Single-mode regenerative amplification in multimode fiber

Henry Haig, Nicholas Bender, Yishai Eisenberg,  Frank Wise, “Single-mode regenerative amplification in multimode fiber,” Optica 10, 1417-1420 (2023)

The peak power performance of ultrafast fiber lasers scales with fiber mode area, but large fibers host multiple modes that are difficult to control. We demonstrate a technique for single-mode operation of highly multimode fiber based on regenerative amplification. This results in a short-pulse fiber source with, to our knowledge, an unprecedented combination of features: high gain (>55 dB) with negligible amplified spontaneous emission, high pulse energy (>50 µJ), good beam quality (𝑀2≤1.3), and transform-limited (300 fs) pulses from a single amplification stage. We discuss peak intensity scaling to much higher levels and other opportunities for short-pulse generation in regenerative fiber amplifiers.

Spectral speckle customization

Nicholas Bender, Henry Haig, Demetrios N. Christodoulides, and Frank W. Wise, "Spectral speckle customization," Optica 10, 1260-1268 (2023)

Speckle patterns are used in a broad range of applications including microscopy, imaging, and light–matter interactions. Tailoring speckles’ statistics can dramatically enhance their performance in applications. We present an experimental technique for customizing the spatio-spectral speckled intensity statistics of optical pulses at the output of a complex medium (a disordered multimode fiber) by controlling the spatial profile of the input light. We demonstrate that it is possible to create ensembles of independent speckle patterns with arbitrary statistics at a single wavelength, simultaneously at multiple decorrelated wavelengths, and even tailored statistics across an entire pulse spectrum.

Femtosecond long-wave-infrared generation in hydrogen-filled hollow-core fiber

Yi-Hao Chen and Jeffrey Moses and Frank Wise, “Femtosecond long-wave-infrared generation in hydrogen-filled hollow-core fiber,” J. Opt. Soc. Am. B 40, 796-806 (2023)

This paper is chosen as Spotlight on Optics.

Generating femtosecond long-wave-infrared (LWIR) pulses is currently restricted to CO₂ lasers and solid-state frequency converters, but waveguide-based Raman red shifting offers a promising alternative. In this study, we used a hydrogen-filled hollow-core fiber to generate LWIR pulses and found that a waveguide structure allows for tailored Raman gain. Using a two-pulse scheme with a two-color source, we achieved a numerical generation of clean 88-fs pulses at 12 μm with 41% total quantum efficiency. Our simulations also shed light on the nonlinear dynamics of the Raman gain, emphasizing the importance of a phonon amplifier for optimal performance.

In this work, especially its supplemental document, we have provided a complete introduction to the gas nonlinearity and its modeling detail. Please read it if you’re interested.

Beam self-cleaning of femtosecond pulses in the anomalous dispersion regime

Wu, H. Pourbeyram, D. N. Christodoulides, and F. W. Wise, “Weak beam self-cleaning of femtosecond pulses in the anomalous dispersion regime,” Opt. Lett. 46, 3312–3315 (2021).

Kerr beam cleaning in graded-index multimode fiber has been investigated in experiments with sub-nanosecond pulses and in experiments with femtosecond pulses at wavelengths where the dispersion is normal.  We report a theoretical and experimental study of this effect with femtosecond pulses and anomalous dispersion.  In this regime, beam-cleaning is observed experimentally.  Beyond the spatial dynamics, with the increase of input pulse energy, there is a strong temporal self-compression of the pulse from 500 fs down to around 30 fs (a factor of 17). Numerical simulations exhibit the qualitative trends of the experiments. Our study provides a way to enhance beam quality and temporal peak power at the same time in graded-index multimode fiber and the anomalous dispersion regime.

Efficient soliton self-frequency shift in hydrogen-filled hollow-core fiber​

Y.-H. Chen, P. Sidorenko, E. Antonio-Lopez, R. Amezcua-Correa, and F. Wise, “Efficient soliton self-frequency shift in hydrogen-filled hollow-core fiber,” Opt. Lett. 47, 285–288 (2022)

SSFS has been considered as a good option for fiber sources with tunable wavelengths for a long time. Particularly, nonlinear microscopy, such as three-photon imaging, requires high peak power at 1300 and 1700 nm to overcome the depth limit of two-photon imaging. During the process, the Raman soliton gradually shifts towards the red color as it moves forward. Although several methods have been utilized to achieve these wavelengths, it seems challenging to increase the pulse energy in solid-glass fibers. Here, we have shown that SSFS can occur efficiently and cleanly in a hydrogen-filled anti-resonant hollow-core fiber. By using hydrogen and short input pulses, we have demonstrated continuous tuning of the wavelength between 1080 and 1600 nm. We have obtained pulse energies in the range of 20 to 110 nJ and durations below 50 fs over this spectral range.

Multimode Mamyshev oscillator

Henry Haig, Pavel Sidorenko, Anirban Dhar, Nilotpal Choudhury, Ranjan Sen, Demetrios Christodoulides, and Frank Wise, "Multimode Mamyshev oscillator," Opt. Lett. 47, 46-49 (2022)

Regular mode-locked lasers make short light pulses by synchronization or “locking” of many longitudinal cavity modes. It was recently shown that the transverse modes of a cavity can also be synchronized in a similar— but more general— form of mode-locking known as “spatiotemporal mode-locking” (STML). These lasers make ultrafast pulses that have spatial structure due to the many transverse modes involved. Understanding of this phenomenally complex phenomenon is limited: STML has so far been demonstrated a handful of times in relatively similar types of multimode fiber lasers. In this project, we study STML in a very different type of cavity architecture— the Mamyshev oscillator. The laser supports a vast array of mode-locked states. Learning to control these states in a meaningful way is a long-term goal which might enable gigawatt-class fiber lasers, or fiber lasers that generate purposefully-structured light for applications.