CN100485509C - Compensating device for special dispersion in use for femtosecond laser - Google Patents

Abstract

A space dispersion compensation device of femto-second laser is prepared for laying opening direction of two parabolic mirror coaxially in opposite mode, setting top point of prism on focus point of one parabolic mirror, enabling prism to rotate by using focus point as axle, laying planar reflector at focus point of another parabolic mirror, enabling said reflector to rotate by using focus point as axle and making I/O light beam be at the same axle.

Description

A kind of spatial dispersion compensation system that is used for femtosecond laser

Technical field

The invention belongs to the femtosecond laser modulation technique, be specifically related to a kind of spatial dispersion compensation system that is used for femtosecond laser, it is particularly useful for femtosecond laser scanning, imaging and laser micro-processing and other fields.

Background technology

It is a kind of technology of widespread use that the angular dispersion characteristic of utilizing prism is carried out the spatial dispersion compensation to femtosecond laser, is particularly useful for aspects such as laser scanning, imaging and Laser Micro-Machining.Prism is a kind of dispersion element that any angular dispersion amount can be provided.But existing spatial dispersion compensation scheme only compensates at a fixing angular dispersion amount, wants to change the angular dispersion compensation rate, and the adjusting of system is very complicated, and can change the time dispersive amount of femtosecond laser.

U.S. Patent No. 6,804, use a prism 1 and two plane mirrors 2,3 to form spatial dispersion compensating module (as Fig. 1) among the 000B2, this invention is primarily aimed at a fixing angular dispersion amount and compensates, when needs change the angular dispersion amount that prism provides, need regulate the position and the angle of plane mirror 2 and 3 simultaneously, regulate very trouble.This invention also can be introduced a certain amount of time dispersive when angular dispersion is provided, cause the femtosecond laser pulsewidth to change.

Summary of the invention

The object of the present invention is to provide a kind of spatial dispersion compensation system that is used for femtosecond laser, this device can be regulated the spatial dispersion compensation rate easily, and can not introduce time dispersive.

The invention provides a kind of spatial dispersion compensation system that is used for femtosecond laser, comprise a prism, two parabolic mirrors and a plane mirror; Two relative and coaxial placements of parabolic mirror opening direction, prism apex is positioned over the focus place of a parabolic mirror, and prism can be the axle rotation with the focus; Plane mirror is positioned over the focus place of another parabolic mirror and can is the axle rotation with the focus; The input and output light beam is coaxial.Wherein, the angle of establishing the optical axis of prism and parabolic mirror is α, and angular dispersion amount that prism provides and the relational expression of angle α are:

$\frac{\mathrm{dD}}{\mathrm{d\&lambda;}}=\frac{\mathrm{dn}}{\mathrm{d\&lambda;}}\frac{n\sin A}{\sqrt{1-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">n</figure-callout>}}^2{\sin }^{2}A-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}\cos 2A+\sin 2A\cos \mathrm{\&alpha;}\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}}}\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}}}$

In the formula, D is the deflection angle of emergent light with respect to incident light, and A is the drift angle of prism, and n is the prismatic refraction rate, and λ is the wavelength of incoming laser beam;

The angle β of the optical axis of plane mirror and first, second parabolic mirror and the corresponding relation formula of angle α:

$\mathrm{\&beta;}=\frac{1}{2}(\frac{\mathrm{\&pi;}}{2}-\mathrm{\&alpha;}-A+{\sin }^{-1}[{(n{\left(\mathrm{\&lambda;}\right)}^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;})}^{1/2}\sin A-\cos A\cos \mathrm{\&alpha;}]).$

The present invention can regulate the spatial dispersion compensation rate easily, when the angular dispersion amount that prism provides changes, only need rotate a level crossing simply and just can make light beam offer the follow-up system use along former direction propagation and with this angular dispersion.The present invention does not change the time dispersive characteristic of femtosecond laser fully when the spatial dispersion amount of any size is provided, guaranteed the independence of spatial dispersion compensating module.Because compact conformation of the present invention, be easy to regulate, and implementation space dispersion measure ground independent regulation under the femtosecond laser time dispersive ground situation can not changed, therefore be applicable to femtosecond laser scanning survey and imaging, laser micro-processing and other fields, being specially adapted to needs in the system of different spaces chromatic dispersion compensation quantity.

Description of drawings

Fig. 1 is a prism and two spatial dispersion compensation system synoptic diagram that plane mirror constitutes;

Fig. 2 is apparatus of the present invention principle schematic;

Fig. 3 is prism and plane mirror rotation mode synoptic diagram;

Fig. 4 is a kind of compact design synoptic diagram of apparatus of the present invention;

Fig. 5 is deflection and the spatial dispersion synoptic diagram of prism to femtosecond pulse;

Fig. 6 is the spatial dispersion amount of equilateral triangle prism and the graph of a relation of angle of light;

The graph of a relation of the angular dispersion amount that Fig. 7 provides to angle [alpha] and prism for the prism off-axis;

Fig. 8 is level crossing rotation angle β and the prism off-axis corresponding relation curve to angle [alpha].

Embodiment

The present invention is further detailed explanation below in conjunction with accompanying drawing and example.

For the independent regulation of implementation space dispersion measure, apparatus of the present invention comprise two parabolic mirrors, a prism and a plane mirror.As shown in Figure 2, and the coaxial placement relative of first, second parabolic mirror 5 with 6 opening directions, prism 4 summits place the focus place of first parabolic mirror 5, and prism can be the axle rotation with the focus of first parabolic mirror 5; Plane mirror 7 is positioned over the focus place of second parabolic mirror 6 and can rotates around focus.The incident in axial direction of incident femtosecond laser, the spectral components by different wave length behind the prism is with the different angles outgoing, and the wavelength angle of long spectral component deflection is less.The parallel beam that sends from the para-curve focus is in parabolical axis outgoing, therefore by the femtosecond laser beam with angular dispersion amount of prism 4 drift angle outgoing through the 5 reflection parallel outgoing in back of first parabolic mirror.Because parabolic mirror 5 and 6 is staggered relatively, parallel beam acts on post-concentrations in the focus of second parabolic mirror 6 through second parabolic mirror 6, the reflection case of light beam is symmetrical fully on parabolic mirror 5 and 6, and the light beam with angular dispersion characteristic that emitted by prism vertex angle this moment has been mapped completely to the focus place of second parabolic mirror 6.Plane mirror 7 is placed at focus place at second parabolic mirror 6, and the direction of accommodation reflex mirror 7 is in axial direction exported femtosecond laser and got final product.

First, second parabolic mirror 5 and 6 summits with prism are mapped completely to another point in the space, and promptly on the focus of parabolic mirror 6, and light beam with angular dispersion amount can be regarded as fully and sends from this point.Therefore with respect to spatial dispersion compensating module shown in Figure 1, the present invention is when providing the angular dispersion value of any size, and angular dispersion length all is to be counted by the focus place of second parabolic mirror 6.The benefit of this design is that the angular dispersion measurement of length is very convenient, and does not worry when needing less angular dispersion length because too closely be blocked and can't obtain by prism.

The concrete rotation mode of prism 4 and plane mirror 7 is seen Fig. 3 among the present invention.Prism 4, parabolic mirror 5,6, plane mirror 7, one dimension universal stage 8,9 all is positioned on the M of plane.Parabolic mirror 5 and coaxial placement relative with 6 opening directions.The focus of parabolic mirror 5 is O1, and line L1 crosses the O1 point perpendicular to the M plane; The focus of parabolic mirror 6 is O2, and line L2 crosses the O2 point perpendicular to the M plane.One dimension universal stage 8 rotation centers place the O1 point, the L1 that can wind the line rotation; One dimension universal stage 9 rotation centers place the O2 point, the L2 that can wind the line rotation.Prism 4 summits are positioned over one dimension universal stage 8 centers, can be around the L1 rotation under one dimension universal stage 8 drives; Plane mirror 7 is positioned over one dimension universal stage 9 centers, can be around the L2 rotation under one dimension universal stage 9 drives.

Be parallel beam between first, second parabolic mirror 5 and 6 among the present invention, the distance between the two can be regulated arbitrarily, can not influence system performance.A kind of compact design of the present invention as shown in Figure 4, first parabolic mirror 5 and plane mirror 7 are positioned at the same side, second parabolic mirror 6 and prism 4 are positioned at the same side.The required space of this scheme is very little.

Prism 4 is a kind of angular dispersion elements, and incident light is had the effect of deviation, and as shown in Figure 5, light is with incident angle I ₁Enter prism 4, emergent light has certain deflection angle D with respect to incident light, and D can be expressed as:

D＝I ₁-A+sin ^-1[(n(λ) ²-sin ²I ₁) ^1/2sin?A-cos?A?sin?I ₁] (1)

Wherein A is the drift angle of prism, and λ is the wavelength of incoming laser beam, and n (λ) is the refractive index of the light wave of λ to wavelength for prism.

The angular dispersion parametric representation of prism is:

$\frac{\mathrm{dD}}{\mathrm{d\&lambda;}}=\frac{\mathrm{dD}}{\mathrm{dn}}\frac{\mathrm{dn}}{\mathrm{d\&lambda;}}---\left(2\right)$

$\frac{\mathrm{dD}}{\mathrm{dn}}=\frac{n\sin A}{\sqrt{1-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">n</figure-callout>}}^2{\sin }^{2}A-{\sin }^2{I}_1\cos 2A+\sin 2A{\sin I}_1\sqrt{n^2-{\sin }^2{I}_1}}\sqrt{n^2-{\sin }^2{I}_1}}---\left(3\right)$

I wherein ₁For light beam incides the angle of prism, A is a prism vertex angle, and n is the prismatic refraction rate, and dn/d λ is the 1st order chromatic dispersion rate of material.

For example, use the femtosecond laser of wavelength as 800nm, drift angle is 60 ° a dispersing prism, and material is ZF ₄Dense flint glass, refractive index is:

$n^2\left(\mathrm{\&lambda;}\right)=1+\frac{B_1{\mathrm{\&lambda;}}^2}{{\mathrm{\&lambda;}}^2-C_1}+\frac{{\mathrm{<figure-callout\; id="2"\; label="B"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">B</figure-callout>}}_2{\mathrm{\&lambda;}}^2}{{\mathrm{\&lambda;}}^2-{\mathrm{<figure-callout\; id="2"\; label="C"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">C</figure-callout>}}_2}+\frac{{\mathrm{<figure-callout\; id="3"\; label="B"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">B</figure-callout>}}_3{\mathrm{\&lambda;}}^2}{{\mathrm{\&lambda;}}^2-C_3}---\left(4\right)$

Wherein

B ₁＝1.61625977，

B ₂＝2.59229334×10 ^-1，

B ₃＝1.07762317，

C ₁＝1.27534559×10 ^-2，

C ₂＝5.81983954×10 ^-2，

C ₃＝1.16607680×10 ²，

When then wavelength is 800nm, dn/d λ=4.98 * 10 ^-5Nm ^-1Prism vertex angle A=60 °,, obtain the spatial dispersion amount that prism provides and the graph of a relation (see figure 6) of incident angle of light by formula (2), (3) mapping.

The present invention can provide the angular dispersion value of any size very easily.Adjust prism 4 and the angle α of the optical axis of parabolic mirror 5,6 and the relational expression of the angular dispersion amount that prism 4 provides:

$\frac{\mathrm{dD}}{\mathrm{d\&lambda;}}=\frac{\mathrm{dn}}{\mathrm{d\&lambda;}}\frac{n\sin A}{\sqrt{1-{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">n</figure-callout>}}^2{\sin }^{2}A-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}\cos 2A+\sin 2A\cos \mathrm{\&alpha;}\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}}}\sqrt{n^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;}}}---\left(5\right)$

The graph of a relation of the angular dispersion amount that Fig. 7 provides with it to the angle [alpha] (see figure 2) for the prism off-axis.

According to required angular dispersion value, the rotating prism off-axis gets final product to assigned address to angle [alpha], and the angle beta of corresponding rotating mirror makes light beam export along axis direction then.The angle β of plane mirror 7 and the optical axis of parabolic mirror 5,6 and prism off-axis are to the corresponding relation formula of angle [alpha]:

$\mathrm{\&beta;}=\frac{1}{2}(\frac{\mathrm{\&pi;}}{2}-\mathrm{\&alpha;}-A+{\sin }^{-1}[{(n{\left(\mathrm{\&lambda;}\right)}^2-{\mathrm{<figure-callout\; id="2"\; label="cos"\; filenames="C200710051249E00081.png"\; state="\{\{state\}\}">cos</figure-callout>}}^2\mathrm{\&alpha;})}^{1/2}\sin A-\cos A\cos \mathrm{\&alpha;}])---\left(6\right)$

Level crossing rotation angle β and prism off-axis are seen Fig. 8 to the corresponding relation of angle [alpha].

The angular dispersion value greater or lesser when needs is to obtain by the prism of selecting different drift angles or different materials for use.

Another very important feature of the present invention is, the present invention can regulate the spatial dispersion amount fully independently and can not influence the time dispersive characteristic of femtosecond laser.On the para-curve arbitrarily some the distance to its focus and directrix equate that and the light that focus is sent is parallel to the outgoing of para-curve axis, therefore the light at any angle that is sent by focus all equates to the plan range perpendicular to axis.The light path that is the light process of different angles emission all equates, can not introduce time dispersive.This feature can guarantee that spatial dispersion is totally independent of time dispersive and regulates.

Claims (2)

1, a kind of spatial dispersion compensation system that is used for femtosecond laser is characterized in that: this device comprises prism (4), first, second parabolic mirror (5,6) and plane mirror (7); Relative and the coaxial placement of opening direction of first, second parabolic mirror (5,6), the summit of prism (4) is positioned at the focus place of first parabolic mirror (5), plane mirror (7) is positioned at the focus place of second parabolic mirror (6), prism (4) serves as the movable installation of axle with first parabolic mirror (5) focus, and plane mirror (7) serves as that the axle activity is installed with second parabolic mirror (6) focus;

If prism (4) is α with the angle of the optical axis of parabolic mirror (5,6), angular dispersion amount that prism (4) provides and the relational expression of angle α are:

$\frac{\mathrm{dD}}{\mathrm{d\&lambda;}}=\frac{\mathrm{dn}}{\mathrm{d\&lambda;}}\frac{n\sin A}{\sqrt{1-n^2{\sin }^{2}A-{\cos }^2\mathrm{\&alpha;}\cos 2A+\sin 2A\cos \mathrm{\&alpha;}\sqrt{n^2-{\cos }^2\mathrm{\&alpha;}}}\sqrt{n^2-{\cos }^2\mathrm{\&alpha;}}}$

In the formula, D is the deflection angle of emergent light with respect to incident light, and A is the drift angle of prism, and n is the prismatic refraction rate, and λ is the wavelength of incoming laser beam;

Plane mirror (7) and the angle β of the optical axis of first, second parabolic mirror (5,6) and the corresponding relation formula of angle α:

$\mathrm{\&beta;}=\frac{1}{2}(\frac{\mathrm{\&pi;}}{2}-\mathrm{\&alpha;}-A+{\sin }^{-1}[{(n{\left(\mathrm{\&lambda;}\right)}^2-{\cos }^2\mathrm{\&alpha;})}^{1/2}\sin A-\cos A\cos \mathrm{\&alpha;}]).$

2, device according to claim 1 is characterized in that: first parabolic mirror (5) and plane mirror (7) are positioned at the same side, and second parabolic mirror (6) and prism (4) are positioned at the same side.

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