Ultrafast Cooperative Phenomena in Coherently Prepared Media: From Superfluorescence to Coherent Raman Scattering and Applications
MetadataShow full item record
Technological progress in commercializing ultrafast lasers and detectors has allowed realization of cooperative processes on an ultrashort time scale, which demand a re-evaluation of the conventional cooperative phenomena with a new insight. Ultrafast cooperative phenomena in coherently prepared media and various applications of superﬂuorescence and coherent Raman scattering are studied in this dissertation. In particular, a simple theoretical testimony on analogy between a cooperative emission and coherent Raman scattering is presented by oﬀering an opportunity to perform parallel research on these two processes from a uniﬁed point of view. On one hand, the superﬂuorescent pulse with a time duration of a few tens of picoseconds (ps) from alkali metal vapor is observed for the ﬁrst time, even though cooperative phenomena in atomic vapor have been extensively studied for more than ﬁve decades. A dense rubidium vapor pumped by ultrashort (100 femtosecond, fs) pulses allows a realization of the ultrafast superﬂuorescence while a time-resolved study of superﬂuorescence is accomplished by using a streak camera with 2 ps time resolution. Experimental research on quantum nature of cooperative emissions has been “frozen” over the years (three decades) possibly because of the technical diﬃculties. Quantum ﬂuctuations of superﬂuorescence development are explored experimentally by taking advantage of the ultra fast streak camera. Presumable applications of the superﬂuorescent pulse in e.g., a remote sensing, and an ultraviolet upconversion of the input infrared laser pulse are presented. The quantum interference due to diﬀerent excitation pathways is revealed by the temporal coherent control technique while observing interferometric signals from alkali metal vapors. On the other hand, a new spectroscopic technique based on ultrafast coherent Raman scattering is developed. The key advantage of the presented technique is to suppress the non-resonant background noise which usually obscures possible applications of the other conventional coherent Raman techniques in practice. A reduction of the background noise is achieved by shaping and delaying the third pulse which probes the coherence of the medium (i.e., an enhancement of speciﬁc vibrations of the target molecules in unison) ﬁrstly prepared by two broadband pulses. We demonstrate a robustness and superiority of signal-to-noise ratio of the developed technique by identifying as few as 10000 bacterial spores at a single laser shot level. Finally, several comparative studies between cooperative and uncooperative processes are presented. A picosecond cooperative phenomenon in a three-photon resonant medium induced by a single as well as two-color ultrashort pulses is investigated. A time-resolved study shows that a picosecond cooperative eﬀect is crucial in the well-established ﬁelds of resonant-enhanced multiphoton ionizations and harmonic generations. We also present a quantitative analysis for spontaneous versus broadband coherent Raman scattering on pyridine molecules. The spontaneous Raman signal is enhanced by 5 orders as a result of cooperative phenomena.
ultrafast cooperative phenomena
coherent anti-Stokes Raman scattering
temporal coherent control
ultrafast streak camera
Gombojav, Ariunbold (2011). Ultrafast Cooperative Phenomena in Coherently Prepared Media: From Superfluorescence to Coherent Raman Scattering and Applications. Doctoral dissertation, Texas A&M University. Available electronically from