Fiber-based Chirped-pulse Amplification Research Articles

Photonic crystal rod-based high-performance ultrafast fiber laser system

Abstract In this paper, we innovatively conduct a Porro prism-based beam pointing stability promotion technique research and realize a high-performance rod-type photonic crystal fiber-based chirped pulse amplification (CPA) system, mainly including a frequency-reduced all-fiber pre-amplification stage, photonic crystal rod-based main amplification stage, and 1600 lines/mm transmission grating-pair compressor. Laser output with average power of 50 W, repetition rates of 500 kHz, pulse energy of 100 μJ, pulse duration of 830 fs, beam quality of M2<1.3, power fluctuation of 0.55% root mean square, and beam pointing drift of 19 μrad/°C over 8 h is realized. The high-performance laser system has an enormous application potential in fundamental research and precision manufacturing fields.

Efficient high-harmonic generation from a stable and compact ultrafast Yb-fiber laser producing 100\xa0\u03bcJ, 350\xa0fs pulses based on bendable photonic crystal fiber

The development of an Yb3+-fiber-based chirped-pulse amplification system and the performance in the generation of extreme ultraviolet (EUV) radiation by high-harmonic generation is reported. The fiber laser produced 100 μJ, 350 fs output pulses with diffraction-limited beam quality at a repetition rate of 16.7 kHz. The system used commercial single-mode, polarization maintaining fiber technology. This included a 40 μm core, easily packaged, bendable final amplifier fiber in order to enable a compact system, to reduce cost, and provide reliable and environmentally stable long-term performance. The system enabled the generation of 0.4 μW of EUV at wavelengths between 27 and 80 nm with a peak at ~45 nm using xenon gas. The EUV flux of ~1011 photons per second for a driving field power of 1.67 W represents state-of-the-art generation efficiency for single-fiber amplifier CPA systems, corresponding to a maximum calculated energy conversion efficiency of 2.4 × 10−7 from the infrared to the EUV. The potential for high average power operation at increased repetition rates and further suggested technical improvements are discussed. Future applications could include coherent diffractive imaging in the EUV, and high-harmonic spectroscopy.

μJ-level, kHz-repetition rate femtosecond fiber-CPA system at 1555 nm

In this work, we demonstrate a high-power, fiber-based chirped pulse amplification (CPA) setup utilizing Er- and Er/Yb-doped fibers, operating at 1555nm central wavelength. The integrated all-fiber pulse-picker allows to reduce the repetition frequency down to the kHz-range, which enables generation of sub-picosecond pulses with energies above 2μJ and pulse peak power exceeding 1MW. The system utilizes an Er/Yb co-doped large mode area fiber in the final amplification stage. Thanks to the used mode-field adapters and fiber-based components, the setup is almost fully fiberized, except the bulk grating pulse compressor. In order to provide compactness and simplicity, the compressor was designed using dense 1100 lines per millimeter gratings, that allow to keep the small grating separation.

Spectral coherence in all-normal dispersion supercontinuum in presence of Raman scattering and direct seeding from sub-picosecond pump

Intensity stability and wavelength correlations of near-infrared supercontinuum generation are studied in all-normal flattened dispersion, all-solid soft glass photonic crystal fiber. We use dispersive Fourier transformation method to measure shot-to-shot resolved spectra under pumping from a sub-picosecond, fiber-based chirped pulse amplification (CPA) system. For the first time to our knowledge, we demonstrate how unconverted radiation from pump, propagating in the photonic cladding of the fiber, improves the measured degree of coherence in the spectrum and influences its wavelength correlation by seeding of multiple four-wave-mixing / Raman scattering components. The presented results suggest a convenient and simple way of stabilizing of shot-to-shot coherence in sub-picosecond fiber laser pumped, normal-dispersion supercontinuum sources by direct, pump-related seeding.

Transform-limited pulses for chirped-pulse amplification systems utilizing an active feedback pulse shaping technique enabling five time increase in peak power

A fiber-based chirped-pulse amplification (CPA) system with an active feedback loop for pulse shaping is experimentally demonstrated. A spectral processor is used in conjunction with a frequency-resolved optical gating measurement to produce high-quality pulses. Spectral phase and intensity shaping are utilized to generate a clean, high-contrast, transform-limited pulse with 15 dB pedestal suppression in the pulse wing tails, resulting in a five time increase in peak power of the CPA system.

光纤结构的毫焦级皮秒啁啾脉冲放大系统

The efficient generation of a 1.17-mJ laser pulse with 360 ps duration using an ytterbium (Yb)-doped fiber amplifier chain seeded by a homemade mode-locked fiber laser is demonstrated experimentally. A specially designed figure-of-eight fiber laser acts as the seed source of a chirped-pulse amplification (CPA) system and generates mode-locked pulses with hundreds of picosecond widths. Two kinds of large-mode-area (LMA) double-clad Yb-doped fibers are employed to construct the pre-amplifier and main amplifier. All of the adopted instruments help avoid severe nonlinearity in fibers to raise sub-nanosecond pulse energy with acceptable signal-to-noise ratio (SNR). The output spectrum of this fiber-based CPA system shows that amplified spontaneous emission (ASE) is suppressed to better than 30 dB, and the onset of stimulated Raman scattering is excluded.

Control of the optical Kerr effect in chirped-pulse-amplification systems using model-based phase shaping

Using phase shaping, the impact of the Kerr effect in a fiber-based chirped-pulse amplification (CPA) system is experimentally controlled. The technique is based on an analytical model describing the spectral phase owing to self-phase modulation in CPA systems. The method relies neither on complex phase measurements nor on time-consuming optimization routines. Nearly transform-limited pulses with energies as high as 1 mJ are produced, and a B integral being as high as 8 rad is accumulated in the main amplifier. The value of the B integral is determined by the method itself.

High Repetition Rate Gigawatt Peak Power Fiber Laser Systems: Challenges, Design, and Experiment

We review the main challenges and give design guidelines for high-peak-power high-average-power fiber-based chirped-pulse amplification (CPA) systems. It is clearly pointed out that the lowest order fiber nonlinearity (NL), namely the self-phase modulation, limits the scalability of high-energy ultrashort pulse fiber amplifiers. Therefore, a distinguished difference arises between the consequences of accumulated nonlinear phase originating from the pulse envelope and initial weak modulations, resulting in a strong recommendation to operate an amplification system as linearly as possible in order to generate high-contrast pulses. Low-NL rare-earth-doped fibers, such as the recently available designs of photonic crystal fibers, are the key element for successful peak power scaling in fiber laser systems. In this paper, we present a detailed analysis and optimization of the extraction characteristics in connection with the accumulated nonlinear phase in such extreme fiber dimensions. Consequently, millijoule pulse energy femtosecond pulses at repetition rates in the 100 kHz range have already been demonstrated experimentally in a Yb-fiber-based CPA system that has even further scaling potential.

Controlling the influence of SPM in fiber-based chirped-pulse amplification systems by using an actively shaped parabolic spectrum

We report on the experimental demonstration of the control of the influence of nonlinearity in fiber-based chirped-pulse amplification (CPA) using active spectral amplitude shaping. By applying a liquid crystal spatial light modulator, the influence of the spectral profile on the recompressed pulse quality is experimentally revealed. The parabolic spectrum is experimentally determined to be very suitable for CPA-systems in which nonlinearity is present. The corresponding nonlinear phase contribution can be efficiently compensated by a conventional grating compressor. In a proof-of-principle experiment using an Yb-doped fiber- CPA-system, control at a B-integral as high as 16 rad is demonstrated. The method allows significant performance improvement of fiber-based chirpedpulse amplification.

Nonlinear distortion free fiber-based chirped pulse amplification with self-phase modulation up to 2π

We demonstrate the removal of 2pi radians of self-phase modulation (SPM) in a fiber-based chirped pulse amplification (CPA) system. Compensation of SPM distortion is achieved in the time domain by using a LiNbO(3) electro-optic phase modulator to emulate a negative nonlinear index of refraction. By synthesizing the drive waveform to the phase modulators with two RF frequencies that are phase-locked to the repetition rate of the seed laser, we achieve large phase compensations using cost-effective narrow band electronics. Our technique is simple, robust and can be readily integrated into existing fiber CPA systems.

Compensation of self-phase modulation in fiber-based chirped-pulse amplification systems

We demonstrate a simple, all-fiber technique for removing nonlinear phase due to self-phase modulation in fiber-based chirped-pulse amplification (CPA) systems. Using a LiNbO3 electro-optic phase modulator to emulate a negative nonlinear index of refraction, we are able to remove 1.0 pi rad of self-phase modulation acquired by pulses during amplification and eliminate nearly all pulse distortion. Our technique is high speed, removes nonlinear phase on a pulse-to-pulse basis, and can be readily integrated into existing CPA systems.

High-average-power femtosecond fiber chirped-pulse amplification system.

Efficient generation of 76-W average power of 400-fs pulses at 75-MHz repetition rate by use of a diode-pumped ytterbium-doped double-clad fiber-based chirped-pulse amplification system is demonstrated. The key element in the system is a diffraction grating compressor consisting of highly efficient transmission gratings in fused silica, allowing recompression at this high power level.

Mode-scalable fiber-based chirped pulse amplification systems

A new generation of compact and robust ultrashort pulse lasers is currently emerging based on rare-earth doped fiber gain media. This paper reviews the development of high-power fiber technology, which recently has led to millijoule energies and /spl sim/10 W average powers from various femtosecond fiber systems. These results indicate that fiber technology has a significant potential to replace conventional solid-state lasers and promises important advantages both for practical use and for achieving high powers and energies. Chirped pulse amplification and different mode-size scaling techniques compose the foundation of this ultrashort-pulse fiber technology. Mode-size scaling can be achieved either by using multimode core fibers, which can produce a diffraction-limited beam at the fiber amplifier output, or by "mode-cleaning" of multimode core fiber output through saturated optical parametric amplification.