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Structured light for atomic physics

Event Details

Event Dates: 

Friday, November 13, 2015 - 12:00pm

Seminar Location: 

  • JILA X590

Speaker Name(s): 

Dr. Vincent Carrat

Speaker Affiliation(s): 

University of Virginia, Charlottesville, VA
Seminar Type/Subject

Scientific Seminar Type: 

  • Other

Seminar Type Other: 

JILA Internal Meeting

Event Details & Abstract: 

Modern optical techniques can be use to shape laser beams in space or in time. These techniques are applicable to a wide range of experiments in atomic physics. In the first part of this talk I'll focus on holographically shaped hollow laser beams for long distance guiding of cold atoms. In the second part I'll switch to amplitude modulated lasers for studying the phase dependence in ionization recombination processes of Rydberg atoms in strong microwave fields.
    2D-MOT is efficient source for cold atom experiments. Unfortunately, the divergence (≈40 mrad) of the atom beam is problematic if the 2D-MOT must be far from the main science area. We have demonstrated a reduction in the size of the beam from 12 mm to 1 mm 300 mm away from our 2D-MOT output by guiding the atomic beam in a blue detuned holographically generated Laguerre-Gaussian (LG) mode. As the atoms are guided in the dark center of the donut shaped LG beam, heating is low compared to a red detuned guide, allowing a longer guiding distance. Holography can generate, in principle, many laser beam shapes allowing, in principle, many ways to guide cold atomic beams. However, the requisite quality of the holographic beam can be hard to reach by currently available spatial light modulators, necessitating some forms of error correction. To this end we have also demonstrated an on-the-fly correction of the spatial light modulator.
    When laser excitation of an atom occurs in the presence of a strong low frequency field, the final atomic state distribution depends on both the energy of the laser excitation and the phase of the low frequency field when the excitation occurs. Examples are APT excitation in the presence of a strong IR field and visible laser excitation in the presence of a microwave field. The phase dependence arises from the the phase dependent energy transfer from the low frequency field to the excited electron. When the laser excitation is in the vicinity of the ionization limit ionization and recombination are observed. We explore how these phase dependence processes vary with laser excitation energy and microwave field amplitude. The excitation laser light is tunable over an 80 GHz range centered on the ionization limit, and is amplitude modulated at 28 GHz synchronously with the 14 GHz microwave field. Surviving bound atomic states of n > 150 are detected. When the laser is tuned above and below the ionization limit phase dependent modulation is observed in the recombination and ionization, respectively. The phase dependent modulation is ≈10% of the total excitation, far greater than the ≈0.1% modulation observed with single ps laser pulse excitation, and in agreement with calculations based on coherent excitation over several microwave cycles.