In the past two decades, ultrashort pulse lasers oscillators and amplifiers became common equipment in the fundamental scientific exploration as well as in handful of industrial applications. Those sources, which by their nature are broadband and coherent, allow exploring processes and dynamics in nature at ultrafast time scale. Due to the extremely high peak power, nonlinear optics in the ultrashort regime results in efficient frequency conversion generation processes. Among the various nonlinear conversion processes, three wave mixing and especially second harmonic generation (SHG) became widely used. Yet, frequency conversion in the ultrashort regime usually exhibits a tradeoff between the conversion bandwidth and the conversion efficiency due to the phase mismatch between the interacting waves. In the last decade, adiabatic frequency conversion method has overcome the tradeoff between conversion efficiency and bandwidth for sum frequency generation, difference frequency generation, Optical parametric amplification and recently in SHG processes. Here, we experimentally demonstrate that an adiabatic design is capable of extremely robust and efficient SHG at power levels characteristic of high-rep-rate femtosecond oscillators. We show that with pulse peak energies of nJ, one can achieve above 50% of energy conversion efficiency for 70fs Ti-Sapphire pulses. Furthermore, the flat conversion response of the presented design allows performing broadband pulse shaping manipulations before the nonlinear optical conversion. More specifically, using a spatial light modulator in a 4-f configuration, we present a tunable pump-probe based on a varying spectral phase profile in the frequency domain. Additionally, we show that by applying a π-step spectral phase, coherent control of the SHG spectrum can be achieved.
Assaf Levanon, Asaf Dahan, Achiya Nagler, Erga Lifshitz, Eyal Bachar, Michael Mrejen, and Haim Suchowski, "Pulse shaping of broadband Adiabatic SHG from a Ti:sapphire oscillator (Conference Presentation)," Proc. SPIE 10516, Nonlinear Frequency Generation and Conversion: Materials and Devices XVII, 105160R (Presented at SPIE LASE: January 30, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2289492.5751428847001.
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