CN2773643Y - Femtosecond pulse dynamic space-time transformation shaping device - Google Patents

Abstract

A femtosecond pulse dynamic space-time transformation shaping device comprises: the frame that constitutes each other by first optics flat board and second optics flat board first optics flat board inlay and be equipped with first reflection formula lens and second reflection formula lens second optics flat board on inlay in proper order equidistantly and be equipped with first high density grating, reflection formula template and second high density grating, the component that first optics flat board was inlayed and is established and the component that inlays on the second optics flat board alternately set up separately each other and satisfy the relational expression: f ═ hcos θ; c-2 fsin θ. In the formula: f is the focal length of the first reflective lens and the second reflective lens; h is the distance between the first optical flat plate and the second optical flat plate; c is the center-to-center distance of each element; and theta is the incident angle of the femtosecond pulse laser. The utility model discloses can carry out the plastic to femto second pulse effectively, simple structure is reliable, and compact is small, and the interference killing feature is strong, can avoid the influence of factors such as air disturbance effectively, and the cost is cheap.

Description

Femtosecond pulse shaping device by dynamic space-time transformation

Technical field:

The utility model relates to femtosecond pulse space-time transformation apparatus for shaping, refers in particular to a kind of based on the femtosecond pulse shaping device by dynamic space-time transformation on the planar optics basis.

Background technology:

As everyone knows, femto-second laser pulse is following obtainable the shortest time course of present human experimentation chamber condition, thus the measurement of femto-second laser pulse and control can not look to by another faster other physical influence realize.Femto-second laser pulse transforms to the spatial domain by the space-time transformation technology with time-domain information, processing by the spatial domain turns back to the important technology that time domain is the shaping of realization femto-second laser pulse, measurement and control again, also is the method for unique and the most effective manipulation femtosecond pulse.Since people such as Heritage introduce this field of femtosecond pulse space-time transformation shaping, obtained developing rapidly, now become an important advanced subject.In application facet, can produce various needed waveforms, be applied in stepless control, safety communication, storage, medical science and the aspects such as biology imaging, chemistry and physics of signal Processing and quantized system.For example reported that femtosecond pulse device that femtosecond pulse that the space-time coherent control of the lattice vibration ripple of the time that depends on and position microscopic size produced the lattice vibration ripple of Terahertz, shaping changes process, the shaping of molecular breakdown and rearrangement as new reactant sets up the three-pulse sequence of a conllinear and be used for nuclear magnetic resonance of bidimensional spectrum etc. in 2003 on science magazine (SCIENCE).The common feature of these reports is all to have used the femtosecond pulse shaping technique to control the shape of ultrashort pulse, storage and recovery direct impulse shape.As seen femtosecond pulse space-time transformation shaping technique has become the focus of current research, is the research important tool of numerous subjects such as physics, materialogy, life science.Can expect that because the importance of femtosecond laser space-time transformation shaping pulse in academic research and extensively real application, it will become one of the main research contents in optoelectronics field.

Formerly technology [1] is (referring to C.Froehly, B.Colombeau, and M.Vampouille, " Shaping and analysis of picosecond light pulses; " Progress in Optics.20,65-153 (1983)) described in is the pulse space-time transformation apparatus for shaping of the most basic, most widely used transmission-type 4f system.Though it has possessed the ability of shaping, poor stability, antijamming capability as machinery and thermal effect a little less than, and have the chromatic dispersion problem of lens.

Formerly technology [2] is (referring to D.H.Reitze, A.M.Weiner, and D.E.Leaird, " Shapingof wide bandwidth 20 femtosecond optical pulses; " Appl.Phys.Lett.61,1260-1262 (1992)) the middle dispersionless transmission-type pulse shaping device of describing.Replace the lens of usefulness formerly can avoid the chromatic dispersion problem of lens with reflective spherical mirror in this device, obtain dispersionless process.But the influence of its antijamming capability such as airflow is inevitable.

Technology [3] (M.C.Nuss, M.Li, T.H.Chiu formerly, A.M.Weiner, and A.Partovi, " Time-to-space mapping of femtosecond pulses; " what describe Opt.Lett.19,664-666 (1994)) is holographic femtosecond pulse shaping technique.Template is formed by two beam interferences, is read by a branch of light wherein again.It has the chromatic dispersion problem of poor anti jamming capability and lens equally, and template is fixed simultaneously, can not realize dynamic shaping.Whole device is compact inadequately, and volume is bigger.

Summary of the invention

The utility model is in order to overcome the deficiency of above-mentioned technology formerly, a kind of femtosecond pulse shaping device by dynamic space-time transformation to be provided, and it is little that it should have a volume, compact conformation, the characteristics that antijamming capability is strong.

The technical scheme that the utility model solves is as follows:

A kind of femtosecond pulse shaping device by dynamic space-time transformation, it is characterized in that its formation comprises: be embedded with first reflective lens and second reflective lens at described first optical flat in the framework that constitutes mutually by first optical flat and second optical flat, be embedded with first high dencity grating, reflective template and second high dencity grating on described second optical flat successively equally spacedly, the discrete interlacedly setting of the element that is embedded on the element that described first optical flat is embedded and second optical flat is also satisfied the following relationship formula:

f＝hcosθ

C＝2fsinθ

In the formula: f is the focal length of first reflective lens and second reflective lens; H is the distance between first optical flat and second optical flat; C is the center distance of each element; θ is the incident angle of femtosecond pulse.

Described first reflective lens and second reflective lens are that eccentric ratio e is the oval grating of constant, and e=sin θ.It is the reflective non-spherical lens that is suitable for oblique incidence.

Described template is reflective phase board, deformable mirror, LCD space light modulator, the micromechanics little tilting mirror of numeral or reflective dynamic space photomodulator.

The utility model is compared the advantage that has with technology formerly:

Compare with technology formerly,, each element is embedded as a whole, so more compact structure owing to adopt the device of slab construction; General apparatus for shaping length needs 40 centimetres at least, and 20 centimetres of the longest needs of the present utility model are so volume is less; Because it is in the box of fixing almost sealing, so stability preferably that has with respect to machinery and thermal effect, be not subject to extraneous in the propagation as interference such as air draughts, and the lens of using in the utility model device are reflective lens, incident wave is only focused on by reflection, and this is higher so efficient is corresponding.

Description of drawings

Fig. 1 is the sectional view of the utility model femtosecond pulse shaping device by dynamic space-time transformation structure.

Fig. 2 is the planimetric map of reflective aspheric surface flat-plate lens 2,

Fig. 3 is the sectional view of the reflective aspheric surface flat-plate lens 2 of Fig. 2 along the y axle.

Embodiment

The utility model is described in further detail below in conjunction with embodiment and accompanying drawing.

See also Fig. 1 earlier, Fig. 1 is the sectional view of the utility model femtosecond pulse shaping device by dynamic space-time transformation structure.There is figure as seen, its formation of the utility model femtosecond pulse shaping device by dynamic space-time transformation comprises: be embedded with first reflective lens 2 and second reflective lens 3 at described first optical flat 11 in the framework that is made of mutually first optical flat 11 and second optical flat 12, on described second optical flat 12, be embedded with first high dencity grating 5 successively equally spacedly, the reflective template 6 and second high dencity grating 7, the discrete interlacedly setting of element that is embedded on the element that described first optical flat 11 is embedded and second optical flat 12 is also satisfied the following relationship formula:

f＝hcosθ

C＝2fsinθ

In the formula: f is the focal length of first reflective lens 2 and second reflective lens 3;

H is the distance between first optical flat 11 and second optical flat 12;

C is the center distance of each element;

θ is the incident angle of femtosecond pulse.

Described first reflective lens 2 and second reflective lens 3 are that eccentric ratio e is the oval grating of constant, and e=sin θ.

Basic foundation of the present utility model is as follows:

Light signal is propagated to another element along folding path from an element at dielectric surface.In fact, this device is the shaping pulse system of a 4f space-time transformation.

Principle of the present utility model mainly is to be based upon on the constant wave filter of linearity, time.Lf can also can be described at frequency domain at time-domain description.In time domain, wave filter can be represented its characteristic with impulse response function h (t), the output e of wave filter _Out(t) can be by input pulse e _In(t) and the Using Convolution of h (t):

e _out(t)＝e _in(t)*h(t)＝∫dt′e _in(t′)h(t-t′) (1)

If input pulse is the δ function, then output only is h (t).Therefore the problem for the specific output pulse shape of the input pulse generation of enough weak points is equivalent to make a linear filter problem that includes desirable impulse response.

At frequency domain, wave filter can be represented its characteristic by frequency response H (ω), the output E of linear filter _Out(ω) be input signal E _In(ω) and frequency response H (ω) long-pending, promptly

E _out(ω)＝E _in(ω)H(ω) (2)

Here e _In(t), e _Out(t), h (t) and E _In(ω), E _Out(ω), H (ω) is respectively that Fourier transform is right, promptly

H(ω)＝∫dth(t)e ^-iωt (3)

$h\left(t\right)=\frac{1}{2\mathrm{\π}}\∫\mathrm{d\ωH}\left(\mathrm{\ω}\right)e^{\mathrm{i\ωt}}---\left(4\right)$

For the input pulse of a δ function, input spectrum E _InBe constant (ω), output spectrum E _Out(ω) equal the frequency response H (ω) of wave filter.Therefore, because Fourier transform relation, the generation of desirable output waveform can be by realizing that the wave filter that has desirable frequency response finishes, and the method for shaping pulse is all described by this frequency field viewpoint.It is to be noted that aberration is very big like this, and is no longer suitable for the lens in the Gaussian optics for being oblique incidence based on the lens spectrum in the femtosecond pulse shaping on the planar optics basis.Here we need redesign a kind of reflective lens that is suitable for planar optics.

The design concept of this reflective lens is as follows:

For the particular design of the reflective lens (claiming diffraction lens again) of planar optics collimation by Shiono and Ogawa (T.Shiono and H.Ogawa, " Diffraction-limited blazedreflection diffractive microlenses for oblique incidence fabricated byelectron-beam lithography; " Appl.Opt.30,3643 (1991)) describe.The structural drawing of the reflective lens that Fig. 2 and Fig. 3 be proposed reflective, be suitable for oblique incidence.8 is the reflection horizon among Fig. 3, and 9 is focus, the 10th, and the plane wave of incident.On X-Y plane, the phasic difference between the spherical wave that plane wave is propagated with the θ angle and assembled along being symmetrical in the optical axis of incident wave axle along the z axle is

Φ (x, y)=n ' k[(x ²+ y ²-2yfsin θ+f ²) ^1/2-f+ysin θ], (5) here

K=2 π/λ (6) λ is the wavelength of free space, n '=1st, and the refractive index of medium air, f is a focal length.Therefore, produce the oblique ejected wave of lens energy aberrationless ground focusing of Φ phasic difference at X-Y plane.The phasic difference of diffraction lens is Φ _F, be to divide with the integral multiple of mould 2 π by Φ:

Φ _F=Φ (x, y)-2m π (7) wherein m be integer, satisfy 0≤Φ _F≤ 2 π.Φ and Φ _FSymmetry on directions X, y _cThe center of axle expression equipotential phase, and Φ is antisymmetric curve on the Y direction, with Φ or | y| changes to a Y direction.This means on the Y-axis at Φ _FIn grating cycle of providing by the wavestrip cycle smaller in positive region.

Then consider the grating modulus of periodicity formula at lens wavestrip edge.From Φ _F=0 can obtain:

$\frac{x^2}{{(\mathrm{m\&lambda;}/n^{\&prime;}\cos \mathrm{\&theta;})}^2+2m{\mathrm{\&lambda;f}/n}^{\&prime;}}+\frac{{(y-y_{\mathrm{cm}})}^2{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="Y20052004034500111.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&theta;}}{{(\mathrm{m\&lambda;}/n^{\&prime;}\cos \mathrm{\&theta;})}^2+2\mathrm{m\&lambda;f}/n^{\&prime;}}=1---\left(8\right)$

Y wherein _Cm=-m λ tan θ/n ' cos θ (9)

Clearly (8) formula represent with (0, y _Cm) be the center, Y is the ellipse of main shaft.y _CmBe proportional to corresponding to the inferior integer m of the oval level in edge.The length of the length of main shaft and minor axis can be expressed as:

S _ym＝2/cosθ[(mλ/n′cosθ) ²+2mλf/n′] ^1/2， (10)

S _xm＝2[(mλ/n′cosθ) ²+2mλf/n′] ^1/2 (11)

If M is the maximal value of m, lens S _xAnd S _yRespectively by S _XMAnd S _YMProvide.M is provided by following formula:

$M=n^{\&prime;}{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="Y20052004034500111.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&theta;}/\mathrm{\&lambda;}[-f+{({\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="Y20052004034500111.png"\; state="\{\{state\}\}">f</figure-callout>}}^2+{\mathrm{<figure-callout\; id="2"\; label="S\; y"\; filenames="Y20052004034500111.png"\; state="\{\{state\}\}">S</figure-callout>}}_y^{}/4)}^{1/2}]---\left(12\right)$

M also demonstrates the sum of grating wavestrip.By formula (10) and (11) as can be known, main shaft with respect to minor axis ratio is:

S _ym/S _xm＝1/cosθ， (13)

Oval eccentricity is defined as according to oval size:

e＝[1-(S _xm/S _ym) ²] ^1/2＝sinθ (14)

Can find out that by (14) formula eccentricity does not rely on a grade inferior m, is only determined by incident angle θ.Therefore, the lens that are suitable for the diffraction limited of oblique incidence are that the oval grating of constant is formed by eccentric ratio e, and depart from-the Y direction their center, is proportional to a grade inferior m.

Calculate the thickness of lens below.The reflective lens that is suitable for oblique incidence is made up of oval grating.For simplifying the analysis, we analyze reflective cylindrical lens, consider the trend of lens in each zone, and the result can be used on the effective incident angle θ in the position of θ _EDemarcate.θ _FZone definitions at lens is:

θ _E＝θcosρ， (15)

Here ρ be and positive Y-axis between angle.For example, θ _E=θ on the positive Y-axis of lens, θ _E=-θ is on the negative Y-axis of lens.θ on X-axis _E=0.

L is the thickness (cylindrical lens) of lens, i.e. groove depth under the reflection horizon, and n is a refractive index of forming the material of the layer that glitters.Phase migration to thin lens is 2Lnkcos θ, and the maximum ga(u)ge of optimized diffraction efficiency is:

L _RIt is that 2 π obtain that=λ/2ncos θ, (16) following formula make each wavestrip edge phasic difference.Therefore the thickness profile of reflection diffraction lens can be written as:

L(x，y)＝L _R[1-Φ _F(x，y)/2π]。(17) can get from equation (17), maximum thickness is relevant with incident angle.For cylindrical lens, this result represents for the lens of oblique incidence an optimum thickness that depends on ρ is arranged.For example, on minor axis, optimum thickness is L _R=λ/2n, and the optimum thickness on main shaft is L _R=λ/2ncos θ.

Such lens do not have aberration, are oval, aspheric concave mirror structures.Because incident wave is only focused on by reflection, the diffraction efficiency of these lens is than higher.In like manner can design the size of lens as required, aperture angle etc.

The femtosecond pulse shaping device by dynamic space-time transformation structure based on planar optics of the present utility model as shown in Figure 1, an one embodiment is: the framework of the hollow medium of the 20cm * 5cm that selects for use * 5cm size.So intermediate medium is that refractive index is 1 air.Each interelement distance is that c equates in this device.Light source 1 is the titanium jewel femto-second laser of 800nm for centre wavelength.

The numerical aperture of lens is defined as during for oblique incidence:

$\mathrm{NA}=n{S}_x/2{({\mathrm{<figure-callout\; id="2"\; label="f"\; filenames="Y20052004034500111.png"\; state="\{\{state\}\}">f</figure-callout>}}^2+S_x^2/4)}^{1/2}---\left(18\right)$

The material of the lens that design with said method in the present embodiment is the glass of refractive index n=1.5, and maximum progression is 20, maximum ga(u)ge L _Max=0.304 μ m, when incident angle θ=28.69 °, focal length is f=h/cos θ=3.85cm, S _x=0.22cm.Relative aperture is f/S _x=17.5, numerical aperture NA=0.6355 (for refractive index n=1.5).Each interelement transversal distance c=2fsin θ=3.697cm.The cross distance of each element is the focal distance f=3.85cm of lens.

In the present embodiment, adopt centre wavelength be the titanium jewel femto-second laser of 800nm as light source, described first high dencity grating 5 and second high dencity grating 7 are the high dencity grating of 1200L/mm.Femtosecond laser 1 incides on first high dencity grating 5 with 28.69 °, and the radio-frequency component separately in the ultrashort pulse is by 5 angular dispersions of first high dencity grating, by Bragg diffraction matching condition d (sin θ _i+ sin θ _d)=λ can get angle of diffraction and also be 28.69 °.Diffraction light shines on first reflective lens 2, on the back focal plane of first reflective lens 2, carried out apart, converge on the reflective template 6 with identical angle of diffraction, again by reflective template 6 shaping back reflections on second reflective lens 3, converge to by second reflective lens 3 on second high dencity grating 7 of same 1200L/mm.At last by this second high dencity grating 7 with 28.69 ° of angle diffraction output beams 4.Second reflective lens 3 is reassembled into a simple light beam 4 of collision mutually to these all radio-frequency components that separate with second high dencity grating 7, so just obtained a shaping output pulse 4, the shape of this output pulse is provided by the pattern of spectrum face cope match-plate pattern 6.Wherein template 6 is a dynamically device such as distorting lens, LCD space light modulator, the little tilting mirror of micromechanics numeral, to realize dynamic time control conversion.

Practice shows that the utility model can carry out shaping to femtosecond pulse effectively, and simple and reliable for structure, compact volume is little, and antijamming capability is strong, can avoid the influence of factors such as air turbulence effectively, and cost is cheap.

Claims (3)

1, a kind of femtosecond pulse shaping device by dynamic space-time transformation, it is characterized in that its formation comprises: by being embedded with first reflective lens (2) and second reflective lens (3) at described first optical flat (11) in first optical flat (11) and the mutual framework that constitutes of second optical flat (12), on described second optical flat (12), be embedded with first high dencity grating (5) successively equally spacedly, reflective template (6) and second high dencity grating (7), the discrete interlacedly setting of element that is embedded on element that described first optical flat (11) is embedded and second optical flat (12) is also satisfied the following relationship formula:

f＝hcosθ

C＝2fsinθ

In the formula: f is the focal length of first reflective lens (2) and second reflective lens (3),

H is the distance between first optical flat (11) and second optical flat (12),

C is the center distance of each element,

θ is the incident angle of femtosecond pulse.

2, femtosecond pulse shaping device by dynamic space-time transformation according to claim 1 is characterized in that described first reflective lens (2) and second reflective lens (3) are that eccentric ratio e is the oval grating of constant, and e=sin θ.

3, femtosecond pulse shaping device by dynamic space-time transformation according to claim 1 is characterized in that described template (6) is reflective phase board, distorting lens, LCD space light modulator, the micromechanics little tilting mirror of numeral or reflective dynamic space photomodulator.

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