Highly scalable femtosecond coherent beam combining demonstrated with 19 fibers.

Coherent beam combining in the femtosecond regime of a record number of 19 fibers is demonstrated. The interferometric phase measurement technique, particularly well suited to phase-lock a very large number of fibers, is successfully demonstrated in the femtosecond regime. A servo loop is implemented to control piezoelectric fiber stretchers for both phase and delay variation compensation. The residual phase errors are below λ/60 rms. Nearly 50% of the total energy is contained in the far-field central lobe. After compression, we obtain a combined pulse width of 300 fs identical to the master oscillator pulse width.

Influence of ASE on the gain distribution in large size, high gain Yb3+:YAG slabs.

Amplified spontaneous emission (ASE) in large size, high gain Yb(3+):YAG slabs severely impacts the gain/energy storage capability. We will discuss numerical simulations and experimental results obtained on large size Yb(3+):YAG slabs. The spatial distribution and temporal evolution is shown under different conditions.

Multiple-wave lateral shearing interferometry for wave-front sensing.

Multiple-wave achromatic interferometric techniques are used to measure, with high accuracy and high transverse resolution, wave fronts of polychromatic light sources. The wave fronts to be measured are replicated by a diffraction grating into several copies interfering together, leading to an interference pattern. A CCD detector located in the vicinity of the grating records this interference pattern. Some of these wave-front sensors are able to resolve wave-front spatial frequencies 3 to 4 times higher than a conventional Shack-Hartmann technique using an equivalent CCD detector. Its dynamic is also much higher, 2 to 3 orders of magnitude.

Beam-focus shaping by use of programmable phase-only filters: application to an ultralong focal line.

We have developed a high-resolution programmable adaptive-optic device based on an optically addressed liquid-crystal electro-optic valve controlled by an achromatic three-wave lateral shearing interferometer. We apply this phase-only filter and loop to shape the far-field pattern of laser beams. As a first application, we theoretically compute and experimentally verify the focus along a line longer than tens of Rayleigh ranges.

Nearly diffraction-limited laser focal spot obtained by use of an optically addressed light valve in an adaptive-optics loop.

We demonstrate correction of laser wave-front distortions by use of an adaptive-optical technique based on a light valve. The setup consists of an achromatic and adjustable-sensitivity wave-front sensor and a wave-front corrector relying on an optically addressed liquid-crystal spatial light modulator. Experimental results with strongly aberrated beams focused close to the diffraction limit are presented for the cw regime. Additional experiments with pulses and measurement of damage thresholds show that this approach is relevant for spatial phase correction of ultraintense laser pulses.

Single-shot wave-front measurements of high-intensity ultrashort laser pulses with a three-wave interferometer.

A simple new three-wave interferometric technique is used to measure, for what is believed to be the first time, the wave front of femtosecond ultrahigh-peak-power pulses carrying a strong B integral (B = 5.26+/-0.15) in a single shot. Wave-front distortions of a terawatt-class laser system are measured with good accuracy (lambda/50) and discussed. These distortions can significantly reduce the focused peak intensity, emphasizing the necessity of implementing adaptive optics in ultrahigh-intensity chirped-pulse amplification lasers.

Wave-front correction of femtosecond terawatt lasers by deformable mirrors.

Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved, for the first time to our knowledge, with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic. Wave-front distortions of a 100-fs laser that are due to third-order nonlinear effects have been compensated for. This technique, which permits correction in a straightforward process that requires no feedback loop, is also used on a 10-TW Ti:sapphire-Nd:phosphate glass laser in the subpicosecond regime. We also demonstrate that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity.