Fabrication and characterization of a NIR-FIR dichroic for the infrared interferometer BETTII

BETTII is a balloon-borne far infrared (FIR: 30-100 μm) interferometer that also uses a near-infrared (NIR: 1-2.5 μm) channel for fine pointing sensing using stars. We have developed an inductive grid dichroic to divide the incoming beam into two components, by reflecting FIR light and transmitting NIR light. The dichroic is fabricated using focused electron beam technology to produce a 1 μm period, 100 nm width metal grid on a sapphire substrate in order to have high reflectance for FIR wavelengths. Here we discuss the design and the detailed manufacturing process for such a dichroic. The transmission and reflectance characteristics are also presented. We discuss them in context of the BETTII requirements.

[1]  C. L. Kuo,et al.  Large-Area Reflective Infrared Filters for Millimeter/Sub-mm Telescopes , 2014 .

[2]  M. M. Pradhan,et al.  Reflection and transmission characteristics of wire gratings in the far infrared , 1969 .

[3]  Antoni Rogalski,et al.  Uncooled long wavelength infrared photon detectors , 2004 .

[4]  Albert-Jan Boonstra,et al.  Observing with the ISO Short-Wavelength Spectrometer , 1996 .

[5]  Paolo Conconi,et al.  Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series , 2012 .

[6]  Shigeyuki Sako,et al.  Developing metal mesh filters for mid-infrared astronomy of 25 to 40 micron , 2008, Astronomical Telescopes + Instrumentation.

[7]  Adrian T. Lee,et al.  South Pole Telescope optics. , 2008, Applied optics.

[8]  Kiyomi Sakai,et al.  Far Infrared Metal Mesh Filters and Fabry-Perot Interferometry , 1983 .

[9]  Ely E. Bell,et al.  Measurement of the far infrared optical properties of solids with a michelson interferometer used in the asymmetric mode: Part I, mathematical formulation∗☆ , 1966 .

[10]  B. Mot,et al.  PILOT: a balloon-borne experiment to measure the polarized FIR emission of dust grains in the interstellar medium , 2014, Astronomical Telescopes and Instrumentation.

[11]  Stephen A. Rinehart,et al.  Flight performance of the attitude control system of the balloon experimental twin telescope for infrared interferometry (BETTII) , 2018, Astronomical Telescopes + Instrumentation.

[12]  Per Friberg,et al.  SCUBA-2: an update on the performance of the 10,000 pixel bolometer camera after two years of science operation at the JCMT , 2014, Astronomical Telescopes and Instrumentation.

[13]  M. Charra,et al.  Metallic mesh properties and design of submillimeter filters , 1981 .

[14]  Karim Djotni,et al.  Cooled optical filters for Q-band infrared astronomy (15-40 μm) , 2016, Astronomical Telescopes + Instrumentation.

[15]  R. Ulrich.  Far-infrared properties of metallic mesh and its complementary structure , 1967 .

[16]  J. Lamarre,et al.  Inductive grids in the resonant region: Theory and experiment , 1985 .

[17]  Peter A. R. Ade,et al.  Optics of Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII): delay lines and alignment , 2016, Astronomical Telescopes + Instrumentation.

[18]  G. Boreman,et al.  Comparison of infrared frequency selective surfaces fabricated by direct-write electron-beam and bilayer nanoimprint lithographies , 2000 .

[19]  Edward J. Wollack,et al.  Compact micromachined infrared bandpass filters for planetary spectroscopy. , 2012, Applied optics.

[20]  Giampaolo Pisano,et al.  A review of metal mesh filters , 2006, SPIE Astronomical Telescopes + Instrumentation.

[21]  P. Belland,et al.  A CW DCN waveguide laser of high volumetric efficiency , 1978 .

[22]  Chris Pearson,et al.  In-orbit performance of the Herschel/SPIRE imaging Fourier transform spectrometer: lessons learned , 2014, Astronomical Telescopes and Instrumentation.

[23]  A. Mitsuishi,et al.  Metal Mesh Filters in the Far Infrared Region , 1963 .

[24]  Takashi Fukui,et al.  Metallic Mesh Bandpass Filters and Fabry-Perot Interferometer for the Far Infrared , 1969 .

[25]  K. Sakai,et al.  Interferometry from 1950 to the present. , 1977 .

[26]  Richard M. Osgood,et al.  Frequency selective surfaces offer new possibilities as reflectance filters in the NIR/visible spectrum , 2008, NanoScience + Engineering.

[27]  E. Pascale,et al.  Pupil re-imaging Cold Delay Line Relay mirrors Detectors Warm Delay Line K-Mirror Left Siderostat Right Siderostat Beam Compressor Beam Compressor Cryostat , 2014 .

[29]  A. Costley,et al.  A Fabry-Perot Interferometer for Plasma Diagnostics , 1979, 1979 International Conference on Submillimeter Waves and Their Applications.