CN1766531A - Laser beam mass M2Factor real-time detector - Google Patents

Abstract

Laser beam quality M²The factor real-time detector comprises a focusing lens, a grating group, a light path regulator and a CCD which are sequentially arranged on the same light path, wherein the output end of the CCD is connected with a computer through a signal line, the focal length of the focusing lens is f, the diameter of the focusing lens is D, the grating group is a compact grating light splitting system which is formed by two gratings which are arranged in an orthogonal mode in a clinging mode, the grating light splitting system can divide a laser beam into a light beam group with 3 multiplied by 3 light beams with equal light intensity, the light path regulator comprises a lens array which is formed by 9 reflecting lenses, the 9 reflecting lenses of the lens array are provided with corresponding fine adjustment screws, and the distance from the zero-order diffraction light beam of the focusing lens to the receiving surface of the CCD through the grating group and the light path regulator is equal to the focal length of the focusing lens. The invention can conveniently measure the quality M of the laser beam²The factors are measured in real time, and the system structure is simple and compact.

Description

Laser beam quality M 2Factor real-time detector

Technical field

The present invention relates to detector, particularly a kind of laser beam quality M ²Factor real-time detector.

Background technology

Laser beam quality M ²The factor is to describe an important techniques index of laser characteristics, is directly connected to the application efficiency of laser instrument.M ²What the factor was described is the difference of actual light beam and desirable fundamental-mode gaussian beam, and it is defined as

$M^2=\frac{\mathrm{\π}}{4\mathrm{\λ}}{d}_w{\mathrm{\θ}}_f$

Wherein, d _wAnd θ _fWaist width and the far-field divergence angle of representing actual light beam respectively, 4 λ/π are the waist width of desirable Gaussian beam and the product of far-field divergence angle.Beam quality M ²The measurement way of the factor can be divided into two classes by principle: a class is the Fourier transform method, measuring distribution of light intensity on the beam waist cross section simultaneously distributes and PHASE DISTRIBUTION, obtain spatial frequency spectrum by Fourier transform again, because the measurement of PHASE DISTRIBUTION is relatively more difficult, the method few people adopt; Another kind of more commonly used, be based on the beamwidth mensuration of beam propagation equation, it also is the recommend method of present iso standard, utilize the beam quality of this class methods Laser Measurement bundle that a variety of means are arranged at present, but most methods all need to find exactly beam waist position, multimetering must be carried out, thereby real-time detection can not be realized.The method of utilizing eccentric Fresnel lens group is the measuring beam mass M in real time ²The factor, but its design is complicated, complex operation, the laser beam to different beam qualities need design different lens simultaneously, can not finish all measurements by single lens combination.

Summary of the invention

The object of the present invention is to provide a kind of laser beam quality M ²Factor real-time detector, it should be able to make things convenient in real time to laser beam quality M ²The factor is measured, and compact conformation.

Technical solution of the present invention is as follows:

A kind of laser beam quality M ²Factor real-time detector, constitute the condenser lens successively that comprises with light path, the grating group, the light path adjuster, CCD, the output terminal of this CCD links to each other with computing machine by signal wire, the focal length of described condenser lens is f, diameter is D, described grating group is by two grating splitting systems of being close to the compactness that the grating of placement forms with orthogonal manner, this grating splitting system can be divided into beam of laser the sets of beams of aplanatic 3 * 3 light beams, described light path adjuster comprises the lens array of being made up of 9 reflecting optics, 9 reflecting optics of this lens array all have corresponding micrometer adjusting screw, and the Zero-order diffractive light beam of described condenser lens is via the grating group, the light path adjuster equals the focal length of this condenser lens to the distance of the face of accepting of CCD again.

The size of the center eyeglass on the described light path adjuster is less than 100Z, and the size of outer eyeglass is greater than 200Z, Z=f in the formula ²λ/π D ², Z=f wherein ²λ/π D ², λ is an optical maser wavelength.

Described grating group is 200Z/ θ to the distance of light path adjuster, and θ is the drift angle of each light beam in the sets of beams in the formula.。

Described computing machine has video frequency collection card and tries to achieve laser beam quality M ²The data processor of the factor.

Advantage of the present invention is:

1, is applicable to the measurement of the laser beam of different wave length and beam quality.

2, easy to use flexibly, reduced the complicacy of practical operation.

3, compact conformation, volume is little, simple structure, easily manufactured.

Description of drawings

Fig. 1 is the structural representation of laser beam quality factor real-time detector of the present invention.

Fig. 2 is the structural representation of light path adjuster of the present invention.

Fig. 3 is data processor general flow chart in the real-time detector of the present invention.

Fig. 4 is in the real-time detector of the present invention, and CCD accepts the spot array instance graph on the face.

Embodiment

The invention will be further described below in conjunction with drawings and Examples, but should not limit protection scope of the present invention with this.

See also Fig. 1 earlier, Fig. 1 is the structural representation of laser beam quality factor real-time detector of the present invention.As seen from the figure, the formation of laser beam quality factor real-time detector of the present invention is: the working direction of the testing laser bundle 1 that sends at laser instrument 10 with light path the condenser lens 2 that sets gradually, grating group 3, light path adjuster 5, CCD7, the output terminal of this CCD7 links to each other with computing machine 12 by signal wire 11, the focal length of described condenser lens 2 is f, diameter is D, described grating group 3 is by two grating splitting systems of being close to the compactness that the grating of placement forms with orthogonal manner, this grating splitting system can be divided into beam of laser the sets of beams 4 of aplanatic 3 * 3 light beams, described light path adjuster 5 is by 9 reflecting optics 511,512 ... 519 lens arrays of forming 51, as shown in Figure 2.9 reflecting optics 511 of this lens array 51,512 ... 519 all have corresponding micrometer adjusting screw 52, each reflecting optics 511 of this light path adjuster 5,512 ... 519 all can be by the angle of each eyeglass in the micrometer adjusting screw 52 adjusting lens arrays 51, to adjust the position of corresponding light beam on the receiving plane 6 of CCD7 in the light beam 4, the hot spot that makes 9 light beams form on the face of accepting 6 of CCD7 neither overlaps each other, can be full of whole CCD again and accept face, in order to guarantee that the scope that 9 hot spots cover is within 2 times of Rayleigh length (Rayleigh range) of laser beam, realizes high-precision measurement.The Zero-order diffractive light beam of described condenser lens 2 equals the focal distance f of this condenser lens 2 to the distance of the face of accepting 6 of CCD7 again via grating group 3, light path adjuster 5.

The size of the center eyeglass 516 on the described light path adjuster 5 is less than 100Z, outer eyeglass 511,512 ... 515,517 ... 519 size is greater than 200Z, Z=f in the formula ²λ/π D ², Z=f wherein ²λ/π D ², λ is an optical maser wavelength.Described grating group 3 is 200Z/ θ to the distance of light path adjuster 5.Described computing machine 12 has video frequency collection card and calculates testing laser beam quality M ²The data processor of the factor.

The working condition of apparatus of the present invention is as follows:

The laser beam 1 that laser instrument 10 sends focuses on through condenser lens 2, the focal length of this condenser lens 2 is f, and the diameter of lens is D, by two grating groups 3 of being close to placement with orthogonal manner, this grating group 3 places on the fixture jointly, forms the grating splitting system of a compactness.This grating splitting system can be divided into beam of laser aplanatic 3 * 3 light beams, forms sets of beams 4, and the drift angle of each light beam is θ in the sets of beams 4.9 light beams in this sets of beams 4 are through each reflecting optics 511,512 of light path adjuster 5 (shown in Figure 2) ... 519 all can be by the angle of each eyeglass in the micrometer adjusting screw 52 adjusting lens arrays 51 separately, to adjust the position of corresponding light beam on the receiving plane 6 of CCD7 in the light beam 4, the hot spot that makes 9 light beams form on the face of accepting 6 of CCD7 neither overlaps each other, can be full of whole CCD again and accept face, realize high-precision measurement.The size of the eyeglass on the light path adjuster 5 is by formula Z=f ²λ/π D ²Decision, wherein λ is an optical maser wavelength, and the size of center eyeglass is less than 100Z, and the size of outer eyeglass is within 2 times of Rayleigh length (Rayleigh range) of laser beam in order to guarantee the scope that 9 hot spots cover greater than 200Z.Grating group 3 is about 200Z/ θ to the distance of light path adjuster 5.The Zero-order diffractive light beam via grating group 3 and light path adjuster 5, again to the distance of the face of accepting 6 of CCD7, equals the focal length of lens by lens 2.The signal that the face of accepting 6 of last CCD7 receives carries out data processing through signal wire 11 input computing machines 12.

The flow process of data processing is as shown in Figure 3:

Frame reads subroutine the data-switching that obtains via video frequency collection card is become to comprise the gray-scale map of 3 * 3 nine hot spots, as shown in Figure 4.The output light of a lot of laser instruments is not the circle symmetry, therefore need measure respectively mutually perpendicular both direction on the beam cross-section, establishes light beam and propagates along the z axle in the rectangular coordinate system, and xsect is positioned at the x-y plane.The subroutine of finding the solution first moment is carried out first moment to the gray-scale map of nine hot spots comprising each hot spot and is found the solution, and its physical significance is to find the solution the center of gravity of light distribution among the hot spot figure.Intensity distribution function first moment on beam cross-section x, the y direction is defined as herein

$\stackrel{\‾}{x}=\frac{\∫\∫\mathrm{xI}(x,y,z)\mathrm{dxdy}}{\∫\∫I(x,y,z)\mathrm{dxdy}}$

$\stackrel{\‾}{y}=\frac{\∫\∫\mathrm{yI}(x,y,z)\mathrm{dxdy}}{\∫\∫I(x,y,z)\mathrm{dxdy}}$ (2)

Wherein I (x, y z) be (x, y, the light intensity function value of z) locating, x is the first moment of normalization intensity distribution function on the beam cross-section x direction, y is the first moment of normalization intensity distribution function on the beam cross-section y direction.Therefore, by the calculating of asking the first moment subroutine can obtain the hot spot gray-scale map the light intensity center of gravity (x, y).At position z place, the second-order moments of the intensity distribution function on the beam cross-section x direction is

${\mathrm{\σ}}_x^2\left(z\right)=\frac{{\∫\∫(x-\stackrel{\‾}{x})}^{2}I(x,y,z)\mathrm{dxdy}}{\∫\∫I(x,y,z)\mathrm{dxdy}}$

${\mathrm{\σ}}_y^2\left(z\right)=\frac{\∫\∫{(y-\stackrel{\‾}{y})}^{2}I(x,y,z)\mathrm{dxdy}}{\∫\∫I(x,y,z)\mathrm{dxdy}}$ (3)

Wherein (x, y z) are (x, y, the light intensity function value of z) locating, σ to I _x ²(z) be the second moment of normalization intensity distribution function on the beam cross-section x direction, σ _y ²(z) be the second moment of normalization intensity distribution function on the beam cross-section y direction.And be expressed as based on the laser linewidth of light distribution second moment:

D _x(z)＝4σ _x(z)

D _y(z)＝4σ _y(z) (4)

D wherein _x(z) be hot spot beamwidth on the x direction, D _y(z) be hot spot beamwidth on the y direction.Therefore, ask the second moment subroutine by asking the resulting light intensity center of gravity of first moment subroutine can try to achieve the second moment of hot spot earlier, and then utilize formula (4) to try to achieve the beamwidth of each hot spot as parameter; Because the locational spot radius of each of laser beam is along with coordinate z expands by hyp rule, thus the curve fitting subroutine to this altogether nine beamwidths carry out match and find the solution, draw the hyperbolic curve interface of testing laser bundle, its formula is as follows:

$D_x^2=A_x+B_{x}z+C_x{z}^2$

$D_y^2=A_y+B_{y}z+C_y{z}^2---\left(5\right)$

Each coefficient by following formula can be obtained the far field beam angle of divergence, beam waist position and waist width by following formula:

$z_{0x}=-\frac{B_x}{2C_x},$ $z_{0y}=-\frac{B_y}{2C_y}$

$d_{\mathrm{\ωx}}=\sqrt{A_x-\frac{B_x}{2C_x}},$ $d_{\mathrm{\ωy}}=\sqrt{A_y-\frac{B_y}{2C_y}}$ (6)

Wherein, z _0x, z _0yRepresent the beam waist position on x, the y direction respectively, d _{ω x}, d _{ω y}Represent the beam waist size on x, the y direction respectively.Finally obtain the M of light beam to be measured by formula (1) ²The factor, wherein, correction factor records in advance, by the incident angle decision of every Shu Guang on the CCD test surface.Beam quality M ²The actual measurement speed of the factor depends primarily on the sampling rate of CCD camera and data collecting card, and what use in this detector is the data collecting card of 120 frame/seconds, so program finds the solution each frame spot array figure, at last with outcome record and show.

Laser beam for different wavelength of laser bundle and different beam qualities, only need to regulate light path adjuster (5), satisfying hot spot on the face of accepting (6) of CCD (7) distributes and neither overlaps each other, can be full of the requirement of the face of accepting (6) of whole CCD (7) again, can measure all laser beam.

Lift a practical measuring examples here:

As shown in Figure 1, the output light 1 of He-Ne laser instrument 10, wavelength 632.8nm focuses on through high-quality condenser lens 2, and this condenser lens is a biconvex lens, focal distance f=300mm, lens diameter D=25mm, laser beam 1 arrives grating group 3 through behind the condenser lens 2, grating group 3 is 50mm apart from condenser lens 2, and grating group 3 is 600mm by the line number ^-1Two etched gratings be close to quadrature and place, utilize (1,0,1) three order diffractions of grating group 3, laser beam 1 is divided into 3 * 3 sets of beams 4 of totally 9 light beams after through grating group 3.The array that light path adjuster 5 is made up of 9 reflecting optics constitutes, as shown in Figure 2,5 each reflecting optics 51 of this light path adjuster all can be by the angle of each eyeglass in the micrometer adjusting screw 52 adjusting lens arrays, to adjust the position of corresponding light beam on the receiving plane 6 of CCD7 in the light beam, the hot spot that makes 9 light beams form on the face of accepting 6 of CCD7 neither overlaps each other, can be full of whole CCD 7 again and accept face 6, realize high-precision measurement.Fig. 4 is for process is except that 3 * 3 Spot Moment systems of battle formations that obtain after making an uproar in the experiment, and from right to left, from top to bottom, the number consecutively of each hot spot is 1～9.

Because the output light of a lot of laser instruments is not the circle symmetry, therefore need be to measuring respectively on the mutually perpendicular both direction on the beam cross-section.If light beam is propagated along the z axle in the rectangular coordinate system, xsect is positioned at the x-y plane.

Sets of beams 4 projects CCD7 through light path adjusters 5 and accepts on the face 6, and there is angle in light beam with the normal of accepting face 6, in this example sets of beams 4 and accept between the normal of face 6 corner dimension as shown in Table 1:

Light beam number	1	2	3	4	5	6	7	8	9
										θ x(rad)	0.4388	0	-0.4388	0.3999	0	-0.3999	0.4388	0	-0.4388
θ y(rad)	0.4475	0.4033	0.4475	0	0	0	-0.4438	-0.4033	-0.4388

Table one

θ wherein _x, θ _yRepresent the radian value of angle on x, y component respectively, the light beam numbering is corresponding with the hot spot numbering on the CCD7.

Because the oblique incidence of light, when light was mapped on the CCD7 camera, hot spot was additionally amplified, consequent hot spot beamwidth magnification A _x, A _yWith inclination angle [theta] _x, θ _yBetween exist to close and to be

$A_x=\frac{1}{\cos {\mathrm{\θ}}_x}$

$A_y=\frac{1}{\cos {\mathrm{\θ}}_y}$ (7)

Inclination angle substitution formula (7) with every bundle incident light on the face of accepting 6 of CCD7 in the example obtains pairing magnification modified value as shown in Table 2

Hot spot number	1	2	3	4	5	6	7	8	9
										A x	1.1047	1	1.1047	1.0857	1	1.0857	1.1047	1	1.1047
A y	1.1092	1.0872	1.1092	1	1	1	1.1073	1.0872	1.1073

Table two

A wherein _x, A _yRepresent the magnification component of hot spot beamwidth on x, y direction respectively.For once measuring together, the magnification modified value is an invariant.

Utilize computer program that each hot spot subgraph among each frame spot array Fig. 4 is found the solution, obtain initial spot width, correspondence obtains revised spot size divided by the magnification modified value in the table two then, and the position z match in conjunction with each hot spot at last solves M ²The factor.Program to the sample data that a frame spot array figure wherein calculates is: on the x direction, waist width is 0.4256mm, and far-field divergence angle is 2.2mrad, $M_x^2=1.1622;$ On the y direction, waist width is 0.4763mm, and far-field divergence angle is 1.8mrad, $M_x^2=1.0641.$ The number of significant digit of above data is program and calculates gained.

Claims (4)

1, a kind of laser beam quality M ²Factor real-time detector, it is characterized in that it comprises the condenser lens (2) of same light path successively, grating group (3), light path adjuster (5), CCD (7), the output terminal of this CCD (7) links to each other with computing machine (12) by signal wire (11), the focal length of described condenser lens (2) is f, diameter is D, described grating group (3) is by two grating splitting systems of being close to the compactness that the grating of placement forms with orthogonal manner, this grating splitting system can be divided into beam of laser the sets of beams (4) of aplanatic 3 * 3 light beams, described light path adjuster (5) comprises by 9 reflecting optics (511,512 ... 519) lens array of Zu Chenging (51), 9 reflecting optics (511 of this lens array (51), 512 ... 519) corresponding micrometer adjusting screw (52) is all arranged, the Zero-order diffractive light beam of described condenser lens (2) is via grating group (3), light path adjuster (5) equals the focal length of this condenser lens (2) to the distance of the face of accepting (6) of CCD (7) again.

2, laser beam quality M according to claim 1 ²Factor real-time detector, the size that it is characterized in that the center eyeglass (516) on the described light path adjuster (5) be less than 100Z, the outer eyeglass (511,512 ... 515,517 ... 519) size is greater than 200Z, Z=f in the formula ²λ/π D ², Z=f wherein ²λ/π D ², λ is an optical maser wavelength.

3, laser beam quality M according to claim 1 ²Factor real-time detector is characterized in that described grating group (3) is 200Z/ θ to the distance of light path adjuster (5), and θ is the drift angle of each light beam in the sets of beams (4) in the formula.

4, laser beam quality M according to claim 1 ²Factor real-time detector is characterized in that described computing machine (12) is to have video frequency collection card and calculate laser beam quality M ²The computing machine of the data processor of the factor.

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