Abstract
We phase-stabilized the carrier-envelope-offset (CEO) frequency of a SESAM modelocked Yb:CaGdAlO₄ (CALGO) thin disk laser (TDL) generating 90-fs pulses at a center wavelength of 1051.6 nm and a repetition rate of 65 MHz. By launching only 2% of its output power into a photonic crystal fiber, we generated a coherent octave-spanning supercontinuum spectrum. Using a standard f-to-2f interferometer for CEO detection, we measured CEO beats with 33 dB signal-to-noise ratio in 100 kHz resolution bandwidth. We achieved a tight lock of the CEO frequency at 26.18 MHz by active feedback to the pump current. The residual in-loop integrated phase noise is 120 mrad (1 Hz-1 MHz). This is, to our knowledge, the first CEO-stabilized SESAM modelocked TDL. Our results show that a reliable lock of the CEO frequency can be achieved using standard techniques in spite of the strongly spatially multimode pumping scheme of TDLs. This opens the door towards fully-stabilized low-noise frequency combs with hundreds of watts of average power from table-top SESAM modelocked thin disk oscillators.
Highlights
The generation of carrier-envelope-offset (CEO) frequency stabilized pulses with multimegahertz repetition rates and hundreds of watts average power is highly attractive for numerous applications in science and industry
Our results show that a reliable lock of the CEO frequency can be achieved using standard techniques in spite of the strongly spatially multimode pumping scheme of thin disk laser (TDL)
Carrier-envelope-phase (CEP) stable pulses with high average power are essential for high-harmonic generation (HHG) at multimegahertz repetition rate, an area with an extremely high scientific potential [1,2,3,4]
Summary
The generation of carrier-envelope-offset (CEO) frequency stabilized pulses with multimegahertz repetition rates and hundreds of watts average power is highly attractive for numerous applications in science and industry. Most commonly used high power CEP-stabilized laser systems are either based on Ti:sapphire amplifiers that are usually limited to the kHz regime, or on multi-stage fiber amplifier systems, which can reach MHz repetition-rates and high average powers [5] but their low Q-factor cavities and strong nonlinearities make the noise reduction more challenging, require careful design schemes for low noise operation [6]. Durations above 200 fs are usually too long to directly support the generation of a coherent octave-spanning spectrum in a nonlinear fiber [20], which is required for standard CEO frequency detection in an f-to-2f interferometer [21] It remained so far unclear whether pump-induced instabilities could potentially increase the noise level of the oscillator such that a stable frequency comb could not be achieved [22]. This work proves that the standard CEO stabilization schemes can be applied for high-power modelocked laser oscillators which are pumped by inexpensive spatially-multimode pump diodes, opening the door to unamplified high-power self-referenced frequency combs with average powers of hundreds of watts
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