Chirped Pulse Amplification Technique Research Articles

1 kHz, 10 mJ, sub-200 fs regenerative amplifier utilizing a dual-crystal configuration of Yb:CaGdAlO4 featuring exceptional beam quality

In order to boost the energy of the femtosecond regenerative amplifier (RA), we adopt the chirped pulse amplification technique to stretch the seed pulses through the Martinez stretcher and inject them into our specially designed dual-crystal regenerative cavity based on the Yb:CaGdAlO4 (Yb:CGA) crystals. To avoid damaging the component coating, we meticulously regulate the size of the cavity mode on the surface of each component within the cavity to ensure that the energy density remains below the damage threshold. The final output of 11.3 mJ pulse energy was obtained at a 1 kHz repetition rate with a power stability of 0.35% over 1 hour, which is the highest energy we know of for the regenerative output of Yb:CGA crystals. Additionally, leveraging the wide gain spectrum of the Yb:CGA crystal, we achieve a spectrum full width at half maximum (FWHM) of 9 nm along with a compressed pulse duration of 198 fs. The combination of the dual-crystal setup, superior thermal properties of the Yb:CGA crystals, quasi-continuous wave pumping approach, and the thermal-insensitive design of the regenerative cavity effectively minimize the thermal impact on the crystals. The output beam exhibits near-diffraction-limited performance, with an M2 value of only 1.05 × 1.06.

Nonlinear pulse compression technique based on in multi-pass plano-cancave cavity

<sec>Ultrafast femtosecond laser system with hundreds of microjoules of energy, operating at a repetition frequency of several kilohertz, has very important applications in many fields such as medicine, mid-infrared laser generation, industrial processing, and vibrational spectroscopy. The chirped pulse amplification technique provides a feasible path to obtain light sources with those parameters. However, the use of chirped pulse amplification increases the technical complexity and cost of the laser system. Recently, the proposal of a multi-pass cell (MPC) nonlinear pulse compression technique has enabled us to obtain high power ultrafast femtosecond pulses with reduced technical complexity and cost. The device requires only two concave mirrors and a nonlinear medium in between. In the past seven years, the multi-pass cell nonlinear pulse compression technique has made great progress, making it possible to obtain ultrashort pulses with average power of more than a few kW and peak power of tens to hundreds of TW.</sec><sec>In this work, we achieve nonlinear pulse compression of a 100-W picosecond laser by using an improved nonlinear pulse compression scheme that combines a hybrid of a plano-cancave multi-pass cell and multi-thin-plate. Using fused silica plates in plano-cancave cavity, the spectral bandwidth (FWHM) of input picosecond laser is broadened from 0.24 nm to 4.8 nm due to self-phase modulation effect, the pulse is compressed to 483 fs by dispersion compensation using grating pairs, which corresponds to a compression factor of 22, and the final output power of 44.2 W is obtained. Compared with traditional MPC, the plano-cancave cavity scheme we developed is a very promising solution for nonlinear compression due to its compactness, more stability and large compression ratio.</sec>

Femtosecond pulsed laser technology and applications

This paper describes femtosecond pulsed laser technology and related applications. The focus is on two core femtosecond pulsed laser technologies: femtosecond pulsed laser generation and amplification. In the generation of femtosecond pulsed lasers, mode-locking techniques, Kerr-lens mode-locking, and semiconductor saturable absorber mirrors are presented; in the amplification of femtosecond pulsed lasers, chirped-pulse amplification and coherent synthesis techniques are presented. This paper analyses the applications of femtosecond pulsed lasers in both the biomedical and manufacturing sectors and gives the development trends as well as the challenges of femtosecond laser technology. Femtosecond lasers are now used in a wide range of applications. Femtosecond pulsed lasers will develop in the directions of high power, miniaturisation, intelligence and precision. Laser tweezers will become the new direction of development in the future.

Generation of 35 fs, 20 μJ, GHz pulse burst by hybrid fiber amplification technique.

We have proposed and demonstrated the generation of a high-energy, ultrashort pulse duration, GHz pulse burst polarization-maintaining fiber amplification system that utilizes both chirped-pulse amplification and self-similar amplification techniques. Such hybrid fiber amplification system produces 22 μJ-energy bursts of 200 pulses with a 1.02-GHz intra-burst pulse repetition rate and a 1-MHz inter-burst repetition rate. The center wavelength of the amplified compressed pulse is 1065 nm, with a 3 dB spectral bandwidth of 65 nm. The pulse duration of optimal compression is ∼35 fs, which represents the shortest pulse duration reported to date for any multi-microjoule class amplification system with a repetition rate at the GHz level. At the same time, only common double-cladding Yb3+-doped fiber is used as the gain fiber, without any large-mode-area Yb3+-doped photonic crystal fiber, makes the system compact and reliable by the simple fusion operation.

Ultrafast Laser Material Damage Simulation-A New Look at an Old Problem.

The chirped pulse amplification technique has enabled the generation of pulses of a few femtosecond duration with peak powers multi-Tera and Peta–Watt in the near infrared. Its implementation to realize even shorter pulse duration, higher energy, and higher repetition rate laser systems relies on overcoming the limitations imposed by laser damage of critical components. In particular, the laser damage of coatings in the amplifiers and in post-compression optics have become a bottleneck. The robustness of optical coatings is typically evaluated numerically through steady-state simulations of electric field enhancement in multilayer stacks. However, this approach cannot capture crucial characteristics of femtosecond laser induced damage (LID), as it only considers the geometry of the multilayer stack and the optical properties of the materials composing the stack. This approach neglects that in the interaction of an ultrashort pulse and the materials there is plasma generation and associated material modifications. Here, we present a numerical approach to estimate the LID threshold of dielectric multilayer coatings based on strong field electronic dynamics. In this dynamic scheme, the electric field propagation, photoionization, impact ionization, and electron heating are incorporated through a finite-difference time-domain algorithm. We applied our method to simulate the LID threshold of bulk fused silica, and of multilayer dielectric mirrors and gratings. The results are then compared with experimental measurements. The salient aspects of our model, such as the implementation of the Keldysh photoionization model, the impact ionization model, the electron collision model for ‘low’-temperature, dense plasma, and the LID threshold criterion for few-cycle pulses are discussed.

Efficient method to improve the distribution probability of dissipative soliton and noise-like pulse in all-normal-dispersion fiber lasers.

Inspired by the chirped pulse amplification technique, herein, we show an efficient method to improve the distribution probability of dissipative soliton and noise-like pulse in all-normal-dispersion fiber lasers by using an intracavity pulse power editing (PPE) technique for the first time. The dissipative-soliton fiber laser is thus simplified into three parts: a PPE link, a saturable absorber (SA), and a spectral filter. Pulse with different peak powers can be edited in the PPE link, then undergo the positive- or reverse-saturable absorption of the SA, and finally pass through the filter. Further, just by assigning the length of single-mode fiber (SMF) at different positions in the PPE link with a fixed cavity length, four pulse patterns, including dissipative soliton (DS), DS molecules, a bound pattern of DS and noise-like pulse (NLP), and pure NLP, can be controllably produced in fiber lasers. The observed bound pattern of DS and NLP is a new addition to the pulse dynamic pattern family. It is found that the longer the SMF after the gain fiber is, the pulse will be severely broadened. This pulse can easily enter the positive-saturable absorption region of most saturated absorption curves, which will increase the probability of DS radiation; if the SMF behind the gain fiber is shorter, the pulse is not severely broadened. The pulse has a high probability of entering the reverse-saturable absorption range of most saturated absorption curves, resulting in a higher likelihood of generating NLP. In experiments, it is only necessary to increase the SMF length between the gain fiber and the isolator to build a DS fiber laser; however, to construct an NLP fiber laser, only the SMF length between the gain fiber and the isolator needs to be shortened. The experimental results agree well with the numerical predictions. The results significantly broaden the design possibilities for pulse lasers, making them much more accessible to produce specific pulse patterns.

Characterizing spatio-temporal aspects of chirped pulse amplification laser micro-cone target interaction

A numerical study of spatio-temporal distortions effect on the output chirped pulse amplification (CPA) laser beam at the interaction with a micro-cone target was developed. For this, several laser configurations based on CPA technique have been designed and complex study for spatio-temporal distortions compensation has been elaborated using a raytracing model from Optica module of Mathematica in order to determine the optimum conditions to streamline the laser field intensification in the vicinity of laser–conical target interaction point. This numerical model offers an effective solution to fine tune the output CPA beam pulse duration or to control or mitigate the current beam pointing fluctuations caused by specific internal processes during experiments in high-power regimes.

Survey of spatio-temporal couplings throughout high-power ultrashort lasers.

The investigation of spatio-temporal couplings (STCs) of broadband light beams is becoming a key topic for the optimization as well as applications of ultrashort laser systems. This calls for accurate measurements of STCs. Yet, it is only recently that such complete spatio-temporal or spatio-spectral characterization has become possible, and it has so far mostly been implemented at the output of the laser systems, where experiments take place. In this survey, we present for the first time STC measurements at different stages of a collection of high-power ultrashort laser systems, all based on the chirped-pulse amplification (CPA) technique, but with very different output characteristics. This measurement campaign reveals spatio-temporal effects with various sources, and motivates the expanded use of STC characterization throughout CPA laser chains, as well as in a wider range of types of ultrafast laser systems. In this way knowledge will be gained not only about potential defects, but also about the fundamental dynamics and operating regimes of advanced ultrashort laser systems.

Review of laser-plasma physics research and applications in Korea

Laser plasmas can be produced when high-power laser beams are focused in matter. A focused laser beam of TW(terawatt)-level high power has an extremely strong electric field, so neutral atoms are immediately ionized by the laser electric field, leading to a laser-produced plasma. The laser plasma can be produced by small table-top TW lasers based on the CPA (chirped-pulse amplification) technique, and now they are rather easily available even in university laboratories. In Korea, there are several CPA-based TW (or even petawatt) lasers in a few institutions, and they have been used for diverse laser plasma physics research and applications, including the laser acceleration for electrons and ions, high-power THz (tera-hertz) generation, advanced light sources, high-energy-density plasmas, plasma optics, etc. This paper reviews some of the laser plasma physics research and applications that have been performed in several universities and research institutes.

Second Harmonic Generation by ultra-fast Lasers in Plasma.

The interaction of laser with plasma gives rise to several novel relativistic nonlinear optical effects. Higher harmonic generation is an important nonlinear effect. High power ultrafast lasers uses chirped pulse amplification technique to reduce duration of pulse and hence produces pulses of extremely high power densities which in turn oscillates electrons in the medium. The velocity of oscillating electron beats with applied frequency giving rise to higher order harmonics. This paper presents the idea of generation of second harmonic waves with the ultra-fast lasers in plasma, phase matching conditions of second harmonic generated by self modulation under paraxial approximations and its application in imaging microscopy.

Status and progress of the J-KAREN-P high intensity laser system at QST

We report on femtosecond petawatt laser pulses at 0.1 Hz that combine both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric CPA (OPCPA) techniques. High temporal contrast of 1012 prior to the main pulse of 10 J output energy has been demonstrated with a cleaned high-energy seeded low gain OPCPA preamplifier. Intensities as high as 1022 W∕cm2 on target have been achieved by focusing a wave-front corrected 0.3 PW laser by adaptive optics and reflective-type optics with an f ∕1.3 off-axis parabolic mirror. We describe the origins of the pre-pulses generated by the post-pulses through non-linear processes and demonstrate the removal of the pre-pulses by switching to optical components with a small wedge angle at our petawatt laser facility. We also briefly introduce some experimental results. Exploration of new regimes in high field science is now possible with the unprecedented laser intensity levels of the J-KAREN-P laser.

A broadband low-chromatic-aberration single grating Offner stretcher by 3D analysis

The single reflective grating Offner stretcher is a general choice in ultra-intense and ultra-short laser based on chirped pulse amplification (CPA) or optical parametric chirp pulse amplification (OPCPA) technique, but the chromatic aberration, which is resulted from spherical aberration in general single grating Offner stretcher, will generate the spatial chirp, especially in the broadband applications. In this paper, a 3D ray-tracing model is founded, and the spherical aberration is analyzed for incident broadband pulses. Further, a modified single grating Offner stretcher is developed to reduce the spherical aberration efficiently. Then the related lower chromatic aberration is analyzed and demonstrated by numerical simulations, which can directly reveal the spatial chirp of the stretched chirped pulses.

Demonstration of a 2 ps, 5 TW peak power, long-wave infrared laser based on chirped-pulse amplification with mixed-isotope CO2 amplifiers

We report generation of 5 TW peak power in a 2 ps pulse at 9.2 µm via chirped-pulse amplification (CPA) in mixed-isotope high-pressure CO2 laser amplifiers. This represents the highest peak power in a single picosecond pulse format and the shortest pulse at terawatt peak power ever achieved in the long-wave infrared (LWIR) spectral range. Maximum demonstrated energy of the compressed pulse is 14 J and minimum period between shots is 20 s. The successful implementation of the chirped pulse amplification technique in a short-pulse gas laser opens a route to development of LWIR laser facilities with tens of terawatts of peak power, thus approaching the number of photons per optical cycle of current near-infrared laser systems based on solid-state active media.

Chirped pulse amplification: review and prospective from diffractive optics [Invited

It is well-known that the chirped pulse amplification (CPA) technique won the award for the 2018 Nobel Prize in Physics to Mourou and Strickland. The compression and stretching using gratings is the essence of the CPA technique for amplifying femtosecond laser pulses. It seems the public is less aware that there are also other structures for compression and stretching of femtosecond laser pulses using other diffractive gratings, such as doubled-density gratings and deep-etched gratings. Therefore, from the view of diffractive optics, the CPA technique is reviewed with different approaches and experimental implementations that are not only useful for a more comprehensive retrospective overview of CPA, but also for the prospective of the CPA technique, which might lead us to new areas of picometer and femtometer optics in the future.

Spatio-temporal structure of a petawatt femtosecond laser beam

The development of optical metrology suited to ultrafast lasers has played a key role in the progress of these light sources in the last few decades. Measurement techniques providing the complete E-field of ultrashort laser beams in both time and space are now being developed. Yet, they had so far not been applied to the most powerful ultrashort lasers, which reach the PetaWatt range by pushing the chirped pulse amplification (CPA) scheme to its present technical limits. This situation left doubts on their actual performance, and in particular on the peak intensity they can reach at focus. In this article we present the first complete spatio-temporal characterization of a PetaWatt femtosecond laser operating at full intensity, the BELLA laser, using two recently-developed independent measurement techniques. Our results demonstrate that, with adequate optimization, the CPA technique is still suitable at these extreme scales, i.e. it is not inherently limited by spatio-temporal couplings. We also show how these measurements provide unprecedented insight into the physics and operation regime of such laser systems.

Suppression of prepulses by a temporal pulse cleaner based on a self-diffraction process for an ultraintense femtosecond laser

In this paper, we suppress prepulses by introducing a temporal pulse cleaner based on a self-diffraction process to an ultraintense and ultrashort chirped-pulse amplification laser facility. The main characteristics of the pulse cleaner are investigated. By optimizing the time delay between two incident pulses and the input energy, the energy of 130 μJ has been achieved for the first-order self-diffraction seed pulse with the maximum conversion efficiency of ∼11%. The spatial beam quality is improved after the pulse cleaner. The first-order self-diffraction seed pulse is stretched, amplified and recompressed by the chirped-pulse amplification technique. The measurement results show that the temporal contrast is improved by more than five orders of magnitude to at least 3 × 1010 for the recompressed first-order self-diffraction pulse when the incident temporal contrast is 1.5 × 105. This enables the laser facility to generate petawatt-class pulses with a nanosecond temporal contrast of higher than 1010.

Overlapped Pulsed Pumping of Tandem Pumped Fiber Amplifiers to Increase Achievable Pulse Energy

It has been reported previously that in the regime appropriate for amplifying femtosecond pulses using the chirped pulse amplification technique in Yb-fiber sources that sub-micro-second pulsed tandem pumping not only provides the thermal benefits of c.w. tandem pumping but also enables strong suppression of ASE. In that case, the pump pulse preceded the signal pulse train. Here we propose a tandem pumping scheme in rare-earth-doped fiber amplifiers, where a train of signal pulses is amplified by a pump pulse which is almost exactly temporally overlapped. Simulations demonstrate that this can be used to create uniform gain across the signal pulse train, even at very high total pulse energies where there would be significant gain shaping in the previous case. In addition the pump is absorbed in a much shorter length, which increases the threshold for nonlinear effects and gain of greater than 26 dB is shown to be readily achievable in an amplifier as short as 1.5 m. This results in increased extractable energy before reaching the threshold for limiting nonlinear effects such as stimulated Raman scattering. These attributes should be attractive for high energy, high average power, ultrashort pulse, coherently combined fiber laser systems.

Generation of ultrafast broadband small angle hundreds MeV electron bunches from laser wakefield acceleration

Electrons can be accelerated to a GeV level in centimeters by plasma wakefield driven by laser. With the development of chirped pulse amplification technique, the accelerating field can reach 100 GV/m. The laser driven wakefield acceleration experiments with ionization injection are carried out using 68 TW (1.7 J, 25 fs) laser and a mixture gas of 99% He and 1% N2. In experiment, the output electron beam has broadband spectrum with a maximum cut-off energy of about 290 MeV and a maximum output energy is quite stable in a certain range of laser focal positions. Two-dimensional particle-in-cell simulation is carried out. It is found that the longitudinal phase space is occupied by the continuously injected electrons and the phase space distribution is quite stable after the laser has propagated several millimeters inside plasma. This acceleration process can lead to quite stable maximum output energy of electron beam. These experiments reveal the physical nature of continuous ionization injection, which is very important for improving the performance of ionization injection.

High-energy femtosecond Yb-doped all-fiber monolithic chirped-pulse amplifier at repetition rate of 1 MHz**Project supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China (Grant No. 2012BAC23B03), the National Key Basic Research Program of China (Grant No. 2013CB922401), and the National Natural Science Foundation of China (Grant No. 11474002).

A high-energy femtosecond all ytterbium fiber amplifier based on a chirped-pulse amplification (CPA) technique at a repetition rate of 1 MHz seeded by a dispersion-management mode-locked picosecond broadband oscillator is studied. We find that the compressed pulse duration is dependent on the amplified energy, the pulse duration of 804 fs corresponds to the maximum amplified energy of 10.5 μJ, while the shortest pulse duration of 424 fs corresponds to the amplified energy of 6.75 μJ. The measured energy fluctuation is approximately 0.46% root mean square (RMS) over 2 h. The low-cost femtosecond fiber laser source with super-stability will be widely used in industrial micromachines, medical therapy, and scientific studies.

Chirped-pulse amplification in a CO_2 laser

Chirped-pulse amplification (CPA) is an integral part of present-day ultra-intense laser systems that normally employ near-infrared (∼1 μm) solid-state lasers. The recently revived interest in expanding the reach of strong-field laser physics into the mid-infrared (mid-IR) spectral domain directs our attention to 9–11 μm carbon-dioxide (CO2) lasers for which progress to reaching high peak intensities has been limited so far. We propose that employing the CPA technique will allow us to realize a new breakthrough toward multiterawatt, ultrafast mid-IR lasers; here we report, to our knowledge, the first implementation of this method for a CO2 laser. Our stretching of a 1 ps, 9 μm pulse to 80 ps improved energy extraction from a regenerative CO2 laser amplifier by 1 order of magnitude. We explain this accomplishment by the reduction in nonlinear absorption and refraction on the amplifier’s optical elements. We consider these findings as being a pivotal step toward establishing next-generation ultra-intense CO2 CPA laser systems for strong-field mid-IR research and its applications.