CN201035284Y - A Spatial Dispersion Compensation Device for Femtosecond Laser - Google Patents

Abstract

The utility model discloses a spatial dispersion compensation device for femtosecond laser, which comprises a prism, two parabolic mirrors and a plane reflection mirror. The opening directions of the two parabolic mirrors are opposite and placed coaxially. The apex of the prism is placed at the focal point of one parabolic mirror, and the prism can rotate around the focal point; the plane reflector is placed at the focal point of the other parabolic mirror and It can rotate around the focal point; the input and output beams are coaxial. The utility model can provide any size of spatial dispersion, is easy to adjust, and does not affect the time dispersion characteristic of the femtosecond laser. The utility model has a simple structure, is easy to adjust and use, and is suitable for the fields of femtosecond laser scanning, imaging, laser microprocessing and the like.

Description

A Spatial Dispersion Compensation Device for Femtosecond Laser

technical field

The utility model belongs to femtosecond laser modulation technology, in particular to a spatial dispersion compensation device for femtosecond laser, which is especially suitable for the fields of femtosecond laser scanning, imaging, laser microprocessing and the like.

Background technique

Using the angular dispersion properties of prisms to compensate the spatial dispersion of femtosecond lasers is a widely used technology, especially in laser scanning, imaging and laser microprocessing. A prism is a dispersive element that can provide any amount of angular dispersion. However, the existing spatial dispersion compensation schemes only compensate for a fixed amount of angular dispersion. To change the amount of angular dispersion compensation, the adjustment of the system is very complicated, and the temporal dispersion amount of the femtosecond laser will be changed.

U.S. Patent No. 6,804,000 B2 uses a prism 1 and two plane mirrors 2, 3 to form a spatial dispersion compensation module (as shown in Figure 1). This invention mainly compensates for a fixed angular dispersion. When it is necessary to change the prism provided When adjusting the amount of angular dispersion, the positions and angles of the plane mirrors 2 and 3 need to be adjusted at the same time, and the adjustment is very troublesome. This invention also introduces a certain amount of time dispersion while providing angular dispersion, resulting in changes in the femtosecond laser pulse width.

Contents of the invention

The purpose of the utility model is to provide a spatial dispersion compensation device for femtosecond laser, the device can easily adjust the spatial dispersion compensation amount, and will not introduce temporal dispersion.

The utility model provides a spatial dispersion compensation device for femtosecond laser, which comprises a prism, two parabolic mirrors and a plane reflector; the opening directions of the two parabolic mirrors are opposite and placed coaxially, Placed at the focal point of a parabolic mirror, the prism can rotate around the focal point; the plane reflector is placed at the focal point of another parabolic mirror and can rotate around the focal point; the input and output beams are coaxial. Among them, the relationship between the angle α between the optical axis of the prism and the parabolic mirror and the angular dispersion provided by it is:

$\frac{\mathrm{<span\; class="notranslate">\; D</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; dn</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; A</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="no"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">no</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}$

In the formula, D is the deflection angle of the outgoing light relative to the incident light, A is the vertex angle of the prism, n is the refractive index of the prism, and λ is the wavelength of the incident laser beam;

The corresponding relationship between the angle β between the plane reflector and the optical axis of the first and second parabolic mirrors and the prism deviation from the axial angle α:

$\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; .</span>$

The utility model can adjust the spatial dispersion compensation very conveniently. When the angular dispersion provided by the prism is changed, it only needs to simply rotate a plane mirror to make the light beam propagate along the original direction and provide the angular dispersion to the subsequent system for use. The utility model does not change the time dispersion characteristic of the femtosecond laser at all while providing the spatial dispersion amount of any size, and ensures the independence of the spatial dispersion compensation module. Because the utility model has a compact structure, is easy to adjust, and can realize the independent adjustment of the spatial dispersion amount without changing the time dispersion of the femtosecond laser, it is suitable for the fields of femtosecond laser scanning measurement and imaging, laser micromachining, etc., especially In systems that require different amounts of spatial dispersion compensation.

Description of drawings

Fig. 1 is a schematic diagram of a spatial dispersion compensation device composed of a prism and two plane mirrors;

Fig. 2 is a schematic diagram of the utility model device principle;

Fig. 3 is the schematic diagram of the rotation mode of prism and plane reflector;

Fig. 4 is a schematic diagram of a compact design scheme of the utility model device;

Figure 5 is a schematic diagram of deflection and spatial dispersion of a femtosecond pulsed laser by a prism;

Fig. 6 is the relationship diagram of the spatial dispersion amount and light incident angle of equilateral triangular prism;

Fig. 7 is a relationship diagram between the prism's off-axis angle α and the amount of angular dispersion it provides;

FIG. 8 is a graph showing the relationship between the rotation angle β of the plane mirror and the off-axis angle α of the prism.

Detailed ways

Below in conjunction with accompanying drawing and example the utility model is described in further detail.

In order to realize the independent adjustment of spatial dispersion, the device of the utility model includes two parabolic mirrors, a prism and a plane reflector. As shown in Figure 2, the first and second parabolic mirrors 5 and 6 opening directions are opposite and coaxially placed, and the prism 4 apex is placed at the focal point of the first parabolic mirror 5, and the prism can be in the form of the first parabolic The focus of the mirror 5 is an axis of rotation; the plane mirror 7 is placed at the focus of the second parabolic mirror 6 and can rotate around the focus. The incident femtosecond laser is incident along the axial direction, and the spectral components of different wavelengths exit at different angles after passing through the prism, and the deflection angle of the spectral components with longer wavelengths is smaller. The beam emitted from the focal point of the parabola exits parallel to the axis of the parabola, so the femtosecond laser beam with angular dispersion emitted from the vertex of the prism 4 exits in parallel after being reflected by the first parabolic mirror 5 . Because the parabolic mirrors 5 and 6 are relatively placed, the parallel light beams converge at the focal point of the second parabolic mirror 6 after passing through the second parabolic mirror 6, and the reflections of the light beams on the parabolic mirrors 5 and 6 are completely symmetrical , at this time, the light beam with angular dispersion characteristic emitted from the prism apex is completely mapped to the focal point of the second parabolic mirror 6 . A plane mirror 7 is placed at the focal point of the second parabolic mirror 6, and the direction of the mirror 7 is adjusted so that the femtosecond laser is output along the axial direction.

The first and second parabolic mirrors 5 and 6 completely map the apex of the prism to another point in space, that is, the focal point of the parabolic mirror 6, and the light beam with angular dispersion can be completely regarded as from this point dispatched. Therefore, compared with the spatial dispersion compensation module shown in FIG. 1 , when the utility model provides any angular dispersion value, the angular dispersion length is calculated from the focal point of the second parabolic mirror 6 . The advantage of this design is that the measurement of the angular dispersion length is very convenient, and when a smaller angular dispersion length is required, there is no need to worry that it cannot be obtained because it is too close to the prism.

The specific rotation mode of the prism 4 and the plane reflector 7 in the utility model is shown in Fig. 3 . The prism 4, the parabolic mirrors 5 and 6, the plane reflector 7 and the one-dimensional rotating table 8 and 9 are all placed on the plane M. The opening directions of the parabolic mirrors 5 and 6 are opposite and placed coaxially. The focus of the parabolic mirror 5 is O1, and the line L1 passing through the point O1 is perpendicular to the M plane; the focus of the parabolic mirror 6 is O2, and the line L2 passing through the point O2 is perpendicular to the M plane. The rotation center of the one-dimensional rotating table 8 is placed at point O1, and can rotate around the line L1; the rotation center of the one-dimensional rotating table 9 is placed at the point O2, and can rotate around the line L2. The apex of the prism 4 is placed in the center of the one-dimensional rotating table 8, and can rotate around L1 driven by the one-dimensional rotating table 8; the plane mirror 7 is placed in the center of the one-dimensional rotating table 9, and can rotate around L2 driven by the one-dimensional rotating table 9 .

In the utility model, parallel beams are formed between the first and second parabolic mirrors 5 and 6, and the distance between them can be adjusted arbitrarily without affecting system performance. A compact design scheme of the present utility model is shown in FIG. 4 , the first parabolic mirror 5 and the plane reflector 7 are located on the same side, and the second parabolic mirror 6 and the prism 4 are located on the same side. This solution requires very little space.

Prism 4 is a kind of angular dispersion element, which has deflection effect on incident light. As shown in Figure 5, light enters prism 4 at incident angle I ₁ , and the outgoing light has a certain deflection angle D relative to incident light. D can be expressed as for:

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

Where A is the vertex angle of the prism, λ is the wavelength of the incident laser beam, and n(λ) is the refractive index of the prism to the light wave with the wavelength λ.

The angular dispersion parameter of a prism is expressed as:

$\frac{\mathrm{<span\; class="notranslate">\; D</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; D</span>}}{\mathrm{<span\; class="notranslate">\; dn</span>}}\frac{\mathrm{<span\; class="notranslate">\; dn</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

$\frac{\mathrm{<span\; class="notranslate">\; D</span>}}{\mathrm{<span\; class="notranslate">\; dn</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; A</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="no"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">no</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; the\; s</span>}{\mathrm{<span\; class="notranslate">\; in</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; sin</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Where I ₁ is the angle at which the light beam is incident on the prism, A is the vertex angle of the prism, n is the refractive index of the prism, and dn/dλ is the first-order dispersion rate of the material.

For example, using a femtosecond laser with a wavelength of 800nm, a dispersive prism with a vertex angle of 60°, and the material is ZF ₄ heavy flint glass, and the refractive index is:

${\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; B</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="B"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">B</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="C"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">C</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="3"\; label="B"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">B</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

in

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 ,

Then when the wavelength is 800nm, dn/dλ=4.98×10 ^-5 nm ^-1 . The apex angle of the prism is A=60°, and the formula (2) and (3) are plotted to obtain the relationship diagram between the spatial dispersion provided by the prism and the incident light angle (see Figure 6).

The utility model can conveniently provide angular dispersion value of any size. Adjust the relationship between the angle α between the optical axis of the prism 4 and the parabolic mirror 5, 6 and the amount of angular dispersion it provides:

$\frac{\mathrm{<span\; class="notranslate">\; D</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; dn</span>}}{\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}}\frac{\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; A</span>}}{\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}\sqrt{{\mathrm{<span\; class="notranslate">\; no</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

FIG. 7 is a graph showing the relationship between the angle α (see FIG. 2 ) and the angular dispersion provided by the prism.

According to the required angular dispersion value, it is enough to rotate the prism away from the axial angle α to a specified position, and then rotate the plane mirror correspondingly by the angle β so that the beam is output along the axial direction. The corresponding relationship between the angle β between the optical axis of the plane reflector 7 and the parabolic mirror 5, 6 and the prism deviation from the axial angle α:

$\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; sin</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; no</span>}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="cos"\; filenames="Y20072008417500081.png"\; state="\{\{state\}\}">cos</figure-callout></span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; /</span>\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; A</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; A</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&alpha;</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

The corresponding relationship between the rotation angle β of the plane mirror and the off-axis angle α of the prism is shown in Fig. 8 .

When a larger or smaller angular dispersion value is required, it can be obtained by selecting prisms with different vertex angles or different materials.

Another very important feature of the utility model is that the utility model can completely independently adjust the amount of spatial dispersion without affecting the temporal dispersion characteristics of the femtosecond laser. The distance from any point on the parabola to its focus and directrix is equal, and the rays emitted by the focus are parallel to the axis of the parabola, so the distances from any point of light emitted by the focus to the plane perpendicular to the axis are equal. That is to say, the optical paths of the light emitted from different angles are equal, and no time dispersion will be introduced. This feature enables the spatial dispersion to be adjusted completely independently of the temporal dispersion.

Claims (2)

1. A spatial dispersion compensation device for femtosecond laser is characterized in that: the device comprises a prism (4), a first parabolic mirror (5), a second parabolic mirror (6) and a plane reflector (7); the opening directions of the first parabolic cylindrical mirror (5) and the second parabolic cylindrical mirror (6) are opposite and coaxially arranged, the vertex of the prism (4) is positioned at the focus of the first parabolic cylindrical mirror (5), the plane reflecting mirror (7) is positioned at the focus of the second parabolic cylindrical mirror (6), the prism (4) is movably installed by taking the focus of the first parabolic cylindrical mirror (5) as an axis, and the plane reflecting mirror (7) is movably installed by taking the focus of the second parabolic cylindrical mirror (6) as an axis;

the relation between the included angle alpha between the prism (4) and the optical axes of the parabolic mirrors (5 and 6) and the angular dispersion provided by the included angle alpha is as follows:

in the formula, D is a deflection angle of emergent light relative to incident light, A is a vertex angle of a prism, n is a refractive index of the prism, and lambda is the wavelength of an incident laser beam;

the corresponding relation between the included angle beta between the plane reflector (7) and the optical axes of the first parabolic mirror (5) and the second parabolic mirror (6) and the off-axis angle alpha of the prism is as follows:

2. the apparatus of claim 1, wherein: the first parabolic mirror (5) and the plane reflector (7) are positioned on the same side, and the second parabolic mirror (6) and the prism (4) are positioned on the same side.

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