T. Kanai

5-fs, multi-mJ, CEP-locked parametric chirped-pulse amplifier pumped by a 450-nm source at 1 kHz

We report on the development of an optical parametric chirpedpulse amplifier at a 1-kHz repetition rate with a 5.5-fs pulse duration, a 2.7-mJ pulse energy and carrier-envelope phase-control. The amplifier is pumped by a 450-nm pulse from a frequency-doubled Ti:sapphire laser.

Sub-two-cycle, carrier-envelope phase-stable, intense optical pulses at 1.6 μm from a BiB 3 O 6 optical parametric chirped-pulse amplifier

We report on the generation of 9.0 fs, 550 μJ, carrier-envelope phase (CEP)-stabilized optical pulses around 1.6 μm at 1 kHz. Few-cycle IR pulses are obtained from a BiB(3)O(6) optical parametric chirped-pulse amplifier. The amplification of nearly octave-spanning ultrabroad pulses without spectral broadening results in good stability in output energy (0.85% rms) and CEP (160 mrad rms). We observed high harmonics in the water window from a neon cell that corresponds to a laser intensity of 4.1×10(14) W/cm(2).

1.5 mJ, 6.4 fs parametric chirped-pulse amplification system at 1 kHz.

We demonstrate an optical parametric chirped-pulse amplification (OPCPA) system with the pulse energy of 1.5 mJ at a 1 kHz repetition rate. The newly developed 100 ps Ti:sapphire pump laser system, which was optically synchronized with OPCPA seed pulses, delivered 10 mJ, 400 nm pump pulses. After three-stage parametric amplification, recompression of the amplifier output from 45 ps to 6.4 fs was performed. The pulse width of 6.4 fs is, to our knowledge, the shortest ever obtained by OPCPA, and the average power of 1.5 W (1.5 mJ, 1 kHz) is believed to be the highest among few-cycle OPCPA systems.

High-average-power light source below 200 nm from a KBe 2 BO 3 F 2 prism-coupled device

Using a 2.3 mm thick KBe(2)BO(3)F(2) crystal optically contacted with CaF(2) in a prism-coupled device, we have obtained an average output power of as much as 360 mW at 200 nm. Long-term stability was verified above a 150 mW level at 200 nm. An output power of 50 mW was also obtained with a narrow spectral width of 0.007 pm at 193.5 nm.

Observing hot carrier distribution in an n-type epitaxial graphene on a SiC substrate

Hot carrier dynamics in the Dirac band of n-type epitaxial graphene on a SiC substrate were traced in real time using femtosecond-time-resolved photoemission spectroscopy. The spectral evolution directly reflects the energetically linear density of states superimposed with a Fermi–Dirac distribution. The relaxation time is governed by the internal energy dissipation of electron–electron scattering, and the observed electronic temperature indicates cascade carrier multiplication.

Quantum path selection in high-harmonic generation by a phase-locked two-color field

We report the results of our studies on the selection of the quantum path in high-harmonic generation (HHG) with a relative-phase-locked two-color laser field. It is shown that by tuning the relative phase between fundamental and second-harmonic fields, The timing of tunnel ionization and subsequent electron trajectories on the sub-cycle time scale can be controlled. We have clearly observed a phase-dependent two-step feature in the harmonic spectra that can be attributed to the selection of two major trajectories in the two-color field HHG.

1.2 mJ sub-4-fs source at 1 kHz from an ionizing gas

We demonstrate a 1.2 mJ, 3.8 fs, carrier-envelope phase-controlled laser source by novel energy-scalable spectral broadening in an ionizing gas medium, which is widely applicable to sub-10-fs multimillijoule laser systems to obtain sub-2-cycle (<4 fs) multi-millijoule pulses.

Studies of advanced soft X-ray laser and coherent higher harmonic generation using intense subpicosecond laser produced high density plasma

Abstract Current activities on our research of soft X-ray lasers and higher harmonic generations using intense, subpicosecond lasers are reviewed. Especially for soft X-ray lasers we experimentally demonstrate that by longitudinally pumping 2-mm-long molybdenum preformed plasma with high-intensity 475 fs duration laser pulse, a highly directive soft-X-ray laser at 18.9 nm wavelength is generated. The divergence of the beam is evaluated to be of the submilliradian order, and only requires pump laser energy of 150 mJ . Simulations show that the pedestal in the main pump pulse can generate electron density and gain profiles with large spatial gradients, which result in the selective amplification of low-order transverse modes. The present result is the demonstration of an efficient and alternative method of improving the spatial coherence of X-ray lasers with amplified spontaneous emission medium, with possibilities of becoming an excellent tool to explore various application experiments. In higher harmonic generation, topics related to observation of blue shift due to collisionless absorption process is described.

Second harmonic generation from KBBF crystal in the deep ultraviolet

By using a KBe/sub 2/BO/sub 3/F/sub 2/ (KBBF) crystal with a size of 10 /spl times/ 10 /spl times/ 1.2 mm/sup 3/ and a special prism coupling technique (PCT), the fourth-harmonic generation of Ti:sapphire laser systems from 200 nm to 179.4-nm has been achieved for the first time. Moreover, by a Ti:sapphire laser with a 50-fs pulse duration and a 1-kHz repetition rate. A conversion efficiency as high as 13% from 400 nm to 200 nm has also been obtained without any surface loss correction.

Ultrafast melting of spin density wave order in BaFe2As2 observed by time- and angle-resolved photoemission spectroscopy with extreme-ultraviolet higher harmonic generation

Transient single-particle spectral function of BaFe