CN107449756A - Ice sheet refractive index and the measuring method and device of thickness in a kind of ICF pellets - Google Patents
Ice sheet refractive index and the measuring method and device of thickness in a kind of ICF pellets Download PDFInfo
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- CN107449756A CN107449756A CN201710481895.9A CN201710481895A CN107449756A CN 107449756 A CN107449756 A CN 107449756A CN 201710481895 A CN201710481895 A CN 201710481895A CN 107449756 A CN107449756 A CN 107449756A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
- G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
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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
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
- G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
Abstract
The present invention relates to ice sheet refractive index in a kind of ICF pellets and the measuring method and device of thickness.The present invention includes light source (can be laser or LED), beam expander, beam splitter, the first speculum, the second speculum, pellet to be measured, Wavefront sensor, lens, ccd image sensor and computer.Light path is divided into by two-way by device, with reference to this two light paths, it is known that ice sheet average thickness, obtain ice sheet mean refractive index；Known ice sheet mean refractive index, obtains ice sheet average thickness；Obtain pellet ice sheet refractive index and thickness.The present invention proposes the double beam system apparatus and method based on optical path difference and deflection of light, measures while the refractive index and thickness of realizing ICF pellet ice sheets.Energy is quick, non-contact measurement, and measurement accuracy is high；The index distribution of pellet ice sheet can also be drawn.
Description
Technical field
The invention belongs to technical field of optical precision measurement, is related to the survey of ice sheet refractive index and thickness in a kind of ICF pellets
Measure method and device.
Background technology
Inertial confinement fusion (ICF) is to realize one of mainstream scheme of controllable nuclear fusion, is had in fusion research
Important meaning.Pellet is assembled as all N beams laser beams, and implosion is so as to induce the core of nuclear fusion, its inner surface finish,
Concentricity, uniformity have extremely harsh requirement.Therefore, it is extremely important to implement quality control to it.
Due to the Multi-layer spherical that pellet is made up of spherical shell, ice sheet and fuel gas etc., directional light can produce sternly after passing through
Weight deviation, and its size is typically from hundreds of um to several mm, between it is macroscopical with it is microcosmic between, therefore to its ice sheet refractive index and thickness
It is larger that degree carries out high precision test difficulty.Have the method for some detection pellets, such as interferometric method, back-lit projection method etc. at present.
Both approaches all have the advantages of contactless, non-destructive, quick.And all by analyzing pellet to by light therein
Caused effect, so as to the refractive index or thickness of inverting ice sheet.In interferometric method, the effect of light wave of the pellet to passing through is shown as
Change to its wavefront；In back-lit projection, the redistribution of the energy after light complexity catadioptric is shown as.But whatsoever side
Method, all it is to need to assume that a value in refractive index or thickness is definite value, and then asks for another value.Certainly will so detection be tied
Fruit meeting is as it is assumed that and produce larger error.
For the detection of pellet, domestic and foreign scholars have carried out substantial amounts of research.U.S.'s lawrence livermore laboratory
Utilize interferometry (Applications of holographic interferometry to cryogenic ICF
Target characterization. (Journal of Vacuum Science and Technology, 1982,
Vol.20,No.4:P1362~1365)).This method can be with the thickness distribution of effectively measuring pellet ice sheet, but its refractive index
But can not measure simultaneously.Refractive index must be used as an estimate, can just solve the thickness of pellet ice sheet.Due to estimate phase
There is error than actual value, therefore counted thickness value also has larger error.Interferometric method has been used in the LMJ projects of France simultaneously
With back-lit projection method (Observer for a thick layer of solid deuterium-tritium using
backlit optical shadowgraphy and interferometry.(Applied optics,2007,VOL.46,
No.33:P8193~8201)), the ice layer thickness at pellet the two poles of the earth is estimated using interferometric method, then ice is solved by back-lit projection
The distribution of thickness degree.The solving precision of this method is higher, but can not equally solve the refractive index and thickness of ice sheet simultaneously.China
Gongwu research institute laser-produced fusion research center, pellet ice sheet inside surface roughness, i.e. pellet are characterized using back-lit projection method
Interior ice layer thickness is distributed (backlight shadowgraph imaging characterized by techniques ICF pellet inside surface roughnesses；(light laser and the particle beams, 2010,
VOL.22,No.12:P2880~2884)).This method can detect pellet ice layer thickness, but can not solve ice sheet simultaneously
Refractive index and thickness.The value of an ice sheet refractive index is necessarily assumed that, can just obtain ice layer thickness.And as it is assumed that mistake can be introduced
Difference, therefore the ice layer thickness finally tried to achieve also has larger error.Above-mentioned detection method, ICF pellets can not be accurately measured simultaneously
The refractive index and thickness of interior ice sheet.Therefore design can accurately measure in ICF pellets the refractive index of ice sheet and the device of thickness and
Method is necessary.
The content of the invention
It is an object of the invention to provide ice sheet refractive index in a kind of ICF pellets and the measuring method and device of thickness.
The present invention includes light source, beam expander, beam splitter, the first speculum, the second speculum, pellet to be measured, wavefront sensing
Device, lens, ccd image sensor, computer.By following proposal, while the refractive index and thickness of ice sheet in ICF pellets are measured,
Have the following steps：
Step 1：The light sent from light source turns into collimated light beam by beam expander, is divided into two beams by beam splitter：It is a branch of straight
Connect through pellet to be measured and received by Wavefront sensor, pellet to be measured is located along the same line with Wavefront sensor；Another beam passes through
After first speculum and the reflection of the second speculum, through pellet to be measured, by lens imaging on ccd image sensor；Will be from
Wavefront sensor obtains wave front chart and handled with obtaining back-lit projection figure from ccd image sensor in computer.Wherein lens
Distance away from pellet center to be measured is twice of 2f of the focal length of lens, and distance of the lens away from ccd image sensor image planes is that lens are burnt
Away from twice of 2f；The distance of pellet Wavefront sensor to be measured is known quantity D.
Step 2：Corresponding to the light path received directly through pellet to be measured by Wavefront sensor；Set through pellet to be measured
The light height of incidence of axis is 0, the height of incidence of the light incidence point light farthest with the vertical range of pellet axis to be measured
For x, height of incidence x is the arithmetic number less than pellet outer radius.Trace is the incident light of x for 0 and height from height respectively.Enter
Penetrate height and pass straight through pellet to be measured for 0 light, received by Wavefront sensor, wavefront is located at by the point that Wavefront sensor receives
Sensor image plane center；And the light that height of incidence is x has multiple deviation on each interface of pellet to be measured, to should light quilt
The point that Wavefront sensor receives is r according to the distance of Wavefront sensor image plane centerk.If this two light are passed by wavefront from inciding
Corresponding optical path difference is k λ when sensor receives, and obtains formula (1)：
OPL(x,n2,t2)-OPL(0,n2,t2)=k λ (1)
Wherein, OPL (x, n2,t2) it is from light path, OPL (0, n corresponding to light incident height x2,t2) it is to enter from height 0
Light path corresponding to the light penetrated；X is light height of incidence, n2For ice sheet refractive index, t2For ice layer thickness.
Because the deviation of pellet acts on, the height that the light incident from height x is reached on Wavefront sensor is no longer x.Root
Formula (2) is listed according to geometrical relationship：
X+ Δ x+Dtan2 ζ=rk (2)
Wherein, x+ Δs x is the height that light is emitted from pellet right endpoint section, and D is pellet right endpoint to Wavefront sensor
The distance of receiving plane, 2 ζ are the deflection angle of beam projecting.
Simultaneous formula (1) and (2).Obtain reaching wavefront biography from light incident height x through pellet geometry deviation by measurement
The height r of sensork, and from height for 0 with height be x incidence light corresponding optical path difference k λ value.Pellet known parameters,
Including pellet outer radius R0, shell thickness t1, spherical shell refractive index n1.As long as ice sheet average thickness is, it is known that ice sheet refraction can be obtained
Rate.
Step 3：For after the first speculum and the reflection of the second speculum, through pellet, existing by lens imaging
Light path in ccd image sensing, extracts the bright ring position on back-lit projection figure, the position is away from CCD on ccd image sensor
Image sensor center distance is X2.High power source of parallel light is projected on transparent pellet, and ccd image sensor receives saturating
The picture of bright pellet is made up of light, and these light are in each multiple catadioptric in layer border of pellet.Backlight on ccd image sensor is thrown
A notable bright ring is had on shadow figure.Because in the system, distance of the lens away from pellet center to be measured is twice of 2f of the focal length of lens,
Distance of the lens away from ccd image sensor image planes is twice of 2f of the focal length of lens.Therefore, for from height X it is incident certain is a branch of
Participate in forming the light of bright ring, distance when it reaches ccd image sensor image planes apart from image plane center is also X2。
Formula (3) can be obtained according to the path of geometrical relationship Geometrical Optics：
In formula, X2For bright ring height, α0For incident ray and the angle of normal,It is emergent ray relative to trunnion axis
Deflection angle.
Multi simulation running shows, | dX2/ dX | a zero point can be produced.Therefore bright ring position X has been drawn2With incident light height X
Relation, formula (4)：
Simultaneous formula (3) and (4).X is light incoming position, n in formula2For ice sheet refractive index, t2For ice layer thickness.By right
Back-lit projection figure carries out image procossing, draws bright ring height X2；Pellet known parameters：Pellet outer radius R0, shell thickness t1, ball
Shell refractive index n1.Known ice sheet refractive index, you can obtain ice layer thickness distribution.
Step 4：In step 2, it is known that ice sheet average thickness, ice sheet mean refractive index can be obtained；In step 3,
Known ice sheet mean refractive index, you can obtain ice sheet average thickness.With reference to this two light paths, solved from refractive index or thickness solves
Start, as the beginning of iteration, there is following process：
1) before iteration starts, pellet relevant parameter is such as：Pellet outer radius R0, pellet spherical shell refractive index n1, pellet spherical shell thickness
Spend t1It is known.The parameter measured for other needs, r is measured by Wave-front measurement experimentk, X is measured by back-lit projection experiment2。
2) initial estimate is carried out to the ice layer thickness of the pellet to be measured；3) thickness value is substituted into the method based on optical path difference to solve
Ice sheet refractive index, this refractive index is substituted into the method based on deflection of light and solves ice layer thickness, its value is designated as n respectively2, t2；Its
Middle n2For the ice sheet refractive index value of presently described pellet, t2For the ice layer thickness value of presently described pellet；4) verify whether that satisfaction changes
For cut-off condition.Compare current n2, t2If continuously differing by more than threshold value with the value of last time three times, threshold value is less than 0.0001,
Then repeat 3)；If continuously being differed three times with the value of last time and being less than the threshold value, iteration cut-off, current n2, t2For final target
Ball ice sheet refractive index and thickness.
Apparatus of the present invention include light source, beam expander, beam splitter, the first speculum, the second speculum, pellet to be measured, wavefront
Sensor, lens, ccd image sensor and computer.Described light source, beam expander, beam splitter, the first speculum are along same level
Line is put successively, and the light-emitting window of light source aligns with the light inlet of beam expander, the light-emitting window of beam expander and the light inlet pair of beam splitter
Together, the light-emitting window of beam splitter transmitted light and the first speculum 4 are in 45 ° of settings.Pellet to be measured is placed in going out for beam splitter reflected light
Optical port side, it is located along the same line with beam splitter light-emitting window；Second speculum is laterally in same straight line with pellet to be measured, vertically
It is in the first speculum on same straight line, and along horizontal line in 45 ° of settings.Second speculum, pellet to be measured, lens, CCD figures
As sensor inverse time is set on the same line, lens are located among pellet to be measured and ccd image sensor, and lens centre is away from treating
Survey pellet center and ccd image sensor image plane center distance are twice of the focal length of lens.Wavefront sensor and beam splitter, treat
Survey pellet to be located along the same line, pellet to be measured is arranged among Wavefront sensor and beam splitter.Wavefront sensor and ccd image
Sensor is connected with computer, obtains wave front chart and back-lit projection figure.
Tested for Wave-front measurement, the receiving plane of Wavefront sensor is positioned at 20~200 at the known distance of pellet rear
Millimeter, Wavefront sensor receive distorted wavefront of the incident light after pellet.
It is laser or LED as preferential light source.
The present invention has following remarkable advantage：
1. proposing the double beam system apparatus and method based on optical path difference and deflection of light first, ICF pellet ice sheets are realized
Refractive index and measure while thickness.Pellet ice sheet folding is solved by being based on optical path difference corresponding to the light path all the way of Wave-front measurement
Rate is penetrated, is based on deflection of light solution thickness corresponding to the light path all the way of back-lit projection, iteration obtains back and forth between the two methods
To the refractive index of pellet ice sheet and the exact value of thickness.
2. relative to existing interferometry, back-lit projection method etc., due to need not pre-suppose that refractive index value or
Thickness value, so in the absence of refractive index or the hypothesis error of thickness value, therefore measurement accuracy significantly improves, and can reach ppm levels
Relative error.
3. the Wave-front measurement used in device is all the way measuring method all the way with back-lit projection, it is respectively provided with fast
The advantages of speed, non-contact measurement, it is possible to achieve the Non-Destructive Testing to pellet.
4. compared with the indirect measurement method of traditional interferometric method measurement pellet ice sheet single parameter, the present invention does not use
Standard pellet, and the parameter such as standard refraction rate, belong to direct measurement.It is more convenient compared to indirect measurement.
5. pellet can be obtained using corresponding to the light path of Wave-front measurement all the way on the basis of mean refractive index is obtained
Wavefront is distributed, and then draws the index distribution of pellet ice sheet.
Brief description of the drawings
Fig. 1 is the overall structure diagram of the present invention；
Fig. 2 is the schematic diagram that ice sheet refractive index is detected based on optical path difference；
Fig. 3 is the schematic diagram that ice layer thickness is detected based on deflection of light；
Fig. 4 is double light path iterative process figure；
Fig. 5 is the simulation result figure of 4 pellets.
Embodiment
As shown in figure 1, ice sheet refractive index and the measurement apparatus of thickness in a kind of ICF pellets, including light source 1, beam expander 2,
Beam splitter 3, the first speculum 4, the second speculum 5, pellet to be measured 6, Wavefront sensor 7, lens 8, the and of ccd image sensor 9
Computer 10.Light source 1, beam expander 2, beam splitter 3, the first speculum 4 are put successively along same horizontal line, the light-emitting window of light source 1 with
The light inlet alignment of beam expander 2, the light-emitting window of beam expander 2 align with the light inlet of beam splitter 3, the light extraction of the transmitted light of beam splitter 3
Mouth is with the first speculum 4 in 45 ° of settings.Pellet 5 to be measured is placed in the light-emitting window side of the reflected light of beam splitter 3, with the light extraction of beam splitter 3
Mouth is located along the same line；Second speculum 5 is laterally in same straight line with pellet 5 to be measured, is vertically in the first speculum 4
On same straight line, and along horizontal line in 45 ° of settings.Inverse time of second speculum 5, pellet to be measured 6, lens 8, ccd image sensor 9
Set on the same line, lens 8 are located among pellet 6 to be measured and ccd image sensor 9, the centre-to-centre spacing of lens 8 pellet 6 to be measured
Center and the centre distance of ccd image sensor 9 are twice of the focal length of lens.Wavefront sensor 7 and beam splitter 3, pellet to be measured 6
It is located along the same line, pellet 6 to be measured is arranged among Wavefront sensor 7 and beam splitter 3.Wavefront sensor 7 and ccd image pass
Sensor 9 is connected with computer, obtains wave front chart 11 and back-lit projection Figure 12.Light source 1 uses laser or LED.
The light emitted from light source 1, by the beam splitting film in beam splitter 3, is divided into orthogonal after beam expander
Two beam collimated lights；It is a branch of directly to get on pellet 6 to be measured, received after pellet 6 to be measured refraction by Wavefront sensor 7, obtain ripple
Preceding Figure 11, for detecting the ice sheet refractive index of pellet 6 to be measured；Another beam is after the first speculum 4 and the second speculum 5 change light path
Get on pellet 6 to be measured, after light passes through pellet 6 to be measured, get on lens 8, by ccd image sensor 9 after the convergence of lens 8
Receive, obtain back-lit projection Figure 12, detected for pellet ice layer thickness.Then, computer 10 collects wave front chart 11 and back-lit projection
Figure 12 detection informations to be iterated analysis.
Ice sheet refractive index and it is the step of the measuring method of thickness based on said apparatus, in a kind of ICF pellets：
Step 1：The light sent from light source 1 turns into collimated light beam by beam expander 2, is divided to by beam splitter 3 for two beams：One
Beam is received directly through pellet 6 to be measured by Wavefront sensor 7, and pellet 6 to be measured is located along the same line with Wavefront sensor 7；Separately
It is a branch of after the first speculum 4 and the reflection of the second speculum 5, through pellet 6 to be measured, be imaged on ccd image by lens 8 and pass
On sensor 9；Handled in computer 10, wave front chart 11 is obtained from Wavefront sensor 7, backlight is obtained from ccd image sensor 9
Perspective view 12.Wherein distance of the lens 8 away from pellet 6 to be measured is twice of 2f of the focal length of lens, and lens are away from ccd image sensor 9
Distance is twice of 2f of the focal length of lens；The distance of the Wavefront sensor of pellet 6 to be measured is known quantity D.
Step 2：As shown in Fig. 2 corresponding to the light path received directly through pellet 6 to be measured by Wavefront sensor 7；Setting
Light height of incidence through the axis of pellet 6 to be measured is 0, and the vertical range of light incidence point and the axis of pellet 6 to be measured is farthest
The height of incidence of light is x (height of incidence x is the arithmetic number less than pellet outer radius).Respectively trace from height for 0 with height
For the incident light of x.The light that height of incidence is 0 passes straight through pellet 6 to be measured, is received by Wavefront sensor 7；And height of incidence
Have multiple deviation on 6 each interface of pellet to be measured for x light, to should light the point of 7 receipts is connect according to ripple by Wavefront sensor
The distance at front sensor image planes 7-1 centers is rk.When finally reaching Wavefront sensor, the light path of this two light is different, so as to
There is optical path difference.Equiphase figure of the light after by pellet is no longer a plane, but aspherical.If this two light
From incide received by Wavefront sensor when corresponding optical path difference be k λ, obtain formula (1)：
OPL(x,n2,t2)-OPL(0,n2,t2)=k λ (1)
Wherein, OPL (x, n2,t2) it is from light path, OPL (0, n corresponding to light incident height x2,t2) it is to enter from height 0
Light path corresponding to the light penetrated；X is light height of incidence, n2For ice sheet refractive index, t2For ice layer thickness.
Because the deviation of pellet acts on, the height that the light incident from height x is reached on Wavefront sensor 7 is no longer x.If
Incident from ray height x, it is r to reach Wavefront sensor 7 away from Wavefront sensor centre-height by the geometry deviation of pelletk.Can
To list formula (2) according to geometrical relationship：
X+ Δ x+Dtan2 ζ=rk (2)
Wherein, x+ Δs x is the height that light is emitted from pellet right endpoint section, and D is pellet right endpoint to Wavefront sensor
The distance of receiving plane, 2 ζ are the deflection angle of beam projecting.
Simultaneous formula (1) and (2).Obtain reaching wavefront biography from light incident height x through pellet geometry deviation by measurement
The height r of sensork, and from height for 0 with height be x incidence light corresponding optical path difference k λ value.Pellet known parameters,
Including pellet outer radius R0, shell thickness t1, spherical shell refractive index n1。
In two equations, there are three unknown numbers：(light height of incidence) x, (ice sheet refractive index) n2, (ice layer thickness) t2。
Obtain an initial n2Or t2Value, you can solve all unknown numbers.As long as it follows that ice sheet average thickness, it is known that
Obtain ice sheet refractive index.
Step 3：As shown in figure 3, for by the first speculum and the second speculum reflection after, through pellet, by saturating
Mirror is imaged on the light path on ccd image sensor 9, and the bright ring position on back-lit projection Figure 12 is extracted on ccd image sensor
Put, the position is X away from ccd image sensor image planes 9-1 centre distances2.High power source of parallel light is projected on transparent pellet,
The picture for the transparent pellet that ccd image sensor receives is made up of light, and these light are in each multiple catadioptric in layer border of pellet.
In back-lit projection figure on ccd image sensor, a notable bright ring 13 is had on back-lit projection figure.Due in the system, lens
Distance away from pellet 6 to be measured is twice of 2f of the focal length of lens, and distance of the lens away from ccd image sensor is twice of the focal length of lens
2f.It follows that the pellet equatorial plane (plane perpendicular to current cross-section where Fig. 3 reference axis longitudinal axis) is complete with the picture in image planes
It is complete consistent.Therefore, for from certain incident height X a branch of light for participating in forming bright ring, it reaches ccd image sensor image planes
When apart from the distance of image plane center be X2.The bright ring contains the thickness of pellet ice sheet and the information of refractive index.
Can be according to the path of geometrical relationship Geometrical Optics：
In formula, α0It is the angle of incident ray and normal,It is deflection angle of the emergent ray relative to trunnion axis.
Bright ring on back-lit projection figure represents the maximum position of energy.Bright ring is being obtained to the back of the body from back-lit projection figure
(bright ring position X is designated as after the distance at light perspective view center2), it is thus necessary to determine that bright ring position and the corresponding relation of incident light height.
Bright ring is formd from the incident light of what height.In analysis, it is impossible to because the low-intensity of light beam, or it is complicated by path
With regard to abandoning light group.Multi simulation running shows, | dX2/ dX | a zero point can be produced.This zero point meets focus in optical system
Feature (Optimal'Tomography'of 2-Layered Targets:3D Parameters Reconstruction
from Shadow Images.(Fusion science and technology,2007,VOL.51,No.4:P705-
716)).Therefore bright ring position X has been drawn2With incident light height X relation, formula (4)：
Simultaneous formula (3) and (4).In formula, by carrying out image procossing to back-lit projection figure, bright ring height X is extracted2；Formula
Middle other amounts, equal operational light incoming position X, ice sheet refractive index n2, ice layer thickness t2, and pellet known parameters, outside pellet
Radius R0, shell thickness t1, spherical shell refractive index n1Express.
In the two equations, there are three unknown numbers：X (light incoming position), t2(ice layer thickness), n2(ice sheet reflects
Rate).So, it is known that ice sheet refractive index, you can obtain ice layer thickness distribution.
Step 4：In the refractive index method for solving based on optical path difference, it is known that ice sheet average thickness, ice sheet can be obtained and put down
Equal refractive index；In the thickness method for solving based on deflection of light, it is known that ice sheet mean refractive index, you can obtain the average thickness of ice sheet
Degree.Both approaches form complementation.With reference to this two light paths, method of the invention can accurately solve the flat of pellet ice sheet simultaneously
Equal refractive index and thickness.Since solving refractive index or thickness solves, the beginning as iteration.
As shown in figure 4, it is double light path iterative process figure；1) before iteration starts, pellet relevant parameter is such as：Pellet outer radius
R0, pellet spherical shell refractive index n1, pellet shell thickness t1It is known.The parameter measured for other needs, is tested by Wave-front measurement
Measure rk, X is measured by back-lit projection experiment2.Wherein, tested for Wave-front measurement, the receiving plane of Wavefront sensor is positioned at
At the known distance of pellet rear (such as 20 millimeters), Wavefront sensor receives distorted wavefront of the incident light after pellet；2) to institute
The ice layer thickness for stating pellet to be measured carries out an initial estimate；3) thickness value is substituted into the method based on optical path difference and solves ice sheet folding
Rate is penetrated, this refractive index is substituted into the method based on deflection of light solves ice layer thickness, and its value is designated as n respectively2, t2；Wherein n2For
The ice sheet refractive index value of presently described pellet, t2For the ice layer thickness value of presently described pellet；4) verify whether to meet that iteration is cut
Only condition.Compare current n2, t2If continuously differing by more than threshold value (being at least 0.0001) with the value of last time three times, repeat
3)；If continuously being differed three times with the value of last time and being less than the threshold value, iteration cut-off, current n2, t2For final pellet ice sheet
Refractive index and thickness.
True ICF pellets now different to 4 sizes and parameter carry out emulation experiment, as shown in table 1.
Table 1
It can be seen that, the pellet used in emulation differs greatly in the parameters such as diameter, shell thickness from table 1, tool
There is certain representativeness.Because pellet is in preparation process, it can produce a certain amount of bubble in its ice sheet and make the actual refraction of ice sheet
Rate is not inconsistent with nominal index of refraction.Document (FIREX foam cryogenic target development:residual void
reduction and estimation with solid hydrogen refractive index measurements.
(Nuclear Fusion,2013,VOL.53,NO.8:P083009)) show, in the case of not doing any specially treated, ice sheet is empty
Gap rate (the ratio between the volume bubbled in ice sheet and the volume of whole ice sheet) is 11%.Provided with ice layer thickness in the case of tight one
Sample, then ice sheet constancy of volume, quality are changed into original 89%.Then there is formula (5)：
The ρ of ρ=0.890 (5)
According to document (Estimated Refractive Index and Solid Density of DT, with
Application to Hollow-Miarospkere Laser Targets.(UCRL-51921,Lawrence
Livermore National Laboratory, 1975)), for all hydrogen isotopes under any temperature, any states of matter, its is right
The refractive index n of 0.55um wavelength and the relation of density p are formula (6)：
N=1+A ' ρ (6)
In formula, A ' is constant.Then there is formula (7):
In formula, n0Refer to ice sheet refractive index during tight, i.e. nominal index of refraction；N refers to ice sheet refractive index when having space.
By pellet (1) exemplified by, as nominal index of refraction n0When=1.16, ice sheet refractive index when voidage is 11% is n=
1.1424.Now the relative error of ice sheet refractive index is 1.52%.It can be seen that it can directly be introduced using ice sheet nominal index of refraction larger
Error.
The refractive index and thickness of pellet ice sheet are solved using the apparatus and method of the present invention.By pellet (1) exemplified by, it is assumed that ice
The initial value of layer average thickness is 99 μm, substitutes into Wave-front measurement method and tries to achieve refractive index, then refractive index is substituted into back-lit projection method and tried to achieve
Thickness, successively iteration.The stopping criterion for iteration set is continuously iterative value three times is less than 0.0001 compared to the gap of last time.
The ice sheet refractive index n of pellet (1)2With thickness t2It is shown with variation relation such as Fig. 5 (a) of iterations, in iteration
Iterated conditional, iteration stopping are reached after 31 times.Observe iterative process to understand, n2With t2It is rapid with iterations rising
Convergence, ice sheet refractive index synchronously change with the change of thickness.After iteration stopping, the relative error of ice sheet refractive index is
4.57ppm, the relative error of ice layer thickness is 14.5ppm.Obviously, all obtained by iterative algorithm, ice sheet refractive index and thickness
Accurate calculating.As shown in Fig. 5 (b), for the ice sheet refractive index of pellet (2), (3), (4) with thickness with the change of iterations
Relation.It can be seen that in the pellet of different structure, iteration also restrains ground very well.Final relative error is also all approximately 0.
Compared to 1.52% relative error of traditional method, relative error of the invention is almost 0.
Claims (4)
1. ice sheet refractive index and the measuring method of thickness in a kind of ICF pellets, it is characterised in that：Including light source, beam expander, beam splitting
Mirror, the first speculum, the second speculum, pellet to be measured, Wavefront sensor, lens, ccd image sensor, computer.By following
Scheme, while the refractive index and thickness of ice sheet in ICF pellets are measured, have the following steps：
Step 1：The light sent from light source turns into collimated light beam by beam expander, is divided into two beams by beam splitter：It is a branch of directly to wear
Cross pellet to be measured to be received by Wavefront sensor, pellet to be measured is located along the same line with Wavefront sensor；Another beam passes through first
After speculum and the reflection of the second speculum, through pellet to be measured, by lens imaging on ccd image sensor；Will be from wavefront
Sensor obtains wave front chart and handled with obtaining back-lit projection figure from ccd image sensor in computer.Wherein lens are away from treating
The distance for surveying pellet center is twice of 2f of the focal length of lens, and distance of the lens away from ccd image sensor image planes is the focal length of lens
Twice of 2f；The distance of pellet Wavefront sensor to be measured is known quantity D.
Step 2：Corresponding to the light path received directly through pellet to be measured by Wavefront sensor；Set through pellet axis to be measured
Light height of incidence be 0, the height of incidence of the farthest light of the vertical range of light incidence point and pellet axis to be measured is x,
Height of incidence x is the arithmetic number less than pellet outer radius.Trace is the incident light of x for 0 and height from height respectively.It is incident high
The light spent for 0 passes straight through pellet to be measured, is received by Wavefront sensor, is located at wavefront sensing by the point that Wavefront sensor receives
Device image plane center；And height of incidence be x light have multiple deviation on each interface of pellet to be measured, to should light by wavefront
The point that sensor receives is r according to the distance of Wavefront sensor image plane centerk.If this two light are from inciding by Wavefront sensor
Corresponding optical path difference is k λ during reception, obtains formula (1)：
OPL(x,n2,t2)-OPL(0,n2,t2)=k λ (1)
Wherein, OPL (x, n2,t2) it is from light path, OPL (0, n corresponding to light incident height x2,t2) it is incident from height 0
Light path corresponding to light；X is light height of incidence, n2For ice sheet refractive index, t2For ice layer thickness.
Because the deviation of pellet acts on, the height that the light incident from height x is reached on Wavefront sensor is no longer x.According to several
What relation lists formula (2)：
X+ Δ x+Dtan2 ζ=rk (2)
Wherein, x+ Δs x is the height that light is emitted from pellet right endpoint section, and D is that pellet right endpoint receives to Wavefront sensor
The distance in face, 2 ζ are the deflection angle of beam projecting.
Simultaneous formula (1) and (2).Obtain reaching Wavefront sensor from light incident height x through pellet geometry deviation by measurement
Height rk, and from height for 0 with height be x incidence light corresponding optical path difference k λ value.Pellet known parameters, including
Pellet outer radius R0, shell thickness t1, spherical shell refractive index n1.As long as ice sheet average thickness is, it is known that ice sheet refractive index can be obtained.
Step 3：For after the first speculum and the reflection of the second speculum, through pellet, scheming by lens imaging in CCD
As the light path in sensing, the bright ring position on back-lit projection figure is extracted on ccd image sensor, the position is away from ccd image
Center sensor distance is X2.High power source of parallel light is projected on transparent pellet, the transparent target that ccd image sensor receives
The picture of ball is made up of light, and these light are in each multiple catadioptric in layer border of pellet.Back-lit projection figure on ccd image sensor
In have a notable bright ring.Due in the system, distance of the lens away from pellet center to be measured is twice of 2f of the focal length of lens, lens
Distance away from ccd image sensor image planes is twice of 2f of the focal length of lens.Therefore, for certain a branch of participation from height X incidences
The light of bright ring is formed, apart from the distance of image plane center is also X when it reaches ccd image sensor image planes2。
Formula (3) can be obtained according to the path of geometrical relationship Geometrical Optics：
In formula, X2For bright ring height, α0For incident ray and the angle of normal,Deviation for emergent ray relative to trunnion axis
Angle.
Multi simulation running shows, | dX2/ dX | a zero point can be produced.Therefore bright ring position X has been drawn2With incident light height X pass
System, formula (4)：
<mrow>
<mfrac>
<mrow>
<msub>
<mi>dX</mi>
<mn>2</mn>
</msub>
</mrow>
<mrow>
<mi>d</mi>
<mi>X</mi>
</mrow>
</mfrac>
<mo>=</mo>
<mn>0</mn>
<mo>-</mo>
<mo>-</mo>
<mo>-</mo>
<mrow>
<mo>(</mo>
<mn>4</mn>
<mo>)</mo>
</mrow>
</mrow>
Simultaneous formula (3) and (4).X is light incoming position, n in formula2For ice sheet refractive index, t2For ice layer thickness.By to backlight
Perspective view carries out image procossing, draws bright ring height X2；Pellet known parameters：Pellet outer radius R0, shell thickness t1, spherical shell folding
Penetrate rate n1.Known ice sheet refractive index, you can obtain ice layer thickness distribution.
Step 4：In step 2, it is known that ice sheet average thickness, ice sheet mean refractive index can be obtained；In step 3, it is known that
Ice sheet mean refractive index, you can obtain ice sheet average thickness.With reference to this two light paths, solved from refractive index or thickness is solved and opened
Begin, as the beginning of iteration, there is following process：
1) before iteration starts, pellet relevant parameter is such as：Pellet outer radius R0, pellet spherical shell refractive index n1, pellet shell thickness t1
It is known.The parameter measured for other needs, r is measured by Wave-front measurement experimentk, X is measured by back-lit projection experiment2.2) it is right
The ice layer thickness of the pellet to be measured carries out an initial estimate；3) thickness value is substituted into the method based on optical path difference and solves ice sheet
Refractive index, this refractive index is substituted into the method based on deflection of light and solves ice layer thickness, its value is designated as n respectively2, t2；Wherein n2
For the ice sheet refractive index value of presently described pellet, t2For the ice layer thickness value of presently described pellet；4) verify whether to meet iteration
Cut-off condition.Compare current n2, t2If continuously differing by more than threshold value with the value of last time three times, threshold value is less than 0.0001, then
Repeat 3)；If continuously being differed three times with the value of last time and being less than threshold value, iteration cut-off, current n2, t2For final pellet ice
Layer refractive index and thickness.
2. ice sheet refractive index and the measurement apparatus of thickness in a kind of ICF pellets, including light source, beam expander, beam splitter, the first reflection
Mirror, the second speculum, pellet to be measured, Wavefront sensor, lens, ccd image sensor and computer.It is characterized in that：Described
Light source, beam expander, beam splitter, the first speculum are put successively along same horizontal line, and the light-emitting window of light source and beam expander enter light
Mouth alignment, the light-emitting window of beam expander align with the light inlet of beam splitter, and the light-emitting window of beam splitter transmitted light is in the first speculum 4
45 ° of settings.Pellet to be measured is placed in the light-emitting window side of beam splitter reflected light, is located along the same line with beam splitter light-emitting window；The
Two-mirror is laterally in same straight line with pellet to be measured, is vertically in the first speculum on same straight line, and along horizontal line
In 45 ° of settings.On the same line, lens are located at the inverse setting of second speculum, pellet to be measured, lens, ccd image sensor
Among pellet and ccd image sensor to be measured, lens centre is away from pellet center to be measured and ccd image sensor centre distance
Twice of the focal length of lens.Wavefront sensor is located along the same line with beam splitter, pellet to be measured, and pellet to be measured is arranged on wavefront biography
Among sensor and beam splitter.Wavefront sensor and ccd image sensor are connected with computer, obtain wave front chart and back-lit projection figure.
3. ice sheet refractive index and the measuring method of thickness in a kind of ICF pellets as claimed in claim 1, it is characterised in that：It is right
Tested in Wave-front measurement, the receiving plane of Wavefront sensor is positioned at 20~200 millimeters of pellet rear known distance, wavefront passes
Sensor receives distorted wavefront of the incident light after pellet.
4. ice sheet refractive index and the measuring method or device of thickness in a kind of ICF pellets as claimed in claim 1 or 2, it is special
Sign is：Described light source is laser or LED.
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