Deceleration of a thermal beam of Rb

The use of diode laser beams that counterpropagate against a thermal beam of Rb to decelerate the atoms to near-zero velocity and bunch their speeds into a very narrow range is reported. As the atoms decelerate, their changing Doppler shift is compensated by increasing the laser frequency. This chirping is easily accomplished with diode lasers because of the strong dependence of their frequency on current. For the intensity used (~16 mW/cm² for the coding laser), the measurements corroborate a computer model that predicts that the Doppler width of the final velocity distribution depends on the spectral width of the cooling laser. For a higher intensity or smaller bandwidth of the cooling laser the measured Doppler width is larger than the model's prediction, but it is limited by the linewidth and power broadening of the probe as well as by the spreading of the velocity distribution induced by the probe. These effects are being eliminated.