CN105571516A - Full field of view low frequency heterodyne interferometer - Google Patents

Abstract

The invention discloses a full field of view low frequency heterodyne interferometer. The full field of view low frequency heterodyne interferometer utilizes an acousto-optic frequency shifter to perform heterodyne interference phase shift, and can effectively prevent a motion piece existing in the interferometer, and has the advantages of improving the measuring accuracy, being high in interference immunity, reducing the difficulty and cost for development, and having more obvious advantages than the advantages of mechanical driving. Besides, the full field of view low frequency heterodyne interferometer utilizes a low frequency difference heterodyne interference and area array detector to perform continuous acquisition so that the acquired information content is more abundant, and is conductive to precise phase calculation. For facial form measurement for a curved surface reflector with large aperture and long focal length, as the light path for measurement is long, the facial form measurement is easily interfered by vibration, air flow and other factors. However, the full field of view low frequency heterodyne interferometer has the capability for restraining the interference of the vibration, air flow and other factors, and combined with the light path designed through combination of the full field of view low frequency heterodyne interferometer, the full field of view low frequency heterodyne interferometer is specifically suitable for facial form measurement for the curved surface reflector with large aperture and long focal length.

Description

A kind of full filed low frequency heterodyne ineterferometer

Technical field

The present invention relates to optical image technology field, particularly relate to a kind of full filed low frequency heterodyne ineterferometer.

Background technology

With the advanced optical equipment that deep-UV lithography machine projection exposure system therefor is representative, great challenge is proposed to the processing of optical element, the integrated of optical system.Interferometer is as high-precision optical element processing and the integrated indispensable core checkout equipment of optical system, and accuracy of detection requires to improve constantly.

The surface characterization test method adopted in traditional optical processing comprises Hartmann sensor method, knife-edge method and consistency profiles etc.These methods also exist the shortcoming that non-digitalization needs subjective interpretation or to be measured of contact damage etc. different respectively, and are difficult to reach higher measuring accuracy, are simple method for measuring.

Detection method is interfered just to be used before century-old, belong to non-contact measurement, and there is the features such as wide range, high sensitivity, high precision, be widely used when high precision test, its principle is that light beam irradiates the reference planes of standard as reference light, another Shu Guangzhao penetrates tested surface and returns with face shape information as measurement light, produces optical path difference thus produce bending interference fringe when two-beam is interfered due to hot spot diverse location phase place difference, can judge that the face shape of tested surface rises and falls.Until the people such as Bruning in 1974 propose Phase-Shifting Interferometry, locking phase Detection Techniques in Communication Theory are incorporated in optical interference art, make to interfere the precision detecting spherical surface shape greatly to improve.Its ultimate principle is through four steps or multistep moves element under test, and to change the phasic difference between test waves and reference wave, light intensity also changes thereupon, thus obtains a series of equation.Finally, the position obtaining element under test (or system) by solving equation group is worth mutually.Phase-Shifting Interferometry is quite ripe, has irreplaceable status in field of optical detection.

As shown in Figure 1, the employing point probe of this interference system carries out the structure of conventional interference system, detects each point phase place on corresponding tested surface by pointwise, but cannot full filed direct detection, and detector easily produces comparatively big error in the process of carrying out two-dimensional scan.In addition, owing to not adopting the acousto-optic frequency shifters of low frequency differences, high-speed area array camera frame frequency is not high enough cannot carry out the detection of full filed face.And the face type of whole tested surface will be obtained, transfer point detector that just must be high-accuracy, transverse shifting yardstick or mobile in the error that moves up and down all require at least to be less than optical wavelength magnitude, this requirement is extremely difficult to realize, and is unpractical concerning the interferometer of reality.

Summary of the invention

The object of this invention is to provide a kind of full filed low frequency heterodyne ineterferometer, there is higher measuring accuracy, and interference free performance is better; Meanwhile, its development difficulty and cost lower.

The object of the invention is to be achieved through the following technical solutions:

A kind of full filed low frequency heterodyne ineterferometer, comprising: laser instrument, 1/2 wave plate, first and second polarization spectroscope, first and second acousto-optic frequency shifters, first and second catoptron, Amici prism, spatial filter, collimating mirror, first and second quarter wave plate, polaroid, reference mirror, standard lens, polaroid, imaging lens and detector; Wherein:

Described laser emitting laser is divided into the orthogonal two-beam in polarization direction through 1/2 wave plate and polarization spectroscope; Wherein light beam injects Amici prism via the first catoptron and first sound optical frequency shifter successively; Another light beam injects Amici prism via second sound optical frequency shifter and the second catoptron successively;

Two-beam carries out conjunction bundle through described Amici prism, closes the light beam after bundle through spatial filter filtering, and enters the second polarization splitting prism and carry out beam splitting after being collimated mirror collimation; Wherein light beam transmission and go out as measurement light, after the first quarter wave plate and standard lens, expose to sample minute surface, and by reflected return according to former road; Another light beam is gone out as with reference to light by the second polarization splitting prism reflection, injects reference mirror, and returned according to former road by reflection after the second quarter wave plate;

Close after again being injected the second polarization spectroscope by the measurement light that reflection returns according to former road with reference light that to restraint be light beam, through a polaroid, two-beam is concerned with at the strength component of same polarization direction again, and by obtaining interference fringe image after imaging lens on planar array detector.

Further, interference signal S (t) that the t in time planar array detector a bit gathered changes is expressed as:

$S\left(t\right)=2E+2Ecos\[2\mathrm{\π}({\mathrm{\ν}}_1-{\mathrm{\ν}}_2)t+2\×\frac{2{\mathrm{\π\ν}}_1(L+R)}{c}\];$

Wherein, E represents the light intensity of two-beam, ν ₁with ν ₂represent the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the coarse relief volume of sample minute surface, and c is the light velocity, and L measures light toward the light path walked relative to reference light during test sample product minute surface more.

As seen from the above technical solution provided by the invention, adopt the phase shift of acousto-optic frequency shifters difference interference, effectively avoid interferometer to there is movement parts, measuring accuracy improves further, anti-interference is good, and development difficulty and cost can reduce, and the advantage comparing Mechanical Driven same is more obvious.In addition, adopt low frequency differences difference interference and planar array detector to carry out continuous acquisition, the quantity of information of acquisition is abundanter, is more conducive to accurately resolving phase place.The face type of heavy caliber, long-focus curved reflector is measured, owing to measuring optical length, especially easily be given a shock, the interference of the factor such as air-flow, the full filed low frequency heterodyne ineterferometer scheme that the present invention adopts has the ability of the factor such as vibration-inhibition, air-flow interference, in conjunction with the light path of the present invention's design, be particularly suitable for the kinetic measurement of face type of heavy caliber, long-focus curved reflector.

Accompanying drawing explanation

In order to be illustrated more clearly in the technical scheme of the embodiment of the present invention, below the accompanying drawing used required in describing embodiment is briefly described, apparently, accompanying drawing in the following describes is only some embodiments of the present invention, for those of ordinary skill in the art, under the prerequisite not paying creative work, other accompanying drawings can also be obtained according to these accompanying drawings.

The schematic diagram of the conventional interference system that Fig. 1 provides for background technology of the present invention;

The structural representation of a kind of full filed low frequency heterodyne ineterferometer that Fig. 2 provides for the embodiment of the present invention;

The signal form schematic diagram that the planar array detector that Fig. 3 provides for the embodiment of the present invention gathers.

Embodiment

Below in conjunction with the accompanying drawing in the embodiment of the present invention, be clearly and completely described the technical scheme in the embodiment of the present invention, obviously, described embodiment is only the present invention's part embodiment, instead of whole embodiments.Based on embodiments of the invention, those of ordinary skill in the art, not making the every other embodiment obtained under creative work prerequisite, belong to protection scope of the present invention.

The structural representation of a kind of full filed low frequency heterodyne ineterferometer that Fig. 2 provides for the embodiment of the present invention, as shown in Figure 2, it mainly comprises: laser instrument, 1/2 wave plate, first and second polarization spectroscope, first and second acousto-optic frequency shifters, first and second catoptron, Amici prism, spatial filter, collimating mirror, first and second quarter wave plate, polaroid, reference mirror, standard lens, polaroid, imaging lens and detector; Wherein:

Described laser emitting laser is divided into the orthogonal two-beam in polarization direction through 1/2 wave plate (can adjust arbitrarily the splitting ratio of two-beam by rotating 1/2 wave plate) and polarization spectroscope; Wherein light beam injects Amici prism via the first catoptron and first sound optical frequency shifter successively; Another light beam injects Amici prism via second sound optical frequency shifter and the second catoptron successively;

Two-beam carries out conjunction bundle through described Amici prism, closes the light beam after bundle through spatial filter filtering, and enters the second polarization splitting prism and carry out beam splitting after being collimated mirror collimation; Wherein light beam transmission and go out as measurement light, after the first quarter wave plate and standard lens, expose to sample minute surface, and by reflected return according to former road; Another light beam is gone out as with reference to light by the second polarization splitting prism reflection, injects reference mirror, and returned according to former road by reflection after the second quarter wave plate;

Close after again being injected the second polarization spectroscope by the measurement light that reflection returns according to former road with reference light that to restraint be light beam, through a polaroid, two-beam is concerned with at the strength component of same polarization direction again, and by obtaining interference fringe image after imaging lens on planar array detector.Said structure has distinguished the two-beam of different frequency in front end with different polarization directions, and rear end utilizes polarization splitting prism two-beam to be separated the crosstalk can avoiding measuring.

In the embodiment of the present invention, first and second acousto-optic frequency shifters can change laser frequency, the shift frequency amount of two acousto-optic frequency shifters is different, difference frequency can be the low difference frequency of several hertz or tens hertz magnitudes, array detector camera adopts tens of or hundreds of hertz of magnitude sample frequency, therefore can the beat signal of accurate detection heterodyne.Interference signal S (t) that the t in time that planar array detector a bit gathers changes is expressed as:

$S\left(t\right)=2E+2Ecos\[2\mathrm{\π}({\mathrm{\ν}}_1-{\mathrm{\ν}}_2)t+2\×\frac{2{\mathrm{\π\ν}}_1(L+R)}{c}\];$

Wherein, E represents the light intensity of two-beam, ν ₁with ν ₂represent the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the coarse relief volume of sample minute surface, and c is the light velocity, and L measures light toward the light path walked relative to reference light during test sample product minute surface more.

Due to the existence of beat frequency, interference fringe can with ν ₁-ν ₂frequency sweeping get up, a point on a bit corresponding tested surface of planar array detector, detector camera continuous acquisition one group of face battle array photo, be one group of data cube, it is a cosine periodic signal that the value of corresponding identical every bit extracts, and is the form of S (t), as shown in Figure 3.As can be seen from signal form, difference, due to the R value difference of coarse fluctuating, causes the signal phase of corresponding point detection on camera different.Utilize Fourier analysis or other data processing method can resolve the phase place often pointing out signal, combine the relief volume carrying out obtaining surface to be measured after denoising, phase unwrapping solution, face type recovery etc. calculate, namely achieve the measurement of full filed heterodyne opposite type.

Embodiment of the present invention such scheme, adopt the phase shift of acousto-optic frequency shifters difference interference, effectively avoid interferometer to there is movement parts, measuring accuracy improves further, and anti-interference is good, and development difficulty and cost can reduce, and the advantage comparing Mechanical Driven same is more obvious.In addition, adopt low frequency differences difference interference and planar array detector to carry out continuous acquisition, the quantity of information of acquisition is abundanter, is more conducive to accurately resolving phase place.The face type of heavy caliber, long-focus curved reflector is measured, owing to measuring optical length, especially easily be given a shock, the interference of the factor such as air-flow, the full filed low frequency heterodyne ineterferometer scheme that the present invention adopts has the ability of the factor such as vibration-inhibition, air-flow interference, in conjunction with the light path of the present invention's design, be particularly suitable for the kinetic measurement of face type of heavy caliber, long-focus curved reflector.

The above; be only the present invention's preferably embodiment, but protection scope of the present invention is not limited thereto, is anyly familiar with those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all should be encompassed within protection scope of the present invention.Therefore, protection scope of the present invention should be as the criterion with the protection domain of claims.

Claims (2)

1. a full filed low frequency heterodyne ineterferometer, it is characterized in that, comprising: laser instrument, 1/2 wave plate, first and second polarization spectroscope, first and second acousto-optic frequency shifters, first and second catoptron, Amici prism, spatial filter, collimating mirror, first and second quarter wave plate, polaroid, reference mirror, standard lens, polaroid, imaging lens and detector; Wherein:

Described laser emitting laser is divided into the orthogonal two-beam in polarization direction through 1/2 wave plate and polarization spectroscope; Wherein light beam injects Amici prism via the first catoptron and first sound optical frequency shifter successively; Another light beam injects Amici prism via second sound optical frequency shifter and the second catoptron successively;

Two-beam carries out conjunction bundle through described Amici prism, closes the light beam after bundle through spatial filter filtering, and enters the second polarization splitting prism and carry out beam splitting after being collimated mirror collimation; Wherein light beam transmission and go out as measurement light, after the first quarter wave plate and standard lens, expose to sample minute surface, and by reflected return according to former road; Another light beam is gone out as with reference to light by the second polarization splitting prism reflection, injects reference mirror, and returned according to former road by reflection after the second quarter wave plate;

Close after again being injected the second polarization spectroscope by the measurement light that reflection returns according to former road with reference light that to restraint be light beam, through a polaroid, two-beam is concerned with at the strength component of same polarization direction again, and by obtaining interference fringe image after imaging lens on planar array detector.

2. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 1, is characterized in that, interference signal S (t) that the t in time that planar array detector a bit gathers changes is expressed as:

$S\left(t\right)=2E+2Ecos\[2\mathrm{\π}(v_1-v_2)t+2\×\frac{2{\mathrm{\πv}}_1(L+R)}{c}\];$

Wherein, E represents the light intensity of two-beam, ν ₁with ν ₂represent the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the coarse relief volume of sample minute surface, and c is the light velocity, and L measures light toward the light path walked relative to reference light during test sample product minute surface more.