CN109631783A - The low-coherent light interferometric measuring means and method of mirror surface spacing on lens group axis - Google Patents
The low-coherent light interferometric measuring means and method of mirror surface spacing on lens group axis Download PDFInfo
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- CN109631783A CN109631783A CN201910057537.4A CN201910057537A CN109631783A CN 109631783 A CN109631783 A CN 109631783A CN 201910057537 A CN201910057537 A CN 201910057537A CN 109631783 A CN109631783 A CN 109631783A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/14—Measuring arrangements characterised by the use of optical techniques for measuring distance or clearance between spaced objects or spaced apertures
Abstract
The invention discloses the low-coherent light interferometric measuring means and method of mirror surface spacing on a kind of lens group axis.This method uses the Michelson interference system of low-coherence light source, and prism wedge group and the optical parallel plate for compensating prism wedge group original state optical path difference are respectively implanted in two optical paths；The plane mirror of optical path where measured lens group replacement optical parallel plate, the optical path difference when two-way interference of light in compensation measurement process is adjusted using prism wedge group；Movable second prism wedge of continuous moving prism wedge group sequentially finds the second prism wedge position when each specular light of lens group generates interference fringe with the reflected light of the plane mirror of optical path where prism wedge group respectively, and record position is read；According to low-coherent light aplanatism principle of interference, spacing on the axis of adjacent two mirror surface of lens group is successively calculated.The invention avoids the phenomenon that interference fringe erroneous judgement occur；And under identical condition, it improves measurement accuracy, simplify debugging and measuring process.
Description
Technical field
The present invention relates to technical field of optical precision measurement, and in particular to the Low coherence of mirror surface spacing on a kind of lens group axis
Light-interference measuring apparatus and method.
Background technique
In optical workshop or laboratory, the method for non-cpntact measurement lens center thickness is common physical measuring methods, packet
The methods of image method, coplanar capacitance method, axial Dispersion Method, confocal method, interferometry are included, these measurement methods mainly utilize on lens
The reflected light information of lower surface realizes the measurement of lens center thickness.
In the above measurement method, image method implementation method is simple, but precision is minimum, in addition to low-coherent light interferometry,
The measurement accuracy of other measurement methods is all at 1 μm or more；Low-coherent light interferometry is as the highest measurement side of current measurement accuracy
Method, measurement accuracy is the need for more complex auxiliary equipment, spectrum or data processing method etc. up to 600nm, if right
Auxiliary equipment and data processing method are further improved, and can be increased to the measurement accuracy of low-coherent light interferometry by 600nm
200nm, and measurement can be scanned to each surface interval of lens group.
Chinese invention patent CN108759698A discloses a kind of low-coherent light interference of more mirror lens group mirror surface spacing
Measurement method and device, wherein method includes: to generate first, second liang of low-coherent light；Prism wedge is placed in the first optical path
Group is made of identical first prism wedge of the angle of wedge and the second prism wedge；In second optical path place optical flat and
It is tested more mirror lens groups；After adjusting measured lens group to appropriate location, along the wedge-shaped rib of the faceted pebble continuous moving second of the angle of wedge
Mirror, so that the successively reflection with another faceted pebble of the angle of wedge of second prism wedge of the reflected light of each mirror surface of measured lens group
Light is produced on CCD camera receiving plane into interference fringe, and according in the second prism wedge moving process, generation is adjacent twice
The position readings of interference fringe are calculated and are tested adjacent mirror facets spacing on more mirror lens group central axises.This method is based on low
The Michelson interference system principle of coherent light, the appropriate location in two-way optical path wherein, is respectively implanted the low-angle angle of wedge
Prism wedge group and optical parallel plate, be tested more mirror lens groups；By along angle of wedge faceted pebble continuous moving prism wedge group
Second prism wedge, fine adjustment compensate the optical path difference when two-way interference of light in measurement process, sequentially find measured lens group
Each specular light faceted pebble outwardly adjacent with the angle of wedge of the second prism wedge of prism wedge group of the low-angle angle of wedge respectively
Reflected light aplanatic interference fringe, and record the second prism wedge when having interference fringe along the direction moving process
Position readings, the mirror surface spacing of more mirror lens groups is calculated, although realizing the mirror surface spacing to more mirror lens groups
Non-contact nondestructive hurt measurement, be quick on the draw, measurement accuracy is high, but has the following disadvantages:
(1) debugging and measurement process in, the reflected light of each mirror surface of measured lens group successively can with before prism wedge group
The reflected light of end face and rear end face generate low coherence interference, lead to the erroneous judgement of interference fringe, cause result mistake, be but not easy by
It was found that；
(2) above-mentioned measurement method operation is slightly complicated, and measurement accuracy is also to be improved.
In view of this, needing to improve existing measurement method, so that easy to operate, precision and measurement result reliability
It improves.
Summary of the invention
That the technical problem to be solved by the present invention is to the measurement methods of mirror surface spacing on existing lens group axis is complicated for operation,
It is easy erroneous judgement, the problem of precision is low and measurement result poor reliability.
In order to solve the above-mentioned technical problem, the technical scheme adopted by the invention is that providing on a kind of lens group axis between mirror surface
Away from low-coherent light interferometric measuring means, including beam splitting block prism, plane mirror, imaging len, CCD camera, optics is flat
Andante and prism wedge group；The prism wedge group is made of identical first prism wedge of the angle of wedge and the second prism wedge, institute
It states the first prism wedge and the second prism wedge complementation is placed, internal two faceted pebbles vis-a-vis are the adjacent ribs of the respective angle of wedge
Face；
Parallel low-coherent light beam splitting after collimation is obtained the first, second low-coherent light by the beam splitting block prism；The
One, the second low-coherent light is reflected by tested axicon group, plane mirror respectively, and along beam splitting cube edge described in backtracking
Mirror is transmitted and is reflected respectively by the beam splitting block prism, the meeting on the receiving plane of the CCD camera after the imaging len
It closes overlapping and generates interference fringe；First, second low-coherent light is respectively formed optical system for testing and reference path；
The optical parallel plate is arranged in the optical system for testing, and it is flat that first low-coherent light passes perpendicularly through the optics
After andante, and by each mirror-reflection in tested axicon group, central axis glazed thread is along backtracking, by the beam splitting cube edge
After mirror transmission, on receiving plane that the CCD camera is reached through the imaging len；
First prism wedge of the prism wedge group is fixed in the reference path, and second prism wedge is along institute
It is in parallel faceted pebble inside the prism wedge group stated vis-a-vis and mobile perpendicular to the direction of rib；Second low-coherent light from
Adjacent with the angle of wedge faceted pebble outwardly of first prism wedge is vertical to be injected, from the adjacent with the angle of wedge of second prism wedge
Faceted pebble outwardly vertically projects, by plane mirror reflection along backtracking, after beam splitting block prism reflection, warp
The imaging len reaches on the receiving plane of the CCD camera；
Second wedge-shaped rib described in direction continuous moving along the parallel faceted pebble of the inside vis-a-vis and perpendicular to rib
Mirror, so that the reflected light of the different mirror surfaces of the tested axicon group successively reflected light with the plane mirror, in CCD camera
Receiving plane on successively generate interference fringe, according to the adjacent moving distance for interfering second prism wedge twice successively,
The spacing of each pair of adjacent mirror facets in tested axicon group is calculated.
In above-mentioned apparatus, each adjacent mirror facets on the central axis of tested axicon group are calculated according to the following formula
Spacing ti,
Wherein, niFor the refractive index for being tested material between adjacent mirror facets in axicon group, npFor the material of prism wedge group
Refractive index, n0For the refractive index of air；α is the angle of wedge of the prism of prism wedge group, xi, xi+1In the respectively described prism wedge group
Second prism wedge is along the parallel faceted pebble vis-a-vis inside the prism wedge group and perpendicular to the direction moving process of rib
In, the position readings of the adjacent interference fringe twice successively generated.
In above-mentioned apparatus, the optical parallel plate is manufactured from the same material with the prism wedge group.
In above-mentioned apparatus, the prism wedge group is arranged in the reference path.
The present invention also provides a kind of low-coherent light interferometric methods of mirror surface spacing on lens group axis, including following step
It is rapid:
The first, second low-coherent light is generated, and is reflected respectively by each mirror surface and plane mirror that are tested axicon group,
It is saturating by being imaged and respectively along backtracking to beam splitting block prism, then after transmiting and reflect through beam splitting block prism respectively
Mirror, generates aplanatism interference fringe on the receiving plane of CCD camera, and the optical path where the first, second low-coherent light is respectively formed
Optical system for testing and reference path；
Place the prism wedge group of optical parallel plate and above structure respectively on optical system for testing and reference path；The wedge
Shape prism group is made of identical first prism wedge of the angle of wedge and the second prism wedge, first prism wedge and the second wedge shape
Prism complementation is placed, and internal two faceted pebbles vis-a-vis are the adjacent faceted pebbles of the respective angle of wedge, and first prism wedge is fixed on
In the reference path, the adjacent faceted pebble outwardly of the angle of wedge is opposite with the beam splitting block prism；Second prism wedge
Can be along the parallel faceted pebble vis-a-vis inside the prism wedge group and the direction of vertical rib is moved, the angle of wedge is adjacent
Faceted pebble outwardly is opposite with plane mirror；
So that the first low-coherent light is first passed perpendicularly through the optical parallel plate of compensation light path, injects the coaxial of measured lens interplanar distance
Lens group, and by each mirror-reflection of axicon group after, axis glazed thread is along backtracking, after beam splitting block prism, warp
It crosses imaging len and enters CCD camera；
Make the second low-coherent light by the faceted pebble outwardly adjacent with the angle of wedge of the first prism wedge vertically by the second wedge
Adjacent with the angle of wedge faceted pebble outwardly of shape prism is vertical to be projected, and after plane mirror reflects, along backtracking, is stood by beam splitting
After square glass prism reflection, enter CCD camera by imaging len；
In parallel faceted pebble inside the prism wedge group vis-a-vis and the second wedge of direction continuous moving of vertical rib
Shape prism, so that the reflected light of each mirror surface of the tested axicon group successively reflected light with the plane mirror, in CCD phase
Interference fringe is successively generated on the receiving plane of machine, and is recorded in the second prism wedge moving process, generates each adjacent two
The position readings x of secondary stripedi, xi+1；
The spacing t of adjacent mirror facets on the central axis of tested axicon group is calculated according to the following formulai,
Wherein, niFor the refractive index for being tested material between adjacent mirror facets in axicon group, npFor the material of prism wedge group
Refractive index, n0For the refractive index of air, α is the angle of wedge of the prism of prism wedge group, xi, xi+1Respectively described second prism wedge
In moving process, the position readings for the adjacent interference fringe twice being sequentially generated, i is positive integer.
In the above-mentioned methods, by reducing the locking angle of first prism wedge and the second prism wedge, measurement essence is improved
Degree.
In the above-mentioned methods, measurement error Δ tiAre as follows:
Wherein, Δ xi、Δxi+1It is parallel rib of the second prism wedge of prism wedge group inside prism group vis-a-vis
Errors in position measurement in face and when the direction of vertical rib is mobile.
Compared with prior art, the present invention is in the optical device positioning for measuring device, using lens group itself
Mirror surface as the reflecting mirror on optical system for testing, and in measurement in reference path using plane mirror as reflection device,
The reflected light for not using the rear end face of prism wedge group is measured as the interference of the aplanatism of reference light and test light, not only
It solves in debugging and measurement process, the reflected light of each mirror surface of measured lens group and the front end face and rear end face of prism wedge group
Reflected light all there may be low coherence interferences, there is the problem of interference fringe erroneous judgement；And compared with same device, same
Under conditions of, measurement accuracy is improved to the former one third；In addition, the present invention is easy to accomplish, debugging with measuring process more
It is simple and easy to operate.
Detailed description of the invention
Fig. 1 is mirror surface spacing schematic illustration on the low-coherent light interferometry lens group axis in the present invention；
Fig. 2 is mirror surface spacing process steps schematic diagram on low-coherent light interferometry lens group axis in the present invention；
Fig. 3 is prism wedge group optical texture schematic diagram in the present invention.
Specific embodiment
The present invention provides a kind of method for measuring mirror surface spacing on lens group axis, realizes Low coherence using optical path compensation mechanism
The interferometry of light, by the way that by Surface scan mode, the method for measuring the spacing on lens group central axis between each mirror surface not only has
There is the advantages that precision is high and changeable, and Non-contact nondestructive measures, and solves the prior art in debugging and measurement process, quilt
The reflected light for surveying each mirror surface of lens group successively can generate low coherence interference with the reflected light of the front end face of prism wedge group, cause to do
The problem of relating to the erroneous judgement of striped.
The present invention is described in detail with specific embodiment with reference to the accompanying drawings of the specification.
As shown in Figure 1, 2, on lens group axis provided by the invention mirror surface spacing low-coherent light interferometric measuring means, packet
It includes:
Low-coherent light light source 1, for generating low-coherent light.
Microcobjective 2, for low-coherent light to be focused into point light source.
Aperture 3, for filtering out the stray light on point light source periphery.
Achromatism collimator objective 4, for the point light source of the Low coherence at aperture 3 to be converted into the directional light of Low coherence
Beam.
Beam splitting block prism 5, for the collimated light beam of the Low coherence issued through achromatism collimator objective 4 to be separated into first
Low-coherent light and the second low-coherent light；Meanwhile to along the first low-coherent light of backtracking and the second low-coherent light carry out transmission or
Reflection.
Axicon group 7 and plane mirror 9 are used to respectively reflect the first low-coherent light and the second low-coherent light and each
From along backtracking, to beam splitting block prism 5, then respectively, congregation is overlapped after beam splitting block prism 5 transmits and reflects；The first,
The place optical path of two low-coherent lights is referred to as optical system for testing and reference path.
Optical parallel plate 6, two surface is strictly parallel, is arranged on optical system for testing, interferes for two-way low-coherent light
When, balance prism wedge group 8 is poor to the dispersion of low-coherent light and the excessive path of compensation 8 original state of prism wedge group, institute
With the optical glass production identical with the use material of prism wedge group 8 of optical parallel plate 6.
Prism wedge group 8 is arranged in reference path, by the first prism wedge 31 (prism wedge group 8 in Fig. 1, Fig. 2
Left side prism) and the second prism wedge 32 (Fig. 1, in 2 prism wedge group 8 right side prism) composition.First prism wedge, 31 He
Second prism wedge 32 can be wedge-shaped right-angle prism in figure, can also be general prism wedge, they are same
It is placed on horizontal plane with complimentary positions, inclined-plane is opposite where two bevel edges and has slight gap in parallel.Using general wedge shape
When prism, a respective proximal surface for two angles of wedge is opposite and has slight gap in parallel.First prism wedge 31 is fixed, the second wedge shape
Prism 32 can be displaced along the movement of inclined-plane (bevel edge) direction and the measurement of the measuring scale by linking of itself, and the second prism wedge 32 is known as
Movable measurement prism wedge.The faceted pebble and beam splitting block prism 5 in the left side of the first prism wedge 31 are opposite, low as second
The plane of incidence of coherent light, the right side faceted pebble and plane mirror 9 of the second prism wedge 32 are opposite, as going out for the second low-coherent light
Penetrate face.
Image-forming objective lens 10 and CCD camera 11, for receiving the first low-coherent light and the second low-coherent light after merging overlapping,
And aplanatism interference fringe is generated on the receiving plane of CCD camera 11.
For low-coherent light, there is the original of dispersion since its spectral region is wider and glass optical component is to low-coherent light
Cause could generate stable interference fringe only under the conditions of two optical paths are aplanatic with respect to the light of low-coherent light central wavelength,
So need to guarantee the two-way light aplanatism of optical system for testing and reference path before measuring, and whether it is observed that interference fringe,
Exactly judge the aplanatic foundation of two-way light.
Therefore before measuring, the position of appropriate adjustment axicon group 7 and plane mirror 9, before making axicon group 7
Surface and plane mirror 9 are respectively to the light after the first low-coherent light and the reflection of the second low-coherent light, by beam splitting block prism 5
Transmission and reflection be able to observe that the aplanatism of low-coherent light is dry on the receiving plane of CCD camera 11 by image-forming objective lens 10
Striped is related to, optical system for testing and reference path two-way light beam are aplanatic at this time.It should be noted that due to being tested axicon
Each mirror surface of group 7 only has the center face element on axis that can regard plane as, and the center face element neighboring area on axis is to be pivoted
Symmetrical spherical surface, so the light beam reflected in the light beam of a certain mirror-reflection of axicon group 7 and reference path is in CCD camera
11 formed interference fringes, centered on be thicker round spot, periphery is circular ring shape striped that is gradually close tapered and disappearing soon.
Specifically, when testing, the first low-coherent light (top is all the way) first passes perpendicularly through optical parallel plate 6,
Inject measured lens interplanar distance axicon group 7, and by a certain mirror-reflection of axicon group 7 after, along backtracking to divide
Beam block prism 5, then by beam splitting block prism 5 transmit after, imaged object lens 10 enter CCD camera 11.
Second low-coherent light (right side is all the way), by the left end face (left side of the first prism wedge 31 of prism wedge group 8
Faceted pebble) vertical incidence, after prism wedge group right end face (the right side faceted pebble of the second prism wedge 32) outgoing, then it is anti-through plane
It penetrates after mirror 9 reflects, along backtracking to beam splitting block prism 5, then is reflected by beam splitting block prism 5, the imaged entrance of object lens 10
CCD camera 11.
At this point, the optical texture of prism wedge group 8 can regard an equivalent optical parallel plate as, when the second prism wedge
32 it is mobile along inclined-plane (bevel edge) direction of itself when, will lead to continuously changing for the equivalent thickness of this equivalent optical parallel plate
Become, and also changes immediately perpendicular to the light path of end face (the left side faceted pebble of the first prism wedge 31) incident parallel light, but emergent light
Direction it is constant, sidesway will not also occur for directional light.
So the effective thickness of appropriate adjustment prism wedge group 8, above-mentioned the first, second Low coherence into CCD camera 11
Light will be overlapped on the receiving plane of CCD camera 11, generate the aplanatism interference fringe of low-coherent light；Determine the second wedge shape at this time
Behind 32 position of prism, continue along mobile second prism 32 in itself inclined-plane (bevel edge) direction, so that each mirror of tested axicon group 7
The reflected light in face, successively with through the light reflected by plane mirror 9 after prism wedge group 8 on the receiving plane of CCD camera 11
Produce aplanatism interference fringe.When according to produced aplanatism interference fringe, the second prism 32 is in the position on inclined-plane (bevel edge) direction
It moves, the spacing of each adjacent mirror facets on the central axis of tested axicon group 7 is calculated.
In the present invention, it uses general low Accuracy Displacement motivation structure for mobile platform, drives the in prism wedge group 8
Two prism wedges 32 are realized along inclined-plane (bevel edge) the direction movement of itself with the low Accuracy Displacement acquisition close to optical axis vertical direction
Along the high precision displacement of optical axis direction, reach the light path fine adjustment and measurement of optical axis direction.
As shown in Fig. 2, the measurement detailed process of axicon group mirror surface spacing is as follows:
Itself inclined-plane (bevel edge) direction of the second prism wedge 32 in figure in measurement process, in prism wedge group 8
It is mobile.Vertical dotted line indicates the new position of its right side faceted pebble after the second prism wedge 32 is mobile, corresponding with lateral dotted line, expression the
In two prisms, 32 moving process, the reflected light of the continuous each mirror surface of the tested axicon group 7 sequentially found is anti-with plane respectively
The reflected light for penetrating mirror 9 generates the position of aplanatism interference fringe.
Step 1: as shown in Figure 1, arranging low-coherence light source 1, microcobjective 2, aperture 3, achromatism collimator objective
4, beam splitting block prism 5, tested axicon group 7, plane mirror 9, image-forming objective lens 10 and CCD camera 11.Adjust colour killing
Poor collimator objective 4 is emitted directional light.Directional light vertical incidence beam splitting block prism 5 isolates the first low-coherent light and second low
Coherent light, and directive axicon group 7 and plane mirror 9 respectively, successively adjust axicon group 7 and plane mirror 9 is each
From position and inclination angle, until observing the reflected light of tested 7 front surface of axicon group and flat on 11 receiving plane of CCD camera
The aplanatism interference fringe of the low-coherent light of the reflected light of face reflecting mirror 9.This striped is to be typically round striped, because coaxial
The front surface of microscope group 7 is usually spherical surface, is linear striped if 7 front surface of axicon group is plane.The step is suitable
It is calibrated in device, because the spectral region of low-coherent light is wider, only in the stringent aplanatic item of two-way low-coherent light
Under part, stable interference fringe could be generated.Therefore, if observe interference fringe, exactly judge whether two-way light is stringent etc.
The foundation of light path.
Step 2: in the optical system for testing where tested axicon group 7, the optical parallel plate 6 of merging compensation light path,
And optical parallel plate 6 is adjusted, make the first low-coherent light perpendicular through optical parallel plate 6, by each mirror-reflection of axicon group 7
Afterwards, axis glazed thread is along backtracking；In 9 place reference path of plane mirror, it is placed in prism wedge group 8.Prism wedge group 8
It, and will not at a distance from optics parallel-plate 6 to beam splitting block prism 5 on optical system for testing to the distance of beam splitting block prism 5
Together, the reflected light to avoid their surface is overlapped in CCD camera 11 generates contingency low-coherent light interference fringe.Adjust wedge
Shape prism group 8 makes the second low-coherent light incident perpendicular to the left side faceted pebble of the first prism wedge 31 of prism wedge group 8, and
After prism wedge group 8 perpendicular to the second prism wedge 32 right side faceted pebble be emitted, then by plane mirror 9 reflect after along original
Road returns；Along mobile second prism wedge in inclined-plane (bevel edge) direction of the second prism wedge 32 itself of prism wedge group 8, until
The anti-of the reflected light of tested 7 front surface of axicon group and plane mirror 9 is observed on the receiving plane of CCD camera 11 again
Penetrate the low-coherent light aplanatism interference fringe of light.The second prism wedge 32 of prism wedge group 8 at this time is write down along its bevel direction
On position readings x1。
Step 3: continuing inclined-plane (bevel edge) direction mobile second of the second prism wedge 32 itself along prism wedge group 8
Prism wedge, successively observes second mirror surface of tested axicon group 7 on 11 receiving plane of CCD camera, third mirror surface,
4th mirror surface ..., the reflected light of i-th of mirror surface, the aplanatism interference fringe with the reflected light of plane mirror 9, and respectively
Write down position readings x of the second prism wedge 32 of prism wedge group 8 at this time on its inclined-plane (bevel edge) direction2, x3, x4...,
xi。
According to the principle of interference of low-coherent light it is found that during measuring the mirror surface spacing of axicon group 7, adjacent two mirror
The reflected light in face successively with the reflection through prism wedge group 8 (adjust prism wedge group 8 during) by plane mirror 9
Light interferes, optical parallel plate of the prism wedge group 8 as equivalent variable thickness, increases thickness and the increment of light path is caused to be equal to
The optical path difference of reflected light of adjacent two mirror surface on axis inside axicon group, be also equal to light on axis by this adjacent two
Twice of the light path in face.
If Refractive Index of Material is n between certain adjacent mirror facets inside axicon group 7i, on this adjacent two mirror surfaces central axis
Spacing is ti, the refractive index of air is n0, the refractive index of the glass material of prism wedge group 8 is np, the angle of wedge of prism wedge group 8
For α, for the second prism wedge 32 of prism wedge group along inclined-plane (bevel edge) direction moving process of itself, adjacent generation twice is dry
The position readings for relating to striped are respectively xi, xi+1, according to aplanatic interference condition, have:
2niti=2 (np-n0)(xi+1-xi)sinα
Acquire the spacing t between this adjacent two mirror surface on central axisiAre as follows:
Its measurement error Δ tiAre as follows:
The Δ x in above formulai、Δxi+1Be prism wedge group 8 the second prism wedge 32 inside prism wedge group vis-a-vis
Parallel faceted pebble in and vertical rib direction it is mobile when errors in position measurement.
Measurement accuracy of the invention is analyzed below.
As shown in figure 3, the second prism wedge 32 namely right angled triangle Δ ABC, move a distance along the direction bevel edge AB
Afterwards, the new position of the dotted line right angled triangle Δ A'B'C' in Fig. 3 is reached.It can be seen that, after being moved to new position, where the angle of wedge
Vertex A is moved to A', and the thickness increment of equivalent parallel plate isIn right angled triangle Δ A'AN, apex angle is locking angle, can
?WithIndicate the distance that the right three shape Δ ABC of right angle is moved along the direction bevel edge AB,
The thickness increment for indicating equivalent optical parallel-plate, then have t=xsin α.
Due to the locking angle very little of prism, for sake of convenience, t is called longitudinal thickness increment here, x is call approximate
Lateral displacement.From formula t=xsin α it is found that 90 ° of α <, then sin α < 1, so there is t < x.The big approximately transversely position of this explanation
Generate small longitudinal thickness increment t with moving x linear scale, once it follows that the locking angle of prism wedge group has determined, big
The measurement error Δ t that approximately transversely displacement measurement errors Δ x passes to longitudinal optical parallel plate thickness increment is linearly to subtract
It is small, therefore improve the measurement accuracy of longitudinal optical parallel plate thickness increment.
For mirror surface spacing on measurement lens group axis, measurement error also corresponding linear reduction.For example, general glass
The refractive index of material is between 1.4~1.7, in error calculation formula described above, the fractional factorial containing refractive index
Ratio is about 0.3, so the factor for influencing error is 0.3 × sin α.Due to 90 ° of the locking angle < < of prism wedge group, then sin α
< < 1, so once it is determined that, mirror surface distance measurement error is also accordingly linear on the axis of axicon group reduces as α.
It can also be seen that the value of the locking angle in prism wedge group is smaller, measurement accuracy is higher.From the general of optics light path
For thought, the fine adjustment and measurement of light path are realized.Since the locking angle of prism wedge group can redesign change, so
The prism group of corresponding locking angle can be designed according to the needs of measurement accuracy, the measurement accuracy control for meeting needs requires.It is theoretical
Upper theory, measurement accuracy can be improved arbitrarily, but be limited by the measurement accuracy of locking angle, and measurement accuracy can not be mentioned unlimitedly
It is high.
Measurement accuracy of the invention is illustrated by comparative experiments calculating below.
Experimental group: mirror surface distance measurement on lens group axis is carried out using low-coherent light interferometric method of the invention.It is false
The precision for determining the traverse measurement ruler of prism wedge is ± 1 μm, then Δ xiWith Δ xi+1The sum of error be ± 2 μm.With the low phase of LED
Dry light is as light source, central wavelength lambda=680nm.Glass material K9 and QK2 be respectively to the refractive index of feux rouges 656.27nm
1.51390 with 1.47590.Feux rouges 680nm and feux rouges 656.27nm wavelength are not much different, and can be approximately considered above-mentioned glass material
Refractive index is also the refractive index to feux rouges 680nm；The refractive index of air is about 1.00029.As shown in Table 1 is experimental group measurement
Precision analysis tables of data, wherein the material of prism wedge group is K9, is tested material between certain two adjacent mirror surface of axicon group
Material is respectively K9 and QK2, there is the measurement accuracy calculated result of the mirror surface spacing in the prism wedge group of the different angles of wedge in table.
Table 1: experimental group measurement precision analysis tables of data.
From table 1 it follows that the prism angle of wedge is got over when distance measurement precision is higher on the axis for requiring axicon group
It is small；The angle of wedge design for changing prism wedge, can make the measurement accuracy of mirror surface spacing on the axis of axicon group meet setting accuracy
Control range in, such as within 18nm, when prism wedge group and tested axicon group material are all K9,1 ° of 30' of α <.
Contrast groups: lens group is carried out using the low-coherent light interferometric method in Chinese invention patent CN108759698A
Mirror surface distance measurement on axis.The precision of the traverse measurement ruler of the prism wedge of contrast groups, Δ xiWith Δ xi+1The sum of error and reality
Test group it is identical, the prism angle of wedge and experimental group of prism wedge group are also approximately uniform；Simultaneously also using LED low-coherent light as light
Source, wherein the material of heart wavelength X=680nm, the prism wedge group of two contrast groups is all K9, is tested axicon group certain
Material is respectively K9 and QK2 between two adjacent mirror surfaces, identical as experimental group；The refractive index of air is about 1.00029；.Such as table 2
Shown in contrast groups measurement precision analysis tables of data.
Table 2: contrast groups measurement precision analysis tables of data.
It is compared by Tables 1 and 2 it is found that use is identical in the case where the prism angle of wedge of prism wedge group is approximately uniform
Prism wedge group same measured lens group is measured, the ratio of precision contrast groups of experimental group are high, experimental group measurement
Precision is about the one third of contrast groups, such as when the contrast groups prism angle of wedge is 1 ° of 26', measurement accuracy 50nm, and experimental group
When the prism angle of wedge is 1 ° of 30', measurement accuracy is then 18nm, significantly larger than contrast groups.
Utilize the low-coherent light interferometric measuring means of mirror surface spacing on said lens group axis, a kind of lens provided by the invention
The low-coherent light interferometric method of mirror surface spacing on group axis, comprising the following steps:
Generate the first, second low-coherent light, they by axicon group front surface (the first mirror surface of front end) and plane
Reflecting mirror reflects respectively, and along backtracking to beam splitting block prism, then transmits and reflect through beam splitting block prism respectively, through at
As object lens merge overlapping on the receiving plane of CCD camera；Optical path where first, second low-coherent light is respectively formed optical system for testing
And reference path；Axicon group, plane mirror, beam splitting block prism, image-forming objective lens and CCD camera position are adjusted, is made
Aplanatic interference fringe is obtained on CCD camera receiving plane；
Place the prism wedge group of optical parallel plate and above structure respectively on optical system for testing and reference path；
So that the first low-coherent light is first passed perpendicularly through optical parallel plate, injects the axicon group of measured lens interplanar distance, and by
After each mirror-reflection of axicon group, along backtracking to beam splitting block prism, then by beam splitting block prism transmission after, through at
As object lens enter CCD camera；
Make the second low-coherent light by the left side faceted pebble of the first prism wedge of prism wedge group vertically into through wedge-shaped rib
After microscope group, vertically projected by the right side faceted pebble of the second prism wedge, it is vertical to beam splitting along backtracking after plane mirror reflects
Square glass prism, then reflected by beam splitting block prism, imaged object lens enter CCD camera；
In parallel faceted pebble inside prism wedge group vis-a-vis and perpendicular to the direction of rib (bevel edge) direction mobile the
Two prism wedges generate the interference fringe of low-coherent light in CCD camera, determine the second prism wedge position readings x at this time1；So
Continue to move the second prism in the parallel faceted pebble inside prism wedge group vis-a-vis and perpendicular to the direction of rib (bevel edge) afterwards,
So that the reflected light of continuous each mirror surface of measured lens group successively with the reflected light of plane mirror, in the receiving plane of CCD camera
Upper generation interference fringe, and record the position readings x of the second prism wedge when generating adjacent striped twicei, xi+1, i is positive whole
Number；
The spacing t of two neighboring mirror surface on the axis of measured lens group is calculated according to the following formulai,
Wherein, niFor the Refractive Index of Material being tested in more mirror lens groups between adjacent mirror facets, npFor the glass of prism wedge group
The refractive index of material, n0For the refractive index of air, xi, xi+1Respectively described second prism wedge is opposite inside prism wedge group
Parallel faceted pebble in and perpendicular in the direction of rib (bevel edge) moving process, generate the position readings of adjacent striped twice.
The invention has the following advantages that
(1) measurement method is contactless, not damaged to the lens group of mirror surface spacing on measured axis；
(2) positioning is measured as the interference technique of light source using the low-coherent light of wide spectrum, be quick on the draw, accuracy
It is good；
(3) in measurement process, longitudinal mirror position scanning of low coherence light beam is realized close to transverse shifting prism wedge, i.e.,
Change longitudinal scanning is approximate transversal scanning, so that interferometer need not stretch or move integrally in measurement process；
(4) with the low Accuracy Displacement mechanism close to optical axis vertical direction, the high precision displacement obtained along optical axis direction is adjusted,
To realize that the high-precision of the light path of optical axis direction is adjusted and measured；
(5) angle of wedge design that prism wedge group can be changed, can make mirror surface distance measurement precision controlling within 20nm；
(6) interference that Low coherence degree light is realized using optical path compensation mechanism, is particularly adapted to the lens group of micro- spacing mirror surface
Axis on mirror surface spacing measurement；
(7) due to when component positions, using lens group from the mirror surface penetrated as the reflecting mirror on optical system for testing, and
It uses plane mirror as reflection device in reference path in measurement, does not use the anti-of the rear end face of prism wedge group
Penetrate light as the aplanatism of reference light and test light interference measure, not only can to avoid debugging and measurement process in, quilt
Survey the Low coherence of the reflected light generation contingency of the reflected light of each mirror surface of lens group and the front end face of prism wedge group or rear end face
Interference, there is the phenomenon that interference fringe erroneous judgement, and compared with same device, under identical condition, measurement accuracy improve to
The former one third.
(8) directly use measured lens group from mirror surface is penetrated as the reflecting mirror on optical system for testing, to determine in measuring device
The position of each optical device, not only the device of measuring device itself is reduced, easy to accomplish, and is debugged with measuring process more
It is simple and easy to operate.
The invention is not limited to above-mentioned preferred forms, and anyone should learn that is made under the inspiration of the present invention
Structure change, the technical schemes that are same or similar to the present invention are fallen within the scope of protection of the present invention.
Claims (7)
1. the low-coherent light interferometric measuring means of mirror surface spacing on a kind of lens group axis, including beam splitting block prism, plane reflection
Mirror, imaging len, CCD camera, optical parallel plate and prism wedge group；The prism wedge group is by identical first wedge shape of the angle of wedge
Prism and the second prism wedge composition, first prism wedge and the second prism wedge complementation are placed, internal two vis-a-vis
A faceted pebble is the adjacent faceted pebble of the respective angle of wedge；It is characterized by:
Parallel low-coherent light beam splitting after collimation is obtained the first, second low-coherent light by the beam splitting block prism；The first,
Second low-coherent light is reflected by tested axicon group, plane mirror respectively, and along beam splitting block prism described in backtracking,
It is transmitted and is reflected respectively by the beam splitting block prism, merged on the receiving plane of the CCD camera after the imaging len
Overlapping generates interference fringe；First, second low-coherent light is respectively formed optical system for testing and reference path；
The optical parallel plate is arranged in the optical system for testing, and first low-coherent light passes perpendicularly through the optical parallel plate
Afterwards, and by each mirror-reflection in tested axicon group, central axis glazed thread is saturating by the beam splitting block prism along backtracking
After penetrating, on receiving plane that the CCD camera is reached through the imaging len；
First prism wedge of the prism wedge group is fixed in the reference path, and second prism wedge is along described
It is in parallel faceted pebble inside prism wedge group vis-a-vis and mobile perpendicular to the direction of rib；Second low-coherent light is from first
The faceted pebble outwardly adjacent with the angle of wedge of prism wedge is injected, from the rib outwardly adjacent with the angle of wedge of second prism wedge
Face is projected, and, along backtracking, after beam splitting block prism reflection, is imaged thoroughly through described after plane mirror reflection
Mirror reaches on the receiving plane of the CCD camera；
Second prism wedge described in direction continuous moving along the parallel faceted pebble of the inside vis-a-vis and perpendicular to rib, makes
It must be tested the reflected lights of the different mirror surfaces of the axicon group successively reflected light with the plane mirror, in connecing for CCD camera
Receipts successively generate interference fringe on face, according to the adjacent moving distance for interfering second prism wedge twice, be calculated by
Survey the spacing of each pair of adjacent mirror facets in axicon group.
2. the apparatus according to claim 1, which is characterized in that tested axicon group is calculated according to the following formula
The spacing t of each adjacent mirror facets on central axisi,
Wherein, niFor the refractive index for being tested material between adjacent mirror facets in axicon group, npFor the refraction of the material of prism wedge group
Rate, n0For the refractive index of air；α is the angle of wedge of the prism of prism wedge group, xi, xi+1Second in the respectively described prism wedge group
In direction moving process of the prism wedge along the parallel faceted pebble vis-a-vis inside the prism wedge group and perpendicular to rib, first
The position readings of the adjacent interference fringe twice generated afterwards.
3. the apparatus according to claim 1, which is characterized in that the optical parallel plate is with the prism wedge group by identical
Material is made.
4. the apparatus according to claim 1, which is characterized in that the prism wedge group is arranged in the reference path.
5. the low-coherent light interferometric method of mirror surface spacing on a kind of lens group axis, which comprises the following steps:
The first, second low-coherent light is generated, and mirror surface and plane mirror by being tested axicon group reflect respectively, and along original
Road returns to beam splitting block prism, then transmits and reflect through beam splitting block prism respectively, after imaging len, in CCD phase
On the receiving plane of machine generate aplanatism interference fringe, the optical path where the first, second low-coherent light be respectively formed optical system for testing and
Reference path；
Place the prism wedge group of optical parallel plate and above structure respectively on optical system for testing and reference path；The wedge shape rib
Microscope group is made of identical first prism wedge of the angle of wedge and the second prism wedge, first prism wedge and the second prism wedge
Complementation is placed, and internal two faceted pebbles vis-a-vis are the adjacent faceted pebbles of the respective angle of wedge, and first prism wedge is fixed on described
In reference path, the adjacent faceted pebble outwardly of the angle of wedge is opposite with the beam splitting block prism；Second prism wedge can edge
In parallel faceted pebble vis-a-vis inside the prism wedge group and direction of vertical rib is mobile, and the angle of wedge is adjacent outwardly
Faceted pebble it is opposite with plane mirror；
So that the first low-coherent light is first passed perpendicularly through the optical parallel plate of compensation light path, injects the axicon of measured lens interplanar distance
Group, and by the mirror-reflection of axicon group after, enter after beam splitting block prism by imaging len along backtracking
CCD camera；
Make the second low-coherent light by the faceted pebble outwardly adjacent with the angle of wedge of the first prism wedge vertically by the second wedge-shaped rib
The faceted pebble outwardly adjacent with the angle of wedge of mirror projects, anti-by beam splitting block prism along backtracking after plane mirror reflects
After penetrating, enters CCD camera by imaging len and enter CCD camera；
In parallel faceted pebble inside the prism wedge group vis-a-vis and the wedge-shaped rib of the direction continuous moving second of vertical rib
Mirror, so that the reflected light of the different mirror surfaces of the measured lens group successively reflected light with the plane mirror, in connecing for CCD camera
Interference fringe is successively generated on receipts face, and is recorded in the second prism wedge moving process, and each adjacent striped twice is generated
Position readings xi, xi+1；
The spacing t of adjacent mirror facets on the central axis of tested axicon group is calculated according to the following formulai,
Wherein, niFor the refractive index for being tested material between adjacent mirror facets in more mirror lens groups, npFor the folding of the material of prism wedge group
Penetrate rate, n0For the refractive index of air, α is the angle of wedge of the prism of prism wedge group, xi, xi+1Respectively described second prism wedge moves
During dynamic, the position readings for the adjacent interference fringe twice being sequentially generated, i is positive integer.
6. according to the method described in claim 5, it is characterized in that, by reducing first prism wedge and the second wedge-shaped rib
The locking angle of mirror improves measurement accuracy.
7. according to the method described in claim 5, it is characterized in that, measurement error Δ tiAre as follows:
Wherein, Δ xi、Δxi+1It is parallel rib of the second prism wedge of prism wedge group inside prism wedge group vis-a-vis
Errors in position measurement in face and when the direction of vertical rib is mobile.
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