Measuring The Shape Of Lasers Without A Vacuum

Using two superimposed lasers, scientists in South Korea have devised a fast and high resolution method to measure ultraviolet, visible and longer wavelength pulses.

AsianScientist (May 30, 2018) – A team of researchers at the Institute for Basic Science (IBS) in South Korea have developed a method to measure the shape of laser pulses in ambient air. They published their findings in Optica.

Experts have sought various means to use laser light to control the behavior of the electrons and manipulate electric currents. However, to achieve these goals, it is essential to know the waveform of a laser pulse and precisely record molecular events. As molecular events occur in just attoseconds (1 as = 10-18 seconds), existing methods to study them rely on the generation of attosecond X-ray pulses, which require detection equipment in vacuum chambers.

In this study, IBS researchers devised an alternative approach called TIPTOE (tunneling ionization with a perturbation for the time-domain observation of an electric field) which needs neither X-rays pulses nor vacuum conditions.

TIPTOE is based on two superimposed laser pulses: a strong pulse and a weak one. Atoms or molecules exposed to intense electric fields, like the ones created by strong laser pulses, can lose some of their electrons in a phenomenon called tunnel ionization.

The TIPTOE method depends on the intensity of the electric field and the tunnel ionization of the electrons of the atoms in the air. Time differences between the strong and the weak superimposed laser pulses cause the electric field intensity to vary.

As a higher electric field intensity corresponds to higher ionization, changes in the electric field are directly reflected by the extent of tunnel ionization. In turn, these changes in tunnel ionization are used to measure the shape of the laser pulse. Since tunneling ionization lasts only 200 attoseconds, the TIPTOE method can provide enough temporal resolution to measure ultraviolet, visible and longer wavelength pulses.

IBS scientists validated TIPTOE by comparing it with the conventional X-ray pulse generation technique, obtaining the same results.

“TIPTOE’s biggest advantage is the universality of this technique at different wavelengths,” explained Dr. Kim Kyung Taec of IBS who led the study.

The article can be found at: Park et al. (2018) Direct Sampling of a Light Wave in Air.


Source: Institute for Basic Science; Photo: Pixabay.
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