Search

We demonstrate for the first time, to our knowledge, an all-polarization-maintaining double-clad neodymium fiber laser operating in the dissipative soliton resonance (DSR) regime where stable mode-locking is achieved using a nonlinear amplifying loop mirror (NALM) with large normal dispersion in a figure-8 cavity design. The laser thereby generates square-shaped nanosecond pulses whose duration linearly scales with pump power from 0.5 up to 6 ns, with a maximum energy of 20 nJ. In addition, output pulses feature a remarkably narrow bandwidth of 60 pm along with a signal-to-noise ratio higher than 80 dB. This study then paves the way toward using such DSR-based sources for efficient frequency doubling in the blue spectral range.

The orthorhombic Tm 3+ :YAlO 3 crystal is promising for laser operation at the H 4 3→F 4 3 (1.5 μm) and H 4 3→H 5 3 (2.3 μm) transitions. Stimulated-emission cross-sections for these transitions are determined with polarized light. Peak values of 0.59×10 -20   cm 2 and 0.80×10 -20   cm 2 are found at 1438 nm and 2275 nm, respectively, both for E∥b. The cross-relaxation defining the upper-laser level lifetime is quantified. Continuous-wave lasing at the H 4 3→H 5 3 transition is achieved with an a-cut 1.5 at.% Tm:YAlO 3 crystal. The laser generated 254 mW at 2273 nm with a slope efficiency of 17.8% and linear polarization (E∥b).

We report on novel upconversion (UC) pumping schemes for 2.3 μm thulium (Tm) lasers (the H 4 3→H 5 3 transition) based on a photon avalanche mechanism populating the intermediate metastable level (F 4 3) acting as an effective ground state. The proposed pump wavelengths are ∼1 and ∼1.5  μm, each one corresponding to a resonant excited-state absorption transition F 4 3→F 2,3 3 and F 4 3→H 4 3, respectively. UC pumping at 1040, 1055, and 1451 nm of 2.3 μm Tm:LiYF 4 lasers is demonstrated. In the former case, the laser generates 102 mW at 2302 nm with a slope efficiency of 14.6% (versus the incident pump power). The laser dynamics is studied. UC pumping is promising for reaching high efficiencies in 2.3 μm Tm lasers.

We report on a novel power scaling strategy for thulium waveguide (WG) lasers relying on in-band pumping by high-brightness Raman fiber lasers (RFLs) and the use of liquid-phase-epitaxy-grown fluoride crystalline thin films for better thermal management. Thulium channel WGs are produced by microstructuring the Tm 3+ :LiYF 4 /LiYF 4 epitaxies via diamond-saw dicing. They are pumped by a RFL based on an erbium master oscillator power amplifier and a GeO 2 -doped silica fiber and emit polarized output at 1679 nm. A CW in-band-pumped (H 6 3→F 4 3) Tm 3+ :LiYF 4 WG laser generates up to 2.05 W of a linearly polarized single-transverse-mode output at 1881 nm with a slope efficiency of 78.3% and a laser threshold of only 12 mW (versus the absorbed pump power).

Practical realization of stable and high brightness sources of ultra-short electron pulses is an important issue in the development of time-resolved electron microscopy for the study of ultra-fast dynamics in materials. Here, we report on the experimental investigation of static (in the dark) and pulsed (under illumination by sub-picosecond laser pulses at 1040 nm) electron emission from single-crystal diamond needles. A significant increase of electron emission current was detected under laser illumination. The nonlinear dependence of the emission current on the laser intensity and on the angle between the needle and the laser beam polarization axis suggests multi-photon emission processes. This interpretation is in agreement with electron spectroscopy measurements performed for electrons emitted at different bias voltages and different laser power levels and repetition rates. The remarkable feature of the diamond emitters is their stability under high average power of laser radiation. This provides a new highly efficient source of photoemitted electrons based on single-crystal diamond.

Quasi-continuous-wave laser operation of 20 at.% Tm:LiYF 4 thin films (84-240 μm) grown by Liquid Phase Epitaxy (LPE) on undoped LiYF 4 substrates is achieved. The 240 μm-thick Tm:LiYF 4 active layer pumped at 793 nm with a simple double-pass scheme generated 152 mW (average power) at 1.91 μm with a slope efficiency of 34.4% with respect to the absorbed pump power. A model of highly-doped Tm:LiYF 4 lasers accounting for cross-relaxation, energy-transfer upconversion and energy migration is developed showing good agreement with the experiment. The pump quantum efficiency for Tm 3+ ions is discussed and the energy-transfer parameters are derived. These results show that LPE-grown Tm:LiYF 4 thin films are promising for ~1.9 μm thin-disk lasers.

Low-loss surface channel waveguides with a cross-section of 30 × 30 μm 2 are produced by diamond saw dicing of 6.2 at.% Tm 3+ , 3.5 at.% Gd 3+ :LiYF 4 films grown by liquid phase epitaxy (LPE) on (001)-oriented bulk undoped LiYF 4 substrates. Pumped by a Ti:Sapphire laser at 783 nm, a continuous-wave Tm:LiYF 4 waveguide laser generated 1.30 W at 1880 nm (for π-polarization) with a slope efficiency of 80% with respect to the absorbed pump power. The laser threshold was at 80 mW. The waveguide morphology was studied revealing low roughness (3 ± 2 μm) as expressed by the propagation losses of <0.3 dB/cm. A combination of LPE and diamond saw dicing is a promising technology for multi-watt single-mode channel waveguide lasers and amplifiers.

The first holmium fluoride waveguide laser, to the best of our knowledge, is reported using a 25-μm-thick Gd 3+ -ion-modified 4.5 at. % Tm 3+ , 0.5 at. % Ho 3+ -codoped LiYF 4 active layer grown by liquid phase epitaxy on (001)-oriented LiYF 4 substrate. Pumped by a Ti:sapphire laser at 797.2 nm, the planar waveguide laser generates 81 mW of continuous-wave (CW) output at ∼2051  nm with a slope efficiency of 24%. Power scaling up to 186 mW at 2051 nm and 2065 nm in quasi-CW regime is demonstrated. The parameters of the Tm 3+ ↔Ho 3+ energy transfer are determined. Tm,Ho:LiYF 4 /LiYF 4 epitaxies are promising for waveguide lasers and amplifiers at above 2 μm.

A passively mode-locked Tm:YLF laser emitting at 2.3 μm is reported for the first time, to the best of our knowledge. The continuous-wave stable mode-locking operation is obtained with a semiconductor saturable absorber mirror at a repetition rate of 100 MHz. The average output power is 165 mW for a pulse duration of 94 ps.

The laser assisted field-evaporation of metals and oxides strongly depends on the illumination conditions. Here we study the effect of laser pulse width using two different laser systems, with a pulse duration of a few tens of femtoseconds and a few tens of picoseconds, respectively. Adjusting the laser wavelength by nonlinear optical conversion systems, we study the evaporation behavior of FeCu and MgO samples. We prove that the laser pulse width does not affect the evaporation behavior, in the range of duration explored. These results are explained taking into account the absorption behavior of nanometric samples and their thermal properties., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Modern diesel injectors operate at very high injection pressures of about 2000 bar resulting in injection velocities as high as 700 m/s near the nozzle outlet. In order to better predict the behavior of the atomization process at such high pressures, high-resolution spray images at high repetition rates must be recorded. However, due to extremely high velocity in the near-nozzle region, high-speed cameras fail to avoid blurring of the structures in the spray images due to their exposure time. Ultrafast imaging featuring ultra-short laser pulses to freeze the motion of the spray appears as an well suited solution to overcome this limitation. However, most commercial high-energy ultrafast sources are limited to a few kHz repetition rates. In the present work, we report the development of a custom-designed picosecond fiber laser generating ∼ 20 ps pulses with an average power of 2.5 W at a repetition rate of 8.2 MHz, suitable for high-speed imaging of high-pressure fuel jets. This fiber source has been proof tested by obtaining backlight images of diesel sprays issued from a single-orifice injector at an injection pressure of 300 bar. We observed a consequent improvement in terms of image resolution compared to standard white-light illumination. In addition, the compactness and stability against perturbations of our fiber laser system makes it particularly suitable for harsh experimental conditions.

A laser based on a ribbon multicore ytterbium doped fiber where different cores amplified different spectral bands, has been mode-locked with a single saturable absorber mirror. Tunable dual wavelength synchronized picosecond pulses were obtained. Compensation of differential cavity roundtrip times was achieved in the fiber.

We report on a passively mode-locked erbium-doped fiber laser featuring a large normal dispersion and emitting high-energy dissipative solitons. Mode-locking is stabilized by the combined actions of a high nonlinearity amplitude modulator and a narrow band spectral filter. The laser routinely delivers highly chirped pulses with more than 38 nJ energy that can be compressed down to 700 fs duration using bulk gratings. Numerical simulations confirm the experimental results and reveal the self-similar pulse evolution along the normal dispersion fibers included inside the cavity.

We report on a passively mode-locked neodymium-doped oscillator featuring a W-type fiber operating at 930 nm. Two different laser configurations with and without dispersion management are investigated to generate high-energy similaritons. Chirped pulses with 2.2 nJ energy that can be compressed to 126 fs are generated in the dispersion-managed cavity. The ANDI-fiber laser delivers parabolic pulses with 5.2 ps duration that can be compressed to 146 fs.

The development of laser-assisted atom probes makes it possible, in principle, to exploit the femtosecond laser pulse not only for triggering ion evaporation from a nanometric field emission tip, but also for generating photons via the radiative recombination of electron-hole pairs in tips made of dielectric materials. In this article we demonstrate a first step towards a correlation of micro-photoluminescence (μ-PL) and laser-assisted tomographic atom probe (LA-TAP) analysis applied separately on the same objects, namely on ZnO microwires. In particular, we assess that the use of the focused ion beam (FIB) tip preparation method significantly degrades the radiative recombination yield of the analyzed microwires. We discuss the strategies to avoid the FIB-induced damage on the optical properties of the sample and how to get beyond the correlated μ-PL and LA-TAP analysis with a coupled approach allowing to perform the two analyses within the same instrument., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Performance scaling of passively mode-locked ultrashort-pulse fiber oscillators in terms of average power, peak power, and pulse energy is demonstrated. A very-large-mode-area fiber laser in an all-positive group-velocity-dispersion ring cavity configuration with intracavity spectral filter, mode-locked by nonlinear polarization evolution, emits 66 W of average power at 76 MHz repetition rate, corresponding to 0.9 μJ pulse energy. The pulses are dechirped to 91 fs outside the cavity with an average power of 60 W remaining after the compressor. The generated pulse peak power is as high as 7 MW.

We report on the generation of high-energy pulses in an all normal dispersion photonic-crystal fiber laser. Two mode-locking techniques with and without passive spectral filtering are studied both numerically and experimentally to address a roadmap for energy scaling. It is found that high-contrast passive modulation is a very promising mode-locking technique for energy scaling in dissipative-soliton laser. Moreover, this technique does not need any additional spectral filtering than the limited gain bandwidth to stabilize high-energy ultrashort pulses. The presented laser generates 110 nJ chirped pulses at 57 MHz repetition rate for an average power of 6.2 W. The output pulses could be dechirped close to the transform-limited duration of 100 fs.

We report on high-energy femtosecond pulse generation from an ytterbium-doped rod-type fiber oscillator emitting around 976 nm. Self-starting and stable single-pulse operation are demonstrated with 4.2 W of average output power at a repetition rate of 8.4 MHz. The resulting energy level reaches 0.5 μJ. Because of the all-normal dispersion of the laser cavity, output pulses are naturally chirped with a duration of 14 ps. External compression using diffraction gratings shortens the pulse duration down to 460 fs., (© 2011 Optical Society of America)

We report on a passively mode-locked fiber laser emitting around 976nm. The self-starting mode locking is achieved in an unidirectional ring cavity by means of nonlinear polarization evolution. Stable single-pulse operation is observed for 480mW of average output power. This all-normal dispersion laser generates naturally chirped pulses with 1ps duration. The repetition rate is 40.6MHz, resulting in 12nJ pulse energy. External compression using bulk grating shortens the pulse duration down to 286fs.

We report the generation of high-energy high-peak power pulses in an all-normal dispersion fiber laser featuring large-mode-area photonic crystal fibers. The self-starting chirped-pulse fiber oscillator delivers 11 W of average power at 15.5 MHz repetition rate, resulting in 710 nJ of pulse energy. The output pulses are dechirped outside the cavity from 7 ps to nearly transform-limited duration of 300 fs, leading to pulse peak powers as high as 1.9 MW. Numerical simulations reveal that pulse shaping is dominated by the amplitude modulation and spectral filtering provided by a resonant semiconductor saturable absorber.

We report on high-energy ultrashort pulse generation from an all-normal-dispersion large-mode-area fiber laser by exploiting an efficient combination of nonlinear polarization evolution (NPE) and a semiconductor-based saturable absorber mode-locking mechanism. The watt-level laser directly emits chirped pulses with a duration of 1 ps and 163 nJ of pulse energy. These can be compressed to 77 fs, generating megawatt-level peak power. Intracavity dynamics are discussed by numerical simulation, and the intracavity pulse evolution reveals that NPE plays a key role in pulse shaping.

We report the generation of sub-150 fs pulses from a passively mode-locked laser featuring a large-mode-area microstructure fiber. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser generates 63 nJ chirped pulses at 22 MHz repetition rate for an average power of 1.4 W. The 2.2 ps output pulses are compressed outside the cavity to 150 fs.

We report on a mode-locked fiber laser featuring an Yb-doped large-mode-area Bragg fiber and exploiting dissipative-soliton pulse shaping. Reliable self-starting mode-locking is achieved using a fast semiconductor saturable absorber mirror. The laser generates 30 nJ chirped pulses at 17 MHz repetition rate for an average power of 510 mW. The 3.2 ps output pulses are compressed outside the cavity to 440 fs.

We report on ultrashort pulse generation from a passively mode-locked erbium fiber laser operating in the highly positive dispersion regime. Highly-chirped pulses with 5.3 ps duration and spectral bandwidth of 8.3 nm are generated. They are extra-cavity compressed down to 757 fs. Numerical simulations confirm the experimental results and show that these pulses could be interpreted as dissipative solitons.

The generation of high-power and stable ultra-short pulses from a passively mode-locked purely normal dispersion fiber laser is reported using the unique combination of a photonic crystal fiber featuring single-polarization, single-mode, and low nonlinearity with a high modulation depth semiconductor saturable absorber mirror. The environmentally-stable, self-starting fiber laser generates 1.6 W of average power at a repetition rate of 63 MHz, corresponding to a pulse energy of 25 nJ. The emitted pulses are positively chirped with a pulse duration of 3.7 ps. They are compressible down to a near transform-limited duration of 750 fs. Numerical simulations are in good agreement with the experimental results.

We report on an all-normal-dispersion mode-locked fiber laser based on a large-mode-area Yb-doped microstructure fiber and using a high nonlinear modulation depth semiconductor saturable absorber mirror. The laser delivers 3.3 W of average output power with positively chirped 5.5 ps pulses at a center wavelength of 1033 nm. The pulse repetition rate is 46.4 MHz, which results in an energy per pulse of 71 nJ. These pulses are extracavity dechirped down to 516 fs by using bulk gratings. The average power of the dechirped pulses is 2.3 W, which corresponds to a peak power of more than 96 kW.

We report on a mode-locked high energy fiber laser operating in the dispersion compensation free regime. The sigma cavity is constructed with a saturable absorber mirror and short-length large-mode-area photonic crystal fiber. The laser generates positively-chirped pulses with an energy of 265 nJ at a repetition rate of 10.18 MHz in a stable and self-starting operation. The pulses are compressible down to 400 fs leading to a peak power of 500 kW. Numerical simulations accurately reflect the experimental results and reveal the mechanisms for self consistent intracavity pulse evolution. With this performance mode-locked fiber lasers can compete with state-of-the-art bulk femtosecond oscillators for the first time and pulse energy scaling beyond the muJ-level appears to be feasible.

On the basis of numerical simulations, we explain the formation of the stable bound soliton pairs that were experimentally reported in a high-power mode-locked ytterbium fiber laser [Opt. Express 14, 6075 (2006)], in a regime where wave-breaking-free operation is expected. A fully vectorial model allows one to rigorously reproduce the nonmonotonic nature for the nonlinear polarization effect that generally limits the power scalability of a single-pulse self-similar regime. Simulations show that a self-similar regime is not fully obtained, although positive linear chirps and parabolic spectra are always reported. As a consequence, nonvanishing pulse tails allow distant stable binding of highly-chirped pulses.

The polarization properties of single-mode optical fibers are theoretically modeled with use of the Jones formalism. The fiber is described as an elliptical birefringent plate. The properties predicted by this model are discussed and lead to the development of a simple experimental method to extract the parameters that describe a real fiber. A magneto-optic method that measures the beat length of the fiber is also presented and gives a more complete description of the fiber. The validity of the model is then clearly established. Finally, the wavelength dependence of the parameters characteristic of the fiber is experimentally investigated.