Amplification Of Femtosecond Pulses Research Articles

Direct amplification of ultrashort pulses in μ-pulling-down Yb:YAG single crystal fibers

We demonstrated that Yb:YAG single crystal fibers have a strong potential for the amplification of femtosecond pulses. Seeded by 230 fs pulses with an average power of 400 mW at 30 MHz delivered by a passively mode-locked Yb:KYW oscillator, the system produced 330 fs pulses with an average power of 12 W. This is the shortest pulse duration ever produced by an Yb:YAG amplifier. The gain in the single crystal fiber reached a value as high as 30 in a simple double-pass configuration.

High power femtosecond chirped pulse amplification in large mode area photonic bandgap Bragg fibers

We report on high power amplification of femtosecond pulses in 40-μm core diameter Yb-doped photonic bandgap Bragg fibers. The robustness to bending and transverse spatial behavior of these fibers is analyzed through simulations. The fibers are used in both stages of a moderately stretched (150 ps) femtosecond chirped pulsed amplification (CPA) system. A compressed average power of 6.3 W is obtained using a low-index polymer-coated Bragg fiber with excellent beam quality and high efficiency, in agreement with numerical simulations. The use of an air-clad Bragg fiber allows us to scale the output power to 47 W at a repetition rate of 35 MHz. This experiment demonstrates the great potential of Bragg fibers to increase the mode area and the power of practical bending-tolerant femtosecond fiber systems.

Femtosecond pulse generation and amplification in Yb-doped fibre oscillator-amplifier system

In recent times ytterbium (Yb) doped fibre-based mode-locked master oscillator and power amplifier have attracted a great deal of interest because of their inherent advantages like flexibility, reliability, compactness, high power handling capability and diffraction limited output beam quality as compared to the solid-state counterpart. But, to successfully develope of high-power femtosecond oscillator-amplifier system based on Ybdoped fibre, an appropriate choice of the mode-locking regime and the amplifier geometry are required. Development of an all-fibre integrated high-power Yb-doped fibre oscillator-amplifier system in which the advantages of a fibre-based system can be fully exploited remained a challenge as it requires the careful optimization of dispersion, nonlinearity, gain and ASE contribution.

High-gain fiber, optical-parametric, chirped-pulse amplification of femtosecond pulses at 1 μm

Fiber-based optical-parametric chirped-pulse amplification is reported at 1μm in a microstructured fiber in the femtosecond regime. The signal has been highly stretched by an Öffner triplet and then amplified with an all-fiber, pulsed-pump, fiber optical-parametric amplifier. More than 30dB gain has been achieved over 8.3nm, and the amplified signal has been recompressed.

High gain broadband amplification of ultraviolet pulses in optical parametric chirped pulse amplifier

We report on a high gain amplification of broadband ultraviolet femtosecond pulses in an optical parametric chirped pulse amplifier. Broadband ultraviolet seed pulses were obtained by an achromatic frequency doubling of the output from a femtosecond Ti:Sapphire oscillator. Stretched seed pulses were amplified in a multipass parametric amplifier with a single BBO crystal pumped by a ns frequency quadrupled Nd:YAG laser. A noncollinear configuration was used for a broadband amplification. The total (after compression) amplification of 2.510(5) was achieved, with compressed pulse energy of 30 microJ and pulse duration of 24 fs. We found that the measured gain was limited by thermal effects induced by the absorption of the pump laser by color centers created in the BBO crystal.

Amplification of Ultraviolet Femtosecond Pulse by a Micro-Pulling Down Method-Grown Ce:LiCAF Crystal in a Prismatic Cell-Type, Side-Pumping Configuration

We propose an efficient side-pumping scheme for ultraviolet (UV) femtosecond pulse amplification in micro-pulling-down (µPD) method-grown Ce:LiCAF using a prismatic cell-type configuration. By uniformly illuminating four sides of a 2-mm-diameter and 30-mm-length Brewster-cut, nearly as-grown crystal, the risk of damage is dramatically reduced. Without using a chirp pulse amplifier scheme, UV femtosecond pulse at 290 nm is amplified 4 times with no significant increase to its pulse duration and B-integral. Our results show that a laser-quality, Ce:LiCAF crystal, efficiently grown by the µPD method and pumped in a prismatic-cell type configuration paves new possibilities in providing high energy UV femtosecond pulses.

Direct Amplification of Femtosecond Pulses in Ytterbium-Doped Fiber Amplifiers

We review three experiments of direct femtosecond pulse amplification in ytterbium-doped fiber amplifiers under increasingly nonlinear propagation conditions, starting from the parabolic regime. The temporal quality of generated compressed pulses is analyzed using frequency-resolved optical gating measurements. Linear or nonlinear compensation of third-order spectral phase allows the generation of clean sub-70 fs pulses with energies in the range of 100 nJ–1 μJ, at repetition rates above 10 MHz.

Optimized amplification of femtosecond optical pulses by dispersion management for octave-spanning optical frequency comb generation

We report a method for optimizing the amplification of femtosecond optical pulses by using dispersion management. The amount of dispersion provided to the seed optical pulse of an erbium-doped fiber (EBF) has an optimal region that enhances the output power of an amplifier. The power enhancement is accompanied by spectral broadening, which originates from adiabatic narrowing in the erbium-doped fiber. The amplified optical pulses can be used to generate an octave-spanning optical frequency comb (OFC) by employing a highly nonlinear fiber (HNLF).

Stretcher-free high energy nonlinear amplification of femtosecond pulses in rod-type fibers

We report on the study of direct amplification of femtosecond pulses in an 80 mum core diameter microstructured Yb-doped rod-type fiber amplifier in the nonlinear regime. The system includes a compact single grating compressor for the compensation of the small dispersion in the amplifier. With a 1250 line/mm (l/mm) grating-based compressor, pulses as short as 49 fs with 870 nJ pulse energy and 12 MW peak power are obtained. Alternatively, the use of a 1740 l/mm grating allows the production of higher quality pulses of 70 fs, 1.25 microJ pulse energy, and 16 MW peak power.

RAMAN AMPLIFICATION AND SUPERLUMINAL PROPAGATION OF ULTRAFAST PULSES BASED ON LOOP SILICON WAVEGUIDES: THEORETICAL MODELING AND PERFORMANCE

In this paper, we report, for the first time to the best of our knowledge, the detailed modeling and performance of Raman amplification and superluminal propagation of weak ultrafast femtosecond optical pulses in nonlinear loop single mode silicon-oninsulator anomalously dispersive optical waveguides. Using the device, theoretical results for 100-fs signal optical pulse show that when the launch peak power of signal pulse is fixed at −10 dBm, the gain value up to 30 dB can be achieved, and the delay time of superluminal propagation can also be adjusted by changing the system parameters, including initial chirp and peak power of pump pulse, initial delay time between pump and signal pulses, and waveguide length, etc.

The Nonlinear Ellipse Rotation in BK7 Glass Plate and its Application

The intensity-dependent nonlinear ellipse rotation of high-energy femtosecond pulse in BK7 glass plate is researched experimentally. The polarization, spectrum and shape of the femtosecond pulse were studied in this process. Based on this scheme, we develop a pulse temporal cleaner, which has been used in our femtosecond chirped pulse amplification (CPA) laser to provide a contrast ratio improvement of 2 orders of magnitude for the milli-joule level fs input pulses. The total transmission efficiency of the cleaner reaches 16.7%.

Impact of pumping configuration on all-fibred femtosecond chirped pulse amplification

We experimentally compared the co- and counter-propagative pumping scheme for the amplification of ultra-short optical pulses. According to pumping direction we show that optical pulses with a duration of 75 fs and 100mW of average output power can be obtained for co-propagative pumping, while pulse duration is never shorter than 400 fs for the counter-propagative case. We show that the impact of non-linear effects on pulse propagation is different for the two pumping configurations. We assume that Self Phase Modulation (SPM) is the main effect in the copropagative case, whereas the impact of Stimulated Raman Scattering is bigger for the counter-propagative case.

Amplification of kW peak power femtosecond pulses in single quantum well InGaAs tapered amplifiers

The amplification of ps and fs pulses with peak powers of up to 4.5kW has been investigated in a single quantum well InGaAs tapered amplifier. The pulses with durations of 100fs or 2ps were generated by a modelocked titanium–sapphire laser. The amplified pulses indicate strong gain saturation and carrier generation due to photon absorption in the laser active region which causes a temporal broadening of the amplified pulses as well as modifications of the optical spectrum. The gain recovery time was measured by a pump–probe experiment. The experimental results are analyzed with respect to the sub-ps gain dynamics which is described by a relaxation time approximation.

Optimum conditions for stimulated Raman scattering, compression, and amplification of supershort pulses in a plasma with compressed gases

This paper discusses features of the process of stimulated Raman scattering for the amplification and compression of femtosecond pulses. The main regularities of the process are analyzed, negative factors that reduce the energy-pumping efficiency are explained, and the optimum conditions of the process for obtaining the greatest energy-conversion efficiency are determined.

GARPUN-MTW: A hybrid Ti:Sapphire/KrF laser facility for simultaneous amplification of subpicosecond/nanosecond pulses relevant to fast-ignition ICF concept

The first stage of the petawatt excimer laser project started at the P.N. Lebedev Physical Institute, implements a development of multiterawatt hybrid GARPUN-MTW laser facility for generation of ultra-high intensity subpicosecond ultraviolet (UV) laser pulses. Under this project, a multi-stage e-beam-pumped 100-J, 100-ns GARPUN KrF laser was upgraded with a femtosecond Ti:Sapphire front-end, to produce combined subpicosecond/nanosecond laser pulses with variable time delay. Attractive possibility to amplify simultaneously short and long pulses in the same large-scale KrF amplifiers is analyzed with regard to the fast-ignition, inertial confinement fusion problem. Detailed description of hybrid laser system is presented with synchronized KrF and Ti:Sapphire master oscillators. Based on gain and absorption measurements at GARPUN amplifier and numerical simulations with a quasi-stationary code, we are predicting that 1.6 J can be obtained in a short pulse at hybrid GARPUN-MTW Ti:Sapphire/KrF laser facility, combined with several tens of joules in nanosecond pulse. Amplified spontaneous emission, which is responsible for the pre-pulse formation on a target, was also investigated: its acceptable level can be provided by properly choosing staged gain or loading the amplifiers by quasi-steady laser radiation. Fluorescence and transient absorption spectra of Ar/Kr/F2 mixtures conventionally used in KrF amplifiers were recorded to find out the possibility for femtosecond pulse amplification at the broadband Kr2F (42Γ → 1,2 2Γ) transition, which benefits in 100 times higher saturation energy density than for KrF (B → X) transition.

Chirped-pulse amplification near the gain-narrowing limit of Yb-doped fiber using a reflection grism compressor

We report a numerical and experimental study of chirped-pulse amplification of femtosecond pulses near the gain narrowing limit of Yb-doped fiber. We show that a strongly inhomogeneous lineshape provides a good description of pulse amplification in the linear regime (nonlinear phase shift ΦNL<1). Compensation of second- and third-order dispersion using a high-efficiency reflection grism compressor is demonstrated in a fiber chirped-pulse amplification system. A Fourier-transform-limited pulse duration of 120 fs is obtained for the highest achieved gain (23 dB).

Complete ground state gain recovery after ultrashort double pulses in quantum dot based semiconductor optical amplifier

Gain recovery dynamics are studied in electrically pumped quantum dot (QD) based semiconductor optical amplifiers (SOAs) after amplification of double femtosecond laser pulses using ultrafast pump-probe spectroscopy with heterodyne detection. The authors observe a distinct change in gain recovery in the ground state when a significant excited state population is achieved. A complete gain recovery is found when two 150fs pulses with 5ps time delay pass through the SOA in resonance to the ground state under high injection currents of 80–100mA. The obtained results open the way for ultrafast (&amp;gt;200GHz) operation in p-doped QD based SOAs at 1.3μm telecommunications wavelengths.

Femtosecond pulse amplification by a two-photon arranged photorefractive amplifier

Femtosecond pulse amplification by a two-photon arranged photorefractive amplifier (TAPA) has been demonstrated. A gain bandwidth of 32 THz has been achieved with an extraction efficiency of 27 %.

Simultaneous pulse amplification and compression in all-fiber-integrated pre-chirped large-mode-area Er-doped fiber amplifier

A large-mode-area Erbium-doped fiber amplifier (LMA-EDFA) based all-fiber-integrated amplified compressor with ultrashort length of 5.37 m and ultralow pumping power (260 mW) is proposed. The LMAEDFA suppresses nonlinear soliton-self-frequency-shift effect happened during femtosecond pulse amplification, in which the fiber laser pulse is reshaped to a low-pedestal hyperbolic-second shape with nearly 100% energy confinement. The pre-chirped amplification from 0.96 to 104 mW and the simultaneous compression of a passively mode-locked fiber laser pulse from 300 to 56 fs is demonstrated. The input pulse energy of 24 pJ is amplified up to 2.6 nJ with shortened pulsewidth of 56 fs and peak power as high as 46 kW.

High-efficiency wide-band metal-dielectric resonant grating for 20 fs pulse compression

More than 95% average efficiency TE-polarisation diffraction over a 200 nm wavelength range centred at 800 nm is obtained by a metal-dielectric grating structure with non-corrugated mirror. 98% maximum -1st order diffraction efficiency and a wide band top-hat spectrum are demonstrated experimentally opening the way to high-efficiency Chirped Pulse Amplification of femtosecond pulses as short as 20 fs.