Energy Ultrashort Pulses Research Articles

A simple intra-beam alignment setup for tiled grating assembly based laser pulse compressor of high energy ultrashort pulse laser systems

A simple intra-beam alignment setup for tiled grating assembly based laser pulse compressor of high energy ultrashort pulse laser systems

1.1 J Yb:YAG picosecond laser at 1 kHz repetition rate.

We demonstrate the generation of 1.1 J pulses of picosecond duration at 1 kHz repetition rate (1.1 kW average power) from a diode-pumped chirped pulse amplification Yb:YAG laser. The laser employs cryogenically cooled amplifiers to generate λ=1030nm pulses with average power of up to 1.26 kW prior to compression with excellent beam quality. Pulses are compressed to 4.5 ps duration with 90% efficiency. This compact picosecond laser will enable a variety of applications that require high energy ultrashort pulses at kilohertz repetition rates.

Low energy pulse compression in hollow core fibers using hydrofluorocarbon molecular gas

Compression of low energy ultrashort laser pulses using a hollow core fiber (HCF) filled with 1-1 difluoroethane (C2H4F2), also known as R152a, is demonstrated. A 45 fs, 16 µJ Ti:Sapphire laser pulse is spectrally broadened in an HCF filled with R152a and subsequently compressed to ∼9 fs with ∼6 µJ pulse energy, which corresponds to a fivefold compression. This affordable and easily accessible gas is promising to compress new generation high average power lasers in conjunction with a flexible HCF setup. Additionally, the influence of the group velocity to the spectral broadening dispersion and its pressure dependence was numerically simulated. At pressures higher than 2.5 bar, the spectral broadening is affected by an interplay between two effects: while it is promoted by a denser gas medium leading to higher nonlinearity, it is hampered at the same time by the lower intensity resulting from the pulse stretching, which causes an overall limitation at higher pressures.

Extreme-Ultraviolet-Initated High-Order Harmonic Generation: Driving Inner-Valence Electrons Using Below-Threshold-Energy Extreme-Ultraviolet Light.

We propose a novel scheme for resolving the contribution of inner- and outer-valence electrons in extreme-ultraviolet (XUV)-initiated high-harmonic generation in neon. By probing the atom with a low-energy (below the 2s ionization threshold) ultrashort XUV pulse, the 2p electron is steered away from the core, while the 2s electron is enabled to describe recollision trajectories. By selectively suppressing the 2p recollision trajectories, we can resolve the contribution of the 2s electron to the high-harmonic spectrum. We apply the classical trajectory model to account for the contribution of the 2s electron, which allows for an intuitive understanding of the process.

Wavelength tunable, high energy femtosecond laser pulses directly generated from large-mode-area photonic crystal fiber

Wavelength tunable high energy ultrashort laser pulses are generated from a large-mode-area photonic crystal fiber in anomalous dispersion (AD) regime. A simplified laser cavity design with one fine polished facet of the fiber as a cavity mirror is used. The intra-cavity dispersion compensation is achieved by a grating pair, the spatial dispersed light from which also have optical spectrum filtering effects combined with the limited aperture of the fiber core. The laser system is able to generate ultrashort pulses ranging from 494fs (with 56nJ pulse energy) to 1.24ps (with 49nJ pulse energy) at 55MHz repetition rate. The filtering mechanism benefits the generation of high energy pulses with narrowing pulse duration in AD regime. An undulation in frequency and time domain is also observed with the increase of the pump power. Furthermore, this laser system is directly used as seed for supercontinuum generation.

Optical pulse compression of ultrashort laser pulses in a multi-hollow-core fiber

By numerical simulations and analysis, we proposed a fiber with multi-hollow-core structure for optical pulse compression of high energy ultrashort laser pulses. In this scheme, different parts of a high-energy flat-top pulse are coupled into different hollow cores of such fiber and each of the cores functions as an independent traditional hollow-core fiber compressor. After the multi-hollow-core fiber, the output beams are collimated and compressed to few-cycle level. Then they can be focused to ultra-high intensity. This method can easily be scaled to compressing pulses of large beam size with high energy without limit in principle.

One stage pulse compression at 1554nm through highly anomalous dispersive photonic crystal fiber

We demonstrate the pulse compression at 1554 nm using one stage of highly anomalous dispersive photonic crystal fibers with a dispersion value of 600 ps/nm∙km. A 1.64 ps pulse is compressed down to 0.357 ps with a compression factor of 4.6, which agrees reasonably well with the simulation value of 6.1. The compressor is better suited for high energy ultra-short pulse compression than conventional low dispersive single mode fibers.

Compositional dependence of g-factor and damping constant of (Gd100-xREx)FeCo alloy films (RE = Yb, Tm, Er)

Time domain magnetization dynamics of (Gd100-xREx)FeCo (RE = Yb, Tm, Er) alloy films with various compositions were measured by pump-probe method using a high energy ultra short pulse fiber laser, and their g-factors and damping constants were estimated. The g-factor of GdFeCo became large near the angular moment compensation point CA, which is qualitatively consistent with the simple mean field model. On the other hand, the damping constants took a maximum near magnetization compensation point, which is not described by the mean field model. Substitution of Tm or Er for Gd results in the significant increase of damping constant; (Gd90Tm10)FeCo and (Gd90Er10)FeCo exhibit roughly 3-6 times large damping constant compared to GdFeCo, while (Gd90Yb10)FeCo has almost the same damping constant as GdFeCo. This means that the damping constant is significantly modified by the orbital moment of RE atoms.

Nonlinear compression in a rod-type fiber for high energy ultrashort pulse generation

We report the use of nonlinear compression in a very large mode-area rod-type photonic crystal fiber. This fiber allows the use of high energy pulses in the few microjoule range. We demonstrate the compression of 4 microJ, 338 fs pulses from a fiber chirped pulse amplification (FCPA) system down to 49 fs, 41 MW peak power pulses at a repetition rate of 200 kHz with an average power of 400 mW. The nonlinear compression setup is composed of a 5-cm-long rod-type fiber and a pair of SF10 prisms. The system was optimized to obtain good temporal quality, with a temporal Strehl ration of 86 % for the compressed 49 fs pulses.

High energy ultrashort pulses via hollow fiber compression of a fiber chirped pulse amplification system

A simple, robust and compact pulse compressor for a high-repetition rate high-peak power fiber chirped pulse amplification system is presented. We use noble-gas-filled hollow fibers for spectral broadening of the optical pulses via self-phase modulation. Subsequent compression with chirped mirrors shortens the pulses by more than a factor of 10. Pulses shorter than 70 fs with pulse energies of the order of 100 mu J have been obtained resulting in a peak power up to 1 GW at 30.3kHz. Additionally, nonlinear polarization rotation has been used for temporal pulse cleaning during the nonlinear compression at 30.3 kHz and 100 kHz, respectively.

Characterization of near-infrared low energy ultra-short laser pulses for portable applications of laser induced breakdown spectroscopy

We report on the delivery of low energy ultra-short (<1 ps) laser pulses for laser induced breakdown spectroscopy (LIBS). Ultra-short pulses have the advantage of high peak irradiance even at very low pulse energies. This opens the possibility to use compact, rare-earth doped fiber lasers in a portable platform for point detection applications using LIBS for elemental analysis. The use of low energy ultra-short pulses minimizes the generation of a broad continuum background in the emission spectrum, which permits the use of non-gated detection schemes using very simple and compact spectrometers. The pulse energies used to produce high-quality LIBS spectra in this investigation are some of the lowest reported and we investigate the threshold pulse requirements for a number of near IR pulse wavelengths (785-1500 nm) and observe that the pulse wavelength has no effects on the threshold for observation of plasma emission or the quality of the emission spectra obtained.

High power and high energy ultrashort pulse generation with a frequency shifted feedback fiber laser

The highest average power that has been achieved with a frequency-shifted feedback modelocked fiber laser is reported. Subpicosecond pulses with 40 kW peak power are obtained by this technique for the first time by using external pulse compression. The pulsing is self starting and environmentally stable. The measured pulse energy in modelocked operation is 120 nJ. The pulses could be compressed to 855 fs. The pulse energy was increased to 1muJ with controlled Q-switched modelocking.

Optical Pulse Compression of Ultrashort Laser Pulses in an Argon-Filled Planar Waveguide

We investigate the possibility of optical pulse compression of high energy ultrashort laser pulses in an argon-filled planar waveguide, based on two level coupled mode theory and the full 3D nonlinear Schrödinger equation. We derive general expressions for controlling the spatial beam profile and the extent of the spectral broadening. The analysis and simulations suggest that the proposed method should be appropriate for optical pulse compression of ultrashort laser pulses with energies as high as 600 mJ.

Ultrashort Pulse Generation with Semiconductor Modelocked Lasers Using Saturable Absorbers Based on Intersubband Transitions in GaN/AlGaN Quantum Wells

ABSTRACTWe present a novel scheme for generating high energy ultrashort pulses in modelocked semiconductor lasers using a fast saturable absorber based upon intersubband transitions (ISBT) in GaN/AlGaN superlattice. The fast electron relaxation time (∼100–300 fs) in this saturable absorber enables the generation of stable sub-100 fs pulses at the communication wavelength (1.55μm) with high pulse energies (5–10 pJ).

Optical parametric generation of femtosecond pulses up to 9 μm with LiInS2 pumped at 800 nm

We demonstrate direct access to the 4.8–9 μm spectral region with 800 nm, 1 kHz pumping of a femtosecond optical parametric amplifier based on the wide-gap wurtzite-type LiInS2. LiInS2 did not exhibit two-photon absorption at 800 nm and seems applicable at this pump wavelength with intensities of the order of 100 GW/cm2 for down-conversion of high energy ultrashort pulses up to its mid-IR edge at ≈12 μm.