Few-cycle High Energy Mid-Infrared Pulse from Ho:YLF Laser

Over the past decade, development of high-energy ultrafast laser sources hasled to important breakthroughs in attoscience and strong-field physicsstudy of atoms and molecules. Coherent pulse synthesis of a few-cyclehigh-energy laser pulse is a promising tool to generate isolated attosecond pulsesvia high harmonics generation (HHG). An effective way to extend the HHG cut-offenergy to the higher values is by making use of long mid-infrared (MIR) driverwavelength, as the ponderomotive potential scales quadratically with the drivingwavelength. If the energies of these driving pulses are properly scaled to multi-mJlevel and few-cycle duration, such pulses can provide a direct path to intriguingattoscience experiments in gases and solids. They can even permit the realizationof a bright coherent table-top HHG sources in the water-window and keV X-rayregion. However, the generation of a high-intensity long-wavelength MIR pulse hasalways been challenging, in particular starting from a high-energy picosecond 2-μmlaser driver that is suitable for further energy scaling of the MIR pulses to multi-mJenergies by utilizing optical parametric amplifiers (OPAs). In this thesis, a front-endsource for such MIR OPA is presented. In particular, a novel and robust strong-fieldfew-cycle 2-μm laser driver directly from picosecond Ho:YLF laser and utilizingKagome fiber based compression is presented. We achieved: a 70-fold compression of140-μJ, 3.3-ps pulses from a Ho:YLF amplifier to 48 fs with 11 μJ energy. The workpresented in this thesis demonstrates a straightforward path towards the generationof few-cycle MIR pulses, and we believe that in the future, the ultrafast communitywill benefit from this enabling technology.The results are summarized in mainly four parts: The first part is focused on thedevelopment of a 2-μm, high-energy laser source as the front-end. Comparison ofavailable technology in general and promising gain media at the MIR wavelengthare discussed. Starting from the basics of an OPA, the design criteria, constraintson the pump & seed source and a proper phase-matching requirement for efficientamplification are discussed. In particular, starting from the challenge of developinga Ho:YLF oscillator, pulse amplification and the problem of gain narrowing areaddressed. In the second part, various nonlinear compression schemes are discussedin general, and specifically, inhibited-coupling Kagome fiber based compressionis discussed and implemented. The experimental results for the generation of afew-cycle, μJ-level 2-μm laser pulses in a two-stage compression scheme are thenpresented. In the third part, the seed pulse generation for the MIR OPA by utilizingsupercontinuum (SC) is presented. The theoretical background of SC generationand the constraints on the pulse duration are discussed. Finally, in the last part, theresults obtained are summarized in conclusion and the outlook in presented. Thefront-end source developed here can be used to generate few-cycle MIR pulses byemploying non-oxide based nonlinear crystals. Moreover, as both the pump and seedpulses are derived from the same laser source, it offers the possibility of generating apassively carrier-envelope phase (CEP) stable idler