after filtering is collimated into parallel light through the first collimating mirror group, and Bessel light beams are generated through the axicon; after light beams pass through the focusing lens group and the first beam splitter, transmitted light beams are focused on the spatial light modulator to form an annular light source, reflected light beams pass through the neutral density filter to be subjected to light intensity attenuation, and the reflected light beams are focused on the alignment camera to assist in adjustment; the axicon is arranged on the guide rail and moves out or into the light path through the guide rail so as to realize the switching between a point light source mode and an annular light source mode;
the fizeau interference test module includes: the device comprises a second beam splitter, a second collimating lens group, a standard transmission flat crystal, a plane to be detected, an imaging lens group and an imaging camera; the random phase annular light source provided by the all-solid-state random phase annular light source module is emitted from the spatial light modulator, reflected by the first beam splitter, enters the Fizeau interference testing module, is collimated into parallel light by the second collimator group after being transmitted by the second beam splitter, irradiates a standard transmission flat crystal and a tested plane and is reflected respectively; the two beams of reflected light are coherently superposed to form interference fringes, the interference fringes are reflected and refracted to an imaging light path through the second beam splitter, and the interference fringes are imaged on an imaging camera through the imaging lens group.
Further, the laser is a tunable semiconductor laser.
Furthermore, the microscope objective and the first collimating lens group are confocal, and the pinhole filter is positioned on a common focal plane of the microscope objective and the first collimating lens group.
Furthermore, the spatial light modulator is positioned on a focal plane of the focusing mirror group, is of a reflection type, a pure phase type or an amplitude and phase type, and the size of the pixel is not more than 20 micrometers.
Further, the alignment camera is located on the other focal plane of the focusing mirror group, and is symmetrical to the spatial light modulator about the beam splitting surface of the first beam splitter. The imaging camera is conjugated with the measured plane.
In the present invention, all elements except the guide rail are flush and coaxial, the axis is defined as the optical axis of the device, and the guide rail is perpendicular to the optical axis of the device.
The device of the invention has two working modes of the annular light source and the point light source. The axicon is arranged on the guide rail and moves out or in the light path through the guide rail so as to realize the switching of two modes: when the light path is moved out, the light path is in a point light source mode, and when the light path is moved in, the light path is in an annular light source mode.
The invention also provides a low-noise Fizeau interference test method based on the all-solid-state random phase annular light source, and the low-noise Fizeau interference test device comprises the following steps:
(1) Installing and adjusting a low-noise Fizeau interference testing device to enable the all-solid-state random phase annular light source module and the Fizeau interference testing module to be respectively aligned and correctly matched;
(2) Repeatedly loading a plurality of groups of phase distributions on the spatial light modulator, and setting the exposure time of the imaging camera to enable the exposure time of the imaging camera to be matched with the repetition period of the phase;
(3) And (3) acquiring an interference pattern after the device is adjusted: adjusting the wavelength of a laser to shift the phase, and sequentially acquiring phase-shifting interferograms with the phase differences of 0, pi/2, pi and 3 pi/2 by using an imaging camera;
(4) And performing phase demodulation, unwrapping and annular light source inclination factor correction on the interferogram to finally obtain a low-noise measured plane shape measurement result.
In the step (1), when the all-solid-state random phase annular light source module is adjusted, all light spots on the alignment camera should coincide at the center of the field of view and have the minimum light spot width.
In the step (2), the phase loaded by the spatial light modulator is different according to the working mode, and the specific steps are as follows:
in ring light source mode, the spatial light modulator repeatedly loads N sets of random phases at a frame rate of 1/T, N >100, and sets the imaging camera exposure time to NT to achieve sufficient coherent noise suppression'
In the point light source mode, the spatial light modulator loads a uniform phase, and the exposure time of the imaging camera is not restricted.
In the step (3), the wavelength tuning step length of the laser is related to the equivalent interference cavity length d of the Fizeau interference test module, and when the phase shift step length is pi/2, the tuning step length delta lambda of the laser is as follows:
wherein λ is the laser center wavelength.
In the step (4), according to the radius r of the annular light source and the focal length f of the collimator lens of the interferometer, correcting the inclination factor of the original surface shape W, wherein the formula is as follows:
wherein (x, y) is a spatial coordinate.
Compared with the prior art, the invention has the following beneficial effects:
according to the device and the method, the influence of coherent noise generated by surface defects of the optical element, dust particles and the like in a Fizeau interference test can be reduced through the all-solid-state random phase annular light source module, the medium-frequency transmission capability of the interferometer is improved, low-noise and high-precision measurement of the surface shape of the planar optical element is realized, and the device and the method can be adapted to spherical surface measurement; meanwhile, the device has a point light source working mode and can be adapted to spherical surface measurement, aspheric surface measurement, free-form surface measurement and transient measurement. The device also avoids the use of mechanical motion components and improves reliability and stability.
Drawings
Fig. 1 is a schematic diagram of a low-noise fizeau interference testing device based on an all-solid-state random phase annular light source according to the present invention.
Detailed Description
The invention will be described in further detail below with reference to the drawings and examples, which are intended to facilitate the understanding of the invention and are not intended to limit it in any way.
As shown in fig. 1, a low-noise fizeau interference testing device based on an all-solid-state random phase annular light source includes an all-solid-state random phase annular light source module and a fizeau interference testing module.
In the all-solid-state random phase annular light source module, laser emitted by a laser 1 passes through a turning mirror 2 and a turning mirror 3 and is focused on a pinhole filter 5 through a microscope objective 4 to complete spatial filtering, a point light source formed after filtering is collimated into parallel light through a first collimating mirror group 6, and a Bessel light beam is generated through an axicon lens 7; after the light beams pass through the focusing mirror group 8 and the first beam splitter 9, the transmitted light beams are focused on the spatial light modulator 10 to form an annular light source, dynamic random phases are loaded by the spatial light modulator 10, and the reflected light beams pass through the neutral density filter 11 to be subjected to light intensity attenuation and are focused on the alignment camera 12 to assist adjustment. The axicon 7 is mounted on the guide rail 13 and can move out of or into the light path through the guide rail 13 to realize the switching between the point light source mode and the annular light source mode.
The random phase annular light source is emitted from the spatial light modulator 10, reflected by the first beam splitter 9, enters the Fizeau interference test module, is transmitted through the second beam splitter 101, is collimated into parallel light by the second collimating mirror group 102, irradiates the standard transmission flat crystal 103 and the measured plane 104 and is respectively reflected; the two reflected lights are coherently superposed to form an interference fringe, and the interference fringe is reflected and refracted by the second beam splitter 101 to an imaging optical path, and is imaged on an imaging camera 106 by an imaging lens group 105.
In the embodiment of the present invention, the laser 1 is a tunable semiconductor laser. The microscope objective 4 and the first collimating lens group 6 are confocal, and the pinhole filter 5 is located on a common focal plane of the microscope objective 4 and the first collimating lens group 6. The spatial light modulator 10 is located on the focal plane of the focusing lens group 8, and is of a reflective type, a pure phase type or an amplitude and phase type, and the pixel size is not more than 20 micrometers. The alignment camera 12 is located at another focal plane of the focusing mirror group 8, and is symmetrical to the spatial light modulator 10 with respect to the beam splitting surface of the first beam splitter 9. The imaging camera 106 is conjugated to the plane under test 104.
In the present invention, all elements except the guide rail 13 are flush and coaxial, which is defined as the optical axis of the apparatus, and the guide rail is perpendicular to the optical axis of the apparatus.
The device of the invention has two working modes of the annular light source and the point light source. The axicon 7 is mounted on the guide rail 13 and moves out of or into the optical path through the guide rail 13 to realize the switching of two modes: when the light path is moved out, the light path is in a point light source mode, and when the light path is moved in, the light path is in an annular light source mode.
The method for carrying out the low-noise Fizeau interference test based on the all-solid-state random phase annular light source by using the device is as follows, taking a plane test as an example:
step 1, installing and adjusting a low-noise Fizeau interference testing device based on an all-solid-state random phase annular light source, so that an all-solid-state random phase annular light source module and a Fizeau interference testing module are respectively aligned and correctly matched. During the adjustment of the device, when the measured plane 104 is not placed, the image collected by the alignment camera 12 should show the reference annular light source reflected by the first beam splitter 9 and the self-collimating annular light source image formed by the reflection of the standard transmission flat crystal 103. The positions of the elements are adjusted until the two circular rings are mutually overlapped and have the minimum ring width, namely the all-solid-state random phase annular light source module and the Fizeau interference testing module are marked to be well assembled and matched respectively, and after the optical path is adjusted, the neutral density filter 11 and the alignment camera 12 can be reserved, removed or used for other purposes.
And 3, acquiring an interference pattern after the device is adjusted: the wavelength of the laser 1 is adjusted to shift the phase, and the phase-shifting interferogram with the phase difference of 0, pi/2, pi, 3 pi/2 is sequentially acquired by using the imaging camera 106. The wavelength tuning step of the laser 1 is related to the equivalent interference cavity length of the fizeau interference test module: when the central wavelength lambda of the laser, the equivalent interference cavity length d and the phase shift step length are pi/2, the tuning step length delta lambda of the laser is as follows:
and 4, carrying out phase demodulation, unwrapping and tilt factor correction on the interference pattern to finally obtain a low-noise measured plane shape measurement result. And correcting the surface shape W by an inclination factor according to the radius r of the annular light source and the focal length f of the collimating lens of the interferometer:
the embodiments described above are intended to illustrate the technical solutions and advantages of the present invention, and it should be understood that the above-mentioned embodiments are only specific embodiments of the present invention, and are not intended to limit the present invention, and any modifications, additions and equivalents made within the scope of the principles of the present invention should be included in the scope of the present invention.
Claims (10)
1. A low-noise Fizeau interference testing device based on an all-solid-state random phase annular light source is characterized by comprising an all-solid-state random phase annular light source module and a Fizeau interference testing module;
the all-solid-state random phase annular light source module comprises: the device comprises a laser, a microscope objective, a pinhole filter, a first collimating lens group, an axicon, a guide rail, a focusing lens group, a first beam splitter, a spatial light modulator, a neutral density filter and an alignment camera; laser is emitted from a laser and is focused on a pinhole filter through a microscope objective to complete spatial filtering; the point light source formed after filtering is collimated into parallel light through the first collimating mirror group, and Bessel light beams are generated through the axicon; after the light beams pass through the focusing lens group and the first beam splitter, the transmitted light beams are focused on the spatial light modulator to form an annular light source, and the reflected light beams pass through the neutral density filter to be subjected to light intensity attenuation and are focused on the alignment camera to assist in adjustment; the axicon is arranged on the guide rail and moves out or into the light path through the guide rail so as to realize the switching between a point light source mode and an annular light source mode;
the fizeau interference test module includes: the device comprises a second beam splitter, a second collimating lens group, a standard transmission optical flat crystal, a plane to be detected, an imaging lens group and an imaging camera; the random phase annular light source provided by the all-solid-state random phase annular light source module is emitted from the spatial light modulator, reflected by the first beam splitter, enters the Fizeau interference testing module, is collimated into parallel light by the second collimator group after being transmitted by the second beam splitter, irradiates a standard transmission flat crystal and a tested plane and is reflected respectively; two beams of reflected light are coherently superposed to form interference fringes, the interference fringes are reflected and refracted to an imaging light path through a second beam splitter, and the interference fringes are imaged on an imaging camera through an imaging lens group.
2. The all-solid-state random phase ring light source-based low-noise Fizeau interference testing device according to claim 1, wherein the microscope objective and the first collimating lens group are confocal, and the pinhole filter is located on a common focal plane of the microscope objective and the first collimating lens group.
3. The all-solid-state random phase annular light source-based low-noise Fizeau interference testing device according to claim 1, wherein the spatial light modulator is located on the focal plane of the focusing mirror group, is of a reflective type, a pure phase type or an amplitude and phase type, and has a pixel size of not more than 20 microns.
4. The all-solid-state random phase annular light source-based low noise fizeau interference testing apparatus of claim 1, wherein the alignment camera is located at another focal plane of the focusing lens group, and is symmetric with the spatial light modulator about the beam splitting surface of the first beam splitter.
5. The all-solid-state random phase annular light source-based low-noise Fizeau interference test device according to claim 1, wherein the imaging camera is conjugated to the plane to be tested.
6. A low-noise fizeau interference test method based on all-solid-state random phase annular light source, characterized in that the low-noise fizeau interference test device of any one of claims 1 to 5 is used, and the method comprises the following steps:
(1) Installing and adjusting the low-noise Fizeau interference testing device to enable the all-solid-state random phase annular light source module and the Fizeau interference testing module to be aligned respectively and to be matched correctly;
(2) Repeatedly loading a plurality of groups of phase distributions on the spatial light modulator, and setting the exposure time of the imaging camera to enable the exposure time of the imaging camera to be matched with the repetition period of the phase;
(3) And (3) acquiring an interference pattern after the device is adjusted: adjusting the wavelength of a laser to shift the phase, and sequentially acquiring phase-shifting interferograms with the phase differences of 0, pi/2, pi and 3 pi/2 by using an imaging camera;
(4) And performing phase demodulation, unwrapping and annular light source inclination factor correction on the interferogram to finally obtain a low-noise measured plane shape measurement result.
7. The all-solid-state random phase annular light source-based low-noise Fizeau interference test method according to claim 6, wherein in step (1), when the all-solid-state random phase annular light source module is adjusted, all light spots on the alignment camera should coincide at the center of the field of view and have the smallest light spot width.
8. The all-solid-state random phase annular light source-based low-noise Fizeau interference test method according to claim 6, wherein in the step (2), the loaded phase of the spatial light modulator is different according to the operation mode, specifically as follows:
in the ring light source mode, the spatial light modulator repeatedly loads N groups of random phases at a frame rate of 1/T, wherein N is more than 100, and the exposure time of the imaging camera is set to NT, so that sufficient coherent noise suppression is realized.
9. The all-solid-state random phase annular light source-based low noise fizeau interference test method of claim 6, wherein in step (3), the wavelength tuning step of the laser is related to the equivalent interference cavity length d of the fizeau interference test module, and when the phase shift step is pi/2, the tuning step Δ λ of the laser is:
wherein λ is the laser center wavelength.
10. The all-solid-state random phase annular light source-based low-noise Fizeau interference test method according to claim 6, wherein in the step (4), the original shape W is corrected by the tilt factor according to the annular light source radius r and the focal length f of the collimator lens of the interferometer, and the formula is as follows:
wherein (x, y) is a spatial coordinate.
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| CN116045836A (en) * | 2023-04-03 | 2023-05-02 | 成都太科光电技术有限责任公司 | Phi 1200mm extremely large caliber plane optical interference testing device |
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| CN116045836A (en) * | 2023-04-03 | 2023-05-02 | 成都太科光电技术有限责任公司 | Phi 1200mm extremely large caliber plane optical interference testing device |
| CN116045836B (en) * | 2023-04-03 | 2023-06-02 | 成都太科光电技术有限责任公司 | Phi 1200mm extremely large caliber plane optical interference testing device |
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