Eric Mottay

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.

On Yb:CaF2 and Yb:SrF2 : Review of spectroscopic and thermal properties and their impact on femtosecond and high power laser performance

We present an overview of laser results we obtained with Yb-doped calcium fluoride and its isotype strontium fluoride. In order to study the laser performance in femtosecond and high power regimes, spectral and thermal properties are first discussed including the potential of these crystals at room and cryogenic temperatures. Experimental demonstrations of high-power and ultrashort pulse oscillators and amplifiers are presented and analyzed.

Transform-limited 100 μJ, 340 MW pulses from a nonlinear-fiber chirped-pulse amplifier using a mismatched grating stretcher–compressor

We report on a compact double-stage ytterbium-doped-fiber chirped-pulse amplifier system delivering high temporal quality 270 fs pulses of 100 microJ energy at a repetition rate of 300 kHz resulting in a peak power of 340 MW. The recompression down to 1.1 times the Fourier limit is based on the exploitation of nonlinear phase shifts associated with mismatched stretcher-compressor units. A 1-m-long ytterbium-doped 80 mum core diameter photonic crystal fiber is implemented as the power amplifier and allows the production of 143 microJ pulses before compression with an accumulated B integral of 17 rad throughout the amplification stages.

Stretcher-free high energy nonlinear amplification of femtosecond pulses in rod-type fibers

We report on the study of direct amplification of femtosecond pulses in an 80 mum core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a 1250 line/mm (l/mm) grating-based compressor, pulses as short as 49 fs with 870 nJ pulse energy and 12 MW peak power are obtained. Alternatively, the use of a 1740 l/mm grating allows the production of higher quality pulses of 70 fs, 1.25 microJ pulse energy, and 16 MW peak power.

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.

Generation of 63 fs 4.1 MW peak power pulses from a parabolic fiber amplifier operated beyond the gain bandwidth limit

We report the generation of 63 fs pulses of 290 nJ energy and 4.1 MW peak power at 1050 nm based on the use of a polarization-maintaining ytterbium-doped fiber parabolic amplification system. We demonstrate that operation of the amplifier beyond the gain bandwidth limit plays a key role on the sufficient recompressibility of the pulses in a standard grating pair compressor. This results from the accumulated asymmetric nonlinear spectral phase and the good overall third-order dispersion compensation in the system.

Multi-meter fiber-delivery and pulse self-compression of milli-Joule femtosecond laser and fiber-aided laser-micromachining

We report on damage-free fiber-guidance of milli-Joule energy-level and 600-femtosecond laser pulses into hypocycloid core-contour Kagome hollow-core photonic crystal fibers. Up to 10 meter-long fibers were used to successfully deliver Yb-laser pulses in robustly single-mode fashion. Different pulse propagation regimes were demonstrated by simply changing the fiber dispersion and gas. Self-compression to ~50 fs, and intensity-level nearing petawatt/cm(2) were achieved. Finally, free focusing-optics laser-micromachining was also demonstrated on different materials.

Yb:YAG single crystal fiber power amplifier for femtosecond sources

We demonstrate a versatile femtosecond power amplifier using a Yb:YAG single crystal fiber operating from 10 kHz to 10 MHz. For a total pump power of 75 W, up to 30 W is generated from the double-pass power amplifier. At a repetition rate of 10 kHz, an output energy of 1 mJ is obtained after recompression. In this configuration, the pulse duration is 380 fs, corresponding to a peak power of 2.2 GW. The M2 beam quality factor is better than 1.1 for investigated parameters.

Ultrashort pulse laser surgery of the cornea and the sclera

The strongly localized interaction process of ultrashort laser pulses with tissue makes femtosecond lasers a powerful tool for eye surgery. These lasers are now routinely used in refractive surgery and other forms of surgery of the anterior segment of the eye. Several clinical laser systems also offer options for corneal grafting and the potential use of ultrashort pulse lasers in glaucoma surgery has been the object of several recent studies which have shown promising results. While devices aimed for interventions in clear tissue may be based on available solid state or fibre laser technology, the development of tools for surgery in more strongly scattering tissue has to account for the compromised tissular transparency and requires the development of optimized laser sources. The present paper focuses on surgery of clear and pathological cornea as well as sclera. It aims to give an overview over typical medical indications for ultrashort pulse laser surgery, the optics of the tissues involved, the available laser technology, the laser–tissue interaction process, and possible future developments.

Highly efficient, high-power, broadly tunable, cryogenically cooled and diode-pumped Yb:CaF2

We present a high-power diode-pumped Yb:CaF(2) laser operating at cryogenic temperature (77 K). A laser output power of 97 W at 1034 nm was extracted for a pump power of 245 W. The corresponding global extraction efficiency (versus absorbed pump power) is 65%. The laser small signal gain was found to be equal to 3.1. The laser wavelength could be tuned between 990 and 1052 nm with peaks that correspond well to the structure of the gain cross-section spectra registered at low temperature.