Background technology
Since nineteen sixty, first ruby laser came out, laser was as the light source of a kind of high brightness, high coherence, high collimation, for daily life and scientific research provide strong tool.Between decades after this, laser technology has obtained significant progress, the people that appear as of pulse laser provide the LASER Light Source that intensity is higher, the time resolution yardstick is shorter, thereby have promoted the swift and violent progress in high field field, the ultrafast field of microcosmic, biological study field.The output pulse width of pulsed laser light source is more and more narrow, pulsewidth from initial microsecond to femtosecond, even Ah second till now, this makes scientific research can be deep into micro kinetics process faster, as inner-shell electron relaxation, the ionization of light tunnel or the like.Ah second's the reach of science makes people enter a brand-new stage to the research of ultrafast physical process.In addition, the shortening of laser pulse on time scale increased the power density of laser widely, for the research of high field physics provides strong instrument.High order harmonic component produces (hereinafter to be referred as HHG) (referring to document A.Scrinzi, M.Ivanov, R.Kienberger and D.M.Villeneuve, J.Phys.B Vol.39, R1,2006 and F.Krausz and M.Ivanov, Rev.Mod.Phys.Vol.81,163,2009), as emerging field in the laser physics, caused people's extensive interest.
Nearly all high order harmonic component is tested resulting harmonic spectrum and is all shown same feature: along with the increase of harmonic number; low-order harmonic efficient is dull to descend fast; one so-called " platform " and then appearred; in platform area; the intensity of harmonic wave descends very slowly with the increase of harmonic number; near some level subharmonic of this platform area end, humorous intensity of wave descends rapidly, occurs ending.Thus, the high order harmonic component spectrum is divided into platform area and cut-off region, referring to Fig. 3.
Half classical model (consulting document P.B.Corkum, Phys.Rev.Lett.Vol.71,1994,1993) that P.B.Corkum proposed in 1993 intuitively and has effectively been described the HHG process, and this process is divided into following three steps:
The first step, the constraint potential barrier deforms under the effect of Intense Laser Field, portions of electronics tunnel ionization (HHG mainly concentrates in this ionization mechanism scope);
In second step, the free electron (ignoring the atom potential field) after the ionization is quickened by laser field, obtains kinetic energy;
In the 3rd step, portions of electronics obtains can be retracted by electric field again after the energy in electric field, and is compound with parent ion, gives off the photon of corresponding energy.
Above-mentioned half three classical step models have foretold that on the one hand the cut-off energy of high order harmonic component satisfies following relation: E
Cutoff=I
p+ 3.17U
p, U wherein
p=9.33 * 10
14I
0λ
2Be ponderomotive force potential energy, I
pBe the ionization potential of atom, unit is eV, I
0Be laser peak intensity, unit is W/cm
2, λ is an optical maser wavelength, the μ m of unit; Explained the high susceptibility of high order harmonic component production process on the one hand to the laser polarization degree.Under the Intense Laser Field effect of elliptical polarization, the electronics that tunnel ionization takes place moves a period of time when returning in light field, relative parent ion generation lateral shift, thus cause the recombination rate of electronics and ion to reduce, and humorous weave efficiency significantly descends and (consults document P.Dietrich, N.H.Burnett, M.Ivanov, and P.B.Corkum, Phys.Rev.A Vol.50, R3585,1994).According to quantum-mechanical theory, the electronics of ionization transmits in light field the diffusion of ripple bag can take place, and the size of electron waves bag depends on the speed of its diffusion and the running time in light field.The center of electron waves bag is a process of compensation mutually with respect to the lateral shift and the diffusion of electron waves bag of parent ion, when electron waves bag center surpasses electron waves bag big or small with respect to the lateral shift of parent ion, electronics and parent ion recombination probability sharply descend, and high order harmonic component intensity weakens rapidly.As seen, HHG is closely related to the sensitiveness and the electron waves bag dynamics of laser field elliptical polarization degree.In addition, the corresponding different electron waves bag in different wavelength of laser field develops, and HHG is closely related to the sensitiveness and the optical maser wavelength of laser field elliptical polarization degree like this.Therefore, the relation that the polarization of Laser Measurement wavelength and HHG relies on is for the electron waves bag dynamics of surveying in the high field physics provides strong instrument.
Summary of the invention
The present invention aims to provide a kind of measurement mechanism and method of measurement of electron waves bag diffusion velocity, this measurement mechanism and method of measurement have simple and more effective characteristics, and this micro kinetics for the evolution of understanding electron waves bag in the high field physics and electronics has great importance.
Core concept of the present invention is: high order harmonic component produces relevant with electron waves bag dynamic process to the sensitiveness of laser elliptical polarization degree, and the evolution of electron waves bag is relevant with optical maser wavelength, utilize and measure the high order harmonic component frequency spectrum, the elliptical polarization dependence of the excitation laser wavelength that screening high order harmonic component frequency spectrum produces and the relation of optical maser wavelength are with the speed of calculating electron waves bag diffusion and the electron waves bag size of different optical maser wavelength correspondences.
Technical solution of the present invention is as follows:
A kind of measurement mechanism of electron waves bag diffusion velocity, characteristics are that its structure comprises chirped pulse laser system and photoparametric amplifier, on the femtosecond laser light path that the photoparametric amplifier of described chirped pulse laser system or its pumping is exported, set gradually quarter-wave plate, planoconvex spotlight, high order harmonic component target chamber and soft x ray grating spectrograph, described chirped pulse structural system output wavelength is the femtosecond laser of 800nm, import to the input light path of described high order harmonic component target chamber via the 800nm high reflective mirror, after removing described 800nm high reflective mirror, described photoparametric amplifier is under the pumping of described chirped pulse laser system, output wavelength enters the input light path of described high order harmonic component target chamber at the continuously adjustable femtosecond laser of 1200~2400nm, described quarter-wave plate is selected according to the wavelength of measuring described femtosecond laser, and be fixed on the center of high-accuracy electronic rotating disk, described planoconvex spotlight is installed on the accurate translation stage that can move along beam direction, has gas box in the described high order harmonic component target chamber, this gas box links to each other with the working gas bottle with gas circuit by micro-adjustable valve, link to each other with gate valve between described high order harmonic component target chamber and the soft x ray grating spectrograph, described high order harmonic component target chamber and soft x ray grating spectrograph are connected to first vacuum pump and second vacuum pump respectively, and described soft x ray grating spectrograph is surveyed the high order harmonic component frequency spectrum that the working gas effect in described femtosecond laser and the described gas box produces.
Described soft x ray grating spectrograph is made of aluminium foil, soft x ray speculum, slit, flat field grating and soft x ray CCD.
Described quarter-wave plate and described high-accuracy electronic rotating disk are coaxial.
A kind of measurement mechanism of above-mentioned electron waves bag diffusion velocity that utilizes carries out the method that electron waves bag diffusion velocity is measured, and comprises the following steps:
1. close the gate valve between high order harmonic component target chamber and the soft x ray grating spectrograph, open first vacuum pump that second vacuum pump that links to each other with the soft x ray grating spectrograph links to each other with the high order harmonic component target chamber successively, after the vacuum degree for the treatment of described high order harmonic component target chamber and soft x ray grating spectrograph all reaches desired vacuum degree, open described gate valve;
2. open described chirped pulse laser system, output wavelength is the femtosecond laser of 800nm, this laser imports to the input light path of high order harmonic component target chamber via three 800nm high reflective mirrors, on this light path, planoconvex spotlight is set, and it is installed on the described accurate translation stage, adjust and move this precision translation stage, make through the light beam of planoconvex spotlight and gas box is punched and made focus be positioned at the center of described gas box;
3. open the working gas bottle, the rotary fine adjustment valve charges into working gas in gas box, soft x ray CCD by described soft x ray grating spectrograph surveys the high order harmonic component frequency spectrum, simultaneously the operating air pressure of adjustments of gas box, laser spot are with respect to the power of the position of gas box and described femtosecond laser with warble, make that working gas interacts in the femtosecond laser of the 800nm with certain peak strength and the described gas box, to obtain highest time harmonic signal;
4. inserting operation wavelength before described planoconvex spotlight is the 800nm quarter-wave plate, this wave plate is fixed on the center of described high-accuracy electronic rotating disk, rotating this high-accuracy electronic rotating disk drives described quarter-wave plate and rotates around incident ray, with the optical axis of regulating this quarter-wave plate and the angle of laser polarization direction, thereby change the elliptical polarization degree of laser, on the principle, when the high order harmonic component signal is the strongest, laser is linearly polarized light, be that the elliptical polarization degree is zero, at this moment, the fast axle or the slow axis of the optical axis of this quarter-wave plate overlap with the polarization direction of described femtosecond laser, described quarter-wave plate does not change the polarization state of laser beam, the corresponding angle of described high-accuracy electronic rotating disk this moment is designated as zero degree, again high-accuracy electronic rotating disk is rotated along clockwise or counter clockwise direction, up to the complete obiteration of described high order harmonic component signal, at this moment the pairing angle of high-accuracy electronic rotating disk is designated as α, (0, α) between every certain angle by described soft x ray CCD survey described wavelength be 800nm be λ
0The high order harmonic component frequency spectrum;
5. close described micro-adjustable valve, treat that the air pressure in the described gas box reduces to zero, survey acquired signal as a setting, the high order harmonic component frequency spectrum of above-mentioned steps collection is deducted background signal, obtain to go the λ of background by described soft x ray CCD
0The high order harmonic component frequency spectrum;
6. remove the high reflective mirror of all 800nm, the laser of chirped pulse laser system output is directly imported to described photoparametric amplifier make pump light, open described photoparametric amplifier, obtain wavelength in the continuously adjustable femtosecond laser output of 1200~2400nm, in selected n the laser wavelength lambda to be measured of described 1200~2400nm
i, i=1 wherein, 2 ..., n; Described 800nm quarter-wave plate is replaced with the middle-infrared band wideband quarter wave plate;
7. selected femtosecond laser wavelength is λ
1, regulating described photoparametric amplifier output optical maser wavelength is λ
1Femtosecond laser, and make this λ
1The peak strength of femtosecond laser after described planoconvex spotlight focuses on is identical with the peak strength of described 800nm femtosecond laser, i.e. laser wavelength lambda
1The cut-off energy E of corresponding high order harmonic component spectrum
CutoffSatisfy following relation: E
Cutoff=I
p+ 3.17U
p, wherein: U
p Be ponderomotive force potential energy, I
pBe the ionization potential of atom, the eV of unit, I
0Be laser peak intensity, unit is W/cm
2, λ
1Be optical maser wavelength, the μ m of unit; Repeating step is 4. 5. adjusting and test link 3., obtains λ
1The high order harmonic component frequency spectrum;
8. selected successively femtosecond laser wavelength is λ
i, i=2 wherein ..., n, repeating step 7. n-1 time obtain corresponding λ successively
2, λ
3..., λ
i..., λ
nThe high order harmonic component frequency spectrum;
9. to described laser wavelength lambda
iI=0 wherein, 1,2, the high order harmonic component frequency spectrum of n, the inferior harmonic wave of certain one-level in the selected cut-off region, with the intensity addition of all pixels of this harmonic wave correspondence,, obtain the relative intensity I of selected harmonic wave and the relation of described high-accuracy electronic rotating disk rotational angle as the relative intensity I of this harmonic wave, the tangent value of this high-accuracy electronic rotating disk rotational angle is the elliptical polarization degree ε of pumping laser, obtain the relative intensity I of selected harmonic wave and the relation curve of elliptical polarization degree ε, i.e. I-ε relation curve, the relative intensity of finding out this harmonic wave from this curve drops to the value ε of the laser elliptical polarization degree of a half correspondence
1/2(λ
i), i=0 wherein, 1,2 ..., n relies on ε with the comprehensive elliptical polarization that obtains selected cut-off region harmonic wave afterwards of the result of gained
1/2(λ
i) and laser wavelength lambda
iRelation curve ε
1/2-λ is with function a λ
bThis curve of match is tried to achieve the value of a, is tried to achieve the peak swing E of laser by the cut-off region photon energy of high order harmonic component spectrum
0, again by a=2.6 π
2m
eCV
s/ peE
0Calculate the speed of electron waves bag diffusion:
V
s=apeE
0/2.6π
2m
ec
With the electron waves bag radius of different optical maser wavelength correspondences be:
Wherein: e, m
e, c is respectively electron charge, electron mass, the light velocity, p ≈ 5.7.
Basic principle of the present invention is as follows:
Intense Laser Field in elliptical polarization
E
0(t) be the temporal envelope of light field, ω is a laser frequency, and ε is the elliptical polarization degree of light field) act on down, with respect to parent ion generation lateral shift, its side-play amount is p ε eE to the electronics of generation tunnel ionization when returning
0λ
2/ m
e(2 π c)
2(consulting document P.Dietrich, N.H.Burnett, M.Ivanov, and P.B.Corkum, Phys.Rev.A Vol.50, R3585,1994).For the impact velocity (being equivalent to the cut-off region harmonic wave) of maximum, p ≈ 5.7, therefore for the ease of contrasting the result of different optical maser wavelengths, we only consider that the elliptical polarization of the harmonic wave of cut-off region relies on, correspondingly, E
0Be the peak swing of light field, because the cut-off energy E of high order harmonic component spectrum
Cutoff=I
p+ 3.17U
p, U
p=9.33 * 10
14I
0λ
2Be ponderomotive force potential energy, I
pBe the ionization potential of atom, the eV of unit, I
0Be laser peak intensity, unit is W/cm
2, λ is an optical maser wavelength, the μ m of unit.The anti-peak strength I that obtains to obtain laser that pushes away of cut-off energy by the high order harmonic component spectrum
0, the peak swing of light field
λ is an optical maser wavelength, e, m
e, c is respectively electron charge, electron mass, the light velocity, and the three is constant.In addition, electron waves wrap in the process of laser field transmission the diffusion of ripple bag take place, and diffusion velocity can be expressed as
(consulting document A.M.Perelomov, V.S.Popov, and M.V.Terent ' ev, Soy.Phys.JETP Vol.24,207,1967).Therefore, if the peak strength of different optical maser wavelength correspondences (is proportional to E
0 2) identical, to a kind of atom, electron waves bag diffusion velocity will remain unchanged.Like this, the electron waves bag size of different optical maser wavelength correspondences be proportional to electronics from tunnel ionization to the compound time of experiencing of parent ion, for the cut-off region harmonic wave, this time is about 0.65 λ/c.As seen, the size of electron waves bag is directly proportional with optical maser wavelength.The center of electron waves bag is a process of compensation mutually with respect to the lateral shift and the diffusion of electron waves bag of parent ion, and when electronics equals the size (radius) of electron waves bag with respect to the lateral shift of parent ion, the intensity of harmonic wave will drop to peak strength I
0Half, at this moment, the elliptical polarization degree of laser is designated as ε
1/2, corresponding ripple bag size is designated as σ
1/2=V
s0.65 λ/c.Can get p ε thus
1/2EE
0λ
2/ m
e(2 π c)
2=V
s0.65 λ/c, i.e. ε
1/2=(2.6 π
2m
eCV
s/ peE
0) λ
-1Therefore, with function a λ
bThe elliptical polarization of match cut-off region harmonic wave relies on
With laser wavelength lambda
i(i=1,2 ... relation curve n), can try to achieve the value of a and b.As mentioned above, in theory, a=2.6 π
2m
eCV
s/ peE
0, b=-1.Therefore, a value that obtains by match and the E that obtains by high order harmonic component spectrum cut-off energy
0Can instead release the speed V of electron waves bag diffusion
s=apeE
0/ 2.6 π
2m
eThe electron waves bag size (radius) of c and different optical maser wavelength correspondences
Technique effect of the present invention:
The present invention utilizes high order harmonic component to produce the sensitiveness of laser elliptical polarization degree and the relation of electron waves bag dynamic process, measure the high order harmonic component frequency spectrum, the elliptical polarization dependence of the excitation laser wavelength that screening high order harmonic component frequency spectrum produces and the relation of optical maser wavelength are calculated the speed of electron waves bag diffusion and the electron waves bag size of different optical maser wavelength correspondences.
Measurement mechanism of the present invention and method of measurement have simple and effective characteristics, and this micro kinetics for the evolution of understanding electron waves bag in the high field physics and electronics has great importance.
Embodiment
The invention will be further described below in conjunction with embodiment and accompanying drawing, but should not limit protection scope of the present invention with this.
See also Fig. 1 earlier, Fig. 1 is the light path schematic diagram of the measurement mechanism specific embodiment of electron waves bag diffusion velocity of the present invention.As seen from the figure, the measurement mechanism of electron waves bag diffusion velocity of the present invention, its structure comprises chirped pulse laser system 1 and photoparametric amplifier 2, on femtosecond laser 4 light paths that the photoparametric amplifier 2 of described chirped pulse laser system 1 or its pumping is exported, set gradually quarter-wave plate 5, planoconvex spotlight 6, high order harmonic component target chamber 7 and soft x ray grating spectrograph 8, described chirped pulse structural system output wavelength is the femtosecond laser of 800nm, import to the input light path of described high order harmonic component target chamber 7 via three 800nm high reflective mirrors 3, after removing described 800nm high reflective mirror 3, described photoparametric amplifier 2 is under the pumping of described chirped pulse laser system 1, output wavelength enters the input light path of described high order harmonic component target chamber 7 at the continuously adjustable femtosecond laser of 1200-2400nm, described quarter-wave plate 5 is selected according to the wavelength of measuring described femtosecond laser, and being fixed on the center of high-accuracy electronic rotating disk 9, described quarter-wave plate 5 is coaxial with described high-accuracy electronic rotating disk 9.Described planoconvex spotlight 6 is installed on the accurate translation stage 10 that can move along beam direction, has gas box 11 in the described high order harmonic component target chamber 7, this gas box 11 links to each other with working gas bottle 13 with gas circuit by micro-adjustable valve 12, link to each other with gate valve 14 between described high order harmonic component target chamber 7 and the soft x ray grating spectrograph 8, described high order harmonic component target chamber 7 and soft x ray grating spectrograph 8 are connected to first vacuum pump 15 and second vacuum pump 16 respectively, and the high order harmonic component frequency spectrum that the working gas effect in 8 pairs of described femtosecond lasers of described soft x ray grating spectrograph and the described gas box 11 produces is surveyed.
Described soft x ray grating spectrograph 8 is made of aluminium foil 17, soft x ray speculum 18, slit 19, flat field grating 20 and soft x ray CCD21.
Described chirped pulse laser system 1 output wavelength is the femtosecond laser 4 of 800nm, described photoparametric amplifier 2 output wavelengths infrared femto-second laser pulse 4 in 1200-2400nm is continuously adjustable.800nm laser is horizontal polarization, and mid-infrared laser is vertical polarization.Regulate the optical axis (fast axle or slow axis) of quarter-wave plate 5 and the angle of laser polarization direction, can change the polarization state of laser, when both angle is 0 when spending, quarter-wave plate does not change the polarization state of laser, when both angle is 45 when spending, laser is circularly polarized light, when both angles are between 0 degree and 45 degree, laser is elliptically polarized light, the tangent value of this angle is defined as the elliptical polarization degree of laser, the i.e. ratio of the electric field amplitude of the electric field amplitude of Tuo Yuan short-axis direction and long axis direction.In order accurately to regulate the elliptical polarization degree of laser, quarter-wave plate is placed the center of high-accuracy electronic rotating disk 9, this rotating disk 9 is a hollow, can guarantee that laser passes through fully.It should be noted that in order to allow rotating disk 9 drive quarter-wave plate 5 and rotate, require both coaxial around incident ray.
Femto-second laser pulse 4 focuses in the gas box 11 in the high order harmonic component target chamber 7 via planoconvex spotlight 6, produces high order harmonic component.In order to regulate laser spot relatively and the position of gas, lens are installed on the accurate translation stage 10.Gas box 11 is made of two thick steel discs of 0.1-0.2mm, and after steel disc was punched by laser focusing, first vacuum pump 15 was taken out the air in the gas box 11.Open micro-adjustable valve 12, charge into working gas in gas box 11, the gas that the gas that micro-adjustable valve 12 injects and first vacuum pump 15 are extracted out can reach dynamic equilibrium.By micro-adjustable valve 12 can the adjustments of gas box air pressure in 11.
The signal that produces in the high order harmonic component target chamber 7 can filter remaining first-harmonic and low order harmonics via aluminium foil 17.The frequency spectrum of high order harmonic component is surveyed by soft x ray CCD in the soft x ray grating spectrograph 8 21.In order to reduce thermal noise, soft x ray CCD21 requires to be operated in low-temperature condition.This soft x ray CCD is two-dimensional array CCD, laterally shows high order harmonic component spectrum, vertically shows the spatial distribution of high order harmonic component, as shown in Figure 3.
In addition, high order harmonic component target chamber 7 links to each other by gate valve 14 with soft x ray grating spectrograph 8.Be furnished with first vacuum pump 15 and second vacuum pump 16 respectively.It should be noted that the volume difference in two parts chamber especially, do not broken through, when vacuumizing, need close gate valve 14 in order to ensure aluminium foil 17.Wait to be extracted into the vacuum degree of requirement, during acquired signal, just open gate valve 14.
Utilize the measurement mechanism of above-mentioned electron waves bag diffusion velocity to carry out the method that electron waves bag diffusion velocity is measured, comprise the following steps:
1. close the gate valve 14 between high order harmonic component target chamber 7 and the soft x ray grating spectrograph 8, open first vacuum pump 15 that second vacuum pump (16) that links to each other with soft x ray grating spectrograph 8 links to each other with high order harmonic component target chamber 7 successively, after treating that described high order harmonic component target chamber 7 all reaches desired vacuum degree with soft x ray grating spectrograph 8, open described gate valve 14;
2. open described chirped pulse laser system 1, output wavelength is the femtosecond laser 4 of 800nm, this laser imports to the input light path of high order harmonic component target chamber 7 via three 800nm high reflective mirrors 3, planoconvex spotlight 6 is set on this light path, and it is installed on the described accurate translation stage 10, adjust and move this precision translation stage 10, make through the light beam of planoconvex spotlight 6 and punch and make focus to be positioned at the center of described gas box 11 gas box 11;
3. open working gas bottle 13, rotary fine adjustment valve 12 charges into working gas in gas box 11, soft x ray CCD21 by described soft x ray grating spectrograph 8 surveys the high order harmonic component frequency spectrum, simultaneously the operating air pressure of adjustments of gas box 11, laser spot are with respect to the power of the position of gas box and described femtosecond laser 4 with warble, make that working gas interacts in the femtosecond laser of the 800nm with certain peak strength and the described gas box 11, to obtain highest time harmonic signal;
4. inserting operation wavelength before described planoconvex spotlight 6 is 800nm quarter-wave plate 5, this wave plate is fixed on the center of described high-accuracy electronic rotating disk 9, rotating the described quarter-wave plate 5 of these high-accuracy electronic rotating disk 9 drives rotates around incident ray, with the optical axis of regulating this quarter-wave plate and the angle of laser polarization direction, thereby change the elliptical polarization degree of laser, on the principle, when the high order harmonic component signal is the strongest, laser is linearly polarized light, be that the elliptical polarization degree is zero, at this moment, the fast axle or the slow axis of the optical axis of this quarter-wave plate overlap with the polarization direction of described femtosecond laser 4, described quarter-wave plate does not change the polarization state of laser beam, with this moment described high-accuracy electronic rotating disk 9 corresponding angles be designated as zero degree, again high-accuracy electronic rotating disk 9 is rotated along clockwise or counter clockwise direction, up to the complete obiteration of described high order harmonic component signal, at this moment high-accuracy electronic rotating disk 9 pairing angles are designated as α, (0, α) between every 0.5 the degree survey the λ that described wavelength is 800nm by described soft x ray CCD21
0The high order harmonic component frequency spectrum;
5. close described micro-adjustable valve 12, treat that the air pressure in the described gas box 11 reduces to zero, survey acquired signal as a setting by described soft x ray CCD21, the high order harmonic component frequency spectrum subtracting background with 4. above-mentioned steps gathers obtains to go the λ of background
0The high order harmonic component frequency spectrum;
6. remove the high reflective mirror of all 800nm, the laser of chirped pulse laser system 1 output is directly imported to described photoparametric amplifier 2 make pump light, open described photoparametric amplifier 2, obtain wavelength in continuously adjustable femtosecond laser 4 outputs of 1200~2400nm, in selected n the laser wavelength lambda to be measured of described 1200~2400nm
i, i=1 wherein, 2 ..., n; Described 800nm quarter-wave plate 5 is replaced with middle-infrared band wideband quarter wave plate 5, and this quarter-wave plate all is suitable for the optical maser wavelength of described middle-infrared band;
7. selected femtosecond laser wavelength is λ
1, regulating described photoparametric amplifier 2 output optical maser wavelengths is λ
1Femtosecond laser, and make this λ
1The peak strength of femtosecond laser after described planoconvex spotlight 6 focuses on is identical with the peak strength of described 800nm femtosecond laser, i.e. laser wavelength lambda
1The cut-off energy E of corresponding high order harmonic component spectrum
CutoffSatisfy following relation: E
Cutoff=I
p+ 3.17U
p,
Wherein:
Be ponderomotive force potential energy, I
pBe the ionization potential of atom, the eV of unit, I
0Be laser peak intensity, unit is W/cm
2, λ
1Be optical maser wavelength, the μ m of unit; Repeating step is 4. 5. adjusting and test link 3., obtains λ
1The high order harmonic component frequency spectrum;
8. selected successively femtosecond laser wavelength is λ
i, i=2 wherein ..., n, repeating step 7. n-1 time obtain corresponding λ successively
2, λ
3..., λ
i..., λ
nThe high order harmonic component frequency spectrum;
9. data processing is referring to Fig. 2, to described laser wavelength lambda
iI=0 wherein, 1,2, the high order harmonic component frequency spectrum of n, the harmonic wave of certain one-level time in the selected cut-off region is referring to Fig. 3, with the intensity addition of all pixels of this harmonic wave correspondence, relative intensity I as this harmonic wave, obtain the relative intensity I of selected harmonic wave and the relation of described high-accuracy electronic rotating disk 9 rotational angles, the tangent value of these high-accuracy electronic rotating disk 9 rotational angles is the elliptical polarization degree ε of pumping laser, obtains the relative intensity I of selected harmonic wave and the relation curve of elliptical polarization degree ε, be I-ε relation curve, the relative intensity of finding out this harmonic wave from this curve drops to the value ε of the laser elliptical polarization degree of a half correspondence
1/2(λ
i), i=0 wherein, 1,2 ..., n relies on ε with the comprehensive elliptical polarization that obtains selected cut-off region harmonic wave afterwards of the result of gained
1/2(λ
i) and laser wavelength lambda
iRelation curve ε
1/2-λ is with function a λ
bThis curve of match is tried to achieve the value of a, is tried to achieve the peak swing E of laser by the cut-off region photon energy of high order harmonic component spectrum
0, again by a=2.6 π
2m
eCV
s/ peE
0Calculate the speed of electron waves bag diffusion:
V
s=apeE
0/2.6π
2m
ec
With the electron waves bag radius of different optical maser wavelength correspondences be:
Wherein: e, m
e, c is respectively electron charge, electron mass, the light velocity, p ≈ 5.7.
What pay special attention to is that suitably the focal length of adjusting output power of laser and planoconvex spotlight 6 is identical with the peak strength of 800nm wavelength laser with the peak strength that guarantees different wave length laser.In addition, quarter-wave plate 5 should be selected according to optical maser wavelength.The details of data processing:
1. the above-mentioned a series of high order harmonic component spectrums that measure are deducted corresponding background signal, remove noise, obtain clean high order harmonic component spectrum, as shown in Figure 3, obtain a series of discrete two-dimension spectrums on the test surface of soft x ray CCD, being the spectrum distribution of harmonic wave laterally, vertically is the spatial distribution of harmonic wave.From left to right, harmonic number reduces successively.For each optical maser wavelength, the harmonic wave (near highest time, but in order to ensure sufficiently high signal to noise ratio, selected harmonic wave can not be too weak) of certain one-level time in the selected cut-off region, with the intensity addition of all pixels of this harmonic wave correspondence, as the relative intensity I of this harmonic wave.
2. to each laser wavelength lambda
i(i=1,2 ... n), describe the relative intensity I of the cut-off region harmonic wave selected and the relation of rotating disk rotational angle θ.The tangent value of this rotating platform rotational angle is the elliptical polarization degree ε (ε=tan θ) of laser.Thereby obtain each laser wavelength lambda
i(i=1,2 ... n) down the relative intensity I of selected cut-off region harmonic wave describes I-ε relation curve with the variation of laser elliptical polarization degree ε, and the relative intensity I that obtains this harmonic wave by this curve drops to the value of the laser elliptical polarization degree of a half correspondence
3. obtain the elliptical polarization dependence that the cut-off region high order harmonic component produces
With laser wavelength lambda
i(i=1,2 ... n) relation curve between is with function a λ
bThis curve of match is tried to achieve the value of a and b.
4. described in summary of the invention, when electronics equals the size (radius) of electron waves bag with respect to the lateral shift of parent ion, the intensity of harmonic wave will drop to original half, i.e. p ε
1/2EE
0λ
2/ m
e(2 π c)
2=V
s0.65 λ/c.Can get thus, the elliptical polarization of cut-off region harmonic wave relies on
With laser wavelength lambda
i(i=1,2 ... n) pass is: ε
1/2=(2.6 π
2m
eCV
s/ peE
0) λ
-1Therefore, in theory, a=2.6 π
2m
eCV
s/ peE
0, b=-1.What we considered is the cut-off region harmonic wave of different optical maser wavelength correspondences, so p ≈ 5.7.Correspondingly, E
0Be the peak swing of light field, counter the pushing away of cut-off energy of being composed by high order harmonic component obtains.C is the light velocity, m
eBe the quality of electronics, e is the electric charge of electronics, and these are constant.Therefore, a value that obtains by match and the E that obtains by high order harmonic component spectrum cut-off energy
0Can instead release the speed V of electron waves bag diffusion
s=apeE
0/ 2.6 π
2m
eThe electron waves bag size (radius) of c and different optical maser wavelength correspondences
Provide a specific embodiment below and come preliminary identification the present invention, be described in detail as follows:
We have chosen 800nm in the experiment, 1300nm, 1400nm, 1500nm, five wavelength of 1800nm, preceding four wavelength focus on 40cm planoconvex spotlight 6,1800nm is unused light, and optical quality is relatively poor, and peak power output is lower, (1.8 * 1014W/cm2) is identical, selects for use 15cm planoconvex spotlight 6 to focus on the peak strength of other optical maser wavelengths in order to make it.The length of gas box 11 is 2mm, and working gas is an argon gas.By a series of measurement, the elliptical polarization that obtains the high order harmonic component generation of different optical maser wavelength correspondences relies on, by function a λ
bMatch obtains the value of a, the counter thus electron waves bag diffusion velocity that obtains after the argon gas ionization that pushes away
Return electron ripple bag size (radius) σ of the electronics of the impact velocity maximum of 800nm Laser Driven
1/2=0.97 ± 0.13nm.The ripple bag diffusion velocity that this method of measurement obtains with rely on the result who obtains by the elliptical polarization of measuring argon gas double ioinization rate and consistently (consult document H.Niikura, F.Legare, R.Hasbani, M.Ivanov, A.D.Bandrauk, D.M.Villeneuve, and P.B.Corkum, Nature, Vol.417,917,2002), this suffices to show that the present invention measures the accuracy and the validity of electron waves bag diffusion velocity.