Efficient Mode-locking Research Articles

Mode-Locking With Ultra-Low Intra-Cavity Pulse Intensity Using Enhanced Kerr Nonlinearity

Kerr lens mode locking strongly depends upon intensity. Low pulse intensity weakens the nonlinear Kerr lens, and eventually mode locking is not supported. We demonstrate efficient mode-locking in a Ti:Sapphire laser oscillator with record-low intra-cavity pulse intensity (18 GW/cm2) and intra-cavity average power (340 mW). Using an additional nonlinear window in the cavity, the Kerr nonlinearity can be enhanced by an order of magnitude compared to the standard Ti:Sapphire cavity, allowing mode locking with an output coupler reflectivity as low as R = 55% and record-low intra-cavity pulse intensity. Our results provide an important new possibility to control mode-locking in cavities with very low intra-cavity pulse intensity, such as semiconductor laser oscillators and high-repetition rate mode-locked lasers.

Picosecond Optical Pulse Generation by Nonlinear Mirror Mode-Locking: A Review

Background/Objectives: This article provides comprehensive review on nonlinear mirror mode-locked laser which is compact, efficient, simplest and stable source of picosecond optical pulse and is of immense research interest. Methods/ Analysis: Starting with the basics of nonlinear mirror mode-locking technique, a chronological development of the subject is presented. Issues with the efficiency and stability of the nonlinear mode-locking are addressed in both theoretical and experimental perspective. Different schemes of nonlinear mirror mode-locking, reported till date, are illustrated and compared in reference to the obtained pulse durations, power scaling, self starting and self sustained efficient modelocking. Findings: Nonlinear mirror, comprising a second harmonic generating crystal and a dichroic output coupler, can mode-lock a laser due to its behaviour analogous to fast saturable absorber. Efficiency of the laser is increased with the diode pumping; however nonlinear mirror is observed prone to passive Q-switching instability. Simultaneously Q-switched and mode-locked operation gives a simple way of increasing the peak power but is of no use because of rapid fluctuations of pulse amplitude and repetition rate. Incorporation of an accousto-optic Q-switch in the laser cavity helps run the laser in actively Q-switched and passively mode-locked regime which provides enormous stability of the Q-switched and modelocked pulse envelops and the enhanced peak power becomes useful. Pure contentious wave mode-locking is obtained by incorporation of additional intensity dependent loss mechanism by way of introducing third harmonic generation in the laser cavity and it gives an inverse saturable nonlinear loss modulation. Inverse saturable nonlinear mirror produces efficient, self sustained and stable contentious wave mode-locked picosecond optical pulse train. Application /Improvement: Nonlinear mirror mode-locked lasers have wide application in micromachining, optical frequency conversion, pumping optical parametric oscillators etc. Propositions are made for getting improved nonlinear mirror mode-locking to get bandwidth limited pulse width.

Mode-locking in Er-doped fiber laser based on mechanically exfoliated Sb_2Te_3 saturable absorber

We demonstrate the usage of a new saturable absorber material – antimony telluride (Sb2Te3) for efficient mode-locking of an Erbium-doped fiber laser. The Sb2Te3 layers were obtained by mechanical exfoliation and transferred onto the fiber connector tip. The all-fiber laser was capable of generating optical solitons with the full width at half maximum of 1.8 nm centered at 1558.6 nm, with 4.75 MHz repetition rate. The pulse energy of the generated 1.8 ps pulses was at the level of 105 pJ.

Er-Doped Fiber Laser Mode-Locked by CVD-Graphene Saturable Absorber

Erbium-doped fiber laser passively mode-locked by bilayer graphene is presented. The graphene layers were grown by chemical vapor deposition (CVD) on Cu substrate and transferred onto a fused silica window, forming a saturable absorber (SA). Low non-saturable losses and modulation depth as high as 55% allowed to achieve soliton pulses with over 11 nm bandwidth and nearly-transform limited 315 fs duration at 1564 nm center wavelength. The paper describes the design of the laser construction, as well as the graphene-SA preparation process. Our study demonstrates, that CVD-Cu graphene transferred on glass substrate may be used for efficient mode-locking of fiber lasers.

Broadly tunable femtosecond mode-locking in a Tm:KYW laser near 2 μm

Efficient mode-locking in a Tm:KY(WO(4))(2) laser is demonstrated by using InGaAsSb quantum-well SESAMs. Self-starting ultrashort pulse generation was realized in the 1979-2074 nm spectral region. Maximum average output power up to 411 mW was produced around 1986 nm with the corresponding pulse duration and repetition rate of 549 fs and 105 MHz respectively. Optimised pulse durations of 386 fs were produced with an average power of 235 mW at 2029 nm.

Theory of a fibre ring laser mode-locked by cross-phase modulation

We have developed a computer model of a novel fibre ring laser, optically mode-locked by cross phase modulation. We have analysed the modulation process in detail, showing that, in the context of the earlier experiment, the nonlinear birefringence induced by cross-phase modulation gives rise to a loss modulation component. Numerical results suggest that this feature is essential if efficient mode-locking is to occur. The importance of attenuation and group delay dispersion in the modulator fibre has been demonstrated.

Efficient self-mode locking of continuous-wave solid-state lasers with resonant nonlinearity in an additional cavity

Parameters of the efficient mode-locking of cw solid-state lasers with saturable absorber in the additional cavity are found on the basis of the laser generation fluctuation model. These parameters form closed ranges. The main features of the efficient mode- locking are associated with the transmission of the additional cavity as a function of the field intensity. It is shown that due to the resonant nonlinearity the efficient mode-locking takes place in the absence of the interferometrical matching of the lengths of the master and additional cavities. It also takes place in the case of the difference of their lengths of up to the value for which the delay of the pulse from the additional cavity according to generation pulse becomes comparable with generation pulse duration.