Femtosecond Chirped Pulse Research Articles

Compact 80 W, 1 MHz Femtosecond Chirped Pulse Amplification Laser System Based on a Yb-Doped Fiber and a Yb:YAG Thin Rod

We present a hybrid chirped pulse amplification (CPA) laser system based on Yb-doped fiber and Yb:YAG thin rod. The laser system demonstrates a novel approach to generate high average power up to the 100-W level by using a Yb:YAG thin rod without pump guiding at room temperature. A Yb-doped all-fiber laser with an output power of 7 W and a repetition rate of 1 MHz is amplified to an output power of 126.2 W in simple and compact two-stage amplifiers consisting of a single fiber crystal (SCF) and a Yb:YAG thin rod. To the best of our knowledge, this is the highest output power of Yb:YAG thin-rod amplifier with good beam quality obtained without pump guiding at room temperature. After using a thin-film polarizer (TFP) to remove the thermal depolarization, a linearly polarized ultrashort pulse laser with an average power of 115.2 W is obtained. An output power of 80.6 W with a pulse width of 580 fs is achieved after pulse compression. The central pulse contains 84.1% of the total pulse energy, corresponding to a pulse peak power of 116.9 MW.

Controlling the dynamics of the plasmonic field in the nano-femtosecond scale by chirped femtosecond laser pulse

Arbitrary control of the electromagnetic field in femto-nano scale has attracted significant research attention in nano-photonics. Although the electromagnetic field controlled in femto-nano scale could be realized by illuminating metallic nanoparticles with femtosecond chirped laser pulses, the quantitative relation of the laser chirp and the temporal evolution of the plasmonic field hasn’t yet been fully revealed. Here, active control of the localized plasmonic field is demonstrated by a chirped femtosecond laser pulse in an asymmetric Au nano-cross system within nm-fs scale using the finite differential time domain method. The transferring of the plasmonic field between the two poles of the nanocross is determined by the laser chirp and exhibits linear dependence on the time interval between the corresponding plasmonic resonant frequencies dispersed in the chirped laser pulse. The arrival time and amplitude of the peak field from the plasmonic hot spot are determined by the superposition of the induced field excited by the on-resonant and off-resonant frequency components distributed in the chirped laser pulse. The peak field would arrive behind the resonant frequency component for sufficient oscillation of the localized field. This relative delay between the resonant frequency and field peak is influenced by the temporal distribution of the resonant frequency in the chirped pulse and the response of localized field interpreted by the damped harmonic oscillator model. This result demonstrates that larger near-field enhancement is determined by not only the temporal sequence of the frequency component modulated by chirp but also the temporal distribution of the resonant frequency.

Femtosecond Chirped Pulse Amplification System with Liquid Crystal Spatial Light Modulator for Spectral Modulation

Femtosecond Chirped Pulse Amplification System with Liquid Crystal Spatial Light Modulator for Spectral Modulation

Generation of Chirped Femtosecond Pulses Near 977 nm Using a Mode-Locked All-Fiber Laser

A cladding-pumped all-fiber chirped femtosecond pulse Yb-doped mode-locked laser operating near 977 nm was demonstrated for the first time. Nonlinear polarization evolution was used as the mode-locking mechanism. The laser was self-starting and extremely stable (the stability of the repetition rate of 41.6 MHz was better than that of 15 Hz). Amplification near 977 nm was achieved using a specially designed cladding-pumped Yb-doped fiber. The main feature of the current laser design was its increased intracavity nonlinearity, which resulted in a strong self-phase modulation and significant widening of the generated pulse spectrum. This nonlinearity allowed us to generate pulses compressible down to a duration of 230 fs using an external diffraction grating compressor.

Semi-Lagrangian Vlasov simulation of the interaction between femtosecond chirped and double laser pulses with a thin plasma slab

The wakefield generation and electrons acceleration in the interaction of femtosecond chirped and double laser pulses with an underdense thin plasma slab is examined by numerical solution of the relativistic Vlasov-Maxwell system of equations using the backward semi-Lagrangian method (BSL). Unlike particle-in-cell methods, the BSL method is free of numerical noise and provides an accurate representation of the distribution function, even in very low density regions of phase space where acceleration and trapping occur. The effect of density fluctuations in low density regions of phase space are important, since they affect the acceleration processes over the following interactions. Therefore, a detailed structure of the distribution function is needed to investigate this process in these regions, which only can be obtained by Vlasov codes. Excitation of wakefields by chirped, chirp free, and double pulse lasers in an underdense plasma slab are simulated using the BSL code and the results are compared. It is shown that by making use of chirped laser pulses, the mean kinetic energy of plasma electrons can be enhanced up to 40% compared with the chirp free case. The investigation of wakefield generation by double laser pulses with a time repetition equal to one plasma period, exhibits amplification of wakefield amplitude after the entrance of the second laser pulse into plasma slab.

基于光谱控制与色散优化的飞秒啁啾脉冲放大系统

基于光谱控制与色散优化的飞秒啁啾脉冲放大系统

High-pulse-quality Yb-fiber amplifier generation of 10 μJ, 250 fs pulses at 500 kHz repetition rate

A high-pulse-quality femtosecond chirped pulse amplifier system based on tunable chirped fiber Bragg grating (CFBG) stretcher is reported. Dispersion of CFBG is fine-tuned designed to match the compressor. By controlling the dispersion of CFBG, net dispersion of the system approaches zero. Laser pulses with 10 μJ pulse energy and duration time of 250 fs after compression at a repetition rate of 500 kHz are obtained. The measured output energy fluctuation of root mean square is 0.3% in 1 h and the M2 factor is 1.07. These results indicate that the laser amplifier exhibits a great potential in industrial processing, military defense and scientific research.

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.

Extension of supercontinuum spectrum, generated in polarization-maintaining photonic crystal fiber, using chirped femtosecond pulses

We present results of experimental and numerical investigation of supercontinuum (SC) generation in polarization-maintaining photonic crystal fiber (PCF) using chirped femtosecond pulses. The initial unchirped pump pulse source was a mode-locked Yb:KGW laser generating 52-nJ energy, 110-fs duration pulses at 1030 nm with a 76-MHz repetition rate. The nonlinear medium was a 32-cm-long polarization-maintaining PCF manufactured by NKT Photonics A/S. We demonstrated the influence of pump pulse chirp on spectral characteristics of a SC. We showed that by chirping pump pulses positively or negatively one can obtain a broader SC spectrum than in the case of unchirped pump pulses at the same peak power. Moreover, the extension can be controlled by changing the amount of pump pulse chirp. Numerical simulation results also indicated that pump pulse chirp yields an extension of SC spectrum.

Using self-phase modulation for temporal compression of intense femtosecond laser pulses

We report a theoretical analysis of the spectrum broadening of intense chirped femtosecond pulses in media with cubic nonlinearity. Subsequent temporal compression of such pulses using a quadratic spectral phase corrector is investigated. Pulse compression from 57 fs to 22 fs is demonstrated experimentally in a petawatt laser beam.

High-energy pulse stacking via regenerative pulse-burst amplification.

Here we present a coherent pulse stacking approach for upscaling the energy of a solid-state femtosecond chirped pulse amplifier. We demonstrate pulse splitting into four replicas, amplification in a burst-mode regenerative Yb:CaF2 amplifier, designed to overcome intracavity optical damage by colliding pulse replicas, and coherent combining into a single millijoule level pulse. The thresholds of pulse-burst-induced damage of optical elements are experimentally investigated. The scheme allows achieving an enhancement factor of 2.62 using a single-stage stacker cavity and, potentially, much higher enhancement factors using cascaded stacking.

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.

Control of electronic populations in porphycene with chirped ultrashort pulses

The degree of optical excitation of porphycene in solution can be controlled by manipulating linear chirp of high intensity ultrashort laser pulses while keeping their energies and spectra constant. Transient absorption, which reflects molecular populations in the ground and the first singlet excited state, varies by over 100% between optimal positively and negatively chirped excitation pulses. The results are discussed invoking coherent vibrational wavepacket dynamics. Full Text: PDF References J. Waluk, Porphycenes: Spectroscopy, Photophysics, and Tautomerism. In CRC Handbook of Organic Photochemistry and Photobiology, M. Oelgemoeller, A. Griesbeck, F. Ghetti, Eds. (CRC Press: Boca Raton, FL, 2012), pp 809-829. CrossRef P. Fita, N. Urbańska, C. Radzewicz, J. Waluk, "Ground- and Excited-State Tautomerization Rates in Porphycenes", Chem. Eur. J. 15, 485 (2009). CrossRef P. Ciąćka, P. Fita, A. Listkowski, M. Kijak, S. Nonell, D. Kuzuhara, H. Yamada, C. Radzewicz, and J. Waluk, J. Phys. Chem. B 119, 2292 (2015). CrossRef P. Nuernberger, G. Vogt, T. Brixner and G. Gerber, "Femtosecond quantum control of molecular dynamics in the condensed phase", Phys. Chem. Chem. Phys. 9, 2470 (2007). CrossRef G. Cerullo, C.J. Bardeen, Q. Wang, C.V. Shank, "High-power femtosecond chirped pulse excitation of molecules in solution", Chem. Phys. Lett. 262 362 (1996). CrossRef C.J. Bardeen, Q. Wang, C.V. Shank, "Selective Excitation of Vibrational Wave Packet Motion Using Chirped Pulses", Phys. Rev. Lett. 75, 3410 (1995). CrossRef P. Tournois, "http://dx.doi.org/10.1016/S0030-4018(97)00153-3", Opt. Comm. 140, 245 (1997). CrossRef W. Demtroder, Laser spectroscopy: basic concepts and instrumentation, 3rd ed. (Springer Press, Berlin, Heidelberg, New York, 2003). CrossRef A. Starukhin, E. Vogel, J. Waluk, J. Phys. Chem. A 102, 9999 (1998). CrossRef P. Fita, C. Radzewicz, J. Waluk, J. Phys. Chem. A, 112, 10753 (2008). CrossRef

Infrared supercontinuum generation in soft-glass photonic crystal fibers pumped at 1560 nm

In this work we present results on supercontinuum (SC) generation in a photonic crystal fiber (PCF) fabricated from lead-bismuth-gallium-oxide glass (PBG-08). Due to high refractive index, high nonlinearity and high transmittance, the PBG-08 glass-based fibers seem to be excellent media for broad supercontinuum generation in the infrared spectral region. In our experiment, a short-length piece of PCF (5-6 cm) is pumped by a femtosecond chirped pulse amplification (CPA) setup, which may be seeded by two different fiber-based oscillators. This compact and cost-effective system allows to generate SC spanning from 900 to 2400 nm. The paper describes in detail the fabrication process of the fiber, as well as the SC generation results.

Toward elucidating the mechanism of femtosecond pulse shaping control in photodynamics of molecules by velocity map photoelectron and ion imaging

The control of photofragmentation and ionization in a polyatomic molecule has been studied by femtosecond chirped laser pulse excitation and velocity map photoelectron and ion imaging. The experiments aimed at controlling and investigating the photodynamics in CH(2)BrCl using tunable chirped femtosecond pulses in the visible wavelength region 509-540 nm at maximum intensities of about 4x10(13) W/cm(2). We observe that the time-of-flight mass spectra as well as the photoelectron images can be strongly modified by manipulating the chirp parameter of ultrashort laser pulses. Specifically, a strong enhancement of the CH(2)Cl(+)/CH(2)BrCl(+) ion ratio by a factor of five and changes in the photoelectron spectra are observed for positively chirped pulses centered near 520 nm. These changes are only observed within a narrow window of wavelengths around 520 nm and only for positively chirped pulses. From the combination of the photoelectron spectra and the ion recoil energy of the CH(2)Cl(+) fragment we can deduce that the parent ionization and fragmentation is induced by a multiphoton excitation with five photons. The photoelectron images and the fragment ion images also provide the anisotropy (beta-parameter) of the various electron bands and fragment ions. We conclude that multiphoton excitation of the highest occupied 22a(') and 8a(") CH(2)BrCl molecular orbitals of Br-character are both involved in the five-photon ionization, however, only excitation of the 22a(') orbital appears to be (mostly) involved in the chirped control dynamics leading to enhanced fragmentation to CH(2)Cl(+)(X A(')) + Br((2)P(3/2)). We propose that a wavepacket following or a time-delay resonance mechanism between the two-photon excited n(x)(Br,22a(')) --> (2A(')) repulsive surface and the three-photon near-resonant n(x)(Br,22a(')) --> Rydberg(A(')) state of the neutral CH(2)BrCl molecule is responsible for the enhanced excitation of the n(x)(Br,22a(')) molecular orbital with up-chirped pulses. This leads to enhanced ionization to a configuration in the CH(2)BrCl(+)(X A(')) continuum just above the dissociation limit of the CH(2)Cl(+) + Br((2)P(3/2)) channel, resulting in enhanced fragmentation.

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.

Prevention of decoherence by two femtosecond chirped pulse trains

We study the vibrational energy relaxation (VER) and collisional dephasing as channels of coherence loss in a vibrational mode that is selectively excited using chirped pulse adiabatic passage in the Raman configuration. Based on the dressed state picture analysis we propose a method to reduce decoherence using femtosecond chirped pulse trains. When applied with a period close to the VER time, the pulse trains allow one to sustain high coherence in the selected vibrational mode.

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%.

Long-delay engraving and recovery of chirped femtosecond pulses by spectro-temporal holography in spectral hole-burning molecular solids

The persistent spectral hole-burning (PSHB) phenomenon observed in molecular doped polymers cooled down to liquid helium temperatures allows the engraving of spectral structures in the inhomogeneous absorption profile of the material. Therefore, a PSHB molecular-doped solid can be programmed in the spectral domain and then converted in an optical processor capable to achieve user-defined optical functions. We demonstrate the high storage capacity of naphthalocyanine-doped polymer materials by engraving and retrieving the phase information stored in femtosecond-chirped pulses, even with nanosecond time delay, which correspond to information registered with sub-GHz spectral resolution. Perspectives for the coherent control of light fields or photochemical processes are also evoked.

Chirped Coherent Anti-Stokes Raman Scattering for High Spectral Resolution Spectroscopy and Chemically Selective Imaging

We describe a simple multiplex vibrational spectroscopic imaging technique based on employing chirped femtosecond pulses in a coherent anti-Stokes Raman scattering (CARS) scheme. Overlap of a femtosecond Stokes pulse with chirped pump/probe pulses introduces a temporal gate that defines the spectral resolution of the technique, allowing single-shot acquisition of high spectral resolution CARS spectra over a several hundred wavenumber bandwidth. Simulated chirped (c-) CARS spectra match the experimental results, quantifying the dependence of the high spectral resolution on the properties of the chirped pulse. c-CARS spectromicroscopy offers promise as a simple and generally applicable high spatial resolution, chemically specific imaging technique for studying complex biological and materials samples.