Q-switched Mode-locked Regime Research Articles

Passively Q-switched mode-locked thulium-doped fiber laser using nonlinear polarization rotation technique

A Q-switched mode-locked (QML) thulium-doped fiber laser based on nonlinear polarization rotation (NPR) and negative group velocity dispersion (GVD) is demonstrated. This regime consists in the generation of a mode-locked (ML) pulse train under a Q-switched (QS) envelope. In this regard, by properly adjusting the polarization controllers and increasing the pump power in a range from 1 to 3 W, QML regime is obtained. With a maximum pump power of 3 W, a QS pulse duration of 1.46 μs and a pulse energy of 5.96 μJ are obtained. The maximum frequencies reached are 26 kHz and 2.63 MHz, corresponding to the Q-switched and mode-locked pulses, respectively. This method for generating a QML at 2 μm has the advantages of being eye-safe and robust, providing an ideal dual-frequency comb (DFC) generation method with high potential for various applications.

Thulium-doped fiber laser mode-locked by nonlinear polarization rotation in a chalcogenide tapered fiber.

We demonstrate a thulium-doped fiber laser that is mode-locked thanks to nonlinear polarization rotation (NPR) in a chalcogenide tapered fiber. The high nonlinearity of the tapered fiber leads to a combined reduction in mode-locking threshold power and cavity length compared to any all-silica NPR based mode-locked lasers. In the continuous wave mode-locking regime, the laser generates stable, tunable solitons pulses. In the Q-switched mode-locked regime, it allows single and multiwavelength pulses, tunable central wavelength and tunable multiwavelength separation.

Self-organization of the Q-switched mode-locked regime in a diode-pumped Nd:YAG laser

A new Q-switched mode-locked generation regime of a solid-state laser, in which a Q-switch is “spontaneously” formed at the frequency of relaxation oscillations, has been observed for the first time. The new generation has been implemented by means of the previously proposed method of an acoustic modulator of a traveling wave in combination with a spherical mirror of a cavity. Stable pulse trains with a repetition frequency of ~30 kHz and a duration of ~2 µs have been observed in the diode-pump Nd:YAG laser with an average output power of ~3 W. Each train contains about 200 equispaced single pulses with a duration of ~45 ps.

Cascaded Four-Wave Mixing in Nonlinear Yb-Doped Fiber Amplifiers

We experimentally demonstrated high-power yellow and near-infrared laser emissions by cascaded four-wave mixing in a nonlinear Yb-doped multimode fiber amplifier, generating 2.0 W at 830 nm and 0.35 W at 594 nm. Moreover, multiple cascaded four-wave mixing processes which generated supercontinuum covering more than four octaves from 398 to 1700 nm was also investigated in Q-switched mode-locking regime. The group velocity matching for pump and parametric waves as well as multimode fiber amplification promoted the cascaded nonlinear frequency mixing processes.

Q-switched mode-locking of an erbium-doped fiber laser using cavity modulation frequency detuning

We present the results of an investigation regarding a Q-switched mode-locked fiber laser scheme based on a cavity modulation frequency detuning technique. The approach is based on undamped laser relaxation oscillations occurring due to frequency detuning in the fundamental cavity resonance frequency. Through a range of experiments with an erbium-doped, fiber-based, ring-cavity laser, this approach has been shown to be capable of generating high-quality Q-switched mode-locked pulses from an optical fiber-based laser. The maximum frequency detuning range for a stable Q-switched mode-locking operation has been observed to vary depending on the pump power used. We found that the highest pulse peak power was obtained at the frequency detuning threshold at which the operation changed from the mode-locking to the Q-switched mode-locking regime.

High power modelocking of a stigmatic bounce geometry laser using a nonlinear mirror

We report the highest average power modelocking of a novel bounce geometry laser using the nonlinear mirror (NLM) technique. A diode-side pumped Nd:YVO4 slab lasing at 1064 nm in a spatially stigmatic bounce-oscillator configuration was modelocked using a type-I phase-matched BiBO nonlinear crystal (NLC) in a NLM arrangement, producing 12 W of self-starting, continuous-wave (CW) modelocking. The system produced a pulse duration of 14 ps at a repetition rate of 110 MHz with high long-term stability and excellent beam quality, with an M 2<1.2 and highly circular beam profile. An investigation was made of the sensitivity of modelocking as a function of air dispersion, by varying the distance between the NLC and output coupler. No optical damage was observed throughout the investigation, even when the system was operated in Q-switched modelocking regime. The system exploits the advantages of NLM modelocking for sustaining high average and peak powers without the onset of optical damage.

Q-switched mode locking with acousto-optic modulator in a diode-pumped Nd:YVO4 laser

The Q-Switched Mode Locking (QML) regime provides the generation of relatively high peak power picosecond pulses train with energies of a few muJ each in a simple resonator. The fully modulated efficient QML regime was demonstrated in the diode-pumped Nd:YVO4 laser. The acousto-optic cell playing a double role of Q-switch and Mode Locker was located near flat output coupler. The two folding mirrors were mounted on the translation stages for matching the resonance frequency of the cavity to the radio frequency of acousto-optic modulator. The QML pulses with envelope durations of 100-150 ns and near 100% modulation depth were observed for wide range of pump powers and repetition rates. Up to 3 W of output average power, 100 muJ of the envelope energy, having approximately 5-8 mode-locked pulses were achieved.

Intracavity frequency-tripling of actively mode-locked diode-pumped Nd:YAG laser

We report the first diode-pumped solid-state laser operating in cw-mode-locked regime and simultaneously achieving intracavity frequency-tripling. This laser provide UV picosecond pulses (λ=355 nm) of 10 ps duration with 0.5 mW average power at 150 MHz repetition rate. A different set of adjustments gave rise to a Q-switched mode-locked regime. Trains of hundred UV pulses of 60 ps duration and 4 W peak power were produced in this latter case at 50 kHz repetition rate.