A mode-locked diode laser frequency comb for ultracold atomic physics experiments

Abstract

This thesis is concerned with the development and characterisation of an actively mode locked diode laser system for the provision of a stable optical frequency comb spanning approximately 1 nm around the D2 spectroscopic line of Rubidium. Through large signal sinusoidal modulation of the laser DC injection current at around 3 GHz, Gaussian pulses of 21 ps are achieved with an associated spectral bandwidth in excess of 1 nm, generating pulses of optimal time-bandwidth product 13. An in-house built air-bearing Michelson interferometer is used to confirm the comb-like structure of the optical emission and a modulation frequency detuning range of 10 MHz is determined.

Through a proof of principle investigation of CW injection locking of the frequency comb, phase coherence of the CW master laser with the modes of the frequency comb is demonstrated over at least 36 GHz. Via CW injection locking, sidemode suppression of 20.6 dB is achieved resulting in an 18% rise in the pulse temporal width and a concomitant reduction in the time-bandwidth product to 1.44, as well as a power dependant phase locking detuning range of up to 370 MHz. In the closing chapters, two CW lasers are shown to be stabilised to the frequency comb via Optical Phase-Locked Loops, a temperature stabilised fibre Mach-Zehnder interferometer is demonstrated for carrier frequency removal from a phase modulated laser, and a novel intra-cavity trace water vapour detection method is introduced.

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Identifiers

ORCID for Timothy Freegarde: orcid.org/0000-0002-0680-1330

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