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This thesis presents the first successful realization of a compact, low-noise, and few-cycle light source in the mid-infrared wavelength region. By developing the technology of pumping femtosecond chromium-doped II-VI laser oscillators directly with the emission of broad-stripe single-emitter laser diodes, coherent light was generated with exceptionally low amplitude noise — crucial for numerous applications including spectroscopy at high sensitivities. Other key parameters of the oscillator's output, such as pulse duration and output power, matched and even surpassed previous state-of-the-art systems. As a demonstration of its unique capabilities, the oscillator's powerful output was used to drive — without further amplification — the nonlinear generation of coherent mid-infrared light spanning multiple octaves. The resulting table-top system uniquely combines high brilliance and ultrabroad spectral bandwidth in the important mid-infrared spectral range.
The rapid development of this technology is comprehensively and lucidly documented in this PhD thesis. Together with a thorough review of literature and applications, and an extensive analysis of the theoretical foundations behind ultrafast laser oscillators, the thesis will serve as a valuable reference for the construction of a new generation of mid-infrared light sources.
Recent advances in lasers capable of emitting ultrashort pulses lasting a mere few femtoseconds (one millionth of one billionth second) has spearheaded the development of novel and powerful spectroscopy techniques. One such technique is field-resolved spectroscopy, which can concurrently characterize the chemical composition over a vast range of different concentrations and with unprecedented sensitivity. If such techniques can be implemented with light that simultaneously covers the entire mid-infrared (MIR) spectral range—where the unique absorption signatures of biologically and medically relevant molecules reside—it will enable the parallel detection and evaluation of numerous chemical specimens and allow the simultaneous tracking of their changes at different time scales. Applied to medical samples—blood droplets from humans for example—it will open a new path for the full and timely monitoring of the health state of individuals, promising the detection of even the most minuscule trace of early illnesses that is impossible to spot with existing technologies. This possibility of identifying abnormalities in seemingly healthy individuals—as considered by current standard of care—will allow treatment to be administered well before any symptoms and suffering would arise, paving the way toward a new personalized and preventive medicine.
A roadblock hindering the advancement of such technology has been the lack of suitable light sources. The ideal source not only needs to fulfill technical criteria including bandwidth, power, pulse duration, stability and efficiency, it also needs to be reliable, user-friendly, and above all: cost-effective to facilitate its wide proliferation and penetration into daily clinical use. Thus far, all potential candidates have been suffering from one or more shortcomings. The first demonstration of the new all-solid-state infrared source technology already outperforms its predecessors by a factor of sixty in terms of peak power.
Motivation
Fundamentals of Ultrashort Pulse Generation
The First Directly Diode-Pumped Few-Cycle Cr-Doped II-VI Laser
Reaching the Performance of State-of-the-Art Fiber-Pumped Systems
Pushing the Peak Power for Direct Mid-Infrared Generation
Conclusion and Outlook