Fiber Chirped Pulse Amplification System Research Articles

High reflectivity, ultraflat-spectrum chirped fiber Bragg grating written using low energy UV femtosecond pulses

Chirped fiber Bragg gratings (CFBGs) have been extensively used in applications such as ultrafast lasers, fiber sensors, and fiber communications. This work presents a comprehensive investigation of CFBG written using a 257 nm femtosecond laser and a linear chirped phase mask. The CFBG, written on a hydrogen-loaded polarization-maintaining fiber, exhibited a center wavelength of 1031.7 nm and a bandwidth of 11.97 nm. The CFBG achieved an average reflectivity of 98.2 % within its bandwidth, demonstrating an ultrahigh flatness of the reflection spectrum with a low spectral reflectivity variance of 0.00003 (σ2). The high group velocity dispersion (GVD) of 60.7 ps2 signifies its potential in fiber chirped pulse amplification systems and dispersion compensation system. Meanwhile, the fs-laser + PM writing method shows advantages of high efficiency and low energy consumption (as low as 2 nJ), owing to the high photosensitivity of the fiber to the UV band, which holds significant promise in fiber grating inscription.

High energy, frequency-doubled thulium-doped fiber chirped-pulse amplification system at 950 nm

High energy, frequency-doubled thulium-doped fiber chirped-pulse amplification system at 950 nm

1 MHz,273 W average power Ytterbium-doped rodtype fiber chirped pulse amplification system

Ytterbium-doped ultrafast fiber lasers are widely used in scientific research, industrial processing, medical diagnosis, and other fields due to their excellent beam quality and high output power. The larger mode area allows the fiber to deliver higher pulse peak power. The commercial rodtype Ytterbium-doped fiber with a core diameter of 85 μm produced by NKT in Denmark can produce ultra-short pulses of the order of 100 watts and 100 microjoules. Based on this rod-type fiber, we constructed a chirped-pulse amplification (CPA) system which uses high-efficiency transmission gratings and temperature-tunable chirped fiber Bragg grating (CFBG) to compensate for dispersion. We investigate the effect of input powers on the amplified power and pulse compression quality, and find that higher input power slows down gain saturation and improve amplification efficiency. At input powers of 20W and 30W, we obtained output powers of 305W and 323W respectively, with an amplification efficiency of about 80%. To reduce the accumulation of nonlinear phase shift, we employ circular polarization amplification. At low output powers (less than 160 W), the effect of nonlinear phase accumulation on the compressed pulse is negligible, and increasing the input power increases the amplification efficiency. When the output power exceeds 200 W, the increased accumulation of nonlinear phase shift degrades the pulse compression quality, which implies that the input power should be appropriately reduced to the power range between 5 W and 20 W. With an input power of 20W and a pump power of 429W, the output power can reach 305W. After pulse compression using a diffraction-grating pair, this rod-type fiber CPA system delivers 1 MHz, 264 fs pulses with 273 W average power. These results provide an important experimental basis for performance optimization of high-power and high-energy ultrafast fiber lasers.

Hybrid Fiber-Single Crystal Fiber Chirped-Pulse Amplification System Emitting More Than 1.5 GW Peak Power With Beam Quality Better Than 1.3

Hybrid Fiber-Single Crystal Fiber Chirped-Pulse Amplification System Emitting More Than 1.5 GW Peak Power With Beam Quality Better Than 1.3

High-power two-color plasma-based THz generation driven by a Tm-doped fiber laser.

We report on the efficient generation of broadband THz radiation based on a two-color gas-plasma scheme. Broadband THz pulses covering the whole THz spectral region, from 0.1-35 THz, are generated. This is enabled by a high-power, ultra-fast, thulium-doped, fiber chirped pulse amplification (Tm:FCPA) system and a subsequent nonlinear pulse compression stage that uses a gas-filled capillary. The driving source delivers 40 fs pulses at a central wavelength of 1.9 μm with 1.2 mJ pulse energy and 101 kHz repetition rate. Owing to the long driving wavelength and the use of a gas-jet in the THz generation focus, the highest reported conversion efficiency for high-power THz sources (>20 mW) of 0.32% has been achieved. The high efficiency and average power of 380 mW of the broadband THz radiation make this an ideal source for nonlinear, tabletop THz science.

Broadband spectral combining of three pulse-shaped fiber amplifiers with 42fs compressed pulse duration.

We demonstrate ultra-broadband spectral combining of ultrashort pulses from Yb-doped fiber amplifiers, with coherently spectrally synthesized pulse shaping, to achieve tens-of-fs pulses. This method can fully compensate for gain narrowing and high order dispersion over broad bandwidth. We produce 42fs pulses by spectrally synthesizing three chirped-pulse fiber amplifiers and two programmable pulse shapers across an 80nm overall bandwidth. To the best of our knowledge, this is the shortest pulse duration achieved from a spectrally combined fiber system at one-micron wavelength. This work provides a path toward high-energy, tens-of-fs fiber chirped-pulse amplification systems.

Burst-mode Yb:fiber chirped pulse amplification system seeded by a multi-soliton bunch fiber laser

We demonstrated a burst-mode Yb:fiber chirped pulse amplification (CPA) system with a seed laser operating in the multi-soliton bunch regime. The multi-soliton bunch operation from a figure-9 fiber laser was obtained by adjusting the pump power properly, where the pulse number can be tuned flexibly from 1 to 3. The CPA system delivers bursts at a repetition rate of 16.34 MHz, while each burst comprise 3 pulses with an interval of 3.96 ns. When the pump power of the main amplifier is increased to 24 W, the maximum output power and energy of the pulse burst is 5.38 W and 329.25 nJ, respectively. The pulse duration could be further reduced to 592 fs with a grating-pair compressor. The proposed scheme provides an alternative seed laser source for burst-mode CPA systems, which will be beneficial to the design of flexible high-power femtosecond lasers.

High-power, femtosecond vortex beams generation in the visible and near-infrared region

Ultrafast vortex beams have been successfully utilized in a wide variety of applications. Here, we report on the generation of the visible and near-infrared cylindrical vector beams with femtosecond pulse duration and tens of Watts average output power. Based on an optimized fiber chirped-pulse amplification system and second harmonic generation technology, Gaussian beams are generated at the visible and near-infrared wavelength, respectively. After mode conversion operation, the high-quality cylindrical vector beams can be obtained with a central wavelength of 1036.13 nm and maximum output power and ultrafast pulse duration of 60.49 W/824 fs for radial vector beams and 59.67 W/783 fs for azimuthal vector beams. In the visible spectral region, the output cylindrical vector beams have a maximum output power of 30.78 W (radial vector beams) and 27.46 W (azimuthal vector beams) at 515.75 nm central wavelength. The pulse durations are measured to be 262 fs for radial vector beam and 273 fs for azimuthal vector beam at the maximum output power. The results demonstrate that the proposed laser systems may pay a promising way to develop high-power femtosecond cylindrical vector beams sources in the visible and near-infrared wavelength for optical communication, super-resolution imaging and laser processing.

Yb-Doped Fiber Chirped Pulse Amplification System Delivering 1 mJ, 231 fs at 1 kHz Repetition Rate

In this paper a single-channel chirped pulse amplification laser system based on Yb-doped photonic crystal fiber was constructed, which achieved a pulse energy output of 1 mJ with a beam quality close to the diffraction limit. Pulsed synchronous pumping was used to suppress amplified spontaneous emission at a repetition rate of 1 kHz. The de-chirped pulse width of 231 fs was achieved by precise systematic dispersion control, and the corresponding peak power reached 3.85 GW.

Hundred-watt level average power CPA system with all-fiberized laser amplifiers based on CFBG stretcher and CVBG compressor

We report on a novel fiber chirped-pulse amplification system with a hundred-watt level average power. All-fiberized laser amplifiers, a chirped fiber Bragg grating stretcher, and a chirped volume Bragg grating compressor make up the system. The chirped fiber Bragg gratings were inscribed in the experiment through the fabrication system built by ourselves, with the parameters fine-tuned during fabrication to match the spectrum after stretching to the source waveband and the spectral width of the chirped volume Bragg grating compressor. A 12 m-long photonic crystal fiber was also used to provide effective spectral bandwidth matching between the pre-amplifier and the chirped fiber Bragg gratings. Meanwhile, the gain fiber length of the amplifiers was suitably selected, and the overall system's spectral matching was achieved. As a result, a compressed average power of 111.4 W was obtained with a pulse duration of 1.5 ps, resulting in peak power of 4.1 MW. The proposed all-fiberized stretcher and amplifier structure significantly decrease the system's volume, increase the system's stability and dependability, and may be used in various applications.

Broadband Fiber Chirped-pulse Amplification System Based on Parabolic Evolution

Broadband Fiber Chirped-pulse Amplification System Based on Parabolic Evolution

Gas-plasma-based generation of broadband terahertz radiation with 640 mW average power.

We present a high-power source of broadband terahertz (THz) radiation covering the whole THz spectral region (0.1-30 THz). The two-color gas plasma generation process is driven by a state-of-the-art ytterbium fiber chirped pulse amplification system based on coherent combination of 16 rod-type amplifiers. Prior to the THz generation, the pulses are spectrally broadened in a multipass cell and compressed to 37 fs with a pulse energy of 1.3 mJ at a repetition rate of 500 kHz. A gas-jet scheme has been employed for the THz generation, increasing the efficiency of the process to 0.1%. The air-biased coherent detection scheme is implemented to characterize the full bandwidth of the generated radiation. A THz average power of 640 mW is generated, which is the highest THz average power achieved to date. This makes this source suitable for a variety of applications, e.g., spectroscopy of strongly absorbing samples or driving nonlinear effects for the studies of material properties.

Towards high energy, minimum duration pulse in Yb-doped fiber CPA system by spectral shaping technique

Spectral shaping is a promising solution for generation of high-energy, short pulse in fiber chirped-pulse amplification (CPA) system. We demonstrated a design of spectral notch filter based on genetic algorithm (GA) with parallel computing and verified through dynamic rate equations. This scheme can simultaneously realize compensation for spectral narrowing and shifting. The overlap between the amplified spectra after pre-shaping and the seed spectrum at different gains are all greater than 97%.

Ultrafast laser processing of ceramics: Comprehensive survey of laser parameters

The productivity and quality of laser micromachining depend on multiple laser parameters that are intricately correlated. For these optimizations, a quick survey of laser parameters is vital. Recently, the authors developed a Yb-doped fiber chirped-pulse amplification system that can control various laser parameters in a wide range (pulse duration: 0.4–400 ps, repetition: single shot to 1 MHz, etc.). In this work, using this laser system, percussion microdrilling of three types of advanced ceramics, AlN, Al2O3, and Y2O3-doped ZrO2, was explored. In the case of the microdrilling of the Al2O3 ceramic, the ablation volume increased about 2–3 times as the pulse repetition increased from 100 Hz to 1 MHz. This suggests a different mechanism because the volume removal became dominant at 1 MHz. Scanning electron microscope observation confirmed a drastic melt formation at 1 MHz. From these, there is an additional volume removal due to the heat accumulation by multipulse irradiation on the Al2O3 ceramic at a higher repetition rate. It was also found that the variation of ablation volume with the pulse duration and fluence exhibited a big difference among these ceramics. A comprehensive survey of ultrafast laser ablation of ceramics was demonstrated.

Carrier-envelope offset stable, coherently combined ytterbium-doped fiber CPA delivering 1 kW of average power.

We present a carrier-envelope offset (CEO) stable ytterbium-doped fiber chirped-pulse amplification system employing the technology of coherent beam combining and delivering more than 1 kW of average power at a pulse repetition rate of 80 MHz. The CEO stability of the system is 220 mrad rms, characterized out-of-loop with an f-to-2f interferometer in a frequency offset range of 10 Hz to 20 MHz. The high-power amplification system boosts the average power of the CEO stable oscillator by five orders of magnitude while increasing the phase noise by only 100 mrad. No evidence of CEO noise deterioration due to coherent beam combining is found. Low-frequency CEO fluctuations at the chirped-pulse amplifier are suppressed by a "slow loop" feedback. To the best of our knowledge, this is the first demonstration of a coherently combined laser system delivering an outstanding average power and high CEO stability at the same time.

Active fiber loop for synthesizing GHz bursts of equidistant ultrashort pulses.

We demonstrate a method to synthesize ultra-high repetition rate bursts of ultrashort laser pulses containing any number of pulses within a burst with identical pulse separation and adjustable amplitude. The key element to synthesize the GHz bursts of ultrashort laser pulses is an active fiber loop. The method was implemented in the fiber chirped pulse amplification system to obtain 72 nJ-energy bursts of 20 pulses with a 2.65 GHz intra-burst pulse repetition rate and a 500 kHz burst repetition rate. The dispersion compensation mechanism ensured a mean pulse duration of 570 fs within the bursts.

130 W, 180 fs ultrafast Yb-doped fiber frequency comb based on chirped-pulse fiber amplification.

We report on a high-power fiber optical frequency comb consisting of a 250-MHz mode-locked fiber laser and a three-stage cascaded fiber chirped-pulse amplification system. After power scaling, the group velocity dispersion and third-order dispersion, generated in fiber stretcher and amplifiers, are compensated by a grism compressor, outputting a 132-W, 180-fs pulse train. The repetition rate and carrier-envelope offset frequency are locked to a Rb clock with the standard deviations of 1.07 and 0.87 mHz, corresponding to the fractional instability of 8.3×10-13 and 1.35×10-19, respectively. Moreover, we investigate the noise characteristics at high average powers, presenting a low-noise property of this high-power fiber OFC.

Compact, high repetition rate, 4.2 MW peak power, 1925 nm, thulium-doped fiber chirped-pulse amplification system with dissipative soliton seed laser.

We report the demonstration of a high average- and peak-power, 1925 nm, thulium-fiber based chirped pulse amplification (CPA) system. A compact, dissipative soliton thulium-fiber, mode-locked seed produced pre-chirped pulses with 25 ps duration, 45 mW output power and repetition rate of 15.7 MHz. After stretching to 105 ps in 83 m of normal dispersion fiber, the pulses were amplified in a core-pumped pre-amplifier and a cladding pumped power amplifier to average output powers of 28 W and 30 W with forward and backward pumping, respectively, with the output power limited only by the available pump power. After a pair of fused silica transmission gratings with an efficiency of 71%, the amplified pulses were re-compressed to 297 fs yielding pulses with a peak power of 4.2 MW (backward pumped) and a pulse energy of 1.27µJ.

High-energy femtosecond pulse shaping, compression, and contrast enhancement using multicore fiber

Nonlinear spatiotemporal dynamics of femtosecond pulses in a hexagonal seven-core silica fiber pumped by a sub-μJ 370fs Er:fiber chirped pulse amplification (CPA) system were studied. Nonlinear pulse shaping and compression in the central core and pedestal coupling to the outer cores were directly measured by frequency-resolved optical gating. Further compression of the pulses spectrally broadened in the multicore fiber down to 53fs was demonstrated. Two orders of magnitude contrast enhancement of the pulses after compression was observed.

Ultrafast thulium fiber laser system emitting more than 1 kW of average power.

In this Letter, we report on the generation of 1060W average power from an ultrafast thulium-doped fiber chirped pulse amplification system. After compression, the pulse energy of 13.2μJ with a pulse duration of 265fs at an 80MHz pulse repetition rate results in a peak power of 50MW spectrally centered at 1960nm. Even though the average heat-load in the fiber core is as high as 98W/m, we confirm the diffraction-limited beam quality of the compressed output. Furthermore, the evolution of the relative intensity noise with increasing average output power has been measured to verify the absence of transversal mode instabilities. This system represents a new average power record for thulium-doped fiber lasers (1150W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality, in general, even considering single-channel ytterbium-doped fiber amplifiers.