We demonstrate the use of two ultrafast fiber laser systems locked together at identical repetition rates of 100 MHz to
achieve a timing resolution below 300 fs for pump-probe experiments. By sweeping the set-point of the locking
electronics, we scan the time delay between the individual pulse trains by 800 ps. This scanning technique requires only
sub-micrometer mechanical motion. Since the temporal scan range is determined electronically, the acquisition can be
limited to regions where meaningful physical data is recorded. We discuss how our technique can approach
asynchronous optical sampling based on GHz repetition rate lasers in terms of data collection efficiency while offering a
number of practical advantages.
We present an overview of nonlinear frequency conversion techniques which we developed and optimised for use with
mode-locked Erbium fiber lasers. Starting with 70 fs, 3 nJ pulses at 1560 nm, we access the entire wavelength band from
500 to 2000 nm without gaps. Across this broad range of wavelengths, we adapt pulse parameters such as temporal
duration and spectral width to the specific application requirements.
Mode-locked Er-doped fiber laser systems built on single-mode fiber technology continue to see a remarkable improvement in their performance characteristics. In this contribution, we present an extremely compact and powerful version of such a laser source, delivering elevated peak powers well in excess of 10 kW in combination with ultrashort pulse durations below 100 fs. Eliminating the need for costly pump sources, external cooling as well as daily re-alignment routines, this laser system opens possibilities for an entirely new class of experiments and applications to a much larger group of users than only dedicated laser institutes. The accessible wavelength range is greatly enhanced by generation of a supercontinuum inside an integrated highly nonlinear fiber. We report output spectra with a bandwidth exceeding one full octave which we utilize for phase stabilization of the laser source. As a first proof of principle, a precise frequency measurement is carried out on a cavity-stabilized diode laser over a time interval of 88 hours without interruption. With regard to the time domain pulse structure, the user can select to re-compress defined parts of the continuum to achieve pulse durations below 30 fs. At the same time, the central wavelength of these pulses is easily shifted over a wavelength interval from 1130 nm to 1400 nm. Based on these findings, we demonstrate the generation of widely tunable light pulses in the visible spectral range by efficient frequency doubling. Potential applications for this novel light source are discussed.
Ultra-high bandwidth continuum generation has been attracting enormous interest for applications in optical frequency metrology, low-coherence tomography, laser spectroscopy, dispersion measurements, sensor techniques and others. The acceptance of this new technology would greatly benefit from the availability of compact and user-friendly sources. High index planar devices provide a versatile and unique approach to continuum generation. The dispersion can be carefully engineered by choosing the material and the geometry of the waveguides. Optical integration can also be provided on the same platform. Hundreds of different waveguides having different and calibrated dispersions can be integrated in few tens of millimeters. Input and output of the 2D guides can be tailored to provide mode matching to fibers and pump lasers by means of single element bulk optics. In this paper for the first time we demonstrate a low-noise, ultra-high bandwidth continuum at 1.55 μm. A bandwidth in excess of 390 nm is obtained by launching energy as low as 50 pJ in a 12 mm short tapered planar waveguides. The pump wavelength was in the normal dispersion regime and was provided by a compact, fiber-based sub-100 femtosecond source.
Ultrabroadband THz spectroscopy is employed to observe how many-particle interactions build up in an extreme non-equilibrium electron-hole plasma. The plasma is photogenerated in bulk GaAs via resonant interband absorption of a 10 fs laser pulse. Subsequently, the dynamics of the complex dielectric function throughout the mid-infrared is directly monitored with uncertainty-limited temporal resolution with a single-cycle THz pulse. Field sensitive detection allows us to measure simultaneously real and imaginary part of the complex dielectric function of the plasma in the multi-THz regime. We show that collective phenomena such as Coulomb screening and plasmon scattering exhibit a delayed onset. This observation is explained in terms of the ultrafast formation of dressed quasiparticles. The time scale for this transient behavior is of the order of the inverse plasma frequency. Our findings support recent quantum kinetic calculations of the temporal evolution of the Coulomb interaction after ultrafast excitation of a dense electron-hole plasma.