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International Laser Science Conference

Progress toward an alexandrite laser trap for potassium atoms

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

Published Jan 1, 1986• 0 citations
Publisher

Abstract

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.

DOI
10.1364/ils.1986.wf7

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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 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).
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.
This thesis describes work to improve the apparatus that cools and loads potassium atoms onto the atom chip. This work consists of two main thrusts: a laser trap translator to help cool and load atoms onto the atom chip and a temperature stabilization system for the lasers that are used to laser cool potassium atoms. The current iteration of the beam translator has the ability to vertically translate a beam ±4.5 mm relative to its incident height. The translator has been shown to not alter the spatial profile of the beam through interference or obstruction. The translator’s rotation has been adjusted to minimize atomic heating once the translator is integrated for use in optical atomic trapping. The translator has been installed on the apparatus but has not yet been tested with ultracold atoms. Furthermore, a feedback system was designed for climate-managing the potassium cooling lasers utilized in the Aubin lab’s ultracold apparatus.