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Applied Optics

Applied Optics

APPLICATIONS-CENTERED RESEARCH IN OPTICS

  • Editor: Joseph N. Mait
  • Vol. 53, Iss. 13 — May. 1, 2014
  • pp: 2886–2891

Laser-generated broadband antireflection structures for freeform silicon lenses at terahertz frequencies

A. Brahm, S. Döring, A. Wilms, G. Notni, S. Nolte, and A. Tünnermann  »View Author Affiliations


Applied Optics, Vol. 53, Issue 13, pp. 2886-2891 (2014)
http://dx.doi.org/10.1364/AO.53.002886


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Abstract

We present a flexible technology to generate broadband antireflection (AR) structures for the terahertz (THz) frequency range on planar and curved surfaces of silicon optics. Ultrashort laser pulses are used to ablate the surface to form a pattern of conical pillars with a period of 30 μm. These subwavelength structures act as an effective medium with gradual transition of the refractive index from air to silicon, which reduces the Fresnel reflection losses. The characterization with the THz time-domain spectroscopy system shows an AR effect for a frequency range of 0.1–1.5 THz with a maximum enhancement of the spectral amplitude by ca. 32% at 0.4 THz for planar surfaces. In addition, we demonstrate laser-generated AR structures on convex silicon lenses of both photoconductive emitter and detector devices. Here, the THz pulse amplitude can be increased by about 28%, and single frequencies even show an improvement of the spectral amplitude up to 58%.

© 2014 Optical Society of America

OCIS Codes
(140.3390) Lasers and laser optics : Laser materials processing
(140.7090) Lasers and laser optics : Ultrafast lasers
(310.1210) Thin films : Antireflection coatings
(300.6495) Spectroscopy : Spectroscopy, teraherz
(050.6624) Diffraction and gratings : Subwavelength structures

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: February 4, 2014
Revised Manuscript: March 18, 2014
Manuscript Accepted: April 3, 2014
Published: April 29, 2014

Citation
A. Brahm, S. Döring, A. Wilms, G. Notni, S. Nolte, and A. Tünnermann, "Laser-generated broadband antireflection structures for freeform silicon lenses at terahertz frequencies," Appl. Opt. 53, 2886-2891 (2014)
http://www.opticsinfobase.org/ao/abstract.cfm?URI=ao-53-13-2886

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