Femtosecond Fiber Chirped-pulse Amplifiers Research Articles

High-repetition-rate, 50-µJ-level, 1064-nm, CPA laser system based on a single-stage double-pass Yb-doped rod-type fiber amplifier

A 1064-nm femtosecond fiber chirped pulse amplification (FCPA) laser system based on a single-stage double-pass Yb-doped rod-type photonic crystal fiber (PCF) amplifier was demonstrated with a pulse repetition rate of 500 kHz, which was specially designed for expected conversion efficiency enhancement of a 10.8 eV source. With a series of Yb:fiber power amplifiers, the average output power was boosted to approximately 35 W. Further, using a transmission gratings-based pulse compressor, an average output power of 27.5 W was achieved, corresponding to a pulse energy of 55 µJ and a compression efficiency of 78.6%. The shortest pulse duration was optimized to be 204 fs, which was also accompanied by obvious pedestal. A pulse duration of 336 fs was also obtained when the pulse quality was at a top priority. To the best of our knowledge, this is the first demonstration of high-repetition-rate high-pulse-energy 1064-nm, instead of 1035-nm, femtosecond laser, based on commercially available Yb-doped rod-type PCF amplifier.

Coherent beam combining of 61 femtosecond fiber amplifiers.

We report on the coherent beam combining of 61 femtosecond fiber chirped-pulse amplifiers in a tiled-aperture configuration along with an interferometric phase measurement technique. Relying on coherent beam recombination in the far field, this technique appears suitable for the combination of a large number of fiber amplifiers. The 61 output beams are stacked in a hexagonal arrangement and collimated through a high fill factor hexagonal micro-lens array. The residual phase error between two fibers is as low as λ/90 RMS, while a combining efficiency of ∼50% is achieved.

High average power coherent femtosecond pulse combining system based on an all fiber active control method

We experimentally demonstrate a high average power coherent polarization beam combining system of two-channel femtosecond fiber chirped-pulse amplifiers based on our all fiber active control method comprising an active phase locking loop and adaptive control loop of optical path drift for the first time. A coherent combining efficiency of 87% is achieved at the combined power of 4.3 W, which drops with the average power scaling. The combined average power finally reaches 313 W with a coherent combining efficiency of 79% and the corresponding compressed pulse duration is 827 fs. The reasons for the loss in combining efficiency are experimentally investigated. Further power scaling is restricted by the deterioration of the laser mode, but it is still possible if the performance of the single femtosecond fiber chirped-pulse amplifier is improved.

基于色散波的1 μm飞秒光纤啁啾脉冲放大系统

基于色散波的1 μm飞秒光纤啁啾脉冲放大系统

Spectral pulse synthesis in large-scale ultrafast coherent combining systems

We propose the use of coherent spectral synthesis to reach shorter pulse durations in the context of massively parallel femtosecond coherent combining laser systems. A preliminary experiment that performs spectral synthesis with two femtosecond fiber chirped-pulse amplifiers is presented, and shows that a significant decrease of the amplified pulse duration compared to single-band amplification is achieved. We also discuss possible implementation of spectral synthesis in a large-scale coherent combining setup.

Optimization of pulse compression in a fiber chirped pulse amplification system by adjusting dispersion parameters of a temperature-tuned chirped fiber Bragg grating stretcher

In this work, we present a femtosecond fiber chirped pulse amplification (FCPA) system with a temperature-tuned chirped fiber Bragg grating (CFBG) stretcher for uncompensated higher-order spectral phase reduction. An improvement in pulse compression through the optimization of temperature distribution along a CFBG stretcher is predicted numerically and verified experimentally by using a CFBG stretcher with four independent thermoelectric cooler (TEC) elements.

Parallel fiber amplifiers with carrier–envelope drift control for coherent combination of optical frequency combs

We demonstrated an active feed-forward method for compensating the relative phase drifts of fiber optical amplifiers. The frequency drifts of relative phase noise were well controlled in a variation range from ± 15 Hz of free-running, to approximately ± 1.5 Hz between the amplifier input and output. Coherent combination of two femtosecond fiber chirped-pulse amplifiers seeded by a Ti:S comb oscillator was achieved, which would benefit frequency comb combination to achieve high accuracy and high power.

Two-channel pulse synthesis to overcome gain narrowing in femtosecond fiber amplifiers

We demonstrate spectral coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using active phase stabilization based on an electro-optic phase modulator, an average power of 10 W before compression and a high gain factor of 30 dB are obtained. At this gain value, 130 fs pulses with a spectral width of 19 nm can be generated, highlighting the strong potential of pulse synthesis for the reduction of the minimum duration of ultrashort pulses in fiber chirped-pulse amplifiers.

530 W, 13 mJ, four-channel coherently combined femtosecond fiber chirped-pulse amplification system

We report on a femtosecond fiber laser system comprising four coherently combined large-pitch fibers as the main amplifier. With this system, a pulse energy of 1.3mJ and a peak power of 1.8GW are achieved at 400kHz repetition rate. The corresponding average output power is as high as 530W. Additionally, an excellent beam quality and efficiency of the combination have been obtained. To the best of our knowledge, such a parameter combination, i.e., gigawatt pulses with half a kilowatt average power, has not been demonstrated so far with any other laser architecture.

Sub 25 fs pulses from solid-core nonlinear compression stage at 250 W of average power

We report on a highpower femtosecond fiber chirped-pulse amplification system with an excellent beam quality (M(2)=1.2) operating at 250 MHz repetition rate. We demonstrate nonlinear compression in a solid-core photonic crystal fiber at unprecedented average power levels. By exploiting self-phase modulation with subsequent chirped-mirror compression we achieve pulse shortening by more than one order of magnitude to 23 fs pulses. The use of circular polarization allows higher than usual peak powers in the broadening fiber resulting in compressed 0.9 μJ pulse energy and a peak power of 34 MW at 250 W of average power (M(2)=1.3). This system is well suited for driving cavity-enhanced high-repetition rate high-harmonic generation.

Impact of spectral phase mismatch on femtosecond coherent beam combining systems

We experimentally investigate the impact of spectral phase mismatch on the coherent beam combining of two femtosecond fiber chirped-pulse amplifiers. By measuring the differential spectral phase, both linear and nonlinear contributions are identified. An accumulated nonlinear phase as high as 6 rad has been measured, for which a combination efficiency of 91% can be obtained by symmetrizing the pump and injection powers. This also allows us to quantitatively separate the spatial and temporal contributions of the nonperfect combining efficiency.

Passive coherent beam combining of two femtosecond fiber chirped-pulse amplifiers

We propose and demonstrate an architecture that achieves passive coherent combination of two femtosecond fiber chirped-pulse amplifiers. The setup consists in the use of a well-balanced amplifying Sagnac interferometer. The experiment shows that the temporal, spectral, and spatial qualities of each beam are retained, with the generation of 250 fs pulses at 35 MHz repetition rate, an uncompressed average power of 10 W, and a combining efficiency of 96%. The behavior of this architecture in the presence of high accumulated nonlinear phase is investigated.

Coherent beam combining of two femtosecond fiber chirped-pulse amplifiers

We demonstrate coherent beam combining of two femtosecond fiber chirped-pulse amplifiers seeded by a common oscillator. Using a feedback loop based on an electro-optic phase modulator, an average power of 7.2 W before compression is obtained with a combining efficiency of 90%. The spatial and temporal qualities of the oscillator are retained, with a recombined pulse width of 325 fs. This experiment opens up a way to scale the peak/average power of ultrafast fiber sources.

Femtosecond fiber CPA system emitting 830 W average output power

In this Letter we report on the generation of 830 W compressed average power from a femtosecond fiber chirped pulse amplification (CPA) system. In the high-power operation we achieved a compressor throughput of about 90% by using high-efficiency dielectric gratings. The output pulse duration of 640 fs at 78 MHz repetition rate results in a peak power of 12 MW. Additionally, we discuss further a scaling potential toward and beyond the kilowatt level by overcoming the current scaling limitations imposed by the transversal spatial hole burning.

High energy femtosecond fiber chirped pulse amplification system with adaptive phase control

We demonstrate increased peak power from an Yb fiber CPA system operating with strong self-phase modulation by shaping the spectral-phase of the input pulses. An adaptive control loop used feedback from the output autocorrelation. We investigated pre-compensation of both SPM phase distortion at high energies, and residual dispersion from mismatched stretcher/compressor technologies at low energies. Phase shaping resulted in improved pulse quality. When using a bulk grating stretcher, shaping increased the autocorrelation peak by a factor of 2.9, and with a fiber stretcher, shaping increased the autocorrelation peak by a factor of 3.4. High-quality 800 fs, 65 microJ recompressed pulses were produced. This technique could benefit a wide variety of fiber amplifier systems and is self-optimising for operation at both low and high pulse energies.

90 W average power 100 μJ energy femtosecond fiber chirped-pulse amplification system

We report on an ytterbium-doped fiber based chirped-pulse amplification system delivering 100 microJ pulse energy at a repetition rate of 900 kHz, corresponding to an average power of 90 W. The emitted pulses are as short as 500 fs. To the best of our knowledge, this is the highest average power ever reported for high-energy femtosecond solid-state laser systems.

High Power Femtosecond Fiber Chirped Pulse Amplification System for High Speed Micromachining

The need for improved precision in a wide variety of micromachining applications has driven scientific interest in ultrashort pulse lasers. Despite numerous demonstrations of reduced heat effect and improved processing quality, the utility of such lasers has been limited by the heavy demands placed upon laser performance. In addition to high contrast laser pulses with minimal pulse-to-pulse fluctuation, an ultrashort pulse laser must provide near diffraction-limited beam quality and robust long-term laser operation with high repetition rate for high processing speeds. We report here on a research prototype, high power femtosecond fiber chirped pulse amplification system. The system produces compressed pulses with energies >50 µJ at >15 W with M 2 1000:1 temporal contrast despite significant self-phase modulation during amplification corresponding to a nonlinear phase delay of ~6π. As a demonstration of high speed femtosecond micromachining, we drill and cut 0.5-mm thick metal, semiconductor and dielectric targets.

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems

We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems.