Semiconductor-based low-noise 100 MHz chirped pulse laser source based on a theta cavity design with an intra-cavity etalon and long-term stabilization

Abstract

This work discusses the development of a frequency chirped, low repetition rate, semiconductor based mode-locked laser having reduced noise over previous demonstrations. Specifically, we present a major upgrade on the 100 MHz harmonically mode-locked Theta (Θ) laser cavity design in the form of the introduction of an intra-cavity fiberized Fabry-Perot etalon. The initial demonstration of the Theta cavity design offered improved energy per pulse and a linearly chirped pulse output compared to conventional cavity designs. Nonetheless, it suffered from pulse-to-pulse timing and energy noise. The noisy operation arises from the harmonic nature of the laser. To mitigate this effect we have inserted a fiberized etalon within the laser cavity. The intra-cavity etalon stores and inter-mixes the pulses of the harmonically mode-locked laser, as well as enforces lasing on a single optical mode-set from the multiple interleaved sets supported by the mode-locked laser due to its harmonic nature. This leads to the generation of a stable optical frequency comb with 100 MHz spacing and the suppression of the RF super-mode noise spurs, which results in a reduction of the laser noise. Due to fiber length drift in both the fiberized laser cavity and the fiberized etalon, a long-term stabilization scheme is necessary. An intra-cavity Hansch - Couillaud scheme is employed. The laser outputs chirped pulses with 10 nm of bandwidth. This work provides an in depth analysis of both the development of the Theta cavity with the intra-cavity etalon and the performance of the developed laser system.