Kerr-lens Mode-locked Operation Research Articles

Kerr-Lens Mode-Locked Yb:BaF2 Laser

We present sub-50 fs soliton pulse generation from a diode-pumped Kerr-lens mode-locked laser based on an Yb3+-doped BaF2 crystal. Utilizing a spatially single-mode, fiber-coupled InGaAs laser diode at 976 nm as a pump source, the Yb:BaF2 laser generates pulses as short as 46 fs at 1060.1 nm with an average output power of 45 mW at a pulse repetition rate of ~65.6 MHz via soft-aperture Kerr-lens mode locking. To the best of our knowledge, this represents the first demonstration of Kerr-lens mode-locked operation of the Yb:BaF2 crystal, as well as the shortest pulse duration ever achieved from any diode-pumped mode-locked laser based on an Yb3+-doped alkaline-earth fluoride crystal.

Kerr-lens mode-locked 49-fs Tm3+:YScO3 single-crystal laser at 2.1 µm.

We report on a continuous wave (CW) and Kerr-lens mode-locked (KLM) Tm3+:YScO3 single-crystal laser centered at 2.1 µm. Efficient CW laser operation with a maximum slope efficiency of 51% was achieved under in-band pumping by an Er:Yb fiber master oscillator power amplifier (MOPA). In KLM operation, pulses as short as 49 fs corresponding to seven optical cycles were achieved at a repetition rate of 96.7 MHz with an average output power of 126 mW. Such short pulse durations are enabled by the inhomogeneously broadened emission spectrum of Tm3+:YScO3 extending to above 2200 nm.

Kerr-Lens Mode-Locking: Numerical Simulation of the Spatio-Temporal Dynamics on All Time Scales

We present a complete numerical analysis and simulation of the full spatio-temporal dynamics of Kerr-lens mode-locking in a laser. This dynamic, which is the workhorse mechanism for generating ultrashort pulses, relies on the intricate coupling between the spatial nonlinear propagation and the temporal nonlinear compression. Our numerical tool emulates the dynamical evolution of the optical field in the cavity on all time-scales: the fast time scale of the pulse envelope within a single round trip, and the slow time-scale between round-trips. We employ a nonlinear ABCD formalism that fully handles all relevant effects in the laser, namely—self focusing and diffraction, dispersion and self-phase modulation, and space-dependent loss and gain saturation. We confirm the validity of our model by reproducing the pulse-formation in all aspects: The evolution of the pulse energy, duration, and gain during the entire cavity buildup, demonstrating the nonlinear mode competition in full, as well as the dependence of the final pulse in steady state on the interplay between gain bandwidth, dispersion, and self-phase modulation. The direct observation of the nonlinear evolution of the pulse in space-time is a key enabler to analyze and optimize the Kerr-lens mode-locking operation, as well as to explore new nonlinear phenomena.

Sub-60-fs ultralow threshold and efficient Kerr-lens mode-locked Yb,Gd:CaSrF2 laser.

In this Letter, using a Yb,Gd:CaSrF2 co-doping mixed crystal, an ultra-low threshold and efficient Kerr-lens mode-locked femtosecond oscillator is realized with a mode-locking threshold as low as 150 mW. With a 200-mW pump power, the shortest pulses are obtained with a pulse duration of 57 fs. A maximum mode-locked output power of 185 mW is observed under a 500-mW pump power, corresponding to an optical-to-optical efficiency of up to 37%. To the best of our knowledge, the 150-mW threshold is the lowest pump power to realize Kerr-lens mode-locking operation in Yb-doped bulk lasers. Furthermore, an optical efficiency of 37% is the highest efficiency in Yb-doped fluoride bulk lasers to date. Our results provide a new basis for high-efficiency and low-threshold Yb-doped ultrafast bulk lasers.

High power diode pumped solid-state femtosecond laser systems

We demonstrate high power direct diode-pumped femtosecond laser based on a commercially available configuration and pumped by multi-diode laser modules delivering high brightness and average power. The multi-diode modules employ beam-combining scheme preserving linear polarization and focusing properties of individual laser diodes. Stable passive Kerr lens modelocked (KLM) laser operation was demonstrated, producing 30 fs pulses at ∼300 mW average output power. A simple approach to numerical modelling of KLM laser operation in cases when longitudinal pump beam exhibits strong astigmatism is also discussed.

Influence of pump beam shaping and noise on performance of a direct diode-pumped ultrafast Ti:sapphire laser.

One of the major factors that limits the widespread use of ultrafast titanium sapphire (Ti:S) lasers in life science is its expensive and complex pump source. Broad area diode laser (BA-DL) based pump sources have high potential to solve this problem, since they are compact, inexpensive and very efficient. However, their non-diffraction limited beam profile makes it challenging to achieve high powers in Kerr-lens mode-locked (KLM) operation of Ti:S lasers. In this work, we show that the ideal way to beam shape two spectrally combined BA-DLs with different beam qualities is to aim for a compromise between matching to the cavity mode diameter and the cavity mode Rayleigh range. We furthermore conclude that the relative intensity noise (RIN) of the BA-DL pumped Ti:S laser, another important parameter for imaging applications, is sufficiently low for a wide range of life science applications. However, for applications that are highly sensitive to noise, new laser diode designs are likely necessary to reduce inherent noise originating within the laser diode.

High-energy self-mode-locked Cr:forsterite laser near the soliton blowup threshold.

At the level of peak powers needed for a Kerr-lens mode-locked operation of solid-state soliton short-pulse lasers, a periodic perturbation induced by spatially localized pulse amplification in a laser cavity can induce soliton instability with respect to resonant dispersive-wave radiation, eventually leading to soliton blowup and pulse splitting of the laser output. Here, we present an experimental study of a high-peak-power self-mode-locking Cr:forsterite laser, showing that, despite its complex, explosion-like buildup dynamics, this soliton blowup can be captured and quantitatively characterized via an accurate cavity-dispersion- and gain-resolved analysis of the laser output. We demonstrate that, with a suitable cavity design and finely tailored balance of gain, dispersion, and nonlinearity, such a laser can be operated in a subcritical mode, right beneath the soliton blowup threshold, providing an efficient source of sub-100-fs 15-20 MHz repetition-rate pulses with energies as high as 33 nJ.

Kerr-lens mode locking of a diode-pumped Yb:KGW laser using an additional intracavity Kerr medium

Kerr-lens mode-locked operation of a Yb:KGW laser pumped by a multimode laser diode with the help of an additional Kerr medium is reported. With an enhanced Kerr lensing effect in the laser cavity operating far from the stability edge limit, the laser delivered 74 fs pulses with an average output power of 500 mW. In the high power regime of operation (>500 mW), the mode-locked laser output was accompanied by a continuous wave background radiation. Owing to the self-phase modulation effect, the laser demonstrated the generation of shorter pulses as compared to the case without an additional Kerr medium.

Kerr-lens mode-locked 2.3-μm Tm3+:YLF laser as a source of femtosecond pulses in the mid-infrared.

We report what is to our knowledge a new source of femtosecond pulses in the mid-infrared, based on a Kerr-lens mode-locked (KLM) Tm3+:YLF laser at 2303nm. An undoped ZnSe substrate was included in the resonator to provide enhanced nonlinear phase modulation during KLM operation. The Tm3+:YLF laser was end-pumped with a continuous-wave Ti3+ : sapphire laser at 780nm. With 880mW of pump power, we generated 514-fs pulses at a pulse repetition rate of 41.5MHz with an average power of 14.4mW. The spectral width (full width at half-maximum) was measured as 15.4nm, giving a time-bandwidth product of 0.44. We foresee that the wide availability of this gain medium, as well as the straightforward pumping scheme near 800nm, will make 2.3-μm, mode-locked Tm3+:YLF lasers versatile sources of ultrashort pulses in the mid-infrared.

Kerr-lens mode-locked polycrystalline Cr:ZnS femtosecond laser pumped by a monolithic Er:YAG laser**Project supported by the National Natural Science Foundation of China (Grant Nos. 61205130, 61465012, and 61564008).

We demonstrated a Kerr-lens mode-locked polycrystalline Cr:ZnS laser pumped by a narrow-linewidth linear-polarised monolithic Er:YAG nonplanar ring oscillator operated at 1645 nm. With a 5-mm-thick sapphire plate for intracavity dispersion compensation, a compact and stable Kerr-lens mode-locking operation was realised. The oscillator delivered 125-fs pulses at 2347 nm with an average power of 80 mW. Owing to the special polycrystalline structure of the Cr:ZnS crystal, the second to fourth harmonic generation was observed by random quasi-phase-matching.

Generation of 15W femtosecond laser pulse from a Kerr-lens mode-locked Yb:YAG thin-disk oscillator**Project supported by the National Basic Research Program of China (Grant No. 2013CB922402), the National Major Instrument Program of China (Grant No. 2012YQ120047), and the National Natural Science Foundation of China (Grant Nos. 11434016 and 61210017).

We demonstrated a robust power-scalable Kerr-lens mode-locked (KLM) operation based on a Yb:YAG thin-disk oscillator. 15-W, 272-fs pulses were realized at a repetition rate of 86.7 MHz with an additional Kerr medium and a 2.5 mm hard aperture in the cavity. 247-fs pulses with an average power of 11 W could also be obtained by using a 2.4 mm hard aperture. Based on this shorter pulse, high efficient second-harmonic generation (SHG) was performed with a 1.7-mm-long LiB3O5 (LBO) crystal. The SHG laser power was up to 5 W with the power fluctuation RMS of 1% measured over one hour.

Direct diode-pumped 58 fs Yb:Sr3Y2(BO3)4 laser

The ultrafast laser performance of Yb:Sr3Y2(BO3)4 (SYB) crystal has been demonstrated for the first time to the best of our knowledge. The Yb:SYB laser was driven to work in SESAM-assisted Kerr-lens mode-locking (KLM) operation, and 58fs pulses were generated at the central wavelength of 1054.6nm. A maximum average output power reached 400mW with a slope efficiency of 13.5%. The experimental results indicated Yb:SYB crystal as a promising candidate for achieving ultrashort lasers.

Diode-pumped Kerr-lens mode-locked femtosecond Yb:YAG ceramic laser**Project supported by the National Major Scientific Instrument Development Project of China (Grant No. 2012YQ120047), the National Natural Science Foundation of China (Grant No. 61205130), and the Fundamental Research Funds for the Central Universities, China (Grant No. JB140502).

We experimentally demonstrated a diode-pumped Kerr-lens mode-locked femtosecond laser based on an Yb:YAG ceramic. Stable laser pulses with 97-fs duration, 2.8-nJ pulse energy, and 320-mW average power were obtained. The femtosecond oscillator operated at a central wavelength of 1049 nm and a repetition rate of 115 MHz. To the best of our knowledge, this is the first demonstration of a Kerr-lens mode-locked operation in a diode-pumped Yb:YAG ceramic laser with sub-100 fs pulse duration.

Kerr-Lens Mode-Locked Femtosecond Yb:GdYSiO5 Laser Directly Pumped by a Laser Diode

We demonstrate the first Kerr-lens mode-locked operation in a diode-pumped Yb:GdYSiO5 oscillator. Under a diode pump power of 5 W, 141 fs pulses with an average power of 237 mW were obtained at a repetition rate of 118 MHz. The central wavelength was at 1094 nm with a bandwidth of 10.1 nm. Shorter pulses were obtained by adjusting the cavity to operate at a shorter wavelength, resulting in 55 fs pulse duration at the central wavelength of 1054 nm with a bandwidth of 23.5 nm.

Gain-Matched Output Couplers for Efficient Kerr-Lens Mode-Locking of Low-Cost and High-Peak Power Cr:LiSAF Lasers

We present a detailed investigation of Kerr-lens mode-locking (KLM) in diode-pumped Cr:LiSAF lasers employing gain-matched output couplers (GMOCs). Single-mode diodes (660 nm, 130 mW) and tapered diodes (685 nm, 1W) were investigated as diode pump sources. We have shown that, by reducing the gain-filtering effect, GMOC enhances t he effective self amplitude modulation depth and provides a significant improvement in both efficiency and robustness of KLM operation. From the single-mode diode pumped system, 13 fs pulses with an average power of 25 mW and a peak power 25 kW have been generated at an incident pump power of only 120 mW (21% optical-to-optical conversion efficiency). The tapered diode pumped Cr:LiSAF oscillator provided pulses as short as 14.5 fs with 106 mW average power and 60 kW peak power at an incident pump power of 940 mW (11% optical-to-optical conversion efficiency). A femtosecond tuning range extending from 807 nm to 919 nm was also realized with sub-50-fs long pulses. To our knowledge, demonstrated optical-to-optical conversion efficiencies, peak powers and fs tuning ranges are record results for Cr:LiSAF laser oscillators. The obtainable pulsewidth and fs tuning range are currently limite d by the dispersion/reflectivity bandwidth of the available optics.

Generation of 73 fs pulses from a diode pumped Kerr-lens mode-locked Yb:YCa₄O(BO₃)₃ laser.

We realized a stable Kerr-lens mode-locked operation in a Yb:YCa₄O(BO₃)₃ laser. Pulses as short as 73 fs were generated at the central wavelength of 1043 nm, with a bandwidth of 19 nm. The femtosecond oscillator operating at a repetition rate of 110 MHz delivers an average output power of 70 mW under 3 W diode pump power. To the best of our knowledge, this is the first demonstration of a pure Kerr-lens mode-locked operation in a diode-pumped Yb:YCa₄O(BO₃)₃ laser.

Generation of 85 fs laser pulses from a diode-pumped Kerr-lens mode-locking Yb:(Y0.9La0.1)2O3 ceramic laser

We experimentally demonstrated a stable diode-pumped Kerr-lens mode-locking femtosecond laser with a Yb3+-doped yttrium lanthanum oxide ceramic. Pulses as short as 85 fs at a central wavelength of 1074.5 nm were obtained at a repetition rate of 118 MHz. The average output power was 80 mW under a 4 W diode pump power. To the best of our knowledge, this is the first demonstration of a Kerr-lens mode-locked operation in a Yb3+-doped yttrium lanthanum oxide ceramic laser with a sub-100 fs pulse width.

Diode-pumped Kerr-lens mode-locked Yb:LYSO laser with 61fs pulse duration.

A stable diode pumped Kerr-lens mode-locked (KLM) Yb:LuYSiO5 (Yb:LYSO) laser of generating 61 fs pulses at a central wavelength of 1055.4 nm is experimentally demonstrated. This is, to the best of our knowledge, the first demonstration of femtosecond KLM operation in Yb:LYSO laser, and it is believed that 61 fs is the shortest pulse duration ever produced from an Yb-doped orthosilicate laser. The average output power of the mode-locked laser is 40 mW and the repetition rate is 113 MHz.

Kerr-lens mode-locked femtosecond polycrystalline Cr^2+:ZnS and Cr^2+:ZnSe lasers

We report the first Kerr-lens mode-locked polycrystalline Cr(2+):ZnS and Cr(2+):ZnSe lasers, with pulse duration of 125 fs at a pulse repetition rate of 160 MHz, emitting around 2.3 - 2.4 µm. The mode-locked lasers were pumped by a radiation of 1550 nm Er-fiber amplifier seeded by semiconductor laser. The long-term stable Kerr-lens mode-locked laser operation with the output power of 30 mW (Cr(2+):ZnS) and 60 mW (Cr(2+):ZnSe) was obtained. We also demonstrate amplification of the fs laser pulse train in a cw pumped single-pass polycrystalline Cr(2+):ZnS laser amplifier.

Diode-pumped 88-fs Kerr-lens mode-locked Yb:Y_3Ga_5O_12 crystal laser

We realized a stable Kerr-lens mode-locked operation in a diode-pumped Yb:Y₃Ga₅O₁₂ laser. Pulses as short as 88 fs at the center wavelength of 1042 nm were obtained at a repetition rate of 159.3 MHz. The maximum output power was 104 mW under the incident pump power of 3.9 W. By comparing the mode-locked characteristics under different output transmissions, we obtained pulses with the highest output power of 330 mW and a duration of 149 fs. To the best of our knowledge, this is the first demonstration of a Kerr-lens mode-locked Yb:Y₃Ga₅O₁₂ laser.