Examination of effects ofTEM01/emph>-mode laser radiation in the trapping of neutral potassium atoms

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 ≲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 ${\mathrm{KHe}}_2$, etc.). Results from these investigations suggest crude lifetimes for trapped atoms of the order of 1 sec.