last update: 24.10.07 gi
The terahertz laboratories of the center allow experiments in a spectral range which stretches from the near- to far-infrared over three decades, including the whole terahertz range. A total of eight lasers and spectroscopic systems provides from small to the world's highest intensities which are used in the spectroscopy of solids.
In the terahertz range high-radiation intensity is of particular interest because it gives rise to a variety of nonlinear phenomena whose characteristic features are basically different from the corresponding effects at microwave frequencies as well as in the range of visible radiation. This is due to the fact that in the electron-radiation interaction the transition from semiclassical physics with a classical field amplitude to the fully quantized limit with photons occurs at terahertz frequencies.
The possibility to vary both the frequency and the intensity of high-power radiation sources in a wide range yields the unique opportunity to study the same physical phenomenon in both limits. By properly varying the frequency or intensity of radiation one can achieve that either the discrete properties of light quanta or the wave character of the radiation field dominates the radiation-matter interaction.
In general, the research with terahertz excitation is supposed to determine the limits of the actual high-frequency electronics and uncover new physical phenomena which enable future electronics at terahertz frequencies.
Current experimental facilities of the Terahertz Center include:
THz and middle infrared radiation in the frequency range from 80 THz to 0.15 THz (wavelength range between 4 µm and 2000 µm). (Sergey Ganichev and Hans Lengfellner)
- Spectroscopic systems:
- Fourier spectrometer for THz spectroscopy with step-scan technique and low temperature cryostat;
- Michelson spectrometer for laser lines definition
- Low and middle power level laser systems:
- cw-operated terahertz laser systems with about 100 mW power
- 60 Watt cw CO2 laser, with frequency doublers
- Q-switch molecular THz laser system
- 2 kW CO2 Q-switch laser
- High power level laser systems:
- Molecular terahertz lasers with radiation intensities up to 10 MW/cm2
- 100 MW pulsed TEA CO2-laser
- Low power detectors: Ge<Ga>, pyroelectric, Golay cells, Ge<Au>
- Moderate and high power detectors with sub-ns time resolution: photon-drag, µ-photoconductivity, photogalvanic
- Space resolved detection of the radiation beam profile
- Polarization detectors: circular and linear photogalvanic effects
- Detectors based on anisotropic thermopower: Yba2Cu3O7-
- THz techniques:
- Temperature variable optical cryostats matched for nonlinear optical and magneto-optical experiments with magnetic field up to 8 T.
- THz optic components
- Polarization technique.
Near infrared, visible and UV radiation
- Space and time resolved femtosecond spectroscopy (Christian Back)
- two mode-locked Titanium-Sapphire laser systems, pulse durations 60-200 fs
- 300 kHz amplified Titanium-Sapphire laser system
- three optical microscope setups for spatially- and time-resolved experiments featuring systems with microscope cryostat, temperatures 3-300 K, spatial resolution 800 nm, microscope setups at ambient temperature, spatial resolution 300 nm
- Time-resolved Faraday, Kerr, and photoluminescence experiments for spin dynamics (Christian Schüller)
- Mode-locked Titanium-Sapphire laser systems, pulse durations 100600 fs
- Optical split-coil magnet cryostat, temperatures 0.4300 K, magnetic fields up to 11.5 T
- Optical microscope setup for spatially- and time-resolved experiments with microscope cryostat, temperatures 3300 K, spatial resolution 1 µm
- Streak-camera system with S1 photocathode, temporal resolution > 2 ps
- Optical spectrometer with CCD detector
- Raman spectroscopy (starting in 2007) (Christian Schüller)
- Triple Raman spectrometer with CCD detector for visible and near-infrared range
- cw Titanium-Sapphire laser system
- Mode-locked Titanium Sapphire laser system for time-resolved Raman experiments
- Microscope setup for spatially-resolved experiments with micro-magnet cryostat, magnetic fields up to 5 T
- Optical methods (including material characterization) (Werner Wegscheider)
- micro-photoluminescence (
Material growth and processing
- MBE systems (Werner Wegscheider)
Two dedicated MBE chambers provide III/V-semiconductor material for:
- two-dimensional charge carrier systems of highest purity, i.e. with highest achievable mobilities as well as quantum well structures with narrow luminescence line widths on various (also non-common) substrate orientations
- spintronic applications in which the ferromagnetic semiconductor GaMnAs is incorporated as spin injector, filter etc.
- Material processing (Dieter Weiss)
- Cleanroom facilities with optical lithography, electron beam lithography, reactive ion etching equipment, parylene coater and metal deposition systems (evaporators and magnetron sputtering)
Transport experiments facilities (including material characterization) (Dieter Weiss)
- 4He-, 3He-cryostats and 3He -4He-dilution refrigerator with superconducting high-field magnets. Highest magnetic field: 19 T. Lowest temperature: ~20 mK. AFM-MFM set up for surface characterization
Analytical applications (Otto Wolfbeis, Vladimir Mirsky)
- Surface plasmon resonance at THz frequencies and its application to study ligand - receptor interactions
- Electrochemical biosensors based on electron tunneling induced by THz irradiation