Transcript Interferometric beam combination

ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
Interferometric beam
combination
Gérard Mourou
Why interferometric beam combination?
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
• 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.
Reaching the highest Intensity:
Moving to a Spherical wave
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010

Focal radius R 
 for  0.16
2
  1?
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
  0.16
0.41
 0.4
 0.7
0.7
Effectively, 1 corresponds to a contracting wave geometry
or to collision of several tightly focused beams.
Interferometric Beam Combining
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
Pump
Pump
23
Phasing Gratings
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
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
19 mars 2009
CEA - Établissement public de recherche à
caractère scientifique, industriel et
commercial
Rôle du miroir segmenté
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
Mise en phase de la
mosaïque de faisceaux
19 mars 2009
CEA - Établissement public de recherche à
caractère scientifique, industriel et
commercial
Concept du miroir segmenté
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
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
Capteur
capacitif
•Chaque vérin est asservi en continu
sur la mesure du capteur
19 mars 2009
CEA - Établissement public de recherche à
caractère scientifique, industriel et
commercial
PZT asservi sur
capteur capacitif
segment
Cadre
Interferometric Beam Combining
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
Pump
Pump
Beam Unbalance / Two basic effects
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
• Thermal effects
• Polarazibility-population difference
Beam Interferometric Balance
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
 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
Thermal expension
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
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 %.
Change of crystal optical length
due to electronic level population
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
• 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%.
CEP
ELI Nuclear Physics meeting, Bucarest Feb1-2, 2010
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.