CN102608682A - Phase diaphragm applied to 4f phase coherent imaging systems - Google Patents
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Abstract
The invention discloses a phase diaphragm applied to 4f phase coherent imaging systems. A round phase object in the phase diaphragm, the unified phase retardation of which is Pi/2, is changed into a positive annular phase object and a negative annular phase object, the two phase retardations of which are Pi/4 and negative Pi/4, so that the sensitivity of a measuring system is increased. Considering that the smaller the phase objects are, the higher the edge diffraction effect on the phase objects can be, preferably, the positive phase object and the negative phase object are chosen to divide the phase diaphragm into three equal parts in practice. The improved phase diaphragm can increase the measurement precision of the system within the range of non-linear phase shift Phi NL greater than negative Pi or less than Pi. For positive small non-linear phase shift (Phi NL equal to 0), the sensitivity is increased by up to 1.65 times; for negative non-linear phase shift, the increase of sensitivity is remarkable; when Phi NL is equal to negative 0.6 Pi, the sensitivity is increased by up to 3.21 times, and particularly, when non-linear phase shift tends to be negative Pi, sensitivity is increased by about 27 times.
Description
Technical field
The present invention relates to a kind of novel phase diaphragm that can improve 4f phase coherence imaging system measuring accuracy.
Background technology
Along with the develop rapidly of art such as optical communication and optical information processing, non-linear photon is learned investigation of materials and is become more and more important.The realization of functions such as optical logic, optics memory, optical transistor, photoswitch and phase place complex conjugate mainly depends on the progress that non-linear photon is learned material.The optical nonlinearity measuring technique is that the non-linear photon of research is learned one of gordian technique of material.Here the 4f phase coherence imaging system that will use (G.Boudebs and S.Cherukulappurath; " Nonl inear optical measurements using a 4f coherent imaging system with phase object "; Phys.Rev.A; 69,053813 (1996)) be exactly a kind of new method of measuring nonlinear refraction coefficient of materials that proposes in recent years.
4f phase coherent imaging method is a kind of measuring method of beam aberration; This method is on 4f system object plane, to place a phase diaphragm; Non-linear object to be measured is placed on the Fourier plane, and on exit facet, receives the method for shoot laser pulse diagram picture with the CCD camera.This method can utilize monopulse to measure the size and the symbol of nonlinear refraction coefficient simultaneously.Phase diaphragm is to make the more phase object of small circular of an area at the center of a circular iris, and the light outer through the light ratio phase object of phase object has positive phase delay.When the nonlinear refractive index of measured material when being positive, the nonlinear images that CCD receives since positive phase contrast strengthen around the strength ratio in the position of phase object.Opposite, when the nonlinear refractive index of measured material for negative the time, a little less than wanting around the strength ratio of the position of the phase object of nonlinear images.
Though 4f phase coherent imaging method utilizes phase diaphragm to realize the size of nonlinear refractive index and the measurement of symbol dexterously, the effect of phase diaphragm is not brought into play fully.If the phase shift of the phase object in the phase diaphragm is become negative, so for material, will produce a negative phase contrast signal in the experiment with positive nonlinear refraction, promptly the intensity of the position of phase object will reduce in the nonlinear images.And for the material of bearing nonlinear refractive index, the intensity of phase object position will increase in the nonlinear images.If can realize the both positive and negative phase contrast simultaneously for same nonlinear material, sensitivity will increase so.
Summary of the invention
In order to give full play to the phase contrast effect of phase object, the present invention provides a kind of improved phase diaphragm, and this phase diaphragm can produce positive phase contrast and negative phase-contrast simultaneously to nonlinear sample to be measured, makes the measurement sensitivity of 4f phase coherence imaging system be improved.
For achieving the above object, the technical scheme that the present invention adopts is:
A kind of phase diaphragm that is applied to the 4f phase coherence imaging system, the phase object that is in the diaphragm center in this phase diaphragm is made up of annular phase object and the circular phase object that is arranged in annular phase object.
Phase diaphragm is to constitute through the phase object that forms through the plating transparent dielectric film at a circular iris center.The bit phase delay that said circular phase object and annular phase object produced is respectively 2m π+π/4 and 2n π-π/4, and wherein m, n are integer.
Through outside the phase object of the unified phase delay of original circle, adding annular phase object, make circular phase object produce the phase delay of π/4, and the phase delay of annular phase object generation-π/4.For nonlinear refractive index is positive sample, in nonlinear images phase delay be the zone of π/4 because positive phase contrast intensity enhancing, and phase delay for the zone of-π/4 since negative phase-contrast intensity reduce.The enhancing of the regional intensity of phase diaphragm or reduce almost equal in the increase of the intensity in the nonlinear images that the positive and negative annular phase diaphragm after improving with the present invention produces and the nonlinear images that reduces under the situation of same intensity incident light, to produce with the phase diaphragm phase object that improves preceding circle.Move the poor of regional average intensity if the definition phase contrast signal is the average intensity and the negative in positive phase shift zone, like this just make the measuring accuracy of system be improved.
Utilize diaphragm of the present invention to divide two parts to carry out, i.e. nonlinear measurement and energy calibration in the measurement that the 4f phase coherence imaging system carries out nonlinear refractive index.The concrete steps of nonlinear measurement are:
(1) takes testing sample away, gather a pulse diagram picture, be called image without image with the CCD camera.
(2) testing sample is placed on the Fourier plane, neutral rate is subtracted sheet be placed on before the nonlinear sample, make the light intensity that shines on the sample be reduced to the range of linearity,, be called linear image with pulse diagram picture of CCD camera collection.
(3) testing sample is placed on the Fourier plane, moved on to after the sample, gather a pulse diagram picture, be called nonlinear images with the CCD camera with before gathering neutral attenuator that linear image is to use.
Energy calibration is that nonlinear sample is taken away, and a certain position that energy meter is placed between two convex lens of 4f system makes laser facula can all get on the energy meter probe.Launch a laser pulse, measure the energy of pulse, gather the reference hot spot of reference path simultaneously with the CCD camera with energy meter.Because all devices all are linear units in the light path at this moment, so according to the size that just can know the incident pulse energy with reference to the power of hot spot.The energy that incides the pulse on the testing sample in the nonlinear measurement process just can calculate through the reference hot spot that same laser pulse produces like this.
After measurement finishes, obtain the value of nonlinear refractive index through the non-linear hot spot of numerical fitting as input with linear beam spot.The sensitivity of experiment is that the strength difference by non-linear diaphragm decides.For the common phase diaphragm that has circular object, the mean intensity in phase object zone and phase object are Δ T with the difference of the mean intensity of exterior domain in the later nonlinear images of definition normalization.Having two positive and negative annular phase diaphragms that phase delay is different after improving for the present invention, the mean intensity that can define phase delay in the normalized nonlinear images and be the border circular areas of π/4 with phase delay is-the mean intensity difference of the annular region of π/4 is Δ T '.
Numerical simulation shows; Under the situation of identical incident intensity; In the nonlinear images of the circular phase object of band after the present invention improves and the positive and negative annular phase diaphragm of annular phase place, the mean intensity in phase object zone is almost equal in the nonlinear images of the mean intensity of the border circular areas of phase delay π/4 and former phase diaphragm.But in the nonlinear images of the phase diaphragm after the present invention improves, the mean intensity of the annular region of phase delay-π/4 will weaken, so Δ T '＞Δ T, and phase diaphragm promptly of the present invention makes the sensitivity of measuring system increase.
The positive and negative annular phase diaphragm that the present invention proposes is compared with previously presented phase diaphragm, and it has the following advantages:
1, can improve the sensitivity of systematic survey, positive non-linear of measurement that both can be sensitive, negative non-linear of measurement that also can be sensitive, and measure negative when non-linear sensitivity improve more obvious.
2, different with positive and negative circular phase diaphragm, positive and negative annular phase diaphragm is the division center symmetry, and is more convenient when adding time dimension when calculating with the polar coordinates programming.
3, because positive and negative circular phase diaphragm is that left semicircle is positive phase shift zone in smaller phase object, and right semi-circle is that negative moves the zone, make very inconvenient; And circle is positive phase shift zone in the positive and negative annular phase diaphragm, and adapter ring is that negative moves the zone, and opposed area is bigger, and institute is so that processing and fabricating.
The raising of the sensitivity of the phase diaphragm after the present invention improves is different along with the variation of sample nonlinear phase shift.The variation of sensitivity is defined as Δ T '/Δ T, can produce vibration in order to make phase contrast signal, the nonlinear phase shift that produces in the assumes samples is :-π＜Φ
NL＜π, the sensitivity of systematic survey nearly all can be improved in this scope.Little phase shift (Φ
NL≈ 0) under the situation, Δ T '/Δ T=1.65 is negative situation for nonlinear phase shift, the increase of sensitivity is very obvious, works as Φ
NLDuring=-0.6 π, the increase of sensitivity can reach Δ T '/Δ T=3.21, works as Φ especially
NLApproaching-during π, about about 27 times of the increase of sensitivity.
Description of drawings
Fig. 1 is a 4f phase coherence imaging system schematic diagram of the present invention.Wherein: 1, laser instrument; 2, phase diaphragm; 3, convex lens; 4, testing sample; 5, convex lens; 6, neutral attenuator; 7, CCD camera; 8, beam splitter; 9, catoptron; 10, convex lens; 11, catoptron; 12, beam splitter; 13, circular phase object; 14, circular phase object; 15, annular phase object.
Fig. 2 is with the phase diaphragm synoptic diagram of circular phase object in the embodiment of the invention.
Fig. 3 in the embodiment of the invention with the phase diaphragm synoptic diagram of circular phase object and annular phase object.
Fig. 4 in the embodiment of the invention with the nonlinear images and the sectional view thereof of the phase diaphragm numerical simulation of circular phase object.
Fig. 5 is with the nonlinear images and the sectional view thereof of the phase diaphragm numerical simulation of circular phase object and annular phase object in the embodiment of the invention.
Fig. 6 be in the embodiment of the invention with the Δ T of circular phase object phase diaphragm with the Δ T ' of the phase diaphragm of positive and negative annular phase object and the graph of a relation of nonlinear phase shift.
Fig. 7 is the variation of embodiment of the invention medium sensitivity and the graph of a relation of nonlinear phase shift.
Fig. 8 is (a) linearity that records with the experiment of the phase diaphragm of circular phase object and annular phase object in the embodiment of the invention, (b) non-linear and (c) the hot spot figure of n.s..
Fig. 9 in the embodiment of the invention with the sectional view match of the non-linear figure of the phase diaphragm of circular phase object and annular phase object.
Embodiment
Below in conjunction with accompanying drawing and embodiment the present invention is further described:
Fig. 1 is the Experimental equipment of 4f phase coherence imaging system.Experimental provision can be divided into measuring system and energy frame of reference two parts.Measuring system is made up of laser instrument 1, phase diaphragm 2, convex lens 3, testing sample 4, convex lens 5, neutral attenuator 6 and CCD camera 7.Wherein convex lens 3 constitute the 4f system with convex lens 5, and phase diaphragm 2 is placed on the object plane of 4f system, and testing sample 4 is on the Fourier plane, and CCD camera 7 received pulse image on the picture plane of 4f system.At first restraint (this part has omitted) among Fig. 1 from the laser that laser instrument 1 sends through expanding; The laser pulse that expands after restrainting forms nearly top-hat light through phase diaphragm 2; The Fourier transform of light beam planoconvex lens 3 converges on the testing sample 4 that is placed on the Fourier plane, because the nonlinear refraction character of testing sample 4 makes the phase place of pulse of incident change.The pulse of surperficial outgoing is received by CCD camera 7 through the inverse Fourier transform of convex lens 5 behind the sample, is called main spot.
The energy frame of reference is made up of beam splitter 8, catoptron 9, convex lens 10, catoptron 11 and beam splitter 12.The laser that comes out from phase diaphragm 2 is divided into two bundles by beam splitter 8, and is wherein a branch of through catoptron 9, convex lens 10, catoptron 11 and beam splitter 12, received by CCD camera 7 at last, is called with reference to hot spot.
Shown in Figure 2 is exactly the common form of phase diaphragm 2, and phase object 13 is circular, the light beam bit phase delay pi/2 of other part of optical beam ratio through phase object 13.Shown in Figure 3 is the phase diaphragm after the present invention improves, and is made up of the phase object of a circle jointly circular phase object 14 and annular phase object 15.Wherein circular phase object 14 produces the phase delay pi/2, and annular phase object 15 produces phase delay-pi/2.
The measurement that utilizes the 4f phase coherence imaging system to carry out nonlinear refractive index divides two parts to carry out, i.e. nonlinear measurement and energy calibration.The concrete steps of nonlinear measurement are:
The first step: take testing sample 4 away, gather a pulse diagram picture, be called image without image with CCD camera 7.
Second step: testing sample 4 is placed on the Fourier plane, neutral rate is subtracted sheet 6 be placed on before the testing sample 4, make the light intensity that shines on the testing sample 4 be reduced to the range of linearity,, be called linear image with pulse diagram picture of CCD camera 7 collections.
The 3rd step: testing sample 4 is placed on the Fourier plane, and the neutral attenuator 6 that uses when before gathering linear image moves on to after the testing sample 4, with pulse diagram picture of CCD camera 7 collections, is called nonlinear images.
Energy calibration is that nonlinear sample 4 is taken away, and a certain position that energy meter is placed between convex lens 3 and the convex lens 5 makes laser facula can all get on the energy meter probe.Launch a laser pulse, measure the energy of pulse, gather the reference hot spot of reference path with CCD camera 7 simultaneously with energy meter.Because all devices all are linear units in the light path at this moment, so according to the size that just can know the incident pulse energy with reference to the power of hot spot.The energy that incides the pulse on the testing sample 4 in the nonlinear measurement process just can calculate through the reference hot spot that same laser pulse produces like this.
Fig. 4 (a) is the nonlinear images that the phase diaphragm by the circular phase object of common band obtains, and accompanying drawing 4 (b) then is the sectional view of accompanying drawing 4 (a) along y=0.The used major parameter of numerical simulation is the phase object radius and the ratio ρ=L of diaphragm radius
p/ R
a=0.5mm/1.5mm ≈ 0.33, testing sample nonlinear phase shift Φ
NL=0.35.Accompanying drawing 5 (a) is to obtain nonlinear images with the phase diaphragm with positive circular phase object and negative annular phase object after improving, and accompanying drawing 5 (b) then is the sectional view of accompanying drawing 5 (a) along y=0.In the simulation ratio of used circular phase object radius and diaphragm radius and sample nonlinear phase shift all with Fig. 4 in identical, and the radius of annular phase object is R
b=1.0mm.Definition is Δ T with the mean intensity of phase diaphragm position and the difference of the mean intensity outside the phase object in the nonlinear images of the phase diaphragm generation of circular phase object.And, with bit phase delay being that the mean intensity of position of the circular phase object of π/4 with bit phase delay is for the nonlinear images that produces with the phase diaphragm of positive and negative annular phase object-difference of the mean intensity of the annular phase object position of π/4 is defined as Δ T '.Can see that from accompanying drawing 4 (b) and accompanying drawing 5 (b) bit phase delay in Δ T and the accompanying drawing 5 (b) in the accompanying drawing 4 (b) is that the difference of mean intensity and the mean intensity outside the phase object of position of semicircle phase object of π/4 is almost equal; Thereby Δ T '＞Δ T, i.e. phase diaphragm after the present invention improves are the measurement sensitivity of system to be improved.
Fig. 6 is with the Δ T of the phase diaphragm of circular phase object and with positive circular phase object and the Δ T ' of the phase diaphragm of the annular phase object of bearing and the relation curve of nonlinear phase shift.Therefrom find out | Φ
NL| in the scope of＜π, Δ T in positive nonlinear phase shift scope sensitivity obviously greater than corresponding negative nonlinear phase shift.In order to study the validity of nonlinear refractive index, suppose nonlinear phase shift π＜Φ
NLBe the scope of our research in the＜π, the purpose of doing like this is excessive and to measuring the influence that produces for fear of nonlinear phase shift.We can find out that also the signal delta T (Δ T ') that in this scope, matches becomes the almost relation with nonlinear phase shift from Fig. 6.And Δ T ' almost is about Φ
NL=0 is centrosymmetric image, and-π＜Φ
NLThe sensitivity of Δ T ' all is higher than Δ T in the scope of＜π, and is particularly evident for the increase of negative nonlinear phase shift sensitivity.The Δ T '/ratio of Δ T and the mapping of the relation curve of nonlinear phase shift are presented in the accompanying drawing 7.In accompanying drawing 7, work as Φ
NLDuring=-0.6 π, the increase of sensitivity can reach Δ T '/Δ T=3.21, works as Φ
NLDuring=-0.5 π, the increase of sensitivity can reach Δ T '/Δ T=2.77; Work as Φ
NL=0 o'clock, Δ T '/Δ T=1.65; Work as Φ
NLDuring=0.5 π, Δ T '/Δ T=1.16.Special when nonlinear phase shift approaching-π, its sensitivity is increased to 27 times.So it is more sensitive when measuring bear nonlinear.The raising of sensitivity is very tangible in negative nonlinear phase shift scope; The multiple that improves along with the increase sensitivity of nonlinear phase shift is constantly reducing; When nonlinear phase shift increased to 0.7 π, the sensitivity before phase diaphragm after the improvement and the improvement much at one.In order to be more clearly visible the raising of phase diaphragm sensitivity of the present invention, part numerical value is listed in the table below.
The raising of the pairing system sensitivity of the different nonlinear phase shifts of table 1
| ?Φ NL(rad) | -π | -0.6π | -1 | 0 | 1 | 0.7π | π |
| ?ΔT′/ΔT | 27 | 3.21 | 2.21 | 1.65 | 1.33 | 1.0 | 0.88 |
Note that the data of mentioning among the present invention are at ratio ρ=0.33 of phase object with the phase diaphragm radius, R
bObtain under the situation of=1.0mm, can be slightly different for the multiple that different experiment condition sensitivity improves, but trend is identical.
Claims (3)
1. a phase diaphragm that is applied to the 4f phase coherence imaging system is characterized in that, the phase object that is in the diaphragm center in the said phase diaphragm is made up of annular phase object and the circular phase object that is arranged in annular phase object.
2. a kind of phase diaphragm that is applied to the 4f phase coherence imaging system according to claim 1, it is characterized in that: said phase object is made up of transparent dielectric film.
3. a kind of phase diaphragm that is applied to the 4f phase coherence imaging system according to claim 1 and 2; It is characterized in that: the bit phase delay that said circular phase object and annular phase object produced is respectively 2m π+π/4 and 2n π-π/4, and wherein m, n are integer.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103760629A (en) * | 2014-01-07 | 2014-04-30 | 苏州大学 | Phase position diaphragm for 4f phase-coherent imaging system |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6130776A (en) * | 1996-09-19 | 2000-10-10 | Olympus Optical Co., Ltd. | Optical microscope which has optical modulation elements |
| US6317261B1 (en) * | 1998-06-30 | 2001-11-13 | Nikon Corporation | Phase contrast observation device |
| CN101169490A (en) * | 2007-11-09 | 2008-04-30 | 苏州大学 | Phase diaphragm for 4f phase coherent imaging system |
| CN101482502A (en) * | 2009-01-08 | 2009-07-15 | 苏州大学 | Single-pulse measurement method for nonlinear refraction coefficient of materials |
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- 2012-03-30 CN CN2012100892048A patent/CN102608682A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6130776A (en) * | 1996-09-19 | 2000-10-10 | Olympus Optical Co., Ltd. | Optical microscope which has optical modulation elements |
| US6317261B1 (en) * | 1998-06-30 | 2001-11-13 | Nikon Corporation | Phase contrast observation device |
| CN101169490A (en) * | 2007-11-09 | 2008-04-30 | 苏州大学 | Phase diaphragm for 4f phase coherent imaging system |
| CN101482502A (en) * | 2009-01-08 | 2009-07-15 | 苏州大学 | Single-pulse measurement method for nonlinear refraction coefficient of materials |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103760629A (en) * | 2014-01-07 | 2014-04-30 | 苏州大学 | Phase position diaphragm for 4f phase-coherent imaging system |
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Application publication date: 20120725 |