Fiber Chirped Pulse Amplification Research Articles

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.

1 MHz repetition rate hollow fiber pulse compression to sub-100-fs duration at 100 W average power

We report on nonlinear pulse compression at very high average power. A high-power fiber chirped pulse amplification system based on a novel large pitch photonic crystal fiber delivers 700 fs pulses with 200 μJ pulse energy at a 1 MHz repetition rate, resulting in 200 W of average power. Subsequent spectral broadening in a xenon-filled hollow-core fiber and pulse compression with chirped mirrors is employed for pulse shortening and peak power enhancement. For the first time, to our knowledge, more than 100 W of average power are transmitted through a noble-gas-filled hollow fiber. After pulse compression of 81 fs, 93 μJ pulses are obtained at a 1 MHz repetition rate.

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.

88 W 05 mJ femtosecond laser pulses from two coherently combined fiber amplifiers

The generation of 0.5 mJ femtosecond laser pulses by coherent combining of two high power high energy fiber chirped-pulse amplifiers is reported. The system is running at a repetition frequency of 175 kHz producing 88 W of average power after the compressor unit. Polarizing beam splitters have been used to realize an amplifying Mach-Zehnder interferometer, which has been stabilized with a Hänsch-Couillaud measurement system. The stabilized system possesses a measured residual rms phase difference fluctuation between the two branches as low as λ/70 rad at the maximum power level. The experiment proves that coherent addition of femtosecond fiber lasers can be efficiently and reliably performed at high B-integral and considerable thermal load in the individual amplifiers.

Multi-gigawatt ultrashort pulses at high repetition rate and average power from two-stage nonlinear compression

We present simple and compact (1.5m x 0.5m footprint) post-compression of a state-of-the-art fiber chirped pulse amplification system. By using two stage nonlinear compression in noble gas filled hollow core fibers we shorten 1 mJ, 480 fs, 50 kHz pulses. The first stage is a 53 cm long, 200 µm inner diameter fiber filled with xenon with subsequent compression in a chirped mirror compressor. A 20 cm, 200 µm inner diameter fiber filled with argon further broadens the spectrum in a second stage and compression is achieved with another set of chirped mirrors. The average power is 24.5 W/19 W after the first/second stage, respectively. Compression to 35 fs is achieved. Numerical simulations, agreeing well with experimental data, yield a peak power of 5.7 GW at a pulse energy of 380 µJ making this an interesting source for high harmonic generation at high repetition rate and average power.

Generation of 400 μW at 175 μm using a two-color Yb fiber chirped pulse amplifier

We have demonstrated the generation of 400 μW of power at ~18 μm by difference-frequency mixing the 1038 and 1105 nm from a two-color, chirped pulse amplification Yb fiber system. A two-color seed is selected from a continuum source and amplified to 300 mW of total power in a two-stage Yb fiber amplifier.

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.

Long-term carrier-envelope-phase stabilized fiber-bulk hybrid laser with millihertz linewidth and 50 W average power

Long-term carrier-envelope-phase stabilization was demonstrated in high-power large-modearea fiber chirped-pulse spectral fraction amplification at 1030 nm of a broadband femtosecond Ti:sapphire laser. The carrier enveloped phase was stably controlled with the maximum average power up to 50 W by pre-compensating the carrier-envelope phase changes in the high-power fiber amplifiers. The locked in loop and out of loop frequency fluctuation was measured to be 1.44 and 46 mHz within half an hour. The locked carrier-frequency exhibited an in loop and out of loop beat signal linewidth of 1.66 and 2.27 mHz, accordingly accumulated phase jitter was estimated to be 0.22 and 0.73 rad, respectively, with the integration range from 10 mHz to 100 kHz. The phase stabilization was measured to change little as the output power increased, confirming negligible amplitude-to-phase noise conversions in the linear high-power fiber chirped pulse amplification.

High-repetition-rate sub-5-fs pulses with 12 GW peak power from fiber-amplifier-pumped optical parametric chirped-pulse amplification

An optical parametric chirped-pulse amplification system delivering pulses with more than 12 GW peak power is presented. Compression to sub-5 fs, 87 μJ and 5.4 fs, 100 μJ is realized at the 30 kHz repetition rate. A high-energy fiber chirped-pulse amplification system operating at 1 mJ pulse energy and nearly transform-limited pulses is used to achieve ultrabroadband amplification in two 2mm beta-barium borate crystals. Precise pulse shaping is used to compress the pulses to a few percentages of their transform limit. Assuming diffraction limited focusing (d<2 μm), peak intensities as high as 10(18) W/cm(2) can be reached.

Fiber chirped-pulse amplification system emitting 38 GW peak power

We report on the experimental demonstration of a fiber chirped- pulse amplification system capable of generating nearly transform-limited sub 500 fs pulses with 2.2 mJ pulse energy at 11 W average power. The resulting record peak power of 3.8 GW could be achieved by combining active phase shaping with an efficient reduction of the acquired nonlinear phase. Therefore, we used an Ytterbium-doped large-pitch fiber with a mode field diameter of 105 µm as the main amplifier.

Long-term stable passive synchronization of 50 µJ femtosecond Yb-doped fiber chirped-pulse amplifier with a mode-locked Ti:sapphire laser

We report long-term stable passive synchronization of a femtosecond Yb-doped fiber chirped-pulse amplifier (CPA) with a mode-locked Ti:sapphire laser for pump-seed synchronization of an optical parametric chirped-pulse amplification (OPCPA) system. The fiber CPA system delivers pulses with a wavelength of 1035 nm, energy of 50 µJ, and duration of 690 fs at a repetition rate of 0.4 MHz. The seed fiber oscillator is passively synchronized with a mode-locked Ti:sapphire laser by injection of the Ti:sapphire laser pulses into the cavity of the fiber oscillator. The second harmonic (SH) output with a wavelength of 518 nm, energy of 18 µJ, and duration of 1.2 ps was prepared for the OPCPA pump. The measured timing jitter between the pump (fiber SH) and the seed (Ti:sapphire) was 42 ± 14 fs, while the jitter between two oscillator outputs was 1.4 ± 0.5 fs. The robust synchronization technique allows long-term stable operation over 8 h.

Optimization of high performance ultrafast fiber laser systems to &gt;10 GW peak power

We show that the peak powers of ytterbium-doped fiber chirped pulse amplification (CPA) can be scaled by at least 1 order of magnitude (in the transform limit) as compared to current systems by using a different spectral region of operation. A simple and fast model for saturated broadband fiber CPA systems is developed and applied to study the impact of the interplay between the spectrally dependent small signal gain and the saturation on the output bandwidth. The influence of self-phase modulation on the recompression of the pulse is discussed. It can be shown that the novel operation regime exhibits superior performance even if nonlinear effects are considered. The numerical results are significant for the design of the next generation of ultrafast high power fiber lasers.

Pulse energy of 151 nJ from ultrafast thulium-doped chirped-pulse fiber amplifier

We report on chirped-pulse amplification of an ultrafast thulium-doped fiber laser. Pulses with an energy of 3.3 nJ and a bandwidth-limited pulse duration of 195 fs could be amplified to 151 nJ, which corresponds to an average power of 5.7 W at 37.6 MHz pulse repetition rate. The maximum output power was limited by the available pump power. The pulses could be dechirped to a duration of 258 fs.

Impact of self-phase modulation on coherently combined fiber chirped-pulse amplifiers

The impact of self-phase modulation on coherently combined ultrafast fiber-based chirped-pulse amplifiers (CPA) is studied. We point out that, in nonlinear CPA regime, the nonlinear phase accumulated in each fiber amplifier can significantly differ from one to another, resulting in serious efficiency degradation of coherent combining. A test bench based on picosecond pulses, and a single fiber amplifier is developed to experimentally demonstrate the effect. The effects that can lead to this nonlinear phase deviation and the induced system limitations are discussed and analyzed.

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.

130-W picosecond green laser based on a frequency-doubled hybrid cryogenic Yb:YAG amplifier

130-W average-power picosecond green laser pulses at 514.5 nm are generated from a frequency-doubled hybrid cryogenic Yb:YAG laser. A second-harmonic conversion efficiency of 54% is achieved with a 15-mm-long noncritically phase-matched lithium triborate (LBO) crystal from a 240-W 8-ps 78-MHz pulse train at 1029 nm. The high-average-power hybrid laser system consists of a picosecond fiber chirped-pulse amplification seed source and a cryogenically-cooled double-pass Yb:YAG amplifier. The M(2) value of 2.7, measured at 77 W of second-harmonic power, demonstrates a good focusing quality. A thermal analysis shows that the longitudinal temperature gradient can be the main limiting factor in the second-harmonic efficiency. To our best knowledge, this is the highest-average-power green laser source generating picosecond pulses.

Nonlinear compression in a rod-type fiber for high energy ultrashort pulse generation

We report the use of nonlinear compression in a very large mode-area rod-type photonic crystal fiber. This fiber allows the use of high energy pulses in the few microjoule range. We demonstrate the compression of 4 microJ, 338 fs pulses from a fiber chirped pulse amplification (FCPA) system down to 49 fs, 41 MW peak power pulses at a repetition rate of 200 kHz with an average power of 400 mW. The nonlinear compression setup is composed of a 5-cm-long rod-type fiber and a pair of SF10 prisms. The system was optimized to obtain good temporal quality, with a temporal Strehl ration of 86 % for the compressed 49 fs pulses.

Distributed nonlinear fiber chirped-pulse amplifier system

A two-stage fiber-based femtosecond amplification system is presented, based on chirped-pulse amplification in highly nonlinear regime. The amount of self-phase modulation is separately adjusted in each stage selecting the proper stretching ratio in order to compensate gain narrowing. Analytical design rules are validated using numerical simulations. Our experimental implementation leads to the generation of high temporal quality 20 microJ 202 fs pulses at repetition rate of 200 kHz, a record duration at this energy level.

High energy ultrashort pulses via hollow fiber compression of a fiber chirped pulse amplification system

A simple, robust and compact pulse compressor for a high-repetition rate high-peak power fiber chirped pulse amplification system is presented. We use noble-gas-filled hollow fibers for spectral broadening of the optical pulses via self-phase modulation. Subsequent compression with chirped mirrors shortens the pulses by more than a factor of 10. Pulses shorter than 70 fs with pulse energies of the order of 100 mu J have been obtained resulting in a peak power up to 1 GW at 30.3kHz. Additionally, nonlinear polarization rotation has been used for temporal pulse cleaning during the nonlinear compression at 30.3 kHz and 100 kHz, respectively.

Compensation of Gain Narrowing by Self-Phase Modulation in High-Energy Ultrafast Fiber Chirped-Pulse Amplifiers

We propose a method to compensate gain narrowing by use of the self-phase modulation effect in a femtosecond fiber chirped-pulse amplifier (CPA). An engineering rule is derived to determine the stretched pulse duration that allows this compensation. Simulations are carried out to validate this idea. A tradeoff is found between achievable pulse duration and output energy, but we show that this technique allows the generation of 100 fs pulses even for high-gain systems, with output energies of the order of 100 ? J. An experimental proof of principle demonstrates the generation of 112 fs, 10 ?J pulses, the shortest high-energy pulse, to our knowledge, generated by a fiber CPA system.