A New Generation of Ultrafast Oscillators for Mid-Infrared Applications

Abstract

The mid-infrared (MIR) spectral range with wavelengths between 2 µm and 20 µm holds tremendous potential for the study of complex biological systems, given the abundance of intense and unique molecular absorption lines that can be detected. Consequently, spectroscopic applications of mid-infrared radiation have garnered enormous attention in recent years. A particularly striking example is the combination of multi-MHz-repetition-rate, few-cycle MIR light sources with electric-field-resolved techniques, enabling the recording of amplitude-and phase-resolved molecular signals with unparalleled specificity and shot noise limited sensitivity. Despite the ever-growing research demand, their widespread use is severely hampered by the lack of low-noise, compact, and ultrafast laser systems.In this dissertation, a new generation of table-top mid-infrared laser sources is presented, bringing cutting-edge laser diode technology and few-cycle Cr 2+ :ZnS/ZnSe solid-state oscillators together for the first time. Not only have these laser systems proven to reliably provide coherent radiation in the 2 µm to 3 µm region, the simultaneous reduction in size and complexity, accompanied by an improved overall efficiency and -most importantly -noise performance, renders this approach as pioneering for future MIR applications.In total, three laser systems are developed, each of them pushing the frontiers of directly diode-pumped laser technology. The first one is driven by a single-emitter indium phosphide laser diode and delivers more than 500 mW of output power combined with pulse durations as short as 45 fs. With this first ever directly diodepumped Kerr-lens mode-locked (KLM) Cr 2+ :ZnS/ZnSe oscillator, experimental results confirm a highly stable operation. In addition, amplitude noise measurements reveal an excellent low-noise performance of the mode-locked laser output.Driven by the desire to match and exceed the performance of more mature fiber-laser-pumped counterparts and also to boost the efficiency of the envisaged downstream applications, the output of two single-emitter pump laser diodes is carefully combined and implemented into a second-generation design. The achieved peak powers are almost three-times higher compared to before, while the low-noise performance of the KLM output is maintained.xii Typically, the design architecture of laser systems used for generating mid-infrared radiation up to several tens of microns includes a sophisticated chain of amplification, pulse compression and parametric conversion stages. Using a powerful few-cycle mid-infrared oscillator as driving laser source instead not only significantly improves the effectiveness of these nonlinear schemes, but could even supersede the need for initial amplification. The presented third-generation system brings the directly diode-pumped Cr 2+ :ZnS/ZnSe solid-state laser technology to a new level; with output peak powers reaching 1 MW and pulse durations as short as 28 fs, direct generation of CEP-stable mid-infrared pulses in a nonlinear optical cryst...

Mid-infrared diode pumped Cr: ZnSe laser continuously tunable from 2.1 μm up to 2.7 μm operated at room temperature

“…Generation of radiation in the above-mentioned mid-IR region offers numerous of potential applications, especially in molecular spectroscopy, remote sensing, medical diagnostics and treatment, as well as in applications related to defense, LIDAR or radar technology or optical switching. It can also be used as an optical frequency standard, and in research -it gives a possibility of pumping for new solid-state lasers or nonlinear (OPO) materials, and others 5,[27][28][29][30][31][32][33][34][35][36][37][38] . Research of Cr 2+ based laser systems at RT contributes to the development of these practical applications.…”