Optical design of the 1.85-m mm-submm telescope in 210–375 GHz band

Yasumasa Yamasaki; Sho Masui; Masanari Okawa; Koki Yokoyama; Taisei Minami; Shota Ueda; Yutaka Hasegawa; Atsushi Nishimura; Toshikazu Onishi; Hideo Ogawa; Nozomi Okada; Kimihiro Kimura; Alvaro Gonzalez; Takafumi Kojima; Keiko Kaneko; Ryo Sakai

doi:10.1117/12.2561955

13 December 2020 Optical design of the 1.85-m mm-submm telescope in 210–375 GHz band

Yasumasa Yamasaki, Sho Masui, Masanari Okawa, Koki Yokoyama, Taisei Minami, Shota Ueda, Yutaka Hasegawa, Atsushi Nishimura, Toshikazu Onishi, Hideo Ogawa, Nozomi Okada, Kimihiro Kimura, Alvaro Gonzalez, Takafumi Kojima, Keiko Kaneko, Ryo Sakai

Author Affiliations +

Proceedings Volume 11453, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X; 114534H (2020) https://doi.org/10.1117/12.2561955
Event: SPIE Astronomical Telescopes + Instrumentation, 2020, Online Only

Conference Poster

Abstract

Currently, we are performing a large-scale survey of molecular clouds toward the Galactic Plane in ¹²CO, ¹³CO, and C¹⁸O(J = 2–1) with the 1.85-m mm-submm telescope from Nobeyama Radio Observatory. In addition, we are proceeding with the preparation of a new project to observe several additional molecular lines including higher transitions of CO isotopes, such as ¹²CO, ¹³CO, and C¹⁸O(J = 2–1, 3–2) simultaneously with a wideband receiver (210–375 GHz). The optics has a Cassegrain reflector antenna with Nasmyth beam-waveguide feed and is composed of Main-reflector, Sub-reflector, ellipsoidal mirrors, and plane mirrors. New wideband optics will be required to achieve this goal. In order to accomplish the optics, we have designed a corrugated horn with a fractional bandwidth of ∼56 %, and frequency independent optics to couple the beam from the telescope onto the horn. The corrugated horn has a conical profile and the variable corrugation depth. It has been optimized by using CHAMP, our targeting return loss of better than −20 dB, cross-polarization loss of better than −25 dB, and far-field good radiation pattern. The simulation of the corrugated horn results in low return loss, low crosspolarization, and symmetric beam pattern in that frequency band. The simulated aperture efficiency of the designed receiver optics on the 1.85-m telescope is above 0.76 at all frequencies by using GRASP. Recently, we have succeeded in simultaneous observation of ¹²CO, ¹³CO, and C¹⁸O(J = 2–1 and 3–2) toward Orion KL with the optics for the first time.

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Yasumasa Yamasaki, Sho Masui, Masanari Okawa, Koki Yokoyama, Taisei Minami, Shota Ueda, Yutaka Hasegawa, Atsushi Nishimura, Toshikazu Onishi, Hideo Ogawa, Nozomi Okada, Kimihiro Kimura, Alvaro Gonzalez, Takafumi Kojima, Keiko Kaneko, and Ryo Sakai "Optical design of the 1.85-m mm-submm telescope in 210–375 GHz band", Proc. SPIE 11453, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X, 114534H (13 December 2020); https://doi.org/10.1117/12.2561955

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