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| Identifier |
000363736 |
| Title |
Πολαριτονικό λέιζερ με πολύ χαμηλό κατώφλι λειτουργίας |
| Alternative Title |
Ultra-low threshold polariton lasing in gaas |
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Author
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Τσώτσης, Παναγιώτης
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Thesis advisor
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Χατζόπουλος, Ζαχαρίας
Σαββίδης, Παύλος
Πελεκάνος, Νικόλαος
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| Abstract |
The unprecedented potential of polariton based devices owes its origin mainly to the bosonic character of polaritons to condense in the same final state, thus requiring no population inversion to achieve lasing. Consequently, it is widely believed that the threshold of a polariton laser is at least two orders of magnitude lower than that of a conventional semiconductor photon laser operating in the weak coupling regime1. The question of how much do GaAs polariton lasers really outperform an optimized photon laser has still to be address.
Here we report a detailed examination of the lasing threshold of semiconductor microcavity at the boundary of the weak to strong coupling transition. The sample is a high Q (P> 8000) 5/2 cavity with 4 sets of 3 GaAs quantum wells placed at the antinodes of the cavity electric field. Under continuous wave non-resonant excitation and at low temperatures (23K) we observe ultralow threshold lasing which originates from the lower polariton state. With increasing temperature (up to 70K) we observe a steady increase of the threshold and simultaneous loss of strong coupling regime which however cannot be explained by a simple argument of temperature dependent broadening of the exciton linewidth. Furthermore, the nearly doubled lasing threshold does not on itself justify such dramatic reduction of exciton oscillator strength and loss of strong coupling regime. Instead we believe the increasing exciton reservoir lifetime with temperature is responsible for nearly tenfold increase of carrier density at same pumping rate leading to collapse of strong coupling regime.
From the point of view of practical devices, it appears that polariton lasing thresholds at least in GaAs based microcavities have yet to prove their true potential to achieve the predicted two orders of magnitude reduction of the threshold. This suggests that further optimization of the efficiency of injection and relaxation mechanisms are necessary before polariton lasers can fulfil their true potential, as extremely low threshold sources of coherent light.
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| Language |
Greek |
| Subject |
Strong coupling lasing |
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Λέιζερ πολαριτονίων |
| Issue date |
2011-03-18 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Physics--Post-graduate theses
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Type of Work--Post-graduate theses
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| Views |
473 |
Πολαριτονικό λέιζερ με πολύ χαμηλό κατώφλι λειτουργίας
