1. State evolution in cold helium Rydberg gas
Max-Born-Institut
State evolution in cold helium Rydberg gas
S. Gerlach1, R. Jung2, G. von Oppen2, U. Eichmann1,2
1 Max-Born-Institute for Nonlinear Optics and Short Pulse Spectroscopy, Max-Born-Str. 2A, D Berlin
2 Institut für Atomare Physik und Fachdidaktik, Technical University Berlin, D Berlin
Overview
Cold metastable helium Rydberg atoms – experimental setup
Why helium ?
H-like system with very small quantum defect for l>0
light atoms : new effects through different dynamics
„condensation effect“ :
fast ions act as condensation seed for cold
metastable helium
Investigation :
cold helium Rydberg gas at low density
Excitation below ionisation threshold with and without electric fields
Study the redistribution of a (n,l) state as a function of time
Nd-YAG Laser
(30Hz system,
10ns pulses)
Dye laser
(+ frequency doubling)
switched
field plate
fast photo detector
(Trigger)
MCP
(ion/electron detection)
Data acquisition
Logics
+Ufp
~10ms
UV-puls
Delay
l = 260 nm
l = 1083 nm
He*- MOT
Properties of Helium
Energy level of metastable helium with excitation scheme
160000
170000
180000
1083 nm
gas discharge
389 nm
Energy [cm-1]
190000
200000
260 nm
Continuum
33S
33P
23P
23S
11S
frequency doubled pulsed Dye laser :
Rydberg excitation +
Ion creation
frequency doubled TiSa-Laser :
Lasercooling
laser diode (1083 nm) :
MOT
Helium Rydberg spectra in electric fields
Increasing electric field
Increasing delay times
delay = 10 µs
Stark l-mixing
electric field of 10 V/cm
Lasercooling of metastable helium
He*-source
(gas discharge)
MOT
transversal
cooling
- “Stark-Slower” -
cooling section
laser diode
 = 1083 nm
1 meter
Parameter of the He* MOT:
number of atoms : ~ 106
density : cm-3
lifetime : up to 900 ms
temperature : ca 1 mK
Above field ionization threshold
Below field ionization threshold
short time scales : all states detected
long time scales : only long-lived
(high l) states survive
Helium Stark manifold
short time scales : only low stark-states (not l=0!)
medium times : all states detected
long times : high l states (long lifetime)
no s-states at
short times!
time resolved level redistribution with a puls ramp
n-state lifetimes
lifetime up to 1.5 ms
Increased up to n~60
Decreasing over n~70 because of ionization
Theoretical occupation
outlook
clarify the role of the permanent dipole(p- vs. s-states)
higher density cloud with more atoms
investigate collisional effects :
three body recombination
“condensation”
plasma effects (back and forth helium Rydberg plasma)