Periodic adjustment of the position of a laser beam spot on a semiconductor saturable absorber mirror in a passively mode-locked solid-state laser

A laser diode end-pumped passively mode-locked Nd：YVO4 solid-state laser with a semiconductor saturable ab- sorber mirror （SESAM）, in which the intracavity laser beam spot on the SESAM can be adjusted periodically, is investigated. Inserting a rectangular prism （RP） into the laser cavity is a promising approach towards the goal of periodically moving the position of the focus spot of the intracavity pulse on the SESAM surface to avoid the long-time irradiation of the laser beam on the same position, thereby solving a series of problems caused by damage to the SESAM and greatly prolonging its usage life. The adjustment of the rectangular prism in the laser cavity does not break the stable continuous wave （CW） mode-locked condition. The laser generates a stable picosecond pulse sequence at 1064 nm with an output power of 3.6 W and a pulse width of 14 ps. The instabilities of the output power and the pulse width are 1.77% and 4.5%, respectively.

Transition state to mode locking in a passively mode-locked erbium-doped fibre ring laser

The transition state between the continuous wave region and the mode-locked region in a passively mode-locked erbium-doped fibre ring laser has been experimentally observed by utilizing the nonlinear polarization rotation technique. When the pump power reaches the mode-locked threshold, the metastable pulse train with a tunable repetition rate is obtained in the transition from the continuous wave state to the passive mode-locked state via proper adjustment of the polarization controller. A simpie model has been established to explain the experimental observation.

On the generation of high-quality Nyquist pulses in mode-locked fiber lasers

Nyquist pulses have wide applications in many areas,from electronics to optics.Mode-locked lasers are ideal platforms to generate such pulses.However,how to generate high-quality Nyquist pulses in mode-locked lasers remains elusive.We address this problem by managing different physical effects in mode-locked fiber lasers through extensive numerical simulations.We find that net dispersion,linear loss,gain and filter shaping can affect the quality of Nyquist pulses significantly.We also demonstrate that Nyquist pulses experience similariton shaping due to the nonlinear attractor effect in the gain medium.Our work may contribute to the design of Nyquist pulse sources and enrich the understanding of pulse shaping dynamics in mode-locked lasers.

Phase-locked single-mode terahertz quantum cascade lasers array

We demonstrated a scheme of phase-locked terahertz quantum cascade lasers(THz QCLs)array,with a single-mode pulse power of 108 mW at 13 K.The device utilizes a Talbot cavity to achieve phase locking among five ridge lasers with first-order buried distributed feedback(DFB)grating,resulting in nearly five times amplification of the single-mode power.Due to the optimum length of Talbot cavity depends on wavelength,the combination of Talbot cavity with the DFB grating leads to better power amplification than the combination with multimode Fabry-Perot(F-P)cavities.The Talbot cavity facet reflects light back to the ridge array direction and achieves self-imaging in the array,enabling phase-locked operation of ridges.We set the spacing between adjacent elements to be 220μm,much larger than the free-space wavelength,ensuring the operation of the fundamental supermode throughout the laser's dynamic range and obtaining a high-brightness far-field distribution.This scheme provides a new approach for enhancing the single-mode power of THz QCLs.

Subharmonic mode locking of a Q-switched Nd:YAG laser

A Q-switched Nd:YAG laser has been actively mode-locked at a subharmonic frequency for the first time,to the authors’knowledge.The laser operation mode is provided by a combination of a traveling wave acousto-optic modulator and a spherical cavity mirror.The dynamics of laser generation is investigated.Pulses with a duration of 70 ps and a peak power of about 10 MW were obtained.Also presented are new results on obtaining high-power[~60 kW]picosecond tunable radiation in the~620 nm region based on frequency conversion of a superluminescent parametric generator pumped by such a laser.

Pushing the boundaries of diode-pumped solid-state lasers for high-energy applications

We report on the successful demonstration of a 150 J nanosecond pulsed cryogenic gas cooled,diode-pumped multi-slab Yb:YAG laser operating at 1 Hz.To the best of our knowledge,this is the highest energy ever recorded for a diodepumped laser system.

High power diode-pumped passively mode-locked Nd:YVO_4 laser at repetition rate of 3.2 GHz

A compact high power diode-pumped passively mode-locked Nd:YVO_4 laser with high repetition rate is realized.Using an Nd:YVO_4 crystal and a semiconductor saturable absorber mirror(SESAM) in the oscillator, the picosecond pulse output with an average power of 1.38 W, a repetition rate of 3.24 GHz, and a pulse duration of 11.4 ps is achieved. After one stage of amplification, the final output power reaches 11.34 W, corresponding to a total optical-to-optical efficiency of about 32%. The root mean square(RMS) value of power fluctuation is demonstrated to be less than 0.6% in 24 hours,showing a superior stability with the compact configuration.

Diode-Pumped Passively Mode-Locked 1079 nm Nd:CaGdAlO_4 Laser

We demonstrate a diode-pumped passively cw mode-locked Nd：CaGdAlO4 laser operating at 1079nm with a semiconductor saturable absorber mirror for the first time to the best of our knowledge. The threshold pump power of the laser is 180mW. A maximum average output power of 93mW is obtained under the pump power of 1.94 W. The pulse duration of the mode-locked pulses is 3.1ps and the repetition rate is 157MHz.

Diode-pumped Kerr-lens mode-locked Ti: sapphire laser with broad wavelength tunability

We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser.Central wavelength tunability as broad as 89 nm(736-825 nm) is achieved by adjusting the insertion of the prism.Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW.The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.

Towards an optimum saturable absorber for the multi-gigahertz harmonic mode locking of fiber lasers

Ultra-high-pulse-repetition-rate lasers are essential for a number of applications, including, e.g., optical communication and ablation-cooled material processing. Despite several techniques to generate pulses with gigahertzrange repetition rate, incorporating mainly short-length resonators, more widespread applications are still limited by the lack of a robust, simple, and cost-effective solution. Here, we report for the first time, to the best of our knowledge, fully passive harmonic mode locking in an all-polarization-maintaining(PM) fiber laser. The design guarantees a fixed polarization state and stable operation, where the cavity harmonic number is controlled by the pump power only. Self-starting operation is provided by the antimony telluride(Sb2Te3) thin-film saturable absorber(SA), which facilitates multiple pulse operation. The SA acts by means of low modulation depth, low saturation fluence, and an inverse slope in the saturable absorption curve. The optimum features of the SA and limiting factors for high-repetition-rate pulse generation in this regime of operation are discussed. As a result, 2.2 ps pulses with 3 GHz repetition rate are generated at 1560 nm wavelength. The study reports a new approach towards an optimal SA for multi-gigahertz pulse generation in practical, all-PM fiber lasers.

Passive harmonic mode locking of gain-guided solitons in erbium-doped fiber lasers

We report the experimental observation of passive harmonic mode locking of gain-guided solitons in erbium-doped fiber lasers either made of purely normal dispersion fibers or operating in the net normal cavity dispersion regime. Harmonic-2 and harmonic-3 mode locking states of the gain-guided solitons with supermode suppression larger than 35 dB have been obtained.

Experimental studies of self-starting passive mode locking Er^(3+)-doped fiber ring soliton laser

The mechanism of femtosecond optical pulse generation in a self-starting Er3+-doped fiber ring solitonlaser and experimental research results are discussed. Using the nonlinear polarization rotation effect of the fiber for sat-urable absorbers （and then self-amplitude modulation） which acts as the mode locking mechanism in an Er3+-dopedfiber ring cavity laser, stable self-starting mode locking pulses have been generated. The shortest output pulse is 269 fs,with the central wavelength of 1.531 μm at the repetition rate of 21.37 MHz. The average output powers of the two terminators of the laser are 0.25 mW and 0.08 mW respectively. The threshold pump power which sustains the mode lock-ing is 15 mW. Under high pump power, the laser works in a high order harmonic mode locking state. The mode lockingpulse durations vs different cavity lengths are also studied.

CsPbBr3 nanocrystal for mode-locking Tm-doped fiber laser

CsPbBr3 nanocrystal is used as the saturable absorber(SA) for mode-locking Tm-doped fiber laser in a ring fiber cavity.The modulation depth, saturable intensity, and non-saturable loss of the fabricated SA are 14.1%, 2.5 MW/cm^2,and 5.9%, respectively.In the mode-locking operation, the mode-locked pulse train has a repetition rate of 16.6 MHz with pulse width of 24.2 ps.The laser wavelength is centered at 1992.9 nm with 3-dB spectrum width of 2.5 nm.The maximum output power is 110 mW with slope efficiency of 7.1%.Our experiment shows that CsPbBr3 nanocrystal can be used as an efficient SA in the 2-μm wavelength region.

Passive Model-locking of 1.5μm InGaAsP Quantum Well Lasers

The generation of ultrashort optical pulse from passively mode-locked InGaAs/InGaAsPquantum well laser diodes is reported.The device consists of two segments:one is reversed-ly biased as a saturable absorber and the other is current forward injected as a gain segment.The optical pulse with 7.8ps duration at 26 GHz repetition rate has been measured from thepassively mode-locked laser with 1.625μm cavity length and 1.53μin emitting wavelength.Some simple descriptions of PMLD characteristics are also given.

Passive harmonic mode-locking of Er-doped fiber laser using CVD-grown few-layer MoS_2 as a saturable absorber

Passive harmonic mode locking of an erbium-doped fiber laser based on few-layer molybdenum disulfide(MoS2)saturable absorber(SA) is demonstrated. The few-layer MoS2 is prepared by the chemical vapor deposition(CVD) method and then transferred onto the end face of a fiber connector to form a fiber-compatible Mo S2SA. The 20 th harmonic modelocked pulses at 216-MHz repetition rate are stably generated with a pulse duration of 1.42 ps and side-mode suppression ratio(SMSR) of 36.1dB. The results confirm that few-layer MoS2 can serve as an effective SA for mode-locked fiber lasers.

Operation of Kerr-lens mode-locked Ti:sapphire laser in the non-soliton regime

A Kerr-lens mode-locked Ti：sapphire laser operating in a non-soliton regime is demonstrated. Dispersive wave generation is observed as a result of third order dispersion in the vicinity of zero dispersion. The characteristics of the Ti：sapphire l^ser operating in a positive dispersion regime are presented, where the oscillator directly generates pulses with duration continuously tunable from 0.37 ps to 2.11 ps, and 36 fs pulses are achieved atter extracavity compression. The oscillation is numerically simulated with an extended nonlinear Schr6dinger equation, and the simulation results are in good agreement with the experimental results.

Passively mode-locked Nd：GdVO4 laser at 912nm

This paper demonstrates the passively mode-locked Nd：GdVO4 laser operating on the ^4F3/2-^4I9/2 transition at 912 nm by using a semiconductor saturable-absorber mirror for passive mode locking, stable continuous wave modelocked 912nm laser was achieved with a repetition rate of 176 MHz. At the incident pump power of 17.7W, 22.6mW average output power of stable mode-locked laser was obtained with a slope efficiency of 0.3%.

An all-polarization-maintaining repetition-tunable erbium-doped passively mode-locked fiber laser

An environmentally stable, repetition rate tunable, all-polarization-maintaining, Er-doped pulse fiber laser with a single-wall carbon nanotubes saturated absorber is demonstrated. The ring laser cavity includes a delay line enabling a tunable repetition rate to vary from 35.52 MHz to 35.64 MHz with continuous mode-locked operation. The laser output parameters confirm that the tunable mode-locked operations are stable. High environmental stability is also confirmed by the -130 dBc/Hz low phase noise, a 70-dB signal-to-noise ratio of radio frequency signals, a low amplitude fluctuation of 5.76 × 10-4, and a low fluctuation of reoetition rate of 12 Hz. The laser shows a high de^ree of oolarization of 93%.

Broadband rhenium disulfide optical modulator for solid-state lasers

Rhenium disulfide(ReS_2), a member of group Ⅶ transition metal dichalcogenides(TMDs), has attracted increasing attention because of its unique distorted 1T structure and electronic and optical properties, which are much different from those of group Ⅵ TMDs(MoS_2, WS_2, MoSe_2, WSe_2, etc.). It has been proved that bulk ReS_2 behaves as a stack of electronically and vibrationally decoupled monolayers, which offers remarkable possibilities to prepare a monolayer ReS_2 facilely and offers a novel platform to study photonic properties of TMDs. However,due to the large and layer-independent bandgap, the nonlinear optical properties of ReS_2 from the visible to midinfrared spectral range have not yet been investigated. Here, the band structure of ReS_2 with the introduction of defects is simulated by the ab initio method, and the results indicate that the bandgap can be reduced from 1.38 to 0.54 eV with the introduction of defects in a suitable range. In the experiment, using a bulk ReS_2 with suitable defects as the raw material, a few-layered broadband ReS_2 saturable absorber(SA) is prepared by the liquid phase exfoliation method. Using the as-prepared ReS_2 SA, passively Q-switched solid-state lasers at wavelengths of 0.64,1.064, and 1.991 μm are investigated systematically. Moreover, with cavity design, a femtosecond passively modelocked laser at 1.06 μm is successfully realized based on the as-prepared ReS_2 SA for the first time. The results present a promising alternative for a rare broadband optical modulator and indicate the potential of ReS_2 in generating Q-switched and mode-locked pulsed lasers. It is further anticipated that this work may be helpful for the design of 2D optoelectronic devices with variable bandgaps.

Bound soliton pulses in a passively mode-locked fibre ring laser

The bound solitons in a passively mode-locked fibre ring laser are observed and their formation mechanism is summarized in this paper. In order to obtain stable bound solitons, a strong CW laser field at the centre of the soliton spectral is necessary to suppress and synchronize the random soliton phase variations.