Few-Cycle High Energy Mid-Infrared Pulse From Ho:YLF Laser

Over the past decade, development of high-energy ultrafast laser sources has led to important breakthroughs in attoscience and strong-field physics study of atoms and molecules. Coherent pulse synthesis of a few-cycle high-energy laser pulse is a promising tool to generate isolated attosecond pulses via high harmonics generation (HHG). An effective way to extend the HHG cut-off energy to the higher values is by making use of long mid-infrared (MIR) driver wavelength, as the ponderomotive potential scales quadratically with the driving wavelength. If the energies of these driving pulses are properly scaled to multi-mJ level and few-cycle duration, such pulses can provide a direct path to intriguing attoscience experiments in gases and solids. They can even permit the realization of a bright coherent table-top HHG sources in the water-window and keV X-ray region. However, the generation of a high-intensity long-wavelength MIR pulse has always been challenging, in particular starting from a high-energy picosecond 2-μm laser driver that is suitable for further energy scaling of the MIR pulses to multi-mJ energies by utilizing optical parametric amplifiers (OPAs). In this thesis, a front-end source for such MIR OPA is presented. In particular, a novel and robust strong-field few-cycle 2-μm laser driver directly from picosecond Ho:YLF laser and utilizing Kagome fiber based compression is presented. We achieved: a 70-fold compression of 140-μJ, 3.3-ps pulses from a Ho:YLF amplifier to 48 fs with 11 μJ energy. The work presented in this thesis demonstrates a straightforward path towards the generation of few-cycle MIR pulses, and we believe that in the future, the ultrafast community will benefit from this enabling technology. The results are summarized in mainly four parts: The first part is focused on the development of a 2-μm, high-energy laser source as the front-end. Comparison of available technology in general and promising gain media at the MIR wavelength are discussed. Starting from the basics of an OPA, the design criteria, constraints on the pump & seed source and a proper phase-matching requirement for efficient amplification are discussed. In particular, starting from the challenge of developing a Ho:YLF oscillator, pulse amplification and the problem of gain narrowing are addressed. In the second part, various nonlinear compression schemes are discussed in general, and specifically, inhibited-coupling Kagome fiber based compression is discussed and implemented. The experimental results for the generation of a few-cycle, μJ-level 2-μm laser pulses in a two-stage compression scheme are then xvi presented. In the third part, the seed pulse generation for the MIR OPA by utilizing supercontinuum (SC) is presented. The theoretical background of SC generation and the constraints on the pulse duration are discussed. Finally, in the last part, the results obtained are summarized in conclusion and the outlook in presented. The front-end source developed here can be used to generate few-cycle MIR pulses by employing non-oxide based nonlinear crystals. Moreover, as both the pump and seed pulses are derived from the same laser source, it offers the possibility of generating a passively carrier-envelope phase (CEP) stable idler.