Intense Laser Optical Optimization for Propagation
Traditionally the intense laser beam at the end of the chain , after compression , has a Gaussian amplitude distribution type, or super- gaussian. This is teh eigenmode of the system and theassociated spatial phase is quasi plane if a deformable mirror is implanted or aberrant if it is not the case . Thus, the propagation conditions of the intense beam are not controlled but simply dictated by the shapes of the amplitude and phase . Whether you're trying to maximize the laser fluence focused on a distant target or optimize the interaction and the position of a set of filaments of plasma beam , the best way to achieve this, is to control the amplitude and initial phase of the laser beam before propagation . But now it seems quite interesting and can be able to fully control the amplitude and phase after compression by formatting using multi- conjugate adaptive optics , which in our case is two deformable mirrors positioned in appropriate plans and by a driving wave sensor based on the principle of phase diversity front. <br />It is thus possible to produce an annular beam, the propagation is controlled or to produce a beam having substantial amplitude modulations to generate for example a network of filaments of controlled spacing . Studies related to these uses seem quite relevant to the DGA applications. Control in the spatial domain of the amplitude and phase is also very interesting when focusing intense lasers, multi- petawatts type plasma physics. This will maximize the illumination during the interaction and therefore take full advantage of the intense laser.
ILOOP will focus on two tasks.
1.achievement of high LIDT femtosecond mirrors :
Will be developed mirrors ( ~ 1 J / cm ² ) for 10 to 15 pulses fs for transporting beam after compression . Currently such mirrors do not exist.
This task will run for the duration of the project with successive iterations over the coatng runs and the provision of test components. This task is divided into four subtasks.
It begins with the design study of the mirror. Prototypes of mirrors are then made ??and characterized in LIDT but also in group velocity dispersion . These two actions are the other two sub -tasks of this task.
2.Boucle multi- conjugate adaptive optics :
The conduct of activities planned for the MCAO is as follows.
We will conduct a first phase of characterization of the laser:
From these measurements, the need in terms of correction and beam shaping and available components, the MCAO system will be defined. For this, the direct model describing the propagation and correction by one or more deformable mirrors will be implemented. From this model, an algorithm will be developed to reverse this problem,
These tools will then lead the design phase by studying the influence of parameters of the correction, of the measurement error and disturbance to be corrected.
The opto- mechanical layout of the laser will be studied and the sensor will be realized.
These sizing will be used to complete and integrate the MCAO on the laser project .
The two scientists project tasks ( mirrors and adaptive optics ) provide the laser beam changes during the progress as per milestones defined subtasks .
All actions inform the task of coordinating the project.
No main results nowadays
The main objective of the ILOOP project is to fully control the beam profile in the plane of interest.
None at that itme
ILOOP targets the optimization of propagation characteristics of femtosecond laser by the use of high damage threshold femtosecond mirrors and multi-conjugate adaptive optics linked to a phase diversity wavefront sensor. This optimisation targets applications such as generation of multi-filaments under controlled beam conditions and target glare. It fits into the theme 5 of this tender and more particularly in the theme 2.5.2. This optimization is carried out along two axes and more precisely in the theme 2.5.3: Development of mirrors with a high damage threshold, and development of a new generation of adaptive optics (called multi-conjugate) to control in spatial phase and amplitude of the beam. Applications of the developments made in this project relate to both civilian and military sector.
Intense laser sources have known many developments since the early 90s, this in order to increase the peak power. Significant progress was also made through average power higher and higher. Developments continue especially for systems such as the Apollon-ILE program in France. The various pillars of European ELI programs in the Czech Republic, Romania and Hungary are under construction and are designed for peak power of 10 PW with pulse durations of 15 fs and an energy of 150 joules. These lasers are at the state of the art, but many other less powerful systems are now under construction by the institutions themselves or purchased from companies such as Thales and Amplitude Technologies. A requirement common to all these systems is to reach highest intensity in the experimental plane, with applications both civilian and military side.
To meet these requirements, these intense laser sources require optical components of high quality (reflectivity, flatness and damage threshold) and also of large dimension.
The spatial beam quality, essential to achieve the desired flux densities, is itself improved by the use of adaptive optics.
The analysis of the state of the art on these two elements shows that substantial improvements in laser performance can be considered. The project will focus on:
- Developing reflective mirrors that will be of high damage threshold to transport the recompressed pulses while reducing the dimensions of the beam. The partner for this development is SAGEM-REOSC. For obvious strategic reasons it is important to have a French supplier of mirrors compatible with femtosecond pulses. These skills are sorely lacking in France today, forcing the French leaders in the field, Amplitude Technologies and Thales to purchase abroad. As part of this project SAGEM-REOSC intends to develop its know-how to position itself as a French supplier of this strategic market.
- Integrating in a femtosecond laser, multi-conjugated adaptive optics coupled to a new wavefront sensor based on the phase diversity to control both spatial amplitude and phase . The partner for the implementation of this loop is the team High Angular Resolution (HRA) of the Department of Theoretical and Applied Optics (DOTA) ONERA, which has a recognized expertise in the design and implementation of adaptive optics. The use of two deformable mirrors placed in two planes allow proper shaping of the beam dynamics in order to optimize its propagation properties (annular or top-hat) and also for focusing.
Monsieur Gilles CHÉRIAUX (Laboratoire d'Optique Appliquée) – email@example.com
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
CNRS Laboratoire d'Optique Appliquée
SAGEM-REOSC SAGEM REOSC
ONERA Département Optique Théorique et Appliquée
Help of the ANR 253,985 euros
Beginning and duration of the scientific project: December 2012 - 24 Months