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NASA STI/Recon Technical Report N

A laser trap for neutral atoms

William C. Stwalley

Published Nov 1, 1985• 0 citations
OpenAlex

Abstract

This project constructed and studied a laser trap for neutral atoms, initially potassium (K). At low densities, such a trap could be used to address a number of fundamental questions, e.g. the interaction of an individual atom with an electromagnetic field, collision dynamics and recombination. The feasibility and limitations of a purely laser trap concept, a corner cube trap , for trapping neutral K atoms are studied. The confinement of the atoms in the two dimensions perpendicular to the laser is provided in the cavity of a newly constructed high power alexandrite laser operating in the (doughnut mode) tuned slightly to the blue side of the resonance line of the K atom. By reflecting the laser back on itself with two mirrors, one caps the ends of the cylindrical trap, resulting in a slightly weaker end plug. Examined are various loss mechanism for the trapped atoms. In particular, K atoms are lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons, if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they recombine with He to form KHe (or KHe2, etc).

Related papers

Laser trap concept for cold potassium atoms

William C. Stwalley, Shawn P. Heneghan, John T. Bahns +1 more

We present our study on the feasibility and limitations of a purely laser trap concept, a corner cube trap, for trapping neutral K atoms. The confinement of the atoms in the two dimensions perpendicular to the laser will be provided in the cavity of a high power alexandrite laser operating in the cw TEM01*, mode (doughnut mode) tuned slightly to the blue side of the resonance line of the K atom. By reflecting the TEM01*, laser back on itself with two mirrors, one caps the ends of the cylindrical trap, resulting in a slightly weaker end plug. This trap concept employs not laser cooling, but rather counterstreaming 4He atoms which are cooled to ≲ 1.5 K, to drastically cool the K atoms to thermal energies well below the trap depth (expected to be ~10 K). We have also examined various loss mechanisms for the trapped atoms. In particular, K atoms can be lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons (recoil or diffusional heating), if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they form KHe (or KHe2, etc.). Results from these investigations will be discussed, suggesting crude lifetimes for trapped atoms of the order of 1 s.

Annual Meeting Optical Society of America•Jan 1, 1985•0 citations

Theoretical Issues Involving Traps for Neutral Spin-Polarized Atoms.

William C. Stwalley

The purpose of this project was to theoretically study and design a laser trap for neutral atoms. At low atomic densities, such a trap could be used to address a number of fundamental questions, e.g., the interaction of an individual atom with an electromagnetic field, collision dynamics, recombination. In particular, after examining a variety of laser-magnet trap concepts, we studied the feasibility and limitations of a 'corner cube' laser trap for potassium atoms based on a near-resonant CW TEM sub 01 ('doughnut mode') alexandrite laser beam with cooling provided by He4 atoms at approx. 1.5 K and designed initial experiments.

•Nov 15, 1984•0 citations

Examination of effects of TEM01/emph> -mode laser radiation in the trapping of neutral potassium atoms

Kuo‐Ho Yang, William C. Stwalley, Shawn P. Heneghan +3 more

We present our study on the feasibility and limitations of a purely one-laser trap concept, a ``corner cube trap,'' for trapping neutral K atoms. The confinement of the atoms in the two dimensions perpendicular to the laser will be provided in the cavity of a high-power alexandrite laser operating in the cw ${\mathrm{TEM}}_{01}^{\mathrm{*}}$ mode (``doughnut mode'') tuned slightly to the blue side of the resonance line of the K atom. By reflecting the ${\mathrm{TEM}}_{01}^{\mathrm{*}}$ laser back on itself with two mirrors, one ``caps'' the ends of the cylindrical trap, resulting in a slightly weaker end plug. This trap concept employs not laser cooling, but rather counterstreaming $^{4}\mathrm{He}$ atoms which are cooled to \ensuremath{\lesssim}1.5 K, to drastically cool the K atoms to thermal energies well below the trap depth (expected to be \ensuremath{\sim}10 K). We have also examined various loss mechanisms for the trapped atoms. In particular, K atoms can be lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons (``recoil'' or ``diffusional'' heating), if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they form KHe (or ${\mathrm{KHe}}_{2}$, etc.). Results from these investigations suggest crude lifetimes for trapped atoms of the order of 1 sec.

Physical Review A•Oct 1, 1986•9 citations

Progress toward an alexandrite laser trap for potassium atoms

K.-H. Yang, X.-Z. Zeng, W. C. Stwalley

A detailed description of a corner-cube laser trap concept inside the cavity of a cw alexandrite laser operating in the TEM 01 * mode and using 4He cooling (at temperature ≲ 1.5 K) for trapping neutral potassium atoms is given in a recent paper.1 We report recent progress made toward the implementation of this trap concept: in optimization of the design of the laser cavity, in the understanding of the thermal lensing effects in the alexandrite laser, and in the status of the cryogenic apparatus.

International Laser Science Conference•Jan 1, 1986•0 citations

Novel Optical Trap of Atoms with a Doughnut Beam

Takahiro Kuga, Yoshio Torii, Noritsugu Shiokawa +3 more

We have constructed a novel optical trap for neutral atoms by using a Laguerre-Gaussian (doughnut) beam whose frequency is blue detuned to the atomic transition. Laser-cooled rubidium atoms are trapped in the dark core of the doughnut beam with the help of two additional laser beams which limit the atomic motion along the optical axis. About ${10}^{8}$ atoms are initially loaded into the trap, and the lifetime is 150 ms. Because the atoms are confined at a point in a weak radiation field in the absence of any external field, ideal circumstances are provided for precision measurements. The trap opens the way to a simple technique for atom manipulation, including Bose-Einstein condensation of gaseous atoms.

Physical Review Letters•Jun 23, 1997•839 citations

Laser cooling, stopping, and magnetic trapping of neutral atoms

William D. Phillips

A thermal atomic Na beam is opposed by a resonantly tuned laser beam. The radiation pressure decelerates and compresses the thermal velocity distribution, bringing the average velocity to zero and reducing the width from ~1000 m/s to a few tens of m/s or less.1 The density of stopped atoms is > 106/cm3 within a bandwidth of a few m/ s. These densities and velocities are suitable for trapping by a number of proposed optical and magnetic traps. Using these stopped atoms, we have demonstrated the first electromagnetic trapping of neutral atoms. The trap, a magnetic quadrupole formed by two separated, coaxial, opposed current loops, confines the atoms by virtue of the force exerted on the Na magnetic dipole moment by the inhomogeneous magnetic field. The time constant for exponential decay of the atomic population in the trap is 0.83(7) s and is limited mainly by collisions with fast background gas atoms. The maximum velocity of atoms contained in the trap is 3.5 m/s, corresponding to a maximum energy of 17 mK.

Annual Meeting Optical Society of America•Jan 1, 1985•0 citations
This project constructed and studied a laser trap for neutral atoms, initially potassium (K). At low densities, such a trap could be used to address a number of fundamental questions, e.g. the interaction of an individual atom with an electromagnetic field, collision dynamics and recombination. The feasibility and limitations of a purely laser trap concept, a corner cube trap , for trapping neutral K atoms are studied. The confinement of the atoms in the two dimensions perpendicular to the laser is provided in the cavity of a newly constructed high power alexandrite laser operating in the (doughnut mode) tuned slightly to the blue side of the resonance line of the K atom. By reflecting the laser back on itself with two mirrors, one caps the ends of the cylindrical trap, resulting in a slightly weaker end plug. Examined are various loss mechanism for the trapped atoms. In particular, K atoms are lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons, if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they recombine with He to form KHe (or KHe2, etc).
We present our study on the feasibility and limitations of a purely laser trap concept, a corner cube trap, for trapping neutral K atoms. The confinement of the atoms in the two dimensions perpendicular to the laser will be provided in the cavity of a high power alexandrite laser operating in the cw TEM01*, mode (doughnut mode) tuned slightly to the blue side of the resonance line of the K atom. By reflecting the TEM01*, laser back on itself with two mirrors, one caps the ends of the cylindrical trap, resulting in a slightly weaker end plug. This trap concept employs not laser cooling, but rather counterstreaming 4He atoms which are cooled to ≲ 1.5 K, to drastically cool the K atoms to thermal energies well below the trap depth (expected to be ~10 K). We have also examined various loss mechanisms for the trapped atoms. In particular, K atoms can be lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons (recoil or diffusional heating), if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they form KHe (or KHe2, etc.). Results from these investigations will be discussed, suggesting crude lifetimes for trapped atoms of the order of 1 s.
The purpose of this project was to theoretically study and design a laser trap for neutral atoms. At low atomic densities, such a trap could be used to address a number of fundamental questions, e.g., the interaction of an individual atom with an electromagnetic field, collision dynamics, recombination. In particular, after examining a variety of laser-magnet trap concepts, we studied the feasibility and limitations of a 'corner cube' laser trap for potassium atoms based on a near-resonant CW TEM sub 01 ('doughnut mode') alexandrite laser beam with cooling provided by He4 atoms at approx. 1.5 K and designed initial experiments.
We present our study on the feasibility and limitations of a purely one-laser trap concept, a ``corner cube trap,'' for trapping neutral K atoms. The confinement of the atoms in the two dimensions perpendicular to the laser will be provided in the cavity of a high-power alexandrite laser operating in the cw TEM01∗{\mathrm{TEM}}_{01}^{\mathrm{*}}TEM01∗​ mode (``doughnut mode'') tuned slightly to the blue side of the resonance line of the K atom. By reflecting the TEM01∗{\mathrm{TEM}}_{01}^{\mathrm{*}}TEM01∗​ laser back on itself with two mirrors, one ``caps'' the ends of the cylindrical trap, resulting in a slightly weaker end plug. This trap concept employs not laser cooling, but rather counterstreaming 4He^{4}\mathrm{He}4He atoms which are cooled to \ensuremath{\lesssim}1.5 K, to drastically cool the K atoms to thermal energies well below the trap depth (expected to be \ensuremath{\sim}10 K). We have also examined various loss mechanisms for the trapped atoms. In particular, K atoms can be lost to the trap if they are multiphoton ionized, if they are heated by absorption and emission of many photons (``recoil'' or ``diffusional'' heating), if they simply have much higher energy than the vast majority of other atoms at 1.5 K, or if they form KHe (or KHe2{\mathrm{KHe}}_{2}KHe2​, etc.). Results from these investigations suggest crude lifetimes for trapped atoms of the order of 1 sec.
A detailed description of a corner-cube laser trap concept inside the cavity of a cw alexandrite laser operating in the TEM 01 * mode and using 4He cooling (at temperature ≲ 1.5 K) for trapping neutral potassium atoms is given in a recent paper.1 We report recent progress made toward the implementation of this trap concept: in optimization of the design of the laser cavity, in the understanding of the thermal lensing effects in the alexandrite laser, and in the status of the cryogenic apparatus.
We have constructed a novel optical trap for neutral atoms by using a Laguerre-Gaussian (doughnut) beam whose frequency is blue detuned to the atomic transition. Laser-cooled rubidium atoms are trapped in the dark core of the doughnut beam with the help of two additional laser beams which limit the atomic motion along the optical axis. About 108{10}^{8}108 atoms are initially loaded into the trap, and the lifetime is 150 ms. Because the atoms are confined at a point in a weak radiation field in the absence of any external field, ideal circumstances are provided for precision measurements. The trap opens the way to a simple technique for atom manipulation, including Bose-Einstein condensation of gaseous atoms.
A thermal atomic Na beam is opposed by a resonantly tuned laser beam. The radiation pressure decelerates and compresses the thermal velocity distribution, bringing the average velocity to zero and reducing the width from ~1000 m/s to a few tens of m/s or less.1 The density of stopped atoms is > 106/cm3 within a bandwidth of a few m/ s. These densities and velocities are suitable for trapping by a number of proposed optical and magnetic traps. Using these stopped atoms, we have demonstrated the first electromagnetic trapping of neutral atoms. The trap, a magnetic quadrupole formed by two separated, coaxial, opposed current loops, confines the atoms by virtue of the force exerted on the Na magnetic dipole moment by the inhomogeneous magnetic field. The time constant for exponential decay of the atomic population in the trap is 0.83(7) s and is limited mainly by collisions with fast background gas atoms. The maximum velocity of atoms contained in the trap is 3.5 m/s, corresponding to a maximum energy of 17 mK.