Louis Daniault

Coherent beam combining of two femtosecond fiber chirped-pulse amplifiers

We demonstrate coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using a feedback loop based on an electro-optic phase modulator, an average power of 7.2 W before compression is obtained with a combining efficiency of 90%. The spatial and temporal qualities of the oscillator are retained, with a recombined pulse width of 325 fs. This experiment opens up a way to scale the peak/average power of ultrafast fiber sources.

Femtosecond fiber chirped- and divided-pulse amplification system

We implement both chirped pulse amplification and divided pulse amplification in the same femtosecond fiber amplifier setup. This scheme allows an equivalent stretched pulse duration of 2.4 ns in a compact tabletop system. The generation of 77 W of compressed average power at 4.8 MHz, together with 320 fs and 430 μJ pulses at a repetition rate of 96 kHz, is demonstrated using a distributed mode-filtering, rod-type, ytterbium-doped fiber. Limitations in the temporal recombining efficiency due to gain saturation inside the fiber amplifier are identified.

Passive coherent combination of two ultrafast rod type fiber chirped pulse amplifiers

Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs and 650 μJ pulses corresponding to 60 W of average power at a repetition rate of 92 kHz. Furthermore, at 2 MHz of repetition rate record coherent combining average powers of 135 W before and 105 W after compression are measured. A combining efficiency higher than 90% is maintained over the whole range of output powers and repetition rates investigated demonstrating the efficiency and robustness of the passive combining technique. The measured pulse-to-pulse relative power fluctuation at high energy is 2%, indicating that the system is essentially immune to environmental phase noise. We believe the passive combining method to be an attractive approach for compact multi-GW peak power femtosecond fiber-based sources.

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers

We propose and demonstrate an architecture that achieves passive coherent combination of two femtosecond fiber chirped-pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac interferometer. The experiment shows that the temporal, spectral, and spatial qualities of each beam are retained, with the generation of 250 fs pulses at 35 MHz repetition rate, an uncompressed average power of 10 W, and a combining efficiency of 96%. The behavior of this architecture in the presence of high accumulated nonlinear phase is investigated.

Amplification of femtosecond pulses in large mode area photonic bandgap Bragg fiber

We demonstrate amplification of femtosecond pulses in large mode area singlemode Yb-doped photonic bandgap Bragg fibers. 260 fs 5 μJ pulses are obtained at 100 kHz repetition rate (1 W of average power).

Energy scaling of ultrafast fiber systems using chirped and divided pulse amplification

The technique known as chirped pulse amplification (CPA) is the most popularly used technique to scale the energy of ultrashort amplification systems. This technique consists in stretching and compressing the pulse upstream and downstream the amplifier to mitigate various deleterious effects and still recover ultrashort pulse duration. However, its implementation is increasingly difficult and costly when the desired stretched pulse duration is greater than 1 ns, due to the increasing size of the gratings and overall optical setup. Such long stretched pulse duration is therefore not used for compact tabletop or industrial systems. The divided-pulse amplification (DPA) idea was proposed more recently [1], and is similar to CPA in the sense that it also consists in redistributing the pulse energy over a time interval larger than the initial pulsewidth to reduce the peak power. In this scheme, a train of several orthogonally polarized delayed pulse replicas is generated and amplified, before final recombination. In this contribution, we propose and demonstrate for the first time to our knowledge a femtosecond fiber amplifier that uses both concepts simultaneously to scale the output energy of a compact (1.2 m × 0.4 m2) femtosecond fiber system. The experimental arrangement is depicted in Fig. 1. The DPA setup is included inside a moderately nonlinear fiber CPA in which the impact of nonlinearities can be partially compensated by the dispersion mismatch of the stretcher and compressor units [2]. Temporal pulse divisions are implemented using two free-space Mach-Zehnder interferometers in which the splitting and recombining elements are thin-film polarizers. Depending on the orientation of the input linear polarization, the power fraction sent in each arm can be adjusted. In particular, one arm can be completely bypassed, reducing the number of replicas generated. The arm length differences in both interferometers are 1.32 m and 0.66 m respectively. On the way to the amplifier, this arrangement therefore generates a train of up to 4 orthogonally polarized chirped pulse replicas separated by a delay of 2.2 ns and be equivalent to a stretching ration > 2 ns.

Femtosecond fiber chirped- and divided-pulse amplification

We implemented for the first time both chirped pulse and divided pulse amplification in the same femtosecond fiber amplifier setup leading to the generation of 430 μJ, 320 fs pulses at 100 kHz.

2 GW peak power ultrafast fiber system using passive coherent beam combining

Using passive coherent beam combining of two ultrafast fiber amplifiers, we demonstrate the generation of high temporal quality 300 fs 650 µJ pulses at 92 kHz repetition rate, corresponding to 60 W average power.

Coherent beam combining of fiber amplifiers in the femtosecond regime

Ytterbium-doped fiber amplifiers present great advantages, but are limited in terms of pulse energy by the small transverse dimensions of the amplifying medium. Coherent combining of fiber amplifiers is a scalable technique that allows the increase of the pulse energy, but is demonstrated so far mostly in CW regime. Here, we report on the coherent beam combining of two identical femtosecond Yb-doped fiber chirped pulse amplifiers, using active control of the phase between the amplifiers by use of an integrated electro-optics phase modulator.

Coherent combining of two femtosecond fiber chirped pulse amplifiers

We demonstrate coherent combining of two fiber chirped pulse amplifiers seeded by a common oscillator. A phase stability of λ/20 is obtained using a fiber electro-optic phase modulator, and the recombined pulsewidth is 485 fs.