We generate broadband pulses covering the Yb: and Tm:silica amplification ranges with a passively phase-locked front end based on Er:fiber technology. Full spectral coherence of the octave-spanning output from highly nonlinear germanosilicate bulk fibers is demonstrated. Seeding of a high-power Tm:fiber generates pulses with a clean spectral shape and a bandwidth of 50 nm at a center wavelength of 1.95 μm, pulse energy of 250 nJ, and repetition rate of 10 MHz. © 2012 Optical Society of America OCIS codes: 320.7160, 140.3510, 190.7110. Applications of ultrafast pulsed radiation are increasingly based on fiber laser technology due to its inherent advantages such as compactness, stability, high power, and turn-key operation. Recently, Tm:silica fiber amplifiers are attracting a lot of attention due to their broad gain bandwidth spanning from 1.85 to 2.1 μm [7]. The long wavelength ensures a relatively high threshold for four-wave-mixing and stimulated Raman processes. Simultaneously, it supports single-mode operation at large mode field diameters [8], thus enabling high peak powers. Up to now, exploiting the full amplification bandwidth of Tm:fiber amplifiers has been limited by a lack of ultrabroadband and coherent seed sources. Only recently, a Tm:fiber oscillator has been introduced, delivering pulses with a duration of 78 fs and a spectral width of 130 nm [9]. Other approaches based on well-established Er:fiber technology may be even more desirable. However, Raman self frequency shifting [10] or supercontinuum (SC) generation in microstructured fibers [11] turned out to be ineffective, since they provide seed pulses flawed by a significant degree of incoherence [3,12].In this Letter, we present a passively phase-locked and ultrabroadband source that is suitable for coherent seeding of both Yb: and Tm:fiber systems. This setup exploits Er:fiber technology combined with frequency conversion in highly nonlinear bulk fibers (HNF). It is worth noting that our approach allows phase coherent operation of synchronized multibranch systems at different amplification wavelengths, thus enabling synthesis of intense pulses down to single-cycle durations [13].Figure 1(a) shows the schematic setup of the system. The seed source starts with a solitonic Er:fiber oscillator modelocked via a saturable absorber mirror. It is followed by a passively carrier-envelope phase-locked amplifier system. The output pulses, centered at 1.55 μm with energies up to 8 nJ at a repetition rate of 40 MHz, are available at up to six distinct branches [14]. The key point of our system is the generation of ultrabroadband seed pulses in a highly nonlinear bulk germanosilicate fiber that we demonstrate to exhibit full spectral coherence. In detail, the 8 nJ output of the Er:fiber system is compressed in a silicon (Si) prism sequence and then coupled into a combination of 9 cm polarization maintaining single-mode fiber (PM-SMF) followed by an 8 mm long germanosilicate HNF [15]. The variable insertion of the Si prism in the compressor stage allows f...

A high power femtosecond Yb:fiber amplifier operating with exceptional noise performance and long term stability is demonstrated. It generates a 10 MHz train of 145 fs pulses at 1.03 μm with peak powers above 36 MW. The system features a relative amplitude noise of 1.5 · 10 −6 Hz −1∕2 at 1 MHz and drifts of the 60 W average power below 0.3% over 72 hours of continuous operation. Until recently, high-power femtosecond systems were limited to kHz repetition rates, and technologies relied mainly on Ti:sapphire as a gain medium. But various concepts based on Ytterbium-doped host materials are arising as an important alternative. In particular, Yb 3 :fiber amplifiers allow to combine power scaling with maximum flexibility for operating at high repetition rates and short pulse durations [1]. All these ingredients are crucial for advanced precision experiments exploiting extreme nonlinearities and/or sub-cycle optics at optimum noise performance and long-term stability. In particular, a high repetition rate ensures maximum detection statistics in the investigation of fundamental quantum phenomena.Femtosecond operation at high average power is facilitated by Yb-doped large mode area photonic crystal fibers (PCF) [2]. These gain elements allow control of nonlinear effects that affect and limit amplification of ultrashort pulses. Employing chirped-pulse amplification (CPA) schemes enables Yb:fiber amplifier systems delivering impressive pulse energies up to the millijoule level [3]. Owing to the large gain bandwidth of Yb-doped silica, pulse compression to the few-hundred femtosecond regime [4 7] proved suitable for implementing high-power frequency combs [4] and generation of high harmonics [8]. One challenge consists of refining the performance of such high-power Yb:fiber amplifiers toward maximum stability in amplitude and phase. In particular, the seed source should display excellent noise robustness and ideally provide a broad spectrum tailored to cover the full Yb-gain bandwidth. In this repory, we present an Yb-doped fiber amplifier system that exploits Er:fiber technology combined with fully coherent frequency conversion in highly nonlinear fibers [9] for generation of the seed light. This approach provides passively phase stable dispersive waves and solitons with hundreds of nm of bandwidth together with intense femtosecond pulses that might serve as intrinsically synchronized energy sources for broadband parametric amplification. The Yb:fiber amplifier employs a fully linear CPA scheme [10] and allows to generate multi-μJ level pulses at 10-MHz repetition rate. The design features two amplifier stages that operate in saturation optimized for low-noise performance and exceptional long-term stability. Figure 1 outlines the schematic setup. The seed source consists of a passively phase-locked Er:fiber system [11]. This laser operates at a wavelength of 1.55 μm with a repetition rate of 40 MHz providing signal at multiple ports. One of them uses an electro-optic modulator (EOM) as a pulse picker to reduce the repeti...

A high‐power femtosecond Yb:fiber system is seeded by a phase‐locked Er:fiber source and drives an ultra‐broadband optical parametric amplifier that operates at 10 MHz repetition rate. The resulting pulses display precise control of the carrier‐envelope phase. Their 8.3 fs temporal duration corresponds to 2.3 optical cycles of the 1100 nm carrier wavelength. Focusing 200 nJ of pulse energy into widegap materials generates optical harmonics up to fifth order. Even in a perturbative regime, strong effects of the carrier‐envelope phase on the emitted spectra are observed.

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