Keisuke Kaneshima

Carrier-envelope phase-dependent high harmonic generation in the water window using few-cycle infrared pulses

High harmonic generation (HHG) using waveform-controlled, few-cycle pulses from Ti:sapphire lasers has opened emerging researches in strong-field and attosecond physics. However, the maximum photon energy of attosecond pulses via HHG remains limited to the extreme ultraviolet region. Long-wavelength light sources with carrier-envelope phase stabilization are promising to extend the photon energy of attosecond pulses into the soft X-ray region. Here we demonstrate carrier-envelope phase-dependent HHG in the water window using sub-two-cycle optical pulses at 1,600 nm. Experimental and simulated results indicate the confinement of soft X-ray emission in a single recombination event with a bandwidth of 75 eV around the carbon K edge. Control of high harmonics by the waveform of few-cycle infrared pulses is a key milestone to generate soft X-ray attosecond pulses. We measure a dependence of half-cycle bursts on the gas pressure, which indicates subcycle deformation of the waveform of the infrared drive pulses in the HHG process.

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).

Generation of carrier-envelope phase-stable mid-infrared pulses via dual-wavelength optical parametric amplification

Carrier-envelope phase-stable mid-infrared pulses spanning from 5 μm to 11 μm with a pulse energy of 5 μJ were produced by difference frequency generation of two-color near-infrared pulses that were produced in a novel inline optical parametric amplifier. The mid-infrared electric waveform was characterized by electro-optic sampling using 6.5-fs pulses at 620 nm.

Generation of ultrashort intense optical pulses at 1.6 μm from a bismuth triborate-based optical parametric chirped pulse amplifier with carrier-envelope phase stabilization

We describe a few-cycle intense optical parametric chirped pulse amplifier (OPCPA) in the IR that is based on bismuth triborate (BiB3O6, BIBO) crystals. Two Ti:sapphire chirped pulse amplification systems are used to generate seed and pump pulses for the OPCPA. Carrier-envelope phase (CEP)-stabilized seed pulses in the IR are produced by difference frequency mixing of white light spanning from the visible to near IR range. The seed pulses, which have a nearly one octave-spanning spectrum around 1.6 μm, are temporally stretched in an acousto-optic programmable dispersive filter and amplified up to 550 μJ in two BIBO-based parametric amplifiers without losing their bandwidth. After compression in a fused silica block, we obtained 9.2 fs optical pulses with a repetition rate of 1 kHz, which comprise less than two optical cycles at 1.6 μm. These optical pulses were used to generate extreme ultraviolet (XUV) high harmonics in krypton. We succeeded in measuring the CEP dependence of the XUV radiation near the silicon L edge around 100 eV, verifying the passive stabilization of the CEP of the sub-two cycle IR pulses. The XUV spectra consist of two half-cycle cutoffs and show a clear transition from a modulated structure to a continuum near the cutoff. The continuum-like spectra as well as their CEP dependence indicate that they originate in a single recombination burst, showing that few-cycle IR OPCPA light sources are capable of generating attosecond pulses in the XUV region.

Sub-Two-Cycle Millijoule Optical Pulses at 1600 nm from a BiB_3O_6 Optical Parametric Chirped-Pulse Amplifier

We report on the generation of 10.1-fs, 1.5-mJ pulses at 1 kHz from a BiB3O6 OPCPA with passive CEP stabilization. This light source is promising for the generation of high-flux isolated soft x-ray pulses.

High-energy half-cycle cutoffs in high harmonic and rescattered electron spectra using waveform-controlled few-cycle infrared pulses

We developed a few-cycle waveform-controlled light source for infrared pulses at that is based on optical chirped-pulse amplification in (BIBO) crystals pumped by Ti:sapphire lasers. Using this source, we observe soft x-ray high harmonics that extend up to a photon energy of , as well as high-energy photoelectrons up to . The spectra of the high harmonics and photoelectrons have clear signatures of half-cycle cutoffs that can be used to extract electronic and molecular dynamics on an attosecond time scale.

Polarization property of high harmonics generated from crystalline semiconductors excited by mid-infrared pulses

Recent advance in generation of strong electric fields in the mid-infrared to terahertz regions triggers research on extremely fast electron transportation in crystalline solids with terahertz to petahertz frequencies and associated high harmonic generation (HHG) in the spectral regions from visible to vacuum ultraviolet beyond typical bandgaps of solids [1, 2]. So far, most of the experiments choose a specific direction, along which the ballistic transportation of electron wavepackets is considered as a radiation source. However a one-dimensional model is not suitable to investigate polarization property of solid high harmonics. Recently, Berry curvature is introduced in a single-particle band to explain the generation of orthogonally polarized even harmonics from intraband current of hexagonal mono-layer MoS2 [3].

Waveform characterization of CEP-stable intense mid-infrared pulses generated via dual-wavelength OPA

We report a novel method to produce two-color near-infrared pulses in an optical parametric amplifier. Five-μJ, carrier-envelop phase-stable mid-infrared pulses are produced by intra-pulse difference frequency generation, and characterized by electro-optic sampling.

Carrier-Envelope Phase Mapping in Laser-Induced Electron Rescattering

We demonstrate the use of the carrier-envelope phase of few-cycle pulses for laser-induced electron diffraction. The phase serves to tune the rescattering energy, which enables a sensitive measurement of differential scattering cross sections.

Generation of Isolated Soft X-Ray Pulses Around the Carbon K -Edge Using CEP-Stabilized Few-Cycle IR Pulses

We generate a 75-eV-wide continuum in the water window via the HHG process using CEP-stabilized, few-cycle IR pulses. A pressure dependence of harmonic spectra indicates sub-cycle deformation of the IR pulses in the process.