Figure 6. Peak density at the center of the sample as a function of the final depth of the evaporative cut on the RF frequency. As evaporation progresses to smaller values of the frequency, the cloud shrinks and cools, causing a modest increase in peak density until the frequency reaches 4.23 MHz. The sudden discontinuity at 4.23 MHz indicates the first appearance of the high-density condensate as the cloud undergoes a phase transition. From Anderson et al. (1995).