CN105674875A - Full visual field low frequency heterodyne point diffraction interferometer - Google Patents

Abstract

The invention discloses a full visual field low frequency heterodyne point diffraction interferometer. An acousto-optic frequency shifter is adopted to shift phase by heterodyne interference so that moving members of the interferometer are avoided, and measurement accuracy is further increased. The interferometer has good anti-interference performance, reduced development difficulty and cost, and compared with mechanical drive, the interferometer has more obvious advantages. Two optical fibers are used to respectively generate measuring light and reference light instead of part of emitting light; the interferometer combines the advantages that optical fiber point diffraction light is easy to access and flexible to adjust; compared with typical optical fiber point diffraction interferometer system, the measurement value aperture diameter range is increased. Besides, beam combination of point diffraction measurement light and reference light is realized by gluing angle ground fiber tips with light splitting plain films, wherein the beam combination is realized through outer sides of the semi-transparent and semi-reflection plain films, interference of diffraction opening edges on wave front of convergence light spots is avoided. The interferometer is easy to operate and has low cost.

Description

A kind of full filed low frequency heterodyne point-diffraction interferometer

Technical field

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

Background technology

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

The surface characterization test method adopted in traditional optical processing includes Hartmann sensor method, knife-edge method and consistency profiles etc. These methods are respectively present non-digitalization and need the subjective different shortcoming such as interpretation or contact damage part to be measured, and are extremely difficult to higher certainty of measurement, are simple method for measuring.

Detection method is interfered just to be used before a century, belong to non-contact measurement, and there is the features such as wide range, high sensitivity, high accuracy, it is widely used when high precision test, its principle is that light beam irradiates the reference plane of standard as reference light, another bundle light irradiates tested surface and returns with face shape information as measuring light, owing to hot spot diverse location phase place difference produces optical path difference thus producing the interference fringe of bending when two-beam is interfered, namely can determine whether that the face shape of tested surface rises and falls. Until Bruning in 1974 et al. proposes Phase-Shifting Interferometry, locking phase Detection Techniques in Communication Theory are incorporated in optical interference art so that interfere the precision of detection spherical surface shape to be greatly improved. Its ultimate principle is through four steps or many moved further element under test, and to change the phase difference between test waves and reference wave, light intensity also changes therewith, thus obtaining a series of equation. Finally, obtain the position of element under test (or system) by solving equation group to be worth mutually. Phase-Shifting Interferometry is quite ripe, has irreplaceable status in field of optical detection.

The development of high accuracy interference detection method can be divided into by interferometer structure and feature: Tai Man-Green's type interferometer, striking rope type interferometer and point-diffraction interferometer etc.

Tradition spherical interference detection method is all that the reference sphere utilizing to have higher surface figure accuracy obtains required reference corrugated, and then compares with the detection corrugated containing tested surface shape information, thus obtains tested surface graphic data.Thus the surface figure accuracy of the plane of reference directly limit the accuracy of detection achieved by conventional interference system on standard mirror, and the appearance of point-diffraction interferometer (PointDiffractionInterferometer is called for short PDI) and development solve this problem well. Point diffractive spherical interferes the basic thought of detection technique to be utilize some diffraction principle to obtain desirable spherical wave, and using the part before diffracted wave as reference wavefront, another part is as detection wavefront, and then can realize the high precision test of spherical surface shape. Point diffraction principle is utilized to obtain ideal spherical face wavefront, avoid in conventional interference detection system owing to standard mirror surface-shaped error is for the restriction of system accuracy of detection, thus the resolution of diffraction limit performance can be reached, and accuracy of detection is made to have good repeatability. Different according to the acquisition mode before a diffracted wave, a diffractive spherical can be interfered detection method be divided into optical fiber point-diffraction to interfere detection method and pin hole point-diffraction interference detection method.

Typical optical fiber point-diffraction interference system is as shown in Figure 1, it utilizes optical fiber to produce some diffraction light, the light sent by short-coherence light source closes bundle respectively after pyramid mirror reflects and is coupled into optical fiber after being divided into two bundles, light beam is as measuring another Shu Zuowei reference light of light, and the pyramid mirror of reference light is carried out machinery phase shift by Piezoelectric Ceramic. It is pointed into measured lens from a light cone part for optical fiber other end outgoing, fiber end face reflection is focused on after return, overlap interference with another part of outgoing light cone, form interferogram, owing to the coherence length of laser is short, mated by the light path of front end, measure light self cannot with the interference of light returned from measured lens, it is avoided that crosstalk. Interferogram is by record respectively after machinery phase shift, such that it is able to calculate the face type of measured lens. But, owing to adopting high-precision Mechanical Moving as phase-moving method, therefore precision is still not high enough, and cost is high, develops difficulty big, the especially measurement to heavy caliber face shape, and precision optical machinery drives precision to reduce, and certainty of measurement also decreases; It addition, a part for employing fiber exit light cone is as measuring light, so measurable minute surface range is subject to bigger restriction.

Typical pin hole point diffraction interferometer system is as shown in Figure 2, it utilizes small pin hole to produce high-precision reference light as an opening diffracting, also it is that the part taking outgoing light cone irradiates measured lens face as measuring light, semi-transparent semi-reflecting film is plated at aperture place, the light focused on overlaps with light cone another part interferences through reflection after returning to aperture, uses the piezoelectric ceramics tested minute surface of promotion to carry out mechanical phase shift measurement. But, the inapplicable bigbore measured target mirror of mechanical phase shift of Piezoelectric Driving, piezoelectric ceramics is difficult accurately drives the object that quality is very big; If it addition, the hot spot that tested minute surface is assembled is relatively big, then returning to aperture place and be easily subject to the interference of aperture edge diffraction, changing Wave-front phase distribution, reduce certainty of measurement and small diffraction aperture complex manufacturing technology, cost is high.

Summary of the invention

It is an object of the invention to provide a kind of full filed low frequency heterodyne point-diffraction interferometer, there is higher certainty of measurement, and interference free performance is better; Meanwhile, it develops difficulty with less costly, and particularly with the measurement of heavy caliber face shape, the advantage comparing Mechanical Driven same becomes apparent from.

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

A kind of full filed low frequency heterodyne point-diffraction interferometer, including: laser instrument, first and second half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through the first half-wave plate and polarization spectroscope;

Wherein light beam passes sequentially through the second half-wave plate, the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

Further, also include: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens.

Further, lifting one's head of first and second single-mode polarization maintaining fiber described is the end face that angle is i, and glued together with described light splitting plane;

If the beam direction of the end face injection that angle is i is at 45 ° with light splitting plane, then:

Wherein, n represents the refractive index of light splitting plane.

Further, interference signal S (t) of the change of t in time planar array detector a bit gathered 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.

A kind of full filed low frequency heterodyne point-diffraction interferometer, including: laser instrument, half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through wave plate and polarization spectroscope;

Wherein light beam passes sequentially through the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

Further, also include: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens.

Further, first and second single-mode polarization maintaining fiber described lift one's head orthogonal and be separated by a distance placement and press close to described light splitting plain film;

Described light splitting plain film is ultra-thin light splitting plain film, and its thickness is less than 1mm.

Further, interference signal S (t) of the change of t in time planar array detector a bit gathered 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.

As seen from the above technical solution provided by the invention, adopt acousto-optic frequency shifters difference interference phase shift, be prevented effectively from interferometer and there is movement parts, certainty of measurement improves further, anti-interference is good, and development difficulty can reduce with cost, and the advantage comparing Mechanical Driven same becomes apparent from. It addition, adopt low frequency differences difference interference and planar array detector to carry out full filed continuous acquisition, it is thus achieved that quantity of information more rich, be more beneficial for accurately resolving phase place; Surface type measurement to heavy caliber, long-focus curved reflector, owing to measuring optical length, it is particularly susceptible to the factor interference such as vibrations, 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 present invention design, it is particularly suitable for the kinetic measurement of the face type of heavy caliber, long-focus curved reflector. Meanwhile, two optical fiber are adopted to produce to measure light and reference light respectively, rather than by a part for emergent light, combine optical fiber point-diffraction light to be readily available, the advantage adjusted flexibly, compares typical optical fiber point-diffraction interferometer system, can improve again measurement range. In addition, the mode adopting the optical fiber head and the light splitting plain film that grind angle glued mutually realizes the conjunction bundle of a diffractometry light and reference light, conjunction is restrainted and realized by the lateral surface of semi-transparent semi-reflecting plain film, it is to avoid the wavefront of focused light spot is subject to the interference at opening diffracting edge, and easily realize, with low cost.

Accompanying drawing explanation

In order to be illustrated more clearly that the technical scheme of the embodiment of the present invention, below the accompanying drawing used required during embodiment is described 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 premise not paying creative work, it is also possible to obtain other accompanying drawings according to these accompanying drawings.

The typical optical fiber point-diffraction interference system schematic diagram that Fig. 1 provides for background of invention;

The typical pin hole point diffraction interferometer system schematic diagram that Fig. 2 provides for background of invention;

The structural representation of a kind of full filed low frequency heterodyne point-diffraction interferometer that Fig. 3 provides for the embodiment of the present invention;

The signal form schematic diagram that the planar array detector that Fig. 4 provides for the embodiment of the present invention gathers;

The structural representation of the another kind of full filed low frequency heterodyne point-diffraction interferometer that Fig. 5 provides for the embodiment of the present invention.

Detailed description of the invention

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, it is clear that described embodiment is only a part of embodiment of the present invention, rather than whole embodiments. Based on embodiments of the invention, the every other embodiment that those of ordinary skill in the art obtain under not making creative work premise, broadly fall into protection scope of the present invention.

The structural representation of a kind of full filed low frequency heterodyne point-diffraction interferometer that Fig. 3 provides for the embodiment of the present invention. As it is shown on figure 3, it specifically includes that

A kind of full filed low frequency heterodyne point-diffraction interferometer, it is characterized in that, including: laser instrument, first and second half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through the first half-wave plate and polarization spectroscope; Meanwhile, the splitting ratio of two-beam can be arbitrarily adjusted by rotating the first half-wave plate;

Wherein light beam passes sequentially through the second half-wave plate, the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

Further, also include: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens; Adjustment for auxiliary optical path Yu interferogram.

Further, lifting one's head of first and second single-mode polarization maintaining fiber described is the end face (first and second angle optical fiber head in Fig. 1) that angle is i, and glued together with described light splitting plane;

If the beam direction of the end face injection that angle is i is at 45 ° with light splitting plane, then:

Wherein, n represents the refractive index of light splitting plane.

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 frequencys, therefore can accurately detect the beat signal of heterodyne. Interference signal S (t) of the change of t in time a bit gathered on planar array detector 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.

Due to the existence of beat frequency, interference fringe can with ν₁-ν₂Frequency scanning get up, a point on a bit corresponding tested surface of planar array detector, one group of face battle array photo of detector camera continuous acquisition, it is 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 4. By signal form it can be seen that difference is different due to the R value of coarse fluctuating, cause 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.

Nearly all adopt Mechanical Driven to carry out phase shift for prior art, reach high accuracy difficulty big, the determination of vulnerability to jamming difference, such scheme of the present invention adopts acousto-optic frequency shifters difference interference phase shift, it is prevented effectively from interferometer and there is movement parts, certainty of measurement improves further, and anti-interference is good, and development difficulty can reduce with cost. The advantage comparing Mechanical Driven same becomes apparent from.

Additionally, adopt low frequency differences difference interference and planar array detector to carry out full filed continuous acquisition, it is thus achieved that quantity of information more rich, be more beneficial for accurately resolving phase place. Surface type measurement to heavy caliber, long-focus curved reflector, owing to measuring optical length, it is particularly susceptible to the factor interference such as vibrations, 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 present invention design, it is particularly suitable for the kinetic measurement of the face type of heavy caliber, long-focus curved reflector.

Meanwhile, two optical fiber are adopted to produce to measure light and reference light respectively, rather than by a part for emergent light, combine optical fiber point-diffraction light to be readily available, the advantage adjusted flexibly, compares typical optical fiber point-diffraction interferometer system, can improve again measurement range.

It addition, the mode adopting the optical fiber head and the light splitting plain film that grind angle glued mutually realizes the conjunction bundle of a diffractometry light and reference light, conjunction is restrainted and is realized by the lateral surface of semi-transparent semi-reflecting plain film, it is to avoid the wavefront of focused light spot is subject to the interference at opening diffracting edge. And easily realize, with low cost.

The embodiment of the present invention also provides for a kind of full filed low frequency heterodyne point-diffraction interferometer, as it is shown in figure 5, it specifically includes that laser instrument, half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through wave plate and polarization spectroscope;

Wherein light beam passes sequentially through the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

Further, it also includes: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens.

In the embodiment of the present invention, the lifting one's head orthogonal and be separated by a distance and place and press close to described light splitting plain film (the first optical fiber head and the second optical fiber head) as shown in Figure 5 of first and second single-mode polarization maintaining fiber described; Described light splitting plain film is ultra-thin light splitting plain film, and its thickness is less than 1mm. Measurement light can be made can to avoid reference light fiber end face through the light that ultra-thin light splitting plain film reflects and not produce veiling glare crosstalk based on this structure.

It addition, interference signal S (t) of the change of t in time a bit gathered on planar array detector 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.

The full filed low frequency heterodyne point-diffraction interferometer that the embodiment of the present invention provides is basically identical with the full filed low frequency heterodyne point-diffraction interferometer principle of previous embodiment, and concrete referring to description above, can repeat no more herein.

The above; being only the present invention preferably detailed description of the invention, but protection scope of the present invention is not limited thereto, any those familiar with the art is in the technical scope of present disclosure; the change that can readily occur in 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 (8)

1. a full filed low frequency heterodyne point-diffraction interferometer, it is characterized in that, including: laser instrument, first and second half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through the first half-wave plate and polarization spectroscope;

Wherein light beam passes sequentially through the second half-wave plate, the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

2. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 1, it is characterised in that also include: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens.

3. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 1, it is characterised in that lifting one's head of first and second single-mode polarization maintaining fiber described is the end face that angle is i, and glued together with described light splitting plane;

If the beam direction of the end face injection that angle is i is at 45 ° with light splitting plane, then:

Wherein, n represents the refractive index of light splitting plane.

4. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 1, it is characterised in that interference signal S (t) of the change of t in time a bit gathered on planar array detector 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.

5. a full filed low frequency heterodyne point-diffraction interferometer, it is characterized in that, including: laser instrument, half-wave plate, polarization spectroscope, first and second acousto-optic frequency shifters, first and second fibre-coupled mirrors, first and second single-mode polarization maintaining fiber, light splitting plain film, imaging lens, planar array detector; Wherein:

The laser of described laser emitting is divided into the orthogonal two-beam in polarization direction through wave plate and polarization spectroscope;

Wherein light beam passes sequentially through the first acousto-optic frequency shifters, the first fibre-coupled mirrors and the first single-mode polarization maintaining fiber and enters light splitting plain film, and as reference light directive imaging lens;

Another light beam time enters light splitting plain film by rising tone optical frequency shifter, the second fibre-coupled mirrors and the second single-mode polarization maintaining fiber, and is pointed into measured lens as measuring light; The measurement light injecting measured lens is launched to light splitting plain film by measured lens, disperses then through light splitting plain film reflective vertical and overlaps with reference light to other direction;

Two-beam after coincidence produces to interfere, and obtains interferogram after imaged camera lens on planar array detector.

6. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 5, it is characterised in that also include: light splitting piece, supervision camera lens and supervision camera;

Described light splitting piece is arranged between light splitting plain film and imaging lens, goes out the light beam after a part overlaps for beam splitting, then through monitoring that supervision camera injected by camera lens.

7. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 5, it is characterised in that the lifting one's head orthogonal and be separated by a distance placement and press close to described light splitting plain film of first and second single-mode polarization maintaining fiber described;

Described light splitting plain film is ultra-thin light splitting plain film, and its thickness is less than 1mm.

8. a kind of full filed low frequency heterodyne point-diffraction interferometer according to claim 5, it is characterised in that interference signal S (t) of the change of t in time a bit gathered on planar array detector 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, ν₁With ν₂Representing the beam frequencies after first and second acousto-optic frequency shifters frequency modulation respectively, R is the relief volume that measured lens is coarse, and c is the light velocity, the light path that L walks relative to reference light when being and measure light toward measured lens surface more.