CN116735156A - Multi-degree-of-freedom telescope test system - Google Patents

Multi-degree-of-freedom telescope test system Download PDF

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Publication number
CN116735156A
CN116735156A CN202310476552.9A CN202310476552A CN116735156A CN 116735156 A CN116735156 A CN 116735156A CN 202310476552 A CN202310476552 A CN 202310476552A CN 116735156 A CN116735156 A CN 116735156A
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beam splitter
light
freedom
reflected
sample
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林栩凌
吴金贵
吴铠岚
王小勇
白绍竣
郭忠凯
王芸
谈宜东
孙倩
郑永超
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Beijing Institute of Space Research Mechanical and Electricity
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Beijing Institute of Space Research Mechanical and Electricity
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    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/10—Beam splitting or combining systems
    • G02B27/106—Beam splitting or combining systems for splitting or combining a plurality of identical beams or images, e.g. image replication
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/02—Testing optical properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/08—Testing mechanical properties
    • G01M11/081—Testing mechanical properties by using a contact-less detection method, i.e. with a camera
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/286—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Chemical & Material Sciences (AREA)
  • Analytical Chemistry (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

The invention relates to a multi-degree-of-freedom telescope test system, which comprises: the device comprises a laser, an acousto-optic modulator, a beam splitter, a transverse beam splitter, a plane reflector, a half wave plate, a quarter wave plate, a pyramid retroreflector, a half mirror, a photoelectric detector, a four-quadrant detector and a digital phase meter; by means of heterodyne interferometry, heterodyne interference signals, differential wavefront phase detection signals and differential power detection signals are combined, multi-degree-of-freedom high-precision measurement is provided, and the change of the structure of the sample to be measured in the respective degrees of freedom is obtained. The interferometer adopted by the method has the characteristics of compact structure, high precision and high efficiency. And in multiple degrees of freedom, the high-precision requirement of the telescope structure stability test is effectively ensured.

Description

Multi-degree-of-freedom telescope test system
Technical Field
The invention relates to a multi-degree-of-freedom telescope test system which can efficiently and accurately measure the structural changes of a sample to be tested in multiple degrees of freedom.
Background
In order to successfully complete the space measurement task, the satellite-borne optical device, such as a telescope, needs to have the characteristics of high stability, portability, inadvisable deformation and the like so as to cope with external influences such as temperature change, vibration and the like and ensure the measurement accuracy. Thus, it is particularly important to pre-test the structural stability of the spaceborne optical device. The optical interferometer is often used as the first choice for testing the structural stability of the telescope due to the characteristics of high precision, high signal to noise ratio and the like. The test light path currently adopted is limited to single-degree-of-freedom directional measurement or is limited by measurement accuracy. Therefore, a test method with compact arrangement, high efficiency, high precision and multiple degrees of freedom needs to be studied.
Therefore, the high-precision multi-degree-of-freedom testing method is provided, and the reference light and the measuring light travel along the same path as much as possible by means of the transverse beam splitter, so that common mode noise is eliminated as much as possible; the change of the structure of the sample to be measured in the respective degrees of freedom can be measured simultaneously by combining the differential wavefront phase detection signal, the differential power detection signal and the phase information, and the method has the characteristic of high efficiency; in addition, the retroreflector, the quarter wave plate and the half mirror are combined, so that the change of the telescope in the rolling degree of freedom can be effectively measured while the compact structure of the light path is ensured. Therefore, the test system can well meet the structural stability test requirement of the satellite-borne optical device, and the test is ensured to be performed efficiently and accurately.
Disclosure of Invention
The invention solves the technical problems that: aiming at the problems that the conventional structural stability testing method is insufficient in precision, limited to single degree of freedom and the like in the prior art, the conventional scheme is optimized, and the high-precision and high-efficiency multi-degree-of-freedom telescope testing method is provided.
The invention solves the technical problems by the following technical proposal:
a multi-degree-of-freedom telescope test system comprises a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a first beam splitter, a second beam splitter, a third beam splitter, a first transverse beam splitter, a second transverse beam splitter, a third transverse beam splitter, a first plane mirror, a second plane mirror, a third plane mirror, a half wave plate, a quarter wave plate, a pyramid retroreflector, a half mirror, a first photoelectric detector, a second photoelectric detector, a first four-quadrant detector, a second four-quadrant detector and a digital phase meter;
the first laser and the second laser respectively output a beam of laser with the wavelength of 1064nm, and then respectively pass through the first acousto-optic modulator and the second acousto-optic modulator to obtain the frequency f 1 Is f 2 After which both beams enter the interferometer;
the first laser outputs the frequency f after frequency shift by the first acousto-optic modulator 1 The reference light of the light source is firstly incident into a first beam splitter, split by the beam splitter and then split into a reflection component and a transmission component; the transmission component enters the first transverse beam splitter, and after being transmitted and reflected by the first transverse beam splitter, the emergent light is two parallel light beams; the two light beams are transmitted by the second beam splitter and reflected by the second plane mirror, and then are incident into the second beam splitter again; after that, the two light beams are reflected to a second transverse beam splitter through a second beam splitter, and are respectively received by a first four-quadrant detector and a first photoelectric detector after being reflected twice; the reflection component is incident to the first plane mirror through the half-wave plate and then reflected to the third beam splitter through the third transverse beam splitter; the light beam passes through the firstAfter the beam splitter, the transmission component is received by a second four-quadrant detector; the reflected component of which is received by a second photodetector;
output by the second laser, and frequency f after frequency shift by the second optical modulator 2 Firstly, the measuring light is transmitted and reflected by a first transverse beam splitter to form two parallel components; after both light beams are transmitted through the second beam splitter, the component reflected to the second beam splitter by the first transverse beam splitter is reflected by the third plane mirror and then enters the second beam splitter again, and then is reflected to the second transverse beam splitter by the second beam splitter, and is received by the first photoelectric detector after being transmitted by the second transverse beam splitter; the component transmitted to the second beam splitter by the first transverse beam splitter passes through the half mirror, and then a part of light beam is reflected back to the second beam splitter by the half mirror, is reflected to the second transverse beam splitter by the second beam splitter, and is transmitted to the second transverse beam splitter and is received by the first four-quadrant detector; the other part of the component passes through the half mirror to the retroreflector; the light beam component entering the retroreflector is reflected by the retroreflector, then enters the second beam splitter again through the quarter-wave plate, and is reflected to the third beam splitter by the beam splitter; after the light beam passes through the third beam splitter, the transmission component is received by the second photoelectric detector, and the reflection component is received by the second four-quadrant detector; the light beams incident on the first photoelectric detector and the first four-quadrant detector interfere respectively to form a light beat, and the light beat is received by the first photoelectric detector and the first four-quadrant detector; the light beams incident on the second photodetector and the second four-quadrant detector will interfere respectively to form a light beat, and then are received by the second photodetector and the second four-quadrant detector respectively;
signals output by the first photoelectric detector, the second photoelectric detector, the first four-quadrant detector and the second four-quadrant detector are input into a digital phase meter after analog-to-digital conversion, and phase information, differential wavefront phase detection signals and differential power detection signals can be obtained after processing;
processing the obtained differential wavefront phase detection signal to obtain the change theta of the sample in the azimuth direction y Variation θ in pitch direction x The method comprises the steps of carrying out a first treatment on the surface of the The differential power detection signal is processed to obtain the change delta x of the sample in the x axis and the change delta y of the sample in the y axis; the change delta z of the sample in the axial direction and the change theta of the rolling freedom degree are obtained by processing the output phase result z The method comprises the steps of carrying out a first treatment on the surface of the Therefore, the deformation and the deflection of the sample to be detected are detected on three translational degrees of freedom and three rotational degrees of freedom, and the aim of measuring the structural stability of multiple degrees of freedom is fulfilled.
The frequency difference Deltaf=f between the reference light and the measuring light 1 -f 2 ＝1MHz。
The adopted beam splitter and the adopted transverse beam splitter are both unpolarized beam splitters, and the transmission ratio is 50:50.
The surface of the retroreflector is respectively stuck with a half mirror and a quarter wave plate, and the half mirror and the quarter wave plate respectively occupy half area.
The third plane reflector and the retroreflector are respectively fixed at two ends of the sample to be measured, so that the change of the dimension of the sample to be measured along the respective degrees of freedom can be measured.
The processing to obtain phase information, a differential wavefront phase detection signal and a differential power detection signal includes:
the four detection pixels on the surface of the first four-quadrant detector respectively receive the light beat signals, and four phase results respectively marked as phi can be obtained after the light beat signals are processed by a digital phase meter A 、Φ B 、Φ C And phi is D The method comprises the steps of carrying out a first treatment on the surface of the Total phase result of the first four-quadrant detectorCan be defined as:
calculating a differential wavefront phase detection signal; the differential wavefront phase detection signal is used for measuring the wavefront deflection angle of two light beams and can be divided into a horizontal signal DWS h And vertical signal DWS v The calculation mode is as follows:
the average light power received by each quadrant of the second four-quadrant detector is obtained by carrying out surface integral on the received light intensity
Wherein Z is the dielectric impedance;E R is a reference photo-electric field component; e (E) M To measure the component of the optical electrical field; the average power of each quadrant is recorded as +.>The DPS signal can be divided into horizontal and vertical signals, respectively denoted DPS h And DPS v The definition is:
variation of the sample in azimuth direction θ y Variation θ in pitch direction x The method comprises the steps of obtaining by processing differential wavefront phase detection signals; the change delta x of the sample on the x axis and the change delta y of the sample on the y axis are obtained through differential power detection signals; axial variation Δz of sample and rolling degree of freedom variation θ z By phase-shifting the output phaseThe bit result is processed and obtained by the following steps:
axial variation Δz of phase signal obtained by first photodetector and first four-quadrant detectorAnd->And (3) obtaining:
Δx, Δy from the differential power detection signal; because the retroreflector is adopted to reflect the light beam, when the structure of the sample is changed in the horizontal or vertical direction, the position of the retroreflector is changed, so that the position of the measuring light beam on the surface of the second four-quadrant detector is moved, and DPS signals are changed; for small range changes, there are:
Δx＝C 1 ·DPS h
Δy＝C 2 ·DPS v
wherein C is 1 、C 2 Is a proportionality coefficient;
θ y ，θ x the wave front phase detection signal is obtained by a differential wave front phase detection signal; for small ranges of offset, the DWS signal is proportional to the corresponding offset angle, and thus:
θ y ∝DWS h
θ x ∝DWS v
the differential wavefront phase detection signal can be calibrated in advance to find the relationship between the differential wavefront phase detection signal and the variation theta, so that the variation can be calculated in the subsequent measurement;
θ z is calculated as follows: when the sample to be measured changes along the rolling direction, the retroreflector rotates along with the sample to be measured, and then the quarter wave plate on the surface of the retroreflector is driven to rotate; so that the angle between the fast axis of the quarter wave plate and the horizontal direction will be changedPerforming chemical treatment; if the laser incident into the quarter wave plate is linearly polarized light, when the polarization direction of the incident linearly polarized light forms a certain included angle alpha with the fast axis of the quarter wave plate, andwhen the emergent light is elliptical polarized light; rotating the quarter wave plate, and changing the ellipsometry rate of the emergent ellipsometric light; for a small range of angular variations, the bias angle and ellipsometry are approximately linear, and thus can be obtained:
k is a proportionality coefficient, a is an elliptic polarization long half shaft, and b is an elliptic polarization short half shaft; the reference light reflected by the beam splitter 1 is linearly polarized light, the half wave plate is rotated to enable the polarization direction of the reference light to form an included angle of 45 degrees with the long axis of elliptical polarized light, and the polarization direction can be obtained by the polarization measuring instrument; at this time, the phase signal change obtained by the second photodetector can be written as:
wherein a is elliptic polarization long half shaft; b is an elliptical polarization short half shaft; gamma is the included angle between the polarization direction of the reference light and the long axis of the elliptical polarized light;is a common mode part; when the initial included angle is 45 degrees, the phase change part caused by polarization is as follows:
i.e. the phase change is equivalent to an ellipsometric change; in addition, because the angle change is smaller, the phase change is equivalent to the ellipsometry rate change in the measuring process; this can be achieved by:
wherein the method comprises the steps ofObtained by the first photodetector, minus +.>Can remove noise introduced by the acousto-optic modulator, thereby obtainingThereby obtaining theta z 。
Compared with the prior art, the invention has the advantages that:
(1) The telescope structure stability testing method with multiple degrees of freedom provided by the invention has the characteristics of high precision and high efficiency by means of heterodyne interferometry and combining phase information, differential wavefront phase Detection (DWS) signals and differential power Detection (DPS) signals, and the structure changes of a sample to be tested on three translational degrees of freedom and three rotational degrees of freedom are measured;
(2) The invention adopts a mode of combining the retroreflector, the half-reflecting mirror and the quarter-wave plate, so that the light path design is more compact and the occupied volume is reduced while the measurement requirement is met, thereby obtaining a more stable light path structure. The stability of the measuring system and the coping capability of the measuring system to environmental changes are effectively improved.
Drawings
FIG. 1 is a flow chart of the present invention;
FIG. 2 is a schematic view of the optical path of the present invention;
FIG. 3 is a schematic top view of the light path of the present invention;
detailed description of the preferred embodiments
The invention relates to a multi-degree-of-freedom telescope test system which comprises a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a first beam splitter, a second beam splitter, a third beam splitter, a first transverse beam splitter, a second transverse beam splitter, a third transverse beam splitter, a first plane reflector, a second plane reflector, a third plane reflector, a half wave plate, a quarter wave plate, a pyramid retroreflector, a half mirror, a first photoelectric detector, a second photoelectric detector, a first four-quadrant detector, a second four-quadrant detector and a digital phase meter, wherein the first beam splitter is arranged on the first side of the first laser;
the retroreflector RR and the plane mirror M3 are first fixed at both ends of the sample to be measured, and thereafter reference light and measuring light are introduced by the lasers 1, 2, respectively. The reference light and the measurement light respectively pass through the acousto-optic modulator, thereby obtaining a frequency difference of 1 MHz.
The reference light is first incident on the beam splitter BS1, split by the beam splitter, and then split into a reflected component and a transmitted component. The transmission component enters the transverse beam splitter LBS1, and after being transmitted and reflected by the transverse beam splitter LBS1, the emergent light is two parallel light beams. The two light beams are transmitted by the beam splitter BS2 and then reflected by the plane mirror M2, and are incident to the beam splitter BS2 again. After that, the two light beams are reflected to a transverse beam splitter LBS2 through a beam splitter BS2, and are respectively received by a four-quadrant detector QPD1 and a photoelectric detector PD1 after being reflected twice; the reference light is incident on the plane mirror M1 through the half wave plate HWP by the reflection component formed after passing through the beam splitter BS1, and is then reflected to the beam splitter BS3 through the transverse beam splitter LBS 3. After passing through the beam splitter BS3, the transmission component is received by the four-quadrant detector QPD 2; its reflected component is received by photodetector PD 2;
the measuring light is first transmitted and reflected by the transverse beam splitter LBS1 to form two parallel components. After the two light beams pass through the beam splitter BS2, the component reflected to the beam splitter BS2 by the transverse beam splitter LBS1 is reflected by the plane mirror M3 and then enters the beam splitter BS2 again, and then is reflected to the transverse beam splitter LBS2 by the beam splitter BS2, and is received by the photodetector PD1 after being transmitted by the transverse beam splitter BS 2; the component transmitted to the beam splitter BS2 by the transverse beam splitter LBS1 will first pass through the half mirror SRM, after which a part of the light beam is reflected back to the BS beam splitter 2 by the half mirror, and then reflected to the transverse beam splitter LBS2 by the beam splitter BS2, and then transmitted to the transverse beam splitter LBS2, and received by the four-quadrant detector QPD 1; the other part of the component passes through the half mirror to the retroreflector RR; the beam component incident on the retroreflector is reflected by the retroreflector, and then enters the beam splitter BS2 again through the quarter-wave plate QWP, and is reflected by the beam splitter to the beam splitter BS3. After passing through the beam splitter BS3, the transmitted component will be received by the photodetector PD 2; the reflected component will be received by the four-quadrant detector QPD 2;
the light beams incident on the photo detector PD1 and the four-quadrant detector QPD1 will interfere respectively to form a light beat, and then are received by the photo detector PD1 and the four-quadrant detector QPD1 respectively; the light beams incident on the photodetector PD2 and the four-quadrant detector QPD2 will interfere to form a beat, respectively, and thereafter received by the photodetector PD2 and the four-quadrant detector QPD2, respectively;
after the phase meter processing, phase information, differential wave front phase detection DWS signals and differential power detection DPS signals can be obtained, and the differential wave front phase detection signals are used for measuring wave front deflection angles of two light beams and can be divided into horizontal signals DWS h And vertical signal DWS v The calculation mode is as follows:
differential power detection DPS signals are divided into horizontal and vertical signals, respectively denoted DPS h And DPS v The definition is:
Δz may be a phase signal obtained by photodetector PD1 and four-quadrant detector QPD1And->And (3) obtaining:
θ y ，θ x can be obtained from the differential wavefront phase detection DWS signal. For small ranges of offset, the DWS signal is proportional to the corresponding offset angle, and thus:
θ y ∝DWS h
θ x ∝DWS v
the differential wavefront phase detection signal can be calibrated in advance to find the relationship between the differential wavefront phase detection signal and the variation theta, so that the variation can be calculated in the subsequent measurement; Δx, Δy may be derived from the differential power probe DPS signal, for a small range of changes:
Δx＝C 1 ·DPS h
Δy＝C 2 ·DPS v
C 1 、C 2 is a proportionality coefficient; when the sample to be measured changes along the rolling direction, the deflection angle and the ellipsometry approximate to linear relation for small-range angle change, thereby obtaining the following components:
k is a proportionality coefficient, a is an elliptic polarization long half shaft, and b is an elliptic polarization short half shaft. The reference light reflected by the beam splitter BS1 is linearly polarized light, and the half wave plate is rotated to enable the polarization direction of the reference light to form an included angle of 45 degrees with the long axis of elliptical polarized light, and the polarization direction can be obtained by the polarization measuring instrument. At this time, the phase signal change obtained by the detector PD2 can be written as:
wherein a is ellipsePolarization long half shaft; b is an elliptical polarization short half shaft; gamma is the included angle between the polarization direction of the reference light and the long axis of the elliptical polarized light;is a common mode part. When the initial included angle is 45 degrees, the phase change part caused by polarization is as follows:
i.e. the phase change is equivalent to an ellipsometric change; also, because the angle change is small, it can be considered that the phase change is equivalent to the ellipsometry change in the measurement process. This can be achieved by:
can be obtained from detector PD1, minus +.>Noise introduced by the acousto-optic modulator can be removed, whereby +.>Thereby obtaining theta z 。
Thus, the changes delta x, delta y and delta z of the sample to be measured in the x, y and z directions can be obtained; and changes in azimuth, pitch, roll direction θ y ，θ x ，θ z 。

Claims (7)

1. The multi-degree-of-freedom telescope testing system is characterized by comprising a first laser, a second laser, a first acousto-optic modulator, a second acousto-optic modulator, a first beam splitter, a second beam splitter, a third beam splitter, a first transverse beam splitter, a second transverse beam splitter, a third transverse beam splitter, a first plane mirror, a second plane mirror, a third plane mirror, a half wave plate, a quarter wave plate, a pyramid retroreflector, a half mirror, a first photoelectric detector, a second photoelectric detector, a first four-quadrant detector, a second four-quadrant detector and a digital phase meter;
the first laser and the second laser respectively output a beam of laser, and then respectively pass through the first acousto-optic modulator and the second acousto-optic modulator correspondingly to obtain a frequency f 1 Is f 2 After which both beams enter the interferometer;
the first laser outputs the frequency f after frequency shift by the first acousto-optic modulator 1 The reference light of the light source is firstly incident into a first beam splitter, split by the beam splitter and then split into a reflection component and a transmission component; the transmission component enters the first transverse beam splitter, and after being transmitted and reflected by the first transverse beam splitter, the emergent light is two parallel light beams; the two light beams are transmitted by the second beam splitter and reflected by the second plane mirror, and then are incident into the second beam splitter again; after that, the two light beams are reflected to a second transverse beam splitter through a second beam splitter, and are respectively received by a first four-quadrant detector and a first photoelectric detector after being reflected twice; the reflection component is incident to the first plane mirror through the half-wave plate and then reflected to the third beam splitter through the third transverse beam splitter; after the light beam passes through the third beam splitter, the transmission component is received by the second four-quadrant detector; the reflected component of which is received by a second photodetector;
output by the second laser, and frequency f after frequency shift by the second optical modulator 2 Firstly, the measuring light is transmitted and reflected by a first transverse beam splitter to form two parallel components; after both light beams are transmitted through the second beam splitter, the component reflected to the second beam splitter by the first transverse beam splitter is reflected by the third plane mirror and then enters the second beam splitter again, and then is reflected to the second transverse beam splitter by the second beam splitter, and is received by the first photoelectric detector after being transmitted by the second transverse beam splitter; the component transmitted to the second beam splitter by the first transverse beam splitter will firstly pass through the half mirror, and then a part of light beam is reflected back to the second beam splitter by the half mirror, and then is reflected to the second transverse beam splitterTransmitting the second transverse beam splitter to the beam splitter and then receiving the beam splitter by the first four-quadrant detector; the other part of the component passes through the half mirror to the retroreflector; the light beam component entering the retroreflector is reflected by the retroreflector, then enters the second beam splitter again through the quarter-wave plate, and is reflected to the third beam splitter by the beam splitter; after the light beam passes through the third beam splitter, the transmission component is received by the second photoelectric detector, and the reflection component is received by the second four-quadrant detector; the light beams incident on the first photoelectric detector and the first four-quadrant detector interfere respectively to form a light beat, and the light beat is received by the first photoelectric detector and the first four-quadrant detector; the light beams incident on the second photodetector and the second four-quadrant detector will interfere respectively to form a light beat, and then are received by the second photodetector and the second four-quadrant detector respectively;
signals output by the first photoelectric detector, the second photoelectric detector, the first four-quadrant detector and the second four-quadrant detector are input into a digital phase meter after analog-to-digital conversion, and phase information, differential wavefront phase detection signals and differential power detection signals can be obtained after processing;
processing the obtained differential wavefront phase detection signal to obtain the change theta of the sample in the azimuth direction y Variation θ in pitch direction x The method comprises the steps of carrying out a first treatment on the surface of the The differential power detection signal is processed to obtain the change delta x of the sample in the x axis and the change delta y of the sample in the y axis; the change delta z of the sample in the axial direction and the change theta of the rolling freedom degree are obtained by processing the output phase result z The method comprises the steps of carrying out a first treatment on the surface of the Therefore, the deformation and the deflection of the sample to be detected are detected on three translational degrees of freedom and three rotational degrees of freedom, and the aim of measuring the structural stability of multiple degrees of freedom is fulfilled.
2. The multiple degree of freedom telescope test system of claim 1, wherein: the frequency difference Deltaf=f between the reference light and the measuring light 1 -f 2 ＝1MHz。
3. The multiple degree of freedom telescope test system of claim 1, wherein: the adopted beam splitter and the adopted transverse beam splitter are both unpolarized beam splitters, and the transmission ratio is 50:50.
4. The multiple degree of freedom telescope test system of claim 1, wherein: the surface of the retroreflector is respectively stuck with a half mirror and a quarter wave plate, and the half mirror and the quarter wave plate respectively occupy half area.
5. The multiple degree of freedom telescope test system of claim 1, wherein: the third plane reflector and the retroreflector are respectively fixed at two ends of the sample to be measured, so that the change of the dimension of the sample to be measured along the respective degrees of freedom can be measured.
6. The multiple degree of freedom telescope test system of claim 1, wherein: the processing to obtain phase information, a differential wavefront phase detection signal and a differential power detection signal includes:
the four detection pixels on the surface of the first four-quadrant detector respectively receive the light beat signals, and four phase results respectively marked as phi can be obtained after the light beat signals are processed by a digital phase meter A 、Φ B 、Φ C And phi is D The method comprises the steps of carrying out a first treatment on the surface of the Total phase result of the first four-quadrant detectorCan be defined as:
calculating a differential wavefront phase detection signal; the differential wavefront phase detection signal is used for measuring the wavefront deflection angle of two light beams and can be divided into a horizontal signal DWS h And vertical signal DWS v The calculation mode is as follows:
the average light power received by each quadrant of the second four-quadrant detector is obtained by carrying out surface integral on the received light intensity
Wherein Z is the dielectric impedance;E R is a reference photo-electric field component; e (E) M To measure the component of the optical electrical field; the average power of each quadrant is recorded as +.>The DPS signal can be divided into horizontal and vertical signals, respectively denoted DPS h And DPS v The definition is:
7. the multiple degree of freedom telescope test system of claim 6, wherein: variation of the sample in azimuth direction θ y Variation θ in pitch direction x The method comprises the steps of obtaining by processing differential wavefront phase detection signals;the change delta x of the sample on the x axis and the change delta y of the sample on the y axis are obtained through differential power detection signals; axial variation Δz of sample and rolling degree of freedom variation θ z The method is obtained by processing the output phase result, and comprises the following specific calculation steps:
axial variation Δz of phase signal obtained by first photodetector and first four-quadrant detectorAnd->And (3) obtaining:
Δx, Δy from the differential power detection signal; because the retroreflector is adopted to reflect the light beam, when the structure of the sample is changed in the horizontal or vertical direction, the position of the retroreflector is changed, so that the position of the measuring light beam on the surface of the second four-quadrant detector is moved, and DPS signals are changed; for small range changes, there are:
Δx＝C 1 ·DPS h
Δy＝C 2 ·DPS v
wherein C is 1 、C 2 Is a proportionality coefficient;
θ y ，θ x the wave front phase detection signal is obtained by a differential wave front phase detection signal; for small ranges of offset, the DWS signal is proportional to the corresponding offset angle, and thus:
θ y ∝DWS h
θ x ∝DWS v
the differential wavefront phase detection signal can be calibrated in advance to find the relationship between the differential wavefront phase detection signal and the variation theta, so that the variation can be calculated in the subsequent measurement;
θ z is of the meter(s)The calculation is as follows: when the sample to be measured changes along the rolling direction, the retroreflector rotates along with the sample to be measured, and then the quarter wave plate on the surface of the retroreflector is driven to rotate; so the included angle between the fast axis of the quarter wave plate and the horizontal direction can be changed; if the laser incident into the quarter wave plate is linearly polarized light, when the polarization direction of the incident linearly polarized light forms a certain included angle alpha with the fast axis of the quarter wave plate, andwhen the emergent light is elliptical polarized light; rotating the quarter wave plate, and changing the ellipsometry rate of the emergent ellipsometric light; for a small range of angular variations, the bias angle and ellipsometry are approximately linear, and thus can be obtained:
k is a proportionality coefficient, a is an elliptic polarization long half shaft, and b is an elliptic polarization short half shaft; the reference light reflected by the beam splitter 1 is linearly polarized light, the half wave plate is rotated to enable the polarization direction of the reference light to form an included angle of 45 degrees with the long axis of elliptical polarized light, and the polarization direction can be obtained by the polarization measuring instrument; at this time, the phase signal change obtained by the second photodetector can be written as:
wherein a is elliptic polarization long half shaft; b is an elliptical polarization short half shaft; gamma is the included angle between the polarization direction of the reference light and the long axis of the elliptical polarized light;is a common mode part; when the initial included angle is 45 degrees, the phase change part caused by polarization is as follows:
i.e. the phase change is equivalent to an ellipsometric change; in addition, because the angle change is smaller, the phase change is equivalent to the ellipsometry rate change in the measuring process; this can be achieved by:
wherein the method comprises the steps ofObtained by the first photodetector, minus +.>Noise introduced by the acousto-optic modulator can be removed, thereby obtaining +.>Thereby obtaining theta z 。
CN202310476552.9A 2023-04-27 2023-04-27 Multi-degree-of-freedom telescope test system Pending CN116735156A (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117537937A (en) * 2024-01-05 2024-02-09 国科大杭州高等研究院 Direction control system for inhibiting nonlinearity of differential wavefront sensing technology

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN117537937A (en) * 2024-01-05 2024-02-09 国科大杭州高等研究院 Direction control system for inhibiting nonlinearity of differential wavefront sensing technology
CN117537937B (en) * 2024-01-05 2024-04-16 国科大杭州高等研究院 Direction control system for inhibiting nonlinearity of differential wavefront sensing technology

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