Here, we take a fresh approach to the real-time oscilloscope via momentary stamping of a traveling optical wave on a quasi-one-dimensional (Q-1D) array (i.e., short, vertically thin, and horizontally wide bunch) of relativistic (MeV) electrons whose velocity is close to the speed of light. However, for the reconstruction of an overall field trace, data should be collected by scanning the relative time delay of probe electrons because the size of electrons sources is not sufficiently large to visualize an entire waveform.
Recently, direct visualization of ultrafast light oscillation was demonstrated by tracing the kinetic energy change of electrons released from molecules 12, metal tips 13, 14, and photocathodes 15, 16. In this context, a charged particle is considered as a most reliable probe of electromagnetic waves because its deflection motion in free space can directly reflect the spatiotemporal field distribution of optical waves without requiring the use of any NLO parametric media. Also, in such nonlinear optical (NLO) conversion techniques for assessing broadband light waves 8, the reconstructed field distribution is prone to be distorted from the original waveform due to imperfect phase-matching features inside NLO materials during frequency conversion processes 9, 10, 11. Recently, temporal imaging with a time lens has emerged as a method for single-shot acquisition of optical waveform 5, 6, 7, but its temporal accuracy should be further improved for broader use. Although extreme ultraviolet pulses opened new frontiers for PHz optical metrology 2, 3, 4, offering a single-shot measurement is still challenging. Real-time measurement of an ultrafast waveform has been a constant desire in many fields of fundamental science and technology 1.
Owing to the use of transversely-wide and longitudinally-short electron bunch and transversely travelling wave, the proposed “single-shot oscilloscope” will open up new avenue for developing the real-time petahertz (PHz) metrology.
As a proof-of-concept experiment, we successfully demonstrated to capture the entire field oscillation of a THz pulse with a sampling rate of 75.7 TS/s. Momentary stamping of the wave, transversely travelling inside a metal slit, on an ultrashort wide electron bunch enables the single-shot recording of an ultrafast optical waveform. We found the unique condition of subwavelength metal slit waveguide for preserving the distortion-free optical waveform during its propagation. Here, we present a real-time ultrafast oscilloscope for time-frozen visualization of a terahertz (THz) optical wave by probing light-driven motion of relativistic electrons. The deflection of charged particles is an intuitive way to visualize an electromagnetic oscillation of coherent light.
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