Y. Akahane

0.85-PW, 33-fs Ti:sapphire laser

We have successfully produced a laser pulse with a peak power of 0.85 PW for a pulse duration of 33 fs in a four-stage Ti:sapphire amplifier chain based on chirped-pulse amplification. To our knowledge this result represents the highest peak power pulses yet produced in any Ti:sapphire chirped-pulse amplification system.

100-TW sub-20-fs Ti:sapphire laser system operating at a 10-Hz repetition rate

We developed a compact three-stage Ti:sapphire amplifier laser system that produced peak power in excess of 100 TW for a pulse duration of less than 19 fs and an average power of 19 W at a 10-Hz repetition rate. A final 40-mm-diameter Ti:sapphire amplifier is pumped by a Nd:YAG master-oscillator-power-amplifier system that produces ~7-J output of 532-nm radiation. The spatial beam quality is approximately 2 times diffraction limited for the full amplified compressed output pulse. With f/3 optics, this system should therefore be capable of producing a focused intensity of ~3x10(20) W/cm(2) .

High-energy, diode-pumped, picosecond Yb:YAG chirped-pulse regenerative amplifier for pumping optical parametric chirped-pulse amplification.

A diode-pumped, cryogenic-cooled Yb:YAG regenerative amplifier utilizing gain-narrowing has been developed. A 1.2-ns chirped-seed pulse was simultaneously amplified and compressed in the regenerative amplifier, which generated a 35-ps pulse with ~8-mJ of energy without a pulse compressor. Second-harmonics of the amplified pulse was used to pump picosecond two-color optical parametric amplification.

Generation of X rays and energetic ions from superintense laser irradiation of micron-sized Ar clusters

AbstractHigh-resolutionK-shell spectra of a plasma created by superintense laser irradiation of micron-sized Ar clusters havebeen measured with an intensity above 10 19 W0cm 2 and a pulse duration of 30 fs. The total photon flux of 2310 8 photons0pulse was achieved for He a1 resonant line of Ar ~l 5 3.9491 A, 3.14 keV !. In parallel with X-raymeasurements,energydistributionsofemittedionshavebeenmeasured.Themultiplychargedionswithkineticenergiesup to 800 keV were observed. It is found that hot electrons produced by high contrast laser pulses allow the isochoricheating of clusters and shift the ion balance toward the higher charge states, which enhances both the X-ray line yield ofthe He-like argon ion and the ion kinetic energy.Keywords: Cluster; High power laser; Isochoric heating; Multiply charged ion; X ray 1. INTRODUCTIONRecent development of ultrashort, high peak-power lasersystems, based on the chirped pulse amplification ~CPA!technique, opens up a new regime of laser–matter inter-action ~Perry & Mourou, 1994!. Nowadays a focusing ofsuch laser pulses produces laser peak intensities well above10

Ultra-broadband optical parametric chirped-pulse amplification using an Yb:LiYF 4 chirped-pulse amplification pump laser

We demonstrate ultra-broadband optical parametric chirpedpulse amplification of 300-nm bandwidth pumped by a broadband pulse delivered from a diode-pumped, cryogenically-cooled Yb:YLF chirped- pulse amplification laser.

Characterization of wave-front corrected 100 TW, 10 Hz laser pulses with peak intensities greater than 1020W∕cm2

An improvement of laser-focused peak intensity has been achieved in a JAERI 100 TW Ti:sapphire chirped-pulse amplifier chain with a feedback controlled adaptive optics system operating at a 10 Hz repetition rate. The Strehl ratio was enhanced to 0.8 by means of a Bimorph deformable mirror with a Shack-Hartmann wave-front sensor. Measurements of optical parameters of the laser pulse and an experimental tunneling ionization yield of helium have practically confirmed focusing to ultrarelativistic intensities of over 1020W∕cm2 within 16% accuracy.

Prepulse-free, multi-terawatt, sub-30-fs laser system

We have built a prepulse-free, multi-terawatt, ultrashort pulse laser system, which combines both conventional laser amplification and optical parametric chirped pulse amplification (OPCPA) techniques. By employing an OPCPA system after the regenerative amplifier in a Ti:sapphire chirped pulse amplification laser chain, we have dramatically enhanced the prepulse contrast by 6 orders of magnitude. A prepulse contrast of better than 4.4 x 10-11 has been measured with a high energy broadband pulse of 24 mJ at 10 Hz repetition rate from the OPCPA system. Using 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, corresponding to the peak powers for OPCPA and four-pass amplifier of 0.5 TW and 5.9 TW, respectively.

X-ray Study of Microdroplet Plasma Formation under the Action of Superintense Laser Radiation

We have measured the X-ray emission spectra of a plasma generated by laser radiation with an intensity above 1019W/cm2 and a pulse duration of 30 fs acting upon an argon jet target with a large abundance of micron-sized clusters. The time variation of the X-ray yield from ions of various multiplicities, calculated within the framework of a nonstationary kinetic model, shows a good qualitative agreement with the experimental time-integrated spectrum.

Multi-millijoule, diode-pumped, cryogenically-cooled Yb:KY(WO 4 ) 2 chirped-pulse regenerative amplifier

A diode-pumped, cryogenically-cooled Yb:KYW regenerative amplifier utilizing chirped-pulse amplification and regenerative pulse shaping has been developed. An amplified pulse with an energy of 5.5 mJ and a broad bandwidth of 3.4 nm is achieved.

Second - harmonic generation of ultra-high intensity femtosecond pulses with a KDP crystal.

We investigated second harmonic generation with ultrahigh intensity femtosecond laser pulses from a terawatt Ti: sapphire laser system. Energy conversion efficiency of about 80 % for a type I potassium dideuterium phosphate crystal was obtained with 130 fs laser pulses at an intensity as high as 192 GW/cm 2.