CN109755847A - A kind of production method of ultrashort laser pulse string - Google Patents
A kind of production method of ultrashort laser pulse string Download PDFInfo
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Abstract
The invention discloses a kind of production methods of ultrashort laser pulse string, by carrying out beat frequency to the laser pulse train for including multiple subpulses with chirping characteristics, obtain include multiple micropulses with quasi sine modulating characteristic ultrashort laser pulse string, by adjusting the time interval for optimizing multiple subpulses, the ultrashort laser pulse string finally generated may be implemented to stack effect, drive photoinjectors to generate corresponding electron beam group with this.Technical solution provided by the invention can be effectively reduced the quantity of electric charge in single micropulse, the micropulse of short length is obtained to which space charge repulsion power be effectively reduced, it can be effectively reduced electronics Electron bunch length, and then the clustering factor of electron beam group is improved, Terahertz coherent radiation power is effectively improved accordingly.
Description
Technical field
The present invention relates to accelerator and Free Electron Laser Technology fields, more specifically, are related to a kind of ultrashort laser
The production method of train of pulse.
Background technique
Terahertz wave band refer to frequency in the electromagnetic wave of 0.1THz-10THz, due to its with penetrability, low photon energy,
Many advantages, such as high bandwidth, spectrum fingerprint characteristic, ultrafast characteristic and unique advantage, for the meaning of research material science and material science
Justice is very great.Development meet application demand terahertz emission source be related fields research hotspot.Terahertz light at present
Generate wideband radiation, the tunable single radio-frequency radiation based on electron-beam excitation etc. generated including the use of ultrafast pulse excitation.Wherein,
The wideband generated using ultrafast pulse is radiated by more and more extensive concern and is reached its maturity；Terahertz based on electron-beam excitation
Hereby in radiation source, the radiation source that periodical torsional movement generates is carried out by undulator by relativistic electron beam and is known as terahertz
Hereby free-electron laser (Terahertz-Free Electron Laser, THz-FEL).
THz-FEL can not only obtain the relevant terahertz light of narrow bandwidth, but also be to be currently available THz high output
The radiation source of power, furthermore this kind of coherent source also have wavelength is continuously adjustable in a wide range of, beam quality is good, light pulse when
Between fine structure and also it is adjustable outstanding advantages of, in Terahertz Technology field and its application study, play an important role, one
It is directly research hotspot both domestic and external.THz-FEL can be divided into oscillator (Oscillator) and once-through type (Single-
Pass) two kinds.Wherein, once-through type THz-FEL is directly produced in undulator using single ultrashort electron beam (or beam group string)
Raw coherent radiation, the physics such as diffraction, sliding that oscillator THz-FEL can be overcome to be faced in generation long wavelength's THz radiation
The adverse effect of effect, just by more and more extensive attention.
Square of the terahertz emission source power of once-through type THz-FEL and the quantity of electric charge of electronic impulse and the clustering factor
It is directly proportional.For pulse electron beam, by taking Gaussian Profile as an example, clustering factor representation are as follows:Wherein ω is
The angular frequency of radiation, σtFor electronic impulse time span.As can be seen that generate the high clustering factor: electronic impulse length should be use up
May be short, the angular frequency of radiation is higher, and electronic impulse length should be shorter.
The quantity of electric charge of generation high power radiation requirement electron beam is as high as possible, electron beam length is as short as possible.But due to
The presence of space charge repulsion power, the quantity of electric charge is bigger, and the length of electron beam is often longer.And it is single to utilize electronic impulse string to replace
Pulse can be effectively reduced sky by sharing the quantity of electric charge to the electron beam group being made of a string of equally spaced micropulses
Between Charge repulsion for obtain short pulse length Electron Beam group limitation.For what is be made of a string of equally spaced micropulses
Electronic impulse string, equally by taking micropulse is Gaussian Profile as an example, the clustering factor be may be expressed as:Wherein time interval of the Δ t between micropulse.The clustering factor will resonate in
A series of resonant frequency ωmIt is first order resonance frequency when=2m π/Δ t, m=1, is second-order resonance frequency when m=2, with such
It pushes away.Micropulse number is more in electron beam group, and the quantity of electric charge of single micropulse is smaller, and micropulse length then can be shorter, finally
It can be obtained by the higher clustering factor.
In THz-FEL device, electron beam group can be excited photoinjectors by driving laser pulse train and be generated, electronics
The initial parameter of beam group is determined that Subsequent electronic beam rolls into a ball the evolution of parameter and space charge is imitated by the parameter of driving laser pulse train
Answer, electron gun internal electric field parameter etc. it is closely bound up.Wherein, during electron beam group accelerates to relativistic velocity, space charge
The influence of effect is occupied an leading position.Therefore, it is desirable to obtain optical autocorrelation, has its source in and obtain ultrashort laser pulse string, and
The method for obtaining ultrashort laser pulse string is also based on the principle of " sharing the quantity of electric charge ", and the quantity of electric charge for including by laser pulse is shared
Into the laser pulse train comprising multiple micropulses, to reduce the quantity of electric charge of single micropulse to overcome space charge effect to draw
The growth of the electron beam micropulses length risen.The main stream approach for generating ultrashort laser pulse string has pulsed reactor area method and beat frequency method two
Kind.Wherein, the method optical path of pulse pile-up is complicated, and influence factor is numerous；Effect of dispersion is strong simultaneously, will lead to laser pulse width
It broadens, dispersion compensation difficulty is big.Beat frequency method can effectively overcome the above-mentioned deficiency of pulsed reactor area method, but the scarcely perceptible pulse that beat frequency method obtains
It is related to broadening amount and beat frequency rate to rush number, and there is a problem of that micropulse number is on the low side, especially low-frequency range micropulse
Number is obvious insufficient；And if obtaining more micropulse number by increasing broadening amount, it will micropulse width is caused to broaden
The negative effect for causing the clustering factor to reduce, it is difficult to electronics Electron bunch length be effectively reduced.
Summary of the invention
In view of this, effectively overcoming existing beat frequency method the present invention provides a kind of production method of ultrashort laser pulse string
The micropulse number of the ultrashort laser pulse string of generation problem on the low side can be effectively reduced electronics Electron bunch length, and then effectively
Improve Terahertz coherent radiation power.
To achieve the above object, technical solution provided by the invention is as follows:
A kind of production method of ultrashort laser pulse string, comprising:
Generate the laser pulse train including multiple subpulses with chirping characteristics, wherein the arteries and veins of each subpulse
Rush equivalent width；
Beat frequency is carried out to the laser pulse train, obtains the ultrashort laser pulse string comprising multiple micropulses.
Compared to the prior art, technical solution provided by the invention has at least the following advantages:
The present invention provides a kind of production method of ultrashort laser pulse string, by including multiple with chirping characteristics
The laser pulse train of subpulse carries out beat frequency, obtain include multiple micropulses with quasi sine modulating characteristic ultrashort laser arteries and veins
Punching string, by adjusting the time interval for optimizing multiple subpulses, the ultrashort laser pulse string finally generated may be implemented to stack effect
Fruit drives photoinjectors to generate corresponding electron beam group with this.Technical solution provided by the invention can be effectively reduced list
The quantity of electric charge in a micropulse can effectively drop so that space charge repulsion power be effectively reduced and obtain the micropulse of short length
Low electronics Electron bunch length, and then the clustering factor of electron beam group is improved, Terahertz coherent radiation power is effectively improved accordingly.
Detailed description of the invention
In order to more clearly explain the embodiment of the invention or the technical proposal in the existing technology, to embodiment or will show below
There is attached drawing needed in technical description to be briefly described, it should be apparent that, the accompanying drawings in the following description is only this
The embodiment of invention for those of ordinary skill in the art without creative efforts, can also basis
The attached drawing of offer obtains other attached drawings.
Fig. 1 is a kind of flow chart of the production method of ultrashort laser pulse string provided by the embodiments of the present application；
Fig. 2 is the flow chart of the production method of another ultrashort laser pulse string provided by the embodiments of the present application；
Fig. 3 is the flow chart of the production method of another ultrashort laser pulse string provided by the embodiments of the present application；
Fig. 4 is the flow chart of the production method of another ultrashort laser pulse string provided by the embodiments of the present application；
Fig. 5 is the flow chart of the production method of another ultrashort laser pulse string provided by the embodiments of the present application；
Fig. 6 is the ultrashort laser pulse string obtained under conditions of beat frequency rate provided by the embodiments of the present application is 0.7THz
Schematic diagram；
Fig. 7 is the ultrashort laser pulse string obtained under conditions of beat frequency rate provided by the embodiments of the present application is 1.0THz
Schematic diagram；
Fig. 8 is the ultrashort laser pulse string obtained under conditions of beat frequency rate provided by the embodiments of the present application is 1.5THz
Schematic diagram；
Fig. 9 be the beat frequency rate that the prior art provides be obtain under conditions of 0.7THz, 1.0THz and 1.5THz it is ultrashort
The schematic diagram of laser pulse train；
Figure 10 is a kind of structural schematic diagram of the generation device of ultrashort laser pulse string provided by the embodiments of the present application；
Figure 11 is the structural schematic diagram of the generation device of another ultrashort laser pulse string provided by the embodiments of the present application；
Figure 12 is the structural schematic diagram of the generation device of another ultrashort laser pulse string provided by the embodiments of the present application.
Specific embodiment
Following will be combined with the drawings in the embodiments of the present invention, and technical solution in the embodiment of the present invention carries out clear, complete
Site preparation description, it is clear that described embodiments are only a part of the embodiments of the present invention, instead of all the embodiments.It is based on
Embodiment in the present invention, it is obtained by those of ordinary skill in the art without making creative efforts every other
Embodiment shall fall within the protection scope of the present invention.
As described in background, in THz-FEL device, electron beam group can excite photocathode by driving laser pulse train
Electron gun and generate, the initial parameter of electron beam group is determined by the parameter of driving laser pulse train, Subsequent electronic beam group parameter
Develop closely bound up with space charge effect, electron gun internal electric field parameter etc..Wherein, relativistic velocity is accelerated in electron beam group
In the process, the influence of space charge effect is occupied an leading position.Therefore, it is desirable to obtain optical autocorrelation, it is super to have its source in acquisition
Short laser pulse string, and the method for obtaining ultrashort laser pulse string is also based on the principle of " sharing the quantity of electric charge ", by laser pulse
The quantity of electric charge for including is shared in the laser pulse train comprising multiple micropulses, thus reduce the quantity of electric charge of single micropulse with gram
Take the growth of electron beam micropulses length caused by space charge effect.The main stream approach for generating ultrashort laser pulse string has pulse
Method of piling and two kinds of beat frequency method.Wherein, the method optical path of pulse pile-up is complicated, and influence factor is numerous；Effect of dispersion is strong simultaneously, meeting
Laser pulse width is caused to broaden, dispersion compensation difficulty is big.Beat frequency method can effectively overcome the above-mentioned deficiency of pulsed reactor area method, but
The micropulse number that beat frequency method obtains is related to broadening amount and beat frequency rate, and there is a problem of that micropulse number is on the low side, especially
It is that low-frequency range micropulse number is obviously insufficient；And if obtaining more micropulse number by increasing broadening amount, it will lead
Causing micropulse width to broaden causes the negative effect of clustering factor reduction, it is difficult to electronics Electron bunch length be effectively reduced.
Based on this, the embodiment of the present application provides the production method and device of a kind of ultrashort laser pulse string, effectively overcomes
The micropulse number for the ultrashort laser pulse string that existing beat frequency method generates problem on the low side, can be effectively reduced electron beam regimental commander
Degree, and then effectively improve Terahertz coherent radiation power.To achieve the above object, technical solution provided by the embodiments of the present application is such as
Under, specifically combine Fig. 1 to Figure 12 that technical solution provided by the embodiments of the present application is described in detail.
Refering to what is shown in Fig. 1, be a kind of flow chart of the production method of ultrashort laser pulse string provided by the embodiments of the present application,
Wherein, the production method of ultrashort laser pulse string includes:
S1, the laser pulse train including multiple subpulses with chirping characteristics is generated, wherein each subpulse
Pulse width is consistent；
S2, beat frequency is carried out to the laser pulse train, obtains the ultrashort laser pulse string comprising multiple micropulses.
As shown in the above, by clapping the laser pulse train for including multiple subpulses with chirping characteristics
Frequently, obtain include multiple micropulses with quasi sine modulating characteristic ultrashort laser pulse string, by adjusting multiple sons are optimized
The time interval of pulse, the ultrashort laser pulse string finally generated may be implemented to stack effect, drive photoinjectors with this
Generate corresponding electron beam group.Technical solution provided by the embodiments of the present application can be effectively reduced the charge in single micropulse
Amount can be effectively reduced electronics Electron bunch length so that space charge repulsion power be effectively reduced and obtain the micropulse of short length, into
And the clustering factor of electron beam group is improved, Terahertz coherent radiation power is effectively improved accordingly.
Refering to what is shown in Fig. 2, the process of the production method for another ultrashort laser pulse string provided by the embodiments of the present application
Figure, wherein provided by the embodiments of the present application to generate the laser pulse train including multiple subpulses with chirping characteristics, comprising:
S11, the second laser pulse including multiple subpulses is generated；
S12, chirp spread is carried out to the second laser pulse, being formed includes multiple subpulses with chirping characteristics
Laser pulse train.
It should be understood that the laser pulse provided by the embodiments of the present application including multiple subpulses with chirping characteristics
String, can be by carrying out chirp spread acquisition to the second laser pulse for including multiple subpulses.Wherein, the embodiment of the present application mentions
What is supplied carries out chirp spread to the second laser pulse, comprising: by the second laser pulse input parallel grating to progress
Chirp spread.
In one embodiment of the application, the second laser pulse provided by the present application including multiple subpulses can lead to
It is obtained after crossing a laser source beam splitting.Refering to what is shown in Fig. 3, for another ultrashort laser pulse string provided by the embodiments of the present application
The flow chart of production method, wherein S11 provided by the embodiments of the present application, generate include multiple subpulses second laser pulse,
Include:
S101, first laser pulse is exported by a laser source；
S102, the first laser pulse beam splitting is handled to obtain multiple subpulses；
S103, beam is closed to all subpulses, forms the second laser pulse including multiple subpulses.
It should be understood that second laser pulse provided by the embodiments of the present application, by a laser source is exported first
Laser pulse is split processing and obtains multiple subpulses, then, carries out conjunction beam to multiple subpulses and is formed including multiple
The second laser pulse of subpulse.First laser pulse provided by the embodiments of the present application is ultrafast femtosecond pulse, pulse duration range
For no more than 150fs, pulse is Fourier transformation limited pulses.And laser source provided by the embodiments of the present application can be vibration
Type titanium sapphire laser device is swung, this application is not particularly limited.
It is provided by the present application that first laser pulse beam splitting is handled to obtain multiple subpulses in one embodiment of the application,
It can be by the direct beam splitting of first laser pulse to be multiple subpulses, wherein the first laser pulse beam splitting is handled to obtain
Multiple subpulses, comprising:
Beam splitting at least once is carried out to the first laser pulse.
It should be understood that can carry out a beam splitting when quantity of multiple subpulses is 2 to first laser pulse, obtain
Sub- first laser pulse to two-way is 2 subpulses.Alternatively, when the quantity of multiple subpulses is greater than 2, to first laser arteries and veins
Obtain two way first laser pulses after rushing in capable first time beam splitting, then in two way first laser pulses all the way or two-way
It is split, is then analogized with this rule again respectively, optimization beam splitting number obtains the subpulse of preset quantity.
Alternatively, in one embodiment of the application, it is provided by the present application that first laser pulse beam splitting is handled to obtain multiple sons
It is multiple subpulses that pulse, which can be by the indirect beam splitting of first laser pulse, wherein is handled the first laser pulse beam splitting
Obtain multiple subpulses, comprising:
Beam splitting at least once is carried out to the first laser pulse and closes beam splitting again after beam operates.
It should be understood that carrying out first time beam splitting simultaneously to first laser pulse when the quantity of multiple subpulses is greater than 2
After closing beam operation, the first laser pulse after obtained first time operation includes two subpulses；Then first time is operated
After second laser pulse afterwards carries out second of beam splitting and closes beam, the first laser pulse after second obtained of operation includes
Four subpulses, are analogized with this rule, are optimized beam splitting and are closed the number of beam operation, finally obtain present count indirectly after beam splitting again
The subpulse of amount.
In one embodiment of the application, the second laser pulse provided by the present application including multiple subpulses can also lead to
Multiple independent laser sources are crossed to obtain.Refering to what is shown in Fig. 4, for another ultrashort laser pulse string provided by the embodiments of the present application
The flow chart of production method, wherein S11 provided by the embodiments of the present application, generate include multiple subpulses second laser pulse,
Include:
S111, respective first laser pulse is exported by multiple laser sources；
S112, the phase for adjusting the first laser pulse, keep the Phase synchronization of each first laser pulse more
A subpulse；
S113, beam is closed to all subpulses, forms the second laser pulse including multiple subpulses.
It should be understood that respectively being exported when the embodiment of the present application obtains second laser pulse to multiple independent laser sources
First laser pulse carry out phase adjusted so that the Phase synchronization of all first laser pulses, each first laser pulsion phase
When in a subpulse, and then obtain multiple subpulses；It obtains including multiple subpulses after then closing beam to multiple subpulse
Second laser pulse.First laser pulse provided by the embodiments of the present application be ultrafast femtosecond pulse, pulse duration range be no more than
150fs, pulse are Fourier transformation limited pulses.And laser source provided by the embodiments of the present application can be oscillator titanium
Sapphire laser is not particularly limited this application.
It should be noted that when method provided by the embodiments of the present application includes multiple laser sources, it can also be to multiple laser
At least one laser source is split in source, and adjusts the pulse of the beam splitting pulse and the laser source not being split outgoing simultaneously
Phase, obtain multiple first laser pulses, this application be not particularly limited.
Refering to what is shown in Fig. 5, the process of the production method for another ultrashort laser pulse string provided by the embodiments of the present application
Figure, wherein beat frequency S2 provided by the embodiments of the present application, is carried out to the laser pulse train, comprising:
S21, by the laser pulse train beam splitting be two way laser pulse trains；
S22, the sub- laser pulse train described in two-way carry out the reflection of different light paths respectively；
S23, make sub- laser pulse train described in the two-way after reflecting that beat frequency occur, obtain ultrashort sharp comprising multiple micropulses
Optical pulse train.
It should be understood that during beat frequency provided by the embodiments of the present application, by adjusting two way laser pulse trains of optimization
Reflection light path can change beat frequency rate, the final width for changing the micropulse in ultrashort laser pulse string and interval.
In one embodiment of the application, the center spacing of adjacent subpulse in the laser pulse train provided by the present application,
Greater than the pulse width of micropulse in the ultrashort laser pulse string, and the pulse for being less than the laser pulse train neutron pulse is wide
Degree.
The analog result of ultrashort laser pulse string shown in reference to the accompanying drawing, to technical solution provided by the present application and now
There is technology to be compared.Wherein, Fig. 6 be obtained under conditions of beat frequency rate provided by the embodiments of the present application is 0.7 THz it is super
The schematic diagram of short laser pulse string, Fig. 7 be obtained under conditions of beat frequency rate provided by the embodiments of the present application is 1.0THz it is super
The schematic diagram of short laser pulse string, Fig. 8 be obtained under conditions of beat frequency rate provided by the embodiments of the present application is 1.5THz it is super
The schematic diagram of short laser pulse string, Fig. 9 are the condition that the beat frequency rate that the prior art provides is 0.7THz, 1.0THz and 1.5THz
Under the obtained schematic diagram of ultrashort laser pulse string.It should be noted that ultrashort laser pulse string shown in Fig. 6-Fig. 8 is all based on
The data that the laser pulse train condition Imitating of subpulse including two with chirping characteristics obtains.
Wherein, the schematic diagram (analog result) of ultrashort laser pulse string shown in fig. 6 provided by the embodiments of the present application is clapped
Frequent rate is 0.7THz, and the time-delay splitting (time interval of two-way subpulse after beam splitting) of Fig. 6 (a) is adjusted to τ `=12.5ps,
The time-delay splitting of Fig. 6 (b) is adjusted to τ `=5.5ps.
The schematic diagram (analog result) of attached ultrashort laser pulse string shown in Fig. 7, beat frequency rate are 1.0 THz, wherein
The time-delay splitting of Fig. 7 (a) is adjusted to τ `=12.5ps, and the time-delay splitting of Fig. 7 (b) is adjusted to τ `=5.5ps.
The schematic diagram (analog result) of attached ultrashort laser pulse string shown in Fig. 8, beat frequency rate are 1.5 THz, wherein
The time-delay splitting of Fig. 8 (a) is adjusted to τ `=12.5ps, and the time-delay splitting of Fig. 8 (b) is adjusted to τ `=4ps.
It is generated it can be seen from attached drawing 6-8 by ultrashort laser pulse string production method provided by the embodiments of the present application
Ultrashort laser pulse string, which has, stacks effect, stacks effect by time-delay splitting τ ' Lai Shixian, finally makes its train of pulse overall length
Can in pulse pile-up scheme quite.
Attached drawing 9 is the schematic diagram of the ultrashort laser pulse string obtained under the conditions of different beat frequencies using existing beat frequency method
(analog result).Wherein, the condition of Fig. 9 (a) and Fig. 6 (b) unanimously, the condition and Fig. 7 (b) of Fig. 9 (b) unanimously, the item of Fig. 9 (c)
Part and Fig. 8 (b) unanimously, traditional beat frequency method and the ultrashort laser pulse string obtained using method provided by the embodiments of the present application
The micropulse number comparison for inside including is as shown in table 1:
| Experimental group | Micropulse number | Control group | Micropulse number | Growth rate |
| Fig. 4 (a) | 7 | Fig. 1 (b) | 11 | 57.14% |
| Fig. 4 (b) | 11 | Fig. 2 (b) | 16 | 45.45% |
| Fig. 4 (c) | 15 | Fig. 3 (b) | 22 | 46.67% |
Table 1
As it can be seen that by ultrashort laser pulse string production method provided by the embodiments of the present application, the single ultrashort laser of generation
The micropulse number for including in train of pulse rises about 50% compared to existing beat frequency method.
It is single in existing beat frequency method and the ultrashort laser pulse string for utilizing method provided by the embodiments of the present application to obtain
The quantity of electric charge of micropulse compares as shown in table 2 (total charge dosage 240pC):
Table 2
As it can be seen that by ultrashort laser pulse string production method provided by the embodiments of the present application, the ultrashort laser pulse of generation
The micropulse quantity of electric charge for including in string surpasses 30% compared to the decline of existing beat frequency method, so that space charge repulsion power be effectively reduced to obtain
The micropulse of short length is obtained, and then improves the clustering factor of electron beam group, correspondingly effectively improves Terahertz coherent radiation power.
Correspondingly, the embodiment of the present application also provides a kind of generation devices of ultrashort laser pulse string, refering to what is shown in Fig. 10,
For a kind of structural schematic diagram of the generation device of ultrashort laser pulse string provided by the embodiments of the present application, wherein ultrashort laser arteries and veins
Rushing the generation device gone here and there includes:
Laser pulse train generates system 10, and the laser pulse train, which generates system 10, has chirp including multiple for generating
The laser pulse train of the subpulse of characteristic, wherein the pulse width of each subpulse is consistent；
And beat frequency system 20, the beat frequency system 20 are used to carry out beat frequency to the laser pulse train, obtain comprising more
The ultrashort laser pulse string of a micropulse.
As shown in the above, by beat frequency system to the laser pulse train including multiple subpulses with chirping characteristics
Carry out beat frequency, obtain include multiple micropulses with quasi sine modulating characteristic ultrashort laser pulse string, by adjusting optimization
The time interval of multiple subpulses, the ultrashort laser pulse string finally generated may be implemented to stack effect, drive photocathode with this
Electron gun generates corresponding electron beam group.Technical solution provided by the embodiments of the present application can be effectively reduced in single micropulse
The quantity of electric charge can be effectively reduced electron beam regimental commander so that space charge repulsion power be effectively reduced and obtain the micropulse of short length
Degree, and then the clustering factor of electron beam group is improved, Terahertz coherent radiation power is effectively improved accordingly.
Refering to what is shown in Fig. 10, the embodiment of the present application offer place laser pulse train generation system 10 may include:
Second laser pulse generation unit 110, the second laser pulse generation unit 110 include multiple sons for generating
The second laser pulse of pulse；
And chirp spread unit 120, the chirp spread unit 120 are used to carry out Zhou to the second laser pulse
Sing broadening, formed include multiple subpulses with chirping characteristics laser pulse train.
It should be understood that the laser pulse provided by the embodiments of the present application including multiple subpulses with chirping characteristics
String, can be by carrying out chirp spread acquisition to the second laser pulse for including multiple subpulses.As shown in Figure 10, the application is real
Applying the chirp spread unit 120 that example provides includes:
Second reflecting module 121, second reflecting module 121 will be for that will receive the second laser pulse and export；
The chirp spread module 122 being set in 121 optical path of the second reflecting module, the chirp spread module 122
Second laser pulse for exporting to second reflecting module carries out first time chirp spread；
The third reflecting module 123 being set in the optical path of the chirp spread module 122, the third reflecting module
123 for will be by the second laser pulse-echo after first time chirp spread to the chirp spread module 122, and the Zhou
It sings after broadening 122 pairs of module second laser pulse second of chirp spread of progress after first time chirp spread, output is extremely
Second reflecting module 121, second reflecting module 121 will be exported by the second laser pulse of second of chirp spread
To the beat frequency system 20.
It should be understood that carrying out chirp spread twice to second laser pulse, it is capable of increasing the broadening of second laser pulse
Amount.Optionally, the chirp spread module provided by the embodiments of the present application is parallel grating pair, wherein parallel grating is to by two
Grating composition that is a staggered relatively and being parallel to each other, and grating provided by the embodiments of the present application can be hologram diffraction formula grating,
To generate the second of linear chrip characteristic (linear function of the instantaneous frequency of light field temporally changes) using its group delay dispersion
Laser pulse.In addition, the embodiment of the present application can also have class using Gires-Tournois interference reflector or prism equity
It is replaced like the optical element of characteristic.
As shown in Figure 10, the second reflecting module 121 provided by the embodiments of the present application can be prism beam splitter (prism
Beam splitter can be the semi-transparent semi-reflecting lens of T:R=50%:50%, or be that beam module side is total transmissivity, another side is complete towards closing
Reflection).And third reflecting module 123 provided by the embodiments of the present application can be a retroreflection prism, for changing
The transmission direction for the second laser pulse by first time chirp spread that chirp spread module 122 exports, returns it to Zhou
It sings and broadens second of the chirp spread of progress of module 122, to increase broadening amount.
In addition, third reflecting module 123 provided by the embodiments of the present application can also be made of plane mirror, such as Figure 12 institute
Show, is the structural schematic diagram of the generation device of another ultrashort laser pulse string provided by the embodiments of the present application, wherein third is anti-
Penetrate module 123 may include two be mutually perpendicular to place plane mirrors, and the mirror surface direction of any one plane mirror and
Normal direction is in 45 degree of angles with the direction for the second laser pulse for being incident to the plane mirror.And second reflection mould
Block can also be plate beamsplitter mirror.
In one embodiment of the application, the second laser pulse provided by the present application including multiple subpulses can lead to
It is obtained after crossing a laser source beam splitting.As shown in Figure 10, the second laser pulse generation unit provided by the embodiments of the present application
110 include:
One laser source 111, the laser source 111 is for exporting first laser pulse；
The laser beam splitter module 112 being set in 111 optical path of laser source, the laser beam splitter module 112 for pair
The first laser pulse beam splitting handles to obtain multiple subpulses；
And it is set to the conjunction beam module 113 in 112 optical path of laser beam splitter module, the conjunction beam module 113 is used for
Beam is closed to all subpulses, forms the second laser pulse including multiple subpulses.
It should be understood that second laser pulse provided by the embodiments of the present application, by a laser source is exported first
Laser pulse is split processing and obtains multiple subpulses, then, carries out conjunction beam to multiple subpulses and is formed including multiple
The second laser pulse of subpulse.First laser pulse provided by the embodiments of the present application is ultrafast femtosecond pulse, pulse duration range
For no more than 150fs, pulse is Fourier transformation limited pulses.Laser source provided by the embodiments of the present application can be oscillator
Titanium sapphire laser device is not particularly limited this application.And conjunction beam module provided by the embodiments of the present application is to close beam
Mirror.
It is provided by the present application that first laser pulse beam splitting is handled to obtain multiple subpulses in one embodiment of the application,
It can be by the direct beam splitting of first laser pulse to be multiple subpulses, wherein the laser beam splitter provided by the embodiments of the present application
Module is used to carry out beam splitting at least once to the first laser pulse, wherein the laser beam splitter module includes:
Beam splitting subsystem, the beam splitting subsystem include first order beam splitting submodule to N grades of beam splitting submodules, every level-one
Beam splitting submodule includes at least one beam splitter, and at least beam splitting all the way of at least one beam splitter of i-stage beam splitting submodule
In optical path, it is correspondingly arranged on one beam splitter of i+1 grade beam splitting submodule, N is the integer greater than 0, and i is just whole no more than N
Number；
And first reflecting module, first reflecting module are used for the multiple sub- arteries and veins for exporting the beam splitting subsystem
Punching is transmitted to the conjunction beam module.
It should be understood that can carry out a beam splitting when quantity of multiple subpulses is 2 to first laser pulse, obtain
Sub- first laser pulse to two-way is 2 subpulses.Alternatively, when the quantity of multiple subpulses is greater than 2, to first laser arteries and veins
Obtain two way first laser pulses after rushing in capable first time beam splitting, then in two way first laser pulses all the way or two-way
It is split, is then analogized with this rule again respectively, optimization beam splitting number obtains the subpulse of preset quantity.
It as shown in Figure 10, is 2 illustrations with the quantity of multiple sub- subpulses, wherein laser beam splitter module 112 includes point
Beam subsystem and the first reflecting module 1122, wherein beam splitting subsystem includes level-one beam splitting submodule, and beam splitting submodule includes
One beam splitter 1121 (T:R 50%:50%, i.e. transmission are equal to reflection).Beam splitter 1121 accesses that laser source 111 exports
One laser pulse is two-way transmission direction and polarization direction mutually vertical subpulse to first laser pulse beam splitting.Wherein,
The polarization direction difference of two subpulses can be to avoid the consistent bring coherent effect in subpulse polarization direction when beat frequency.
Then, the two-way subpulse that beam splitter 1121 exports is transmitted to by the guidance of the first reflecting module 1122 and closes beam module
113.First reflecting module 1122 provided by the embodiments of the present application may include being made of multiple reflective mirrors.As shown in Figure 10,
One reflecting module 1122 can be made of 4 reflective mirrors, wherein the mirror surface direction of any one reflective mirror and normal direction with enter
The transmission direction of the subpulse of reflective mirror is incident upon in 45 degree of angles, two-way subpulse transmission side after the first reflecting module 1122
To and polarization direction still maintain and be mutually perpendicular to.
As shown in Figure 10, conjunction beam module 113 provided by the embodiments of the present application can be by the first reflecting module 1122 indirectly
It is set in the optical path of beam splitter 1121, that is, the two-way subpulse of beam splitter 1121 respectively corresponds to two reflective mirrors, and divides equally
It is not closed in beam module 113 by being transmitted to after the reflection of respective two reflective mirrors.Further, it is also possible to beam splitter 1121
It is adjusted with the position for closing beam module 113, reduces the quantity of reflective mirror, be provided by the embodiments of the present application as shown in figure 11
The structural schematic diagram of the generation device of another ultrashort laser pulse string, wherein close beam module 113 and be placed directly in beam splitter
On 1121 reflected light path, and the first reflecting module 1122 is set on the transmitted light path of beam splitter 1121, wherein first is anti-
It penetrates module 1122 and may include two and be mutually perpendicular to the reflective mirrors (such as plane mirror) placed, and the mirror surface of any one reflective mirror
Direction and normal direction are in 45 degree of angles with the transmission direction for the subpulse for being incident to reflective mirror, will be divided by two reflective mirrors
The subpulse guidance of the transmitted light path output of beam mirror 1121, which is transmitted to, closes beam module 113.
In one embodiment of the application, beam splitter in beam splitting submodule provided by the present application can also use half-wave plate
Combination with polarizing beam splitter mirror replaces, and is not particularly limited to this application.
Alternatively, in one embodiment of the application, it is provided by the present application that first laser pulse beam splitting is handled to obtain multiple sons
It is multiple subpulses that pulse, which can be by the indirect beam splitting of first laser pulse, wherein the laser provided by the embodiments of the present application
Beam splitting module be used for to the first laser pulse carry out at least once beam splitting and close beam operation after beam splitting again, wherein institute
Stating laser beam splitter module includes:
First order beam splitting closes beam submodule to N grades of beam splitting and closes beam submodule, and is set to the N grades of beam splitting and closes Shu Zi
Beam splitting submodule in the optical path of module, it includes that a beam splitter and one is set to the beam splitter that beam submodule is closed in each grade of beam splitting
Light combination mirror in optical path, and the beam splitting submodule is a beam splitter, N is the integer greater than 0；
And first reflecting module, first reflecting module are used for the two-way pulse for exporting the beam splitting submodule
It is transmitted to the conjunction beam module.
It should be understood that carrying out first time beam splitting simultaneously to first laser pulse when the quantity of multiple subpulses is greater than 2
After closing beam operation, the first laser pulse after obtained first time operation includes two subpulses；Then first time is operated
After second laser pulse afterwards carries out second of beam splitting and closes beam, the first laser pulse after second obtained of operation includes
Four subpulses, are analogized with this rule, are optimized beam splitting and are closed the number of beam operation, finally obtain present count indirectly after beam splitting again
The subpulse of amount.
In one embodiment of the application, the second laser pulse provided by the present application including multiple subpulses can also lead to
It crosses multiple independent laser sources to obtain, that is, the second laser pulse generation unit provided by the embodiments of the present application includes:
Multiple laser sources, each laser source is for exporting respective first laser pulse；
The phase adjustment block being set in the optical path of the multiple laser source, the phase adjustment block is for adjusting institute
The phase for stating first laser pulse makes the multiple subpulses of Phase synchronization of each first laser pulse；
And it is set to the conjunction beam module in the phase adjustment block optical path, the conjunction beam module is used for all sons
Beam is closed in pulse, forms the second laser pulse including multiple subpulses.
As shown in Figure 10, the beat frequency system 20 provided by the embodiments of the present application includes:
Beam splitting intervention module 210, the beam splitting intervention module 210 are used to be that two ways swash by the laser pulse train beam splitting
Optical pulse train；
The reflecting mirror 220 being respectively arranged in the 210 two-way optical path of beam splitting intervention module, and the reflecting mirror 220
The direction of mirror surface laser pulse train corresponding to its is vertical, and two reflecting mirrors 220 are used for the sub- laser pulse described in two-way
String carries out the reflection of different light paths respectively, so that beat frequency occurs for sub- laser pulse train described in the two-way after reflection.
Further, in order to reduce the error of optical path difference, the beam splitting intervention module provided by the embodiments of the present application is flat
Plate beam splitter (T:R 50%:50%, i.e. transmission are equal to reflection), wherein laser pulse train beam splitting is two-way by plate beamsplitter mirror
After sub- laser pulse train, after each way laser pulse train is reflected by respective reflecting mirror, carried out in plate beamsplitter Jing Chu
Beat frequency forms the ultrashort laser pulse string including multiple micropulses with quasi sine modulating characteristic.
It should be understood that during beat frequency provided by the embodiments of the present application, by adjusting two way laser pulse trains of optimization
Reflection light path can change beat frequency rate, the final width for changing the micropulse in ultrashort laser pulse string and interval.
In one embodiment of the application, the center spacing of adjacent subpulse in the laser pulse train provided by the present application,
Greater than the pulse width of micropulse in the ultrashort laser pulse string, and the pulse for being less than the laser pulse train neutron pulse is wide
Degree.
The embodiment of the present application provides the production method and device of a kind of ultrashort laser pulse string, by including multiple tools
There is the laser pulse train of the subpulse of chirping characteristics to carry out beat frequency, obtains including multiple micropulses with quasi sine modulating characteristic
Ultrashort laser pulse string, by adjusting the time interval for optimizing multiple subpulses, the ultrashort laser pulse string finally generated can
Effect is stacked to realize, drives photoinjectors to generate corresponding electron beam group with this.Technology provided by the embodiments of the present application
Scheme can be effectively reduced the quantity of electric charge in single micropulse, so that space charge repulsion power be effectively reduced and obtain short length
Micropulse can be effectively reduced electronics Electron bunch length, and then improve the clustering factor of electron beam group, effectively improve terahertz accordingly
Hereby coherent radiation power.
The foregoing description of the disclosed embodiments enables those skilled in the art to implement or use the present invention.
Various modifications to these embodiments will be readily apparent to those skilled in the art, as defined herein
General Principle can be realized in other embodiments without departing from the spirit or scope of the present invention.Therefore, of the invention
It is not intended to be limited to the embodiments shown herein, and is to fit to and the principles and novel features disclosed herein phase one
The widest scope of cause.
Claims (9)
1. a kind of production method of ultrashort laser pulse string characterized by comprising
Generate the laser pulse train including multiple subpulses with chirping characteristics, wherein the pulse of each subpulse is wide
Degree is consistent；
Beat frequency is carried out to the laser pulse train, obtains the ultrashort laser pulse string comprising multiple micropulses.
2. the production method of ultrashort laser pulse string according to claim 1, which is characterized in that generating has including multiple
The laser pulse train of the subpulse of chirping characteristics, comprising:
Generate the second laser pulse including multiple subpulses；
Chirp spread is carried out to the second laser pulse, forms the laser pulse including multiple subpulses with chirping characteristics
String.
3. the production method of ultrashort laser pulse string according to claim 2, which is characterized in that generating includes multiple sub- arteries and veins
The second laser pulse of punching, comprising:
First laser pulse is exported by a laser source；
The first laser pulse beam splitting is handled to obtain multiple subpulses；
Beam is closed to all subpulses, forms the second laser pulse including multiple subpulses.
4. the production method of ultrashort laser pulse string according to claim 3, which is characterized in that the first laser arteries and veins
Beam splitting is rushed to handle to obtain multiple subpulses, comprising:
Beam splitting at least once is carried out to the first laser pulse.
5. the production method of ultrashort laser pulse string according to claim 3, which is characterized in that the first laser arteries and veins
Beam splitting is rushed to handle to obtain multiple subpulses, comprising:
Beam splitting at least once is carried out to the first laser pulse and closes beam splitting again after beam operates.
6. the production method of ultrashort laser pulse string according to claim 2, which is characterized in that generating includes multiple sub- arteries and veins
The second laser pulse of punching, comprising:
Respective first laser pulse is exported by multiple laser sources；
The phase for adjusting the first laser pulse makes the multiple subpulses of Phase synchronization of each first laser pulse；
Beam is closed to all subpulses, forms the second laser pulse including multiple subpulses.
7. the production method of ultrashort laser pulse string according to claim 2, which is characterized in that the second laser arteries and veins
Rush in row chirp spread, comprising:
By the second laser pulse input parallel grating to progress chirp spread.
8. the production method of ultrashort laser pulse string according to claim 1, which is characterized in that the laser pulse train
Carry out beat frequency, comprising:
It is two way laser pulse trains by the laser pulse train beam splitting；
The sub- laser pulse train described in two-way carries out the reflection of different light paths respectively；
Beat frequency occurs for sub- laser pulse train described in the two-way after making reflection.
9. the production method of ultrashort laser pulse string according to claim 1, which is characterized in that in the laser pulse train
The center spacing of adjacent subpulse greater than the pulse width of micropulse in the ultrashort laser pulse string, and is less than the laser
The pulse width of train of pulse neutron pulse.
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