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Itakura, Ryuji*; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi*
High Power Laser Science and Engineering, 4, p.e18_1 - e18_5, 2016/06
Times Cited Count：4 Percentile：25.13(Optics)We demonstrate that the methodology of frequency-resolved optical gating (FROG) is applicable to time-resolved reflection spectroscopy of a plasma mirror in the vacuum-ultraviolet (VUV) region. Our recent study has shown that a VUV waveform can be retrieved from a VUV reflection spectrogram of a plasma mirror formed on a fused silica (FS) surface by irradiation with an intense femtosecond laser pulse. Simultaneously, the increase in the reflectivity with respect to the Fresnel reflection of the unexcited FS surface can be obtained as a time-dependent reflectivity of the plasma mirror. In this study, we update the FROG analysis procedure using the least-square generalized projections algorithm. This procedure can reach convergence much faster than the previous one and has no aliasing problem. It is demonstrated that a significantly chirped VUV pulse as long as 1 ps can be precisely characterized.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
Optics Express (Internet), 23(9), p.10914 - 10924, 2015/05
Times Cited Count：17 Percentile：65.18(Optics)We propose and experimentally demonstrate a method for characterizing vacuum ultraviolet (VUV) pulses based on time-resolved reflection spectroscopy of fused silica pumped by an intense laser pulse. Plasma mirror reflection is used as an ultrafast optical switch, which enables us to measure frequency-resolved optical gating (FROG) traces. The VUV temporal waveform can be retrieved from the measured FROG trace using principal component generalized projections algorithm with modification. The temporal profile of the plasma mirror reflectivity is also extracted simultaneously.
Nakano, Motoyoshi; Otobe, Tomohito; Itakura, Ryuji
no journal, ,
We have studied branching into two spin-orbit levels (J = 3/2 and 1/2) of Kr and Xe in induced by intense ultra-violet laser pulse (398 nm, 80 fs) with photoelectron momentum imaging. In the case of Xe, when the laser intensity increased from 9 to 26 TW/cm
, the branching ratio [J=3/2]/[J=1/2] in the five-photon ionization increases from 0.65 to 1.25. In the case of Kr, the ratio is almost constant in this intensity range, but the angular distributions change significantly. We performed ab initio calculation and compared it with the experimental results.
Nakano, Motoyoshi; Otobe, Tomohito; Itakura, Ryuji
no journal, ,
no abstracts in English
Itakura, Ryuji; Nakano, Motoyoshi; Chen, J.*; Nakajima, Takashi*
no journal, ,
We are trying to monitor and control electron dynamics for laser-material processing and laser-reaction control, which might be applicable for isotope selection and element separation. In this study, a photoelectron spectrometer with ultrafast vacuum UV pulses has been developed and applied for the characterizing the VUV spectral phase. In parallel, the intensity dependence of branching into two different ionization states of Kr
is investigated.
Nakano, Motoyoshi; Otobe, Tomohito; Itakura, Ryuji
no journal, ,
no abstracts in English
Fukahori, Shinichi*; Nakano, Motoyoshi; Yamanouchi, Kaoru*; Itakura, Ryuji
no journal, ,
Dissociative ionization of methanol in an intense laser field is investigated using photoelectron-photoion coincidence momentum imaging. Energy and angular correlations between a photoelectron and a fragment ion reveal the ionization and subsequent electronic excitation processes. It is revealed that the photoelectron angular distributions correlated with the CH
formation strongly depend on the energy of the counterpart photoelectron.
Fukahori, Shinichi*; Nakano, Motoyoshi; Yamanouchi, Kaoru*; Itakura, Ryuji
no journal, ,
Dissociative ionization of methanol is investigated. We confirm the presence of the two types of ionization and electronic excitation pathways based on the channel-specific photoelectron spectra and the energy correlation between the photoelectron and the fragment recoil. Furthermore, from the three dimensional momenta of the photoelectron and the CH
fragment ion detected in coincidence, energy-resolved molecular-frame photoelectron angular distributions are obtained.
Fukahori, Shinichi*; Nakano, Motoyoshi; Yamanouchi, Kaoru*; Itakura, Ryuji
no journal, ,
We investigate the mechanism of the electronic excitation of singly charged methanol cation in dissociative ionization of methanol cation in intense laser fields based on photoelectron-photoion coincidence momentum imaging. From three independent experimental results such as (1) channel specific photoelectron spectra, (2) energy correlation of photoelectrons and fragment ions and (3) angular correlation of electron emission and fragment recoil, two types of ionization and electronic excitation pathways are revealed.
Nakano, Motoyoshi*; Otobe, Tomohito; Itakura, Ryuji
no journal, ,
We have performed photoelectron momentum imaging for multiphoton ionization of Kr in UV laser fields. As the laser intensity increases to 38 TW/cm
, we have found an anomalous photoelectron angular distribution in 5 photon ionization to P
showing the enhanced photoelectron emission in the direction perpendicular to the laser polarization direction.
Fukahori, Shinichi*; Nakano, Motoyoshi*; Yamanouchi, Kaoru*; Itakura, Ryuji
no journal, ,
We investigate dissociative ionization of methanol in an intense laser field using photoelectron-photoion coincidence momentum imaging. We have measured channel-specific photoelectron angular distibutions as well as photoelectron energy spectra and energy correlations between photoelectrons and fragment ions. It is revealed that the photoelectron angular distributions reflect the character of the electronic states prepared at the photoelectron emission.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
We demonstrate a new method for characterizing VUV waveform based on time-resolved reflection spectra using a plasma mirror formed by an intense femtosecond laser pulse. The VUV waveform is retrieved using the FROG algorithm.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
When solid material is irradiated with an intense laser pulse, a number of electrons are excited to move freely. If the density of free electrons in the solid exceeds the critical density, the excited solid exhibits high reflectivity as a plasma mirror. In order to monitor electronic excitation dynamics, we have developed a time-resolved reflection spectrometer in the VUV range. Using an algorithm of frequency-resolved optical gating, we can obtain the time-resolved reflectivity of fused silica irradiated with an intense NIR pulse as well as the temporal waveform of a VUV probe pulse.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
We propose and demonstrate a method for characterizing VUV waveform based on time-resolved reflection spectra using a plasma mirror formed by an intense laser pulse. The VUV waveform is retrieved using the frequency-resolved optical gating algorithm.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
This study represents a method for simultaneous measurement of a VUV waveform and time-dependent reflectivity of plasma mirror. We use a plasma mirror as ultrafast optical switching formed by an intense laser pulse and perform frequency-resolved optica gating measurement. The waveform of the VUV pulse and the time-dependent reflectivity of the plasma mirror can be retrieved with excellent agreement between obsereved and retrieved FROG traces.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
We propose and experimentally demonstrate a new type of frequency-resolved optical gating (FROG) based on time-resolved reflection measurement with a plasma mirror. A VUV waveform can be extracted with FROG retrieval algorithms. In addition, time-dependent reflectivity of a plasma mirror is extracted through retrieval of a FROG trace.
Itakura, Ryuji; Kumada, Takayuki; Nakano, Motoyoshi*; Akagi, Hiroshi
no journal, ,
We demonstrate that a plasma-mirror formed by an intense femtosecond laser pulse is utilized as an ultrafast optical switch and that frequency-resolved optical gating in the vacuum ultraviolet region is feasible. Additionally, our method is useful to monitor the laser-plasma dynamics.
