Broadband Auston-Type Photoconductive Field Sampling in Gallium Phosphide

The ability to directly measure the electric field of light enables novel observations of light-matter interactions, proving a powerful tool in modern ultrafast science [1]. Techniques such as attosecond streaking and nonlinear photoconductive sampling (NPS) [1], [2] exploit nonlinearities in gases or solids in order to achieve short gating events that enable field sampling in the near-infrared (NIR) and visible spectral ranges. The dependency of these techniques on strong-field ionisation constrains their sensitivity. Presented here is a method for the detection of broadband near-infrared fields spanning more than one octave from 110 to 220 THz, based on linear absorption in gallium phosphide (GaP). In contrast to NPS, this Auston-type [3] linear photoconductive sampling (LPS) approach circumvents complex vacuum setups, avoids phase-matching and does not require high power or high pulse energy to sample the electric field of light. By applying a short visible-UV (VIS-UV) pulse to GaP, an appreciable change in the carrier density (within a few femtoseconds) occurs. This change in carrier density acts as a gating event, permitting the detection of electric fields across the near-infrared.