spectrum
DESCRIPTION
applied voltage (U1,U2). applied voltage (U3,U4 ). Max-Born-Institut. R. Jung 1 , R. Schumann 2 , S. Gerlach 1 , T. Kwapien 1 , U. Eichmann 2 , G. von Oppen 1. 1 Technische Universität Berlin, Institut für Atomare und Analytische Physik, Hardenbergstrasse 6, D-10623 Berlin - PowerPoint PPT PresentationTRANSCRIPT
2 23 3S P
60
80
100
120
140
160
180
200
220
23P1
23P1
23S1
23S1
cross-over-line
phot
odet
ecto
r sig
nal [
arb.
units
]
laser frequency15 20 25 30 35 40 45
FWHM ~ 5,2 MHz
pow
er [a
rb.u
nits
]
frequency [MHz]
spectrum beat signal
characteristics of the used diode lasers for transversal cooling and trapping
For stabilizing the diode lasers we use the mean of saturation spectroscopy.We extract the control signal out of the spectrum of the -transition.The laser linewidth of the diode lasers is determined to about 5 MHz by measuring the beat signal on a fast photodetector.
transversal cooling and deflection of the He* beam
To separate the metastable helium atoms from the ground-state atoms, the He* source is placed off-axis, so that only the metastables will be deflected into the “Stark-slower”-section by the use of the diode laser at = 1083 nm.
0,000 0,005 0,010 0,015 0,020-0,5
0,0
0,5
1,0
1,5
2,0
2,5
3,0
3,5
4,0 without laser deflection + transversal cooling
inte
nsity
[arb
.uni
ts]
time of flight [s]
R. Jung1, R. Schumann2, S. Gerlach1, T. Kwapien1, U. Eichmann2, G. von Oppen1
1 Technische Universität Berlin, Institut für Atomare und Analytische Physik, Hardenbergstrasse 6, D-10623 Berlin2 Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Max-Born-Str. 2A, D-12489 Berlin
Magneto-Optical Trapping of “Stark-Slowed” Metastable Helium Atoms
Max-Born-Institut
goal :
- study of ionisation dynamics of metastable helium atoms in a trap
- cold collisions of ultraslow He*
- storage of metastable helium atoms in an electro-dynamical trap
- realization of a storage-ring for slow helium atoms
trapping and guiding He* atoms by means of dynamical electric
fieldsOur aim is to construct a trap or an atom-guide for helium atoms based on rotating electric fields. Simulations show the possibility to hold helium atoms with v < 2 m/s against gravity.With variable structures of the rods it will be possible to get a storage-ring for metastable helium atoms, where we can study ultracold collisions of He*.
electrodes : calculated trajectory :
Getting a closed trajectory of a trapped atom, we used following parameters:
trap dimensions:distance of the rods 8 mmradius of the rods 2 mm
applied voltage : U = 20,0 kVfrequency of the applied voltage : = 3000 Hz
outlook
principle of laser cooling by the use of the Stark effect
polarisability : scalar(33P) = 4.279 MHz/(kV/cm)2
tensor(33P) = 0.084 MHz/(kV/cm)2
scalar(23S) = 0.076 MHz/(kV/cm)2
160000
165000
170000
175000
180000
185000
20
= 31.9 GHz
21
= 2.27 GHz
20
21
23P0
23P1
23P2
1083 nm 20
= 8772.517(16) MHz
21
= 658.548(69) MHz
e--Helium Stoßanregung
in Gasentladung
389 nm
33D
31D
21
20
33P2
33P1
33P0
33P
31P
0
21P
23P
31S
33S
21S
23S
11S
Ener
gie
[cm
-1]
ener
gy [
cm-1]
discharge
0 10 20 30 40 50-200
-100
0
100
200
33P
2, |m
J|=2
33P2, |m J|=1
33P1, m J=0
Starkaufspaltung des 33P2-Niveaus
Ener
gie
[MH
z]
elektrische Feldstärke [kV/cm]
0 10 20 30 40 50-10
-8
-6
-4
-2
0
2
4
6
8
10
33P
2
33P1
33P
0
Starkverschiebung des 33P-Multipletts
Ener
gie
[GH
z]
elektrische Feldstärke [kV/cm]
ener
gy [
GH
z]en
ergy
[M
Hz]
stark-splitting of the 33P2-niveau
stark-shift of the 33P-multiplett
electric field [kV/cm]
electric field [kV/cm]
- energy levels of helium up to n = 3
0,000 0,005 0,010 0,015 0,020
0,000
0,002
0,004
0,006
0,008
0,010
0,012
0,014
0,016
0,018v
He-atoms ~ 10 m/s
U3 [kV]
25,1
25,0
24,5
24,0
23,5
22,5
ion-
sign
al [a
rb. u
nits
]
time of flightMOT
[s]
fixed applied voltage - first two field plates: U1 = 12,1 kV; U2 = 18,6 kVdetuning - longitudinal cooling laser ~ -2,3 GHzdetuning - MOT diode laser: ~ -8 MHz
Shown are TOF-spectra of cooled helium atoms taken from the MOT-MCP while varying the applied voltage of the third field plate.The increase of the signal was due to the interaction between the MOT-laser and helium atoms (vatoms ~ 10 m/s) at U3 = 25,1 kV.
- results of laser cooling
trapping of metastable helium atoms in a magneto-optical trap
-0,5 0,0 0,5 1,0 1,5 2,0
0,00
0,05
0,10
0,15
0,20
0,25
0,30
He*-beam ON
Loading of the Magneto-Optical Trap
MC
P c
urr
ent
(MO
T)
[arb
.un
its]
time [s]
0,0 0,5 1,0 1,5 2,0
0,00
0,05
0,10
0,15
0,20
0,25
0,30
He*-beam blocked
Decay of the Magneto-Optical Trap
time [s]
MC
P c
urr
ent
(MO
T)
[arb
.un
its]
Shown is the loading and the decay of our MOT. field-gradient (z-axis) : dB/dz = 6,4 Gauss/cmdetuning of the MOT-laser : = -7 MHzdiameter of the trapping laser beam : d = 2 cm
lifetime of the trap : 240 ms
vstart ~ 1000 m/s
setup of He*-source and cooling section :
LN2-cooledHe*-source(discharge)
transversalcooling
diode laser=1083 nm
deflection of He* -Stark-Slower -longitudinal cooling section
MOT
apature
setup of the magneto-optical trap :
cooled helium atoms(v < 20 m/s)
gold-coated mirror
MCP-detector
/4-plate
/4-platemagnetic field coils
(anti-helmholtz-configuration)
longitudinal cooling laser= 389 nm
MOT diode laser= 1083 nm
0.0005 0.001 0.0015 0.002
-20000
-10000
10000
20000
0.0005 0.001 0.0015 0.002
-20000
-10000
10000
20000
0.0005 0.001 0.0015 0.002
-20000
-10000
10000
20000
0.0005 0.001 0.0015 0.002
-20000
-10000
10000
20000
applied voltage (U3,U4)
applied voltage (U1,U2)
-1 -0.75 -0.5 -0.25 0.25 0.5 0.75 1
-1
-0.75
-0.5
-0.25
0.25
0.5
0.75
1
U1 U3
U2U4