超快光学-第09章-非线性三阶效应ppt课件.ppt

《超快光学-第09章-非线性三阶效应ppt课件.ppt》由会员分享，可在线阅读，更多相关《超快光学-第09章-非线性三阶效应ppt课件.ppt（43页珍藏版）》请在淘文阁 - 分享文档赚钱的网站上搜索。

1、中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Third-order nonlinearities:Four-wave mixingThird-harmonic generationInduced gratingsPhase conjugationNonlinear refractive indexSelf-focusingSelf-phase modulationContinuum generatio

2、n中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Third-harmonic generation3wwTHG MediumWe must now cube the input field:Third-harmonic generation is weaker than second-harmonic and sum-frequency generation,so the third harmonic

3、is usually generated using SHG followed by SFG,rather than by direct THG.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Noncollinear third-harmonic generationWe can also allow two different input beams,whose frequencies can be

4、different.So in addition to generating the third harmonic of each input beam,the medium will generate interesting sum frequencies.THGmediumSignal#1Signal#2w ww www中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Third-order diffe

5、rence-frequency generation:Self-diffractionConsider some of the difference-frequency terms:NonlinearmediumSignal#1Signal#2www ww w中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识SamplemediumSignalwwwThe excite-probe geometryOne

6、field can contribute two factors,one E and the other E*.This will involve both adding and subtracting the frequency and its k-vector.This effect is automatically phase-matched!The excite-probe beam geometry has many applications,especially to ultrafast spectroscopy.The signal beam can be difficult t

7、o separate from the input beam,E1,however.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识NonlinearmediumWave plateyielding 45polarizationSignalwwwPolarization gatingHere field#2 contributes two factors,one E and the other E*.Bu

8、t one is vertically polarized,while the other is horizontally polarized.This yields a signal beam thats orthogonally polarized to the input beam E1.If E1 is horizontally polarized,the signal will be vertically polarized:This arrangement is also automatically phase-matched.Its also referred to as pol

9、arization spectroscopy due to its many uses in both ultrafast and frequency-domain spectroscopy.The input beam in the signal beam direction is rejected by polarizer!中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识xThe irradiance

10、 of two crossed beams is sinusoidal,inducing a sinusoidal absorption or refractive index in the mediuma diffraction grating!An induced grating results from the cross term in the irradiance:Many nonlinear-optical effects can beconsidered as induced gratings.xxx xTime-independent fringes中国中国历历史上吸烟的史上吸

11、烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Diffraction off an induced gratingA third beam will then diffract into a different direction.This results in a beam thats the product of E1,E2*,and E3:This is just a generic four-wave-mixing eff

12、ect.x中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Induced gratingsPhase-matching condition:Assume:The diffracted beam has the same frequency and k-vector magnitude as the probe beam,but its direction will be different.butDiff

13、ractedsignalwex1wex2wsig=wprwprqexzqprqsigx中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Phase-matching induced gratingsPhase-matching:z-component:x-component:wexwexwprqexzqprqsigxThe minus sign is just the excite-probe effect

14、.The“Bragg Condition”中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Induced gratingswith different frequenciesNonlinearmediumDiffractedsignalwww w w3w3Phase-matching condition:This effect is called non-degenerate four-wave mixi

15、ng.In this case,the intensity fringes sweep through the medium:a moving grating.The set of possible beam geometries is complex.I wrote a thesis on this!中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Acousto-optics involves diff

16、racting light off a grating induced by an acoustic wave.Acousto-optics works because acoustic waves have about the same wavelengths as(visible)light waves.Such diffraction can be quite strong:70%.Acousto-optics is the basis of useful devices.QuartzDiffractedbeamw wacousticwAcoustic transducerPressur

17、e,density,and refractive-index variations due to acoustic waveInputbeamAn acoustic wave induces sinusoidal density,and hence sinusoidal refractive-index,variations in a medium.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Indu

18、ced gratings with plane waves and more complex beams(of the same frequency)All such induced gratings will diffract a plane wave,reproducingthe distorted wave:A plane wave and avery distorted waveA plane wave and a slightly distorted wave Two plane wavesA plane wave and aslightly distorted waveE2 and

19、 E3 are plane waves.Holography is an induced-grating process.One of the write beams has a complex spatial patternthe image.Different incidence angles correspond to different fringe spacings.Different object views are stored as different fringe spacings.A third beam(a plane wave)diffracts off the gra

20、ting,acquiring the image infor-mation.Different fringe spacings yield different diffraction angleshence 3D!The light phase stores the angular info.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Phase conjugationWhen a nonlinear

21、-optical effect produces a light wave proportional to E*,the process is called a phase-conjugation process.Phase conjugators can cancel out aberrations.The second traversal through the medium cancels out the phase distortion caused by the first pass!Distorting mediumA phase-conjugate mirror reverses

22、 the sign of the phase A normal mirror leaves the sign of the phase unchanged中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Phase conjugation=Time reversalA light wave is given by:If we can phase-conjugate the spatial part,we h

23、ave:Thus phase conjugation produces a time-reversed beam!中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Degenerate four-wave mixingConsider only processes with three input frequenciesand an output frequency that are identical.I

24、dentical frequencies=degenerate.Degenerate four-wave mixing gives rise to an amazing variety of interesting effects.Some are desirable.Some are not.Some are desirable some of the time and not the rest of the time.Because the k-vectors can have different directions,well distinguish between them(as we

25、ll as the fields):中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Single-field degenerate four-wave mixingSingle-field degenerate four-wave mixing gives rise to“self”effects.These include:Self-phase modulationSelf-focusing(whole

26、-beam and small-scale)Both of these effects participate in the generation of ultrashort pulses!If just one beam is involved,all the k-vectors will be the same,as will the fields:So the polarization becomes:中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，

27、提高人民健康的危害，提高师师生的控烟意生的控烟意识识Degenerate 4WM means a nonlinearrefractive index.So the refractive index is:Recall the inhomogeneous wave equation:and the polarization envelope(the linear and nonlinear terms):Substituting the polarization into the wave equation(assuming slow variation in the envelope of E

28、 compared to 1/w):since中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Nonlinear refractive index(contd)Usually we define a nonlinear refractive index,n2:The refractive index in the presence of linear and nonlinear polarizations

29、:Assume that the nonlinear term n0:Now,the usual refractive index(which well call n0)is:So:So:since:中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识The nonlinear refractive index magnitude and response timeA variety of effects g

30、ive rise to a nonlinear refractive index.Those that yield a large n2 typically have a slow response.Thermal effects yield a huge nonlinear refractive index through thermal expansion due to energy deposition,but they are very very slow.As a result,most media,including even Chinese tea,have nonlinear

31、refractive indices!vibrational中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Whole-beam self-focusingThis is precisely the behavior of a lens!But one whose focal power scales with the intensity.If the beam has a spatial Gaussia

32、n intensity profile,then any nonlinear medium will have a spatial refractive index profile that is also Gaussian:Near beam center:The nonlinear refractive index,causes beams to self-focus.The phase delay vs.radial co-ordinate will be:中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可

33、以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Small-scale self-focusingSuch filaments grow exponentially with distance.And they grow from quantum noise in the beam,which is always there.As a result,an intense ultrashort pulse cannot propagate through any medium without degenerating into a ma

34、ss of tiny highly intense filaments,which,even worse,badly damage the medium.If the beam has variations in intensity across its profile,it undergoessmall-scale self-focusing.Each tiny bump in the beam undergoes its own separate self-focusing,yielding a tightly focused spot inside the beam,called a“f

35、ilament.”IntensityPosition中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Small-scale self-focusing vs.distance:SimulationA somewhat noisy beam becomes a very noisy one.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛

36、苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Real examples of beam filamentationAll peak powers are in the 15 to 35GW/cm2 range.All beams began life smooth!中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识The self

37、-phase-modulated pulse develops a phase vs.time proportional to the input pulse intensity vs.time.Self-phase modulation&continuum generationThe further the pulsetravels,the moremodulation occurs.A flat phase vs.time yields the narrowest spectrum.If we assume thepulse starts with a flat phase,then SP

38、M broadens the spectrum.This is not a small effect!A total phase variation of hundreds can occur!A broad spectrum generated in this manner is called Continuum.That is:Pulse intensity vs.time中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的

39、控烟意生的控烟意识识The instantaneous frequency vs.time in SPMA 10-fs,800-nm pulse thats experienced self-phase modulation with a peak magnitude of 1 radian.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Self-phase-modulated pulse in the

40、 frequency domain The same 10-fs,800-nm pulse thats experienced self-phase modulation with a peak magnitude of 1 radian.Its easy to achieve many radians for phase delay,however.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识A h

41、ighly self-phase-modulated pulseA 10-fs,800-nm pulse thats experienced self-phase modulation with a peak magnitude of 10 radians Note that the spectrum has broadened significantly.When SPM is very strong,it broadens the spectrum a lot.We call this effect continuum generation.中国中国历历史上吸烟的史上吸烟的历历史和史和现现

42、状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Continua created by propagating 500-fs 625nm pulses through 30 cm of single-mode fiber.The Supercontinuum Laser Source,Alfano,ed.Broadest spectrum occurs for highest energy.LowEnergyMediumEnergyHighEnergy

43、Experimental continuum spectrum in a fiber中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Continuum generation simulationsInput Intensity vs.time(and hence output phase vs.time)Output spectrum:Instantaneously responding n2;maxim

44、um SPM phase=72p radiansThe Super-continuumLaser Source,Alfano,ed.Original spectrum is negligible in width compared to the output spectrum.Oscillations occur in spectrum because all frequencies occur twice and interfere,except for inflection points,which yield maximum and minimum frequencies.Dw中国中国历

45、历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Continuum generation simulationOutput phase vs.time(input intensity vs.time,due to slow response)Output spectrum:Noninstantaneously responding n2;maximum SPM phase=72p radiansThe Superc

46、ontinuumLaser Source,Alfano,ed.Asymmetry in phase vs.timeyields asymmetry in spectrum.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Experimental continuum spectraInputwavelength625-nm(70 fs and 2 ps)pulses in Xe gasL=90 cmThe

47、SupercontinuumLaser Source,Alfano,ed.Data taken by Corkum,et al.p=15&40 atm中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Ultraviolet continuum4-mJ 160-fs 308-nm pulses in 40 atm of Ar;60-cm long cell.Lens focal length=50 cm.Go

48、od quality output mode.The SupercontinuumLaser Source,Alfano,ed.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识308 nm input pulse;weak focusing with a 1m-focal-length lens.The Super-continuumLaser Source,Alfano,ed.UV Continuum

49、in Air!Continuum is limited when GVD causes the pulse to spread,reducing the intensity.中国中国历历史上吸烟的史上吸烟的历历史和史和现现状、所采取的措施以及由此状、所采取的措施以及由此带带来的痛苦和灾来的痛苦和灾难难，可以，可以进进一步了解吸烟一步了解吸烟对对人民健康的危害，提高人民健康的危害，提高师师生的控烟意生的控烟意识识Continuum in airBeam profile of a high-power beam(1000Pcr)after 15m.Note the multiple filamen

50、tation.Use a negatively chirped pulse to pre-compensate for the dispersion of air.Then“temporal focusing”occurs.The self-focusing can compensate diffraction:light bullets!Usually this only happens for pieces of the beam:filamentation,and its messy.Conical emission from a fs beam in air,near the crit