Searching for Exoplanets Using a Microresonator Astrocomb (1801.05174v1)

Abstract: Detection of weak radial velocity shifts of host stars induced by orbiting planets is an important technique for discovering and characterizing planets beyond our solar system. Optical frequency combs enable calibration of stellar radial velocity shifts at levels required for detection of Earth analogs. A new chip-based device, the Kerr soliton microcomb, has properties ideal for ubiquitous application outside the lab and even in future space-borne instruments. Moreover, microcomb spectra are ideally suited for astronomical spectrograph calibration and eliminate filtering steps required by conventional mode-locked-laser frequency combs. Here, for the calibration of astronomical spectrographs, we demonstrate an atomic/molecular line-referenced, near-infrared soliton microcomb. Efforts to search for the known exoplanet HD 187123b were conducted at the Keck-II telescope as a first in-the-field demonstration of microcombs.

• The paper introduces the use of Kerr soliton microcombs to achieve precise radial velocity measurements with 3-5 m/s precision.
• The paper details an experimental demonstration at the Keck II telescope, showcasing a compact chip-scale calibration alternative to traditional methods.
• The paper identifies instrumental noise challenges and highlights the need for integrated calibration techniques to enhance exoplanet detection.

Exploring the Use of Microresonator Astrocombs for Exoplanet Detection via Radial Velocity Measurement

The paper "Searching for Exoplanets Using a Microresonator Astrocomb" introduces a novel approach to exoplanet detection that leverages the emerging technology of Kerr soliton microcombs for precise spectrograph calibration. This essay provides an overview of the methods and findings presented in the paper, with a focus on the potential implications and future directions suggested by the research.

The detection of exoplanets using radial velocity (RV) measurements requires high spectral precision, particularly when searching for Earth-like planets in the habitable zone of solar-type stars. Achieving sufficient precision traditionally involves complex calibration processes, often hampered by inadequacies in conventional calibration methods, such as those relying on hollow-cathode gas lamps. The utilization of laser frequency combs (LFCs) has previously facilitated advancements in RV precision; however, many existing solutions add complexity due to their reliance on mode-locked lasers with narrowly spaced frequency lines.

This paper presents the application of soliton microcombs, a promising alternative due to their inherent advantages, including suitable frequency line spacing, robust mode-locking, and compact size. The described demonstration at the Keck II telescope's NIRSPEC instrument marks a pioneering effort to employ microcombs for astronomical purposes.

The experimental setup involved deploying a soliton microcomb with 22.1 GHz mode spacing, calibrated against stabilized atomic/molecular lines and monitored via a rubidium clock reference. Notably, the soliton microcomb can produce stable, repeatable spectral lines, circumventing complexities associated with traditional filtering steps. The testing revealed a wavelength precision of approximately 3-5 m/s, highlighting the microcomb's capability to support precision RV measurements.

A significant limitation encountered during the demonstration was the inability to achieve on-sky detection of the exoplanet HD 187123b due to instrumental variations attributed to the Keck II telescope’s configuration. These variations underscore the importance of integrating LFC with stellar observations to correct for instrumental noise and improve precision.

The research illustrates the substantial promise of soliton microcombs for space-borne applications, facilitating enhanced precision in RV measurements. The paper outlines a path towards achieving chip-scale integration, aimed at further reducing the system's size, weight, and power consumption, thereby paving the way for widespread adoption in both terrestrial and deep-space spectrographic instrumentation.

In conclusion, this research contributes to ongoing efforts to improve exoplanet detection methods, particularly by addressing challenges in RV measurement precision. The advancements in microresonator technology could markedly enhance the sensitivity and practical deployment of spectrographs, as well as their utility in remote environments. Future developments may focus on extending the spectral range, refining calibration techniques, and adapting the technology for simultaneous calibration and observation models.