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August 17, 2018

Ultrashort, intense laser pulses produced in the mid-infrared

Scientists have generated extremely short, high-power laser pulses at long wavelengths

small image of ultrashort laser pulse

Figure 1: A strong, ultrashort laser pulse with a wavelength in the mid-infrared interacts with a copper plate.

© 2018 RIKEN Center for Advanced Photonics

Ultrashort, intense laser pulses in the mid-infrared region have been generated by four RIKEN scientists1. This achievement promises to open the way to explore the ultrafast dynamics of electrons in materials.

High-power, ultrashort laser pulses at wavelengths just longer than those detectable by the human eye are routinely created in the laboratory by commercial laser systems. Because they pack a lot of light energy in a very short interval, these pulses are used to probe fundamental physical processes that occur in high electrical and magnetic fields.

Scientists would love to create such pulses at even longer wavelengths in order to explore processes that are not accessible using shorter wavelength lasers. For example, mid-infrared pulses that are a few tens of femtoseconds (10−15 seconds) long and have a few terawatts (1012 watts) of power could be used to excite electron plasmas, effectively creating table-top particle accelerators. But it is challenging to generate high-power, ultrashort laser pulses at longer wavelengths.

One way to generate short pulses with longer wavelengths would be to stretch a weak mid-infrared pulse in time and then process it so that its longer wavelength components are separated—or chirped—from its shorter wavelength ones. The chirped pulse could then be amplified by a special crystal and subsequently compressed. The amplification requires using a separate, high-intensity laser pulse known as the pump pulse, which should be about 1 picosecond (10−12 seconds) long for the amplification process to work and to avoid damaging the crystal. Unfortunately, such ultrafast pump lasers with high energies are still being developed.

small picture of Bing Xue, Eiji J. Takahashi and Yuxi Fu

Bing Xue (left), Eiji J. Takahashi (center) and Yuxi Fu (right), together with colleague Katsumi Midorikawa have generated intense, ultrashort laser pulses in the mid-infrared range.

© 2018 RIKEN

Now, Eiji J. Takahashi, Yuxi Fu and two other colleagues at the RIKEN Center for Advanced Photonics have generated short, high-peak-intensity laser pulses with a wavelength of 3.3 micrometers (Fig. 1). They achieved this by chirping both the pulse to be amplified and the pump pulse. This strategy allowed the team to use a commercially available amplification crystal and a widely used pump laser. The pulses at 3.3 micrometers had a relatively high energy, and once compressed, they exhibited a peak power approaching those needed for investigating physical phenomena in high fields.

The researchers now intend to obtain higher peak powers by optimizing their technique. “We plan to obtain even shorter and stronger mid-infrared laser pulses using the same technology,” says Fu.

Such pulses could eventually be used to generate soft x-ray pulses with durations of the order of attoseconds (10−18 seconds). “These x-ray pulses could be used to image the ultrafast ‘dancing’ of electrons,” comments Fu.

References

  1. Fu, Y., Xue, B., Midorikawa, K. & Takahashi, E. J. TW-scale mid-infrared pulses near 3.3 µm directly generated by dual-chirped optical parametric amplification. Applied Physics Letters 112, 241105 (2018). doi: 10.1063/1.5038414 (Link)