光帆宇宙船の実験的開発 (The Pressure to Explore: Caltech Researchers Take First Experimental Steps Toward Lightsails that Could Reach Distant Star Systems)

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2025-01-30 カリフォルニア工科大学 (Caltech)

カリフォルニア工科大学(Caltech)の研究チームは、レーザーで超薄膜の「ライトセイル」を推進し、ミニチュア宇宙探査機を超高速で近隣の恒星系まで到達させる構想の実現に向け、初の実験的ステップを踏み出しました。この取り組みは、2016年にスティーブン・ホーキング氏とユーリ・ミルナー氏が開始した「ブレイクスルー・スターショット・イニシアチブ」の一環です。研究チームは、シリコンナイトライド製の厚さ50ナノメートルの膜を用いて、レーザーの放射圧がセイルに及ぼす力を測定するプラットフォームを開発しました。この実験により、理論的な提案から実際の観測と測定への重要な一歩が踏み出されました。

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ライトセイル膜の直接放射圧測定 Direct radiation pressure measurements for lightsail membranes

Lior Michaeli,Ramon Gao,Michael D. Kelzenberg,Claudio U. Hail,Adrien Merkt,John E. Sader & Harry A. Atwater
Nature Photonics  Published:30 January 2025
DOI:https://doi.org/10.1038/s41566-024-01605-w

光帆宇宙船の実験的開発 (The Pressure to Explore: Caltech Researchers Take First Experimental Steps Toward Lightsails that Could Reach Distant Star Systems)

Abstract

Ultrathin lightsails propelled by laser radiation pressure to relativistic speeds are currently the most promising route for flyby-based exoplanet exploration. However, there has been a notable lack of experimental characterization of key parameters essential for lightsail propulsion. Here we present a platform for optomechanical characterization and model development of laboratory-based lightsail prototypes. We propose an approach for simultaneous measurement of optical forces and powers based on the multiphysics dynamics induced by the excitation laser beam. By modelling the lightsail with a 50-nm-thick microscopic silicon nitride membrane suspended by compliant springs, we quantify force from off-resonantly driven displacement and power from heating-induced mechanical mode softening. With this approach, we calibrate the measured forces to the driving powers by operating the device as a micromechanical bolometer. We report radiation pressure forces of 70 fN using a collimated beam of 110 W cm−2 and noise-robust common-path interferometry. Moreover, we quantify the effects of incidence angle and spot size on the optical force and explain the non-intuitive trend by edge scattering. As lightsails will also experience lateral forces, we demonstrate measurement of in-plane motion via grating interferometry. Our results provide a framework for comprehensive lightsail characterization and optomechanical manipulation of macroscopic objects by radiation pressure forces.

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