Laser cooling of ions bound to a Penning trap

MgII ions which are confined in a room temperature Penning trap have been cooled to <= 0.5 K by scattering photons which are nearly resonant with the 3s2Ssub(1/2) reversible 3p2Psub(3/2) transition. The magnesium loaded into the trap has a natural isotopic abundance consisting of approx. 80% 24Mg, and approx. 10% each 25Mg and 26Mg. The 24Mg is radiatively cooled and it subsequently cools the 25,26Mg by long range Coulomb collisions. This allows the use of a 'cooling ion' being used in conjunction with a more complex species of spectroscopic interest. Experiments using two lasers are reported where one laser is fixed in frequency and provides the cooling source and the other laser is swept in frequency. By monitoring the scattered light from the second laser, an optical spectrum of MgII ions is obtained. Because the Doppler width of the cooled ions is reduced, the three isotopic lines are clearly resolved. (orig.)