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Prof. Francois Legare 





"Frequency domain Optical Parametric Amplification" by Prof. Francois Legare, Institut National de la Recherche Scientifique, Canada. Abstract: The universal dilemma of gain narrowing occurring in fs amplifiers prevents ultrahigh power lasers from delivering fewcycle pulses. This problem is overcome by a new amplification concept: Frequency domain Optical Parametric Amplification – FOPA [1,2]. It enables simultaneous upscaling of peak power and amplified spectral bandwidth and can be performed at any wavelength range of conventional amplification schemes, however, with the capability to amplify singlecycle pulses. The key idea for amplification of octavespanning spectra without loss of spectral bandwidth is to amplify the broad spectrum "slice by slice" in the frequency domain, i.e. in the Fourier plane of a 4fsetup. Opposed to traditional schemes where amplification takes place in time domain, we propose to amplify different spectral parts independently of each other in the spectral domain. Therefore, the pulse's input spectrum is spectrally dispersed and then several individual narrowband optical parametric crystals are used whereby each is tuned for optimal amplification of its corresponding spectral slice. The striking advantages of this scheme, are its capability to amplify (more than) one octave of bandwidth without shorting the corresponding pulse duration. This is because ultrabroadband phase matching is not defined by the properties of the nonlinear crystal employed but the number of crystals employed. In the same manner, to increase the output energy one simply has to increase the spectral extension in the Fourier plane and to add one more crystal. Thus, increasing pulse energy and shortening its duration accompany each other.
A proof of principle experiment was carried out at the Advanced Laser Light Source (ALLS) on the subtwo cycle IR beam line [3] and yielded record breaking performance in the field of fewcycle IR lasers. 100μJ twocycle pulses from a hollow core fibre compression setup were amplified to 1.43mJ without distorting spatial or temporal properties. Pulse duration at the input and after FOPA remains the same. Recently, we have started upgrading this system to be pumped by 250 mJ to reach 40 mJ twocycle IR fewcycle pulses. [1] B. E. Schmidt et al. “Frequency domain optical parametric amplification.,” Nature Commun. 5, 3643 (2014). [2] P. Lassonde et al. “High gain Frequency domain Optical Parametric Amplification”, IEEE J. Sel. Top.Quant. Electr. 21, 8700410 (2015). [3] B. E. Schmidt et al. "CEP stable 1.6 cycle laser pulses at 1.8 µm," Opt. Express 19, 68586864 (2011). 

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