Chirped Pulse Amplification Technique Research Articles

Two-pass full-tiled grating compressor with real-time monitoring and control for XG-III petawatt-class laser facility

A two-pass, full-tiled grating compressor with a unique feedback control system for precise alignment was realized in an XG-III petawatt-class laser facility, based on the chirped-pulse amplification (CPA) technique. Far-field images of both 0th order and −1st order diffraction light of a tiled grating assembly (TGA) were recorded using a CCD camera, by which the tiling errors of the TGA can be identified and corrected in real-time without disturbing the main beam. A final compressed pulse of 615 fs (FWHM) with a focal spot about 1.1 times the diffraction limited (DL) size was achieved.

Numerical evaluation of ultrabroadband parametric amplification in YCOB

The technique of optical parametric chirped pulse amplification has the potential to generate high-energy few-cycle pulses at high repetition rates, thanks to its high fidelity and ultrabroadband capability. The biaxial nonlinear crystal yttrium calcium oxyborate (YCOB) exhibits a favorable set of optical and thermal properties for these purposes. We evaluate numerically the performance of this crystal as the nonlinear medium in a parametric amplifier for a wide range of phase-matching parameters. We explore optimized ultrabroadband noncollinear optical parametric amplification by operating at phase-matching angles outside the principal planes.

Pump channel of parametric amplifier of terawatt femtosecond Yb laser system

In this paper, we study some components of a terawatt femtosecond laser system operating with a pulse repetition rate of 1 kHz under development. The system consists of optically synchronized pump and amplification channels; the amplification channel is based on parametric amplification in an LBO crystal, and the pump channel is based on diode-pumped Yb3+-doped laser media at 80 K. In the pump channel, picosecond pulses are generated. The system is based on the chirped-pulse amplification technique. For the pump channel, parameters and alignments of the holographic grating-based stretcher-compressor system are determined. A diode-pumped (up to 1 kW) Yb:Y2O3 ceramic multipass amplifier operating at 77 K was designed. The data can be used in the development of cryogenic multistage femtosecond laser systems operating in a kilohertz pulse-repetition-rate mode.

Theoretical model to suppress parasitic lasing in large-aperture Ti:sapphire amplifiers using a temporal dual-pulse pump

Transverse parasitic lasing (PL) in large-aperture Ti:sapphire (Ti:S) crystals is a critical factor that limits the energy achievable with the chirped-pulse amplification (CPA) technique. We propose a method to suppress PL effects in large-aperture Ti:S amplifiers by using a temporal dual-pulse pump. Theoretical simulations based on the experimental parameters in 2.0PW Ti:S laser system are performed to predict the transverse gain as a function of pumping time and output energy. By optimizing the temporal profile of the pump beam as well as the time delay between the input seed and pump pulses, we can minimize PL effects in Ti:S crystals. This method is applicable to larger-aperture Ti:S crystals pumped at higher pump fluence and energy, and is potential to develop a ~10PW laser system.

High pulse energy 2 µm femtosecond fiber laser

In the paper, a 2 µm high energy fs fiber laser and amplification system is presented based on Tm doped fibers. The seed laser was designed to generate pulse train at 2024 nm at a repetition rate of 2.5 MHz. An AOM was used as a pulse picker to further lower the repetition rate down to 100 kHz. Two-stage fiber pre-amplifiers and a high energy large mode area (LMA) fiber amplifier were used to boost pulse energy up to 54 µJ before pulse compressor with chirped pulse amplification technique. After compressor, pulse energy of 36.7µJ and pulse duration of 910 fs and were obtained.

Recent progress in the development of pulse compression gratings

The PETAL facility uses chirped pulse amplification (CPA) technique. This system needs large pulse compression gratings that request damage threshold better than 4 J/cm2 in normal beam at 1.053 μm for 500 fs pulses. In this paper, we will show recent grating designs with either multilayer dielectrics or hybrid metal-dielectric structures. We have shown in previous works that damage threshold is driven by the enhancement of the near electric field inside the pillars of the grating. This was evidenced from a macroscopic point of view by means of laser damage testing. We will show that damage morphology during damage initiation at the scale of the grating groove is also consistent with this electric field dependence.

Gaussian wave-packet reshaping into conical via parametric amplification of the far field

In this paper we propose a method for pulsed conical wave parametric amplification (PCWPA) with subsequent spatio-temporal compression during propagation in free space. It is numerically demonstrated that Gaussian wave-packet can be reshaped into pulsed conical wave (PCW) just by means of lens and nonlinear crystal. We point out that performing the far field amplification of the PCW is the key for generation of localized PCWs with ultrahigh intensities. It allows to form ultra-intense and propagation invariant wave-packets capable to propagate over many Rayleigh range in the desired material. The method exploits achromatic phase matching and empowers the parametric amplification of bandwidths corresponding to few-cycle light pulses with Gaussian temporal spectrum. In contrast to ordinary chirped-pulse amplification technique it does not require a pulse compressor, thus greatly facilitates the parametric amplification of few-cycle light pulses.

High average power picosecond pulse generation from a thulium-doped all-fiber MOPA system

We report a stable highly-integrated high power picosecond thulium-doped all-fiber MOPA system without using conventional chirped pulse amplification technique. The master oscillator was passively mode-locked by a SESAM to generate average power of 15 mW at a fundamental repetition rate of 103 MHz in a short linear cavity, and a uniform narrow bandwidth FBG is employed to stabilize the passively mode-locked laser operation. Two-stage double-clad thulium-doped all-fiber amplifiers were used directly to boost average power to 20.7 W. The laser center wavelength was 1962.8 nm and the pulse width was 18 ps. The single pulse energy and peak-power after the amplication were 200 nJ and 11.2 kW respectively. To the best of our knowledge, this is the highest average power ever reported for a picosecond thulium-doped all-fiber MOPA system.

Broadband femtosecond OPCPA system driven by the single-shot narrow-band iodine photodissociation laser SOFIA

A two-stage optical parametric amplifier driven by a frequency-tripled beam from the high-energy iodine laser system SOFIA was built. This single-shot Optical Parametric Chirped Pulse-Amplification facility (OPCPA) and the system synchronizing the pump and signal pulses are described in detail. The chirped seed pulse of a Ti:sapphire oscillator running at the central wavelength of 800 nm is amplified in the two-stage (LBO and KDP) optical parametric amplifier over 108 times. The amplified spectral bandwidth of 68 nm corresponds to the pulse duration of 14 fs when a transform-limited pulse is assumed. This implies a compressed pulse of TW power. Systematic gain measurements reveal a good match with the theoretical predictions. Signal and idler beam fluence profiles are presented. The suitability of the iodine photo-dissociation laser as a pump source for the OPCPA technique is thus proved for the first time experimentally. A distinctive feature of the iodine laser is its very narrow gain bandwidth (<0.1 cm−1) and, therefore, the conventional chirped-pulse amplification technique does not lead to pulse durations at the femtosecond level.

Application of unfolding technique to dispersion calculating of reflective grating dispersion delay lines in the chirped pulses amplifier

Dispersion delay lines (such as the compressor and the stretcher) consisting of reflective optical elements (mirrors and reflection diffraction gratings), are now widely used in chirped-pulse amplification technique. It is shown that for their calculations the unfolding technique can be applied. According to this technique, the dispersion of the compressor and the stretcher can be characterized by the "zero-distant pulse fronts" in their spatial chirps.

Ultrafast lasers: A new frontier for optical materials processing

In the last years, ultrashort laser pulses have gone through the laboratory walls to burst into the industrial arena as a tool for material micro- and nanoprocessing. The number of industrial fields and specific applications is steadily growing, reaching the nanotechnology applications. Now, we celebrate the 25th anniversary of the CPA (chirped pulse amplification) technique which made available intense ultrashort (subpicosecond) pulses able to induce ablation of any material. This contribution tries to review the fundamentals of ultrafast lasers as well as some of their applications, emphasizing the processing of optical materials.

Compact diode-pumped 11 kW Yb:YAG Innoslab femtosecond amplifier

We demonstrate a compact diode-pumped Yb:KGW femtosecond oscillator-Yb:YAG Innoslab amplifier master oscillator power amplifier (MOPA) with nearly transform-limited 636 fs pulses at 620 W average output power, 20 MHz repetition rate, and beam quality of M(x)(2) = 1.43 and M(y)(2) = 1.35. By cascading two amplifiers, we attain an average output power of 1.1 kW, a peak power of 80 MW, and a 615 fs pulse width in a single linearly polarized beam. The power-scalable MOPA is operated at room temperature, and no chirped-pulse amplification technique is used.

Laser–matter interaction at ultra-relativistic intensities

The chirped-pulse amplification technique has opened up a completely new scenario in laser–matter interaction. Radiation intensities in excess of 1018 W/cm2, leading to relativistic electron motion in the laser field, induce phenomena (sometimes very spectacular) concerning laser pulse propagation, particle acceleration and generation of energetic electromagnetic radiation. The suitable utilization of such phenomena allows for several applications, including the fast ignition of an inertially confined fusion target, the production of energetic particles (electrons, protons, ions and positrons), and X-gamma rays for medical diagnostics and therapy.

High-spatiotemporal-quality petawatt-class laser system

We have developed a femtosecond high-intensity laser system that combines both Ti:sapphire chirped-pulse amplification (CPA) and optical parametric CPA (OPCPA) techniques and produces more than 30 J broadband output energy, indicating the potential for achieving peak powers in excess of 500 TW. With a cleaned high-energy seeded OPCPA preamplifier as a front end in the system, for the compressed pulse without pumping the final amplifier, we found that the temporal contrast in this system exceeds 10(10) on the subnanosecond time scales, and is near 10(12) on the nanosecond time scale prior to the peak of the main femtosecond pulse. Using diffractive optical elements for beam homogenization of a 100 J level high-energy Nd:glass green pump laser in a Ti:sapphire final amplifier, we have successfully generated broadband high-energy output with a near-perfect top-hat-like intensity distribution.

Melt dynamics of aluminum irradiated with ultrafast laser radiation at large intensities

Ablation of bulk aluminum has been investigated in situ using ultrafast laser radiation produced by chirped-pulse amplification technique (tp=80fs, λ=800nm). Melt dynamics and the contribution of the amplified spontaneous emission (ASE) to the ablation have been studied experimentally and numerically for laser fluences well above ablation threshold (F≲103×Fthr). Using transient quantitative phase microscopy (TQPm), dimensions and volume of ejected vapor, melt droplets, and liquid jets has been investigated. Computational analysis of the optical phase images has been used to determine the total volume of ejected material. A series of time-resolved phase images of vaporized material and/or melt, which are induced by n=1..8 pulses on an aluminum target, are obtained by means of TQPm up to temporal delay τ=1.65μs after irradiation. Increase in material ejection rate is observed at delays τ≈300ns and τ≈1.1μs after the incident pulse. For large irradiation intensities a considerable contribution of ASE to ablation dynamics has been detected. Ex situ measurements of the ablated material by means of white-light interferometry and scanning electron microscopy provides corresponding factual removed volumes and highlight the pulse-to-pulse morphology changes.

Decrease of pulse-contrast in nonlinear chirped-pulse amplification systems due to high-frequency spectral phase ripples

It is analytically shown that weak initial spectral phase modulations cause a pulse-contrast degradation at the output of nonlinear chirped-pulse amplification systems. The Kerr-nonlinearity causes an energy-transfer from the main pulse to side-pulses during nonlinear amplification. The relative intensities of these side-pulses can be described in terms of Bessel-functions. It is shown that the intensities of the pulses are dependent on the magnitude of the accumulated nonlinear phase-shift (i.e., the B-integral), the depth and period of the initial spectral phase-modulation and the slope of the linear stretching chirp. The results are applicable to any type of laser amplifier that is based on the technique of chirped-pulse amplification. The analytical results presented in this paper are of particular importance for high peak-power laser applications requiring high pulse-contrasts, e.g. high field physics.

Diode-pumped lasers for ultra-high peak power

The generation of the highest laser peak intensities at a high degree of system compactness can be achieved by combining modern diode-pump technologies with the chirped pulse amplification technique. In principle, the spectroscopic properties of the gain medium determine the scaling laws of both high output pulse energy and short pulse duration. Here we introduce a novel criterion classifying laser materials with respect to their ability to generate pulses of highest peak power in a diode-pumped solid state laser system. Furthermore, amplified spontaneous emission as well as laser damage issues affecting the efficiency and compactness of a laser amplifier system are discussed.

Introduction of SILEX-I Femto-second Ti:sapphire laser Facility

We have built a Ti:sapphire laser system, referred to as SILEX-I, with a peak power of 286TW for a pulse duration of 30fs using chirped-pulse amplification technique. A number of spectral and spatio-temporal beam control measures have been taken and near-diffraction limited focal spots have been obtained which, to our knowledge, are the best far fields ever measured for any existing high-power Ti:sapphire laser system without deformable mirror corrections.

TU‐D‐BRA‐04: Laser‐Accelerated Protons for Radiation Therapy

Recent developments in the field of laser engineering, specifically the invention of chirped pulse amplification technique made it possible to achieve laser light intensities reaching 1022 W/cm2 range. In this review, we will show that such laser intensities are sufficient to accelerate protons to therapeutic energy ranges, provided that proper laser‐target parameters are chosen. In the majority of recent laser‐matter interaction experiments, the proton energy spectra coming out of the interaction chamber are thermal making it impossible to use these protons in hadron therapy. This necessitates the development of a particle selection device that would deliver quasi‐monoenergetic particles suitable for medical applications. We will discuss earlier proposed particle selection system and show the dosimetric characteristics of protons coming out of this device. Using “real” patient data and physical characteristics (phase‐space distribution) of selected particles we will discuss the inter‐comparison studies between photon intensity‐modulated plans on one hand and intensity‐modulated plans based on laser‐accelerated protons on the other. In concluding remarks, we will describe the current challenges facing the project and ways to resolve them.

Development of a high-contrast, high-peak power, Ti:Sapphire/OPCPA laser system

We report on a high-contrast, high-peak power laser system, which combines both conventional laser amplification and optical parametric chirped pulse amplification (OPCPA) techniques. By employing an OPCPA system after a regenerative amplifier, we have enhanced the prepulse contrast by six orders of magnitude. A prepulse contrast of better than 4.4 × 10−11 has been measured with a high-energy broadband pulse of 24 mJ at a 10 Hz repetition rate from the OPCPA system. With a subsequent four-pass Ti:sapphire amplifier, we have achieved an amplified energy of 279 mJ and an ultrashort recompressed amplified pulse duration of 23.5 fs. We also discuss the basic design aspects and present our preliminary experimental investigations for higher energy operation to a multijoule.