High-quality Pulse Compression Research Articles

Dispersion engineering in nonlinear multipass cells for high-quality pulse compression

A dispersion-engineered multipass cell operating in the enhanced frequency regime is presented. Through the use of dispersive cavity mirrors, the nonlinear interaction is reshaped resulting in a smoother broadened spectrum, which yields a significant improvement in compressed pulse quality. The 70 W average power output of an Yb:fiber laser at 50 kHz repetition rate is compressed from 205 fs to 32 fs with more than 96% of the energy contained in the temporal main feature of the pulse. This first, to the best of our knowledge, experimental demonstration of a pulse quality improvement through enhanced frequency chirping in a multipass cell displays the opportunities for dispersion-tailored pulse compression.

Spatially homogeneous few-cycle compression of Yb lasers via all-solid-state free-space soliton management.

The high power and variable repetition-rate of Yb femtosecond lasers makes them very attractive for ultrafast science. However, for capturing sub-200 fs dynamics, efficient, high-fidelity and high-stability pulse compression techniques are essential. Spectral broadening using an all-solid-state free-space geometry is particularly attractive, as it is simple, robust and low-cost. However, spatial and temporal losses caused by spatio-spectral inhomogeneities have been a major challenge to date, due to coupled space-time dynamics associated with unguided nonlinear propagation. In this work, we use all-solid-state free-space compressors to demonstrate compression of 170 fs pulses at a wavelength of 1030nm from a Yb:KGW laser to ∼9.2 fs, with a highly spatially homogeneous mode. This is achieved by ensuring that the nonlinear beam propagation in periodic layered Kerr media occurs in spatial soliton modes, and by confining the nonlinear phase through each material layer to less than 1.0 rad. A remarkable spatio-spectral homogeneity of ∼0.87 can be realized, which yields a high efficiency of >50% for few-cycle compression. The universality of the method is demonstrated by implementing high-quality pulse compression under a wide range of laser conditions. The high spatiotemporal quality and the exceptional stability of the compressed pulses are further verified by high-harmonic generation. Our predictive method offers a compact and cost-effective solution for high-quality few-cycle-pulse generation from Yb femtosecond lasers, and will enable broad applications in ultrafast science and extreme nonlinear optics.

High-quality pulse compression in a novel architecture based on a single-mode fiber cascading a nonlinear optical loop mirror

A novel all-fiber low-pedestal pulse compression scheme is proposed and investigated. The scheme is based on an anomalously dispersive single-mode fiber (SMF) cascading a nonlinear optical loop mirror (NOLM) with another anomalously dispersive SMF in the loop. Numerical results show that excellent pulse compression and pedestal reduction can be achieved by using the proposed scheme.

Influence of gain coefficient on the self-similar pulses propagation in a dispersion-decreasing fiber

This paper first investigates the influence of the dispersion-decreasing optical fiber structure on the self-similar pulses interaction and compression. The dynamic of the evolution of a pair of self-similar pulses in a dispersion-decreasing optical fiber with normal group-velocity dispersion (ND-DDF) under different gain coefficient g0 of DDF is analyzed, and the chirp evolution is also studied to analyze the propagation characteristic of self-similar pulses. The numerical simulations show that the change of gain coefficient g0 of DDF can impact directly on the linear chirp of the self-similar pulses. We find out that the smaller g0 can generate better high-quality femto-second pulses than the higher g0 after pulses compression. Finally, we got a pair of ultra-short pulses with a FWHM of 124fs at g0=0.015m−1, indicating efficient and high-quality pulse compression.

Highly Nonlinear Dispersion Increasing Fiber for Femtosecond Pulse Generation

The optical pulse evolution in a highly nonlinear normal dispersion-increasing fiber has been considered, both experimentally and theoretically. It was found that large spectral broadening in tapered waveguides could occur without temporal instabilities and impose the linear frequency modulation, i.e., chirp, required for high-quality pulse compression. The pedestal-free pulses have been demonstrated after dechirping in a standard single-mode fiber.

Femtosecond fiber laser for high-stability and high-quality pulse compression

We demonstrate a femtosecond fiber master oscillator power amplifier system of high-stability and high-quality pulse compression, which is applied to corneal refractive surgery. The nonlinear-polarization-evolution mode-locking in a hybrid-cavity Yb-fiber oscillator consisting of both polarization-maintaining (PM) and non-PM fibers is demonstrated. In this paper, the PM-fibers introduced into the mode-locked fiber oscillator partially replace non-PM fibers. This alternative approach is conducive to reducing the adverse effect of uncontrolled fiber birefringence, which originates from the on-PM fiber suffering environmental temperature fluctuation and mechanical vibration. Once the length of non-PM fiber is comparable to the fiber beat length, the uncontrolled fiber birefringence caused by environment starts to abate the laser robustness, repeatability, and reliability of mode-locking. The stability becomes notoriously worse for long-cavity Yb-fiber oscillators. The PM-fibers adopted in the mode-locked fiber oscillator could improve the mode-locked stability of nonlinear-polarization-evolution self-started with long-cavity Yb-fiber oscillators. We study the dependence of the compressed pulse quality on the parameters of input pulse pre-chirp injected into the Yb-doped fiber amplifier. Due to the nonlinear-chirp and third order dispersion, the mode-locked pulse shape in time-domain will produce distortion during power being amplified in the Yb-doped fiber amplifier. A diffraction grating to adjust the pre-chirp of the input pulse from positive value to negative value launched into the Yb-doped fiber amplifier is placed between mode-locked Yb-fiber oscillator and Yb-doped fiber amplifier. We vary the pre-chirp by changing the distance between the diffraction grating and triangular prism and then adjust the second grating pair to compress the amplified pulses into its shortest pulse duration of full-width at half maximum measured by an autocorrelator. The experimental results show that the best compression quality of mode-locked pulse occurs at the negative pre-chirp with a measured pulse width of 183 fs. Deviation from this optimum pre-chirp degrades the compressed-pulse quality and features an increased temporal pedestal. The fiber laser produces self-started mode-locking at a repetition rate of 19.4 MHz, an average power of 1.2 W, a pulse width of 183 fs. The homemade femtosecond fiber laser is used to perform surgery on ex vivo pig corneas. The surgey shows that the light burst of femtosecond laser in corneal tissues could cut pig corneas, which proves that the femtosecond fiber laser satisfies the surgical operation requirements of animal corneas.

Optimization of femtosecond Yb-doped fiber amplifiers for high-quality pulse compression

We both theoretically and experimentally investigate the optimization of femtosecond Yb-doped fiber amplifiers (YDFAs) to achieve high-quality, high-power, compressed pulses. Ultrashort pulses amplified inside YDFAs are modeled by the generalized nonlinear Schrödinger equation coupled to the steady-state propagation-rate equations. We use this model to study the dependence of compressed-pulse quality on the YDFA parameters, such as the gain fiber's doping concentration and length, and input pulse pre-chirp, duration, and power. The modeling results confirmed by experiments show that an optimum negative pre-chirp for the input pulse exists to achieve the best compression.

Distortion of parabolic pulse due to higher-order effects in a dispersion-decreasing fiber

Considering Third-order Dispersion (TOD) and Stimulated Raman Scattering effect (SRS) simultaneously, the properties of the self-similar parabolic pulse evolution in a dispersion-decreasing optical fiber with normal group-velocity dispersion are firstly investigated in our paper. Our results show that parabolic pulses are distorted and the characteristic of exactly self-similarity will be lost due to the High-order effects. When only the TOD is taken into account, the chirp still reveals highly linear but glows into asymmetric which causes the waveform appearing optical wave breaking. When only considering SRS, the pulse still reveals highly linear chirp only linearity range narrow down, resulting in delaying the self-similar evolution. When considering SRS and TOD simultaneously, parabolic pulses are distorted less and the characteristic of exactly self-similarity will be better due to SRS effect than only considering TOD effect. The highly linear chirp in optical pulse still allows for efficient and high-quality pulse compression by use of dispersion compensation technique.

Generation of very flat optical frequency combs from continuous-wave lasers using cascaded intensity and phase modulators driven by tailored radio frequency waveforms

We demonstrate a scheme based on a cascade of lithium niobate intensity and phase modulators driven by specially tailored RF waveforms to generate an optical frequency comb with very high spectral flatness. In this Letter, we demonstrate a 10 GHz comb with 38 comb lines within a spectral power variation below 1 dB. The number of comb lines that can be generated is limited by the power handling capability of the phase modulator, and this can be scaled without compromising the spectral flatness. Furthermore, the spectral phase of the generated combs in our scheme is almost purely quadratic, which, as we will demonstrate, allows for high-quality pulse compression using only single-mode fiber.

Interaction between parabolic pulses in a dispersion-decreasing fiber

The properties of the self-similar parabolic pulses interaction in a dispersion-decreasing optical fiber with normal group-velocity dispersion are firstly investigated in our paper. We find that two parabolic pulses separated by a time-delay create oscillation with a sinusoidal fit at the beginning of their overlap, and then further evolve into a train of asymptotic dark solitons. Additionally, outside the overlap regime, the evolution is equal to a single pulse’ propagating behavior. The chirp after interaction in the parabolic pulses still allows for efficient and high-quality pulse compression.

Full Characterization of Low-Power Picosecond Pulses From a Gain-Switched Diode Laser Using Electrooptic Modulation-Based Linear FROG

We use a linear frequency-resolved optical gating technique based on electrooptic modulation to fully characterize for the first time the highly chirped pulses from a 1.06-m Fabry-Perot laser diode and design a chirped fiber Bragg grating to provide high-quality pulse compression. With this grating, we achieved 18-ps pulses at a repetition rate of 1.35 GHz with a time-bandwidth product of 0.7.

Soliton compression in dispersion decreasing fibers

Dispersion decreasing fibers (DDF) have been recognized to be useful for efficient soliton pulse compression. High-quality pulse compression has been obtained in DDF and the input power requirements are significantly lower ап that for soliton- effect compression. The maximum compression factor is determined by the ratio of input to output dispersion and typically limited to about 20. Using DDF with optimum dispersion profile it is possible to obtain pedestal-free pulses of less than 200fs duration.

Parabolic pulse generation by use of a dispersion-decreasing fiber with normal group-velocity dispersion.

We propose a new method for generating a parabolic pulse by use of a dispersion-decreasing fiber with normal group-velocity dispersion. When a hyperbolic dispersion-decreasing structure is employed, the pulse evolves into a linearly chirped pulse with an exact parabolic intensity profile without radiating dispersive waves. The highly linear chirp in the parabolic pulse allows for efficient and high-quality pulse compression.

Controllable Raman-like nonlinearities from nonstationary, cascaded quadratic processes

We show that useful non-instantaneous nonlinear phase shifts can be obtained from cascaded quadratic processes in the presence of group velocity mismatch. The two-field nature of the process permits responses that can be effectively advanced or retarded in time with respect to one of the fields. There is an analogy to a generalized Raman-scattering effect, permitting both red and blue shifts of short pulses. We expect this capability to have many applications in short-pulse generation and propagation, such as the compensation of Raman-induced effects and high-quality pulse compression, which we discuss.

Generation of nearly transform limited fs-pulses by pulse compression of an APM YAG laser

High-quality pulse compression is reported of a continuous wave Nd:YAG laser with additive pulse modelocking. Pulses with a duration of 310 fs and a peak power of 3.7 kW were obtained. A time-bandwidth product of 0.36 was achieved by spectral windowing techniques.