Due to fast carrier dephasing and relaxation, in solid state systems a few μeV resolution are sufficient for most optical experiments. One focal point of Experimental Physics 2 is finding semiconductor structures, where these mechanisms are suppressed. One example is the yellow 1S exciton series in cuprous oxide with linewidth ≤ 1 μeV. In an experiment such narrow linewidth can directly be observed with high resolution spectroscopy techniques.
The combination of narrow linewidths and a large exciton binding energy of about 90 meV allows us to observe and investigate Rydberg excitons, which are the semiconductor analogues of Rydberg atoms: Atoms, where at least one of the electrons is excited into a state with huge principal quantum number n. As the spatial extension, polarizability and dipole interactions of such states scale non-linearly with n, Rydberg states show exaggerated properties. We have observed Rydberg excitons with principal quantum numbers as large as 25, which corresponds to excitons with a spatial extent of 2 μm - the equivalent of more than 10 billion crystal unit cells or 10 times the wavelength of the excitation laser inside the crystal. Due to the strong interaction between excitons with large n, a phenomenon called Rydberg blockade occurs: The presence of excitons shifts the energy needed to excite further excitons and therefore results in a blockade effect, which is a cornerstone of quantum information technology. Whether it is possible to realize such strong interactions that the presence of a single exciton is sufficient to completely prevent the excitation of further excitons is a subject of current research.
In our lab there are a dye-laser (res 1MHz) and a TiSaphire-laser (res 100kHz) available for high resolution transmission experiments. Additionally luminescence is detected with a CCD behind a double monochromator. For use in second order the overall resolution of these devices is 10µeV. Such a high resolution is useful only for cooled solids. This is done with various cryostats for different applications. In time resolved measurements we use an electro-optical modulator for the creation of laser pulses with variable shapes
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Location & approach
The campus of TU Dortmund University is located close to interstate junction Dortmund West, where the Sauerlandlinie A 45 (Frankfurt-Dortmund) crosses the Ruhrschnellweg B 1 / A 40. The best interstate exit to take from A 45 is "Dortmund-Eichlinghofen" (closer to Campus Süd), and from B 1 / A 40 "Dortmund-Dorstfeld" (closer to Campus Nord). Signs for the university are located at both exits. Also, there is a new exit before you pass over the B 1-bridge leading into Dortmund.
To get from Campus Nord to Campus Süd by car, there is the connection via Vogelpothsweg/Baroper Straße. We recommend you leave your car on one of the parking lots at Campus Nord and use the H-Bahn (suspended monorail system), which conveniently connects the two campuses.
TU Dortmund University has its own train station ("Dortmund Universität"). From there, suburban trains (S-Bahn) leave for Dortmund main station ("Dortmund Hauptbahnhof") and Düsseldorf main station via the "Düsseldorf Airport Train Station" (take S-Bahn number 1, which leaves every 20 or 30 minutes). The university is easily reached from Bochum, Essen, Mülheim an der Ruhr and Duisburg.
You can also take the bus or subway train from Dortmund city to the university: From Dortmund main station, you can take any train bound for the Station "Stadtgarten", usually lines U41, U45, U 47 and U49. At "Stadtgarten" you switch trains and get on line U42 towards "Hombruch". Look out for the Station "An der Palmweide". From the bus stop just across the road, busses bound for TU Dortmund University leave every ten minutes (445, 447 and 462). Another option is to take the subway routes U41, U45, U47 and U49 from Dortmund main station to the stop "Dortmund Kampstraße". From there, take U43 or U44 to the stop "Dortmund Wittener Straße". Switch to bus line 447 and get off at "Dortmund Universität S".
The AirportExpress is a fast and convenient means of transport from Dortmund Airport (DTM) to Dortmund Central Station, taking you there in little more than 20 minutes. From Dortmund Central Station, you can continue to the university campus by interurban railway (S-Bahn). A larger range of international flight connections is offered at Düsseldorf Airport (DUS), which is about 60 kilometres away and can be directly reached by S-Bahn from the university station.
The H-Bahn is one of the hallmarks of TU Dortmund University. There are two stations on Campus Nord. One ("Dortmund Universität S") is directly located at the suburban train stop, which connects the university directly with the city of Dortmund and the rest of the Ruhr Area. Also from this station, there are connections to the "Technologiepark" and (via Campus Süd) Eichlinghofen. The other station is located at the dining hall at Campus Nord and offers a direct connection to Campus Süd every five minutes.
The facilities of TU Dortmund University are spread over two campuses, the larger Campus North and the smaller Campus South. Additionally, some areas of the university are located in the adjacent "Technologiepark".