Co and Fe catalysts. This is achieved by increasing the density of catalyst nanoparticles up to an order of magnitude as a result of controlled cooling by up to a temperature difference of 200 ºC below the initial temperature. Systematic in situ kinetics studies performed during laser-induced CVD growth of CNTs from Co and Fe thin film catalysts showed that the CNT yield was maximized for a finite temperature difference (~200 and 100 ºC for Co and Fe, respectively) and cooling time (~ 20 s). We extended these studies to non-isothermal CVD growth in a traditional tube furnace, which produced vertically aligned CNT arrays under conditions that normally produce sparse bundled CNTs (i.e. under isothermal conditions). The observed enhancement in CNT yields over a wide range of cooling rates (from 0.5 to ~10 ºC/s) offer an effective tool to further optimize the yield of CNTs from various metallic catalysts. More importantly, the observed improvements in yield can be achieved without the need for additional source materials (thicker catalysts, additional carbon, or other growth promoters) or additional processing (i.e. additional deposition and annealing steps).