Beryllium ions in segmented Paul trap Spectroscopy of Ultimate objective is spectroscopy of 1s2s transition in is a hydrogenlike oneelectron system suitable for further testing of fundamental theories eg QED ID: 536107
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Slide1
Cade Perkins
Beryllium ions in segmented Paul trapSlide2
Spectroscopy of
Ultimate objective is spectroscopy of 1s-2s transition in
is a hydrogen-like one-electron system, suitable for further testing of fundamental theories, e.g. QED.
There is no suitable cooling transition in
But
may be cooled sympathetically via Coulomb interaction with co-stored, laser-cooled ionsSome candidate ions with cooling transitions reachable by current laser systems: , , Magnesium ions have been explorer more by this group primarily due to accessible laser systems
Slide3
Beryllium ions as coolant
Similar charge-to-mass ratio of the coolant and cooled ions is necessary for reaching lower temperatures.
Graph shows result of molecular dynamics simulation of
20
ions of given mass,
sympathetically cooled
by 60 coolant ions inlinear Paul trap. is only of thelisted laser-cooledcandidate ions tocool mass-4 ions(i.e. ) tomilli-Kelvin temperatures. Okada, et. al. Phys. Rev. A, vol. 81, p. 013420, 2010Slide4
Laser-cooling level scheme for
Primary cooling and fluorescence transition:
(
Fraunhofer
D2 transition)at 313.133 nmHyperfine splitting must be “bridged” to keep the excited state from decaying to a hyperfine level outside the optical pumping transition Slide5
Laser cooling system
626 nm generated by sum frequency generation (SFG) of two infrared OrangeOne fiber lasers from Menlo Systems:1051 nm from ytterbium-doped fiber laser
1550 nm from erbium-doped fiber laser
313 nm generated by second harmonic generation (SHG) in
BBO crystal in Hänsch-Couillaud doubling cavity.
Split 313 nm beam and frequency-shift each side to “bridge” hyperfine splitting in 2s ground state by using double-pass AOM setup.Slide6
Sum Frequency Generation
Batteiger
, V., Ph.D. Dissertation, LMU, 2011
Single-pass through bulk Periodically Poled Lithium
Niobate
(PPLN) crystalBoth fundamental beams are mode matched for optimum SFGUp to 5 W output from each fiber lasers, with linewidthabout 70 MHzHave obtained up to2.16 W red light at 626 nm, far beyond requirementsSlide7
Sum Frequency Generation
Both fiber laser beams were characterized for proper mode matching into PPLN crystalSlide8
Sum Frequency Generation
Mode matching using basic Gaussian beam ray tracing.
Used
GaussianBeam
v0.4 software for convenient modeling:http
://gaussianbeam.sourceforge.net/
1051 nm beam1550 nm beamCommon focusing lensF = 60 mmSlide9
Sum Frequency Generation
Both fiber lasers are
tunable
by temperature control of oscillator.
They also allow feedback/finer control via piezoelectric actuator
- currently not used.Overall tunable range spans both the D1 and D2 transition, allowing for various cooling and re-pumping schemes.
SFG Tunable range+253 GHz-223 GHzSlide10
Second Harmonic Generation
Monitor and tune 626nm wavelength in absence of wavelength meter for UV light
.
8mm BBO Crystal
Demonstrated 580
mW of 313nm light before the double-pass AOM Slide11
AOM
Beam splitter
Double-pass AOM Setup
Robin, J., Masters thesis, LMU, 2012
Acousto
-optical Modulator (AOM) generates an acoustic wave moving inside a transparent medium (e.g. quartz crystal).
An incident optical beam undergoes a Doppler shift. The frequency shift is equal to the acoustic frequency and can be negative or positive – selected by incident angle. (Much of the original beam passes through the AOM unchanged.)Further, the acoustic wave establishesa periodic density “grating”, thereby diffracting the shifted beam by some angle.Slide12
AOM
Beam splitter
Double-pass AOM Setup
Robin, J., Masters thesis, LMU, 2012
In the double-pass setup, the shifted, 1
st
diffracted order is reflected back along the same path.When the shifted beam passes back through the AOM, it produces a beam shifted twice the acoustic frequency from the original.Passing in the other direction, the shifted beam is again diffracted, but the angleis in the opposite direction so that it now overlaps with the original beam. This is a critical featureof the double-pass setup, because it allows minor frequencyadjustment without causingthe output beam to wander.Slide13
AOM
Beam splitter
Double-pass AOM Setup
Robin, J., Masters thesis, LMU, 2012
The final result: Two overlapping beams which center wavelengths bridge the hyperfine splitting of Beryllium ground state:
313.1327 nm
313.1331 nmSlide14
Segmented Ion Trap
RF applied to large solid electrodes
12 independent segmented electrode pairs
provide tight axial
confinement
and field shaping for ion shuttlingSlide15
Tank Circuit and Helical Resonator
Design reference:
Siverns
, J. D., et al. (2012). "On the application of radio frequency voltages to ion traps via helical resonators."
Applied Physics B-Lasers and Optics
107(4): 921-934
.Upon initial trap construction, resonator was measured to have Q factor of > 400, very good for RF tank circuit.After trap completion and connection of various feedthrough components (e.g. ovens and DC power supplies), Q factor is only about 100, comparable to other tank circuit designs.Slide16
Imaging System
Single
condenser:
asphericon
A50-80FPX-X-S, fused silica
asphere
Electron Multiplying Charge Coupled Device (EMCCD) camera:Andor iXon X3 model DU-885K, claimed to be able to detect single-photon eventsMagnification currently x7.2. Planned addition of microscope objective will give about x90 magnification