Petahertz-scale nonlinear photoconductive sampling in air

Abstract

The electric field waveform of a light field can be used to unlock a detailed recording of its interaction with matter, but accessing it requires a measurement with subfemtosecond temporal resolution. We demonstrate nonlinear photoconductive sampling of light fields at optical frequencies in ambient air. The resulting detection method provides broadband electric field measurement in an inexpensive setup using a self-healing medium. A direct comparison is made between detection in air and in quartz, validating the technique up to 0.7 PHz. This provides both a simple route toward field metrology and a new platform for future studies in attosecond physics without the need for complex vacuum setups or sophisticated sample preparation.

The emergence of macroscopic currents in photoconductive sampling of optical fields

“…where v x and v ⊥ is the velocity in detection direction and perpendicular to it, respectively, and where l mfp is energydependent. These formulas should also be applicable to femtosecond streaking [16]/PHz-scale nonlinear photoconductive sampling [17].…”

“…With photoconductive field sampling in solids, a much simpler solution has been presented [9]. Recently, the same concepts have been applied in air for the measurement of the CEP and electric field [15][16][17], which offers additional advantages: they are easier to use since they eliminate the requirement of sample fabrication and inherently use a refreshable target. Moreover, the microscopic response at the atomic/molecular level can be numerically calculated using the time-dependent Schrödinger equation (TDSE), and may be modeled and interpreted in the framework of the strong-field approximation (SFA) and the simpleman's model (SMM) [18].…”

“…There is no rigorous model that connects the microscopic single electron dynamics to the macroscopic current signal that is measurable on the electrodes. The macroscopic aspects of signal formation were largely ignored even though processes such as electron scattering are expected to play an important role [16,17]. Apart from Refs.…”

“…1d), since the total charge scales linearly with pressure, while the mean-free path scales inversely, keeping the dipole strength constant. While these heuristic models have been invoked in the interpretation of previous results [16,17,40], their validity has been debated and they failed to provide quantitative predictions. Clearly, to further advance our understanding of ultrafast photoconductive sampling in gases, a quantitative model for the macroscopic signal formation is crucial.…”

Ultra-broadband photonic sampling of optical waveforms

“…Optical-field sampling techniques take advantage of some process that lasts much less than an optical cycle of the measured light wave. Most of them rely on the generation of free electrons either by a weak extreme ultraviolet pulse [11][12][13] or by a strong optical pulse [14][15][16][17][18][19] . The ability of such techniques to detect weak signals is limited by undesirable effects associated with ionization.…”