A kind of tunable broad band intermediate infrared laser system
阅读说明：本技术 一种可调谐宽带中红外激光系统 (A kind of tunable broad band intermediate infrared laser system ) 是由 钟亥哲 梁成川 胡斌 梁兆星 李瑛� 范滇元 于 2019-10-10 设计创作，主要内容包括：本申请涉及一种可调谐宽带中红外激光系统,系统包括：脉冲激光器产生的脉冲激光,经分束镜分成两束脉冲激光,第一束脉冲激光经过第一脉冲展宽器,到达耦合镜,第二束脉冲激光经过宽带信号光产生器得到宽带信号光,宽带信号光经过第二脉冲展宽器,到达耦合镜,第一束脉冲激光和宽带信号光共同经过耦合镜,进入非线性晶体,得到放大后的宽带信号光、闲频光和残余泵浦光。通过分光镜,将闲频光、放大后的宽带信号光和残余泵浦光分离,脉冲压缩器将分离后的闲频光的脉宽压缩,得到中红外超短脉冲激光。通过本申请中的可调谐宽带中红外激光系统,可以得到可调谐的中红外超短脉冲激光。(This application involves a kind of tunable broad band intermediate infrared laser systems, system includes: the pulse laser that pulse laser generates, it is divided into two bundle of pulsed laser through beam splitter, first bundle of pulsed laser passes through the first pulse stretcher, reach coupling mirror, second bundle of pulsed laser obtains broadband signal light by broadband signal photogenerator, broadband signal light passes through the second pulse stretcher, reach coupling mirror, first bundle of pulsed laser and broadband signal light pass through coupling mirror jointly, into nonlinear crystal, amplified broadband signal light, ideler frequency light and remnant pump light are obtained.By spectroscope, ideler frequency light, amplified broadband signal light and remnant pump light are separated, the Pulse Compression of the ideler frequency light after separation is obtained mid-infrared ultra-short pulse laser by pulse shortener.By the tunable broad band intermediate infrared laser system in the application, available tunable mid-infrared ultra-short pulse laser.)
1. a kind of tunable broad band intermediate infrared laser system, which is characterized in that the system comprises: pulse laser, beam splitter, First pulse stretcher, broadband signal photogenerator, optical path delayer, the second pulse stretcher, coupling mirror, nonlinear crystal, Spectroscope, pulse shortener；
The pulse laser that the pulse laser generates, is divided into two bundle of pulsed laser, the first bundle of pulsed laser through the beam splitter By first pulse stretcher, the coupling mirror is reached, the second bundle of pulsed laser passes through the broadband signal photogenerator Broadband signal light is obtained, the broadband signal light passes through second pulse stretcher, reaches the coupling mirror, first beam Pulse laser and the broadband signal light pass through the coupling mirror jointly, and first beam pulse projected through the coupling mirror swashs Light and the broadband signal light obtain amplified broadband signal light, ideler frequency light and remnant pump into the nonlinear crystal Light is separated the ideler frequency light, amplified broadband signal light and remnant pump light, the pulse pressure by the spectroscope The Pulse Compression of the ideler frequency light after separation is obtained mid-infrared ultra-short pulse laser by contracting device, wherein first beam pulse Laser is pump light；
The optical path delayer is arranged between first pulse stretcher and the coupling mirror or the second pulse exhibition Between wide device and the coupling mirror, by introducing preset time delay, make first bundle of pulsed laser and the broadband signal Light time synchronization；
Chirp direction by first bundle of pulsed laser of chirp spread, with the broadband signal light by chirp spread On the contrary；First bundle of pulsed laser and the broadband signal light make optically erasing in the nonlinear crystal, obtain institute State amplified broadband signal light, ideler frequency light and remnant pump light；The bandwidth of the ideler frequency light, by the phase of the nonlinear crystal Position coupling bandwidth determines.
2. system according to claim 1, which is characterized in that the nonlinear crystal is to meet II class quasi-phase matched The periodic polarized lithium columbate crystal of sector structure, first bundle of pulsed laser are o polarised light, and the broadband signal light is that e is inclined Shake light, and the ideler frequency light is o polarised light.
3. system according to claim 2, which is characterized in that by following one way in which, to the spare time of generation The central wavelength of frequency light is adjusted:
Adjust the central wavelength of the broadband signal light of the broadband signal photogenerator output；
Adjust the delay that the optical path delayer introduces；
Correspondingly, needing to adjust the pump light and broadband letter for the phase matched for guaranteeing the ideler frequency center wavelength of light Number transversely acting region of the light in the periodic polarized lithium columbate crystal of sector structure for meeting II class quasi-phase matched；
On this basis, by adjusting second pulse stretcher to the chirp spread amount of the broadband signal light, to described Broadband signal light and the chirp ratio of the pump light are adjusted, and optimize the bandwidth of the ideler frequency light and described tunable with this The energy conversion efficiency of broadband intermediate infrared laser system.
4. system according to claim 1, which is characterized in that the broadband signal photogenerator is supercontinuum generation device Or optical parametric generator.
5. system according to claim 1, which is characterized in that the pulse laser is 790nm Ti:Sapphire laser femtosecond laser Device.
6. system according to claim 1, which is characterized in that the spectroscope for it is highly transmissive to the ideler frequency light, to institute State pump light and the amplified broadband signal light high reflection, or to the ideler frequency light high reflection, to the pump light The highly transmissive dichroic mirror with the amplified broadband signal light.
Technical field
This application involves technical field of ultrafast laser, more particularly to a kind of tunable broad band intermediate infrared laser system.
Background technique
Due to lacking suitable laser gain medium, the only laser of only a few specific wavelength being capable of swashing by stimulated radiation Optical medium directly generates.Currently, the commercialization laser of energy level type is concentrated mainly on 1-2 μm of near infrared band.Between close red Middle infrared band between Terahertz (THz) outside, is very important electromagnetic radiation wave band.Typical middle infrared wavelength is 3- 5 μm, just correspond to second " window " of atmosphere and the dactylogram of most molecules.Mid-infrared ultra-short pulse laser is the narrow energy of research With the dynamics problems such as semiconductor and superlattices multiple quantum wells interband transient state transition process, intramolecular and intermolecular energy transfer Important means.Using optical second order nonlinear effect, the energy transmission between three kinds of different frequency laser can be guided.Wherein Optically erasing (Optical Parametric Amplification, hereinafter referred to as OPA), can be by the pump of short wavelength Pu light (such as titanium precious stone laser), by non-linear lower conversion, the mid-infrared laser of energy transmission to long wavelength.
OPA relies on the advantages that its high-gain, wide bandwidth, broad tuning, becomes the most common skill of pulsed infrared laser in generation Art means.For ultra-short pulse laser, if wanting to obtain enough transfer efficiencies in time-limited nonlinear crystal, need with The pulse laser of very high peak power pumps, and the peak power of pump light can be limited to the damage threshold of nonlinear crystal, Thus it is difficult to directly generate ultrashort superpower middle pulsed infrared laser.Optical parameter chirped pulse amplification (OPCPA) combines chirp The advantages of pumping of pulse amplifying (CPA) long pulse and OPA high-gain, it can get the pulse laser of ultrahigh peak power.Usual feelings Under condition, the phase-matching condition of OPCPA is optimized based on flashlight centre wavelength, to the gain highest of central wavelength.But by In nonlinear crystalline material there are dispersion, the still difficult wideband phase matching for realizing single-stage optically erasing causes a departure middle cardiac wave The phase misalignment dosage of long spectral components increases, and gain reduces, and then leads to narrowing for OPCPA gain bandwidth, limits output The extreme bandwidth of ultra-short pulse laser.
Therefore, the prior art has much room for improvement.
Summary of the invention
The technical problem to be solved by the present invention is to optically erasings to be limited by lens lesion threshold value, can only obtain lower conversion Efficiency and optical parameter chirped pulse amplification are difficult to realize the problem of wideband phase matching, and the application provides a kind of tunable width Band intermediate infrared laser system, available tunable mid-infrared ultra-short pulse laser.
The present invention provides a kind of tunable broad band intermediate infrared laser system, the system comprises: pulse laser, beam splitting Mirror, the first pulse stretcher, broadband signal photogenerator, optical path delayer, the second pulse stretcher, coupling mirror, non-linear crystalline substance Body, spectroscope, pulse shortener；
The pulse laser that the pulse laser generates, is divided into two bundle of pulsed laser, the first beam pulse through the beam splitter Laser passes through first pulse stretcher, reaches the coupling mirror, and the second bundle of pulsed laser is produced by the broadband signal light Raw device obtains broadband signal light, and the broadband signal light passes through second pulse stretcher, reaches the coupling mirror, and described the One bundle of pulsed laser and the broadband signal light pass through the coupling mirror jointly, the first beam arteries and veins projected through the coupling mirror Impulse light and the broadband signal light obtain amplified broadband signal light, ideler frequency light and remnants into the nonlinear crystal Pump light is separated the ideler frequency light, amplified broadband signal light and remnant pump light, the arteries and veins by the spectroscope Compressor is rushed by the Pulse Compression of the ideler frequency light after separation, obtains mid-infrared ultra-short pulse laser, wherein first beam Pulse laser is pump light；
The optical path delayer is arranged between first pulse stretcher and the coupling mirror or second arteries and veins It rushes between stretcher and the coupling mirror, by introducing preset time delay, makes first bundle of pulsed laser and the broadband Signal light time synchronization；
Chirp by first bundle of pulsed laser of chirp spread, with the broadband signal light by chirp spread It is contrary；First bundle of pulsed laser and the broadband signal light make optically erasing in the nonlinear crystal, obtain To the amplified broadband signal light, ideler frequency light and remnant pump light；The bandwidth of the ideler frequency light, by the nonlinear crystal Phase matched bandwidth determine.
Optionally, the nonlinear crystal is the periodic polarized lithium niobate crystal of sector structure for meeting II class quasi-phase matched Body, first bundle of pulsed laser are o polarised light, and the broadband signal light is e polarised light, and the ideler frequency light is o polarised light.
Optionally, by following one way in which, the central wavelength of the ideler frequency light of generation is adjusted:
Adjust the central wavelength of the broadband signal light of the broadband signal photogenerator output；
Adjust the delay that the optical path delayer introduces；
Correspondingly, needing to adjust the pump light and the width for the phase matched for guaranteeing the ideler frequency center wavelength of light Transversely acting area of the band signal light in the periodic polarized lithium columbate crystal of sector structure for meeting II class quasi-phase matched Domain；
On this basis, right by adjusting second pulse stretcher to the chirp spread amount of the broadband signal light The chirp ratio of the broadband signal light and the pump light is adjusted, with this optimize the ideler frequency light bandwidth and it is described can Tune the energy conversion efficiency of broadband intermediate infrared laser system.
Optionally, the broadband signal photogenerator is supercontinuum generation device or optical parametric generator.
Optionally, the pulse laser is 790nm ti:sapphire laser femto-second laser.
Optionally, the spectroscope be it is highly transmissive to the ideler frequency light, to the pump light and the amplified broadband Signal light high reflection, or to the ideler frequency light high reflection, high to the pump light and the amplified broadband signal light The dichroic mirror of transmission.
Compared with prior art, the embodiment of the present invention has the advantage that
By the tunable broad band intermediate infrared laser system in the application, reduce the pulse as caused by group-velocity mismatch The influence of sliding, moreover, it is contrary with the chirp of the broadband signal light to have benefited from the pump light, and, the satisfaction Width of the periodic polarized lithium columbate crystal of II class quasi-phase matched (PPLN) in reversed chirp mid-infrared light parametric amplification Band phase matching characteristics, the available broader ideler frequency light wider than the pump light, the broadband signal light belt.
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 some embodiments recorded in invention, for those of ordinary skill in the art, without creative efforts, It is also possible to obtain other drawings based on these drawings.
Fig. 1 is a kind of structural schematic diagram of tunable broad band intermediate infrared laser system in the embodiment of the present invention；
Fig. 2 a is the schematic diagram of the initial bandwidth relationship of pump light, signal light and ideler frequency light in the embodiment of the present invention；
Fig. 2 b is middle width strip of embodiment of the present invention phase matched structural schematic diagram；
Fig. 3 is the group velocity characteristic value of pump light in the embodiment of the present invention, different wave length signal light and corresponding ideler frequency light Curve synoptic diagram；
Fig. 4 is that 790nm pump light imitates the conversion of the small signal optically erasing of 1030nm signal light in the embodiment of the present invention Rate and generation~3.4 μm of ideler frequency light bandwidth with different chirp ratios (α s/ α p) change curve；
Fig. 5 is 790nm pump light in the embodiment of the present invention to 1100nm-1500nm tunable signal light optically erasing Transfer efficiency and the ideler frequency light bandwidth of generation with signal light wavelength change curve.
Specific embodiment
In order to enable those skilled in the art to better understand the solution of the present invention, below in conjunction in the embodiment of the present invention Attached drawing, technical scheme in the embodiment of the invention is clearly and completely described, it is clear that described embodiment is only this Invention a part of the embodiment, instead of all the embodiments.Based on the embodiments of the present invention, those of ordinary skill in the art exist Every other embodiment obtained under the premise of creative work is not made, shall fall within the protection scope of the present invention.
In general, optically erasing (OPA) is limited by lens lesion threshold value, lower transfer efficiency can only obtain, and beche-de-mer without spike Measuring chirped pulse amplification (OPCPA) is then the phase matched for being difficult to realize wide bandwidth.
To solve the above-mentioned problems, the present invention provides a kind of tunable broad band intermediate infrared laser systems, with wide bandwidth Chirped pulse laser is reduced by the time chirp opposite to pump light, signal light incoming direction due to group velocity as pump light While spending the influence that pulse caused by mismatch slides, initial bandwidth ideler frequency more broader than pump light, signal light bandwidth has been obtained Light.On this basis, using meeting the periodic polarized lithium columbate crystal of II class quasi-phase matched in reversed chirp mid-infrared light Wideband phase matching properties in parametric amplification can complete effective optical parameter of wide bandwidth in extremely wide wave-length coverage Amplification, obtains the ultra-short pulse laser of tunable middle infrared band.
With reference to the accompanying drawing, the various non-limiting embodiments that the present invention will be described in detail.
Firstly, using tunable broad band intermediate infrared laser system to generate tunable middle infrared excess in the embodiment of the present application The theoretical foundation of short-pulse laser is described as follows:
The optically erasing process of three wave mixing must meet energy and the conservation of momentum, i.e.,
ωp=ωs+ωi(1)
kp=ks+ki(2)
Wherein, ωp、ωs、ωiRespectively indicate the angular frequency of pump light, signal light and ideler frequency light, kp、ks、kiTable respectively Show the wave vector of pump light, signal light and ideler frequency light.Phase matched (Δ k=kp-ks-kiIt=0) is optically erasing available energy Measure the basic demand of conversion.Under normal conditions, phase matched is that the central wavelength based on pump light, signal light optimizes.Due to There are dispersions for nonlinear crystalline material, are theoretically only capable of realizing phase matched to single wavelength.To the optically erasing of wide bandwidth Process, signal light include the spectrum of wide bandwidth, and more or less to the spectral components for deviateing central wavelength there is phase mismatch (Δk≠0).Amount of mismatch is bigger, and gain is lower.Generally, phase matched bandwidth determines the gain bandwidth of optically erasing, Limit the extreme bandwidth of output ultra-short pulse laser.
To Δ k with centre frequency ω0Make Taylor expansion, have:
Wherein,Indicate group velocity, Δ ω=α (t-t0), indicate to change over time relative in The offset of heart angular frequency (works as t=t0, ω=ω0, Δ ω=0),Second order and other higher order dispersion terms are represented,Indicate the linear chrip coefficient of chirped pulse, υp、υs、υiRespectively indicate pump light, signal light and ideler frequency light Group velocity, Δ ωp、Δωs、ΔωiRespectively indicate the angular frequency deviation amount of pump light, signal light and ideler frequency light.
As can be seen that when ratio (chirp ratio) σ of signal light and the linear chrip of pump light meets
Single order item in formula (3) is cancelled out each other just, and Δ k is only determined by second order and other higher order dispersion terms, at this point, can Obtain extremely wide phase matched bandwidth.Wherein, αp、αsRespectively indicate the linear chrip coefficient of pump light and signal light.
The mode that the embodiment of the present application is amplified using reversed chirp photoparametric, chirp pump light and chirp signal light Time chirp is contrary, i.e. Δ ωp、ΔωsSymbol is opposite.Thus, as shown in Figure 2 a, Δ ωi=Δ ωp-Δωs, theoretical On, available initial bandwidth ideler frequency light more broader than pump light, signal light bandwidth.But by optically erasing, final energy The bandwidth of the ideler frequency light accessed is still determined by the phase matched bandwidth of optically erasing.Realize effective optical parameter of wide bandwidth Amplification, not only needs the central wavelength of chirp pump light, chirp signal light to meet phase matched, deviates other the one of central wavelength One corresponding spectral components should also meet phase matched as far as possible.
As shown in Figure 2 b, due to introducing contrary time chirp respectively to pump light and signal light, it can The corresponding relationship of time-domain corrective action light (pump light, signal light, ideler frequency light) difference spectral components, makes relatively independent pumping The spectral components of light and signal light can meet phase matched, realize the perfect phase matched and high conversion efficiency of full spectrum Optically erasing.So that the single order item of Δ k is cancelled out each other just, realize the phase matched of wide bandwidth, needs signal light and pumping The chirp ratio σ of light and the group velocity characteristic value of pump light, signal light and ideler frequency lightIt is equal.To a certain The optically erasing process of specific wavelength, group velocity characteristic value is definite value, and to obtain the broader ideler frequency light of initial bandwidth, visitor It is negative value that chirp ratio σ is required in sight, so needing to use group velocity characteristic value accordingly for different optically erasing processes For the nonlinear crystal of negative value.On this basis, the chirp ratio σ for optimizing signal light and pump light, makes itself and group velocity characteristic valueIt is equal, that is, the transfer efficiency of reversed chirp photoparametric amplification and the output band of ideler frequency light can be improved It is wide.
It should be noted that group velocity characteristic value determines that wideband phase matches the Zhou of required signal light and pump light It sings and compares, and then determine the bandwidth ratio of the signal light and pump light that participate in optically erasing.Obviously, Δ ωs/ΔωpWhen being -1 It is best to be mixed effect, it is broadening (not busy that is, compared to the bandwidth of incident pump light, signal light that optimal ideler frequency light bandwidth can be obtained The promotion ratio of the initial bandwidth of frequency light).This needs group velocity characteristic valueIt is -1, i.e. ideler frequency light Group velocity should be the arithmetic average of signal light, pump light.If group velocity characteristic value excessively deviates -1, in order to realize wide bandwidth Phase matched, it is obvious to be added in pump light, the linear chrip difference on signal light, will necessarily sacrifice part signal light, or pumping The spectrum of light is lost the meaning of mixing at the same time.So in practical applications, either from the angle of energy utilization Or the angle promoted from bandwidth, situation of the group velocity characteristic value near -1 have more application value.
Fig. 3 gives under different crystal, out of phase matching way, 790nm pump light and different wave length signal light and right The group velocity eigenvalue graph for answering ideler frequency light, including the different nonlinear crystals such as LN, KTP, LBO, YCOB and PPLN, and The outs of phase matching ways such as I type-Ⅱphase matching, II type-Ⅱphase matching, 0 class quasi-phase matched and II class quasi-phase matched.
As shown in figure 3, although most of body material crystals can provide negative group velocity characteristic value in specific wavelength, It is that applicable wave-length coverage is extremely limited, shows as the steep curve of negative territory.Even if combining above-mentioned a variety of non-linear Crystal is also only capable of realizing wideband phase matching in limited discrete narrow-band.In addition to body material crystals, it is based on quasi-phase matched (QPM) periodic polarized crystal is another potential selection, in order to use the maximum nonlinear factor d33 of crystal, usually The quasi-phase matched mode (eee) of 0 class can be used.But as shown in figure 3, meet the periodic polarized of II class quasi-phase matched Lithium columbate crystal (oeo) not only has stable group velocity to close in extremely wide spectral region (980nm-1500nm 790nm) It is (gentle group velocity eigenvalue graph), corresponding group velocity characteristic value is also in ideal sectionThis is periodic polarized to meet the sector structure of II class quasi-phase matched Lithium columbate crystal realizes that output the tunable of pulse laser wavelength provides theoretical basis.
The present invention provides a kind of tunable broad band intermediate infrared laser systems, as shown in Figure 1, including pulse laser 1； Beam splitter 2；First pulse stretcher 3；Broadband signal photogenerator 6；Optical path delayer 4；Second pulse stretcher 7；Coupling mirror 8；Nonlinear crystal 9；Spectroscope 10；Pulse shortener 11.
In the embodiment of the present application, the pulse laser that the pulse laser 1 exports, is divided into two pulses through beam splitter 2 Laser.
First bundle of pulsed laser passes through first pulse stretcher 3, reaches the coupling mirror 8.
Second bundle of pulsed laser obtains broadband signal light, the broadband signal light by the broadband signal photogenerator 6 By second pulse stretcher 7, the coupling mirror 8 is reached.Specifically, second bundle of pulsed laser enters super continuous spectrums Generator or optical parametric generator generate tunable broadband signal light, then, will be described in broadband signal light introducing Second pulse stretcher 7 obtains tunable wideband chirp signal light.
First bundle of pulsed laser and the broadband signal light pass through the coupling mirror 8 jointly.It is penetrated through the coupling mirror 8 First bundle of pulsed laser and the broadband signal light out obtain amplified broadband letter into the nonlinear crystal 9 Number light, ideler frequency light and remnant pump light, by the spectroscope 10, by the ideler frequency light, amplified broadband signal light and residual The separation of remaining pump light, the pulse shortener 11 by the Pulse Compression of the ideler frequency light after separation, obtain in infrared ultrashort arteries and veins Impulse light, wherein first bundle of pulsed laser is pump light.
The optical path delayer 4 is arranged between first pulse stretcher 1 and the coupling mirror 8 or described second Between pulse stretcher 7 and the coupling mirror 8, by introducing preset time delay, make first bundle of pulsed laser and described Broadband signal light time synchronization.
Chirp by first bundle of pulsed laser of chirp spread, with the broadband signal light by chirp spread It is contrary；First bundle of pulsed laser and the broadband signal light make optically erasing in the nonlinear crystal, obtain To the amplified broadband signal light, ideler frequency light and remnant pump light；The bandwidth of the ideler frequency light, by the nonlinear crystal Phase matched bandwidth determine.
Optionally, the nonlinear crystal 9 is the periodic polarized lithium niobate of sector structure for meeting II class quasi-phase matched Crystal, first bundle of pulsed laser are o polarised light, and the broadband signal light is e polarised light, and the ideler frequency light is o polarised light.
Optionally, by following one way in which, the central wavelength of the ideler frequency light of generation is adjusted:
Adjust the central wavelength of the broadband signal light of the broadband signal photogenerator output；
Adjust the delay that the optical path delayer introduces；
Correspondingly, needing to adjust the pump light and the width for the phase matched for guaranteeing the ideler frequency center wavelength of light Transversely acting area of the band signal light in the periodic polarized lithium columbate crystal of sector structure for meeting II class quasi-phase matched Domain；
On this basis, right by adjusting second pulse stretcher to the chirp spread amount of the broadband signal light The chirp ratio of the broadband signal light and the pump light is adjusted, with this optimize the ideler frequency light bandwidth and it is described can Tune the energy conversion efficiency of broadband intermediate infrared laser system.
Optionally, the broadband signal photogenerator 6 is supercontinuum generation device (Supercontinuum Generation, SG) or optical parametric generator (Optical Parametric Generation, OPG).
Optionally, the pulse laser 1 is 790nm ti:sapphire laser femto-second laser.
Optionally, the spectroscope 10 be it is highly transmissive to the ideler frequency light, to the pump light and the amplified width Band signal light high reflection, or to the ideler frequency light high reflection, to the pump light and the amplified broadband signal light Highly transmissive dichroic mirror.
Due to first bundle of pulsed laser (the i.e. described pump light) by chirp spread, with the institute by chirp spread The time chirp for stating broadband signal light is contrary, so, substantially available initial bandwidth is than the pump light, described wide The broader ideler frequency light of band signal light belt width.Using meeting the periodic polarized lithium columbate crystal of II class quasi-phase matched anti- Wideband phase matching properties into chirp mid-infrared light parametric amplification, the present invention can be in extremely wide wave-length coverages ([email protected]), completes effective optically erasing of wide bandwidth；On this basis, described to meet the quasi- phase of II class The matched periodic polarized lithium columbate crystal of sector structure can further realize the broad tuning of output pulse laser wavelength.
Specifically, in the embodiment of the present application, the pulse laser 1 is the Ti:Sapphire laser femtosecond pulse laser of 790nm. The nonlinear crystal 9 is the periodic polarized lithium columbate crystal of sector structure for meeting II class quasi-phase matched, and farmland is grown 7.2 It is continuously adjusted in μm -9.1 μ ms.The broadband signal photogenerator 6 is supercontinuum generation device.The spectroscope 10 is pair Ideler frequency light is highly transmissive, to the dichroic mirror of pump light and amplified broadband signal light high reflection.
The application provides a kind of specific tunable broad band intermediate infrared laser system, by tunable broad band mid-infrared laser system The process that system obtains tunable mid-infrared ultra-short pulse laser is as follows: the Ti:Sapphire laser femtosecond pulse laser 1 of the 790nm is defeated Pulse laser out is divided into two bundles pulse laser through beam splitter 2, wherein a bundle of pulsed laser is as pump light, by first arteries and veins It rushes stretcher 3 and chirp spread is made to the pump light；Another bundle of pulsed laser enters the supercontinuum generation device 6, obtains The broadband signal light that 980nm-1500nm is tunable, then by second pulse stretcher 7 to the tunable broadband signal Light chirp spread, wherein the chirp by the pump light of chirp spread, with the broadband signal light by chirp spread It is contrary；The pump light is introduced into optical path delayer 4, suitable time delays is introduced, makes the pump light and the width Band signal light time synchronization, then respectively enter the coupling mirror 8.
The pump light and the broadband signal light through the coupling mirror 8 outgoing meet the quasi- phase of II class into described The periodic polarized lithium columbate crystal 9 of the sector structure matched, by optically erasing, obtain amplified broadband signal light ,~ 4.1-1.7 μm of tunable middle ultra-wideband ideler frequency light and remnant pump light.By the dichroic mirror 10, by the ideler frequency light With the amplified broadband signal light, and, remnant pump light separation, then compressed by the pulse shortener 11 described The pulsewidth of ideler frequency light finally obtains~4.1 μm -1.7 μm tunable mid-infrared ultra-short pulse lasers.
Further, the coupledwave equation based on full dimension, the operation to the tunable broad band intermediate infrared laser system Situation has made detailed numerical simulation.
Theoretically, under the premise of the chirp of pump light time is constant, only by the time chirp of broadband signal light adjust to Appropriate value, so that the instantaneous frequency at chirp signal light each moment of the chirp pump light and wide bandwidth of wide bandwidth is all just full Sufficient phase matched is just able to achieve optimal wideband phase matching.
It is assumed that the length for meeting the periodic polarized lithium columbate crystal of sector structure of II class quasi-phase matched is 5mm, farmland is long It is fixed on 7.5 μm.Pump light is the Ti:Sapphire laser femtosecond pulse of 790nm, and spectrum is in Gaussian Profile, initial transform limit Pulsewidth (TL) is 100fs (1/e2High half-breadth), through 500 times of chirp spreads, the pulsewidth of pump light is broadened to 50ps.Signal light is The central wavelength that supercontinuum generation device generates is 1030nm, spectrum is sufficiently wide and is the super continuum light of super-Gaussian distribution.Pumping Light initial beam intensity is 1GW/cm2, signal light initial beam intensity is the 1% of pump light initial beam intensity.
Fig. 4 gives 790nm pump light in the present embodiment and imitates to the conversion of the small signal optically erasing of 1030nm signal light Rate and generation~3.4 μm of ideler frequency light bandwidth with different chirp ratio α s/ α p change curve.As shown in figure 4, transfer efficiency and To~3.4 μm of ideler frequency light bandwidth can all change with the variation of chirp ratio α s/ α p, wherein the maximum value of transfer efficiency occurs In α s/ α p=~-0.65.Compare, by Fig. 2 provide as a result, the theoretical value of optimal chirp ratio α s/ α p can be derived simply It is~-0.7.Nuance therein is primarily due to the theoretical value that Fig. 2 is provided and only accounts for single order color in nonlinear crystal It dissipates, has ignored the influence of second order and other higher order dispersions.And the bandwidth of~3.4 μm of ideler frequency lights is then in α s/ α p=~-0.75 Reach maximum.
Comprehensive theory derives with numerical simulation as a result, firmly believing, adjusts the chirp signal light of wide bandwidth and the Zhou of wide bandwidth It sings the chirp ratio of pump light, is at optimal value, the conversion effect of the tunable broad band intermediate infrared laser system can be improved Rate and in infrared ideler frequency light output bandwidth.
In order to realize tunable broad band intermediate infrared laser system output mid-infrared ultra-short pulse laser wavelength can It tunes, the nonlinear crystal 9 in the embodiment of the present invention is the periodic polarized niobic acid of sector structure for meeting II class quasi-phase matched Crystalline lithium.The sector structure periodic polarized crystal periodic polarized crystal long compared to single farmland, can be directed to different centers The broadband signal light of wavelength, by changing the lateral work of broadband signal light and pump light in sector structure periodic polarized crystal With region, its farmland length is continuously adjusted, realizes the phase matched to the broadband signal light of different central wavelengths.
It is put based on the periodic polarized lithium columbate crystal for meeting II class quasi-phase matched in reversed chirp mid-infrared light parameter Wideband phase matching properties during big.It not only has in extremely wide spectral region (980nm-1500nm 790nm) steady Fixed group velocity relationship (gentle group velocity eigenvalue graph), corresponding group velocity characteristic value is also in ideal sectionOn the basis of meeting to broadband signal center wavelength of light phase matched, The second pulse stretcher of corresponding fine tuning makes the chirp of broadband signal light and pump light ratio to the chirp spread amount of broadband signal light It is optimal, tunable mid-infrared ultra-short pulse laser can be obtained.
Specifically, the central wavelength of the broadband signal light of adjustment supercontinuum generation device output, or change optical path delay The delay (being equal to the central wavelength of the broadband signal light of change and pump light interaction) that device introduces；And fine tuning pumps accordingly The transversely acting of Pu light, broadband signal light in the periodic polarized lithium columbate crystal of sector structure for meeting II class quasi-phase matched The chirp spread of region, i.e. change farmland long (requirement for meeting phase matched) and the second pulse stretcher to broadband signal light Amount, i.e. change chirp ratio (meeting the matched requirement of wideband phase), make the chirp of broadband signal light and pump light than optimal Obtain tunable mid-infrared ultra-short pulse laser.
Fig. 5 be in the embodiment of the present invention 790nm pump light to 1100nm-1500nm tunable signal light optically erasing Transfer efficiency and the ideler frequency light bandwidth of generation with signal light wavelength change curve.It is assumed that meeting the sector of II class quasi-phase matched The length of structural periodicity poled lithium Niobate is 10mm, and farmland is grown to be continuously adjusted in 7.8 μm of -9.1 μ m.Pump light is The Ti:Sapphire laser femtosecond pulse of 790nm, spectrum are in Gaussian Profile, and initial transform limit pulsewidth (TL) is 100fs (1/e2 High half-breadth), through 1000 times of chirp spreads, the pulsewidth of pump light is broadened to 100ps.Signal light is the generation of supercontinuum generation device Central wavelength be 1100nm-1500nm it is tunable, spectrum it is sufficiently wide and be super-Gaussian distribution super continuum light.Pump light is initial Light intensity is 0.8GW/cm2, the initial beam intensity of signal light is the 1% of pump light initial beam intensity.
Wherein, solid line is the broadband signal light for different central wavelengths, and corresponding second pulse stretcher of finely tuning is to broadband The chirp spread amount of signal light, broadband signal light and pump light chirp is more bent than the characteristic in the case of being optimized to respective optimal value Line.Dotted line is to assume that the indicatrix ideally of dispersion is not present in nonlinear crystalline material.Due to meeting the quasi- phase of II class The matched periodic polarized lithium columbate crystal in position has stable group velocity relationship in the spectral region of 1100nm-1500nm (as shown in Figure 2), even if fixed broadband signal light and pump light chirp than it is constant in the case where, still can be in above-mentioned wave band Obtain gentle efficiency, bandwidth tuning curve.On this basis, if the broadband signal light of different central wavelengths, phase can be directed to The second pulse stretcher should be finely tuned to the chirp spread amount of the broadband signal light of different central wavelengths, by broadband signal light and pumping Light chirp ratio is optimized to respective optimal value, can advanced optimize the transfer efficiency of the tunable broad band intermediate infrared laser system The output bandwidth of infrared ideler frequency light in and.Especially in the spectral region of 1250nm-1500nm, the output bandwidth of ideler frequency light Hardly influenced by the variation of broadband signal center wavelength of light.This indicatrix (solid line) has been fairly close to assume non-linear crystalline substance The result (dotted line) ideally of dispersion is not present in body material.
Each technical characteristic of above embodiments can be combined arbitrarily, for simplicity of description, not to above-described embodiment In each technical characteristic it is all possible combination be all described, as long as however, the combination of these technical characteristics be not present lance Shield all should be considered as described in this specification.
The several embodiments of the application above described embodiment only expresses, the description thereof is more specific and detailed, but simultaneously It cannot therefore be construed as limiting the scope of the patent.It should be pointed out that coming for those of ordinary skill in the art It says, without departing from the concept of this application, various modifications and improvements can be made, these belong to the protection of the application Range.Therefore, the scope of protection shall be subject to the appended claims for the application patent.