1. Interferometric beam combination Gérard Mourou

2. Why interferometric beam combination? • While maintaining higher peak power, it provides a way to: • Enhance cooling, • Decrease the confocal volume significantly, • Decrease optics size, • Flexibility on beam architecture:parallel bundle or 4p arrangement • Control of the CEP.

3. Reaching the highest Intensity: Moving to a Spherical wave Focal radius Exact solution for arbitrary : A.M. Fedotov, K.Yu. Korolev, M.V. Legkov, SPIE Proceedings Vol. 6726, 672613, 2007 [arXiv:0705.2775] Diffraction limit is taken into account automatically .16 0.41 0.7 Effectively, 1 corresponds to a contracting wave geometry or to collision of several tightly focused beams.

4. Interferometric Beam Combining Pump Pump 23

5. Phasing Gratings Mosaïque de faisceaux type PETAL Les réseaux ne sont pas dans un même plan, ils sont installés sur des supports individuels. Des réglages tilts et piston sont possibles mais il faut combiner grandes courses et sensibilités, le tout fonctionnant sous vide CEA - Établissement public de recherche à caractère scientifique, industriel et commercial R.C.S. PARIS B 775 685 019

6. Rôle du miroir segmenté Mise en phase de la mosaïque de faisceaux CEA - Établissement public de recherche à caractère scientifique, industriel et commercial R.C.S. PARIS B 775 685 019

7. Concept du miroir segmenté 1mm • Un cadre supporte les 4 segments • Chaque segment est maintenu en trois points • Le positionnement suivant Z est assuré au niveau de chacun des 3 points par un vérin piézo • Un capteur capacitif mesure la position en Z de la face avant du segment en regard de chaque vérin • Chaque vérin est asservi en continu sur la mesure du capteur Capteur capacitif PZT asservi sur capteur capacitif segment CEA - Établissement public de recherche à caractère scientifique, industriel et commercial R.C.S. PARIS B 775 685 019 Cadre

8. Interferometric Beam Combining Pump Pump

9. Beam Unbalance / Two basic effects • Thermal effects • Polarazibility-population difference

10. Beam Interferometric Balance  Thermal expansion Because the heat dumped in the crystal is only .5J/cm3 for a crystal length of 5cm and a fluence of 2J/cm3. DT~ .05 C, corresponding to DL~< 410-6cm

11. Thermal expension The pump is only 30ns, so it will take effect after 20 microseconds.The time for the sound to propagate across the crystal. What counts is the difference between two pump beams in energy. This difference is ~±2%. The conclusion is that the beam to beam optical path Difference after the pump is a very small fraction of the wavelength, i.e. 1 %. The

12. Change of crystal optical lengthdue to electronic level population • Refractive index change, accompanies the change in population of electronic levels. • This effect unlike the thermal refraction is very prompt. It will follow the pump and the laser signal as the beam. • Calculation for small gain of 100 in Ti:sapphire (O. Antipov), shows that it is of a wave. This effect will be of the order of a wave /50 for a beam unbalance of 2%.

13. CEP In the case of interferometric addition the CEP should not be a question because CEP come from the difference between phase velocity and group velocity.