Improving supersonic flights with femtosecond laser filamentation.

When a flying object becomes supersonic, a concomitant increase in drag leads to a considerable rise in fuel consumption. We show experimentally that an embarked terawatt femtosecond laser can significantly decrease this drag. We measured a 50% transient reduction of drag on a test model placed in a supersonic wind tunnel at Mach 3. This effect was initiated by the thin hot air column created in front of the supersonic object by filamentation of the laser pulse. We also show that this technique offers possibilities for steering.

Piston and tilt interferometry for segmented wavefront sensing.

We present a novel interferometric technique dedicated to the measurement of relative phase differences (pistons) and tilts of a periodically segmented wavefront. Potential applications include co-phasing of segmented mirrors of Keck-like telescopes as well as coherent laser beam combining. The setup only requires a holes mask selecting the center part of each element, a diffracting component, and a camera. Recorded interferogram is made of many subareas with sinusoidal fringe pattern. From each pattern, piston is extracted from fringe shift and tilts from fringe frequency and orientation. The pattern analysis is simple enough to enable kilohertz rate operation. The λ ambiguities are solved by a two-wavelength measurement. This technique is compatible with a very high number of elements and can be operated in the presence of atmospheric turbulence.

Tomographic diffractive microscopy with a wavefront sensor.

Tomographic diffractive microscopy is a recent imaging technique that reconstructs quantitatively the three-dimensional permittivity map of a sample with a resolution better than that of conventional wide-field microscopy. Its main drawbacks lie in the complexity of the setup and in the slowness of the image recording as both the amplitude and the phase of the field scattered by the sample need to be measured for hundreds of successive illumination angles. In this Letter, we show that, using a wavefront sensor, tomographic diffractive microscopy can be implemented easily on a conventional microscope. Moreover, the number of illuminations can be dramatically decreased if a constrained reconstruction algorithm is used to recover the sample map of permittivity.

Repetition rate increase and diffraction-limited focal spots for a nonthermal-equilibrium 100-TW Nd:glass laser chain by use of adaptive optics.

Dynamic wave-front correction is applied before each shot on a 100-TW, 30-J/300-fs high-power laser facility by use of an adaptive-optics system. This system allows us to increase the repetition rate of high-energy lasers while maintaining excellent and constant beam focusability with a Strehl ratio of >0.75 despite the amplifiers' not being in thermal equilibrium. The best results in terms of the highest Strehl ratio and intensities are obtained when locking the system on wave-front sensing after pulse recompression.

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.