Amplification Of Femtosecond Pulses Research Articles

Femtosecond pulse amplification at 1770 nm using thulium- and terbium-doped fluoride fibers

Femtosecond pulse amplification at 1770 nm using thulium- and terbium-doped fluoride fibers

Amplification of femtosecond pulses with AI-assisted spectral phase modulation

We report our investigation on ultrashort laser pulse optimization using an AI algorithm in a system consisting of a mode-locked oscillator, a spectral phase shaper, and a highly nonlinear amplifier. We analyzed the performance of the pulse optimization process as a function of two main parameters: the resolution of spectral phase modulation and the number of agents in the algorithm. We showed that the algorithm could find an optimum phase profile for the seed pulse, which allowed for a reduction of the FWHM of the amplified pulse by 10 fs (from 46 to 36 fs), and significantly reduced the intensity of the side-pulse by a factor of 4.6. Importantly, the algorithm used does not require any training and optimizes the pulse shape without any knowledge about the input pulse parameters or the parameters of the amplifier. We believe the proposed system might be a convenient test bed for evaluating various AI-based algorithms in a pulse optimization task.

Design of a large-mode-area tapered fiber amplifier for amplification of ultrashort laser pulses at 1535 nm wavelength

We design a W-type large-mode-area erbium doped tapered fiber with effective mode area varying from 1770 µm2 to 840 µm2with tolerance ± 0.0005 in refractive indices of different layers of fiber. The beam quality of the pulses is ensured by effective single-mode operation. We investigate the amplification of high power femtosecond pulses in this fiber by using nonlinear Schrodinger equation including gain term. It is solved using split-step Fourier method for both up-tapered (effective mode area increasing along the length) and down tapered (effective mode area decreasing along the length) fiber configurations at centered around 1535 nm wavelength. In both configurations of fiber, input pulse parameters like peak power, pulse width, and fiber length are calculated for maximum amplification with the least amount of pulse shape distortion. In down-tapered configuration, we numerically demonstrate the amplification of 1 kW peak power, 560 fs duration pulse to 3.6 MW peak power, 12 fs amplified pulse. In up-tapered configuration, we obtain the amplification of 2 kW, 565 fs input pulse to ∼7.9 MW peak power, ∼11 fs pulse. The fiber is useful for amplifying high-power laser pulses, and the resulting pulses can be used for laser processing, spectroscopy, and remote sensing.

High efficient optical parametric amplification of femtosecond pulses in MgO doped PPLN crystals at 3.4 µm

High efficient optical parametric amplification of femtosecond pulses in MgO doped PPLN crystals at 3.4 µm

High average power amplification of femtosecond pulses based on the Yb:CaYAlO4 crystal.

In this paper, we demonstrated the direct amplification of femtosecond pulses with the Yb:CaYAlO4 crystal for the first time. A compact and simple two-stage amplifier delivered amplified pulses with the average powers of 55.4 W for σ-polarization and 39.4 W for π-polarization at the center wavelengthes of 1032 nm and 1030 nm, corresponding to 28.3% and 16.3% optical-to-optical efficiencies, respectively. These are to the best of our knowledge the highest value achieved with a Yb:CaYAlO4 amplifier. Upon using a compressor consisting of prisms and GTI mirrors, a pulse duration of 166-fs was measured. Thanks to the good thermal management, the beam quality (M2) parameters <1.3 along each axis were maintained in each stage.

Amplification of femtosecond pulses based on χ(3) nonlinear susceptibility in MgO.

We experimentally demonstrate large, widely tunable gain using Kerr instability amplification in MgO. By pumping the crystal near optical damage at 1.4×1013W/cm2 by a femtosecond Ti:sapphire laser, we amplify visible and near-infrared pulses by factors >5000 or a gain g≈17/mm. We temporally characterize the pulses to show that they are 42 fs in duration, much shorter than the pump pulse. In the non-collinear setup, the angle between the pump and seed selects the amplified wavelength, where we find certain angles amplify both the visible and near-infrared simultaneously. We find that near the maximum pumping intensities, higher-order nonlinearities may play a role in the amplification process.

High-power ultrafast thin-disk multipass amplifiers for efficient laser-based manufacturing

Abstract Thin-disk multipass amplifiers represent one of the most powerful approaches to scale the average and peak powers of ultrafast laser systems. The present paper presents the amplification of picosecond and femtosecond pulses to average powers exceeding 2 and 1 kW, respectively. Second-harmonic generation in lithium-triborate crystals with powers higher than 1.4 kW and 400 W at a wavelength of 515 nm with picosecond and femtosecond pulse durations, respectively, are also reported. Furthermore, third-harmonic generation was demonstrated with output powers exceeding 250 W at a wavelength of 343 nm. Finally, processing of silicon, metals, and polycrystalline diamond with fs pulses at an average power of 1 kW is presented to demonstrate removal rates that are improved by orders of magnitude as compared to state-of-the-art techniques.

Amplification of femtosecond and picosecond pulses using large mode area Erbium-doped fiber at 1530 nm wavelength

We present amplification of short and ultrashort laser pulses at 1530-nm center wavelength using a large mode area Er-doped fiber (LMA-EDF). The mode area of about 1700 μm2 tremendously increases the power handling capacity of the fiber and helps in achieving up to ∼ 17 dB/m gain with 10 W power of 980-nm wavelength pump. The LMA fiber used here is a 3-layer W-type fiber designed to have effective single mode operation with higher order mode discrimination and sufficient mode spacing between the first few modes to avoid any possible mode coupling. In particular, we numerically demonstrate the amplification of 300 fs, 1 kW peak power pulses to ∼ 20 fs, ∼2.6 MW peak power pulses in 1.5-m propagation distance, and of 50 ps, 1 kW peak power pulses to ∼ 65 ps, ∼26 MW peak power pulses in 3-m propagation distance of the LMA-EDF. The generated pulses would be useful in applications such as eye-safe remote sensing and 3D laser processing of silicon.

Ytterbium laser system for studying parametric amplification of femtosecond pulses with a centre wavelength of ∼2 μm

A laser system is developed with an optical synchronisation of a femtosecond signal with a pump channel. The signal of a driving ytterbium fibre laser with a 60 MHz repetition rate of stretched femtosecond pulses is amplified in energy from several nanojoules to 0.4 mJ at a pulse repetition rate of 3 kHz in a wideband amplifier and then is compressed in time to 250 fs. The obtained radiation is used for generating femtosecond laser pulses with a centre wavelength of ∼2 μm, pulse energy of above 20 μJ, duration of several field oscillations, and phase stabilisation between the electromagnetic field and envelope. The other pulse of the driving fibre laser provides optical synchronisation and a minimal time delay and is directed to a regenerative Yb : YAG disk amplifier for amplification to an energy of 4 mJ at a pulse repetition rate of 3 kHz and duration of 20 ps. A multipass disk amplifier is developed for further increasing the energy of pump chirped pulses to an energy of 70 mJ at a pulse repetition rate of 10 Hz and duration of 400 ps for studying parametric amplification under sub-nanosecond pumping.

Coherent power amplification of third-order harmonic femtosecond pulses at thin-film up-conversion nanoparticles

Third harmonic generation (THG) is a nonlinear optical process attractive in high-resolution interfacial studies, sub-wavelength light manipulation, and bio-molecular detection due to its capability of converting low-energy quanta into a quantum of a higher energy. One of the limitations in utilizing THG is its low power conversion efficiency; thus, various THG enhancement methods have been researched by involving plasmonic coupling effects or utilizing electric band gap resonances at quantum dots or two-dimensional materials. Meanwhile, lanthanide ion-doped up-conversion nanoparticles (UCNPs) can be excited by a multi-photon process similar to THG, but its interaction or resonance with THG has not been studied to date. In this Communication, we demonstrate the first coherent amplification of third-order harmonic femtosecond pulses at multi-layered UCNP thin-film with an amplification factor of 7.8. This amplification is made by the resonance interaction of incident femtosecond laser field, generated third-order harmonics, and the electric band gaps of UCNPs. The power contribution of the third-order harmonic and the up-conversion luminescence (UCL) is strongly dependent on the sample geometry due to the reabsorption effect. For in-depth understanding of the emission characteristics, spectral-domain, time-domain, radio-frequency (RF) domain, and polarization-dependence analysis were addressed. This coherent amplification of third harmonic (TH) at UCNP thin-films enables us to attain higher power, shorter wavelength, and ultra-short femtosecond pulses generated from a simple thin-film structure near to the target samples, which will pave a way to an ultrafast short-wavelength laser platform for material characterization, sub-wavelength photonics, and biomolecular detection.

Femtosecond tuning dynamics of organic amplifiers based on injection into DFB resonators of slant gratings

We report regenerative amplification of femtosecond laser pulses locked by injection of supercontinuum spectrum into a distributed feedback (DFB) microcavity constructed by slant gratings. Destroying the symmetry of the DFB resonance modes about the normal injection, the slant grating not only enabled concentration of the energy amplification on single modes, but also facilitate continuously tuning of the amplification in a broad band. The injection has locked efficiently the amplification spectrum, the transverse mode and the direction of the output beam, as well as the pulse length. In-plane amplification using a thin-film DFB device and injection locking supplies an important approach to produce high-quality ultrashort-pulsed laser beam from organic semiconductors. Advantages of injection-locked amplification techniques are also largely extended.

Yb:CALYO-based femtosecond chirped pulse regenerative amplifier for temporally resolved pump-probe spectroscopy

Diode-pumped femtosecond chirped pulse regenerative amplifiers based on Yb3+-materials are of practical importance for wide range of scientific, industrial and biomedical applications. The aim of this work was to study the amplification of broadband chirped femtosecond pulses in regenerative amplifier based on Yb3+:CaYAlO4crystal.Such systems use femtosecond mode-locked lasers as seed pulse sources and amplify nJ-seed pulses to sub-mJ energy range. Most chirped pulse regenerative amplifier systems described in the literature use seed lasers with typical pulse spectral width at the level of 10–15 nm full width at half maximum (FWHM) that limit the seed pulse duration of about 90 fs and amplified pulse duration at the level of 200 fs due to strong influence of gain narrowing effect on the amplified pulse parameters. Yb3+-doped crystals with wide and smooth gain bandwidth as an active medium of chirped femtosecond pulse regenerative amplification systems allow to reduce negative contribution of gain narrowing effect and lead to shortening of amplified pulses. In this research we study the chirped pulse regenerative amplification of broad-band femtosecond pulses (60 nm spectral width FWHM) in the Yb3+:CaYAlO -based chirped pulse regenerative amplifier. Substantial reduction of the amplified pulse duration down to 120 fs (19.4 nm spectral width FWHM) with average power of 3 W at 200 kHz pulse repetition frequency was demonstrated without any gain narrowing compensation technique.The results of experimental investigation of broad-band seeded Yb3+:CaYAlO -based chirped pulse regenerative amplifier are reported for the first time to our knowledge. 120 fs-pulses (19.4 nm FWHM) with average output power of 3 W were demonstrated without any gain narrowing compensation technique. Despite the significant reduction of amplified pulse duration the task of improvement group velocity dispersion balance (including high orders of group velocity dispersion) remains relevant.

Shaping and amplification of wavelength-tunable mid-infrared femtosecond pulses generated by intra-pulse difference-frequency mixing with spectral focusing

Mid-infrared (MIR) laser pulses ranging from 2 to 2.5 μm are generated from a single supercontinuum (SC) pulse by intra-pulse difference-frequency mixing (DFM) with a spectral focusing scheme (SF-DFM). By controlling the spectral phase of the SC pulse with a 4f-pulse shaper utilizing a liquid crystal spatial light modulator, SF-DFM enables us to vary the center wavelength, the bandwidth, and the pulse shape of MIR laser pulses, which are amplified by an optical parametric amplifier using a periodically poled LiNbO3 crystal.

Generation and subsequent amplification of few-cycle femtosecond pulses from a picosecond pump laser

Using a new approach, in which generation of femtosecond pulses as short as a few field cycles is implemented directly from the radiation of a picosecond pump laser, pulses with the microjoule energy, the repetition rate 10 kHz, and the duration less than 26 fs are generated in the spectral range 1.3 − 1.4 μm. In the process of generating this radiation, use was made of a method providing passive phase stabilisation of the carrier oscillation of the electromagnetic field and its slow envelope. The radiation spectrum was converted into the range of parametric amplification in the BBO crystal by the broadband second harmonic generation; the pulse was parametrically amplified up to the microjoule level and compressed by chirped mirrors to a duration of 28 fs.

Light amplification by seeded Kerr instability.

Amplification of femtosecond laser pulses typically requires a lasing medium or a nonlinear crystal. In either case, the chemical properties of the lasing medium or the momentum conservation in the nonlinear crystal constrain the frequency and the bandwidth of the amplified pulses. We demonstrate high gain amplification (greater than 1000) of widely tunable (0.5 to 2.2 micrometers) and short (less than 60 femtosecond) laser pulses, up to intensities of 1 terawatt per square centimeter, by seeding the modulation instability in an Y3Al5O12 crystal pumped by femtosecond near-infrared pulses. Our method avoids constraints related to doping and phase matching and therefore can occur in a wider pool of glasses and crystals even at far-infrared frequencies and for single-cycle pulses. Such amplified pulses are ideal to study strong-field processes in solids and highly excited states in gases.

Optimisation of the parameters of a broadband multibeam-pumped optical parametric amplifier

We report the results of the numerical simulation of the output amplifier stage of a high-power laser system based on parametric amplification of femtosecond pulses in an LBO crystal under multibeam pumping. A technique is described for choosing an optimal amplifier configuration with an arbitrary number of pump beams to provide a wide spectral gain band with a minimum loss due to parametric diffraction. The results of simulating the parametric amplification, amplification efficiency, and spatial profile of amplified radiation with allowance for the interference of amplified parasitic beams are presented. A possibility of eliminating the spatial modulation of the amplified radiation intensity, which occurs when using spatial filters, is demonstrated. An increase in the number of pump beams is found to rise the amplified pulse duration, slightly (from 20 to 21 fs) for incoherent pump beams and more significantly (to 25 fs) for coherent beams. The amplification efficiency is reduced from 23% to 21% in the former case and to 11% in the latter case.

Optimization of a multibeam-pumped optical parametric amplifier.

The results of numerical simulation of the output amplifier cascade of a powerful laser system based on the parametric amplification of femtosecond pulses in an LiB3O5 crystal with multiple beams pumping are presented. The improved technique for choosing pump beam angles with minimal parasitic amplification is presented. Differences of carrier-resolving versus envelope simulations are discussed. Results for pulse energy, duration, and fraction of parasitic energy are presented. It has been established that with an increase in the number of pump beams up to 11 beams, the duration of the amplified pulse increases insignificantly from 20 to 21fs in the case of incoherent pumping beams and increases to 26fs in the case of coherent ones. At the same time, the amplification efficiency decreases from 23% to 21% in the first case and drops to 10% in the second case. Influence of small-scale, self-focusing of the pump field interference pattern on peak intensity is discussed.

Fe2+-doped CdSe single crystal: growth, spectroscopic and laser properties, potential use as a 6 µm broadband amplifier

We report on the successful growth of single crystals of Fe2+:CdSe by seeded physical vapor transport (SPVT) technique with doping within the growing process and subsequent annealing in Se vapor. Luminescence lifetime measurements, spectroscopic studies of 5E–5T2 transition of Fe2+ in CdSe, and laser experiments were performed. The lifetime of the 5T2 energy level was measured to be 20 ± 5 ns at a room temperature (RT) of 290 K. At liquid nitrogen (LN) temperature, luminescence kinetics displayed a non-exponential decay, which can be fitted to a bi-exponential function with time constants τ1 = 6 µs and τ2 = 29 µs. As much as 3.2 mJ of output energy at 5.2 µm with 27% absorbed pump energy slope efficiency of an Fe2+:CdSe laser was achieved at RT under 2.94 µm nanosecond Er:YAG laser pumping. The Fe2+:CdSe laser was tuned from 4.63 to 6.10 µm. Obtained characteristics of Fe2+:CdSe indicate that the crystal can be considered a promising medium for amplification of femtosecond pulses in the middle infrared range up to 6 µm.

Self-frequency-shifted solitons in a polarization-maintaining, very-large-mode area, Er-doped fiber amplifier.

We demonstrate soliton self-frequency-shifted, femtosecond-pulse amplification in a newly-developed, polarization-maintaining, Er-doped, very-large-mode-area fiber amplifier. The PM-VLMA Er fiber had a core diameter of 50 μm, an effective area of ~1050 μm2, and Er absorption of 50 dB/m. The measured birefringence beat length of the PM-VLMA Er fiber was 14.1 mm. The soliton wavelength could be shifted by more than 90 nm. The soliton generation process resulted in remarkably clean, 86 fs pulses with 21 nJ energy at 1650 nm and 244 kW peak power from an all-fiber, fusion spliced system without bulk-optics for pulse compression. The polarization extinction ratio of the soliton was greater than 40 dB, and the M2 was 1.1. The fully polarization-maintaining fiber laser system provides robust and stable soliton generation. Peak-to-peak variation in the soliton wavelength, measured over the course of an hour was only 0.03% and pulse energy variation was only 0.5%.

High-power all-fiber femtosecond chirped pulse amplification based on dispersive wave and chirped-volume Bragg grating.

We report a high-power all-fiber-integrated femtosecond chirped pulse amplification system operating at 1064 nm, which consists of a dispersive wave source, a fiber stretcher, a series of ytterbium-doped amplifiers and a chirped volume Bragg grating (CVBG) compressor. The dispersive wave is generated by an erbium-doped mode-locked fiber laser with frequency shifted to the 1 μm region in a highly nonlinear fiber. With three stages of ytterbium-doped amplification, the average output power is scaled up to 125 W. Through CVBG, the pulse duration is compressed from 525 ps to 566 fs, the average output power of 107 W with a high compression efficiency of 86% is achieved, and the measured repetition rate is 17.57 MHz, corresponding to the peak power of 10.8 MW.