Showing papers on "Chirped pulse amplification published in 2018"

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

Abstract: In this Letter, we report on the generation of 1060 W average power from an ultrafast thulium-doped fiber chirped pulse amplification system. After compression, the pulse energy of 13.2 μJ with a pulse duration of 265 fs at an 80 MHz pulse repetition rate results in a peak power of 50 MW spectrally centered at 1960 nm. Even though the average heat-load in the fiber core is as high as 98 W/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 (1150 W uncompressed) and ultrashort pulse fiber lasers with diffraction-limited beam quality, in general, even considering single-channel ytterbium-doped fiber amplifiers.

Time- and angle-resolved photoemission spectroscopy of solids in the extreme ultraviolet at 500 kHz repetition rate

Abstract: Time- and angle-resolved photoelectron spectroscopy (trARPES) employing a 500 kHz extreme-ultravioled (XUV) light source operating at 21.7 eV probe photon energy is reported. Based on a high-power ytterbium laser, optical parametric chirped pulse amplification (OPCPA), and ultraviolet-driven high-harmonic generation, the light source produces an isolated high-harmonic with 110 meV bandwidth and a flux of more than $10^{11}$ photons/second on the sample. Combined with a state-of-the-art ARPES chamber, this table-top experiment allows high-repetition rate pump-probe experiments of electron dynamics in occupied and normally unoccupied (excited) states in the entire Brillouin zone and with a temporal system response function below 40 fs.

Relativistic few-cycle pulses with high contrast from picosecond-pumped OPCPA

Abstract: For experiments in plasma, nuclear, and high-energy physics, there is a strong demand for laser pulses exhibiting relativistic intensity, few-cycle pulse duration, and a very high contrast. Here we present a picosecond-pumped optical parametric chirped pulse amplification (OPCPA) system delivering pulses at 10 Hz repetition rate with the following key parameters: a compressed pulse duration of less than 7 fs (close to the Fourier limit), a contrast of better than 1011 starting from 1 ps before the main pulse, and a peak intensity of 6.9×1019 W/cm2 achieved with an off-axis parabolic mirror (f/1.6). In a proof-of-principle experiment, these pulses were used to generate high harmonics from solid surfaces with photon energies exceeding 55 eV. These results underline the promising perspectives of the reported system for relativistic light–matter interaction experiments and attosecond science.

Improvement of the focusing ability by double deformable mirrors for 10-PW-level Ti: sapphire chirped pulse amplification laser system.

Abstract: Double deformable mirrors (DMs) with different actuator densities are cascaded to optimize the wavefront aberrations to improve the focus intensity of the Shanghai super-intense ultrafast laser facility (SULF), which plans to generate 10 PW laser pulse. The beam aberrations near the focal spot are corrected from 0.556 um to 0.112 um in RMS by a 300-mm DM with a large stroke installed after the compressor. After then, it is further optimized to 0.041 um using a 130-mm DM with a high spatial resolution working after the main amplifier. The corrected beam is focused to 2.75 × 2.87 um2 at the full width at half maximum (FWHM) with an f/2.5 off-axis parabolic mirror (OAP), which contains approximately 27.69% energy. A peak intensity of 2 × 1022 W/cm2 is achieved at the output of 5.4 PW, and it could exceed 1023 W/cm2 in the SULF 10 PW laser facility using an f/1.8 OAP.

2.6 mJ/100 Hz CEP-stable near-single-cycle 4 μm laser based on OPCPA and hollow-core fiber compression

Abstract: A carrier-envelope-phase-stable near-single-cycle mid-infrared laser based on optical parametric chirped pulse amplification and hollow-core fiber compression is demonstrated. A 4 μm laser pulse with 11.8 mJ energy is delivered from a KTA-based optical parametric chirped pulse amplification (OPCPA) with 100 Hz repetition rate, and compressed to 105 fs by a two-grating compressor with efficiency over 50%. Subsequently, the pulse spectrum is broadened by employing a krypton gas-filled hollow-core fiber. Then, the pulse duration is further compressed to 21.5 fs through a CaF2 bulk material with energy of 2.6 mJ and energy stability of 0.9% RMS, which is about 1.6 cycles for a 4 μm laser pulse. The carrier envelope phase of the near-single-cycle 4 μm laser pulse is passively stabilized with 370 mrad.

Spectral pulse shaping of a 5 Hz, multi-joule, broadband optical parametric chirped pulse amplification frontend for a 10 PW laser system.

Abstract: We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4 J pulses at a repetition rate of 5 Hz. It will serve as a frontend for the 1.5 kJ, <150 fs, 10 PW laser beamline currently under development by a consortium of National Energetics and Ekspla. The spectrum of the OPCPA system is precisely controlled by arbitrarily generated waveforms of the pump lasers. To fully exploit the high flexibility of the frontend, we have developed a 1D model of the system and an optimization algorithm that predicts suitable pump waveform settings for a desired output spectrum. The OPCPA system is shown to have high efficiency, a high-quality top-hat beam profile, and an output spectrum demonstrated to be shaped consistently with the theoretical model.

Self-calibrating d-scan: measuring ultrashort laser pulses on-target using an arbitrary pulse compressor

Abstract: In most applications of ultrashort pulse lasers, temporal compressors are used to achieve a desired pulse duration in a target or sample, and precise temporal characterization is important. The dispersion-scan (d-scan) pulse characterization technique usually involves using glass wedges to impart variable, well-defined amounts of dispersion to the pulses, while measuring the spectrum of a nonlinear signal produced by those pulses. This works very well for broadband few-cycle pulses, but longer, narrower bandwidth pulses are much more difficult to measure this way. Here we demonstrate the concept of self-calibrating d-scan, which extends the applicability of the d-scan technique to pulses of arbitrary duration, enabling their complete measurement without prior knowledge of the introduced dispersion. In particular, we show that the pulse compressors already employed in chirped pulse amplification (CPA) systems can be used to simultaneously compress and measure the temporal profile of the output pulses on-target in a simple way, without the need of additional diagnostics or calibrations, while at the same time calibrating the often-unknown differential dispersion of the compressor itself. We demonstrate the technique through simulations and experiments under known conditions. Finally, we apply it to the measurement and compression of 27.5 fs pulses from a CPA laser.

μJ-level Raman-assisted fiber optical parametric chirped-pulse amplification.

Abstract: We experimentally demonstrate the amplification of chirped pulses in a fiber optical parametric chirped pulse amplifier up to 1 μJ. This high energy level originates from combined Raman and parametric processes in a specially designed solid core photonic bandgap fiber. Output pulses are recompressed up to 560 fs. These performances make this all-fiber system compatible with first stages of bulk amplification chains.

Continuous every-single-shot carrier-envelope phase measurement and control at 100 kHz.

Abstract: With the emergence of high-repetition-rate few-cycle laser pulse amplifiers aimed at investigating ultrafast dynamics in atomic, molecular, and solid-state science, the need for ever faster carrier-envelope phase (CEP) detection and control has arisen. Here we demonstrate a high-speed, continuous, every-single-shot measurement and fast feedback scheme based on a stereo above-threshold ionization time-of-flight spectrometer capable of detecting the CEP and pulse duration at a repetition rate of up to 400 kHz. This scheme is applied to a 100 kHz optical parametric chirped pulse amplification few-cycle laser system, demonstrating improved CEP stabilization and allowing for CEP tagging.

Normal-dispersion fiber optical parametric chirped-pulse amplification

Abstract: We demonstrate a fiber optical parametric chirped-pulse amplifier pumped in the normally dispersive regime. This approach is readily scalable, offering a route to microjoule-level, femtosecond pulses at new wavelengths. As a first demonstration, we pump with chirped pulses at 1.03 μm and seed with a continuous-wave beam at 0.85 μm, and are able to generate idlers at 1.3 μm with durations as short as 210 fs or energies as high as 180 nJ.

Continous every-single-shot carrier-envelope phase measurement and control at 100 kHz

Abstract: With the emergence of high-repetition-rate few-cycle laser pulse amplifiers, aimed at investigating ultrafast dynamics in atomic, molecular and solid state science, the need for ever faster carrier-envelope phase (CEP) detection and control has arisen. Here we demonstrate a high speed, continuous, every-single-shot measurement and fast feedback scheme based on a stereo above-threshold ionization time-of-flight spectrometer capable of detecting the CEP and pulse duration at a repetition rate of up to 400 kHz. This scheme is applied to a 100 kHz optical parametric chirped pulse amplification (OPCPA) few-cycle laser system, demonstrating improved CEP stabilization and allowing for CEP tagging.

Progress of the injection laser system of SG-II

Abstract: A high power laser system was used to drive the ignition of inertial confinement fusion (ICF), of which the high energy, the uniform focal spot, the accurate laser waveform, and the synchronization between the laser beams are key parameters. To accomplish this, global laser characteristics control should be assured, which was the main purpose of the injection laser system. In this paper, the key technological progress involved in the improvement of the performance of the injection laser of SG-II is reported, including frequency domain control, time domain control, near-field spatial shaping, pre-amplifier technology, and the optical parametric chirped pulse amplification pump source.

A viable laser driver for a user plasma accelerator

Abstract: The construction of a novel user facility employing laser-driven plasma acceleration with superior beam quality will require an industrial grade, high repetition rate petawatt laser driver which is beyond existing technology However, with the ongoing fast development of chirped pulse amplification and high average power laser technology, options can be identified depending on the envisioned laser–plasma acceleration scheme and on the time scale for construction Here we discuss laser requirements for the EuPRAXIA infrastructure design and identify a suitable laser concepts that is likely to fulfill such requirements with a moderate development of existing technologies

Effect of temporally modified ultra-short laser pulses on ion acceleration from thin foil targets

Abstract: We demonstrate the significant enhancement of ion energy from the interaction of intense, chirped pulse amplification based ultrashort laser pulse with thin foil targets by adjusting the laser temporal characteristics with a simple adjustment of grating pair separation inside the pulse compressor. The laser pulse was focused to a maximum intensity of 3.2 × 1019 W/cm2 on to thin metallic foil targets of submicron thickness. The pulse duration was varied from 25 to 500 fs by adjusting the laser pulse compressor grating separation for fixed laser pulse energy (2.1 J). Contrary to the conventional belief, we found that the ion acceleration is not optimum at the shortest laser pulse duration and, thus, at highest intensity as predicted by the previous intensity scaling data. Instead, stretched pulses are better suited for efficient ion acceleration. In addition to this, we found a contrasting effect with respect to the sign of the laser chirp for almost the same laser pulse duration. In particular, we show 70% enhancement in maximum ion energy (from 6 MeV to 10 MeV) with positively chirped 250–350 fs stretched pulses. On the contrary, negatively chirped pulses show gradual monotonic reduction in ion energy and flux. Independent electron energy spectra measurement along the laser forward direction exhibits a strong correlation with proton data. The temporal pulse skewness arising due to displaced grating separation is believed to be responsible for this asymmetric proton acceleration behaviour. Efficient absorption of positively modified skewed pulses (shallow rise time and sharp fall) along with the characteristic ion acceleration time can qualitatively explain the experimental result. The present study can be very much important for efficient ion acceleration based on modern day compact, ultra-short pulse 100 TW to PW class lasers.

A Compact High-Average-Power Femtosecond Fiber-Coupled Two-Color CPA System

Abstract: A compact, high-average-power, sub-picosecond, two-color (1025 and 1085 nm) fiber-coupled, chirped pulse amplification Yb:fiber laser is reported. Two colors are selected from a continuum using a chirped fiber Bragg grating, which are then amplified in a two-stage Yb:fiber amplifier system. The preamplifier is fully fiber-coupled, improving significantly the stability and efficiency compared to the former bulk-optic system. The system delivers two-color pulses with the total average power of 2.3 W (1.9 W at 1025 nm and 0.4 W at 1085 nm) at a 65 MHz repetition rate. The FWHM duration of the final compressed output pulses of each color is 900 and 600 fs. The amplified spectrum showed insignificant spontaneous emission between the colors, indicating that the separation could be further increased.

Half of Nobel Prize in Physics honors the inventors of chirped pulse amplification

Abstract: The laureates circumvented an intrinsic limitation in laser technology to develop an amplification protocol now found in nearly every high-power, ultrafast system.

Reducing electric-field-enhancement in metal-dielectric grating by designing grating with asymmetric ridge.

Abstract: Diffraction gratings are an essential optical component of high-power, short-pulse lasers. The maximum output of high-power pulsed lasers is always determined by laser resistance of gratings and this resistance is strongly dependent on the local near electric field intensity in the grating structure. We presented a novel method of reducing electric-field-enhancement in metal-dielectric grating by designing asymmetric grating ridge while maintaining high diffraction performance. Compared with the common isosceles trapezoidal grating, the grating with asymmetric ridge got a 0.04% reduction of diffraction efficiency in TE polarization at 1053 nm incident wavelength but a 21.3% reduction of maximal electric-field-enhancement in grating structure. This method can be applied to any surface-relief gratings to reduce the electric-field-enhancement for improving the laser induced damage threshold (LIDT) of grating and supporting the grating-based chirped pulse amplification (CPA) system to develop into higher peak-power levels.

Photodarkening-Induced Phase Distortions and Their Effects in Single-Channel and Coherently Combined Yb-Doped Fiber Chirped Pulse Amplification Systems

Abstract: We use numerical simulations to investigate the effects of photodarkening (PD) on pulse compression and coherent combination following chirped-pulse amplification in Yb-doped fiber amplifiers. Even though we increase the pump power to keep the pulse energy constant, PD degrades the pulses due to phase distortions resulting from heating acting already within a pulse as well as to increased self-phase modulation if the fiber length is optimized for the PD-free fiber at beginning of life. By contrast, in a fiber shorter than this, the drop in peak power is a relatively modest 35% even at a PD propagation loss as large as 5 dB, thus providing effective mitigation against PD-induced phase distortions. The improvements extend to the combination efficiency of beam-combined systems.

Experimental investigation on pulse-contrast degradation caused by surface reflection in optical parametric chirped-pulse amplification

Abstract: In this Letter, we experimentally explore the pulse-contrast degradation caused by surface reflection in optical parameter chirped-pulse amplification. Different pump-to-signal conversion efficiencies and post-pulses with different intensities are obtained by changing the seed-pulse or pump-pulse energy and inserting etalons with different reflection coefficients, respectively. The contrast measurements show that the generated first pre-pulse intensity is proportional to the product of the surface reflection intensity ratio and the square of the pump-to-signal conversion efficiency.

Femtosecond Lasers for Ophthalmic Surgery Enabled by Chirped-Pulse Amplification

Abstract: Eyes on the Prize This year’s Nobel Prize in Physics, awarded to Donna Strickland and Gerard Mourou, recognizes their invention that enabled the development of femtosecond lasers. These lasers have...

Carrier-envelope-phase stable, high-contrast, double chirped-pulse-amplification laser system

Abstract: We present the first carrier-envelope phase stable chirped pulse amplifier (CPA) featuring high temporal contrast for relativistic intensity laser-plasma interactions at 1 kHz repetition rate. The laser is based on a double-CPA architecture including XPW filtering technique and a high-energy grism-based compressor. 8 mJ, 22 fs pulses are produced with 10-11 temporal contrast at -20 ps and a CEP drift of 240 mrad RMS.

Numerical Simulations of Transfer of Spatial Beam Aberrations in Optical Parametric Chirped-Pulse Amplification

Abstract: In this paper, the spatial characteristics of the optical parametric chirped-pulse amplification (OPCPA) process were numerically studied when initial pump beam was aberrated. Numerical results showed that the spatial walk-off effect transferred phase modulation partly to the signal beam as the pump phase was modulated. Moreover, the modulation amplitude became increasingly severe as the nonlinear length extended. In the absence of phase aberration in the initial input signal, the induced phase aberration in the output signal was assumed as the differential form of the pump beam phase. As the pump beam intensity was modulated, the spatial walk-off effect reduced the influence of pump beam noise on beam quality and the angular spectrum but reduced signal gain simultaneously; thus, it may do more harm than good in the OPCPA process. In the case of a non-diffraction-limited pump beam, the greater the beam quality factor , the lower the conversion efficiency of the output signal in the OPCPA process. These results have important guiding significance for optimized design of an OPCPA system for high power laser.

1-MHz high power femtosecond Yb-doped fiber chirped-pulse amplifier

Abstract: A practical femtosecond polarization-maintaining Yb-doped fiber amplifier enabling 153 fs transform-limited pulse duration with 32 μJ pulse energy at 1 MHz repetition rate corresponding to a peak power of 0.21 GW is demonstrated. The laser system based on chirped-pulse amplification (CPA) technique is seeded by a dispersion managed, nonlinear polarization evolution (NPE) mode-locked oscillator with spectrum bandwidth of 31 nm at 1040 nm and amplified by three fiber pre-amplifying stages and a rod type fiber main amplifying stage. The laser works with beam quality of M2 of 1.3 and power stability of ∼0.63p (root mean square, RMS) over 24 hours will be stable sources for industrial micromachining, medical therapy and scientific research.

Investigation of optical parametric fluorescence suppression with a quencher pulse in an optical parametric chirped-pulse amplification laser

Abstract: The mechanism of suppressing optical parametric fluorescence (OPF) with a quencher pulse in an optical parametric chirped-pulse amplification (OPCPA) laser is investigated. A simplified theoretical model of this phenomenon is presented, and numerical simulations and experimental demonstrations are performed for explanation and verification. The results show that, although the improvement of the temporal contrast usually is limited, the generation and amplification of the OPF in an OPCPA process does be suppressed by the injection of a quencher pulse, and the suppression capability can be slightly enhanced by increasing the quencher-pulse energy. We believe that this work will be helpful in designing high-peak-power lasers with high temporal contrast.