The mode-locked fluoride fiber laser (MLFFL) is an exciting platform for directly generating ultrashort pulses in the mid-infrared (mid-IR). However, owing to difficulty in managing the dispersion in fluoride fiber lasers, MLFFLs are restricted to the soliton regime, hindering pulse-energy scaling. We overcame the problem of dispersion management by utilizing the huge normal dispersion generated near the absorption edge of an infrared-bandgap semiconductor and promoted MLFFL from soliton to breathing-pulse mode-locking. In the breathing-pulse regime, the accumulated nonlinear phase shift can be significantly reduced in the cavity, and the pulse-energy-limitation effect is mitigated. The breathing-pulse MLFFL directly produced a pulse energy of 9.3 nJ and pulse duration of 215 fs, with a record peak power of 43.3 kW at 2.8  μm. Our work paves the way for the pulse-energy and peak-power scaling of mid-IR fluoride fiber lasers, enabling a wide range of applications.

/pdf/mode-locked-2-8-m-m-fluoride-fiber-laser-from-soliton-to-541m5rthxv.pdf

Mode-locked 2.8- μ m fluoride fiber laser: from soliton to breathing pulse

Dual action of quantum-dot saturable absorber and Kerr lens mode locking of a diode-pumped Yb:KGW laser was demonstrated. The laser delivered 105 fs pulses with 2.5 W of average power and >300 kW of peak power.

Quantum-dot saturable absorber and Kerr lens mode-locked Yb:KGW laser with >300 kW of peak power

The recently introduced wavelength-modulation spectroscopy with 1f-phase detection (WMS-$$\theta _{1f}$$) technique showed promising results with potentially improved measurement precision over the popular 1f-normalized WMS-nf (WMS-nf/1f) technique. Like WMS-nf/1f, WMS-$$\theta _{1f}$$ enjoys the typical benefits of WMS methods, including low-frequency noise rejection, correction for non-absorbing losses, and insensitivity to the broadband absorption spectra of interfering species. In this work, we performed a detailed analysis of the spectrally resolved scanned-wavelength WMS-$$\theta _{1f}$$ measurement technique and its direct comparison against the expected performance of scanned-wavelength WMS-nf/1f and scanned-wavelength direct-absorption spectroscopy (SDAS) measurements. This simulation-based analysis identified specific operating regimes in which the performance of WMS-$$\theta _{1f}$$ measurements in terms of accuracy is expected to be greater than the performance of WMS-nf/1f or SDAS. Additionally, improved guidelines for the optimal selection of laser-tuning parameters, including an explicit optimization of the optical scan depth parameter, were developed. Experiments with a CO2 static cell perturbed by a high-speed air jet corroborated the simulation-based findings. Finally, a practical demonstration of a WMS-$$\theta _{1f}$$ sensor for measuring temperature and H2O mole fraction in the exhaust of a CH4/air flat-flame burner was presented, with the results confirming model predictions of the superior precision of WMS-$$\theta _{1f}$$ relative to WMS-nf/1f and SDAS.

Analysis of laser absorption gas sensors employing scanned-wavelength modulation spectroscopy with 1f-phase detection

A high-power, high-repetition-rate, broadband tunable femtosecond optical parametric oscillator (OPO) is constructed based on KTiOAsO4 crystal, pumped by a 755 MHz mode-locked Yb:KGW laser With 7 W pump power, the OPO generates as much as 232 W of signal power at 155 μm and 131 W of idler power at 305 μm, corresponding to a total conversion efficiency of 518% Operating at 151 MHz repetition rate, the wavelength of the signal covers 141-171 μm with a tunable idler range of 261-384 μm The idler bandwidth is more than 180 nm over the entire mid-infrared range By compensating intracavity dispersion, the signal pulse has a nearly Fourier transform-limited duration of 129 fs at 152 μm

Watt-level widely tunable femtosecond mid-infrared KTiOAsO 4 optical parametric oscillator pumped by a 1.03 μm Yb:KGW laser

Rotating detonation engines (RDEs) require novel diagnostic tools to better understand complex detonation behavior and improve performance. To this end, a single-ended laser absorption sensor for in situ, time-resolved measurements of temperature, H2O, CO2, and CO concentrations has been developed and deployed within the annulus of a hydrogen/ethylene/air-fed RDE. With a measurement rate of 44 kS/s, the sensor delivers four co-aligned, mid-infrared laser beams into the annular detonation chamber and captures the back-reflected radiation through a single optical port. A ray-tracing optimization algorithm, designed to maximize signal-to-noise ratio and beam-perturbation tolerance, was used to determine the optimal sensor optical configuration. Wavelength-modulation spectroscopy (WMS) further compensated for interference sources in the harsh detonation environment. Time-resolved and time-averaged sensor measurements of gas temperature and species at equivalence ratios of 0.74, 0.87, and 1.03 are presented.

Time-resolved, single-ended laser absorption thermometry and H2O, CO2, and CO speciation in a H2/C2H4-fueled rotating detonation engine

We demonstrate a harmonically pumped femtosecond optical parametric oscillator (OPO) laser using a frequency-doubled mode-locked Yb:KGW laser at a repetition rate of 75.5 MHz as the pump laser. Based on a bismuth borate nonlinear crystal, repetition rates up to 1.13 GHz are realized, which is 15 times that of the pump laser. The signal wavelength is tunable from 700 nm to 887 nm. The maximum power of the signal is 207 mW at the central wavelength of 750 nm and the shortest pulse duration is 117 fs at 780 nm. The beam quality (M2 factor) in the horizontal and vertical directions of the output beam are 1.077 and 1.141, respectively.

/pdf/harmonically-pump-a-femtosecond-optical-parametric-433u3j6sln.pdf

Harmonically pump a femtosecond optical parametric oscillator to 1.13 GHz by a femtosecond 515 nm laser

We have demonstrated a high power diode-pumped mode-locked femtosecond Yb:KGW laser with semiconductor saturable absorber mirror (SESAM). By using an output coupler with 10% transmittance, the laser delivered 160-fs pulses with average output power of 7.6 W at a repetition rate of 78 MHz, corresponding to pulse energy of 97 nJ and peak power of 606 kW.

https://iopscience.iop.org/article/10.1088/1674-1056/28/4/044205/pdf

7.6-W diode-pumped femtosecond Yb:KGW laser*

We have demonstrated a high-repetition-rate tunable femtosecond dual-signal-wavelength optical parametric oscillator (OPO) based on BiB3O6 (BiBO) crystal, synchronously pumped by a frequency-doubled mode-locked Yb:KGW laser. The cavity is simple since no dispersion compensators are used in the cavity. The wavelength range of dual-signal is widely tunable from 710 to 1000 nm. Tuning is accomplished by rotating phase-matching angle of BiBO, and optimizing cavity length and output coupler. Using a 3.75 W pump laser, the maximum average dual-signal output power is 760 mW at 707 and 750 nm, leading to a conversion efficiency of 20.3% not taking into account the idler power. Our experimental results show a non-critical phase-matching configuration pumped by a high peak power laser source. The operation of the dual-signal benefits from the balance of phase matching and group velocity mismatching between the two signals.

Tunable, high-repetition-rate, dual-signal-wavelength femtosecond optical parametric oscillator based on BiB 3 O 6

Generation of Femtosecond Laser Pulse at 1.43GHz from an Optical Parametric Oscillator Based on LBO Crystal

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