We have proposed and demonstrated a very simple and robust femtosecond optical-parametric chirped-pulse
amplification scheme in which an even order dispersion of an idler pulse is compensated by passing through an identical
positive dispersive material used for temporal stretching a signal pulse. By compressing the idler pulses having a
negatively chirp in this manner, high power sub-100 fs pulses were successfully obtained with only a transparent glass
block used for the stretcher and compressor.
M. Sherrill, J. Abdallah, G. Csanak, E. Dodd, Y. Fukuda, Y. Akahane, M. Aoyama, N. Inoue, H. Ueda, K. Yamakawa, A. Ya Faenov, A. Magunov, T. Pikuz, I. Yu. Skobelev
A model that solves simultaneously both the electron and atomic kinetics was used to generate synthetic X-ray
spectra to characterize high intensity ultrashort-laser-driven target experiments. A particle-in-cell simulation
was used to model the laser interaction for both cluster and foil targets and provided the initial electron energy
distribution function (EEDF) for a Boltzmann solver. Previously reported success in the spectroscopic characterization
of an irradiated Ar cluster target has motivated the authors to apply this technique in a feasibility study
to assess the possibility of recording time resolved spectra of a 10 micron Ti foil target irradiated by a 500 fs,
I= 1.0 × 1018W/cm2 short-pulse laser. Though this model suggests that both Ar cluster and Ti foil plasmas are
held in a highly non-equilibrium state for both the EEDF and the ion level populations for several picoseconds,
the spectral line features of the foil experiment was shown to evolve too quickly to be seen by current ultrafast
time resolved spectrometers.
60 mJ chirped-pulse power was obtained using a diode-pumped regenerative amplifier with a cooled Yb:YLF crystal at 20 Hz repetition rate. After temporal compression, 36 mJ, 795 fs pulses were generated. Our numerical calculation shows that 100 mJ output power at 1 kHz would be obtained by using a sapphire-sandwiched laser material and a 2-pass amplification scheme in regenerative cavity.
High resolution x-ray emission spectra of plasma created by laser irradiation of rare-gas (Ar, Kr, Xe) clusters have been measured at laser intensities over 1019 W/cm2 and 30-fs pulse duration. To make these measurements possible, in addition to the effort to decrease a prepulse intensity using Pockels cell switches, micron-size clusters were produced using a specially designed conical nozzle. The Boltzmann equation and a detailed collisional radiative model are solved simultaneously as a function of time to model the time integrated x-ray spectra of the transient plasma. The results are quantitatively in good agreement with the experimentally observed x-ray emission spectra of Ar clusters.
The soft x-ray emission from He-like and H-like were obtained by using the double nozzle gas-puff (Nitrogen, and Oxygen) target irradiated by the laser which delivered a laser energy of 50 mJ in 400 ps pulse width. Efficient absorption of the incident laser energy into the double gas-puff target was demonstrated experimentally such as 15%, and 29% for Nitrogen and Oxygen, respectively. The sub keV x-ray emission from He-β(1s2-1s2p, 1s2-1s3p, and 1s2-1s4p) lines are observed around the 0.4 nm wavelength region by using the double nozzle Argon gas-puff target irradiated by a 5 J, 1 ns, 1 μm laser. Using the gas-puff target irradiated by a femto-second laser pulse, highly ionized ions of Cr-, Fe- and Ni-like Kr at the 5 - 20 nm wavelength region have been observed in a laser produced plasma. However, the intensity of the x-ray emissions from double nozzle gas-puff target are lower than that from the single nozzle gas-puff targets, using the Krypton gas. Using xenon gas, the intensity of the x-ray emissions from double nozzle gas-puff target is equivalent to that from the single nozzle target.
A 24-mJ diode-pumped chirped-pulse regenerative amplifier with a cooled Yb:LiYF4 crystal has been developed. A 10-mJ pulse energy with sub-ps pulse duration was obtained with a 660 fs pulse duration after compression.
We describe the demonstration of the high pulse energy and high efficiency second-harmonic generation (SHG) at 532-nm using large aperture CsLiB6O10 (CLBO) crystals for the first time to our knowledge. A pulsed green energy of 25 J has been generated with 34 J of input 1064-nm Nd:glass laser radiation using a two-stage crystal architecture. High conversion efficiency of 74% has been attained at fundamental laser intensity of only 370MW/cm2. This result represents the highest green pulse energy ever reported using the CLBO crystals. We discuss in detail the design and performance of SHG using CLBO crystals.
Regenerative pulse shaping is used to overcome gain narrowing during ultrashort pulse amplification. We have demonstrated multiple spectral filters for broadening the amplified spectrum. We have produced amplified pulses with an energy of approximately 5 mJ and bandwidths of approximately 100 nm, or nearly 3 times wider than the gain narrowing limit of Ti:sapphire.
Techniques for the production of multiterawatt, sub-20-fs, optical pulses via chirped pulse amplification are discussed. Regenerative pulse shaping is used to control gain narrowing during amplification and an optimized, quintic-phase-limited, dispersion compensation scheme is used to control higher order phase distortions over a bandwidth of approximately 100 nm. Transform-limited, 18-fs pulses of 4.4-TW peak power have been produced in a Ti:sapphire- based, chirped pulse amplification system at a repetition rate of 50 Hz. Extensions to shorter durations and peak powers approaching 100 TW are also described.
Laser-generated, hard x-rays are produced in a > 1018 W/cm2 focus of an ultrashort-pulse laser system. The application of ultrashort-duration, laser-generated x-rays to diagnostic medical imaging is discussed. Time-gated detection allows removal of scattered radiation, improved image quality and possible reduction of patient exposure. Methods for improvement of x-ray yield, design of appropriate drive lasers, and applications to mammography and angiography are also discussed.
Our goal is to watch the evolution of matter on the atomic length scale and on the time scale on which elementary chemical reactions take place. We present initial experiments made in collaboration between UCSD and the INRS laboratory in Canada, on time-resolved ultrafast, 3 ps temporal resolution, near-edge x-ray absorption of gas phase SF6 at 2.4 keV (4.89 A). We can see both the initial presence of the F atoms around the S and their absence after photodissociation produced by pumping with an intense optical pulse. Simulations of ultrafast EXAFS and diffraction experiments are presented. We are constructing an ultrahigh intensity laser to generate ultrafast x-ray pulses from laser-produced plasmas. This laser is especially designed to achieve high average power, short pulse duration and high intensity to produce very high temperature solid density plasmas and ultrahot electrons for ultrafast hard x-ray production at high x-ray photon flux, which should enable us to perform a variety of ultrafast x-ray absorption and diffraction experiments. Finally, we discuss several means to measure the duration of subpicosecond x-ray pulses.
Phase and amplitude control during multiterawatt, ultrashort-pulse amplification is discussed. Methods for efficient energy extraction and scaling to 100-TW peak powers are outlined.
We describe a complete solid state 1.5 terawatt, 150 femtosecond laser system operating at 10 Hz repetition, based on titanium-doped sapphire amplifiers and use of the technique of chirped-pulse amplification (CPA). The design and performance of the system is described. Special emphasis on the tunability of the system from 760 nm to 860 nm is also discussed.
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