Abstract
Femtosecond modelocked lasers with multi-gigahertz pulse repetition rates are attractive sources for all applications that require individually resolvable frequency comb lines or high sampling rates. However, the modelocked laser architectures demonstrated so far have several issues, including the need for single-mode pump lasers, limited output power, Q-switching instabilities and challenging cavity geometries. Here, we introduce a technique that solves these issues. In a two-dimensionally patterned quasi-phase-matching (QPM) device, we create a large, low-loss self-defocusing nonlinearity, which simultaneously provides SESAM-assisted soliton modelocking in the normal dispersion regime and suppresses Q-switching induced damage. We demonstrate femtosecond passive modelocking at 10-GHz pulse repetition rates from a simple straight laser cavity, directly pumped by a low-cost highly spatially multimode pump diode. The 10.6-GHz Yb:CaGdAlO4 (Yb:CALGO) laser delivers 166-fs pulses at 1.2 W of average output power. This enables a new class of femtosecond modelocked diode-pumped solid-state lasers with repetition rates at 10 GHz and beyond.
Highlights
To date, there are several approaches for generating frequency combs with large comb-line spacings such as electro-optic (EO) combs[16,17,18], microresonator combs[19, 20], Kerr lens modelocked (KLM) solid-state lasers[21, 22] or comb-line filtering of e.g. modelocked fibre lasers in the few-hundred MHz-regime
A compelling approach to obtain such a tuneable selfdefocusing nonlinearity is via the cascading of quadratic nonlinearities (CQN)[29]
A potential drawback of the CQN technique are the losses associated to residual second-harmonic generation (SHG)
Summary
There are several approaches for generating frequency combs with large comb-line spacings such as electro-optic (EO) combs[16,17,18], microresonator combs[19, 20], Kerr lens modelocked (KLM) solid-state lasers[21, 22] or comb-line filtering of e.g. modelocked fibre lasers in the few-hundred MHz-regime. As an alternative to GHz KLM lasers, a robust fibre-based oscillator with a repetition rate of a few 100 MHz and filtering the comb lines using Fabry–Pérot cavitites has been sucessfully demonstrated as a way to reach comb-line spacings in the multi-gigahertz regime[24]. The complexity of such a system can rapidly increase depending on the number of external cavities that need to be locked to achieve sufficient supression of the unwanted intermediate comb lines. We introduce a new class of ultrafast lasers based on a simple straight cavity which solves the problems described above
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