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We demonstrate plasma-mirror frequency-resolved optical gating (PM-FROG) using a liquid-sheet jet of water and characterize a waveform of a high-repetition laser pulse(1 kHz) in the ultraviolet (UV) region. The measured PM-FROG trace is reconstructed by the least-squares generalized projections algorithm. The retrieved UV spectral phase is consistent with that by self-diffraction FROG. The complex reflection coefficient of a plasma mirror is discussed in terms of the free electron density dependence. The PM-FROG technique is applicable to not only the pulse characterization, but also the investigation of ionization dynamics of a liquid.

We employ (1) a liquid-sheet jet of water as a target to extend the applicable repetition rate to 1 kHz and (2) a UV pulse to evaluate the validity of the waveform obtained by PM-FROG with another pulse characterization technique. In addition, we discuss time-dependent complex reflection coefficient of the plasma mirror by using the Drude model., International Symposium on Ultrafast Intense Laser Science

Pulse characterization in the vacuum-ultraviolet (VUV) region is not trivial. Since the photon energy is smaller than the ionization potentials, two-photon absorption is required to characterize a VUV waveform by the photoelectron spectroscopy. Recently, we developed an alternative method based on the time-resolved reflection spectroscopy. In this plasma-mirror frequency resolved optical gating (PM-FROG) technique, ultrafast switching of the reflectivity of a plasma mirror generated by focusing intense near-infrared (NIR) pulses on a solid target is used as a gate function. Since reflective optics is employed, this technique can be used for the characterization of broadband pulses. However, due to a damage of the solid target by laser ablation, the applicable repetition rate of PM-FROG was limited. In this study, we developed the time-resolved reflection spectroscopy with a liquid-sheet target to extend the application range, and demonstrated the eligibility of the waveform obtained by PM-FROG in a UV region. We also discussed the obtained plasma-mirror reflectivity as a function of the free-electron density to understand underlying physics of plasma formation., CLEO/Europe-EQEC 2019

水の液膜ジェットをターゲットとし、近赤外光で生成したプラズマミラーにより反射された紫外光のスペクトルを遅延時間を変えながら計測した。FROGアルゴリズムを用いた再構築計算の結果、繰り返し周波数1kHzの超短パルスの時間波形に加え、プラズマミラーの反射率の時間変化が得られた。得られた結果はDrudeモデルに基づいた計算結果と定性的に一致し、本手法を用いて液体のイオン化ダイナミクスの研究が可能なことが示唆された。, 光・量子ビーム科学合同シンポジウム2019

我々は液膜ジェットをターゲットとした時間分解反射分光法の開発を進めてきた。近赤外光で生成したプラズマミラーによって反射された紫外光の分光計測をおこなった。その結果、繰り返し周波数１kHzの超短パルスの波形計測が可能なだけでなく、プラズマミラーの反射率の時間変化の情報が得られることが明らかとなった。得られた結果は、Drudeモデルに基づいた計算結果と定性的に一致を示した。, 第35回化学反応討論会

プラズマミラー周波数分解光ゲート計測（PM-FROG）法の高繰り返し化および妥当性の検証を目的とし、液膜ジェットをターゲットとした時間分解反射分光計測を紫外領域のパルスを用いておこなった。得られたFROG信号に対してLSGPAを用いた再構築計算をおこない、パルス幅52fsと評価することができた。また、得られた結果は幅広く用いられているSD-FROG法による測定とよい一致を示し、PM-FROG法の妥当性が示された。, 第66回応用物理学会春季学術講演会

プラズマミラー周波数分解光ゲート（PM-FROG）法に基づいた真空紫外パルス（波長 132 nm）の波形計測および液膜ジェットを用いた波形計測について報告する。, 京都大学エネルギー理工学研究所 ゼロエミッションエネルギー研究拠点 平成３０年度共同利用・共同研究成果報告会

We demonstrate photoacoustic wave propagation with a plane wavefront in liquid water using a terahertz (THz) laser pulse. The THz light can effectively generate the photoacoustic wave in water because of strong absorption via a stretching vibration mode of the hydrogen bonding network. The excitation of a large-area water surface irradiated by loosely focused THz light produces a plane photoacoustic wave. This is in contrast with conventional methods using absorbers or plasma generation using near-infrared laser light. The photoacoustic wave generation and plane wave propagation are observed using a system with a THz free-electron laser and shadowgraph imaging. The plane photoacoustic wave is generated by incident THz light with a small radiant exposure of

Organic semiconductor microcavities forming strongly-coupled exciton polaritons are interesting system due to their nonlinear coherent emission observed even at room temperature. Here we investigate the incident angle and photon energy dependent photoemission from a planar organic microcavity to evaluate the relaxation efficiency toward the bottom of the lower polariton branch. We observe nonlinear increase of the vertical emission from the microcavity when the sample is pumped resonantly in the lower polariton branch with the incident angle of 30 to 55 degrees. The observed results support the fast and efficient relaxation of organic microcavity polaritons within the lower polariton branch.