1. M.C. Baruch, W.G. Sturrus, N.D. Gibson, and D.J. Larson, Phys. Rev. A 45, 2825 (1992); N.D....
1
1. M.C. Baruch, W.G. Sturrus, N.D. Gibson, and D.J. Larson, Phys. Rev. A 45, 2825 (1992); N.D. Gibson, B.J. Davies, and D.J Larson, Phys. Rev. A 48, 310 (1993); M.C. Baruch, T.F. Gallagher, D.J. Larson, Phys. Rev. Lett. 65, 1336 (1990). 2. C.H. Bryant et al, Phys. Rev. Lett. 58, 2412 (1987). 3. W.A.M. Blumberg, R.M. Jopson, D.J. Larson, Phys. Rev. Lett. 40, 1320 (1978); W.A.M. Blumberg, W.M. Itano, D.J. Larson, Phys. Rev. A 19, 139 (1979). 4. I. Yu. Kiyan and D.J. Larson, Phys. Rev. Lett. 73, 943 (1994); J.N. Yukich, C.T. Butler, and D.J. Larson, Phys. Rev. A 55, 3303 (1997). 5. H.F. Krause, Phys. Rev. Lett. 64 1725 (1990). 6. C.H. Greene, Phys. Rev. A 36, 4236 (1987), H. Crawford, Phys. Rev. A 37, 2432 (1988). 7. M.L. Du and J.B. Delos, Phys. Rev. A 38, 5609 (1988). 8. M.L. Du, Phys. Rev. A 40, 1330 (1989); I.I. Fabrikant, Phys. Rev. A 43, 258 (1991). 9. Q. Wang and A.F. Starace, Phys. Rev. A 48, R1741 (1993); Q. Wang and A.F. Starace, Phys. Rev. A 51, 1260 (1995); Q. Wang and A.F. Starace, Phys. Rev. A 55, 815 (1997). 10. A.D. Peters, C. Jaffe, and J.B. Delos, Phys. Rev. Lett. 73, 2825 (1994); A.D. Peters, C. Jaffe, and J.B. Delos, Phys. Rev. A 56, 331 (1997). 11. Z.Y. Liu and D.H. Wang, Phys. Rev. A 55, 4605 (1997); Z.Y. Liu and D.H. Wang, Phys. Rev. A 56, 2670 (1997). 12. M.L. Du and J.B. Delos, Phys. Rev. Lett. 58, 1731 (1987); M.L. Du and J.B. Delos, Phys. Rev. A 38, 1931 (1988); W.P. Reinhardt, J. Phys. B 16, L635 (1983). Photodetachm ent + - - - - - + - - - - - Conclusio ns Acknowledgements Photodetachment in Parallel Electric and Magnetic Fields J.N. Yukich, Davidson College, Davidson, North Carolina Abstra ct We investigate photodetachment from negative ions in a homogeneous 1.0 Tesla magnetic field and a parallel electric field of ~ 15 V/cm. Calculations show that an electric field of 10 V/cm or more should considerably diminish the Landau structure in the detachment cross section. 8 The ions are produced and stored in a Penning ion trap. We present preliminary results showing roughly a 30 % decrease in the modulation at the first Landau level with addition of the electric field. We also discuss future experiments. Active Layer Motivation This work has been supported by: • Research Corporation • Davidson College • University of Virginia • John D. and Catherine T. MacArthur Foundation References D etachm entcrosssection in B field - + photon → X + e - onsidered as ½ of an electron-atom collision. inimum energy needed to detach is called the electron affinity”, analogous to photoelectric effect. lectron detaches as plane wave into continuum. Detachment in Magnetic Fields • Departing electron executes cyclotron motion in field. • Motion in plane perpendicular to B is quantized to Landau levels separated by cyclotron ω = eB/m e . • For typical B = 1.0 Tesla, ω ≈ 30 GHz, period = 36 ps. • Electron revisits atomic core once every cyclotron period. • Motion along axis of field is continuous, non-quantized. • Quantized Landau levels add structure to detachment cross section. Structure results from electron wave function interfering with itself as it revisits core. Background ent in combined E, B fields has received extensive theoretical attention, but little experimental attention. 8-12 parallel E field: pushes the electron away from the atomic core as it executes cyclotron motion; diminishes s the wave function interference, and thus the Landau structure in the cross section. ct found with motional Stark field of a thermally energetic ion. Such fields diminish resolution of magnetic ure and spectroscopy. (both full quantum-mechanical and semi-classical) predict: 10 V/cm parallel to 1.0 Tesla should y diminish Landau structure, 30 V/cm should almost completely eliminate Landau structure. Experimental technique duced by dissociative attachment from a carrier gas, using hot tungsten filament. pped and stored in Penning ion trap (see figures below), with B = 1.0 Tesla. 3 detachment cross section probed with highly-tunable, single-mode, amplified diode laser (see MOPA below). electric field achieved by superimposing a ~ 1 MHz radio frequency on the trap endcaps. On time scale of one n period, electric field appears ~ static to the ions. D iode seed D iode am plifier Ion trap MOPA: 250 m W single-m ode tunable Spectrum A nalyzer 8 G H z FSR W avem eter to 0 .02 c m -1 Apparatus Penning ion trap system • Trap consists of three hyperbolic electrodes coaxial with B field. • Biased trap endcaps form nearly-harmonic axial potential well. • Heterodyne detection system measures relative trapped ion population before and after laser illumination. Diode laser master oscillator power amplifier • Commercial diode laser seeds a high-gain tapered diode amplifier. • Highly-tunable, single-mode output. • Monitored by Fabry-Perot spectrum analyzer measured by traveling Michelson-interferometer wavemeter. Preliminary data Future Work Ion trap apparatus, showing UHV vacuum, 2.0 Tesla electromagnet and magnet power supply. Optical apparatus, showing diode laser MOPA in foreground and wavemeter electro-optics. Preliminary data showing ratio of S - ions surviving laser illumination near the 2 P 3/2 → 3 P 2 threshold (electron affinity). Structure observed at the first Landau level is diminished when the electric field is added (B = 1.0 Tesla). -20 0 20 40 60 80 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 W ithoutE fie ld W ith E fie ld (1 4 V /cm ) F ra ctio n o f io n s su rvivin g R e la tive fre q u e n cy (G H z) • Modulation structure at the first Landau level observed to be diminished by ~ 30 % when electric f of ~ 14 V/cm is added parallel to the 1.0 Tesla field. • Observations are consistent with theory predictions, but more detailed observations/analysis are n • Motional Stark fields present in the ion trap (~ 8 V/cm) may play a significant role in diminishin magnetic field structure in the detachment cross section. • Current and future work will investigate identical phenomena in O - , which is easily accessible wi diode laser MOPA. • To investigate: What happens at higher E fields? What field is necessary to completely eliminate magnetic field structure? How is this condition approached with increasing electric field? • Evaporative cooling of trapped ion population: does a reduced motional Stark effect enhance the m field structure? Can we improve spectroscopic resolution of Landau levels? • Replace hot tungsten filament with cold field-emission electron source to reduce further the trap population temperature. • Possible time-domain Ramsey interferometry of cyclotron wavepackets, with and without electric fi • Possible investigations with THz radiation: momentum kick given to electron by a half-cycle puls yield further insight into the detached electron’s interaction with the neutral core.
-
Upload
jaden-bickford -
Category
Documents
-
view
215 -
download
0
Transcript of 1. M.C. Baruch, W.G. Sturrus, N.D. Gibson, and D.J. Larson, Phys. Rev. A 45, 2825 (1992); N.D....
1. M.C. Baruch, W.G. Sturrus, N.D. Gibson, and D.J. Larson, Phys. Rev. A 45, 2825 (1992); N.D. Gibson, B.J. Davies, and D.J Larson, Phys.
Rev. A 48, 310 (1993); M.C. Baruch, T.F. Gallagher, D.J. Larson, Phys. Rev. Lett. 65, 1336 (1990).2. C.H. Bryant et al, Phys. Rev. Lett. 58, 2412 (1987). 3. W.A.M. Blumberg, R.M. Jopson, D.J. Larson, Phys. Rev. Lett. 40, 1320 (1978); W.A.M. Blumberg, W.M. Itano, D.J. Larson, Phys. Rev. A
19, 139 (1979). 4. I. Yu. Kiyan and D.J. Larson, Phys. Rev. Lett. 73, 943 (1994); J.N. Yukich, C.T. Butler, and D.J. Larson, Phys. Rev. A 55, 3303 (1997). 5. H.F. Krause, Phys. Rev. Lett. 64 1725 (1990).6. C.H. Greene, Phys. Rev. A 36, 4236 (1987), H. Crawford, Phys. Rev. A 37, 2432 (1988).7. M.L. Du and J.B. Delos, Phys. Rev. A 38, 5609 (1988).8. M.L. Du, Phys. Rev. A 40, 1330 (1989); I.I. Fabrikant, Phys. Rev. A 43, 258 (1991).9. Q. Wang and A.F. Starace, Phys. Rev. A 48, R1741 (1993); Q. Wang and A.F. Starace, Phys. Rev. A 51, 1260 (1995); Q. Wang and A.F.
Starace, Phys. Rev. A 55, 815 (1997).10. A.D. Peters, C. Jaffe, and J.B. Delos, Phys. Rev. Lett. 73, 2825 (1994); A.D. Peters, C. Jaffe, and J.B. Delos, Phys. Rev. A 56, 331 (1997). 11. Z.Y. Liu and D.H. Wang, Phys. Rev. A 55, 4605 (1997); Z.Y. Liu and D.H. Wang, Phys. Rev. A 56, 2670 (1997). 12. M.L. Du and J.B. Delos, Phys. Rev. Lett. 58, 1731 (1987); M.L. Du and J.B. Delos, Phys. Rev. A 38, 1931 (1988); W.P. Reinhardt, J. Phys. B
16, L635 (1983).
Photodetachment
+
-
-
-
-
-
+
-
-
- -
-
Conclusions
Acknowledgements
Photodetachment in Parallel Electric and Magnetic Fields
J.N. Yukich, Davidson College, Davidson, North Carolina
Abstract
We investigate photodetachment from negative ions in a homogeneous 1.0 Tesla magnetic field and a parallel electric field of ~ 15 V/cm. Calculations show that an electric field of 10 V/cm or more should considerably diminish the Landau structure in the detachment cross section.8 The ions are produced and stored in a Penning ion trap. We present preliminary results showing roughly a 30 % decrease in the modulation at the first Landau level with addition of the electric field. We also discuss future experiments.
Active Layer
Motivation
This work has been supported by:• Research Corporation• Davidson College• University of Virginia• John D. and Catherine T. MacArthur Foundation
References
Detachment cross section in B field
• X- + photon → X + e-
• Considered as ½ of an electron-atom collision.• Minimum energy needed to detach is called the “electron affinity”, analogous to photoelectric effect.• Electron detaches as plane wave into continuum.
Detachment in Magnetic Fields
• Departing electron executes cyclotron motion in field.• Motion in plane perpendicular to B is quantized to Landau levels separated by cyclotron ω = eB/me.• For typical B = 1.0 Tesla, ω ≈ 30 GHz, period = 36 ps.• Electron revisits atomic core once every cyclotron period.• Motion along axis of field is continuous, non-quantized.• Quantized Landau levels add structure to detachment cross section. Structure results from electron wave function interfering with itself as it revisits core.
Background
• Photodetachment in combined E, B fields has received extensive theoretical attention, but little experimental attention.8-12
• Effect of a parallel E field: pushes the electron away from the atomic core as it executes cyclotron motion; diminishes or eliminates the wave function interference, and thus the Landau structure in the cross section.
• Similar effect found with motional Stark field of a thermally energetic ion. Such fields diminish resolution of magnetic field structure and spectroscopy.
• Calculations (both full quantum-mechanical and semi-classical) predict: 10 V/cm parallel to 1.0 Tesla should considerably diminish Landau structure, 30 V/cm should almost completely eliminate Landau structure.
Experimental technique
• Ions produced by dissociative attachment from a carrier gas, using hot tungsten filament.
• Ions trapped and stored in Penning ion trap (see figures below), with B = 1.0 Tesla.3
• Relative detachment cross section probed with highly-tunable, single-mode, amplified diode laser (see MOPA below).
• Parallel electric field achieved by superimposing a ~ 1 MHz radio frequency on the trap endcaps. On time scale of one cyclotron period, electric field appears ~ static to the ions.
Diode seed Diode amplifier
Ion trap
MOPA: 250 mW single-mode tunable
SpectrumAnalyzer
8 GHz FSR
Wavemeter to 0.02 cm-1
Apparatus
Penning ion trap system• Trap consists of three hyperbolic electrodes coaxial with B field.• Biased trap endcaps form nearly-harmonic axial potential well.• Heterodyne detection system measures relative trapped ion population before and after laser illumination.
Diode laser master oscillator power amplifier• Commercial diode laser seeds a high-gain tapered diode amplifier.• Highly-tunable, single-mode output.• Monitored by Fabry-Perot spectrum analyzer measured by traveling Michelson-interferometer wavemeter.
Preliminary data
Future Work
Ion trap apparatus, showing UHV vacuum, 2.0 Teslaelectromagnet and magnet power supply.
Optical apparatus, showing diode laser MOPA inforeground and wavemeter electro-optics.
Preliminary data showing ratio of S- ions surviving laser illumination near the 2P3/2 → 3P2
threshold (electron affinity). Structure observed at the first Landau level is diminished when the electric field is added (B = 1.0 Tesla).
-20 0 20 40 60 80
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1.1
Without E field With E field (14 V/cm)
Fra
ctio
n o
f io
ns
surv
ivin
gRelative frequency (GHz)
• Modulation structure at the first Landau level observed to be diminished by ~ 30 % when electric field of ~ 14 V/cm is added parallel to the 1.0 Tesla field.
• Observations are consistent with theory predictions, but more detailed observations/analysis are needed.
• Motional Stark fields present in the ion trap (~ 8 V/cm) may play a significant role in diminishing magnetic field structure in the detachment cross section.
• Current and future work will investigate identical phenomena in O-, which is easily accessible with the diode laser MOPA.
• To investigate: What happens at higher E fields? What field is necessary to completely eliminate the magnetic field structure? How is this condition approached with increasing electric field?
• Evaporative cooling of trapped ion population: does a reduced motional Stark effect enhance the magnetic field structure? Can we improve spectroscopic resolution of Landau levels?
• Replace hot tungsten filament with cold field-emission electron source to reduce further the trapped ion population temperature.
• Possible time-domain Ramsey interferometry of cyclotron wavepackets, with and without electric fields.
• Possible investigations with THz radiation: momentum kick given to electron by a half-cycle pulse may yield further insight into the detached electron’s interaction with the neutral core.
