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Journal Articles

Electron and ion coincidence momentum imaging of multichannel dissociative ionization of ethanol in intense laser fields

Itakura, Ryuji; Hosaka, Koichi*; Yokoyama, Atsushi; Ikuta, Tomoya*; Kannari, Fumihiko*; Yamanouchi, Kaoru*

Progress in Ultrafast Intense Laser Science XI; Springer Series in Chemical Physics, Vol.109, p.23 - 42, 2015/00

We investigate the multichannel dissociative ionization of ethanol in intense laser fields by the photoelectron-photoion coincidence momentum imaging and identify separately the ionization and subsequent electronic excitation in ethanol. From the energy correlation between a photoelectron and a fragment ion, we reveal the amount of the internal energy gained by ethanol cations from the laser field varies depending on the respective ionization and electronic excitation pathways.

Journal Articles

Photoionization of atoms and molecules by intense EUV-FEL pulses and FEL seeded by high-order harmonic of ultrashort laser pulses

Iwasaki, Atsushi*; Sato, Takahiro*; Owada, Shigeki*; Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Kannari, Fumihiko*; Yagishita, Akira*; et al.

Reza Kenkyu, 40(9), p.687 - 690, 2012/09

no abstracts in English

Journal Articles

Separation of ionization and subsequent electronic excitation for formation of electronically excited ethanol cation in intense laser fields

Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Itakura, Ryuji

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(19), p.191002_1 - 191002_5, 2011/10

 Times Cited Count:8 Percentile:39.78(Optics)

Ionization and subsequent electronic excitation occurring within the same laser pulse (400 nm, 96 fs, 1.3$$sim$$18 TW/cm$$^{-2}$$) are separately investigated by measuring in coincidence an electron and a product ion produced from C$$_{2}$$H$$_{5}$$OH. We reveal that the nascent population in the electronically excited C$$_{2}$$H$$_{5}$$OH$$^{+}$$ prepared by the ionization decreases as the laser intensity increases, while the subsequent electronic excitation is enhanced through the resonant electronic transitions. Ionization and electronic excitation mechanisms are described based on the electronic state distributions of C$$_{2}$$H$$_{5}$$OH$$^{+}$$.

Journal Articles

XUV-FEL spectroscopy; He two-photon ionization cross-sections

Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.

Europhysics News, 42(5), P. 10, 2011/09

The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He$$^{+}$$ on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.

Journal Articles

Determination of the absolute two-photon ionization cross section of He by an XUV free electron laser

Sato, Takahiro*; Iwasaki, Atsushi*; Ishibashi, Kazuki*; Okino, Tomoya*; Yamanouchi, Kaoru*; Adachi, Junichi*; Yagishita, Akira*; Yazawa, Hiroki*; Kannari, Fumihiko*; Aoyama, Makoto; et al.

Journal of Physics B; Atomic, Molecular and Optical Physics, 44(16), p.161001_1 - 161001_5, 2011/08

 Times Cited Count:33 Percentile:84.31(Optics)

The resonant and non-resonant two-photon single ionization processes of He were investigated using intense free electron laser light in the extreme ultraviolet (XUV) region (53.4-61.4 nm) covering the 1s-2p and 1s-3p resonant transitions of He. On the basis of the dependences of the yield of He$$^{+}$$ on the XUV light-field intensity at 53.4, 58.4, 56.0 and 61.4 nm, the absolute values of the two-photon ionization cross sections of He at the four different wavelengths and their dependence on the light-field intensity were determined for the first time.

Journal Articles

Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphore laser

Togashi, Tadashi*; Takahashi, Eiji*; Midorikawa, Katsumi*; Aoyama, Makoto; Yamakawa, Koichi; Sato, Takahiro*; Iwasaki, Atsushi*; Owada, Shigeki*; Okino, Tomoya*; Yamanouchi, Kaoru*; et al.

Optics Express (Internet), 19(1), p.317 - 324, 2011/01

 Times Cited Count:88 Percentile:96.89(Optics)

The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.

Journal Articles

Selective bond breaking in dissociative ionization of ethanol induced by tailored intense laser fields

Itakura, Ryuji; Yamanouchi, Kaoru*; Kannari, Fumihiko*

Advances in Multi-Photon Processes and Spectroscopy, Vol.19, p.93 - 115, 2010/03

It is demonstrated that the branching ratio between the C-C and C-O bond breaking processes in the dissociative ionization of ethanol is controlled by tailoring the intense laser pulse shape. Through systematic investigation of the dependence of the parameters of the laser pulses on the yield ratio between the two dissociation pathways, mechanisms of bifurcating into the two pathways are discussed. The important key factors for determining the yield ratio were found to be the pulse duration and wavelength. It was proposed that the nonadiabatic electronic excitation is efficiently induced by the wave packet evolution within the laser pulse duration.

Journal Articles

Non-adiabatic transition in C$$_{2}$$H$$_{5}$$OH$$^{+}$$ on a light-dressed potential energy surface by ultrashort pump-and-probe laser pulses

Yazawa, Hiroki*; Shioyama, Tadamasa*; Hashimoto, Hiroshi*; Kannari, Fumihiko*; Itakura, Ryuji; Yamanouchi, Kaoru*

Applied Physics B, 98(2-3), p.275 - 282, 2010/02

 Times Cited Count:4 Percentile:26.11(Optics)

We experimentally investigate the dynamics of vibrational wave packets on the light-dressed-potential energy surface (LD-PES) of C$$_{2}$$H$$_{5}$$OH$$^{+}$$ using a pump-and-probe pulse excitation scheme. The probability of non-adiabatic transition at 800 nm from the singly ionized ground state to the repulsive excited state leading to C-O bond breaking is enhanced when a probe laser pulse is delayed by around 180 fs. At this pulse delay, on the other hand, C-C bond breaking is significantly suppressed. Therefore, the deformation of LDPES is considered to change the direction of the wave packet traveling originally along the C-C stretching into the direction along the C-O stretching. This non-adiabatic transition leading to the redirection of the dissociating wave packet is found to occur more efficiently at the probe laser wavelengths at 400 nm than at 800 nm. The critical pulse delay is still around 180 fs even at 400 nm.

Journal Articles

Controlling the dissociative ionization of ethanol with 800 and 400 nm two-color femtosecond laser pulses

Yazawa, Hiroki*; Shioyama, Tadamasa*; Suda, Yoshitaka*; Yamanaka, Mio*; Kannari, Fumihiko*; Itakura, Ryuji; Yamanouchi, Kaoru*

Journal of Chemical Physics, 127(12), p.124312_1 - 124312_5, 2007/09

 Times Cited Count:9 Percentile:32.99(Chemistry, Physical)

Ethanol molecules were irradiated with a pair of temporally overlapping ultrashort intense laser pulses (10$$^{13}$$-10$$^{14}$$ W/cm$$^{2}$$ with different colors of 400 and 800 nm, and the dissociative ionization processes have been investigated. The yield ratio of the C-O bond breaking with respect to the C-C bond breaking was varied in the range of 0.17-0.53 sensitively depending on the delay time between the two laser pulses, and the absolute value of the yield of the C-O bond breaking was found to be increased largely when the Fourier-transform limited 800 nm laser pulse overlaps the stretched 400 nm laser pulse, demonstrating an advantage of the two-color intense laser fields in controlling chemical bond breaking processes.

Oral presentation

Selective bond breaking of ethanol in intense laser fields

Itakura, Ryuji; Yamanouchi, Kaoru*; Yazawa, Hiroki*; Shioyama, Tadamasa*; Kannari, Fumihiko*

no journal, , 

Recent progress in ultrashort pulsed laser technology has enabled us to control chemical reaction dynamics in intense laser fields. In this study, we investigate responses of ethanol to a train of intense laser pulses by changing systematically the parameters such as the number of pulses within a train and the chirp rate of respective pulses. It is confirmed that the most critical factor governing the bond breaking dynamics is an overall temporal width of laser pulses as far as laser pulses with the central wavelength of 800 nm and the spectral width of 26 nm are adopted. The smoothly connected pulses in a train to be a single long pulse ($$sim$$1 ps FWHM) shows larger ratio of the C-O bond breaking than the pulse train with temporally isolated multiple pulses. However, when the temporal separation between the pulses becomes shorter than 100 fs, the branching ratio between the two bond breaking pathways shows no difference from that by a smoothly lengthened pulse. We also perform the adaptive pulse shaping in order to find an optimal solution for obtaining the maximum branching ratio. By the analysis of the optimized laser pulses, it is found that the temporal fine structure within a laser pulse appearing in the range less than 100 fs does not influence the branching ratio, and that the overall temporal duration of a laser pulse is a major factor in determining the branching ratio.

Oral presentation

Photoelectron-photoion coincidence imaging for dissociative ionization of ethanol in intense UV laser fields

Ikuta, Tomoya; Hosaka, Koichi; Itakura, Ryuji; Akagi, Hiroshi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Yokoyama, Atsushi

no journal, , 

Recently, using a photoelectron-photoion coincidence momentum imaging apparatus, we found two possible pathways for the dissociative ionization of ethanol in intense NIR laser fields: one pathway is the direct access to the electronically excited states leading to the dissociation, the other is the stepwise excitation through the ionization to the electronic ground state. In this study, we investigate the dissociative ionization in intense UV laser with the same technique and compare the results with those with the NIR pulses.

Oral presentation

Dissociative ionization of ethanol in intense UV laser fields studied by photoelectron-photoion coincidence momentum imaging

Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Yokoyama, Atsushi; Kannari, Fumihiko*

no journal, , 

When ethanol molecules are irradiated with an intense UV pulse (400 nm,100 fs, I = 10 TW/cm$$^{2}$$), channel-specific photoelectron momentum images correlated with C$$_{2}$$H$$_{5}$$OH$$^{+}$$, C$$_{2}$$H$$_{4}$$OH$$^{+}$$, CH$$_{2}$$OH$$^{+}$$, and C$$_{2}$$H$$_{5}$$$$^{+}$$ show different features, suggesting that different electronic and vibrational state distributions are prepared upon the ionization for the respective product ion channels.

Oral presentation

Dissociative ionization of ethanol in intense UV laser fields observed by photoelectron-photoion coincidence momentum imaging

Ikuta, Tomoya; Itakura, Ryuji; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Yokoyama, Atsushi

no journal, , 

When ethanol molecules are irradiated with an intense UV pulse (400 nm, 100 fs, 15$$sim$$33 TW/cm$$^{2}$$), channel-specific photoelectron momentum images correlated with C$$_{2}$$H$$_{5}$$OH$$^{+}$$, C$$_{2}$$H$$_{4}$$OH$$^{+}$$, CH$$_{2}$$OH$$^{+}$$, and C$$_{2}$$H$$_{5}$$$$^{+}$$ show different features, suggesting that different electronic and vibrational state distributions are prepared upon the ionization for the respective product ion channels. Basically, the electronic ground state and the first electronically excited state are prepared upon the ionization, and then the subsequent interaction between the ion and the laser field takes place, leading to the respective reaction channels.

Oral presentation

Dissociative ionization of ethanol in intense UV laser fields studied by photoelectron-photoion coincidence momentum imaging

Ikuta, Tomoya; Itakura, Ryuji; Hosaka, Koichi*; Akagi, Hiroshi; Yamanouchi, Kaoru*; Kannari, Fumihiko*; Yokoyama, Atsushi

no journal, , 

Dissociative ionization of ethanol is more efficiently induced by intense ultraviolet laser fields than by intense near-infrared laser fields. In this study, our concern are focused on the electronic excitation dynamics in dissociative ionization of ethanol in intense ultraviolet laser fields. Photoelectron-photoion coincidence measurement allows us to understand the dissociation mechanism in terms of electronic excitation.

Oral presentation

Photoelectron-photoion coincidence momentum imaging for dissociative ionization of ethanol in two color laser fields

Ikuta, Tomoya; Itakura, Ryuji; Hosaka, Koichi*; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*

no journal, , 

We investigate the dissociative ionization dynamics of ethanol in two color (UV-NIR) laser fields using photoelectron-photoion coincidence momentum imaging. The details of the ionization dynamics for the respective reaction channels are elucidated. The reaction mechanism in terms of the electronic excitation is discussed.

Oral presentation

Ionization of ethanol and subsequent electronic excitation in ethanol cation in intense laser fields

Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*

no journal, , 

Using photoelectron-photoion coincidence technique, we identify two ionization routes of ethanol to the electronic ground state and the electronically excited state of ethanol cation in intense ultraviolet (UV) laser fields (400 nm, 96 fs). The population ratio of the electronically excited state with respect to the electronic ground state of C$$_{2}$$H$$_{5}$$OH$$^{+}$$ at the instant of the ionization decreases significantly as the laser intensity increases from 1.3 to 18.1 TW/cm$$^{2}$$. It is also revealed that the probability of the subsequent electronic excitation of C$$_{2}$$H$$_{5}$$OH$$^{+}$$ within the same pulse is enhanced as the laser intensity increases.

Oral presentation

Photoelectron-photoion coincidence spectroscopy of ethanol in two-color intense laser fields

Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*

no journal, , 

Photoionization dynamics of ethanol in two-color (400 and 800 nm) intense laser fields is investigated using photoelectron-photoion coincidence spectroscopy. It is found that the fragment ion CH$$_{2}$$OH$$^{+}$$ is formed dominantly through the ionization to the electronically excited state by the 400-nm pulse when a 400-nm pulse and a 800-nm pulse are temporally separated. When a 400-nm pulse is temporally overlapped with a 800-nm pulse, the ionization to the electronically excited state by the 400-nm pulse is significantly suppressed, indicating that the ionization channel to the electronically excited state is closed due to the AC stark up-shift by the 800-nm pulse.

Oral presentation

Dissociative ionization dynamics of ethanol in intense laser fields; Energy correlation between photoelectron and fragment ion

Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*

no journal, , 

We investigate dissociative ionization of ethanol induced by intense laser fields using photoelectron-photo ion coincidence momentum imaging. Our attentions are focused on the energy correlation between an electron and a fragment ion produced from an identical ethanol molecule. We reveal that the internal energy gained from laser fields depends on the ionization and fragmentation pathways. We discuss the ionization and dissociation mechanism based on the experimental results depending on the laser characteristics.

Oral presentation

Energy correlation of photoelectron and fragment ion in dissociative ionization of ethanol in intense laser fields

Itakura, Ryuji; Ikuta, Tomoya*; Hosaka, Koichi*; Akagi, Hiroshi; Yokoyama, Atsushi; Yamanouchi, Kaoru*; Kannari, Fumihiko*

no journal, , 

We investigate dissociative ionization of ethanol induced by intense laser fields using photoelectron-photo ion coincidence momentum imaging. Our attention is focused on the correlation between (1) photoelectron energy reflecting the state of ethanol cation at ionization and (2) kinetic energy of a fragment ion. From the observed correlation maps, we clarified that the internal energy gained from the laser field strongly depends on the ionization and dissociation pathways.

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