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The optical laboratory of nanostructure material and devices laboratory (NMDL) covers instrumentations enabling a variety of spectroscopic and microscopic characterizations including: photoluminescence (PL) spectroscopy, Fourier Transform Infrared (FTIR) Spectroscopy, cathodoluminescence (CL) spectroscopy, spectroscopic ellipsometry, and optical microscopy etc.

Two separate home-designed PL stations currently are in operation. A cw PL (figure 1) station is capable of performing conventional cw PL and PL excitation (PLE) spectroscopy on both solid and solution samples at room or cryogenic temperature (down to 2K). It covers the visible and NIR wavelength region with a number of excitation sources (ion laser, Ti:S laser, lamp source etc.) and detectors (GaAs photomultiplier tube and Ge detector etc). Raman studies are also possible on this cw PL setup because of its one meter double monochromator with high stray light rejection. For the last 10 years this PL setup has been the main work-horse for optical characterization of the self-assembled epitaxial nanostructure. Being home-designed other than standard PL and PLE, this setup is so flexible that it has been adapted for many other measurements such as absorption, photocurrent, and electroluminescence etc whenever research needs.

A second PL (figure 2, 3) station is designed for more advanced studies especially on our current work of integrated epitaxial and colloidal nanostructure. Other the standard cw PL and cryogenic capability, it can also perform time resolved PL (TRPL) measurement. Here the cw PL measurement is performed by spectrometers coupled to liquid Nitrogen cooled CCD array (for Visible) or InGaAs array (for NIR) detectors, and therefore has superior sensitivity. The TRPL is based on time-correlated single-photon-counting (TC/SPC) detection mechanism. An ion-laser pumped cavity-dumped femto-second Ti:S oscillator (Coherent Mira900D with pulse switch) is used for pulsed excitation which currently covers NIR (700nm-1000nm) wavelength range but can be readily adapted to UV-Vis range (250nm-500nm) via frequency doubling/tripling. PL generated from sample is spectrally dispersed by a 1/4m subtractive monochromator and detected by a Hamamatsu micro-channel plate photomultiplier tube (MCP-PMT) with S1 cathode covering 400nm-1200nm wavelength range. The time resolution of this TRPL setup is ~10ps.

A FTIR setup (figure 4) is also available at NMDL for to perform absorption and photocurrent measurements of the SAQD arrays and QDIP device structures in the 1-20 µm wavelength range. A low temperature cryostat enables variable temperature absorption and photocurrent measurements from 1.8 K to room temperature.

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