It is reported that scientists have developed a method to measure the shape of laser pulses in ambient air. It does not require a vacuum environment or X-ray pulses compared to existing waveform research methods. The method known as TIPTOE can be applied to laser pointers of different wavelengths including ultraviolet, visible or longer wavelengths.
TIPTOE (time-domain observation of the ionized electric field of the tunnel by interference) uses tunnel ionization to measure the time characteristics of the laser pulse waveform.
When an atom or molecule exposed to a strong electric field (such as an atom or molecule produced by a strong laser pulse) is ionized by a tunnel, some electrons may be lost. This TIPTOE method uses two superimposed laser pulses (one strong pulse and one weak pulse) and will observe its characteristics by tunneling electrons based on electric fields and electrons in the air. The time difference between the strong and weak superimposed laser pulses will result in a change in the electric field strength. Higher electric field strength corresponds to higher ionization. Therefore, any change in the electric field will be reflected in the tunnel ionization. These tunnel ionization changes will be used to measure the shape of the laser pointer pulse. Since tunnel ionization lasts only 200 aseconds, the TIPTOE method can provide long enough time resolution to measure pulses of ultraviolet, visible, and longer wavelengths.
Scientists at the Institute for Basic Science in Korea validated TIPTOE by comparing traditional X-ray pulse techniques. Both methods yield the same result. The effectiveness of this method was confirmed by using a Hertz optical oscilloscope that covers single-cycle laser pulses for different dispersion conditions from 500 nm to 1 μm.
According to the researchers, the TIPTOE method provides a complete time characterization of the laser field over a broad spectrum of ambient air, including the carrier envelope phase of the laser pulse, providing a versatile tool for accurately measuring the laser field.