© (2006) Nature Phys.

Characterizing and manipulating attosecond pulses of light are notoriously hard owing to their short duration (~10-15 s) and extreme wavelength (XUV). Now, scientists in Canada have reported a new in situ measurement approach that could make the task much easier and add a new level of control1.

Whereas pulse characterization schemes usually measure the pulses in a separate location after they have been generated, Dudovich et al. have now succeeded in extracting information about the attosecond pulses while they are still within their nonlinear birth place. The team’s attosecond pulses are made by focusing 30 fs laser pulses into an argon gas jet — a tried and trusted approach that induces the extreme optical nonlinear effects that are required. However, the trick to the new measurement scheme is to use a very weak blue laser beam to probe the production process within the gas jet without significantly modifying it. The team then extracts the length of the attosecond pulses by analysing the resulting modulation of the even harmonics that they contain.

The scientists have also demonstrated that by increasing the power of the blue probe beam the technique can also actually directly control attosecond pulse generation. For example, by changing the phase of a more powerful probe beam the researchers have shown that it is possible to switch the attosecond emission between even and odd harmonics. The authors also speculate that in the future the approach could offer an extensive means for pulse manipulation, enabling pulses to be focused as they are made or split into replica pulses thanks to the creation of control-beam inspired time-dependent lenses or beam splitters.