At the Rowland, the Speck Lab studied the response of systems to ultrafast electromagnetic pulses. These pulses have a temporal width of approximately 1 ps and a peak field of over 1 kV/cm when focussed. Due to their extremely short pulse width, most systems respond to these pulses in an impulsive manner implying that we are observing their temporal response to a delta function excitation as opposed to their frequency domain response. This provides complementary information to typical continuous-wave spectroscopy.
Of the many systems that have interesting impulse response functions, they studied two in particular. First, the response of highly excited Rydberg atoms to a train of unipolar pulses that provide impulsive kicks to the valence electron. Here these kicks change the momentum of the electron and induce rapid population redistribution. Second, the same pulse also provides a unipolar magnetic field that we use to probe the response of magnetic thin films to ultrafast magnetic pulses. The Speck Lab developed techniques to apply and then observe the response to these pulses in free space.