Rectangular flat-top beam shaper
The invention relates to a beam shaping system for providing a square or rectangular laser beam having a controlled intensity profile (uniform, super gaussian or cosine corrected for example) from an incident non-uniform beam intensity profile laser beam source (a Gaussian profile, a profile with astigmatism or any non-rotationally symmetric and non-uniform profile for example). The beam shaping system uses a first acylindrical lens for shaping the incident laser beam along a first axis and a second acylindrical lens orthogonally disposed relative to the first acylindrical lens and for shaping the incident beam along a second axis. The thereby provided light beam is a rectangular beam having a controlled intensity distribution in the far field.
1) Field of the Invention
The invention relates to laser beam shaping. More particularly, the invention relates to a beam shaping system for providing a square or rectangular laser beam with controlled intensity distribution.
2) Description of the Prior Art
While most laser sources and more precisely laser diodes sources produce an astigmatic beam of light having a substantially non-uniform intensity profile, numerous laser applications require a uniform illumination of a rectangular target. Such applications include biomedical applications, such as bio-detection, wherein, for example, a uniform illumination of a blood sample is required. Other applications include micromachining, microscopy, night vision and range finding of distant object.
Shaping a Gaussian-like laser beam using diffractive optics can provide a flat-top laser beam. One drawback of diffractive beam shapers is the wavelength dependency of their optical response. Another drawback is the low efficiency. Diffractive beam shapers are thus not suitable for wide spectrum or multiple wavelength illumination.
Refractive beam shaping techniques are efficient and provide low wavelength dependency. Conventional refractive techniques using aspherical lenses are suitable for generating a rotationally symmetrical flat-top beam from a rotationally symmetrical Gaussian input beam, but they are not adapted to shape an incident beam that is not rotationally symmetrical, like laser diode beams. Laser diodes have an elliptical intensity profile and suffer from astigmatism.
U.S. Pat. No. 4,826,299 to Powell, provides a lens for expanding a laser beam along one axis in order to provide a laser line of uniform intensity and width. Such a diverging lens has an acylindrical surface defined by a base curve in the shape of an angle with a rounded apex. The radius of curvature of the acylindrical surface is thus smaller in the center and increases smoothly towards both ends. As described in Powell, the acylindrical surface fits to a base curve defined in a Cartesian coordinate system (x,y,z) by the following equation:
wherein c is a curvature constant and Q is a conic constant, and wherein the product Q·c lies between 0.25 and 50 mm−1 and Q is less than −1. The second surface of the acylindrical lens may either be flat or cylindrical.
Acylindrical lenses have been created and used in the prior art for providing a laser line of uniform intensity. Laser lines are used, for example, for alignment purposes. The provided laser line should then be long and thin. Acylindrical lenses described in Powell provides a high divergence to provide the required line length.
SUMMARY OF THE INVENTIONThe invention relates to a beam shaping system for providing a square or rectangular laser beam having a controlled intensity profile (uniform, super gaussian or cosine corrected for example) from an incident non-uniform beam intensity profile laser beam source (a Gaussian profile, a profile with astigmatism or any non-rotationally symmetric and non-uniform profile). The beam shaping system uses a first acylindrical lens for shaping the incident laser beam along a first axis and a second acylindrical lens orthogonally disposed relative to the first acylindrical lens and for shaping the incident beam along a second axis. The thereby provided light beam is a rectangular beam having a controlled intensity distribution in the far field.
This light beam may be collimated using a collimating lens system for maintaining its intensity profile and size over a significant distance and maintain the controlled intensity profile (i.e. flat-top, cosine corrected, etc.).
Alternatively, the light beam may be focused for an efficient illumination of a typically submillimeter dimensioned target with a controlled intensity distribution at the Fourier plane of the focusing lens.
Furthermore, a diffractive or refractive beam splitter, a micro lenses array for example, may be used to generate a multiple rectangular flat-top pattern arranged in a row or in a two-dimensional array.
The present invention provides a way to independently shape the intensity profile of a light beam along two mutually independent and perpendicular axis. Suppose a normal Cartesian coordinates system X, Y and Z, Z being the propagation axis of the light beam. The present invention can be used to provide, for example, a laser beam with a flat top intensity distribution along the X axis and a cosine fourth corrected intensity distribution along the Y axis.
One aspect of the invention provides a beam shaping system for providing a shaped beam substantially rectangular and having a controlled intensity profile in a far field region, from an incident beam having a predetermined intensity profile along a first and a second axis. The beam shaping system comprising a first and a second acylindrical lens each having a primary acylindrical surface with a base curve. The first and the second acylindrical lenses are disposed substantially orthogonally to one another. The first acylindrical lens is for shaping the incident beam along the first axis and the second acylindrical lens is for shaping the incident beam along the second axis, thereby providing the substantially rectangular shaped beam. The base curve of the first lens fits a first equation in a Cartesian coordinate system (x,y), the first equation being
c1 being a first curvature constant, Q1 being a first conic constant and ƒ1(x) being a first correction function, the first correction function being continuous. The base curve of the second lens fits a second equation in another Cartesian coordinate system (x,y), the second equation being
c2 being a second curvature constant and Q2 being a second conic constant and f2(x) being a second correction function, the second correction function being continuous.
Another aspect of the invention provides a rectangular beam light source for providing a substantially rectangular shaped beam having a controlled intensity profile. The rectangular beam light source comprises an incident light source for providing an incident beam having a predetermined cross-sectional intensity profile along a first axis and a second axis, and a first and a second acylindrical lens each having a primary acylindrical surface with a base curve. The first and the second acylindrical lenses being disposed substantially orthogonally to one another. The first acylindrical lens is for shaping the incident beam along the first axis and the second acylindrical lens is for shaping the incident beam along the second axis, thereby providing the substantially rectangular shaped beam. The base curve of the first lens fits a first equation in a Cartesian coordinate system (x,y). The first equation being
c1 being a first curvature constant, Q1 being a first conic constant and ƒ1(x) being a first correction function, the first correction function being continuous. The base curve of the second lens fits a second equation in another Cartesian coordinate system (x,y). The second equation being
c2 being a second curvature constant and Q2 being a second conic constant and ƒ2(x) being a second correction function, the second correction function being continuous.
Yet another aspect of the invention provides a beam shaping system for providing a substantially rectangular beam having a controlled intensity profile from an incident beam having a predetermined intensity profile along a first axis and a second axis. The beam shaping system comprises a first and a second acylindrical lens each having a primary acylindrical surface having a base curve substantially in the shape of an angle with a rounded apex. The first lens is for shaping the incident beam along the first axis and the second lens is for shaping the incident beam along the second axis. The first and the second acylindrical lenses are disposed substantially orthogonally to one another, thereby providing the substantially rectangular shaped beam in a far field region.
Still another aspect of the invention provides a beam shaping system for providing a substantially rectangular beam having a controlled intensity profile from an incident beam having a predetermined intensity profile along a first axis and a second axis. The beam shaping system comprises a first and a second lens each having a primary acylindrical surface having a base curve with a radius of curvature that varies along the base curve. The radius of curvature is smaller in a center of the base curve and increases smoothly towards both of extremities of the base curve. The first lens and the second lens are disposed orthogonally to one another. The first lens is for shaping the incident beam along the first axis and the second lens is for shaping the incident beam along the second axis, thereby providing the substantially rectangular beam in a far field region.
In this specification, the term “acylindrical surface” is intended to mean a surface generated by a straight line which moves so that it always intersects a given plane curve called the base curve, and remains normal to the plane of the base curve, the base curve not consisting of a segment of a circle. A “cylindrical surface” is intended to mean a surface as defined above but the base curve consisting of a segment of a circle.
Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
DETAILED DESCRIPTIONNow referring to the drawings,
Since the beam shaping system 100 includes a different acylindrical shaping lens 112,114 for each orthogonal axis, the two orthogonal axes of the intensity profile are shaped independently.
In this embodiment, the incident laser beam A is an elliptical beam (see
The first and the second acylindrical lenses 112,114 are a positive lenses. The input surface 130 of the first acylindrical lens 112 is a convex acylindrical surface having a variable radius of curvature along the X-axis. The radius of curvature is smaller in the center of the surface and increases smoothly toward both X-extremities of the lens. It results in a greater divergence in the center of the lens which spreads out the beam in the center while containing it on the edges. The optical intensity is thus spatially redistributed and, when the curvature and the conic constants are suitably adapted to the incident beam intensity profile, it provides a controlled intensity distribution along the X-axis. The first acylindrical lens 112 expends the incident beam A along the X-axis to provide a diverging beam intensity profile along the X-axis. At the output of the first acylindrical lens 112, the beam intensity profile remains substantially unchanged along the Y-axis. The output surface 132 of the first acylindrical lens 112 is a planar surface. Alternatively, the output surface 132 could by a cylindrical surface diverging (or converging) along the X-axis for reducing or increasing the optical power of the lens.
The second acylindrical lens 114 is orthogonally disposed relative to the first acylindrical lens 112 in order to shape the incident beam intensity profile along the Y-axis. The second acylindrical lens 114 is similar to the first acylindrical lens 112 but the exact shape of the input 130,134 and output 132,136 surfaces of the first 112 and the second lens 114 are independently selected as a function of the X and Y-profiles of the incident beam A and of the required intensity profile of the resulting rectangular beam B.
The two acylindrical lenses 112,114 substantially fits to a base curve defined in a Cartesian coordinate system (x,y,z) by the following equation:
wherein c is a curvature constant and Q is a conic constant.
A continuous correction function ƒ(x) can be added, the correction function being defined by
wherein ai are small value constants for small added corrections.
Typically, the acylindrical lenses 112,114 are made of glass with an index of refraction lying between 1.4 and 2, but other transparent materials such as polycarbonate and silicones can alternatively be used. In this embodiment, the first acylindrical lens 112 is made of Bk7 glass by Schott™ and has a divergence of 5 mrad, a curvature constant c1 of 0.0118 and a conic constant Q1 of −25000, and the second acylindrical lens 114 is also made of Bk7 glass but has a divergence of 17 mrad, a curvature constant c2 of 0.0250 and a conic constant Q2 of −2500.
It is noted that, alternatively, the acylindrical surface of one or both acylindrical lenses could be a concave surface, thereby providing a negative lens instead of a positive lens. Furthermore, in the embodiment of
It is noted that, according to simulations, an appropriate absolute value of the product Q·c lies between about 0.25 and 1000 mm−1 and that Q should be less than −1.
It is noted that the incident laser beam source could alternatively be any mono-mode or multi-mode laser source with a wavelength from about 275 to 1600 μm, such as an argon laser, an excimer laser or a tunable laser source. In some specific applications, it is required that the target be quite uniformly illuminated with a laser light comprising two or more wavelength components. The two or more wavelength components can be provided by combining two or more laser source beams and providing the combined incident laser beam to the beam shaping system 100. The beam shaping system 100 having low wavelength dependency, it is adapted to similarly shape the various wavelength components.
The far field is defined as the distance where the intensity profile is completely formed, i.e. where z>>φ/FA, wherein φ is the input beam diameter and FA the fan angle. This condition needs to be respected in order to have a completely formed pattern. In this case, FA=5 mrad and φ=1.4 mm for the first acylindrical lens 112 and FA=17 mrad and φ=2.6 mm. Accordingly, the far field is defined by a distance z>>300 mm.
A principle of optics provides that the beam intensity profile in the far field of a system is imaged at the Fourier plane (focal plane) using the focusing lens system. Using a focusing lens system with a short focal length, it is possible to produce a small rectangularly shaped beam profile in the near field with a controlled intensity profile. The size of the focused pattern is given by bs=2*f*tan(FA/2), wherein f is the focal length of the focusing lens system and FA is the divergence of the acylindrical lenses 512,514.
The retro-focus focusing lens system 516 comprise a negative (diverging) lens device 518, e.g. a double concave lens with a focal length of −18 mm, and a positive (converging) lens device 520, e.g. a positive achromatic doublet with a focal length of 20 mm. The negative lens device 518 is located between the acylindrical lenses 512,514 and the positive lens device 520. The retro-focus focusing system 516 has a total focal length of 10 mm and a working distance of 30 mm. Used in pair with the pair of crossed acylindrical lenses 512,514 respectively having a divergence of 17 mrad and 34 mrad, a 200×500 μm rectangular flat-top profile is generated. The resulting flat-top profile is illustrated in
In order to provide low aspherical aberration, the positive lens device 520 is an achromatic doublet but any other positive lens device, such as a simple biconvex lens, could alternatively be used. Furthermore, it is contemplated that the negative lens device 518 and the positive lens device 520 may use aspheric lenses to eliminate spherical aberrations.
It is noted that, alternatively, a simple positive lens arrangement could be used as focusing lens means.
It is noted that, the equations defining the acylindrical surfaces are adapted to the incident beam intensity profile. In a case where two or more laser sources are combined up-front for providing more than one wavelength components, the intensity distribution should ideally be alike for each wavelength components on the incident beam. If it is not the case, the output intensity distribution corresponding to each wavelength component will differ and may deviate from the target profile. If the application does not tolerate relaxed uniformity requirements on one of the wavelength components, the beam intensity profiles of the sources may be matched up-front.
The point source D is longitudinally stretched because of the spherical aberration of the pair of crossed acylindrical lenses 812,814. However it is still possible to quasi collimate the rectangular beam provided at the output of the system 100.
Since the point sources of the two crossed acylindrical lenses 812,814 are located at different positions along the propagation distance, the system has astigmatism aberration. Thus, to eliminate the astigmatism and to further improve the collimation, two orthogonally independent collimating systems could alternatively be used.
Similarly, the focusing system of
The embodiments of the invention described above are intended to be exemplary only. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.
Claims
1. A beam shaping system for providing a shaped beam substantially rectangular and having a controlled intensity profile in a far field region, from an incident beam having a predetermined intensity profile along a first and a second axis, said beam shaping system comprising: y = c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2 + f 1 ( x ), y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 ) 1 / 2 + f 2 ( x ),
- a first and a second acylindrical lens each having a primary acylindrical surface with a base curve, said first and said second acylindrical lenses being disposed substantially orthogonally to one another, said first acylindrical lens for shaping said incident beam along said first axis and said second acylindrical lens for shaping said incident beam along said second axis, thereby providing said substantially rectangular shaped beam;
- wherein said base curve of said first lens fits a first equation in a Cartesian coordinate system (x,y), said first equation being
- c1 being a first curvature constant, Q1 being a first conic constant and ƒ1(x) being a first correction function, said first correction function being continuous; and
- wherein said base curve of said second lens fits a second equation in another Cartesian coordinate system (x,y), said second equation being
- c2 being a second curvature constant and Q2 being a second conic constant and ƒ2(x) being a second correction function, said second correction function being continuous.
2. The beam shaping system as claimed in claim 1, wherein a magnitude of the absolute value of the product Q1·c1 and a magnitude of the absolute value of the product Q2·c2 lie between 0.25 and 1000 mm−1 and wherein Q1 and Q2 are less than −1.
3. The beam shaping system as claimed in claim 1, wherein said first acylindrical lens and said second acylindrical lens each comprise a secondary surface, each of said secondary surface being one of a planar surface and a cylindrical surface.
4. The beam shaping system as claimed in claim 1, wherein said first and said second acylindrical lenses are positive lenses.
5. The beam shaping system as claimed in claim 1, wherein an input surface of said first and said second acylindrical lenses is said primary surface.
6. The beam shaping system as claimed in claim 1, further comprising collimating lens means for collimating said shaped beam.
7. The beam shaping system as claimed in claim 6, wherein said collimating lens means comprise a first cylindrical collimating lens for collimating said shaped beam along said first axis and a second cylindrical collimating lens for collimating said shaped beam along said second axis in order to eliminate an astigmatism caused by a distance between said first and said second acylindrical lenses.
8. The beam shaping system as claimed in claim 6, wherein said first acylindrical lens has a first point source and said second acylindrical lens has a second point source and wherein said collimating lens means comprise a first cylindrical collimating lens for collimating said shaped beam along said first axis and a second cylindrical collimating lens for collimating said shaped beam along said second axis, said a first cylindrical collimating lens having a first focal length and being located at one first focal length distance from said first point source and said second cylindrical collimating lens having a second focal length and being located at one second focal length distance from said second point source.
9. The beam shaping system as claimed in claim 1, further comprising focusing lens means for focusing said shaped beam, said focusing lens means comprising a positive lens device.
10. The beam shaping system as claimed in claim 9, wherein said focusing lens means further comprise a negative lens device positioned between said second acylindrical lens, said negative lens device for providing a retro-focus focusing lens system.
11. The beam shaping system as claimed in claim 9, wherein said focusing lens means comprise a first cylindrical focusing lens for focusing said shaped beam along said first axis and a second cylindrical focusing lens for focusing said shaped beam along said second axis in order to eliminate an astigmatism of said shaped beam.
12. The beam shaping system as claimed in claim 1, wherein said incident beam has astigmatism.
13. The beam shaping system as claimed in claim 1, wherein said incident beam is a substantially collimated and rotationally symmetrical Gaussian beam.
14. The beam shaping system as claimed in claim 1, wherein said incident beam is non-rotationally symmetrical.
15. The beam shaping system as claimed in claim 1, wherein said shaped beam has at least one of a cosine corrected, a super-gaussian and a uniform intensity profile along each one of said first and said second axes, in a far field region.
16. The beam shaping system as claimed in claim 1, further comprising beam splitting means for producing a pattern of a plurality of substantially rectangular beams.
17. The beam shaping system as claimed in claim 16, wherein said beam splitting means comprises a diffractive beam splitter.
18. A rectangular beam light source for providing a substantially rectangular shaped beam having a controlled intensity profile, said rectangular beam light source comprising: y = c 1 x 2 1 + ( 1 - ( 1 + Q 1 ) c 1 2 x 2 ) 1 / 2 + f 1 ( x ), y = c 2 x 2 1 + ( 1 - ( 1 + Q 2 ) c 2 2 x 2 ) 1 / 2 + f 2 ( x ),
- an incident light source for providing an incident beam having a predetermined cross-sectional intensity profile along a first axis and a second axis; and
- a first and a second acylindrical lens each having a primary acylindrical surface with a base curve, said first and said second acylindrical lenses being disposed substantially orthogonally to one another, said first acylindrical lens for shaping said incident beam along said first axis and said second acylindrical lens for shaping said incident beam along said second axis, thereby providing said substantially rectangular shaped beam;
- wherein said base curve of said first lens fits a first equation in a Cartesian coordinate system (x,y), said first equation being
- c1 being a first curvature constant, Q1 being a first conic constant and ƒ1(x) being a first correction function, said first correction function being continuous; and
- wherein said base curve of said second lens fits a second equation in another Cartesian coordinate system (x,y), said second equation being
- c2 being a second curvature constant and Q2 being a second conic constant and ƒ2(x) being a second correction function, said second correction function being continuous.
19. The rectangular beam light source as claimed in claim 18, wherein a magnitude of the absolute value of the product Q1·c1 and a magnitude of the absolute value of the product Q2·c2 lie between 0.25 and 1000 mm−1 and wherein Q1 and Q2 are less than −1.
20. The rectangular beam light source as claimed in claim 18, wherein said first acylindrical lens and said second acylindrical lens each comprise a secondary surface, each of said secondary surface being one of a planar surface and a cylindrical surface.
21. The rectangular beam light source as claimed in claim 18, further comprising collimating lens means for collimating said shaped beam.
22. The rectangular beam light source as claimed in claim 18, further comprising focusing lens means for focusing said shaped beam, said focusing lens means comprising a positive lens device.
23. The rectangular beam light source as claimed in claim 22, wherein said focusing lens means further comprise a negative lens device positioned between said second acylindrical lens, said negative lens device for providing a retro-focus focusing lens system.
24. The rectangular beam light source as claimed in claim 18, wherein said shaped beam has at least one of a cosine corrected, a super-gaussian and a uniform intensity profile along each one of said first and said second axes, in a far field region.
25. A beam shaping system for providing a substantially rectangular beam having a controlled intensity profile from an incident beam having a predetermined intensity profile along a first axis and a second axis, said beam shaping system comprising:
- a first and a second acylindrical lens each having a primary acylindrical surface having a base curve substantially in the shape of an angle with a rounded apex, said first lens for shaping said incident beam along said first axis and said second lens for shaping said incident beam along said second axis;
- wherein said first and said second acylindrical lenses are disposed substantially orthogonally to one another, thereby providing said substantially rectangular shaped beam in a far field region.
26. The beam shaping system as claimed in claim 25, wherein said first acylindrical lens and said second acylindrical lens each comprise a secondary surface, each of said secondary surface being one of a planar surface and a cylindrical surface.
27. The beam shaping system as claimed in claim 25, further comprising collimating lens means for collimating said shaped beam.
28. The beam shaping system as claimed in claim 25, further comprising focusing lens means for focusing said shaped beam, said focusing lens means comprising a positive lens device.
29. The beam shaping system as claimed in claim 28, wherein said focusing lens means further comprise a negative lens device positioned between said second acylindrical lens, said negative lens device for providing a retro-focus focusing lens system.
30. The beam shaping system as claimed in claim 25, wherein said shaped beam has at least one of a cosine corrected, a super-gaussian and a uniform intensity profile along each one of said first and said second axes, in a far field region.
31. A beam shaping system for providing a substantially rectangular beam having a controlled intensity profile from an incident beam having a predetermined intensity profile along a first axis and a second axis, said beam shaping system comprising:
- a first and a second lens each having a primary acylindrical surface having a base curve with a radius of curvature that varies along said base curve, said radius of curvature being smaller in a center of said base curve and increasing smoothly towards both of extremities of said base curve;
- wherein said first lens and said second lens are disposed orthogonally to one another, said first lens for shaping said incident beam along said first axis and said second lens for shaping said incident beam along said second axis, thereby providing said substantially rectangular beam in a far field region.
32. The beam shaping system as claimed in claim 31, wherein said first acylindrical lens and said second acylindrical lens each comprise a secondary surface, each of said secondary surface being one of a planar surface and a cylindrical surface.
33. The beam shaping system as claimed in claim 31, further comprising collimating lens means for collimating said shaped beam.
34. The beam shaping system as claimed in claim 31, further comprising focusing lens means for focusing said shaped beam, said focusing lens means comprising a positive lens device.
35. The beam shaping system as claimed in claim 34, wherein said focusing lens means further comprise a negative lens device positioned between said second acylindrical lens, said negative lens device for providing a retro-focus focusing lens system.
36. The beam shaping system as claimed in claim 31, wherein said shaped beam has at least one of a cosine corrected, a super-gaussian and a uniform intensity profile along each one of said first and said second axes, in a far field region.
Type: Application
Filed: Jan 4, 2007
Publication Date: Jul 10, 2008
Inventor: Francis Cayer (Saint-Eustache)
Application Number: 11/649,223
International Classification: G02B 27/09 (20060101); G02B 27/30 (20060101);