WO2012120505A1

WO2012120505A1 - Variable laser beam shaping assembly

Info

Publication number: WO2012120505A1
Application number: PCT/IL2012/000119
Authority: WO
Inventors: Zvi Kotler; Michael ZANOU; Yosef VARSHAL; Michael MANEVICH
Original assignee: Orbotech Ltd.; Jerusalem College Of Technology
Priority date: 2011-03-08
Filing date: 2012-03-06
Publication date: 2012-09-13

Abstract

A variable laser beam shaping assembly including at least one diffractive transparent substrate defining an interior volume, a liquid crystal layer disposed in the interior volume, the liquid crystal layer having at least one generally flat surface and a voltage supply subassembly operative to apply a variable voltage across the liquid crystal layer.

Description

VARIABLE LASER BEAM SHAPING ASSEMBLY

REFERENCE TO RELATED APPLICATIONS

Reference is made to U.S. Provisional Patent Application Serial No. 61/450,355 filed March 8, 2011, entitled "Adaptive Beam Shaping Apparatus," the entire disclosure of which is hereby incorporated by reference herein and priority thereof is hereby claimed pursuant to 37 CFR 1.78(a) (4) and (5)(i).

FIELD OF THE INVENTION

The present invention relates to variable laser beam shaping generally.

BACKGROUND OF THE INVENTION

The following publications are believed to represent the current state of the art:

PCT Published Application No. WO2010030575 A2;

U.S. Published Patent Application No. US2009/0316097;

D. Ganic, X. Gan, M. Gu, M. Hain, S. Somalingam, S. Stankovic and T. Tschudi, Generation of doughnut laser beams by use of a liquid-crystal cell with a conversion efficiency near 100%, Optics Letters, Vol. 27, No. 15, pp. 1351 - 1353 2002;

J.Liang, R.N. Kohn, Jr., M.F. Becker, and D.J. Heinzen, 1.5% root-mean- square flat-intensity laser beam formed using a binary-amplitude spatial light modulator, Applied Optics, Vol. 49, No. 8, pp. 1323-1330, 2010;

Karen Asatryan, Vladimir Presnyakov, Amir Tork, Armen Zohrabyan, Aram Bagramyan and Tigran Galstian, Optical lens with electrically Variable Focus Using an Optically Hidden Dielectric Structure, Optics Express, Vol. 18, No. 13, pp. 13981-13992, 2010; and

Haotong Ma, Pu Zhou, Xiaolin Wang, Yanxing Ma, Fengjie Xi, Xiaojun Xu, and Zejin Liu, Near-diffraction-limited annular flattop beam shaping with dual phase only liquid crystal spatial light modulators, Optics Express, Vol. 18, No. 8, pp. 8251-8260, 2010.

SUMMARY OF THE INVENTION

The present invention seeks to provide an improved variable laser beam shaping assembly.

There is thus provided in accordance with a preferred embodiment of the present invention a variable laser beam shaping assembly including at least one diffractive transparent substrate defining an interior volume, a liquid crystal layer disposed in the interior volume, the liquid crystal layer having at least one generally flat surface and a voltage supply subassembly operative to apply a variable voltage across the liquid crystal layer.

Preferably, the variable laser beam shaping assembly also includes at least one of a lens and a mirror. Additionally, the at least one of a lens and a mirror is a spherical lens. Additionally or alternatively, the at least one of a lens and a mirror is disposed downstream of the at least one diffractive transparent substrate.

In accordance with a preferred embodiment of the present invention the voltage supply subassembly includes first and second electrodes and the interior volume is bounded by the first and second electrodes. Additionally, the variable voltage is applied to the first and second electrodes.

Preferably, the voltage supply subassembly includes a stabilized AC voltage source and a potentiometer. In accordance with a preferred embodiment of the present invention the variable laser beam shaping assembly is operative in at least one of a reflective mode and a transmissive mode.

Preferably, the variable laser beam shaping assembly is operative to output various beam shapes by changing the voltage. Alternatively, the variable laser beam shaping assembly is operative to output identical beam shapes for different laser wavelengths by changing the voltage.

In accordance with a preferred embodiment of the present invention the at least one diffractive transparent substrate includes first and second substrate elements.

There is also provided in accordance with another preferred embodiment of the present invention a variable laser beam shaping assembly including at least one transparent substrate configured to have different thicknesses at different locations thereon and defining an interior volume having different thicknesses at different locations thereon, a liquid crystal layer disposed in the interior volume, the liquid crystal layer having at least one generally flat surface and a voltage supply subassembly operative to apply a variable voltage across the liquid crystal layer and including at least one electrode which is not flat and whose configuration corresponds to the different thicknesses of the at least one transparent substrate.

Preferably, the at least one electrode has a segmented configuration. Additionally or alternatively, the at least one transparent substrate is a diffractive transparent substrate.

In accordance with a preferred embodiment of the present invention the variable laser beam shaping assembly also includes at least one of a lens and a mirror. Additionally, the at least one of a lens and a mirror is a spherical lens. Alternatively or additionally, the at least one of a lens and a mirror is disposed downstream of the at least one diffractive transparent substrate.

In accordance with a preferred embodiment of the present invention the variable laser beam shaping assembly is operative to output various beam shapes by changing the voltage. Alternatively or additionally, the variable laser beam shaping assembly is operative to output identical beam shapes for different laser wavelengths by changing the voltage.

BRIEF DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be understood and appreciated from the following detailed description, taken in conjunction with the drawings in which:

Figs. 1A and IB are simplified illustrations of the operation of a variable beam shape laser constructed and operative in accordance with preferred embodiments of the present invention operative in respective transmissive and reflective modes of operation;

Fig. 1C is a simplified illustration of the operation of a variable beam shape laser constructed and operative in accordance with another preferred embodiment of the present invention operative in a reflective mode of operation;

Fig. 2A is a simplified not-to-scale illustration of the structure of a diffractive laser beam shaping assembly constructed and operative in accordance with a first preferred embodiment of the present invention;

Fig. 2B is a simplified not-to-scale illustration of the structure of a diffractive laser beam shaping assembly constructed and operative in accordance with a second preferred embodiment of the present invention;

Fig. 3A is a simplified, partially cut away, generally to scale sectional illustration of the structure of the diffractive laser beam shaping assembly of Fig. 2A; and

Fig. 3B is a simplified, partially cut away, generally to scale sectional illustration of the structure of the diffractive laser beam shaping assembly of Fig. 2B.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is now made to Fig. 1A, which is a simplified illustration of the operation of a variable beam shape laser constructed and operative in a transmissive mode of operation in accordance with a preferred embodiment of the present invention.

As seen in Fig. 1A, a laser 100, preferably a laser emitting at a wavelength of between 350 nm and 2000 nm, outputs a laser beam 101 which initially extends along an axis 102 which impinges on a variable laser beam shaping assembly 110, constructed and operative in accordance with a preferred embodiment of the present invention.

The laser beam shaping assembly 110 preferably includes a lens 112, such as a spherical lens, which is disposed typically downstream of a diffractive transparent substrate 114, preferably having an axis of circular symmetry 115 which is arranged parallel to axis 102. The diffractive transparent substrate 114 preferably defines an interior volume 116, which has at least one flat surface, is preferably filled with a liquid crystal material, forming a liquid crystal layer 118, and is bounded by first and second electrodes 120 and 122. A voltage supply subassembly 124, typically comprising a stabilized AC voltage source and a potentiometer, is preferably operative to apply a selectably variable voltage to electrodes 120 and 122, across the liquid crystal layer 118. It is appreciated that Fig. 1A illustrates operation in a transmissive mode.

A desired shaped laser beam output through lens 112 may be redirected, as by a folding mirror 126, to a target 128 on a substrate 130. It is appreciated that alternatively lens 112 may be disposed upstream of diffractive transparent substrate 114. As a further alternative, lens 112 may be obviated if diffractive transparent substrate 114 is configured to have suitable optical power.

Reference is now made to Fig. IB, which is a simplified illustration of the operation of a variable beam shape laser constructed and operative in a reflective mode of operation in accordance with a preferred embodiment of the present invention.

As seen in Fig. IB, a laser 140, preferably a laser emitting at a wavelength of between 350 nm and 2000 nm, outputs a laser beam 141 along an axis 142, which laser beam impinges on a variable laser beam shaping assembly 150, constructed and operative in accordance with a preferred embodiment of the present invention.

The laser beam shaping assembly 150 preferably includes at least one diffractive transparent substrate 114, whose axis of circular symmetry 115 is angled with respect to axis 142. Diffractive transparent substrate 114 defines an interior volume 116, having at least one flat surface and preferably filled with a liquid crystal material, forming a liquid crystal layer 118, and bounded by first and second electrodes 120 and 122. A voltage supply subassembly 124, typically comprising a stabilized AC voltage source and a potentiometer, is preferably operative to apply a selectably variable voltage to electrodes 120 and 122, across the liquid crystal layer 118. A mirror 166 is preferably arranged immediately adjacent to and downstream of diffractive transparent substrate 114 to reflect a laser beam which has passed once through the diffractive transparent substrate 114 back through diffractive transparent substrate 114.

A lens 168, such as a spherical lens, is disposed typically downstream of at least one diffractive transparent substrate 114 and mirror 166. It is appreciated that Fig. IB illustrates operation in a reflective mode. It is appreciated that alternatively lens 168 may be disposed upstream of diffractive transparent substrate 114. As a further alternative, lens 168 may be obviated if diffractive transparent substrate 114 is configured to have suitable optical power.

A desired shaped laser beam output through lens 168 may be redirected, as by a folding mirror 170, to a target 172 on a substrate 174.

Reference is now made to Fig. 1C, which is a simplified illustration of the operation of a variable beam shape laser constructed and operative in a reflective mode of operation in accordance with another preferred embodiment of the present invention.

As seen in Fig. 1C, a laser 180, preferably a laser emitting at a wavelength of between 350 nm and 2000 nm, outputs a laser beam 181 along an axis 182, which laser beam impinges on a variable laser beam shaping assembly 190, constructed and operative in accordance with a preferred embodiment of the present invention.

The laser beam shaping assembly 190 preferably includes at least one diffractive transparent substrate 114, whose axis of circular symmetry 115 is arranged parallel to axis 182. Diffractive transparent substrate 114 defines an interior volume 116, having at least one flat surface and preferably filled with a liquid crystal material, forming a liquid crystal layer 118, and bounded by first and second electrodes 120 and 122. A voltage supply subassembly 124, typically comprising a stabilized AC voltage source and a potentiometer, is preferably operative to apply a selectably variable voltage to electrodes 120 and 122, across the liquid crystal layer 118. A mirror 186 is preferably arranged immediately adjacent to and downstream of diffractive transparent substrate 114 to reflect a laser beam which has passed once through the diffractive transparent substrate 114 back through diffractive transparent substrate 114.

In the embodiment shown in Fig. 1C, a beam splitter 188 is preferably located between laser 180 and diffractive transparent substrate 114, such as to transfer laser beam 181 emitted from laser 180 towards diffractive transparent substrate 114 and to deflect laser beam 181 when reflected by mirror 186. Preferably, a wave plate 189, such as a quarter lambda plate, is placed between beam splitter 188 and diffractive transparent substrate 114 to provide proper phase shifting of laser beam 181 when retuned by mirror 186.

A lens 192, such as a spherical lens, is disposed typically downstream of at least one diffractive transparent substrate 114, and mirror 186 and beam splitter 188. It is appreciated that Fig. 1C illustrates operation in a reflective mode. It is appreciated that alternatively lens 192 may be disposed upstream of diffractive transparent substrate 114. As a further alternative, lens 192 may be obviated if diffractive transparent substrate 114 is configured to have suitable optical power.

A desired shaped laser beam output through lens 192 may be redirected, as by a folding mirror 194, to a target 196 on a substrate 198.

It is a particular feature of an embodiment of the present invention and particularly of the structure and operation of the diffractive transparent substrate 114 that various beam shapes may be selected by changes in the voltage across the liquid crystal layer 118.

For example, as seen at A in Fig. 1A, where the voltage is 0.5Volt, a generally Gaussian beam shape is realized. In another example, as seen at B, where the voltage is +1.3 Volt, a generally ring beam shape is realized. In a further example, as seen at C, where the voltage is +1.5 Volt, a generally top hat beam shape is realized. For the reflective embodiment of Figs. IB and 1C, various beam shapes may also be realized by varying the applied voltage.

It is a particular feature of the present invention that the diffractive transparent substrate 114 is operative to provide an identical laser beam shape for a variety of laser wavelengths by varying the voltage across electrodes 120 and 122.

Reference is now made to Figs. 2A and 3A, which illustrate the structure of a first embodiment of a diffractive transparent substrate useful in the variable beam shape laser of Figs. 1A, IB and 1C.

In the illustrated embodiment of Fig. 2A, the diffractive transparent substrate 114 comprises first and second substrate elements 202 and 203, made of a transparent material, such as glass, which are preferably generally disk-like and extend generally perpendicularly to axis 115, one or both of which are formed with diffractive patterns thereon and preferably define respective facing surfaces 204 and 205, each of which is coated with an electrically conductive coating, such as indium tin oxide of thickness between 10 - 150 nanometers, to define respective electrodes 206 and 207. Respective facing surfaces 208 and 209 of electrodes 206 and 207 are each coated with an electrically non-conductive coating, such as polyimide of thickness between 100 - 500 nanometers, which define liquid crystal orientation layers 210 and 212, respectively, which engage the liquid crystal layer 118. The surfaces of the liquid crystal orientation layers 210 and 212, which engage the liquid crystal layer 118, are rubbed or otherwise conditioned to have a generally common orientation, thereby to uniformly orient the liquid crystal accordingly.

Precise spacing between liquid crystal orientation layers 210 and 212 is provided by any suitable technique, preferably the provision of a collection of spacing beads 224, typically spherical beads formed of glass or a suitable material, such as Teflon, of diameter between 3 and 50 microns.

The liquid crystal layer 118 is circumferentially bounded by a circumferential band of adhesive 226, preferably epoxy, which preferably seals the entire circumference of diffractive transparent substrate 114 and holds it together as well as retaining beads 224 in desired locations. Alternatively, precise spacing between liquid crystal orientation layers 210 and 212 is achieved by spacers produced using conventional photolithography techniques. In the illustrated embodiment of Figs. 2A and 3 A, surface 204, electrode 206 and liquid crystal orientation layer 210 are each generally flat and surface 205, electrode 207 and liquid crystal orientation layer 212 are each formed with a diffractive pattern. In the illustrated embodiment of Figs. 2A and 3A, the diffractive pattern of the electrode 207 is a pattern of concentric circular portions, preferably including a generally circular central raised portion 240 arranged about axis 115 and, spaced therefrom and coaxial therewith, a circular raised ring portion 242. Both of portions 240 and 242 have generally flat surfaces, which preferably lie in the same plane, perpendicular to axis 115 and face liquid crystal orientation layer 210. Portion 240 has a side surface 246 which is generally perpendicular to the plane of the flat surface of portion 240. Portion 242 has side surfaces 248 and 250 which are generally perpendicular to the plane of the flat surface of portion 242. Preferred dimensions of the various portions and layers and their separations are indicated in Fig. 3A. It is appreciated that other dimensions may also be applicable depending on the configuration of the apparatus.

Reference is now made to Figs. 2B and 3B, which illustrate the structure of a second embodiment of a diffractive transparent substrate useful in the variable beam shape laser of Figs. 1 A, IB and 1C.

In the illustrated embodiment of Fig. 2B, the diffractive transparent substrate 114 comprises first and second substrate elements 302 and 303, made of a transparent material, such as glass, which are preferably generally disk-like and extend generally perpendicularly to axis 115, one or both of which are formed with diffractive patterns thereon and preferably define respective facing surfaces 304 and 305, each of which is coated with an electrically conductive coating, such as indium tin oxide of thickness between 10 - 150 nanometers, to define respective electrodes 306 and 307.

As distinct from the embodiment of Figs. 2A and 3 A, in the embodiment of Figs. 2B and 3B, there is provided a flattening layer 308, which lies adjacent electrode 307 and is preferably formed of an electrically insulative material, such as silicon dioxide or Norland Optical Adhesive, available from Norland Products, Inc., Cranbury, NJ 08512, USA.

Respective facing surfaces 310 and 312 of electrode 306 and flattening layer 308 are each generally flat and extend perpendicular to axis 115 and are each coated with an electrically non-conductive coating, such as polyimide of thickness between 100 - 500 nanometers, which define liquid crystal orientation layers 314 and 316, respectively, which engage the liquid crystal layer 118. The surfaces of the liquid crystal orientation layers 314 and 316, which engage the liquid crystal layer 118, are rubbed or otherwise conditioned to have a generally common orientation, thereby to uniformly orient the liquid crystal accordingly.

Precise spacing between liquid crystal orientation layers 314 and 316 is provided by any suitable technique, preferably the provision of a collection of spacing beads 324, typically spherical beads formed of glass or a suitable material, such as Teflon, of diameter between 3 and 50 microns.

Liquid crystal layer 118 is circumferentially bounded by a circumferential band of adhesive 326, preferably epoxy, which preferably seals the entire circumference of diffractive transparent substrate 114 and holds it together as well as retaining beads 324 in desired locations. Alternatively, precise spacing between liquid crystal orientation layers 314 and 316 is achieved by spacers produced using conventional photolithography techniques.

In the illustrated embodiment of Figs. 2B and 3B, surface 304, electrode 306 and liquid crystal orientation layer 314 are all generally flat and surface 305, electrode 307 and an underside surface 328 of flattening layer 308 are each formed with a diffractive pattern. In the illustrated embodiment of Figs. 2B and 3B, the diffractive pattern of electrode 307 is a pattern of concentric circular portions, preferably including a generally circular central raised portion 340 arranged about axis 115 and, spaced therefrom and coaxial therewith, a circular raised ring portion 342. Both of portions 340 and 342 have generally flat surfaces, which preferably lie in the same plane perpendicular to axis 115. Portion 340 has a side surface 348 which is generally perpendicular to the plane of the flat surface of portion 340. Portion 342 has side surfaces 350 and 352, which are generally perpendicular to the plane of the flat surface of portion 342. Preferred dimensions of the various portions and layers and their separations are indicated in Fig. 3B. It is appreciated that other dimensions may also be applicable depending on the configuration of the apparatus.

In another embodiment of the present invention, the variable beam shape laser is used in conjunction with a UV laser for shaping the profile of a UV laser beam. This embodiment is similar to the embodiments described in Figs. 1A - 3B, however, the following changes are necessary as a result of changes in materials properties needed in order to overcome excessive absorption of the UV light in the device. This embodiment includes UV transparency down to a wavelength of about 350nm.

In this UV embodiment, transparent substrates, such as the first and second substrate elements 202 and 203 of Figs. 2A & 3 A and first and second substrate elements 302 and 303 of Figs. 2B & 3B, are preferably, fused-silica or quartz substrates, which are generally transparent in the selected wavelengths. Additionally, the transparent conducting layer, such as electrodes 206 and 207 in Figs. 2A & 3A and electrodes 306 and 307 in Figs 2B & 3B, is preferably of thickness between 10 - 20nm to minimize UV absorption. Similarly, the alignment layer, such as alignment layer 210 and 212 in Figs. 2 A & 3 A and alignment layers 314 and 316 in Figs. 2B & 3B, is preferably of a thickness of about lOOnm. Preferably, the liquid crystal material used in this embodiment for liquid crystal layer 118 is selected to provide minimal absorption in the relevant UV spectrum. For example, for UV wavelengths in the range 350nm to 400nm, preferably nematic liquid crystal material, such as 4-trans- '-n- exy\- cyclohexyl-isothiocyanatobenzene (6CHBT) available from Military University of Technology, Warsaw, Poland, is used.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention includes both combinations and subcombinations of features recited in the claims as well as modifications thereof which would occur to a person of ordinary skill in the art upon reading the foregoing and which are not in the prior art.

Claims

1. A variable laser beam shaping assembly comprising:

at least one diffractive transparent substrate defining an interior volume; a liquid crystal layer disposed in said interior volume, said liquid crystal layer having at least one generally flat surface; and

a voltage supply subassembly operative to apply a variable voltage across said liquid crystal layer.

2. A variable laser beam shaping assembly according to claim 1 and also comprising at least one of a lens and a mirror.

3. A variable laser beam shaping assembly according to claim 2 and wherein said at least one of a lens and a mirror is a spherical lens.

4. A variable laser beam shaping assembly according to claim 2 or claim 3 and wherein said at least one of a lens and a mirror is disposed downstream of said at least one diffractive transparent substrate.

5. A variable laser beam shaping assembly according to any of claims 1 - 4 and wherein:

said voltage supply subassembly comprises first and second electrodes; and

said interior volume is bounded by said first and second electrodes.

6. A variable laser beam shaping assembly according to claim 5 and wherein said variable voltage is applied to said first and second electrodes.

7. A variable laser beam shaping assembly according to any of claims 1 - 6 and wherein said voltage supply subassembly comprises:

a stabilized AC voltage source; and a potentiometer.

8. A variable laser beam shaping assembly according to any of claims 1 - 7 and wherein said variable laser beam shaping assembly is operative in at least one of a reflective mode and a transmissive mode.

9. A variable laser beam shaping assembly according to any of claims 1 - 8 and wherein said variable laser beam shaping assembly is operative to output various beam shapes by changing said voltage.

10. A variable laser shaping beam assembly according to any of claims 1 - 8 and wherein said variable laser beam shaping assembly is operative to output identical beam shapes for different laser wavelengths by changing said voltage.

11. A variable laser shaping beam assembly according to any of claims 1 - 10 and wherein said at least one diffractive transparent substrate comprises first and second substrate elements.

12. A variable laser beam shaping assembly comprising:

at least one transparent substrate configured to have different thicknesses at different locations thereon and defining an interior volume having different thicknesses at different locations thereon;

a liquid crystal layer disposed in said interior volume, said liquid crystal layer having at least one generally flat surface; and

a voltage supply subassembly operative to apply a variable voltage across said liquid crystal layer and including at least one electrode which is not flat and whose configuration corresponds to the different thicknesses of said at least one transparent substrate.

13. A variable laser beam shaping assembly according to claim 12 and wherein said at least one electrode has a segmented configuration.

14. A variable laser beam shaping assembly according to claim 12 or claim

13 and wherein said at least one transparent substrate is a diffractive transparent substrate.

15. A variable laser beam shaping assembly according to any of claims 12 -

14 and also comprising at least one of a lens and a mirror.

16. A variable laser beam shaping assembly according to claim 15 and wherein said at least one of a lens and a mirror is a spherical lens.

17. A variable laser beam shaping assembly according to claim 15 or claim

16 and wherein said at least one of a lens and a mirror is disposed downstream of said at least one diffractive transparent substrate.

18. A variable laser beam shaping assembly according to any of claims 12 -

17 and wherein said voltage supply subassembly comprises:

a stabilized AC voltage source; and

a potentiometer.

19. A variable laser beam shaping assembly according to any of claims 12 -

18 and wherein said variable laser beam shaping assembly is operative in at least one of a reflective mode and a transmissive mode.

20. A variable laser beam shaping assembly according to any of claims 12 - 19 and wherein said variable laser beam shaping assembly is operative to output various beam shapes by changing said voltage.

21. A variable laser shaping beam assembly according to any of claims 12 -

19 and wherein said variable laser beam shaping assembly is operative to output identical beam shapes for different laser wavelengths by changing said voltage.