Ultra-broadband superradiant pulses from femtosecond laser pumped InP based quantum well laser diode

Laser techniques, such as gain / Q switching, mode-locking, have successfully overcome the energy restriction of gain clamping in the stead-state operated lasers, and allowed the generation of giant pulses with short pulse durations. However, gain saturation further limits the amount of stored energy in a gain medium, and therefore limits the possible maximum pulse energy obtained by laser techniques. Here we circumvent both gain clamping and the capacity limitation of energy storage by operating the double-quantum-well laser diode chips on ultrafast gain-switching model using femtosecond (fs) laser pulses as the optical pump. The advantage of our pumping approach is that the fs pulse can instantly produce a very large number of carriers, and therefore enable the formation of non-equilibrium coherent e-h BCS-like condensate state in a large energy region from the lowest QW subband edges to the highest subband and then obtain the ultra-broadband superrandiant pulses.Superradiance (SR) or the coherent spontaneous emission is not a new quantum optics phenomenon, which has been proposed in 1954 by R. Dicke, even earlier than the invention of laser. It is famous as by its ultrashort duration, high peak power, high coherence and high timing jitter. Recently, femtosecond SR pulses have been generated from semiconductors. This investigation has revived both theoretical and experimental studies of SR emission.In this thesis, we have demonstrated the generation of intense, delayed SR pulses from the InP based double quantum well laser diode at room temperature. The 1040 nm femtosecond laser was applied as the optical pumping source, and when the pump power is high enough, the cooperative recombination of e-h pairs from higher order quantum energy levels can occur to generate SR bursts earlier than the cooperative emission from the lower quantum energy levels. Then, ultra-broadband TM polarized SR pulses have been firstly generated at room temperature. Our experiments also provide a well prospect of ultra-high energy light pulse generation based on SR, besides, the ultra-broadband spectrum is promising for applications in a diverse range of fields, including optical coherent tomography and spectroscopy.Graphene, a truly 2D material, has stimulated a vast amount of research in recent years. In our work, we have wet transferred the CVD grown monolayer graphene onto the top of our LD chips. With the combination of graphene on top of QW LD, the evanescent field of TM polarized modes can well interact with top graphene layer, and therefore, produce a dramatically modulation of the output power, and optical spectra of output pulses. The graphene-on-DQW LD will be promising to explore the novel devices, such as optical modulator, which will greatly promote the applications of SR emission in near future.激光技術，諸如增益 / Q調製，鎖模，已經成功克服了穩態激光器存在的增益箝制現象，從而產生了脈寬窄，峰值功率高的巨脈衝。然而，增益飽和現象又進一步限制了增益介質的儲能上限，因而設定了激光技術產生的脈衝的能量上限。在這裡，我們以飛秒激光為光泵,使量子阱激光器工作在超快增益調製模式, 從而有效地規避了增益箝制和儲能限制。这种泵浦方式的优势在于可以瞬间产生极大量的载流子，從而可以在一个很宽的能带区间内（从量子阱的最低能级到最高能级）形成非平衡相干类BCS状态的电子空穴对的凝聚态，从而产生宽频超辐射。超輻射（SR），或稱為相干的自發輻射並非是一個新的量子光學現象，早在1954年就被由R. Dicke提出了，比發明激光器還早。SR以它脈衝時間短，峰值功率高，相干性好，以及脈衝定時抖動高等特點而聞名。近來，不同的研究組報導了他們用半導體材料產生了SR, 復興了理論和實驗雙方面對SR的研究。在這篇論文中，我們論證了如何用飛秒激光泵浦雙量子阱激光二極管產生高功率帶有延時的超辐射脈衝。當泵功率足夠高時，高量子能級的電子空穴對先於低能級的電子空穴對發生超輻射，從而第一次在室溫下得到了超寬頻譜的超輻射脈衝。此外，我們證明了超輻射光是TM偏振的。根據我們的結果可以預測關於SR的超高能量脈衝的研究以及相关应用具有光明的發展前景，比如，SR可用於包括光學相干斷層成像和光譜學等的各種各樣的先進領域。石墨烯，真正的2D材料，近年來激發了巨大的研究熱潮。我們用濕法轉移的方法將化學氣相沉積生長的單層石墨烯鋪到我們的樣品表面。這使TM偏振模式的漸逝場能很好地與石墨烯層作用，因此，顯著調製SR脈衝的功率和頻譜。石墨烯與多量子阱激光二極管的結合將大大推動了新型器件的研究，如光調製器等，這將大大改善SR的應用前景。Liu, Jingjing.Thesis (Ph.D.)--Chinese University of Hong Kong, 2015.Includes bibliographical references.Abstracts also in Chinese.Title from PDF title page (viewed on 21, December, 2016).Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only.Detailed summary in vernacular field only