Principal Investigator Rajeev Ram
This project is a collaborative effort with Prof. Bawendi’s group, whose goal is to gain a better understanding of how to model exciton dephasing in nanocrystals. Specifically, we plan to more thoroughly characterize how the absorbtion of CdSe nanocrystals changes as a function of temperature, nanocrystal composition, and pump modulation frequency using the pump probe setup shown below.
In our setup the pump laser is used to burn a spectral hole in the nanocrystal sample, while the probe laser is used to monitor the shape of the spectral hole. By more thoroughly characterizing how the shape of the spectral hole changes under different circumstances, we hope to develop more accurate models to describe both intrinsic dephasing of nanocrystals and how nanocrystals interact with their environment on short time scales (~1 ms). Hopefully, this information will be useful to engineers who wish to develop applications incorporating nanocrystals.
The diode lasers can output 5 mw of power at 635 nm. We can tune the lasers about 30 GHz continuously or by about 1 THz discontinuously (because of mode hops) by changing either the bias current or operating temperature. An acousto optic modulator is used to chop the pump beam up to 50 MHz. A Fabry Perot Etalon is used to monitor the detuning of the probe laser. A Helium cryostat is used to cool the samples to 5 K.
Phedon Palinginis, et al (working in Hailin Wang’s group at University of Oregon) have measured a 1.5 GHz absorbtion linewidth in CdSe/ZnS capped nanocrystals using a similar experimental setup. (As far as we know this is the narrowest linewidth ever measured for CdSe nanocrystals.) Our plan is to further characterize how the absorbtion of CdSe nanocrystals changes in order to better understand the physics relevant to nanocrystals.