Tracking femtosecond laser pulses in space and time

We show that the propagation of a femtosecond laser pulse inside a photonic structure can be directly visualized and tracked as it propagates using a time-resolved photon scanning tunneling microscope. From the time-dependent and phase- sensitive measurements, both the group velocity and the phase velocity are unambiguously and simultaneously determined. It is expected that this technique wilt find applications in the investigation of the local dynamic behavior of photonic crystals and integrated optical circuits

Simultaneous measurement of nanoscale electric and magnetic optical fields

Control of light–matter interactions at the nanoscale has advanced fields such as quantum optics1, photovoltaics2 and telecommunications3. These advances are driven by an improved understanding of the nanoscale behaviour of light, enabled by direct observations of the local electric fields near photonic nanostructures4, 5, 6. With the advent of metamaterials that respond to the magnetic component of light7, 8, schemes have been developed to measure the nanoscale magnetic field9, 10, 11, 12. However, these structures interact not only with the magnetic field, but also with the electric field of light. Here, we demonstrate the essential simultaneous detection of both electric and magnetic fields with subwavelength resolution. By explaining our measurements through reciprocal considerations, we create a route towards designing probes sensitive to specific desired combinations of electric and magnetic field components. Simultaneous access to nanoscale electric and magnetic fields will pave the way for new designs of optical nanostructures and metamaterials

Ultrafast evolution of photonic eigenstates in k-space\ud

Periodic structures have a large influence on propagating waves. This holds for various types of waves over a large range of length scales: from electrons in atomic crystals1 and light in photonic crystals2, 3, 4 to acoustic waves in sonic crystals5. The eigenstates of these waves are best described with a band structure, which represents the relation between the energy and the wavevector (k). This relation is usually not straightforward: owing to the imposed periodicity, bands are folded into every Brillouin zone, inducing splitting of bands and the appearance of bandgaps. As a result, exciting phenomena such as negative refraction6, 7, auto-collimation of waves8, 9 and low group velocities10, 11, 12 arise. k-space investigations of electronic eigenstates have already yielded new insights into the behaviour of electrons at surfaces and in novel materials13, 14, 15, 16. However, for a complete characterization of a structure, an understanding of the mutual coupling of eigenstates is also essential. Here, we investigate the propagation of light pulses through a photonic crystal structure using a near-field microscope17, 18. Tracking the evolution of the photonic eigenstates in both k-space and time allows us to identify individual eigenstates and to uncover their dynamics and coupling to other eigenstates on femtosecond timescales even when co-localized in real space and time.\ud \ud \ud --------------------------------------------------------------------------------\u