Optical cavity in the relativistic regime for laser propulsion

Year: 2025

Authors: Lorenzi F., Salasnich L., Pelizzo MG.

Autors Affiliation: Univ Padua, Dipartimento Fis & Astron Galileo Galilei, Via Marzolo 8, I-35131 Padua, Italy; Ist Nazl Fis Nucl, Sez Padova, Via Marzolo 8, I-35131 Padua, Italy; Univ Padua, Ist Nazl Ott, Via Nello Carrara 1, I-50019 Sesto Fiorentino, Italy; Univ Padua, Padua QTech Ctr, Via Gradenigo 6A, I-35131 Padua, Italy; Univ Padua, Dipartimento Ingn Informaz, Via Gradenigo 6A, I-35131 Padua, Italy; CNR, Ist Foton & Nanotecnol, Via Trasea 7, I-35131 Padua, Italy; Univ Padua, Ctr Ateneo Studi & Att Spaziali Giuseppe Colombo, Via Venezia 15, I-35131 Padua, Italy.

Abstract: Laser propulsion has been proposed for relativistic interstellar flights, but it faces the significant challenge of requiring extremely powerful laser radiation due to the inherently low momentum transfer between the beam and the sail. The photon-recycling technique increases thrust by transferring momentum through multiple reflections within a cavity setup, formed by the lightsail and a ground-based mirror in a laser system array. In this work, a delay differential model is developed to describe the evolution of the beam and thrust, incorporating both the Doppler effect and the round-trip time delay experienced by each beam component. With optimized multilayer reflectors, the thrust performance gain is shown to be significant for interstellar flight, although limited by diffraction and the necessity of removing harmful redshifted radiation that could overheat the lightsail. By balancing thrust performance with thermal stability, we derive a simple condition for determining the spectral requirements of the mirrors. Given a selected laser wavelength, this condition fully specifies the necessary properties of the cavity mirrors, enabling the same system to effectively support a range of launch protocols.

Journal/Review: PHYSICAL REVIEW APPLIED

Volume: 24 (3)      Pages from: 34033-1  to: 34033-12

KeyWords: Lightsail; Transit; Design
DOI: 10.1103/pkn5-9mb4