Optical Spectroscopy and Photonics Facilities
Fourier Transform Spectroscopy
We use a top-of-the-line Bruker Vertex 80v vacuum FTIR spectrometer for optical measurements (reflectance and transmittance) from room to liquid helium temperature. Different configurations of detectors and beam splitters allow measurements over an ultra-wide spectral range (from 30,000 to 30 cm-1 or 0.3 to 330 mm) with high resolution (better than 0.06 cm-1, resolving power > 300,000:1 in the visible range).
Rapid scan with >110 spectra/s and step-scan data acquisition (t>10 ns) are also available for time-resolved photoinduced absorption and photoluminescence measurements in conjunction with a compact Q-Switched Nd:YAG oscillator (Quantel - Brilliant EaZy, 330mJ in 5ns @1064nm) and higher harmonic generation.
The FTIR spectrometer is equipped with the Hyperion 2000 infrared confocal microscope to add mapping capabilities with attenuated total reflectance (ATR) and grazing angle objectives.
A home-built photocurrent measuring system is used for responsivity and external quantum efficiency measurements of photodetectors and photovoltaics from 180 to 5000 nm at steady-state or low modulation frequencies.
Fast (t>10 ps) transient photocurrent measurements based on adaptations of the Auston switch technique as well as time-of-flight and photo-CELIV measurements are used for the determination of charge carrier density, mobility and lifetime over a wide time span. The core of the setup is a fast sampling oscilloscope (LeCroy WaveExpert 100H with 70 GHz sampling head).
A 100 fs Ti:sapphire amplified laser system from Quantronix (Ti-Light +Integra-C, >2.5 mJ @ 1KHz repetition rate ) is used for pump-probe, THz, and fast photocurrent spectroscopy. The 800 nm fundamental wavelength can be tuned by second (400 nm) and third (267 nm) harmonic generation, white-light continuum (WLC) generation, or by a WLC-seeded collinear Optical Parametric Amplifier (Palitra-FS-IR3 VIS3, 460 nm to 22 mm).
Micro-Raman and Micro-Photoluminescence
A micro-Raman/photoluminescence mesurement and imaging system was constructed by coupling an upright microscope (Nikon Eclipse LV100D) with a multi-line Kr-Ar ion laser (SpectraPhysics Stabilite 2018, 20W CW), a 785 nm fiber laser (B&W Tek, 500 mW), and a monochromator (Horiba-JY Triax 330) equipped with a liquid nitrogen cooled Si CCD (Horiba-JY Symphony). The system allows botth diascopic and episcopic illumination for bright and dark field imaging, and the temeperature can be varied from -196°C to 600°C in a heating/freezing stage (Linkam THMS600).
Electromagnetic modeling relies on NTU's High Performance Computing Centre (HPCC). The high-end IBM System x iDataplex cluster is powered by Intel® Xeon® processor 5500 series. With 274.64 Mflops (millions of floating point operations per second) per watt, it is also ranked on the Green500 list as the 29th most energy efficient supercomputers in the world!
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