Abstract
A dielectric lens with high refractive index is suitable for focusing cryogenic devices in millimeter-wave bands when an appropriate anti-reflection (AR) coating is applied. Two types of AR coatings for silicon and alumina were studied at the millimeter-wave (220 GHz) band: one is by direct machining of mixed epoxy for a silicon lens array, while the other is by laser machining of an antireflective subwavelength structure for a large alumina lens used in a re-imaging optics system. The millimeter-wave optical properties of silicon, alumina, aluminum nitride, and Stycast epoxies were measured with a Fourier Transform Spectrometer (FTS) at cryogenic temperatures. The measured refractive index of the AR coating with a mixture of Stycast 1266 (n = 1.68) and Stycast 2850FTJ (n = 2.2) for silicon at 30 K was 1.84. The thickness of the epoxy AR coating was precisely controlled with direct machining. Transmittance of the AR-coated silicon substrate, measured with FTS, was approximately 95 % at the center frequency of the 220 GHz band with a bandwidth of 25 % at 27 K. An antireflective subwavelength structure was designed for an alumina sample with periodic cylindrical holes. The measured 220-GHz-band transmittance was above 90 % with a bandwidth of 25 % at 25 K.
Similar content being viewed by others
Notes
Oshima prototype engineering.
References
P.K. Day et al., Nature 425, 817–821 (2003)
K.D. Irwin et al., Appl. Phys. Lett. 69, 1945–1947 (1996)
A. Baryshev et al., IEEE Trans. THz Sci. Technol. 1, 112–123 (2011)
J.W. Fowler et al., Appl. Opt. 46, 3444–3454 (2007)
T. Tomaru et al., Proc. SPIE 8452, 84521H (2012)
T. Nitta et al., IEEE Trans. THz Sci. Technol. 3, 56–62 (2013)
A. Suzuki et al., Proc. SPIE. 8452, 84523H (2012)
J. Lau et al., Appl. Opt. 45, 3746–3751 (2006)
A.J. Gatesman et al., IEEE Microw. Guided Wave Lett. 10, 264–266 (2000)
H.-W. Hübers et al., Infrared Phys. Technol. 42, 41–47 (2001)
T. Kamizuka et al., Proc. SPIE. 8450, 845051 (2012)
H. Matsuo et al., Publ. Astron. Soc. Japan 50, 359–366 (1998)
E.V. Loewenstein, D.R. Smith, Appl. Opt. 10, 577–583 (1971)
E.V. Loewenstein et al., Appl. Opt. 12, 398–406 (1973)
M. Barucci et al., Cryogenics 39, 963–966 (1999)
D.H. Raguin, G.M. Morris, Appl. Opt. 32, 1154–1167 (1993)
Acknowledgments
The authors would like to thank A. Suzuki (U.C. Berkeley) and T. Matsumura, Y. Inoue (KEK) for useful discussions. This work was supported by MEXT/JSPS KAKENHI Grant Number 21111003, 21244023, 25247022, 24111712.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Nitta, T., Sekiguchi, S., Sekimoto, Y. et al. Anti-reflection Coating for Cryogenic Silicon and Alumina Lenses in Millimeter-Wave Bands. J Low Temp Phys 176, 677–683 (2014). https://doi.org/10.1007/s10909-013-1059-3
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10909-013-1059-3