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Optical Parametric Chirped-Pulse Amplification (OPCPA)
Published in Chunlei Guo, Subhash Chandra Singh, Handbook of Laser Technology and Applications, 2021
After the invention of laser amplification, shorter and shorter light pulses with increasing intensity were generated. This direct amplification reached its limits due to non-linear effects and damage in the amplifier medium triggered by the high intensities. The chirped-pulse amplification (CPA) technique (Chapter 22 'CPA' by Donna Strickland; Strickland and Mourou, 1985) mitigated these difficulties and permitted to reach much higher laser energies and intensities. Furthermore, this made intense lasers available for a broad range of applications, therefore their inventors, Donna Strickland and Gerard Mourou, obtained the Nobel Prize in 2018. A certain spectrum supports a minimum (so-called Fourier limited) pulse duration, which is a natural lower limit defined by the Fourier transformation. The next limit in laser development towards even shorter pulses is posed by the laser materials providing finite gain bandwidth and therefore longer pulses.
Lasers in Medicine: Healing with Light
Published in Suzanne Amador Kane, Boris A. Gelman, Introduction to Physics in Modern Medicine, 2020
Suzanne Amador Kane, Boris A. Gelman
Because pulsed lasers store up energy and emit it in one extremely short pulse, rather than in a continuous beam, this results in extraordinarily high power levels during the brief pulse time. A typical pulse duration, indicated as tw in Figure 3.19b, is several nanoseconds (10−9 s), and a typical pulse carries enough energy (on the order of several J) to vaporize a small volume of tissue. The repetition rate is typically several pulses per second (1–10 Hz). This gives huge instantaneous powers during a pulse of over one million watts (1 megawatt), with correspondingly high power densities. One of the techniques for generating high-intensity optical pulses of very short duration is called chirped pulse amplification (CPA). Donna Strickland and Gérard Mourou, the scientists who invented this technology, were awarded the 2018 Nobel Prize in Physics. (They shared the Nobel Prize with Arthur Ashkin, who developed optical tweezers, devices in which laser light is used to trap microscopic objects, a valuable tool used to study and manipulate biological molecules and components of cells.)
Diffraction Gratings for High-Intensity Laser Applications
Published in Barat Ken, Laser Safety Tools and Training, 2017
The technique of chirped-pulse amplification (CPA) (Strickland and Mourou, 1985) uses one or more gratings with other optics in a “stretcher” to temporally disperse a low-energy, broadband, short-pulse beam by a factor of about 103. The stretched beam is then amplified by conventional gain media without undergoing nonlinear self-focusing. Gains of about 106 are possible. The amplified, stretched pulse is then sent through a “compressor,” typically containing two to four gratings that undo the temporal dispersion of the stretcher to create an intense pulse of nearly the initial pulse duration. A schematic of CPA is shown in Figure 7.2. The requirements of the compressor gratings in particular are quite demanding. Typical compressor designs use four grating bounces.4 The beam size and intensity are in large part limited by the size and damage threshold of the compressor gratings. Therefore, maximizing the efficiency and damage threshold of the gratings has an enormous impact on energy delivered to the target as well as the cost of the laser system.
1-Hz Bead-Pellet Injection System for Fusion Reaction Engaged by a Laser HAMA Using Ultra-Intense Counter Beams
Published in Fusion Science and Technology, 2019
Yoshitaka Mori, Yasuhiko Nishimura, Katsuhiro Ishii, Ryohei Hanayama, Yoneyoshi Kitagawa, Takashi Sekine, Yasuki Takeuchi, Nakahiro Satoh, Takashi Kurita, Yoshinori Kato, Norio Kurita, Toshiyuki Kawashima, Osamu Komeda, Tatsumi Hioki, Tomoyoshi Motohiro, Atsushi Sunahara, Yasuhiko Sentoku, Eisuke Miura, Akifumi Iwamoto, Hitoshi Sakagami
Using a repetitive, 100-fs ultra-intense laser, the engagement of 1-Hz-injected flying pellets involving fusion neutron reaction has been demonstrated.24,25 The deuterated polystyrene (CD) bead pellets, after free falling for a distance of 18 cm at 1 Hz, are successfully engaged by two counter laser beams from a diode-pumped assist, ultra-intense HAMA laser.26 Irradiated pellets with laser intensity of 4.7 10 W/cm produce D(d, n)He–reacted neutrons with a maximum yield of 9.5 10 /4 steradian (sr)/shot. The development of ultra-intense laser with repetitive operation beyond 1 Hz by the introduction of chirped pulse amplification27 (CPA) into a Ti-sapphire laser28–30 has succeeded in fusion neutron generation with a laboratory-scale laser size31–34 and demonstration of compact inertial fusion experiments.35–37 Therefore, an injection system associated with the present CPA laser system can build a small-scale integrated IFE system that induces fusion neutron generation with repetitive operation. The development of this small-scale integrated IFE system opens up a promising roadmap to realize an effective IFE reactor by stepping up the amount of fusion reactions using laser drivers that are presently available.
Enhanced attosecond pulse generation in the vacuum ultraviolet using a two-colour driving field for high harmonic generation
Published in Journal of Modern Optics, 2018
P. Matía-Hernando, T. Witting, D. J. Walke, J. P. Marangos, J. W. G. Tisch
The experimental setup is shown in Figure 1. A chirped-pulse amplification laser system operating at a repetition rate of 1 kHz (Femtolaser GmbH, Femtopower HE) emits 30 fs pulses centered at a wavelength of 790 nm, with an energy up to 2.5 mJ per pulse. The output from this source was divided in two beams by a 50/50 beamsplitter, consisting of a broadband low-dispersion coating on a 1 mm fused silica substrate (FemtoOptics, OA237). The reflected beam was focused into a hollow-core fibre differentially pumped with neon gas, where the pulses were spectrally broadened via self-phase modulation and compressed to few-cycle duration with a set of chirped mirrors and a pair of fused silica wedges [28]. The CEP of these few-cycle pulses was locked with a feedback system consisting of a pair of f-to-2f interferometers, with residual shot-to-shot fluctuations below 250 mrad [29]. The beam transmitted by the beamsplitter was loosely focused into a thin BBO nonlinear crystal for type-I second-harmonic generation. A broadband half-wave plate was used to rotate the polarization of the second harmonic beam to match the fundamental.
Reflected and transmitted second harmonics generation by an obliquely p-polarized laser pulse incident on a vacuum-plasma interface
Published in Waves in Random and Complex Media, 2018
The achievement of generation of strong laser pulse by chirped-pulse amplification technology opened the new research of area called the laser-plasma interaction [1,2]. This interaction is used in the number of areas including laser-plasma acceleration [3–5], inertial confinement fusion [6,7], relativistic self-focusing [8,9], optical harmonic generation [10–18], photoelectron spectroscopy [19] and so on. High harmonic generation as a source of coherent light at short wavelength attracts great attention due to a wide range of applications, such as Extreme Ultraviolet (EUV) non-linear optics and attosecond physics. The high-order harmonic generation has been analyzed both experimentally and theoretically in the research related to laser-plasma interaction [11,17,20,24]. Among these, the second-harmonic (SH) generation has unique place in laser produced plasma [25,26]. The phase matching between the generated harmonic and fundamental waves has an important role in harmonic generation process. The phase-match relativistic third harmonic generation in forward direction have been experimentally observed by varying the temporal delay and the energy of the laser pulse [27]. In a plasma having density ripple, the ripple provides additional momentum required for resonant enhancement of harmonic power [28–32]. On the other hand, a transverse magnetic field can be introduced to provide the required additional momentum for the harmonic radiation [33–38]. In a plasma with a ripple density and in the presence of magnetic field, generation of SH becomes faster as magnetic field increases owing to the strong coupling between magnetic field and laser pulse, while ripple density provides phase matching between fundamental and SH beam [39]. It has been observed that self-focusing of laser pulse significantly affects the SH generation (SHG) in plasma [40–49].