Q-switched Mode-locked Operation Research Articles

Passively Q-switched mode-locking of Tm:YAP laser based on Cr:ZnS saturable absorber

Using a Cr:ZnS wafer as the saturable absorber, diode-pumped passively Q-switched mode-locking of a Tm:YAP laser at 1976 nm has been realized for the first time, to the best of our knowledge, and nearly 100% modulation depth of Q-switched mode-locking was achieved. The width of the mode-locked pulse was estimated to be about 980 ps with a repetition rate of 350 MHz within a roughly 300-ns-long Q-switched pulse envelope. A maximum output power of 940 mW was obtained, corresponding to the Q-switched pulse energy of 0.55 mJ. The emission wavelength evolution between the continuous-wave and Q-switched mode-locked operations was presented and discussed. The experimental results indicate that the Cr:ZnS absorber is a promising saturable absorber for passively Q-switched mode-locking operation around 2 μm.

Diode-pumped continuous-wave and femtosecond Cr:LiCAF lasers with high average power in the near infrared, visible and near ultraviolet.

We demonstrate continuous-wave (cw), cw frequency-doubled, cw mode-locked and Q-switched mode-locked operation of multimode diode-pumped Cr:LiCAF lasers with record average powers. Up to 2.54 W of cw output is obtained around 805 nm at an absorbed pump power of 5.5 W. Using intracavity frequency doubling with a BBO crystal, 0.9 W are generated around 402 nm, corresponding to an optical-to-optical conversion efficiency of 12%. With an intracavity birefringent tuning plate, the fundamental and frequency-doubled laser output is tuned continuously in a broad wavelength range from 745 nm to 885 nm and from 375 to 440 nm, respectively. A saturable Bragg reflector is used to initiate and sustain mode locking. In the cw mode-locked regime, the Cr:LiCAF laser produces 105-fs long pulses near 810 nm with an average power of 0.75 W. The repetition rate is 96.4 MHz, resulting in pulse energies of 7.7 nJ and peak powers of 65 kW. In Q-switched mode-locked operation, pulses with energies above 150 nJ are generated.

Graphene Q-Switched Mode-Locked and Q-Switched Ion-Exchanged Waveguide Lasers

In this letter, we present the use of monolayer graphene saturable absorbers to produce Q-switched and Q-switched mode-locked operation of Yb and Yb:Er-doped phosphate glass waveguide lasers, respectively. For the 1535-nm-wavelength Yb:Er laser, the Q-switched pulses have repetition rates up to 526 kHz and contain mode-locked pulses at a repetition frequency of 6.8 GHz. The measured 0.44-nm bandwidth should allow pulses as short as $\sim 6$ ps to be generated. Maximum average output powers of 27 mW are obtained at a slope efficiency of 5% in this mode of operation. For the 1057-nm-wavelength Yb laser, Q-switched pulses are obtained with a repetition rate of up to 833 kHz and a maximum average output power of 21 mW. The pulse duration is found to decrease from 292 to 140 ns and the pulse energy increase from 17 to 27 nJ as the incident pump power increases from 220 to 652 mW.

反射式二硫化钼可饱和吸收体实现Nd∶YVO4激光器的调Q和调Q锁模输出

反射式二硫化钼可饱和吸收体实现Nd∶YVO₄激光器的调Q和调Q锁模输出

Experimental investigation on Q-switching and Q-switched mode-locking operation in gold nanorods-based erbium-doped fiber laser

We report on the generation of Q-switched and Q-switched mode-locked (QML) pulses in an erbium-doped fiber ring laser by using a polyvinyl alcohol (PVA) -based gold nanorod (GNR) saturable absorber (SA). The PVA-based GNR SA has a modulation depth of ∼4.8% and a non-saturable loss of ∼26.9% at 1.5 μm. A Q-switched pulse train with a repetition rate varying from 18.70 to 39.85 kHz and a QML pulse train with an envelope repetition rate tuning from 20.31 to 31.50 kHz are obtained. Moreover, the lasing wavelengths of the Q-switched pulses can be flexibly tuned by introducing a narrow bandwidth, tunable filter into the laser cavity. The results demonstrate that the GNRs exhibit good optical performance and can find a wide range of applications in the field of laser technology.

\(Q\) -Switched Mode-Locked Nd:YVO4Laser by Topological Insulator Bi2Te3Saturable Absorber

By using a reflection type of topological insulator Bi 2 Te 3 as saturable absorber that was prepared by a hydrothermal intercalation/exfoliation method, we have demonstrated the stable Q-switched mode-locked operation of Nd:YVO 4 solid-state laser. Its maximum output power can reach up to 247 mW with respect to the absorbed pump power of 6.39 W. To the best of our knowledge, this is the first report for passively Q-switched mode-locking Nd:YVO 4 solid-state laser at 1-μm wavelength using a topological insulator Bi 2 Te 3 as saturable absorber. In the experiment, we have also observed the stable Q-switched operation with pulse width as short as 2 μs, output power 183 mW, and repetition rate up to 151.5 kHz.

The laser performance of a novel disordered Yb:CTGG crystal

The diode-end-pumped passively Q-switched and Q-switched mode-locked Yb:Ca2.85Ta1.80Ga3.10O12 (CTGG) lasers with V3+:YAG as the saturable absorber have been demonstrated. In the Q-switched regime, an average output power of 1.6W was obtained under the absorbed pump power of 8.6W. The shortest pulse width was 36.8ns with a pulse repetition rate of 30kHz, corresponding to a single pulse energy of 53μJ and a peak power of 1.44kW, respectively. Moreover, smooth shifts observed in output wavelength from 1034.4 to 1039.3nm with the increased absorbed pump power were attributed to the thermal effects. For the Q-switched mode-locking operation, the average output power of 638mW was obtained with a pulse repetition rate of 38MHz.

Experimental demonstration of an Er-doped fiber ring laser mode-locked with a Tm–Ho co-doped fiber saturable absorber

Mode-locking operation of an Er-doped fiber laser with a Tm–Ho co-doped fiber saturable absorber is demonstrated for the first time. Q-switching, Q-switched mode-locking and CW mode-locking operation modes are observed sequentially with increase of the pump power. In the mode-locking operation mode, a repetition rate at the fundamental cavity frequency of 9.05 MHz is obtained with a pulse duration of 46.3 ns. By rotating the polarization controller, a repetition rate up to 887 MHz is achieved, and the pulse duration is shortened to 0.548 ns.

Multilayer graphene for Q-switched mode-locking operation in an erbium-doped fiber laser

We report the laser operation of Q-switched mode-locking (QML) in an erbium-doped fiber laser by using a multilayer graphene saturable absorber (SA), which consists of 22-layer of graphene fabricated by the chemical vapor deposition method. Based on our balanced twin detector measurement, the graphene sample is confirmed to show a saturable intensity of 3.375MW/cm2 and an absolute modulation depth of 40.27%. It is demonstrated that this graphene SA can readily produce high quality QML pulses. At the pump power of 391.9mW, the stable mode-locked pulse train with the Q-switched envelope repetition rate of 16.98kHz and the envelope width of 13.84μs are achieved. The maximal main pulse peak power can reach up to 35.89W. This verifies that the multilayer graphene can be still applied as an effective saturable absorber for passively Q-switched mode-locked operation.

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.

Passively Q-switched mode-locking Erbium-doped fiber laser with net-normal dispersion using nonlinear polarization rotation technique

We experimentally demonstrate a passively Q-switched mode-locking (QML) operation in an Erbium-doped fiber ring laser with net normal dispersion by using nonlinear polarization rotation technique. A 2 m long section of dispersion compensating fiber (DCF) with extra large positive dispersion was inserted into the cavity to ensure the fiber laser working in the region of net positive dispersion. By carefully adjusting the polarization controller, both uniform dissipative mode-locking pulses with fundamental repetition rate and QML pulse trains with tunable repetition rate from 71.58 to 98.83 kHz are achieved. It is found that the QML operation is caused by the interaction between the polarization state of the pulse and the intracavity polarizer.

Diode-pumped passively Q-switched and Q-switch mode-locked Nd:YVO4 laser using single-wall carbon nanotube based saturable absorber

We present the performance of diode end-pumped Nd:YVO4 laser in Q-switched and Q-switched mode-locking oscillation using a single-walled carbon nanotube based saturable absorber, which was fabricated using similar vertical evaporation technique. The average output power, repetition rate and pulse width of the Q-switched laser output were studied with different output couplers. The maximum average output power was 130 mW. For Q-switched mode-locking operation, the repetition rate of the mode-locked pulses concentrated in the Q-switched envelope was 58 MHz. The repetition rate of the Q-switched envelope maintained at 18 kHz, while the pulse width decreased along with the increasing of pump power. The maximum average output power was 53 mW.

Q-switched mode-locking in an erbium-doped femtosecond fiber laser based on nonlinear polarization rotation

An erbium-doped fiber laser based on nonlinear polarization rotation (NPR) and negative group velocity dispersion (GVD) is built up. Two different Q-switched mode-locked (QML) operation states which can be distinguished by the properties in time and frequency domains are demonstrated. Besides the QML, stable continuous-wave mode-locked pulses centered at 1560 nm wavelength with pulse-width of 670 fs, harmonic mode-locking, Q-switching, and pulse splitting have been observed, respectively.

High efficiency passively Q-switched mode-locking Nd:GdVO 4 laser with LT-In 0.25Ga 0.75As saturable absorber

The generation of passively Q-switched mode-locking operation with 100% modulation depth has been observed from a diode-pumped Nd:GdVO 4 laser with a low temperature In 0.25Ga 0.75As saturable absorber, which was grown by the metal–organic chemical–vapor deposition technique and acted as saturable absorber as well as output coupler. The repetition rate and pulse duration of the mode-locked pulses concentrated in the Q-switch envelop were 455 MHz and 12 ps, respectively. The average output power was 1.8 W and the slope efficiency was 36%.

Thermal effects investigation and cavity design in passively mode-locked Nd:YVO4 laser with a SESAM

A diode-pumped passively mode-locked Nd:YVO4 laser with a five-mirror folded cavity is presented by using a semiconductor saturable absorber mirror (SESAM). The temperature distribution and thermal lensing in laser medium are numerically analyzed to design a special cavity which can keep the power density on SESAM under its damage threshold. Both the Q-switched and continuous-wave mode-locked operation are experimentally realized. The maximum average output power of 8.94W with a 9.3ps pulse width at a repetition rate of 111MHz is obtained under a pump power of 24W, correspondingly the optical slope efficiency is 39.2%.

Mode-locking Stability Adjustment of a Kerr-lens Mode-locked Ti:sapphire Laser, Analyzed by a Recently Developed Real-time Spectrum Analyzer

This is a report on the mode-locking stability of a Kerr-lens mode-locked Ti:sapphire, measured by a newly developed noise measurement method. Mode-locking stability is monitored via a power spectrum, which is obtained by irradiating optical pulses onto a fast photodiode, and by processing the detected signal using a recently developed real-time spectrum analyzer. The mode-locking stability of the Ti:sapphire laser strongly depends on pump power and becomes unstable as pump power decreases from an optimum power level. Amplitude fluctuation and Q-switched mode-locking are notably observed as the main causes for a break in a continuous-wave (CW) mode-locking operation. Moreover, chaotic frequency hopping is observed in a Q-switched mode-locking operation. A real-time spectrum analyzer provides a time-varying power spectrum, which enables easy adjustment for stable CW mode-locking operation of ultra-fast solid state lasers.

Q-switching stability limits of continuous-wave passive mode locking

The use of a saturable absorber as a passive mode locker in a solid-state laser can introduce a tendency for Q-switched mode-locked operation. We have investigated the transition between the regimes of cw mode locking and Q-switched mode locking. Experimental data from Nd:YLF lasers in the picosecond domain and soliton mode-locked Nd:glass lasers in the femtosecond domain, both passively mode locked with semiconductor saturable absorber mirrors, were compared with predictions from an analytical model. The observed stability limits for the picosecond lasers agree well with a previously described model, while for soliton mode-locked femtosecond lasers we have developed an extended theory that takes into account nonlinear soliton-shaping effects and gain filtering.

Bidirectional Kerr-lens mode-locked femtosecond ring laser

We report the first bidirectional operation of a Kerr-lens mode-locked femtosecond Ti:sapphire laser. Kerr-lensing was used both to mode-lock the laser and to limit the pulse energy through passive negative feedback. Q-switched mode-locked operation was also observed in the same cavity at a period of 4 to 7 μs. The unidirectionality/bidirectionality of that operation could be controlled with an intracavity semiconductor configured as an energy limiter. A simple ABCD matrix method correctly predicts the locations of the apertures to achieve the positive feedback required for continous wave mode-locking and the negative feedback for continuous wave bidirectional operation. The numerical model also estimates the observed beat frequency of 80–150 kHz.

Generation of 33-fs pulses from a passively mode-locked Cr^3+:LiSrAlF_6 laser

Femtosecond and picosecond operating regimes of an argon-ion-pumped Cr(3+):LiSrAlF(6) laser, passively mode locked using a saturable absorber, are described. At low absorber concentrations, self-starting cw mode locking is demonstrated, which yields pulses as short as 33 fs after extracavity prism compensation. At higher concentrations, both cw mode-locked and Q-switched mode-locked operation is possible. the recovery time of the absorber is discussed.

Spectroscopic and lasing characteristics of samarium doped glass fibre

The fluorescence spectra of trivalent samarium doped glass fibres are described. In silica glass Sm3+ has a narrow fluorescence of 2.2 nm f.w.h.m. at a wavelength of 650 nm. The influence of fluorescence line narrowing and large external electric fields on this line is reported. Visible laser emission is obtained at this wavelength when the fibre is pumped in a Fabry Perot cavity. The performance of the laser in continuous, Q-switched and self mode-locked operation is described. The basic theory of self-mode-locking is presented.