Ultrafast Optical Pulses

Ultrafast pulses on the femtosecond time scale allow fundamental processes, such as atomic transitions, to be measured. To investigate the formation of optical pulses, an argon ion laser was used to pump a titanium-doped sapphire laser. The mode-locked output of this laser was measured with a spectrometer and an autocorrelator to find a frequency pulse width of σω = 86 ± 3 rad/ps and a temporal pulse width of σt = 14 ± 1 fs. The Heisenberg uncertainty principle demands that σωσt ≥ 1, where the minimum uncertainty corresponds to a transformlimited pulse; for this investigation, σωσt = 1.2 ± 0.1, so our pulse was nearly transform-limited. This conclusion is supported by overlaying the measured autocorrelation function with one calculated from the frequency spectrum, assuming a transform-limited Gaussian pulse; the two curves are nearly identical.