CN110471101A - Impulse gamma X-ray detection X method and detection system based on laser polarization modulation - Google Patents
Impulse gamma X-ray detection X method and detection system based on laser polarization modulation Download PDFInfo
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Abstract
In order to solve the low technical problem of existing active laser probe gamma ray detection method sensitivity, the present invention provides a kind of impulse gamma X-ray detection X methods and detection system based on laser polarization modulation.Detection method comprising steps of 1) by gamma ray by radiate conversion crystal be converted to non-equilibrium free carrier, make radiate conversion crystal material refractive index occur transient changing；2) probe laser is incident to radiation conversion crystal, obtains different refractivity corresponding horizontal and/or vertical polarisation component transmissivity and/or reflectance curve；3) according to resulting different refractivity corresponding horizontal and/or vertical polarisation component transmissivity and/or reflectance curve, a certain polarized light component is chosen as polarized light component to be measured, and the analyzing optical path designed for filtering out the polarized light component to be measured；4) the transient state knots modification of the polarized light component intensity to be measured caused by radiation conversion crystal Refractive Index of Material transient changing is measured and recorded.
Description
Technical field
The present invention relates to a kind of impulse gamma X-ray detection X methods and spy using laser polarization and crystal refractive index modulation
Examining system.
Background technique
As ICF (Inertial Confinement Fusion), inverse Compton scattering source, free-electron laser etc. are super
The emergence and development of fast radiation source, conventional " radiation-electricity " Detection Techniques are due to being limited to space charge effect, the time of system
Responding ability usually fastest to sub- ns (nanosecond) magnitude, can no longer meet the detection demand of ultrafast radiation pulse.
Excess carrier generates extremely short (< 1ps) with the relaxation time in semiconductor, so that impulse gamma ray induced semiconductor is rolled over
It is very fast to penetrate rate transient changing process, this is that the study groups such as U.S.'s livermore laboratory are obtained in the way of Laser Active Detection
The main reason for ultrafast time response result of system (< 10ps).The existing pulsed radiation detection method based on laser microprobe has two
A key link: first is that ray particle to be converted to the transient changing of Refractive Index of Material using semiconductor crystal, then by refractive index
Transient changing is modulated in interferometer measurement arm；Second is that measuring and recording the transient changing of laser interference signal.It is ground according to these
Study carefully as a result, on the one hand proving to use a laser as spy using there is the semiconductor of short carrier lifetime as radiation conversion medium
The measurement of ultrafast pulse gamma ray time spectrum may be implemented in needle；On the other hand spirit is detected currently based on the system of the detection method
Sensitivity is very low, is the maximum short slab of the Detection Techniques, in addition, because the radiation detection technology based on laser means is all " main
It is dynamic " detection, usually all there is laser direct current background, turns when using the photoelectricity of the high-gains such as photomultiplier tube or optic streak camera
When parallel operation part, the DC laser the high more is unfavorable for measuring, and may cause permanent damage to devices such as big photomultiplier tubes
It is bad.How to further enhance Laser Modulation effect, change the technical thought of laser sensing Refractive Index of Material variation, improve radiation →
Laser integrates transfer efficiency, is that the active detection system of this kind of laser obtains more highly sensitive key point, this be also after
Continuous research and the realistic meaning for exploring more various novel " radiation-light (Rad-Optic) " Detection Techniques.
Summary of the invention
In order to solve the low technical problem of existing active laser probe gamma ray detection method sensitivity, the present invention is mentioned
A kind of impulse gamma X-ray detection X method and detection system based on laser polarization modulation is supplied.
The technical solution of the invention is as follows:
Based on the impulse gamma X-ray detection X method of laser polarization modulation, it is characterized in that, comprising steps of
1) gamma ray is converted into non-equilibrium free carrier by radiating conversion crystal, makes to radiate conversion crystal material
Refractive index occur transient changing；
2) probe laser is incident to radiation conversion crystal, probe laser is obtained according to Fresnel theorem and is incident to radiation turn
Different refractivity corresponding horizontal and/or vertical polarisation component transmissivity and/or reflectance curve when changing crystal, thus by spoke
The transient state variations in refractive index for penetrating conversion crystal material is converted to the transient changing of laser polarization component；
3) according to the resulting different refractivity of step 2) is corresponding horizontal and/or the transmissivity of vertical polarisation component and/or
Reflectance curve chooses a certain polarized light component as polarized light component to be measured, and designed for filtering out the polarised light to be measured
The analyzing optical path of component；
4) it is strong to measure and record the polarized light component to be measured caused by radiation conversion crystal Refractive Index of Material transient changing
The transient state knots modification of degree.
Further, radiation conversion crystal employed in step 1) should have sufficiently fast non-equilibrium free carrier to relax
Henan time (compared with pulse length to be measured, usually in sub- ps magnitude), the absorption limit for radiating conversion crystal are less than the probe and swash
The wavelength of light keeps radiation conversion crystal transparent to probe laser.
Further, radiation conversion crystal employed in step 1), incident end face should make polishing treatment, to guarantee to swash
The uniformity at light incidence interface at least guarantees that its incident end face implements polishing for only utilizing the situation of front end face reflected light；This
Outside, incident end face should be parallel as far as possible with outgoing end face.
Further, radiation conversion crystal employed in step 1) is Preset grating semiconductor, and has certain anti-spoke
Performance is penetrated, to ensure the repeatability of measurement process and result, such as GaAs, InP, GaN, InGaAsP, CdTe, ZnO etc..
Further, between step 1-2), probe laser is carried out to expand processing, the beam spot after expanding should be less than pulse
The beam spot size of gamma ray, to improve detectivity.
Further, in step 2), the incident angle of probe laser is according to the transmissivity and/or reflection for radiating conversion crystal
Rate curve determines.
Further, choosing a certain polarized light component as the principle of polarized light component to be measured in step 3) is:
If the refractive index for radiating conversion crystal reduces, volume reflection or the vertical polarization point of horizontal polarisation component should be chosen
The transmission amount of amount is as polarized light component to be measured；
If the refractive index for radiating conversion crystal increases, the transmission amount or vertical polarization point of horizontal polarisation component should be chosen
The volume reflection of amount is as polarized light component to be measured.
Further, in step 4), mode there are two types of the transient state knots modifications of polarized light component intensity to be measured is measured and recorded:
One is the single surveys that polarized light component pulse to be measured is carried out using photodetector outfit oscillograph or optic streak camera
Amount and record；Another kind is the laser for obtaining polarized light component to be measured by Multiple-Scan using the autocorrelative mode of laser pulse
Impulse waveform mostly uses michelson interferometer optical path to realize.
Further, in step 2), will radiation conversion crystal to be located at laser resonance intracavitary, probe laser is filled using radiation and is changed
The brewster angle incidence of crystal is rolled over according to difference when probe laser is incident to radiation conversion crystal is obtained according to Fresnel theorem
Penetrate the reflectance curve of the corresponding horizontal polarisation component of rate；In step 3), the volume reflection of horizontal polarisation component is chosen as to be measured
Polarized light component.
The present invention also provides a kind of arteries and veins for realizing the above-mentioned impulse gamma X-ray detection X method based on laser polarization modulation
Gamma-ray detection system is rushed, is characterized in that, comprising: the laser and radiation conversion crystal set gradually along optical path；
Diaphragm, half-wave plate, polarization splitting prism and Glan prism are disposed in the reflection of radiation conversion crystal or transmitted light path；
It further include the laser signal of the laser signal for recording polarization splitting prism reflection and the output of Glan prism
Laser pulse measurement and record system.
Further, beam expanding lens is additionally provided between laser and radiation conversion crystal.
Further, laser pulse measurement and record system include the first detector, the second detector and oscillograph；First
Detector is used for the reflection laser of detecting polarization Amici prism, and the second detector is used to detect the laser letter of Glan prism output
Number；First detector and the second detector are connected with oscillograph；First detector, the second detector are used to turn laser signal
It is changed to electric impulse signal, oscillograph is for recording the electric impulse signal.
Further, the first detector and the second detector using photomultiplier tube, photoelectric tube, ultrafast photodiode or
Microchannel plate.
Further, when use brewster angle incidence radiates conversion crystal, and selection reflecting light level polarized component work
When for testing laser amount, laser pulse measurement uses optic streak camera with record system.
The invention has the advantages that
1. non-equilibrium free carrier is generated in pulse X, gamma ray incidence semiconductor crystal, by changing local current-carrying
Subnumber density can change the refractive index of semiconductor crystal, studies have found that for semiconductor dies such as GaAs, indium phosphide, gallium nitride
Body and its compound semiconductor as base, the semiconductor refractive index knots modification that impulse gamma ray introduces only are in
0.01~1 level.In order to solve the problems, such as that existing active laser probe gamma ray detection method sensitivity is low, the present invention
Pulse gal has been successfully established from laser polarization and crystal Fresnel principle using refractive index transient changing amount as intermediate quantity
Functional relation S (E) between horse ray signal and laser polarization component.
2. the present invention has both ultrafast time response ability and compared with high detection sensitivity.
The present invention is converted the variable quantity of crystal refractive index using the relationship between polarization characteristics of lasers and crystal refractive index
It is laser polarization characteristic component in the transmissivity of semiconductor die body interface or the knots modification of reflectivity, so that system sensitivity is promoted
Very convenient, most direct mode is exactly to improve the initial power of probe light, and letter is exported under same transmissivity or reflectivity
Number with initial beam intensity I0It is linear to increase, and then realize that ultrafast pulse radiating particle detects target.
3. the single measurement that the non-equilibrium free carrier service life in semiconductor may be implemented in the present invention.
The method of measurement semiconductor dynamic process is mainly to use laser pump (ing)-probe experimental method of standard at present,
The maximum advantage of the present invention is single measurement, can more accurately reflect the dynamic changing process of entire carrier.No matter in addition,
Refractive index variable quantity is positive or is negative, and the present invention can choose the increase that different polarized components is converted to laser, because
It can all be surveyed when this refractive index variable quantity is positive and negative.
4. the present invention realizes impulse gamma ray and converts to the fidelity of laser signal, " probe unit " and light easy to accomplish
The separation of power conversion device can be used the long-distance nondestructive transmission that optical fiber carries out signal, when signal is stronger, can be directly used
Ultrafast photodiode (thering is the product that the response time is 10ps or so to sell) measurement laser signal, then using high bandwidth number
Oscillograph recording, thus the measurement of the ultrafast ray pulse time spectrum of 100ps or less easy to accomplish.
It, can be by this 5. polarizer (polarization splitting prism, Glan prism) extinction ratio that the present invention uses is sufficiently high
Back light disappears to close to 0, so that it is long-irradiated can to exempt direct current light when using laser measuring equipments such as photomultiplier tubes
Problem.
6. there is design spirit since radiation conversion crystal material can be selected and be designed according to particle situation to be measured
Feature living, universality is strong can also be used to measure other radiating particles such as neutron, proton using suitable material.
7. the angular range of probe light incident radiation conversion crystal of the present invention is wide (can not be Brewster's angle), therefore real
In the application of border, optical path is easy to align with.
Detailed description of the invention
Fig. 1 is the schematic illustration of detection method of the present invention.
Fig. 2 is the light channel structure (light path design based on passed component modulation) of detection system of the present invention.
Fig. 3 is the light channel structure (light path design based on the modulation of polarization by reflection component) of detection system of the present invention.
Fig. 4 is the intracavity modulation system confirmatory experiment schematic layout pattern (only surveying reflection) based on detection method of the present invention.
Fig. 5 is the corresponding reflected light vertical polarisation component reflectance curve of ZnO crystal difference Δ n, and dotted line indicates ZnO in figure
The reflectance curve of laser vertical polarisation component after refractive index increases 0.5, chain-dotted line indicate laser after ZnO refractive index reduction 0.5
The reflectance curve of vertical polarisation component.
Fig. 6 is the corresponding reflecting light level polarized component reflectance curve of ZnO crystal difference Δ n, and dotted line indicates ZnO in figure
The reflectance curve of laser level polarized component after refractive index increases 0.5, chain-dotted line indicate laser after ZnO refractive index reduction 0.5
The reflectance curve of horizontal polarisation component.
Fig. 7 is the corresponding transmitted light vertical polarisation component transmittance graph of ZnO crystal difference Δ n, and dotted line indicates ZnO in figure
The transmittance graph of laser vertical polarisation component after refractive index reduces 0.5, chain-dotted line indicate laser after ZnO refractive index increase 0.5
The transmittance graph of vertical polarisation component.
Fig. 8 is the corresponding transmitted light horizontal polarisation component transmittance graph of ZnO crystal difference Δ n, and dotted line indicates ZnO in figure
The transmittance graph of laser level polarized component after reducing 0.5 is reflected, chain-dotted line indicates laser after ZnO refractive index increase 0.5
The transmittance graph of horizontal polarisation component.
Fig. 9 is to choose ZnO:Ga crystal to be used as radiation conversion body, what the He-Ne laser of 632.8nm obtained when being probe light
The comparison of confirmatory experiment result and monitoring signals, monitoring signals are to measure the same model photomultiplier tube of laser waveform directly according to letter
Number.
Figure 10 is to choose GaAs semiconductor crystal as radiation conversion body, using the Nd:YAG solid state laser light of 1064nm
The comparison of confirmatory experiment result and monitoring signals that beam obtains when being probe light, monitoring signals are obtained using PIN semiconductor detector
.
Fig. 2, description of symbols in 3:
1- beam expanding lens, 2- radiate conversion crystal, 3- diaphragm, 4- half-wave plate, 5- polarization splitting prism, 6-Glan prism, 7-
Oscillograph.
Specific embodiment
Below in conjunction with attached drawing, the invention will be further described.
As shown in Figure 1, detection method provided by the present invention, be related to five key links: (A) gamma ray passes through radiation
Conversion crystal is converted to non-equilibrium free carrier, (B) free carrier cause radiate conversion crystal refractive index transient changing,
(C1) or (C2) refraction index changing causes in probe laser reflection and transmitted component different polarized component amplitude to change,
(D1) or (D2) polarized component variable quantity by resonant cavity realizes that amplification, (E) by outer optical path realize specific polarized light component
Change measurement, and then realizes the measurement of Pulsed radiation field time spectrum.
If the refractive index for radiating conversion crystal reduces (radiation induced semiconductor refraction index changing direction is mostly to reduce), should adopt
The transmission amount of the volume reflection or vertical polarisation component of using horizontal polarization is as modulated quantity (i.e. tested polarized light component)；If spoke
The refractive index for penetrating conversion crystal increases, then should be using the transmission amount of horizontal polarization or the volume reflection of vertical polarisation component as quilt
Modulation voltage (tested polarized light component)；
It, can be with if the refractive index of radiation conversion crystal reduces, and when incidence angle is less than Brewster's angle (such as 10 °)
Measure the horizontal polarisation component amplitude variation of transmitted light.
The detection method of impulse gamma ray of the present invention is mostly single measurement, and for the impulse gamma with PRI characters
The measurement of source time spectrum, the method for the present invention can also utilize the technology path of laser interference, be obtained by Multiple-Scan ultrafast
(100ps or less) impulse gamma raytime composes waveform.
It is that will radiate conversion crystal (GaAs semiconductor) to be placed on the intracavitary schematic layout pattern of laser resonance (only shown in Fig. 4
Survey reflection), it is one of the mode of detection method lifting system detectivity of the present invention.Increased by the intracavitary optical signal of laser resonance
Benefit, to achieve the purpose that further to promote gamma ray detection sensitivity.In order to reduce radiation conversion crystal in laser resonance
Intracavitary insertion loss, radiation conversion crystal and laser incident angle need to be in strict accordance with brewster angle incidences.When with cloth scholar this
When special angle incidence, general measure radiates the horizontal polarisation component amplitude variation in conversion crystal reflected light, also can measure and transmits
Radiate the vertical polarisation component amplitude variation of conversion crystal.
Further, since detectivity can not only be promoted by resonant cavity, accordingly it is also possible to not use resonance
Chamber, and the variable quantity of laser polarization feature is directly measured, to realize the measurement target of low intensity pulse gamma ray time spectrum.
From the perspective of the realization of the system of above-mentioned detection method, technically there are two key links: first is that radiation conversion
Effective modulation of the crystal refractive index transient effect to reflected light polarized component, second is that polarized component transient changing process to be measured can
By measurement and record.
As other " radiation-light " detection methods based on semiconductor refractive index modulation, detection system time response determines
Generation and relaxation time due to free carrier non-equilibrium in semiconductor, and wherein the relaxation time of carrier actually reflects
Be free carrier service life, can be by using the semiconductor with ultrashort carrier lifetime, to realize that 10ps is below
System time responding ability, and existing " radiation-light " detection method is due to being based on external interference measurement scheme, it is brilliant due to radiating conversion
Body thickness and detection system time response are contradiction amounts, therefore the system sensitivity of existing method is very low, it is difficult to realize MeV grades
The measurement target of low intensity pulse gamma ray time spectrum.The present invention and the main distinction of existing " radiation-light " detection method are just
Be embodied in the measurement approach of refraction index changing amount, we by refraction index changing amount be modulated to probe laser polarization thoroughly/reflectivity,
The effective way of lifting system sensitivity is increased with this.
Based on above-mentioned theory, the system realization of detection method of the present invention has following two mode:
It is illustrated in figure 2 a kind of realization of impulse gamma ray detecting system of the present invention, the program is transmitted based on laser
Polarized component modulation, including the laser, beam expanding lens 1 (nonessential), radiation conversion crystal 2, light set gradually along same optical path
Door screen 3, half-wave plate 4, polarization splitting prism 5 and Glan prism 6；Diaphragm 3 is located on the transmitted light path of radiation conversion crystal 2；Glan
Prism 6 is located on the transmitted light path of polarization splitting prism 5；It further include the laser signal for recording the reflection of polarization splitting prism 5
And the laser pulse measurement and the system of record of the laser signal of the output of Glan prism 6.
The principle of the program:
Impulse gamma ray to be measured is impinged perpendicularly on into radiation conversion crystal 2, is generated in radiation conversion crystal 2 non-flat
Weigh free carrier, realizes radiation conversion crystal refractive index transient state modulation.The wavelength of laser output is greater than radiation conversion crystal 2
After the probe laser (horizontal linear polarization light or non-polarized light) of absorption limit is expanded via beam expanding lens 1, with a certain suitable
Angle (angle is determined according to the intrinsic refractive index of radiation conversion crystal material) is incident in radiation conversion crystal 2, according to luxuriant and rich with fragrance alunite
Your theorem, radiates in the transmitted light of conversion crystal 2 that there are horizontal polarisation component TpWith vertical polarisation component TsTwo polarized components,
The stray light in transmitted light is filtered using diaphragm 3, controls polarization direction with half-wave plate 4, then inclined by two with polarization splitting prism 5
Vibration component is separated；Since Glan prism 6 has very high extinction ratio, it can be used for improving " purity " of polarized component, then
Probe laser can use Image relaying optic path into laser pulse measurement and record system.
As shown in figure 3, realizing for the another of impulse gamma ray detecting system of the present invention, the program is anti-based on laser
Polarized component modulation is penetrated, including the laser, beam expanding lens 1 (nonessential) and radiation conversion crystal 2 set gradually along optical path；In spoke
It penetrates on the reflected light path of conversion crystal 2 and is disposed with diaphragm 3, half-wave plate 4, polarization splitting prism 5 and Glan prism 6；Also wrap
The laser pulse for including the laser signal that laser signal and Glan prism 6 for recording the reflection of polarization splitting prism 5 export is surveyed
Amount and record system.
The principle of the program:
Impulse gamma ray to be measured is impinged perpendicularly on into radiation conversion crystal 2, is generated in radiation conversion crystal 2 non-flat
Weigh free carrier, realizes radiation 2 refractive index transient state of conversion crystal modulation.The probe laser of laser output enters at an angle
It is mapped to radiation 2 surface of conversion crystal, particularly, when to radiate the brewster angle incidence of conversion crystal 2 to radiating conversion crystal 2
When middle, according to Fresnel theorem, being radiated in the reflected light of conversion crystal 2 in principle only includes vertical polarisation component Rs, horizontal
Polarized component RpIt is 0, but when the free carrier that impulse gamma generates makes the refractive index for radiating conversion crystal 2 change
Afterwards, so that radiating the horizontal polarisation component R in the probe laser that conversion crystal 2 reflectspIt is no longer 0, and horizontal polarisation component RpInstead
The increment for penetrating rate is just only related with impulse gamma ray, in this case can be 0 in the direct current background principle of probe laser, this
It is that existing " radiation-light " detection method institute is irrealizable.Diaphragm 3 in optical path is for filtering stray light and radiation conversion crystal
The reflected light of 2 rear end faces, the effect of other components and principle are consistent with scheme shown in Fig. 1, and details are not described herein.
There are two types of sides with record system for laser pulse measurement in impulse gamma ray detecting system shown in Fig. 2, Fig. 3
Case:
The first scheme be include the first detector D1, the second detector D2 and oscillograph 7；First detector D1 is for visiting
The reflection laser of polarization splitting prism 5 is surveyed, the second detector D2 is used to detect the laser signal of the output of Glan prism 6；First visits
Device D1 and the second detector D2 is surveyed to be connected with oscillograph 7.First detector D1, the second detector D2 are used to turn laser signal
It is changed to electric impulse signal, oscillograph 7 is for recording the electric impulse signal.First detector D1, the second detector D2 can be used
Photomultiplier tube, photoelectric tube, ultrafast photodiode or microchannel plate.
Second scheme is to be suitable for the measurement ultrafast arteries and veins of 10ps or less using the direct recording laser signal of optic streak camera
Rush X/ γ time spectrum.
In implementation shown in Fig. 2, Fig. 3:
The output wavelength of laser is chosen according to the absorption spectrum of radiation conversion crystal 2, and the output wavelength of laser is answered
It is within the transparency range of radiation conversion crystal 2.The type of laser can be DC laser device, be also possible to pulse laser
Device, when using pulse laser, pulse width need to be greater than the pulse width of impulse gamma ray to be measured, laser power or
The higher the better for energy stability.In addition, laser power is higher, system detectivity is higher.When laser is linearly polarized laser
When output, the higher the better for degree of polarization (at least more than 100:1), when surveying the horizontal polarisation component of transmitted light, it usually needs will enter
It penetrates laser and vertical polarization is changed to by horizontal polarization first, because the output of most linearly polarized laser devices is horizontal polarization.
The case where polarization splitting prism 5 is mainly used for highway surveying.Situation higher for detectivity demand, can be with
Beam is suitably included using beam expanding lens 1 before laser beam is incident, and then increases sensitive volume volume.
When initial laser is not polarization light output, needs to increase a laser polarization device and be polarized for laser, that is, produce
Raw linearly polarized light, main principle is that device should have high extinction ratio and low laser absorption loss when selection.
Radiating conversion crystal 2 is semiconductor or other optical crystals, when selection other than the output wavelength of cooperation laser,
Also need to consider according to the specific requirement of detection system sensitivity semiconductor or optical crystal and impulse gamma ray phase interaction
Section problem；In addition, the time response and concrete specification of semiconductor or optical crystal are required according to radiating particle to be measured
Feature is specifically designed, and the one side of semiconductor or optical crystal incident light must do polishing treatment, and another side is equal whether polishing
It can be used.It particularly, such as will be by the way of intracavity modulation (it is intracavitary that radiation conversion crystal be placed in laser resonance), then only
Brewster angle incidence can be used, and amount to be modulated is the reflectivity of laser level polarization.
Therefore, the selection for radiating conversion crystal 2 mainly follows following principle:
(1) gamma action section with higher, and there are radiated transients index of refraction effects, it is enough non-flat to generate
Weigh free carrier, such as GaAs, InP, GaN:Mg, CdTe Preset grating semiconductor；
(2) the corresponding limit that absorbs of forbidden bandwidth is less than probe optical wavelength, keeps radiation conversion crystal itself transparent to probe light；
(3) radiation conversion crystal generally answers twin polishing to handle, to guarantee the uniformity at laser light incident interface, for only sharp
With the situation of front end face reflected light, at least guarantee incident end face implements polishing, in addition, two end faces of radiation conversion crystal should use up
Amount is parallel；
(4) the excess carrier service life is short enough in radiation conversion crystal, guarantees that system time response is sufficiently fast；
(5) there is certain anti-radiation performance, to ensure the repeatability of detection system measurement process and result.
Theoretical basis of the invention is optics Fresnel formula, carries out deriving analysis according to different polarization component, is easy to obtain
Obtain probe laser incidence zincite crystal shown in Fig. 5-8 (one of radiation conversion crystal) Shi Butong laser polarization component
Thoroughly, reflectance curve, these curves are the basic foundations for choosing probe laser amount to be modulated, wherein RpWith TpIndicate horizontal polarization
Component, RsWith TsVertical polarisation component is represented, has the zincite crystal refractive index variable quantity that gamma ray introduces in document report logical
Often in 0.01~1 range, the relativeness of zincite crystal variations in refractive index anterioposterior curve is shown for clarity, is adopted in calculating
With 0.5 variable quantity.For example, from fig. 6, it can be seen that when the incidence angle of probe laser be Brewster's angle when, horizontal polarization
Reflectivity is 0, when impulse gamma ray particle is incident in zincite crystal, since refraction index changing (reduction) leads to incidence
Zincite crystal actual Brewster's angle in front and back can change, and chain-dotted line curve is on block curve, therefore in oxygen
Change zinc crystal refractive index change processes in horizontal polarisation component reflectivity can with the reduction of zincite crystal refractive index and
Increase, reflectivity this variable quantity by measuring horizontal polarisation component be obtained with impulse radiation particle " when it is m- strong
The time spectrum waveform of degree ".
Confirmatory experiment is using the He-Ne laser of linear polarization output as probe laser, optical maser wavelength 623.8nm, function
Rate 17mW.Using semiconductor crystal ZnO:Ga as radiation conversion crystal, crystal refractive index 2.008, corresponding Brewster's angle
It is 63.5 °, the high current gamma ray source that radiographic source is generated using " Qiangguang-I " accelerator.Such as Fig. 2, semiconductor crystal ZnO:Ga is consolidated
Determine on a spinstand, probe laser measures reflected light according to principle according to the brewster angle incidence of semiconductor crystal ZnO:Ga
In horizontal polarisation component, reflecting light level polarized component becomes 0 at this time in principle, i.e., for horizontal polarization light incidence when, instead
Penetrating light is 0, but since laser polarization degree is limited, and reflected light is really to be in the state of minimum value, using common photomultiplier tube
Photoelectric conversion is carried out, the digital oscilloscope for being then transmitted to 1GHz bandwidth again is recorded, and radiation source monitoring signals are by same model
Photomultiplier tube directly shines (appropriate shielding) and provides.
Confirmatory experiment result is as shown in Figure 9, it can be seen that pulse front edge meets well, three peak positions of peak position
Clearly to differentiate, the performance of pulse back edge noise is also almost the same.The more actual gamma source signal of the trailing edge portion of measured signal
Slow, main cause is to test the semiconductor crystal used as gallium-doped zinc oxide crystal, and theoretically its carrier generates
Quickly, but the purer zincite crystal of relaxation time is many slowly, therefore, we by experiment directly confirm this method can
Row.When carrying out ultrafast pulse measurement, need that carrier is selected to generate relaxation time all brilliant in sub- ps radiation conversion below
Body, such as GaAs, InP.
Figure 10 show the experimental result based on GaAs crystal, and due to the reason of absorption of crystal limit, probe laser is used instead
The horizontal polarization light of 1064nm wavelength, radiographic source use the X-ray pulse of peak energy about 370keV, and vertical incidence GaAs is partly led
Body, pulse strength > 109Ph./pulse, nominal pulse width 15ns, exit end pulsed dosage are 4mR-7mR.Crystal coupling
The reflected light of output filters out horizontal polarisation component through polarization splitting prism first, to increase extinction ratio, in polarization splitting prism
Glan (Glan) prism is added in transmitted light path, the horizontal polarisation component of coupling output is finally transferred to the light of lead screen
In electric multiplier tube, photomultiplier tube used by testing is 9850B, and 1kV is arranged in negative high voltage.The monitoring of X-ray source waveform with show
Wave device trigger signal is provided by standard PIN detector, time response about 10ns, voltage -400V.It can be seen that system waveform with
Source feature meets well, and rear " secondary peak " along superposition is that the gain media of pulsed X-ray irradiation solid state laser introduces, practical
It can be eliminated by reinforcing shielding or background scale in.From Figure 10 can obtain roughly detectivity be 5.43 ×
10-17C·cm2(photon energy value is 150KeV).
Detection system detectivity analysis based on detection method of the present invention:
Gamma detection sensitivity is one of key feature amount of detection system, and higher sensitivity is that detection system design is excellent
The one of target changed.According to the output measure feature of detection system, is generally defined in conjunction with detectivity, can derive base
In the impulse gamma ray detecting system sensitivity general expression of laser polarization modulation.It might as well assume to polarize with reflecting light level
Component is polarized light component to be measured, and incident laser is horizontal linear polarization light, and with brewster angle incidence, then impulse gamma ray is most
The power transience variable quantity of laser vertical polarisation component caused by end are as follows:
Refractive index variable quantity Δ n (t) determined by the non-equilibrium free carrier concentration Δ N (t) that gamma ray introduces, with
This output quantity modulated as laser polarization, in conjunction with the signal times magnification of laser resonator gain of light coefficient and laser measuring equipment
Number, so that it may obtain the output quantity of detection system.Then available detection method sensitivity general expression:
It enablesParticle energy for gamma ray and radiation conversion crystal interaction converts effect
Rate then has:
G is laser resonator gain coefficient, G in formulaAFor laser measuring equipment signal amplification factor, Pi,||For incident laser
Power, ηγThe non-equilibrium freedom generated for the energy conversion efficiency of impulse gamma ray in the semiconductors, i.e., single gammaphoton
Carrier number, theory can be obtained when estimating by monte carlo method, θ1For the incidence angle of probe laser, for other polarized components
The case where can have similar expression formula.
Therefore, according to the detection system sensitivity general expression S (E) based on horizontal polarization reflectivity modulation, in conjunction with spy
Survey method working principle, it can be seen that if putting aside laser measurement and recording the signal gain of system, detection method of the present invention
The factor of two aspects of laser and material can also be related generally to by other approach come lifting system detectivity:
(1) probe optical output power is the most direct mode of lifting system detectivity.Principle according to the method for the present invention,
The actual modulation effect of impulse gamma ray signal is the transmissivity or reflectivity of polarisation-affecting component, therefore, in transmissivity
Or under conditions of reflectivity is certain, improving incident optical power can be improved signal amplitude, and then reaches system detectivity and mention
The purpose risen is primarily limited to the fuel factor and polarizer of semiconductor it should be noted that laser power can not infinitely increase
Limited extinction ratio.
(2) laser incident angle is also one of the approach of lifting system sensitivity.According to the transmissivity of each polarized component and
Reflectance curve situation of change can be seen that not to be that each polarized component could be obtained in Brewster Angle Position maximum
Therefore modulation voltage according to different materials, can optimize laser incident angle according to the curve of calculating.
(3) in the way of resonant intracavity modulation it is another advantage that detection method has higher sensitivity.It can be using half
Conductor is realized the modulation of polarised light coupling efficiency by refractive index modulation, passed through as laser resonator output coupling mirror
The amplification of modulated signal can be realized in the interacvity gain of laser, obtains detectivity more higher than chamber external system.
(4) semicoductor radiating transfer efficiency is the determinant of non-equilibrium free carrier concentration, is cut using gamma effect
The higher semiconductor material in face can promote detection system sensitivity to a certain extent, impulse gamma ray generate it is non-equilibrium from
It can use monte carlo method by carrier concentration to be estimated.This obvious factor is pervasive, and due to finite thickness,
By energization deposition efficiency come lifting system sensitivity it is not the advantage of this detection method, and is limited to probe optical wavelength
And it is difficult to carry out.
Claims (15)
1. the impulse gamma X-ray detection X method based on laser polarization modulation, which is characterized in that comprising steps of
1) gamma ray is converted into non-equilibrium free carrier by radiating conversion crystal, makes the folding for radiating conversion crystal material
It penetrates rate and transient changing occurs；
2) probe laser is incident to radiation conversion crystal, probe laser is obtained according to Fresnel theorem and is incident to radiation conversion crystalline substance
Different refractivity corresponding horizontal and/or vertical polarisation component transmissivity and/or reflectance curve when body, so that radiation be turned
The transient state variations in refractive index for changing crystalline material is converted to the transient changing of laser polarization component；
3) according to the resulting different refractivity of step 2) corresponding horizontal and/or vertical polarisation component transmissivity and/or reflection
Rate curve chooses a certain polarized light component as polarized light component to be measured, and designed for filtering out the polarized light component to be measured
Analyzing optical path；
4) the polarized light component intensity to be measured caused by radiation conversion crystal Refractive Index of Material transient changing is measured and recorded
Transient state knots modification.
2. the impulse gamma X-ray detection X method according to claim 1 based on laser polarization modulation, it is characterised in that: step
It is rapid 1) employed in radiation conversion crystal should have a sufficiently fast non-equilibrium free carrier relaxation time, radiate conversion crystal
Absorption limit be less than the probe laser wavelength.
3. the impulse gamma X-ray detection X method according to claim 1 based on laser polarization modulation, it is characterised in that: step
It is rapid 1) employed in radiation conversion crystal, incident end face should make polishing treatment, and its incident end face should use up with outgoing end face
Amount is parallel.
4. the impulse gamma X-ray detection X method according to claim 1 based on laser polarization modulation, it is characterised in that: step
It is rapid 1) employed in radiation conversion crystal be Preset grating semiconductor, and have certain radiation resistance.
5. the impulse gamma X-ray detection X method according to claim 1 to 4 based on laser polarization modulation, feature
It is: between step 1-2), probe laser is carried out to expand processing, the beam spot after expanding should be less than the beam of impulse gamma ray
Spot size.
6. the impulse gamma X-ray detection X method according to claim 5 based on laser polarization modulation, it is characterised in that: step
It is rapid 2) in, the incident angle of probe laser is determined according to the transmissivity and/or reflectance curve of radiation conversion crystal.
7. the impulse gamma X-ray detection X method according to claim 6 based on laser polarization modulation, it is characterised in that: step
Rapid 3) the middle a certain polarized light component of selection is as the principle of polarized light component to be measured:
If the refractive index of radiation conversion crystal reduces, the volume reflection or vertical polarisation component of horizontal polarisation component should be chosen
Transmission amount is as polarized light component to be measured；
If the refractive index of radiation conversion crystal increases, the transmission amount or vertical polarisation component of horizontal polarisation component should be chosen
Volume reflection is as polarized light component to be measured.
8. the impulse gamma X-ray detection X method according to claim 7 based on laser polarization modulation, it is characterised in that: step
It is rapid 4) in, measuring and recording the transient state knots modification of polarized light component intensity to be measured, there are two types of modes:
One is the lists that polarized light component pulse to be measured is carried out using photodetector outfit oscillograph or optic streak camera
Secondary measurement and record；
Another kind is the laser pulse for obtaining polarized light component to be measured by Multiple-Scan using the autocorrelative mode of laser pulse
Waveform.
9. the impulse gamma X-ray detection X method according to claim 1 based on laser polarization modulation, it is characterised in that:
In step 2), radiation conversion crystal is located at that laser resonance is intracavitary, probe laser filled using radiation change crystal cloth scholar this
Special angle is incident, and it is corresponding horizontal inclined to obtain different refractivity when probe laser is incident to radiation conversion crystal according to Fresnel theorem
The reflectance curve of vibration component；
In step 3), the volume reflection of horizontal polarisation component is chosen as polarized light component to be measured.
10. the impulse gamma X-ray detection X method according to claim 1 based on laser polarization modulation, it is characterised in that:
If the probe laser for being incident to radiation conversion crystal in step 2) is horizontal linear polarization light, with brewster angle incidence, step
It is rapid 3) in the reflected light of horizontal polarisation component for polarized light component to be measured, then the incident angle θ of probe laser1, probe laser
Incident power Pi,||It chooses according to the following formula:
In above formula:
ηγFor the particle energy transfer efficiency of gamma ray and radiation conversion crystal interaction；
G is laser resonator gain coefficient；
GAFor laser measuring equipment signal amplification factor；
Δ n (t) is refractive index variable quantity；
Δ N (t) is the non-equilibrium free carrier concentration that gamma ray introduces.
11. realizing the pulse of any impulse gamma X-ray detection X method based on laser polarization modulation of claim 1-10
Gamma-ray detection system characterized by comprising the laser and radiation conversion crystal set gradually along optical path；It is radiating
Diaphragm, half-wave plate, polarization splitting prism and Glan prism are disposed in the reflection of conversion crystal or transmitted light path；
It further include the laser of the laser signal of the laser signal for recording polarization splitting prism reflection and the output of Glan prism
Impulsive measurement and record system.
12. impulse gamma ray detecting system according to claim 11, it is characterised in that: converted in laser and radiation
Beam expanding lens is additionally provided between crystal.
13. impulse gamma ray detecting system according to claim 11, it is characterised in that: laser pulse measurement and record
System includes the first detector, the second detector and oscillograph；Reflection of first detector for detecting polarization Amici prism swashs
Light, the second detector are used to detect the laser signal of Glan prism output；First detector and the second detector are and oscillograph
It is connected；First detector, the second detector are used to be converted to laser signal electric impulse signal, and oscillograph is for recording the electricity arteries and veins
Rush signal.
14. impulse gamma ray detecting system according to claim 13, it is characterised in that: the first detector and second is visited
It surveys device and uses photomultiplier tube, photoelectric tube, ultrafast photodiode or microchannel plate.
15. impulse gamma ray detecting system according to claim 11, it is characterised in that: laser pulse measurement and record
System uses optic streak camera.
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