Normal-dispersion fiber optical parametric chirped-pulse amplification
Walter Fu and Frank W. Wise, “Normal-dispersion fiber optical parametric chirped-pulse amplification,” Opt. Lett. 43, 5331-5334 (2018).
An ongoing limitation of fiber lasers is their lack of broad wavelength tunability. Here, we address this problem using fiber optical parametric chirped-pulse amplification (FOPCPA), which combines the energy capacity of chirped pulse amplification with the spectral flexibility of optical parametric amplification and the practical benefits of fiber. Notably, this is the first FOPCPA to be pumped in the normally-dispersive regime, which permits phase-matching far from the pump wavelength.
The system operates by coupling a stretched, broadband pump pulse and a continuous-wave signal into a photonic crystal fiber. At each point in time, the monochromatic signal interacts via four-wave-mixing with a different wavelength of the chirped pump, resulting in an idler that is chirped in exactly the same manner as the pump. Scalability follows from the timescale-invariance of this process: stretching the pump at constant peak power likewise stretches the idler at constant peak power, increasing the energy without affecting the dechirped duration. By exploiting this property, we are able to convert pulses from the Yb-band to the important bio-imaging window near 1300 nm, with energies of >100 nJ and femtosecond-scale durations.
9/11/2018 – Walter travels to the far-away country of Canada to visit colleagues and friends at Université Laval! Pictured below in the company of Réal Vallée and Simon Duval.
Megawatt peak power from a Mamyshev oscillator
Zhanwei Liu, Zachary M. Ziegler, Logan G. Wright, and Frank W. Wise. “Megawatt peak power from a Mamyshev oscillator” Optica, Vol. 4, Issue 6, pp. 649-654 (2017).
Historically, it has been really tough to make an ultrafast fiber laser that is both environmentally stable and that has good performance (i.e., it has similar performance as a Ti:sapphire oscillator). Recently, several groups have realized that a pair of spectral filters, each offset from the center of the laser gain spectrum, can be used as an effective saturable absorber. An intense pulse will experience nonlinear spectral broadening within fiber in between the filters, and can oscillate stably in a ring cavity formed in this way – a laser we call a ‘Mamyshev oscillator’ (see figure). Low-intensity pulses, or continuous-wave lasing, are meanwhile strongly attenuated. This mechanism, first proposed by Pavel Mamyshev for signal regeneration in telecommunications, is fully compatible with environmentally-stable laser designs. In this paper, we show that the Mamyshev oscillator can, when combined with the self-similar evolution of parabolic pulses, actually support extraordinary performance. Our initial experiments already show 10 times higher peak power than the previous state-of-the-art, and we are optimistic about further improvements.