Motivations for a New Experiment
Intensity Enhancement Cavity
MOT Laser
References[1] S.K. Dutta et al., PRL 85, 5551-5554(2000)[2] K.C. Younge et al., New J. Phys. 12, 023031(2010)
[3] K.C. Younge et al., PRL 104, 173001(2010)[4] S.E. Anderson et al., PRL 107, 263001(2011)
Laser Spectroscopy of Rydberg Atoms in Deep Optical LatticesYun-Jhih Chen and Georg Raithel
University of Michigan, Ann Arbor USA
Various cavity modes captured by an IR camera. Only the Gaussian TEM00 mode is used at this time.
lattice laser
The concentric cavity will be later inserted into a one foot tall ultra-high vacuum chamber. The fab-rication of the chamber and most of its attach-ments has been completed. Presently, we are working on the final integration of all components of the experiment.
We have recently built two amplified 780nm distributed Bragg reflector (DBR) laser systems as our MOT lasers. The lasers are compact and movable, mode-hop-free, and insensitive to mechanical fluctuations.
External Chamber
Designed by Stefan Zigo
Tapered Ampli�er& Cooling Block
to Saturated Spectroscopy
extra entrance to TA
780nm DBR Laser Diode
Cylindrical Lens Galilean Telescope
piezo
λ/4
EOM
1064nmlaser
PDH detectorPID regulator
scope
phasemodulation
PID
beam
pro
�le
The cavity is locked to the laser.
top
bottom
Tripod
The bottom cavity mirror sits on a tripod. The cavity length can be adjusted by changing the position of the tripod. To enhance the stability, we have fabricated three aluminium mounts of different styles to achieve a stable position of the tripod. The method mimics the three-point contact design of a regular mirror mount.
mirror mount
cavity mirror
screw
plane-parallel confocal(L=R)
concentric(L=2R)
concave-convex
hemispherical
Stable cavities. Only the concentric cavity focuses at the center.
Pound-Drever-Hall TechniqueWe use the PDH technique to stabi-lize the cavity length relative to the 1064nm lattice laser (linewidth 100 kHz). The light reflected from the cavity is detected and mixed with the RF that drives the EOM. The mixer output is processed in a PID regulator. The PID output is applied to three piezos, which push one of the cavity mirrors and correct the cavity length. In practice, only one of the piezos is necessary for PDH stabilization. The other two piezos are separately controlled with DC signals to fine-tune the cavity.
The new POL experiment utilizes a concentric cavity to enhance the intensity of the lattice laser and to produce the optical lattice with required lattice depth. The concentric cavity is composed of two spherical mirrors with high reflectivity. The radius of curvature of the mirrors is 2.5cm, and hence the cavity length is 5cm. The calculated finesse of the cavity is about 600, so the laser intensity can be enhanced hundreds of times. The free spectral range and FWHM are about 3000 MHz and 5MHz, respectively.
Cavity Design
top view
MCP
Adiabatic Potentials Rydberg atoms in an optical lattice have three types of motion: the motion of the center of mass, the motion of the Rydberg electron relative to the core, and the quiver motion of the Rydberg electron. The time scales of each motion differ from the others by a factor of order 1000, so the adiabatic potentials can be numerically calculated by applying the Born-Oppenheimer approximation. The quiver motion generates a ponderomotive potential, which is added as a perturba-tion to the Rydberg electon’s Hamiltonian. Diagonalization yields the perturbed Rydberg energy levels, which depend on center-of-mass position (z0 in the figure). Plotting the energy levels vs z0 yields the adiabatic potentials that govern the center-of-mass motion.
relative motion
quiver motion(fastest)
center of mass
(slowest)
e- core
Adiabatic potentials for a Rydberg atom inside a 1D optical lattice with lattice depth 2 GHz [2]. Left:n=30. Right:n=45. mj is �xed to 2.5 in both plots. The wavefunction of each adiabatic potential is a superposition of states with di�erent angular momentum quantum number l.
IntroductionRydberg atoms are atoms in highly excited states. An optical trap for Rydberg atoms, which we refer to as a ponderomotive optical lattice (POL), was proposed in 2000 [1]. Unlike optical lattices for ground-state atoms, the lattice potential seen by a Rydberg atom is the ponderomo-tive potential of a free electron weighted by the Rydberg atom wave-function. Significant differences between a POL and a conventional op-tical lattice arise from the respective types of atom-field coupling and the giant size of Rydberg atoms.
The details of our current POL experiment can be found in refer-ences [3] and [4]. In order to resolve all the adiabatic potentials shown above, a lattice with depth of several GHz is necessary. Our
considerations are:1) We would like the separation between adiabatic po-tentials larger than excitation laser linewidth.2) The lattice must be deep enough to mix S and D states with the higher angular momentum states to make the adiabatic potentials accessible by our two-photon excitation.
In the new setup, the optical lattice will be produced inside an opti-cal resonator, which can easily provide a lattice depth of 10 GHz.
5P3/2
5S1/2
Ryd
480 nm
780 nm
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