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1. Route towards extreme optical pulsation in linear cavity ultrafast fibre lasers

   https://doi.org/10.1038/s41598-018-31725-7  

   Akosman, Ahmet E.; Sander, Michelle Y. (September 2018, Scientific Reports)

   Abstract Pathways towards the generation of extreme optical pulsation in a chaotic transition regime in a linear fibre laser cavity configuration are presented. In a thulium mode-locked fibre laser, extreme events that can be controllably induced by manipulating the cavity birefringence for pulse energies exceeding the single soliton pulse operating regime are studied in detail for the first time. While a solitonic pulsation structure at the fundamental repetition rate is maintained, additional energy is shed in a chaotic manner, leading to broader spectral generation and shorter pulse durations whose behaviour deviates significantly from a classical statistical distribution. These pulses display markedly different characteristics from any previously reported extreme events in fibre lasers associated with multiple solitons and pulse bunching, thus presenting a novel observation of extreme pulsation. Detailed noise studies indicate that significant enhancement of relaxation oscillations, modulation instability and the interplay with reabsorption mechanisms contribute in this transient chaotic regime. The extreme pulsation generated in a compact fibre laser without any additional nonlinear attractors can provide an attractive platform to accelerate the exploration of the underlying physics of the chaos observed in mode-locked laser systems and can lead to novel fibre laser cavity designs. 

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2. High peak power, sub-ps green emission in a passively mode locked W-cavity VECSEL

   https://doi.org/10.1364/OE.384439  

   Meyer, Jason_T; Lukowski, Michal_L; Hessenius, Chris; Wright, Ewan_M; Fallahi, Mahmoud (February 2020, Optics Express)

   We report on the experimental results of a passively mode-locked vertical external cavity surface emitting laser (VECSEL), implemented in a W-cavity configuration, using a lithium triborate (LBO) crystal for intra-cavity second harmonic generation (SHG) at 528 nm. The W-cavity configuration allows separation of the crystal from the semiconductor saturable absorber mirror (SESAM), enabling independent control over the Gaussian beam sizes at the crystal, chip, and SESAM. This optimized cavity demonstrated a second harmonic pulse width of ~760 fs at a frequency of 465 MHz and 230 mW average output power, resulting in a peak pulse power of 580 W. 

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3. All-normal dispersion fiber laser with a bandwidth tunable fiber-based spectral filter

   https://doi.org/10.1364/OL.398049  

   Khanolkar, Ankita; Ge, Xiaowei; Chong, Andy (August 2020, Optics Letters)

   We investigate numerically and experimentally an all-fiber, bandwidth tunable spectral filter comprising birefringent fibers. The spectral bandwidth tunability of the filter is based on the compensation of birefringence in polarization maintaining fibers. This unique filter allows mode-locked operation of a fiber oscillator with the ability to generate distinct laser modes with different output spectral shapes and pulse evolutions. 

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4. Energy-efficient pathway for selectively exciting solute molecules to high vibrational states via solvent vibration-polariton pumping

   https://doi.org/10.1038/s41467-022-31703-8  

   Li, Tao E.; Nitzan, Abraham; Subotnik, Joseph E. (July 2022, Nature Communications)

   Abstract Selectively exciting target molecules to high vibrational states is inefficient in the liquid phase, which restricts the use of IR pumping to catalyze ground-state chemical reactions. Here, we demonstrate that this inefficiency can sometimes be solved by confining the liquid to an optical cavity under vibrational strong coupling conditions. For a liquid solution of¹³CO₂solute in a¹²CO₂solvent, cavity molecular dynamics simulations show that exciting a polariton (hybrid light-matter state) of the solvent with an intense laser pulse, under suitable resonant conditions, may lead to a very strong (>3 quanta) and ultrafast (<1 ps) excitation of the solute, even though the solvent ends up being barely excited. By contrast, outside a cavity the same input pulse fluence can excite the solute by only half a vibrational quantum and the selectivity of excitation is low. Our finding is robust under different cavity volumes, which may lead to observable cavity enhancement on IR photochemical reactions in Fabry–Pérot cavities. 

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5. Relative timing jitter in a counterpropagating all-normal dispersion dual-comb fiber laser

   https://doi.org/10.1364/OPTICA.458339  

   Prakash, Neeraj; Huang, Shu-Wei; Li, Bowen (June 2022, Optica)

   The counterpropagating all-normal dispersion (CANDi) fiber laser is an emerging high-energy single-cavity dual-comb laser source. Its relative timing jitter (RTJ), a critical parameter for dual-comb timing precision and spectral resolution, has not been comprehensively investigated. In this paper, we enhance the state-of-the-art CANDi fiber laser pulse energy from 1 nJ to 8 nJ. We then introduce a reference-free RTJ characterization technique that provides shot-to-shot measurement capability at femtosecond precision. The measurement noise floor reaches $1.6\times <\#comment/>{10}^{-<\#comment/>7}{\mathrm{f}\mathrm{s}}^2/\mathrm{H}\mathrm{z}$, and the corresponding integrated measurement precision is only 1.8 fs (1 kHz, 20 MHz). With this characterization tool, we are able to study the physical origin of the CANDi laser’s RTJ in detail. We first verify that the cavity length fluctuation does not contribute to the RTJ. Then we measure the integrated RTJ to be 39 fs (1 kHz, 20 MHz) and identify the pump relative intensity noise (RIN) to be the dominant factor responsible for it. In particular, pump RIN is coupled to the RTJ through the Gordon–Haus effect. Finally, solutions to reduce the free-running CANDi laser’s RTJ are discussed. This work provides a general guideline to improve the performance of compact single-cavity dual-comb systems such as the CANDi laser, benefitting various dual-comb applications. 

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