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.
10/6/2017 – New paper published in Science on spatiotemporal mode-locking. This work was also featured in the Cornell Chronicle.
8/3/2017 – Do you want to do fast simulations of pulse propagation in multimode fiber? Just use our code, created in collaboration with Pavel Lushnikov from the University of New Mexico.
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.
Spatiotemporal dynamics of multimode optical solitons
L. G. Wright, W. H. Renninger, D. N. Christodoulides, and F. W. Wise. “Spatiotemporal dynamics of multimode optical solitons”. Opt. Express 22, 3492-3506 (2015).
We launch pulses into multimode fiber, exciting multiple spatial modes. We show how nonlinear interactions between the modes give rise to a multimode soliton. A multimode soliton is a non-dispersing wavepacket that contains several distinct spatial mode components, and propagates through the fiber without changing its shape due to a balance between nonlinear and linear effects. We observe spatiotemporal soliton fission – the disintegration of an optical pulse into distinct multimode soliton components with different spatiotemporal properties. Lastly, we observe the effect of stimulated Raman scattering on multimode solitons. This causes them to shift to longer wavelengths, while maintaining their multimode soliton characteristics.
Multimode fiber acts as an intermediate-dimensional system. As the size of the fiber becomes infinite, optical dynamics are (3+1)-D (space+time). Meanwhile, as the fiber becomes small it becomes single mode, so that optical dynamics can be described using only (1+1) dimensions. Analytically, stable spatiotemporal solitons are expected for some region (blue) between 1 and 3 spatial dimensions. It is in this regime that multimode solitons are expected.
Ultrafast fiber lasers based on self-similar pulse evolution: a review of current progress
A. Chong, L. G. Wright and F. W. Wise “Ultrafast fiber lasers based on self-similar pulse evolution: a review of current progress ” Rep. Prog. Phys. 78, 113901 (2015).
We summarize the state of research on lasers based on self-similar pulse evolutions, including passive similariton, amplifier similariton, and others. Self-similar fiber lasers are conceptually different from other kinds of short-pulse lasers. This distinction allows for exciting new laser design options.
Characteristic steady-state round trip evolutions of the pulse chirp for different mode-locking regimes. Solid lines indicate the chirp of the pulse, while dashed lines indicate the local dispersion of the cavity. In the highlighted plot, the lines show the difference of the pulse from a parabolic pulse.
Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves
L. G. Wright, S. Wabnitz, D. N. Christodoulides, F. W. Wise “Ultrabroadband Dispersive Radiation by Spatiotemporal Oscillation of Multimode Waves ” Phys. Rev. Lett. 115, 223902 (2015).
We show that intense pulses in multimode fiber oscillate in space and time, and that this creates resonant radiation across the electromagnetic spectrum. This work provides a route to tunable sources of ultrashort pulses from IR to ultraviolet and beyond. Dreaming, this work could lead to a fiber-format alternative to the free-electron laser.
The resonant dispersive radiation is diffracted off a grating onto a piece of white paper.
Divided Pulse Lasers
We show that divided-pulse amplification can be used within a laser cavity to increase the pulse energy of a soliton fiber laser. In divided-pulse amplification, pulses are split up N times prior to amplification. After amplification, they are recombined into a single pulse. By reducing the peak intensity within the gain fiber, each split copy can be amplified to the single-pulse limit, and therefore the final recombined pulse can have N times higher energy. This work was featured in Spotlight on Optics.
Diagram of a general divided pulse laser. Pulses are divided before ampification in the gain fiber, then recombined before being output. A saturable absorber mirror (SAM) is used for mode-locking, while a dispersive delay (DD) can provide dispersion.