In this article, we review progress in the development of high peak-power ultrafast lasers, and discuss in detail the design issues which determine the performance of these systems. Presently, lasers capable of generating terawatt peak powers with unprecedented short pulse duration can now be built on a single optical table in a small-scale laboratory, while large-scale lasers can generate peak power of over a petawatt. This progress is made possible by the use of the chirped-pulse amplification technique, combined with the use of broad-bandwidth laser materials such as Ti:sapphire, and the development of techniques for generating and propagating very short (10–30 fs) duration light pulses. We also briefly summarize some of the new scientific advances made possible by this technology, such as the generation of coherent femtosecond x-ray pulses, and the generation of MeV-energy electron beams and high-energy ions.

/pdf/high-power-ultrafast-lasers-20ipbk9mdb.pdf

High power ultrafast lasers

The prospects for ultrashort pulse duration and ultrahigh intensity using optical parametric chirped pulse amplifiers

Ultrafast optics has undergone a revolution in the past two decades, driven by new
methods of pulse generation, amplification, manipulation, and measurement. We review
the advances made in the latter field over this period, indicating the general
principles involved, how these have been implemented in various experimental
approaches, and how the most popular methods encode the temporal electric field of a
short optical pulse in the measured signal and extract the field from the data.

Characterization of ultrashort electromagnetic pulses

Diffraction gratings were discovered during the 18th century, and they are now widely used in spectrometry analysis, with outstanding achievements spanning from the probing of single molecules in biological samples to the analysis of solar systems in astronomy. The fabrication of high-quality diffraction gratings requires precise control of the period at a nanometer scale. The discovery of lasers in the 1960s gave birth to optical beam lithography in the 1970s. This technology revolutionized the fabrication of diffraction gratings by offering highly precise control of the grating period over very large scales. It is surprising to see that a few years after, the unique spectral properties of diffraction gratings revolutionized, in turn, the field of high-energy lasers. We review in this paper the physics of diffraction gratings and detail the interest in them for pulse compression of high-power laser systems.

/pdf/diffraction-gratings-from-principles-to-applications-in-high-8eupgng34m.pdf

Diffraction gratings: from principles to applications in high-intensity lasers

This paper studies gratings engraved in multilayer dielectric stacks for ultra high intensity laser compressors application. We design various grating profiles with high reflected efficiencies for 1780 l/mm multilayer dielectric gratings (MLD). Each grating is defined to exhibit a different electric field maximum value in the pillars of the grating. A damage testing facility operating at 1.053 μm, 500 fs pulse duration is used to damage test the parts manufactured from these designs. It is evidenced that for fixed incident angle and materials the damage of the grating is directly related to the electric field intensity maximum in the material, which depends on the groove profile. Laser induced damage thresholds of 5 J/ cm2 are experimentally reached with very high and uniform efficiencies.

https://hal-cea.archives-ouvertes.fr/cea-01053352/document

Effect of electric field on laser induced damage threshold of multilayer dielectric gratings

Sensitivity of alignment is one of the major issues in the stretcher-compressor devices used for chirped pulse amplification. In this paper we discuss the temporal aberrations induced by the different kinds of misalignments of the gratings and we emphasize the importance of spatially transverse effects. We discuss simple criteria for minimizing these faults. Finally, we introduce the basic principles of self-compensation and present such a set-up based on symmetry considerations. >

Temporal aberrations due to misalignments of a stretcher-compressor system and compensation

High-energy petawatt lasers using the chirped-pulse amplification technique require meter-sized gratings to limit the beam fluence on the surface of the grating. An alternative, studied by many groups, is a mosaic grating consisting of smaller, coherently added gratings. We propose what we believe to be a new compression scheme consisting of beam phasing instead of grating mosaic phasing. This synthetic aperture compression scheme allows us to control the beam thanks to a unique segmented mirror equipped with three degrees of freedom. With this configuration, the beam is divided into small subapertures adapted to the classical grating size. After compression, these subapertures are coherently added before the focusing stage. Therefore the alignment processes are simplified.

Synthetic aperture compression scheme for a multipetawatt high-energy laser.

High-energy petawatt lasers use series of spatial filters in their amplification section. The refractive lenses employed introduce longitudinal chromatism that can spatially and temporally distort the ultrafast laser beam after focusing. To ensure optimum performances of petawatt laser facilities, these distortions need to be corrected. Several solutions using reflective, refractive, or diffractive optical components can be addressed. We give herein a review of these various possibilities with their application to the PETAL (Petawatt Aquitaine Laser at the Laser Integration Line facility) laser beamline and show that diffractive-based corrections appear to be the most promising.

/pdf/chromatism-compensation-of-the-petal-multipetawatt-high-dbo7jdv46z.pdf

Chromatism compensation of the PETAL multipetawatt high-energy laser.

A multi-Petawatt high-energy laser PETAL coupled to the Ligne d’Int´ Laser (LIL) is under construction in the Aquitaine Region in France. This Petawatt laser will be dedicated to academic experiments in the fields of high energy density physics and ultra high intensity. Nd : glass laser chain coupled with the chirped pulse amplification (CPA technique allows delivery of high energy. Optical parametric CPA for pre-amplification and a new compression scheme will be implemented. PETAL is designed to deliver 3.6 kJ of energy in 500 fs on a target corresponding to 7.2 PW. The PETAL beam linked to the up to 60 kJ ns UV beams from the LIL will present new scientific research opportunities. (Some figures in this article are in colour only in the electronic version)

/pdf/overview-of-petal-the-multi-petawatt-project-in-the-lmj-ifn5auhx7y.pdf

Overview of PETAL, the multi-Petawatt project in the LMJ facility

Seeded nanosecond Q-switched Nd:YAG lasers working with an unstable resonator and a variable reflectivity mirror are widely used, for they represent useful sources for stable and repeatable light–matter interaction experiments. Moreover, in most setups, the fundamental wavelength is converted to higher harmonics. When the injection seeder is turned off, random longitudinal mode beating occurs in the cavity, resulting in strong variations of the temporal profile of the pulses. The generated spikes can then be ten times higher than the maximum of equivalent seeded pulses. This strong temporal incoherence is shown to engender spatial incoherence in the focal plane of such unseeded pulses leading to an instantaneous angular displacement of tens of µrad. This effect is even more pronounced after frequency conversion.

C. Rouyer

Papers

Temporal aberrations due to misalignments of a stretcher-compressor system and compensation

Synthetic aperture compression scheme for a multipetawatt high-energy laser.

Chromatism compensation of the PETAL multipetawatt high-energy laser.

Overview of PETAL, the multi-Petawatt project in the LMJ facility

Experimental evidence of temporal and spatial incoherencies of Q-switched Nd:YAG nanosecond laser pulses