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VERSION:2.0
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SUMMARY:Extreme ultraviolet attosecond light beams with fractional angular
  momentum
DTSTART:20240205T140000
DTEND:20240205T150000
DTSTAMP:20260925T123632Z
UID:a4d205d38824bd45a842b03548a7ba82d7eb0c87f204a4b6ed468752
CATEGORIES:Conferences - Seminars
DESCRIPTION:Dr. Martin Luttmann\n\nUniversité Paris-Saclay\, CEA\, CNRS\,
  France\nLight beams\, just like massive objects\, can carry angular momen
 tum.The spin angular\nmomentum of light (SAM) is linked to the polarizatio
 n of the field: each photon in a circularly\npolarized beam carries a well
 -defined SAM S=1 (in units of the Planck’s constant). In the\n90’s\, a
  second form of optical angular momentum\, the orbital angular momentum (O
 AM)\,\nwas rediscovered\, and associated with “vortex beams”. Photons 
 in a vortex beam carry a\nquantum L=l of OAM\, where l can be any integer 
 number. Thus\, the eigenvalues of the total\nangular momentum of ligh\, J=
 L+S\, are also integers. During the past decades\, different\nways of mani
 pulating the SAM and OAM via nonlinear optical processes have been\nreport
 ed. Extending these capabilities to the extreme ultraviolet (EUV) spectral
  domain\,\nusing free electron laser (FEL)\, synchrotrons\, or high harmon
 ic generation (HHG) sources\,\ngives access to time-resolved applications 
 at femtosecond and attosecond time scales.\nIn this presentation\, we will
  see that things get more complicated when both the SAM and\nthe OAM are s
 imultaneously present in a light beam\, as is the case for exotic light fi
 elds\nwhose polarization and phase vary in space. Such beams obey certain 
 types of rotational\nsymmetry\, and are eigenstates of a “generalized an
 gular momentum” (GAM). Remarkably\,\nthis new angular momentum can take 
 half-integer values\, i.e. the photons in such modes\ncan carry a quantum 
 of angular momentum equal to half the Planck’s constant\, a value\nnorma
 lly associated with fermionic particles. The polarization of GAM modes gen
 erally\nexhibits a Möbius strip topology. Here\, we prepare an intense in
 frared GAM beam and use it\nto drive HHG in a jet of gas (see Figure). By 
 implementing novel angular momentum\nmeasurement techniques in the EUV\, w
 e find experimentally that the harmonic of order q\ncarries a GAM equal to
  q times that of the driver\, while its SAM and OAM are ill-defined. We\nc
 onclude that\, in some situations\, the GAM is the “good” quantum numb
 er\, efficiently\ndescribing the nonlinear interaction. Such ultrafast EUV
  beams with fractional angular\nmomentum could provide original tools to e
 xplore new kinds of dichroism in molecules or\nmagnetic systems.\n 
LOCATION:MXF 312 https://plan.epfl.ch/?room==MXF%20312
STATUS:CONFIRMED
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