Abstract

A diffractive beam homogenizer, based on an array of square, off-axis, continuous-relief diffractive microlenses, for use with an excimer laser has been studied. We originally fabricated the homogenizer by direct-write electron-beam lithography, from which we made replicas in UV-grade fused silica by hot embossing and reactive ion etching. Atomic force microscopy measurements of original and replicated elements showed the accuracy of the replication fidelity. One of the replicated homogenizers was evaluated together with a KrF excimer laser. The homogenized beam had a flat-top profile with 31% of the beam energy contained within an area where the beam intensity was above a threshold level of 90% of the maximum intensity.

© 1997 Optical Society of America

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References

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  1. T. Znotins, “Industrial applications of excimer lasers,” in Excimer Lasers and Optics, T. S. Luk, ed., Proc. SPIE710, 55–62 (1986).
  2. M. Gower, P. T. Rumsby, D. T. Thomas, “Novel applications of excimer lasers for fabricating biomedical and sensor products,” in Excimer Lasers: Applications, Beam Delivery Systems, and Laser Design, J. A. Greer, ed., Proc. SPIE1835, 133–142 (1993).
    [CrossRef]
  3. K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).
  4. Y. Carts, “Cylindrical lens arrays homogenize excimer beam,” Laser Focus World 27 (11), 39 (November1991).
  5. H. Nishihara, T. Suhara, Micro Fresnel Lenses of Vol. 24 of Progress in Optics (Elsevier, New York, 1987).
  6. W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
    [CrossRef]
  7. S. Kawata, I. Hikima, Y. Ichihara, S. Watanabe, “Spatial coherence of KrF excimer lasers,” Appl. Opt. 31, 387–396 (1992).
    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  11. M. T. Gale, “Replication,” in Micro-optics: Elements, Systems and Applications, H. P. Herzig, ed. (Taylor and Francis, London, 1997).
  12. L. Baraldi, “Heissprägen in Polymeren für die Herstellung integriert-optischer Systemkomponenten,” Ph.D. dissertation (Eidgenössische Technische Hochschule, Z̈rich, Switzerland, 1994).
  13. L. Baraldi, R. E. Kunz, J. Meissner, “High-precision molding of integrated optical structures,” in Miniature and Micro-Optics and Micromechanics, N. C. Gallagher, C. Roychoudhuri, eds., Proc. SPIE1992, 21–29 (1993).
    [CrossRef]
  14. F. P. Shvartsman, “Replication of diffractive optics,” in Diffractive and miniaturized Optics, S. H. Lee, ed., Critical Reviews SPIECR49, 165–186 (1993).
  15. M. Rothschild, “Optical materials for excimer laser applications,” Opt. Photonics News 4, 8–15 (May1993).
    [CrossRef]
  16. S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
    [CrossRef]
  17. A-K. Holmèr, S. Hård, “Laser machining experiment with an excimer laser and a kinoform,” Appl. Opt. 34, 7718–7723 (1995).
    [CrossRef]

1996 (1)

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

1995 (3)

1994 (1)

1993 (1)

M. Rothschild, “Optical materials for excimer laser applications,” Opt. Photonics News 4, 8–15 (May1993).
[CrossRef]

1992 (1)

1991 (1)

Y. Carts, “Cylindrical lens arrays homogenize excimer beam,” Laser Focus World 27 (11), 39 (November1991).

Baraldi, L.

L. Baraldi, “Heissprägen in Polymeren für die Herstellung integriert-optischer Systemkomponenten,” Ph.D. dissertation (Eidgenössische Technische Hochschule, Z̈rich, Switzerland, 1994).

L. Baraldi, R. E. Kunz, J. Meissner, “High-precision molding of integrated optical structures,” in Miniature and Micro-Optics and Micromechanics, N. C. Gallagher, C. Roychoudhuri, eds., Proc. SPIE1992, 21–29 (1993).
[CrossRef]

Bengtsson, J.

Carts, Y.

Y. Carts, “Cylindrical lens arrays homogenize excimer beam,” Laser Focus World 27 (11), 39 (November1991).

Däschner, W.

Eisner, M.

S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
[CrossRef]

Ekberg, M.

Gale, M. T.

M. T. Gale, “Replication,” in Micro-optics: Elements, Systems and Applications, H. P. Herzig, ed. (Taylor and Francis, London, 1997).

Gorzellik, P.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Gower, M.

M. Gower, P. T. Rumsby, D. T. Thomas, “Novel applications of excimer lasers for fabricating biomedical and sensor products,” in Excimer Lasers: Applications, Beam Delivery Systems, and Laser Design, J. A. Greer, ed., Proc. SPIE1835, 133–142 (1993).
[CrossRef]

Håard, S.

Hård, S.

Haselbeck, S.

S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
[CrossRef]

Herzig, H-P.

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Hikima, I.

Holmèr, A-K.

Hopfmüller, A.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Ichihara, Y.

Kawata, S.

Kuittinen, M.

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Kunz, R. E.

L. Baraldi, R. E. Kunz, J. Meissner, “High-precision molding of integrated optical structures,” in Miniature and Micro-Optics and Micromechanics, N. C. Gallagher, C. Roychoudhuri, eds., Proc. SPIE1992, 21–29 (1993).
[CrossRef]

Larsson, M.

Lee, S. H.

Mann, K. R.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Meissner, J.

L. Baraldi, R. E. Kunz, J. Meissner, “High-precision molding of integrated optical structures,” in Miniature and Micro-Optics and Micromechanics, N. C. Gallagher, C. Roychoudhuri, eds., Proc. SPIE1992, 21–29 (1993).
[CrossRef]

Nikolajeff, F.

Nishihara, H.

H. Nishihara, T. Suhara, Micro Fresnel Lenses of Vol. 24 of Progress in Optics (Elsevier, New York, 1987).

Piper, E.

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Rothschild, M.

M. Rothschild, “Optical materials for excimer laser applications,” Opt. Photonics News 4, 8–15 (May1993).
[CrossRef]

Rumsby, P. T.

M. Gower, P. T. Rumsby, D. T. Thomas, “Novel applications of excimer lasers for fabricating biomedical and sensor products,” in Excimer Lasers: Applications, Beam Delivery Systems, and Laser Design, J. A. Greer, ed., Proc. SPIE1835, 133–142 (1993).
[CrossRef]

Schild, R.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Schreiber, H.

S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
[CrossRef]

Schwider, J.

S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
[CrossRef]

Shvartsman, F. P.

F. P. Shvartsman, “Replication of diffractive optics,” in Diffractive and miniaturized Optics, S. H. Lee, ed., Critical Reviews SPIECR49, 165–186 (1993).

Singer, W.

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Stöffler, W.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Suhara, T.

H. Nishihara, T. Suhara, Micro Fresnel Lenses of Vol. 24 of Progress in Optics (Elsevier, New York, 1987).

Thomas, D. T.

M. Gower, P. T. Rumsby, D. T. Thomas, “Novel applications of excimer lasers for fabricating biomedical and sensor products,” in Excimer Lasers: Applications, Beam Delivery Systems, and Laser Design, J. A. Greer, ed., Proc. SPIE1835, 133–142 (1993).
[CrossRef]

Wagner, H.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Wangler, J.

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Watanabe, S.

Wolbold, G.

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

Znotins, T.

T. Znotins, “Industrial applications of excimer lasers,” in Excimer Lasers and Optics, T. S. Luk, ed., Proc. SPIE710, 55–62 (1986).

Appl. Opt. (5)

Laser Focus World (1)

Y. Carts, “Cylindrical lens arrays homogenize excimer beam,” Laser Focus World 27 (11), 39 (November1991).

Opt. Eng. (1)

W. Singer, H-P. Herzig, M. Kuittinen, E. Piper, J. Wangler, “Diffractive beamshaping elements at the fabrication limit,” Opt. Eng. 35, 2779–2787 (1996).
[CrossRef]

Opt. Photonics News (1)

M. Rothschild, “Optical materials for excimer laser applications,” Opt. Photonics News 4, 8–15 (May1993).
[CrossRef]

Other (9)

S. Haselbeck, M. Eisner, H. Schreiber, J. Schwider, “Reactive ion etching of microlens arrays into fused silica,” in Nonconventional Optical Imaging Elements, J. Nowak, M. Zajak, eds. Proc. SPIE2169, 142–146 (1994).
[CrossRef]

H. Nishihara, T. Suhara, Micro Fresnel Lenses of Vol. 24 of Progress in Optics (Elsevier, New York, 1987).

T. Znotins, “Industrial applications of excimer lasers,” in Excimer Lasers and Optics, T. S. Luk, ed., Proc. SPIE710, 55–62 (1986).

M. Gower, P. T. Rumsby, D. T. Thomas, “Novel applications of excimer lasers for fabricating biomedical and sensor products,” in Excimer Lasers: Applications, Beam Delivery Systems, and Laser Design, J. A. Greer, ed., Proc. SPIE1835, 133–142 (1993).
[CrossRef]

K. R. Mann, A. Hopfmüller, P. Gorzellik, R. Schild, W. Stöffler, H. Wagner, G. Wolbold, “Monitoring and shaping of excimer laser beam profiles,” in Laser Technology Distribution Profiles: Measurement and Applications, J. M. Darchuk, ed., Proc. SPIE1834, 184–194 (1992).

M. T. Gale, “Replication,” in Micro-optics: Elements, Systems and Applications, H. P. Herzig, ed. (Taylor and Francis, London, 1997).

L. Baraldi, “Heissprägen in Polymeren für die Herstellung integriert-optischer Systemkomponenten,” Ph.D. dissertation (Eidgenössische Technische Hochschule, Z̈rich, Switzerland, 1994).

L. Baraldi, R. E. Kunz, J. Meissner, “High-precision molding of integrated optical structures,” in Miniature and Micro-Optics and Micromechanics, N. C. Gallagher, C. Roychoudhuri, eds., Proc. SPIE1992, 21–29 (1993).
[CrossRef]

F. P. Shvartsman, “Replication of diffractive optics,” in Diffractive and miniaturized Optics, S. H. Lee, ed., Critical Reviews SPIECR49, 165–186 (1993).

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Figures (15)

Fig. 1
Fig. 1

Optical setup for homogenizing a laser beam: An array of microlenses divides the beam into small beamlets, and a large-aperture spherical focusing lens overlaps all the partial beams in the focal plane of the focusing lens, yielding a uniform flat-top beam profile. The focusing lens can be placed either in front of or behind the microlens array.

Fig. 2
Fig. 2

Microscope picture of original diffractive homogenizer, fabricated in resist by direct-write electron-beam lithography. The homogenizer consists of an array of 30 × 30 continuous-relief, square, off-axis, diffractive microlenses. The lens diameter is 820 µm and the focal length is 60 mm.

Fig. 3
Fig. 3

AFM picture of one corner between four diffractive lenses in original homogenizer.

Fig. 4
Fig. 4

Schematic picture of hot-embossing flatbed press used for the replication of diffractive structures into polymeric films, coated on fused-silica substrates.

Fig. 5
Fig. 5

Schematic picture of home-built reactive ion etcher used for transfer of microstructures from polycarbonate into an underlying fused-silica substrate. The etch gases were CHF3 and O2, with varying amounts of O2

Fig. 6
Fig. 6

q factor, defined as the etch rate in fused silica divided by the etch rate in polycarbonate, as a function of varying amounts of O2. The etching experiments were carried out in a home-built reactive ion etcher that favored the anisotropic etching part.

Fig. 7
Fig. 7

AFM picture of parts of one diffractive lens; original homogenizer in resist fabricated by direct-write electron-beam lithography.

Fig. 8
Fig. 8

AFM picture of parts of one diffractive lens; electroformed metal negative of the original in form of a first-generation Ni master.

Fig. 9
Fig. 9

AFM picture of parts of one diffractive lens: a replicated homogenizer embossed in a thin polycarbonate film coated on a fused-silica substrate.

Fig. 10
Fig. 10

AFM picture of parts of one diffractive lens: an all-fused-silica homogenizer with the embossed microrelief transferred into the fused-silica substrate by RIE.

Fig. 11
Fig. 11

Trace of the etched diffractive lens shown in Fig. 10. The relief depth of the diffractive structure is almost perfectly matched to the refractive index of the material and the wavelength used.

Fig. 12
Fig. 12

Optical setup for measuring a homogenized KrF excimer laser beam. To measure the laser-beam intensity profile, we put a glass plate in the homogenized plane and detected the fluorescent light with a CCD camera. By inserting a planoconcave cylinder lens as shown, we made the beam divergent in the direction of the long axis of the coherence areas. The edge sharpnesses in the two directions of the homogenized beam can then be found to be equal in a plane in the vicinity of the focal plane of the spherical lens.

Fig. 13
Fig. 13

(a) Intensity distribution of the emitted beam from a KrF excimer laser; (b) cross section through the profile shown in Fig. 13(a).

Fig. 14
Fig. 14

(a) Intensity distribution of a homogenized beam with a replicated and etched array of off-axis, diffractive microlenses; (b) cross section through the profile shown in Fig. 14(a).

Fig. 15
Fig. 15

(a) Intensity distribution of a homogenized beam with use of a commercial homogenizer based on an array of refractive microlenses; (b) cross section through the profile shown in Fig. 15(a).

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