One million times brighter than the sun - white light as an extremely short impulse

Scientists at the Leibniz Universität Hannover, the Weierstrass Institute for Applied Analysis and Stochastics and the Max Born Institute for Nonlinear Optics and Short Pulse Spectroscopy have developed a new method for generating optical white light pulses in the visible and near infrared spectral range. These pulses can be compressed to extremely short durations, which makes up only a single oscillation of the light wave.

The generation of white light from spectrally narrow band laser radiation is one of the most fascinating processes in nonlinear optics. This mechanism has found wide variety of uses in spectroscopy, metrology, and medical imaging. At comparatively low light outputs, light sources based on optical fibers offer excellent spatial coherence properties and a small radiation area. White light radiation sources can therefore achieve a spectral radiance that makes them millions of times brighter than the sun.

The spectral coherence properties of such radiation sources, however, are comparatively modest. This means that while the light of the white light source can be well focused on a very small area, it is impossible to time the concentration of the pulse energy over a small time interval. In the current issue of the journal Physical Review Letters [PRL 110, 233901 (2013)] Ayhan Demircan ask, Shalva Amiranashvili, Carsten Brée and Günter Steinmeyer, a new solution to get around this fundamental problem of laser and white light sources. This proposal provides for using two light pulses at different wavelengths for white light generation in an optical fiber. For this one must choose the wavelengths of the pulses so that they propagate with nearly the same speed in the fiber. Similar to a surfer who measures a wave, the two pulses can then undergo a long-lasting bond that leads to an intense nonlinear interaction. This interaction quickly fills the spectral gap between the two pulses with coherently generated new spectral components.

Fig. 1 Numerical simulations of the two-color excitation of the fiber-based white light generation. A soliton pulse is coupled into a glass fiber with a slight time delay together with a pulse in the normal dispersion range. Here, the soliton can get its temporal profile until it meets the slowly widening dispersive wave. As soon as both impulses meet, they are temporally coupled to each other and then interact strongly with each other. Only a tiny portion of the dispersive wave can traverse the barrier created by the soliton.

Simulation calculations show that the supercontinuum generated in this way enables the generation of pulses with two optical cycles duration without further compression measures. By using suitable dispersion compensation, even the generation of a one-cycle pulse should be possible. In contrast to single-color generation of white light supercontinua, the new source spectra show a relatively smooth intensity profile, making it particularly interesting for new applications in medical imaging. Overall, this results in a variety of previously impossible applications of this fascinating new bright white light source.

Original publication

Compressible octave spanning supercontinuum generation by two-pulse collisions

A. Demircan, Sh. Amiranashvili, C. Brée, G. Steinmeyer

Physical Review Letters 110 (2013) 233901/1-5