Dr. Negar Hekmat Profile

Dr. Negar Hekmat

at Ruhr-Univ Bochum

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Publications (2)

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Proceedings Article | 30 March 2020 Presentation

High average power ultrafast terahertz sources with MHz repetition rate (Conference Presentation)

Frank Meyer, Negar Hekmat, Tim Vogel, Alan Omar, Samira Mansourzadeh, Felix Fobbe, Martin Saraceno, Yicheng Wang, Clara Saraceno

Proceedings Volume 11348, 113480H (2020) https://doi.org/10.1117/12.2555388

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Ultrafast Terahertz sources with high average power are of increasing interest for various spectroscopic investigations, currently limited by signal-to-noise ratio. A straightforward path to increase the average power of THz sources is to make use of state-of-the-art femtosecond near infrared driving lasers with higher average power than the commonly used Ti:Sa lasers. Diode pumped solid state lasers based on Yb now reliably provide from hundreds of watts up to kilowatts of average power with sub-ps pulses, while THz generation with more than a few tens of watts driving power remains widely unexplored. Among these technologies, modelocked thin-disk oscillators are particularly attractive to drive high power, high repetition rate THz sources, providing hundreds of watts directly from a compact one-box oscillator without the need for any additional amplification stages, thereby reducing the overall system complexity. Here, we will present our recent results using optical rectification (OR) in GaP and Lithium Niobate (LN), driven by a home-built Yb:YAG femtosecond modelocked thin-disk oscillator with an average power of more than 100 W at 13 MHz repetition rate. Using GaP, we achieve milliwatt average power levels with a bandwidth extending > 6 THz making this an ideal tool for THz-TDS for example of absorptive samples. Using the tilted pulse front scheme in LN, we achieve THz powers exceeding 40 mW at 13 MHz repetition rate, which represents the highest average power of any THz sources with MHz repetition rate. Additionally to these results, we will present our ongoing investigation of thermal effects and further average power scaling of OR in this unusual excitation regime.

Proceedings Article | 8 May 2018 Open Access

Mode-locked thin-disk lasers and their application for high-power THz generation

F. Meyer, N. Hekmat, F. Fobbe, S. Mansourzadeh, C. Saraceno

Proceedings Volume 10638, 106381H (2018) https://doi.org/10.1117/12.2312016

KEYWORDS: Terahertz radiation, Ultrafast lasers, Oscillators, Mode locking, High power lasers, Laser applications, Ultrafast phenomena, Laser systems engineering, Amplifiers

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Progress in the performance of high-power ultrafast lasers continues to give momentum to many fields of science and technology. Nowadays, ultrafast laser systems delivering hundreds of watts of average power with pulse energies ranging from hundreds of microjoules to hundreds of millijoules start to be even commercially available. In particular, disk lasers have consistently been at the forefront of this progress: their geometry is particularly well-suited for power and energy scaling of ultrashort pulses. Among these laser systems based on the disk technology, one particular technology is particularly attractive as a potential path to achieve the desired level from a simple, one-box, multi-MHz repetition rate oscillator: mode-locked thin-disk oscillators can reach hundreds of watts of average power with femtosecond pulses at multi-MHz repetition rate. Exponential progress in the achievable levels is only an illustration of their enormous potential. So far, these oscillators reach up to 275 W average power, and pulse energies up to 80 μJ, both based on Yb:YAG thin-disk lasers. This talk will review latest progress achieved with this technology and next steps and challenges towards further scaling, as well as their prospect as compact driving sources for the generation of high-power THz radiation.

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