Thorsten Ergler

Determination of the carrier-envelope phase of few-cycle laser pulses with terahertz-emission spectroscopy

The availability of few-cycle optical pulses opens a window to physical phenomena occurring on the attosecond timescale. To take full advantage of such pulses, it is crucial to measure1,2,3,4 and stabilize1,2 their carrier-envelope (CE) phase, that is, the phase difference between the carrier wave and the envelope function. We introduce an approach to determine the CE phase by down-conversion of the laser light to the terahertz (THz) frequency range by means of plasma generation in ambient air, an isotropic medium where optical rectification (down-conversion) in the forward direction is only possible if the inversion symmetry is broken by electrical or optical means5,6,7,8,9,10. We show that few-cycle pulses directly produce a spatial charge asymmetry in the plasma. The asymmetry, associated with THz emission, depends on the CE phase, which allows determination of the phase by measurement of the amplitude and polarity of the THz pulse.

Wavelength Dependence of the Suppressed Ionization of Molecules in Strong Laser Fields

We study ionization of molecules by an intense laser field over a broad wavelength regime, ranging from 0.8 to 1.5 μm experimentally and from 0.6 to 10 μm theoretically. A reaction microscope is combined with an optical parametric amplifier to achieve ionization yields in the near-infrared wavelength regime. Calculations are done using the strong-field S-matrix theory and agreement is found between experiment and theory, showing that ionization of many molecules is suppressed compared to the ionization of atoms with identical ionization potentials at near-infrared wavelengths at around 0.8 μm, but not at longest wavelengths (10 μm). This is due to interference effects in the electron emission that are effective at low photoelectron energies but tend to average out at higher energies. We observe the transition between suppression and nonsuppression of molecular ionization in the near-infrared wavelength regime (1-5 μm).

On the Wavelength Dependence of the Suppressed Ionization of Molecules in Strong Laser Fields

We study ionization of molecules and atoms with same IP by intense laser field from 0.6-10 μm. A trend from ionization-suppression to non-suppression is found for many molecules as a function of wavelength.

Measurement of the Carrier-Envelope Phase of Few-Cycle Laser Pulses by THz-Emission Spectroscopy

THz-emission from laser-generated plasmas opens a way to measure the carrier-envelope phase of few-cycle optical pulses, a parameter of critical significance for numerous experiments with sub-10-fs light pulses.

Carrier-envelope-phase dependent down-conversion of intense few-cycle laser-pulses to terahertz frequencies

We report a new method for carrier-envelope-phase determination, based on electro-optical detection of the THz pulse emitted from a plasma generated by the few-cycle pulses being characterized.

Microscopic description for THz generation in plasmas induced by few-cycle laser pulses

We present a microscopic description for the polarization induced in a plasma by few-cycle optical pulses in isotropic gaseous media. The resulting asymmetric polarization allows for optical rectification and THz emission.