Optical methods allow real-time investigations on the shortest time scales, which are not accessible by other methods. With lasers, light pulses of 100 attoseconds can be generated today (1 attosecond = 10-18s = one billionth of a billionth of a second). Scientists at the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) in Berlin have now set a record for the shortest man-controllable time of 12 attoseconds. They report about it in Nature Photonics.
Light is a very high frequency electromagnetic wave. For visible light, a single oscillation of the oscillating electric field takes only about 1200-2500 attoseconds. In ultrashort light pulses, the light performs only a few oscillations. In order to achieve the maximum possible field strength, the center of the pulse must coincide with a maximum of the field, which corresponds to the phase position shown in Fig. (Red line). Pulses from conventional short-pulse lasers show large fluctuations in the position of the field maxima relative to the pulse center and do not reach the maximum field strength in a stable manner. Therefore, methods have been developed in recent years, with which the position of the field maxima, that is, the phase of the light oscillation, can be stabilized.
Together with the Viennese laser company Femtolasers, MBI researchers led by Günter Steinmeyer have now developed a new method with which they can specifically change the phase position of the light oscillation outside the laser. In contrast to the previously used methods, the laser is no longer actively intervened, whereby fluctuations in the laser power and pulse duration are avoided and a high long-term stability is achieved. Rather, the correction of the phase position outside the laser in a so-called acousto-optical frequency shifter, which is fed directly without control with the measurement signal. "This direct correction of the phase position dramatically simplifies many experiments in attosecond physics and frequency metrology," Steinmeyer is convinced.
So far, a stabilization of the position of the field node in the range of about 100 attoseconds (10-16 s, corresponding to 1/20 of the wavelength) was possible, which also corresponds to the shortest attosecond pulses achieved so far. The new method has now succeeded in reducing this limitation to 12 attoseconds (1.2 x 10-17 s, 1/200 of the wavelength). For the first time, the sound barrier of the atomic time unit (24 attoseconds) was undershot, marking the order of magnitude of the fastest conceivable processes in the atomic shell. This opens up new possibilities for exploring the fastest processes occurring in nature.
The record was achieved in close collaboration with the company Femtolasers, which provided a specially optimized laser for the experiments. Based on this cooperation, the new procedure was immediately transferred. Femtolasers is already working on a commercial implementation of this new process.