Nonreciprocal Terahertz Second-Harmonic Generation in Superconducting NbN under Supercurrent Injection

Second-harmonic generation

The goal of this experiment in nonlinear optics is to study the conversion of a (very small) fraction of laser light from its original wavelength of 980 nm (i.e. invisible to the naked eye) to its second-harmonic at a wavelength of 490 nm. This conversion takes place by mild focussing of an intense laser beam in a nonlinear birefringent crystal of BBO (= β BaBO4). You will study the physical pr...

Energy-gap dynamics of superconducting NbN thin films studied by time-resolved terahertz spectroscopy.

Using time-domain terahertz spectroscopy we performed direct studies of the photoinduced suppression and recovery of the superconducting gap in a conventional BCS superconductor NbN. Both processes are found to be strongly temperature and excitation density dependent. The analysis of the data with the established phenomenological Rothwarf-Taylor model enabled us to determine the bare quasiparti...

Interferometric second harmonic generation microscopy.

We describe a novel second harmonic generation (SHG) microscope that employs heterodyne detection by interfering the epi directed SHG from a sample with SHG from a reference crystal. In addition, the microscope provides complementary reflectance information based on optical coherence microscopy (OCM). The instrument features dual balanced detection to minimize the effect of source fluctuations,...

Silicon-based Terahertz Signal Generation with Multi-phase Sub-harmonic Injection Locking Technique

X-ray second harmonic generation.

We report clear experimental evidence for second harmonic generation at hard x-ray wavelengths. Using a 1.7 Å pumping beam generated by a free electron laser, we observe second harmonic generation in diamond. The generated second harmonic is of order 10 times the background radiation, scales quadratically with pump pulse energy, and is generated over a narrow phase-matching condition. Of import...