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Annual Meeting Optical Society of America

Laser trap concept for cold potassium atoms

William C. Stwalley, Shawn P. Heneghan, John T. Bahns, Kuo‐Ho Yang

Published Jan 1, 1985• 0 citations
Publisher

Abstract

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.

DOI
10.1364/oam.1985.wv6

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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

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•Aug 9, 2019•0 citations
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.
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.
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).
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.
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.
The main goal of this research is to cool potassium-41 atoms to ultracold temperatures (<10 μK) in order to study the spin dynamics of atom to atom interactions. However, our current goal is to finish constructing the apparatus that will allow us to confine and cool these atoms in three dimensions. This apparatus will cool and confine the potassium atoms in 3 steps. First, the atoms will be cooled and trapped in our 3D magneto-optical trap. This step of the experiment will cool the atoms near the Doppler-cooling limit, which for potassium atoms is 145 μK. Second, atoms will be loaded into a FORT (far off resonance trap) with an expected depth of 25 μK. In order to cool the atoms below the Doppler-cooling limit, we will use sub-Doppler cooling techniques. What is particularly unique about our experiment is that we plan to use an octupole magnetic field to achieve sub-Doppler cooling. In typical laser cooling experiments sub-Doppler temperatures are achieved when the quadrupole magnetic field is off, which leaves the atoms untrapped. Third, once the atoms have been loaded into the FORT one last cooling mechanism will be implemented. This mechanism is referred to as evaporative cooling and will cool the atoms below 10 μK.