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Spatiotemporal mode-locking in multimode fiber lasers

Spatiotemporal mode-locking in multimode fiber lasers

L.G. Wright, D.N. Christodoulides, and F.W. Wise (2017) “Spatiotemporal mode-locking in multimode fiber lasers,” Science 358 (6359), 94-97.

Unlike a conventional single-mode, ‘one-dimensional’ laser, the frequencies of a multimode, multidimensional laser are ordinarily very complicated (figure below, top left, where different colors correspond to different spatial modes). However, we showed that, for a properly designed laser (bottom), the laser’s frequencies would adjust automatically into an organized, synchronized pattern (figure top right), corresponding to the emission of a 3D, multimode laser pulse at regular intervals. Pulses from this laser might eventually allow very sophisticated light-matter interactions, especially with complex molecules (different modes of the laser may interact with different ‘modes’, specific transitions, of molecules or other matter). We have some moderately crazy ideas to realize PW or even EW (exawatt) lasers with this approach.

Simple depiction of spatiotemporal mode-locking

Megawatt peak power from a Mamyshev oscillator

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.

Schematic of the demonstrated system.

High-power femtosecond pulses without a modelocked laser

High-power femtosecond pulses without a modelocked laser

Walter Fu, Logan G. Wright, and Frank W. Wise. “High-power femtosecond pulses without a modelocked laser” Optica, Vol. 4, Issue 7, pp. 831-834 (2017).

Modelocked lasers have long been a mainstay of ultrafast optics. However, they face ongoing challenges regarding long-term reliability, and can only emit pulses at regular intervals. Here, we present an alternative approach by seeding a fiber amplifier with a gain-switched diode. Gain-switched diodes emit pulses that are much longer and less coherent than those from modelocked oscillators. We address these issues using fiber nonlinearities: a Mamyshev regenerator isolates a coherent component of the pulse, and subsequent parabolic amplification allows the pulses to be compressed to 140 fs with 13 MW of peak power. Starting with a gain-switched diode means our system is highly robust and can in principle be electronically triggered in arbitrary pulse patterns. This flexibility may facilitate machining or microscopy sources (where pulses must be synchronized to scanning optics) or enable new types of functional neuroimaging (where specific neurons must be illuminated without saturating an entire sample).

Schematic of the demonstrated system.

7/21/2017 – Check out the latest issue of Cornell Engineering Magazine for an article on undergraduate research opportunities, starring our own Zack Ziegler! Meanwhile, Frank returns from giving an invited lecture at  International Symposium on Ultrafast Photonics Technologies at Southampton and three talks at NLO in Hawaii.

6/12/2017 – Congratulations to Yuxing Tang, who will soon start his new job as an associate at Wells Fargo, and Zhanwei Liu, who will do the same at CoAdna Photonics! Yuxing recently attended convocation, and is the 27th PhD student to graduate from the Wise group.