Search

Self-phase modulation produced by propagation of a 50-fs laser pulse in a hollow-core fiber capillary filled with argon gas was used to broaden the bandwidth from 30 nm to 250 nm. A subsequent compressor utilizing a pair of gratings and cylindrical optics compressed the pulse to 12.5 fs. A liquid-crystal spatial light modulator (SLM) was placed in the compressor, and an evolutionary algorithm based on feedback from the second-harmonic signal was used to control the SLM and optimize the pulse duration. The algorithm increased the second-harmonic signal by a factor of two, indicating that it has substantially improved on the 12.5-fs pulse duration.

The output pulses of a noncollinearly phase-matched optical parametric amplifier (NOPA) are fully characterized by spectral phase interferometry for direct electric-field reconstruction (SPIDER). The SPIDER setup has been optimized for online diagnosis of tunable visible pulses with a 1 kHz repetition rate and 10–40 fs duration. The compression of the NOPA pulses by different prism sequences and commercially available chirped mirrors is investigated. For flexible phase control the end mirror of a fused-silica prism compressor has been replaced by a deformable mirror. With an evolutionary strategy guided by the spectral phase information of the SPIDER, optimal compression of the NOPA pulses to a 7.6 fs duration is achieved.

We demonstrate stretch and recompression of a sub-10-fs pulse utilizing a broadband pulse stretcher, a dispersion compensator with a spatial light modulator, and a broadband pulse compressor for ∼10-fs Ti:sapphire chirped-pulse amplification system. Our calculation suggests that the dispersion compensator is useful for dispersion compensation of a Ti:sapphire chirped-pulse amplification system, including multi-pass amplifiers.

We numerically simulated the pulse formation in a femtosecond Ti:sapphire laser and investigated the effect of a discrete distribution of dispersion and self-phase modulation. It was found that the discreteness in an actual femtosecond laser leads to pulse broadening and deviation of the pulse shape from that of a fundamental soliton. The high-order dispersion of quartz prisms was effective in relaxing the pulse broadening induced by discreteness. The discreteness effect on the pulse contrast in a femtosecond laser was investigated.

An intense ultrashort optical pulse has been quasi-continuously generated using a superconducting RF linac-based free-electron laser at a wavelength of 22.5 μm. The pulse shape and width are measured by second-order optical autocorrelation with a birefringent Te crystal. At synchronism of the optical resonator, the pulse shape is a smooth single pulse with an FWHM width of 255 fs and energy of 74 μJ. A train of subpulses is developed by increasing the desynchronism of the optical resonator. The measured results are in good agreement with numerical simulation.

Relativistic self-guiding and Raman forward scattering of an intense ultrashort laser pulse propagating in an underdense plasma were studied using a terawatt Ti:sapphire laser system. The dependence of these processes on the duration and frequency chirp of the laser pulse was investigated by detuning the pulse compressor. It was observed that the efficiency of Raman forward scattering is enhanced for a positively chirped pulse and diminished for a negatively chirped pulse. In addition, as a result of the dependence on pulse duration and peak power, an optimal duration for Raman forward scattering was found for fixed pulse energy and spectral bandwidth. On the other hand, relativistic self-guiding of the laser pulse was affected by the pulse duration while no dependence on the chirp was observed.

A general expression of dispersion for pairing double-prism compressor with arbitrary apex angle is presented and a limitation to generate negative group-delay dispersion (GDD) for broadband spectrum is obtained. By use of this compressor with spectral shaping filters and chirped mirrors, 2 mJ, 17.5 fs pulses from a compact 10-pass kilohertz Ti:sapphire amplifier system are generated.

Propagation of an intense femtosecond laser pulse through a transparent nonlinear medium such as dielectric leads to a number of phenomena. In our experiment we observed complex spatial, spectral, and temporal structures appearing in the initially smooth femtosecond laser pulse when the pulse power is comparable to or higher than the critical power for self-focusing. We have also developed a complete, 3-dimensional theoretical model to describe the observed phenomena.

The generalized theory of double-mode electrostatic dispersing prism for time-domain compressing electron pulse is presented. The fundamental difference between the two modes of o mode and e mode lies in the dispersive dependence of electron’s time of flight on its initial kinetic energy at prism entrance: the electrons with higher initial axial energy definitely have longer time of flight for o mode, while not the case for e mode, which results from the electron pulse’s Ushaped motion in the prism. The dispersive dependence of time of flight constitutes the mechanism of electron pulse compression for each mode. An example is given to demonstrate the issue of parameter choosing for the prism and to verify its tunable performance of electron pulse compression.

The position of wavelength in a grating spectrometer depends mainly on the line frequency and the working angle of the grating, as calculated by Eqs. (2.1), (2.4), and (2.5), and derivations. A prism spectrometer will output a certain wavelength as a function of the prism dispersion, which depends on the RI of the prism at the wavelength of interest, the angle of the prism, and the illumination angle, as calculated by Eq. (3.3). However, there are more parameters that affect the actual wavelength output: the internal angles of the spectrometer, which are part of the above equations, and the actual temperature, which can change the wavelength, as described by Eq. (2.31). Furthermore the output position of a wavelength can change with the illumination of the entrance and after the instrument experiences vibrations or shock. It should be noted that any modification of the beam travel inside the spectrometer can affect the calibration. It follows that the energy axis (wavelength, wavenumber, photon energy) needs to be checked frequently and calibrated sometimes.

Progressive developments in temporal shaping of short laser pulses offer entirely new approaches at influence and investigate laser-matter-interactions. Commonly used parameters for describing the behavior of short or ultrashort pulses or pulse trains are fluence and intensity. However, fluence does not imply any information about the temporal behavior of energy input during specific pulse duration τ while using the pulse intensity as describing parameter is more meaningful. Nevertheless it still is an averaging over pulse duration and no change in intensity can be determined if the temporal pulse shape changes within a certain combination of pulse duration and pulse energy. Using a flexible programmable MOPA fiber laser experimental studies on the impact of temporal energy distribution within one single laser pulse in micro machining applications were therefore carried out. With this laser source a direct modulation of the temporal pulse shape in the nanosecond regime can easily be controlled. Experiments were carried out with moved as well as with un-moved beam resulting in areas and dimples respectively drilling holes. The presented results clearly show that any averaging over pulse duration results in missing information about time-dependent interactions but can at the same time lead to significant differences in ablation results. Thus, resulting surface roughness Sa can be decreased up to 25 % when changing the pulse shape at constant parameters of fluence and pulse peak power at a pulse duration of 30 ns. It can be observed that the combination of an intensity peak and a lower edge within one pulse can lead to increasing ablation efficiency as well as higher ablation quality compared to the commonly used Gaussian-like temporal pulse shape.

Femtosecond optical pulses of 1550-nm wavelength propagated in a dispersion-managed single-mode optical fibre link consisting of a 50-m dispersion compensation fibre, a 250-m dispersion-shifted fibre, and a 300-m standard dispersion fibre are characterised by high-sensitivity two-photon absorption frequency-resolved optical gating. Output pulse spectrogram shows pulse trailing wings in the short and long wavelength parts of the time-spectral distribution of pulse intensity, and implies dominance of third-order chromatic dispersion in ultrashort pulse propagation in the fibre link. Numerical simulation using a nonlinear pulse propagation equation, including the experimental characteristics of chromatic dispersion in the fibre link, produces a theoretical output pulse shape qualitatively consistent with that of output pulse shape reconstructed from the experimental pulse spectrogram.

The performance characteristics of generated soliton and anti-Stokes pulses for the wavelength tunable ultrashort soliton pulse generation system are discussed for different fiber dispersion parameters of β2 and β3 at the pump wavelength. Numerical analysis showed that the broadband wavelength tunability is improved as both the absolute value of negative β2 and the value of β3 are decreased. When β3 is the usual value, the best performance of broadband continuous wavelength tunability which broadens symmetrically to the pump wavelength is obtained for β3 of around 蜢2 psβ2/km. The reason for this is that the behaviors of both the generated soliton and anti-Stokes pulses are due to the β2. Through simulations for different fiber dispersion parameters of β2 or β3 we obtained interesting results. When β3 is negative and the zero dispersion wavelength is set at the longer wavelength side than the pump wavelength, such as around 2 μm, it is possible to convert the generated soliton into new components at the longer wavelength side over 2 μm.

Compact system of wavelength tunable ultrashort soliton pulse generation has been demonstratedusing modelockedfemtosecond fiber laser and polarization maintaining (PM) fiber. The wavelengths of generated pulsescan be changed continuously by merely varying fiber input power. The generated pulses are almost transformlimited ideal soliton pulses. Two-colored soliton pulses can be generated simultaneously usingthe birefringenceof PM fibers. Using the dispersion shifted PM fibers, in addition to the soliton pulse, the anti-stokespulse is generated at the shorter wavelength side. Using the diameter reduced PM fibers and dispersion shiftedPM fibers, the wavelength tunable ultrashort pulses can be generated in the wide wavelength region of 1.3-2.0μm. In this paper, the characteristics of wavelength tunable soliton pulse are described withthe principles and applications.

A new fiber dispersion measurement method by utilizing a periodically swept-wavelength pulse light source is proposed and demonstrated. The periodic pulse timing variation of the pulse train induced by wavelength sweeping can be directly detected by a radio-frequency spectrum analyzer. Experiments by using an asynchronous mode-locked fiber soliton laser as the swept-wavelength pulse source have been successfully carried out to demonstrate the feasibility.

We performed calculations for a chirped-pulse-amplification laser system with a sub-100-fs pulse duration including the finite size of gratings in an aberration-free stretcher/compressor design. Both the higher-order phase dispersion and the spectral clipping, which is due to the finite size of the optics in the stretcher and the compressor, are taken into account in the calculation. We discuss the influence of both phase dispersion and spectral clipping on the important parameters of the recompressed pulse, such as pulse duration, pulse contrast, and peak intensity, employing different phase-dispersion compensation methods. The calculations show that the use of a small compressor grating reduces the higher-order phase errors and smoothes the sharp spectral cut-off caused by spectral clipping in the stretcher, which consequently improves the pulse contrast ratio of the main pulse to the pedestal.

We have developed ultrashort pulse generation by the electrooptic modulation method, where continuous-wave laser light of any wavelength can be converted to trains of ultrashort optical pulses with a variable and high repetition frequency by means of an electrooptic phase modulator for the generation of deeply chirped light, and an optical group-delay-dispersion circuit or an optical synthesizer for the compression of the chirped light. Adopting the technologies of domain inversion and guided-wave optics to this electrooptic modulation method, it will be possible to realize integrated ultrashort optical pulse generators.

A long cavity fiber-integrated semiconductor ring laser is demonstrated at 10 GHz. The temporal and spectral characteristics of a harmonically mode-locked laser pulse were described in detail. The laser pulse of 18 ps was compressed to a transform-limited pulse duration of 6.8 ps using an opposite dispersion chirp compensator in an anomalous dispersion regime.

We have investigated both experimentally and numerically the characteristics of wavelength tunable femtosecond soliton pulse generation using a pulse width variable fiber laser and two different types of polarization maintaining fibers. The generated soliton shows the feature of the pulsewidth becoming almost constant at - 250 fs under any conditions of the pump pulse for 220m fiber. High conversion efficiency from pump pulse to a generated soliton pulse accounting for as much as 73% can be obtained. This efficiency decreases with increase in the input power or wavelength shift. A superior conversion efficiency and broad wavelength shift can be obtained by using a more shortened pump pulse. In the numerical calculations, it is predicted that under a condition of constant power of pump pulse, the maximum wavelength shift is achieved when the soliton number N is -1.4. The difference of mode field diameter and the group velocity dispersion (GVD) coefficient β2 affect the wavelength shift and conversion efficiency. Using the fiber with small mode field diameter and small absolute value of GVD coefficient β2, a high conversion efficiency and large wavelength shift can be obtained.

We fully characterize a high-peak-power, ultrashort laser pulse in a Ti:sapphire chirped-pulse amplification laser system. The contrast, temporal, and spectral phases of the 20-fs pulse are determined by using high-dynamic-range cross-correlation and frequency-resolved optical gating techniques. Minimization of the total phase error can be achieved by balancing the phase terms of the group delay dispersion and quartic. The laser system is currently being applied to perform high-field atomic ionization experiments at 1020 W/cm2.

A SLALOM (semiconductor laser amplifier in the loop mirror) for optical frequency multiplication and pulse compression is presented theoretically. The influence of the relatively slow turn-on transition of the SLA and the window size to the switching window is discussed, and is neglected, instead of the sudden step for the transition in the short control pulse case in a previous paper 1. We make use of the two windows, which are created by the appropriate parameters of the proposed configuration, to multiply the optical pulse rate in the relatively long control pulse case. When the second window disappears in the short control pulse case, the device can be used as a pulse compressor. Analysis demonstrates that the 10 Gbit/s optical clock signal can be doubled to 20 Gbits/s, and a 100 ps pulse can be compressed to 34 ps at a rate of 2.5 Gbits/s with this device. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 24: 187–191, 2000.

This paper presents a theoretical and experimental study of wavepacket interferences created with a combination of two coherent ultrashort laser pulses: a chirped pulse and a Fourier-transform-limited pulse. We show that when the central wavelength of the pulse sequence is scanned, different behaviour is observed between the optical interference regime (pulse overlap in time) and the quantum interference regime (no pulse overlap). The theoretical analysis of the process is given together with experimental results in the (4s-4p) one-photon transition in potassium atoms.

The fundamental physical mechanism responsible for the self-focussing, filamentation, supercontinuum generation and conical emission of a powerful ultrashort laser pulse in a transparent optical medium is reviewed. The propagation can be described by the model of moving focus modified by the defocussing effect of the self-induced plasma through multiphoton interaction with the medium. Spatial and temporal self-phase modulation in both the neutral Kerr medium and the plasma transform the pulse into a chirped (elongated) and strongly deformed pulse both temporally and spatially. The manifestation of the deformation is supercontinuum generation and conical emission. A new phenomenon of refocussing was observed. It is due to the diffraction of the trailing part of the pulse by the plasma that results in a ring structure of positive index changes surrounding the plasma column. This ring structure refocuses the pulse partially. The measured coherence lengths of the various frequencies components of the supercontinuum are independent of the optical media used and are essentially equal to that of the pump laser pulse when compared to an incoherent white light source. We thus justify that such a deformed pulse with a very broad spectrum could be called a chirped white light laser pulse.

In this paper, we propose and discuss an array-grating compressor that is used in high power chirped-pulse amplification Nd:glass laser systems. Theoretical models including various angular errors are developed for the optical design of the array-grating compressor. With a criterion that the stretch in the duration of the compressed pulse due to the combining imperfection must be kept below 25%, we carry out the optical design of the array-grating compressor for a 0.5 ps pulse duration and a 1-m laser-beam diameter. The limitations to groove-width difference, parallelism, and planar are also discussed.

We have designed a compact solid compressor by stimulated Brillouin scattering (SBS) consisting of two right-angle prisms and a fused-silica glass block. A 13 ns Nd:YAG laser pulse was temporally compressed to a 1.2 ns phase-conjugated pulse in fused-silica glass at a 1064 nm wavelength. The maximum reflectivity of the SBS was over 95% without optical damage. The compressed pulse brightness was about 10-fold higher than that of the incident pulse.

A compact transmissive waveguide-type dispersion compensation device that uses waveguide grating routers is proposed. This device provides dispersion compensation in long-haul fiber transmission lines and can also be used as a pulse compressor for ultrashort optical pulse generation. A device for the pulse compression of picosecond-length optical pulses has been designed and is numerically analyzed. The proposed device works as a compact (on the centimeter order) and transmissive pulse compressor for picosecond optical pulses.

Theoretical and experimental results are presented for ultrafast, chirped-pulse amplifier compressors that contain only the final, high-peak power grating in vacuum. The designs are compact and the adjustments of the compressor gratings are at atmosphere. The optical aberrations and dispersion of the system are found to be negligible for the compression of 25-fs pulses. The application of the hybrid vacuum-atmosphere compressor is robust with respect to a broad range of wavelengths and optical configurations.

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 /spl mu/s, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser.

Optical pulse generation and compression have been numerically studied in anomalous dispersion decreasing fibers (DDF). We show that evolution of modulation instability observed with chirped wave packets in tapered fibers produces the mechanism for generation of ultra-short pulses with high repetition rates. The role of modulation instability and Raman self-scattering has been also discussed. The simulations show that pulse chirping enhances self-Raman scattering at early stages of pulse propagation and improves compression of the generated pulses. It is also shown that the presence of amplitude and frequency modulation of the seed wave provide essential impact on the pulse train formation. The new method for increasing the pulse train repetition rate through frequency modulation of the seed wave has been proposed.

We study the application of tunable ultrafast laser pulses in micropatterning self- assembled organic monolayer (SAMs) employing non collinear optical parametric amplification (NOPA). SAMs are ultrathin organic monolayers, which can be used in a variety of ways to assemble functionalized surface structures. In our study, we investigate the characteristics of SAMs as monomolecular resists during etching of gold. NOPA is a versatile method which provides the generation of ultrafast laser pulses, with a tunable wavelength in the visible and near infrared range. Due to the noncollinear geometry, a broadened spectral range can be amplified. The NOPA delivers wavelengths in the range of 480 nm to 950 nm at laser pulse lengths in the sub- 30 femtosecond range using a prism compressor after the nonlinear conversion. The ultrashort laser technology together with the advantages of the NOPA system guarantee high precision and allows us to determine the optimum conditions of sub-wavelength patterning by studying the effects of the fluence and the wavelength. At the same time, single-pulse processing allows us to selectively remove the ultrathin organic coating, while it ensures short processing time. In our study we used thiol-based SAMs as ultrathin layers on gold-coated glass substrates with a film thickness of 1-2 nm and 40 nm respectively.

A femtosecond pulse generated from a self-mode-locked Ti:sapphire laser was found to split into two or even three pulses. The time separation between these split pulses was found to depend on the pulse width. More interestingly, a slight disturbance could cause this time separation to increase further, not continuously, but by a multiple of a time constant. The pulse splitting could be due to side-lobe pulse generation by the separate action of the negative group-velocity dispersion and self-phase modulation in the laser cavity.

In distributed-feedback (DFB) dye lasers pumped by a nanosecond-pulse laser, a train of picosecond spikes is generated by the relaxation oscillation. A single spike with a pulse duration of 50 ps is extracted in a plastic-waveguide DFB dye laser using a quenching technique. To compress this to femtosecond pulse, a new type of integrated pulse compressor is proposed, and its performances are analyzed. The compressor is composed of a plastic waveguide in which amplifier dye and saturable dye are alternatively doped. Computer simulation shows that the 50-ps pulse is compressed to 120 fs by passing through four stages of amplifier and saturable absorber pair. Using this scheme, we expect to construct a very compact and simple ultrashort pulse generator in which the whole system is integrated on a chip of a plastic waveguide.

We generate broadband nonlinear-dispersive similaritons of up to 75 THz FWHM bandwidth (160 nm at 800 nm central wavelength) in LMA-5 single-mode photonic crystal fiber, and compress them to 15 fs using a hybrid grating-prism dispersive delay line. We numerically and experimentally show the large tunability of third-order dispersion of such a hybrid dispersive delay line.

A simple method for generation of 160 GHz soliton-like ultrashort pulse train at 850 nm is proposed and demonstrated numerically.

A mode-locked Nd3+:LGS laser of running with femtosecond pulse was demonstrated. By using SF10 prism pair for dispersion compensation, 278 fs transform-limited pulse trains at the central wavelength of 1084 nm have been obtained.

A single-shot transient-grating frequency-resolved optical gating (TG-FROG) device was set up to measure UV ultrashort pulse laser with pulse duration within 10ps.The performance of the device was demonstrated by experimental data measured on discharge-pumped KrF laser which is operated in 10Hz repeated frequency mode,and on electronbeam- pumped KrF laser which is only operated in single-shot mode.For the former,the TG-FROG can distinguish the changes of the pulse shape,spectrum and phase when the pulse chirp is changed.For the later,the TG-FROG finds that the pulse shape has multiple peaks whose pulse duration is about 2ps,and the spectrum is modulated whose bandwidth is about 1.3nm,and the corresponding phases present parabolic structure.

The Orion laser facility provides a capability for performing high energy density plasma physics experiments at AWE. The laser consists of ten long pulse (nanosecond) beam lines delivering a total of 5 kJ at 351 nm with 0.1-5 ns temporally shaped pulses and two short pulse Petawatt beam lines, each producing 500 J in 0.5 ps with intensities to target > 1021 W/cm2. The short pulse beam architecture is that of an OPCPA (optical parametric chirped pulse amplifier).

Date of Conference: 12-16 May 2013 There is much progress in Yb-fiber oscillator-amplifier systems, which enable generation of high-repetition-rate, microjoule energies and sub-picosecond pulse widths [1,2]. Given the extremely large total gain factors to reach microjoules starting from nanojoules, which is often in the range of 40-60 dB, due to losses, and the impact of mismatched high-order dispersion as temporal stretching and compression of pulses by large factors (30-40 dB) need to be employed. As a result of these challenges, most of the Yb-fiber amplifiers have resulted in pulse durations of several 100 fs or longer. While pulse durations in this range are suited for some applications, there are many cases where 100-fs or shorter pulses in microjoule range are required. Gain narrowing can be effectively countered by self-phase modulation (SPM) [3] by limiting amplification factor in each stage of amplification and through careful optimization of SPM and inversion level along the gain fiber. The conceptual template is readily present in the evolution of the pulse inside the oscillator cavity, where gain factors are often in the 10-50 range per roundtrip. To the extend that the B-integral and the gain distribution along the amplifier can be kept identical to the oscillator by proper scaling of the chirped pulse width and fiber mode area, the original oscillator can be preserved in arbitrary number of amplification stages. Here, we demonstrate a highly fiber-integrated master-oscillator power-amplifier (MOPA) system, from which - 1 μJ pulses are extracted and externally compressed to 100 fs by arranging amplification in each stage as close as possible to the intra-cavity evolution. To our knowledge, these results are the shortest demonstrated from all-fiber-integrated amplifier at the microjoule level. © 2013 IEEE.

This paper demonstrates a simple, very fast and single-shot 2D method that can be used for high precision characterization for the angular dispersion of broadband laser pulses. This method offers a quick online tool for the alignment of the stretcher-compressor system of chirped pulse amplification (CPA) lasers as well as for real time monitoring the driving laser beam of the single attosecond pulses generated via light house effect.

We demonstrated a 25-GHz subpicosecond pulse generator based on a single phase modulator and dual-stage fiber-based pulse compressor. Optical pulse with a FWHM of 800 fs was obtained and multiplexed to 400 GHz experimentally.

Optical ultrashort pulses are used in wide application areas, such as a light source for millimeter/terahertz wave sources for high-speed wireless communication systems, optical sampling technologies, and so forth. For these applications, ultrashort pulse sources are required to have compactness, high stability, low timing jitter, and tunability in both wavelength and repetition rate for high accuracy measurements. An ultrashort optical pulse source using a Mach-Zehnder-modulator (MZM)-based flat comb generator (MZ-FCG) and a nonlinear pulse compressor is a good candidate for such a source. However, the peak power of femtosecond pulses is limited by the compression condition of the pulse compressor. In this paper, we report on high peak power pulse generation by combining the MZ-FCG ultrashort pulse source with a chirped pulse amplifier (CPA).

By using the pulse propagation equation in the nonlinear dispersive medium, the effects of second- and third-order group-velocity dispersion on pulse evolution in the stretching, amplification and compressing are studied when chirped pulse amplification is applied to the pulses of a width

The construction of a two-photon/confocal microscope system is described in detail. For two-photon illumination, a Ti:sapphire modelocked laser generating 62-fs pulses at 715 nm was used. The effect of the optical train on illumination pulse width was examined and the observed increase in pulse duration was almost completely removed by the addition/adjustment of a prism compressor system. The imaging capabilities of the two-photon microscope are demonstrated and it is shown that the imaging performance of the two-photon microscope is similar to that of a conventional confocal microscope. With two-photon illumination, the resolution (full width at half-maximum intensity) was 0.42 microM (x-y) and 0.81 microM axially, while with single-photon illumination (at 488 nm in the same instrument with a confocal pinhole detector) the resolution was 0.3 microM (x-y) and 0.75 microM axially. The results are discussed with regard to the general problem of femtosecond pulse distortion in an optical system and a simple procedure for optimal pulse restoration is described.

We have performed laboratory experiments to study long distance propagation of large bandwidth ultrashort laser pulses in air. Initial pulse length, frequency chirping, and laser pulse energy were varied where the maximum propagation distance was up to 105 m. We have demonstrated the compression of initially negatively chirped low intensity laser pulses due to the linear group velocity dispersion of air. The characteristics of the compressed pulse such as pulse duration and spectral chirping were found to be significantly affected by the laser pulse intensity, with higher intensities corresponding to longer minimum compressed pulse duration.

The decay of N=2 solitons, initiated by a step increase in dispersion, is demonstrated as a means of generating pulse pairs having wavelengths that are shifted to either side of the input wavelength. Varying the magnitude of the dispersion step controls the wavelength separation. Partial recovery of the original soliton is also demonstrated by using a reverse dispersion step at a farther location.

A new architecture which is based on the chirped pulse amplification scheme is proposed to increase the pulse energy of the mode-locked fiber laser. The idea was applied to a passively mode-locked laser using an ytterbium (Yb/sup 3+/)-doped double-clad silica fiber. Mode-locking was achieved by nonlinear polarization evolution associated to frequency-shifted feedback technique for self-starting. A compressor and a stretcher, based on diffraction gratings, permitted us to manage the dispersion and to reduce the pulse power in the fiber. The laser delivered chirped pulses at 1050 nm with 11.8-nJ energy at a 9.3-MHz repetition rate (110-mW average power) which were subsequently compressed to 196-fs duration.

In the paper, a 2 µm high energy fs fiber laser and amplification system is presented based on Tm doped fibers. The seed laser was designed to generate pulse train at 2024 nm at a repetition rate of 2.5 MHz. An AOM was used as a pulse picker to further lower the repetition rate down to 100 kHz. Two-stage fiber pre-amplifiers and a high energy large mode area (LMA) fiber amplifier were used to boost pulse energy up to 54 µJ before pulse compressor with chirped pulse amplification technique. After compressor, pulse energy of 36.7µJ and pulse duration of 910 fs and were obtained.

A novel pulse stretching-compression system suitable for kHz-rate chirped-pulse amplification of ≈10 fs pulses in Ti:sapphire systems is demonstrated. The material dispersion of the system components used for pulse selection and isolation broadens the wide-band seed pulses by a factor of ≈300, allowing amplification up to the submillijoule energy range. The compressor consists of a pair of prisms and newly-developed chirped multilayer dielectric mirrors for compensating high order dispersion. Using this simple scheme a recompression of unamplified pulses down to 15 fs with a throughput as high as 80% is demonstrated.

During high-intensity laser propagation in a plasma, the group velocity of a laser pulse is subjected to change with the laser intensity due to alteration in refractive index associated with the variation of the nonlinear plasma density. The pulse front sharpened while the back of the pulse broadened due to difference in the group velocity at different parts of the laser pulse. Thus the distortion in the shape of the laser pulse is expected. We present 2D particle-in-cell simulations demonstrating the controlling the shape distortion of a Gaussian laser pulse using a parabolic plasma channel. We show the results of the intensity distribution of laser pulse in a plasma with and without a plasma channel. It has been observed that the plasma channel helps in controlling the laser pulse shape distortion. The understanding of evolution of laser pulse shape may be crucial while applying the parabolic plasma channel for guiding the laser pulse in plasma based accelerators.