A phase-modulated laser system of ultra-low phase noise for compact atom interferometers

• Published in: Journal of the Korean Physical Society Vol. 67; no. 2; pp. 318 - 322
• Main Authors: Lee, Ki-Se, Kim, Jaewan, Lee, Sang-Bum, Park, Sang Eon, Kwon, Taek Yong
• Format: Journal Article
• Language: English
• Published: Seoul The Korean Physical Society 01.07.2015; 한국물리학회
• Subjects: Mathematical and Computational Physics; Particle and Nuclear Physics; Physics; Physics and Astronomy; Theoretical; 물리학; Optical phase-lock; Atom interferometer; Phase modulation
• ISSN: 0374-4884; 1976-8524
• DOI: 10.3938/jkps.67.318

A compact and robust laser system is essential for mobile atom interferometers. Phase modulation can provide the two necessary phase-coherent frequencies without sophisticated phase-locking between two different lasers. However, the additional laser frequencies generated can perturb the atom interferometer. In this article, we report on a novel method to produce a single high-power laser beam composed of two phase-coherent sidebands without the perturbing carrier mode. Light from a diode laser is phase-modulated by using a fiber-coupled electro-optic modulator driven at 3.4 GHz and passes through a Fabry-Perot cavity with a 6.8 GHz free spectral range. The cavity filters the carrier mode to leave the two first-order sidebands for the two-photon Raman transition between the two hyperfine ground states of 87 Rb. The laser beam is then fed to a single tapered amplifier, and the two sidebands are both amplified without mode competition. The phase noise is lower than that of a state-of-the-art optically phase-locked external-cavity diode laser (−135 dBrad 2 /Hz at 10 kHz) at frequencies above 10 Hz. This technique can be used in all-fiber-based laser systems for future mobile atom interferometers.