Development of an Interference Filter-Stabilized External-Cavity Diode Laser for Space Applications

Abstract

The National Time Service Center of China is developing a compact, highly stable, 698 nm external-cavity diode laser (ECDL) for dedicated use in a space strontium optical clock. This article presents the optical design, structural design, and preliminary performance of this ECDL. The ECDL uses a narrow-bandwidth interference filter for spectral selection and a cat’s-eye reflector for light feedback. To ensure long-term stable laser operation suitable for space applications, the connections among all the components are rigid and the design avoids any spring-loaded adjustment. The frequency of the first lateral rocking eigenmode is 2316 Hz. The ECDL operates near 698.45 nm, and it has a current-controlled tuning range over 40 GHz and a PZT-controlled tuning range of 3 GHz. The linewidth measured by the heterodyne beating between the ECDL and an ultra-stable laser with 1 Hz linewidth is about 180 kHz. At present, the ECDL has been applied to the principle prototype of the space ultra-stable laser system.

Research on Narrow Linewidth External Cavity Semiconductor Lasers

“…In 2020, Zhang L et al [49] used a narrow-band interference filter for spectral selection, and used a cat-eye reflector for optical feedback to design an ECSL. The ECSL works near 698.45 nm.…”

Design and fabrication of a compact, high-performance interference-filter-based external-cavity diode laser for use in the China Space Station

“…Limited to the circumstance of the lack of an ultra-narrow-linewidth USL system, the linewidth of the IF-ECDL cannot be determined currently. However, based on previous literatures, the linewidth of the IF-ECDL with such a configuration should be at a level of kilohertz (kHz) [15,19,20] .…”

“…By adjusting the incidence angle of laser beam on the IF, the longitude mode can be selected. Previous study has proved that the IF-based ECDL (IF-ECDL) is less sensitive to acoustic, thermal, vibration, and mechanical disturbances than Littman-Metcalf or Littrow-based ECDLs [15] . With these advantages, the IF-ECDL is currently the most suitable design for space missions among all ECDL designs.…”

“…Consequently, the IF-ECDL was selected as the most feasible option in the Project d'Horloge Atomique a Refroidissement d'Atomes en Orbite (PHARO) project, the SOC2 (space optical clock) project in the International Space Station (ISS), and the SOLC in the CSS [16][17][18] . Following that, several prototypes of IF-ECDLs have been developed in laboratories [15,19,20] . Performance requirements of the IF-ECDL for the SOLC have been achieved by these prototypes.…”

Testing gravity with cold atom interferometry: Results and prospects

“…The SOC (Space Optical Clock) ESA R&D activity led to the demonstration of compact and transportable Sr optical clocks [341] and the development of the relevant technology for a space mission on the ISS [342]. Similar efforts are ongoing in China [343].…”