Injection-locking of violet laser diodes with a 3.2GHz offset frequency for driving Raman transitions in 43Ca+

TL;DR

This paper demonstrates injection-locking of violet diode lasers with a 3.2GHz offset for precise Raman transition driving, achieving narrow linewidths and stable output suitable for quantum applications.

Contribution

It introduces a method to lock two violet diode lasers with a large offset frequency using optical injection locking and an acousto-optic modulator, achieving high coherence.

Findings

Linewidth of <=10Hz at 3.2GHz beat note

Up to 20mW output power per slave laser

Effective injection locking with minimal injection power

Abstract

Two cw single-mode violet (397nm) diode lasers are locked to a single external-cavity master diode laser by optical injection locking. A double-pass 1.6GHz acousto-optic modulator is used to provide a 3.2GHz offset frequency between the two slave lasers. We achieve up to 20mW usable output in each slave beam, with as little as 25 \mu W of injection power at room temperature. An optical heterodyne measurement of the beat note between the two slave beams gives a linewidth of <=10Hz at 3.2GHz. We also estimate the free-running linewidth of the master laser to be approximately 3MHz, by optical heterodyning with a similar device.