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Time-resolved terahertz (THz) spectroscopy is applied for a microcrystalline film of methylammonium lead bromide perovskite, CH3NH3PbBr3, to observe the carrier dynamics around the band edge. The ultrafast response of the transmitted THz electric field amplitude after carrier generation is modeled with a biexponential curve with ∼5 and 180 ps time constants, which are ascribed to Auger and electron-hole recombination processes, respectively. From the pump photon energy dependence of the time evolution of the THz electric field amplitude, it is shown that the bound exciton states and free interband excited carrier states show a clearly different temporal response. These measurements support the idea that the bound excitons generated in CH3NH3PbBr3 remain as stable excitons even at room temperature (RT). This is in clear contrast to the cases in CH3NH3PbI3 in which the excitons and band-edge free carriers are interchangeable at RT.

We develop a high-speed two-dimensional (2D) terahertz (THz) color imaging system for practical applications. This system performs THz time-domain spectroscopy (THz-TDS) measurements in one-dimensional (1D) space simultaneously to reduce the spatial scan from 2D to 1D and obtains the 2D THz color image in which the spectral data is possessed in each pixel. We realize measurements on the image with 750 × 1000 pixels (13 mm × 25 mm) with the spatial resolution of 1.5 mm within 10 seconds. This is two orders of magnitude faster than conventional THz color imaging methods. High-speed 2D THz color imaging will be used in non-destructive and non-invasive inspections of industrial products and biological tissues in the future.

レーザーによる物質の操作と観測において、光が到達し得ない領域の物資に対して、光から熱、さらに圧力波へのエネルギー変換から間接的に行う手法が、レーザー誘起衝撃波もしくは光音響波法として知られている。本研究では、非破壊非侵襲な手法として、長波長レーザー光（テラヘルツ～中赤外光）を用いた水中光音響波発生法を開発し、音響波の発生とその観測を行った。本研究により、水中を10μm程度しか透過しない長波長光を用いて、水中、特に生体分子の操作・観測を行える事が示唆された。これは理研保科、東北大原田らの先行研究によるテラヘルツ光による水溶液や細胞中のアクチン分子切断の結果を解釈する一つのてがかりになると言える。本講演では、テラヘルツ光と中赤外光を用いた光音響波発生と観測手法について紹介し、その波及効果について議論する。, 第12回テラバイオミーティング

We perform a beat-frequency-resolved analysis for two-dimensional electronic spectroscopy using a high-speed and stable 2D electronic spectrometer and few-cycle visible laser pulses to disentangle the vibrational coherences in an artificial fluorescent protein. We develop a highly stable ultrashort light source that generates 5.3-fs visible pulses with a pulse energy of 4.7 µJ at a repetition rate of 10 kHz using multi-plate pulse compression and laser filamentation in a gas cell. The above-5.3-fs laser pulses together with a high-speed multichannel detector enable us to measure a series of 2D electronic spectra, which are resolved in terms of beat frequency related to vibrational coherence. We successfully extract the discrete vibrational peaks behind the inhomogeneous broadening in the absorption spectra and the vibrational quantum beats of the excited electronic state behind the strong incoherent population background in the typical 2D electronic spectra.

We demonstrate photoacoustic (PA) wave generation at an air–water interface using a mid-infrared (MIR) laser pulse and observe its propagation in liquid water by shadowgraph imaging. The PA wave reaches a depth of more than 4 mm, which is over 100 times deeper than the penetration depth of MIR light in water. As one of the applications of the PA wave, we quantitatively analyze the ethanol mole fraction in a water–ethanol mixed solution. We achieve the generation of PA waves induced by a compact MIR laser system, which provides a new tool for imaging and inspecting the object in water.

極短パルスレーザー技術の発展によりフェムト秒・アト秒パルスの発生が可能となり、真空紫外・極端紫外領域における新しい波形計測法の開拓が求められている。我々は真空紫外領域での全光学的な波形計測法として，高強度フェムト秒レーザーを固体表面に集光した際に，生成するプラズマの密度が急峻に変化することを利用したプラズマミラー周波数分解光ゲート (PM-FROG) 法を開発してきた。本研究では，PM-FROG 法の高繰り返しレーザーへの適用および得られた結果の妥当性の評価を目的とし，液膜ジェットをターゲットとした紫外領域での時間分解反射分光計測を行った。また，本手法によりパルス波形と同時に得られるプラズマミラーの超高速な複素反射率の時間変化について物理モデルを検討した。, 原子衝突学会第46回年会

The relativistic Doppler reflection of terahertz (THz) light from a photoinduced moving plasma front in a silicon wafer irradiated by an optical pump light was investigated. The intensity and the phase shift spectra of the reflected THz light were investigated by THz time-domain spectroscopy with broadband electro-optic sampling in a thin GaP crystal. The frequency up-shift factor, which is a ratio of averaged frequencies from after to before Doppler reflection, was measured to be $\mathrm{\ensuremath{\Gamma}}=2.02$ with a pump energy density of $3.3\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{J}/\mathrm{m}{\mathrm{m}}^{2}$ at a wavelength of 800 nm. The frequency up-shift increased as optical pump energy density increased. The frequency up-shift was reproduced by evaluating the moving plasma front whose spatial carrier density distribution depended on the pump energy density.

The influence of the terahertz (THz) radiation for deep tissues has been neglected due to its strong absorption by water molecules on the surface of the skin. In this report, we found for the first time the demolishing effect of the THz pulsed radiation on actin filaments located in aqueous solution with a few millimeters in depth. This result demonstrates that the THz photon energy propagates in water with several millimeters in depth, possibly as shockwave, and affected actin filaments. Thus, it is implicated that THz waves have the potential to manipulate functions of proteins and cells in deep tissues.

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. 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

Time-resolved terahertz (THz) spectroscopy is applied for a microcrystalline film of methylammonium lead bromide perovskite, CH

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 photo-electron spectroscopy. Recently, we developed an alternative method based on the time-resolved reflection spectroscopy [1]. 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 compared the obtained plasma-mirror reflectivity as a function of the time-delay with the FDTD calculation to understand underlying physics of plasma formation.

Our recent experimental research on terahertz (THz) irradiation of actin filaments, which serve as representative biopolymer materials, is summarized in this review. We found that pulsed THz waves with energy density of ∼10−4 J cm−2 (∼108 W cm−2 at the peak) generate acoustic waves efficiently in the aqueous media. These acoustic waves propagated deeply into the water and demolished the actin filaments in living HeLa cells that were submerged into the cell culture medium. The results implied that THz pulsed irradiation affects the biomolecules in the tissues, even if these molecules are located a few millimeters away from the body surface. In contrast, irradiation using THz waves with lower peak power of the order of ∼W cm−2 induces the elongation of the actin biopolymer without thermal or acoustic effects. The polymerization of actin molecules plays essential roles in cell motility, growth, differentiation and gene expression. Therefore, our results indicate that THz waves could be applicable to artificial manipulation of cellular functions.

The relativistic Doppler reflection of terahertz (THz) light from a photoinduced moving plasma front in a silicon wafer irradiated by an optical pump light was investigated. The intensity and the phase shift spectra of the reflected THz light were investigated by THz time-domain spectroscopy with broadband electro-optic sampling in a thin GaP crystal. The frequency up-shift factor, which is a ratio of averaged frequencies from after to before Doppler reflection, was measured to be Gamma = 2.02 with a pump energy density of 3.3 μJ/mm2 at a wavelength of 800 nm. The frequency up-shift increased as optical pump energy density increased. The frequency up-shift was reproduced by evaluating the moving plasma front whose spatial carrier density distribution depended on the pump energy density.

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

We have developed an efficient contact grating device for generating terahertz waves. This device has a very high diffraction efficiency and a wide spectral width. The device has a bi-angular filter and a Fabry-Perot-type structure, which are composed of dielectric multilayers. The bi-angular filter is designed to reflect the 0th-order wave and transmit the −1st-order diffraction wave. Numerical calculations indicate that the new device has a maximum diffraction efficiency over 99% and a spectral width of approximately 20 nm. We measured a high efficiency of 90% over a broad spectral range using a fabricated device.

We applied terahertz (THz) time-domain spectroscopy (THz-TDS) to reveal the mechanism of the relativistic Doppler reflection of THz light from a photo-induced plasma front in a silicon wafer. The frequency up-shift caused by the Doppler reflection was identified by measurement of the reflected THz waveforms and compared to the calculated results obtained using the one-dimensional finite-difference time-domain (1D-FDTD) method. We explored not only the intensity but also the phase spectra of the reflected THz light in order to further understand the mechanism of the relativistic Doppler reflection.

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.

Organic semiconductor microcavities forming strongly coupled exciton-polaritons are interesting systems 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 towards the bottom of the lower polariton branch. We observe nonlinear increase in the vertical emission from the microcavity when the sample is pumped resonantly to the lower polariton branch with an incident angle of 30 to 55°. The observed results support the fast and efficient relaxation of organic microcavity polaritons within the lower polariton branch.

We applied terahertz (THz) time-domain spectroscopy to reveal the mechanism of the relativistic Doppler reflection of THz light from a photoinduced plasma front in a silicon wafer. The frequency upshift caused by the Doppler reflection was identified by measurement of the reflected THz waveforms and compared to the calculated results obtained using the one-dimensional finite-difference time-domain method. The relation between the energy density of the pump light and the frequency upshift was also explored. We found that the interaction time of the moving plasma front and the reflected THz pulse is a key factor in understanding the mechanism of the relativistic Doppler reflection.

We have proposed a novel design for a contact grating setup with an incorporated Fabry-Perot resonator for intense terahertz (THz) light generation. This setup is scalable and extremely compact as compared with the conventional LiNbO 3 prism setup. We evaluated the THz generation process in the device by experimental and calculated studies, and optimized the device to obtain maximum THz output.

We have proposed an improved contact grating device for generating terahertz waves efficiently and have succeeded in developing the device with a very high diffraction efficiency and a wide spectral width. This device has a bi-angular filter and a Fabry–Perot-type structure, which are composed of dielectric multilayers. The bi-angular filter is designed to reflect the 0th-order wave and transmit the–1st-order diffraction wave. Numerical calculations indicate that the new device has a maximum diffraction efficiency over 99% and a spectral width of approximately 20 nm. We measured a high efficiency of 90% over a broad spectral range using a fabricated device.

We have examined a technique of complex shaping of mid-infrared femtosecond laser pulses towards accurate and precise control of rovibrational wave packets of molecules in the ground electronic state. A Germanium acousto-optics modulator was used as a device for the pulse shaping. In order to characterize the shaped pulses precisely, sum-frequency cross-correlation frequency-resolved optical gating was introduced for the analysis of both amplitude and phase of the electric fields. The mid-infrared pulses were shaped and characterized with a frequency resolution better than 4.5 cm −1 . Such a resolution is supposed to be sufficient for the realization of quantum gate operations with high fidelity, which is one of the most challenging applications of rovibrational wave packet manipulation of molecules. In order to demonstrate the precision of our method of shaping and its characterization, we have generated shaped pulses that will realize Hadamard and NOT quantum gates with rovibrational states of a CO molecule.

A novel design for a contact grating device with an incorporated Fabry-Perot resonator is proposed for high-power terahertz (THz) light generation. We deposited a multilayer consisting of Ta(2)O(5) and Al(2)O(3) on a magnesium-doped stoichiometric LiNbO(3) substrate and fabricated grating grooves on the outermost layer. The multilayer was designed such that conditions for a Fabry-Perot resonator were satisfied for light diffracted by the grating. Consequently, the fraction of light transmitted into the LiNbO(3) substrate, i.e., the diffraction efficiency, was enhanced by the resonator. The diffraction efficiency of the fabricated device was 71%, which is close to the calculated value of 78% from the optimized design. THz light generation was also demonstrated with the contact grating device. The THz output of 0.41 μJ was obtained using near-infrared pump light of 2.7 mJ.

We have developed a high average power picosecond laser system dedicated to intense terahertz (THz) pulse generation. The system is a chirped pulse amplification laser equipping with a Yb:YAG thin-disk amplifier. The Yb:YAG thin-disk regenerative amplifier at room temperature provides pulses with energy over 10 mJ and spectral bandwidth of 1.2 nm at a repetition rate of 1 kHz. In a pulse compressor, the laser pulse is compressed to be 1.3 ps. By employing this picosecond pulse as a pump source, THz pulses at the center frequency of 0.3 THz with energy over a few microjoules have been generated at 1 kHz repetition rate by the optical rectification in Mg-LiNbO 3 crystal.

We realize the relativistic Doppler reflection of THz light from a counter-propagating plasma mirror in silicon (Si) with a practically simple geometry, which allows us to easily apply the frequency up-shift to the THz optics. The average frequency of the reflected THz light is 1.4 times higher than that of the input THz light. In view of application, the important facts are that the frequency up-shift can be achieved by a low pump energy density (1.3 μJ mm−2), and that shifted frequency is almost constant in the pump energy range above this threshold.

A novel design for a contact grating device with an incorporated Fabry-Perot resonator is proposed for high-power terahertz light (THz) generation. We deposited a multilayer consisting of Ta 2 O 5 and Al 2 O 3 on a magnesium-doped stoichiometric LiNbO 3 substrate and fabricated grating grooves on the outermost layer. The multilayer was designed such that conditions for a Fabry-Perot resonator were satisfied for light diffracted by the grating. Consequently, the diffraction efficiency was enhanced by the resonator. The diffraction efficiency of the fabricated device was 77%. THz light generation was also demonstrated with the contact grating device.

Ultraviolet photodissociation of the NO dimer is studied with femtosecond time-resolved photoelectron imaging (TR-PEI) spectroscopy. Pump pulses in the range 200–235 nm are employed, while probe pulses are kept at 300 nm. The time dependencies of the observed photoelectron kinetic energies and photoelectron angular distributions support a picture in which valence state optically excited in the dimer evolves on a time scale of

Femtosecond time-resolved photoelectron imaging (TR-PEI) is applied to the (1 + 2‘) resonance-enhanced multiphoton ionization of pyrazine (1,4-diazabenzene) via the S1 state. The intersystem crossing (ISC) from the S1 (nπ*) to the T1 (nπ*) state and the ionization dynamics from 3s and 3pz Rydberg states are investigated. Rotational revival features, observed in the time-resolved photoelectron intensities from the T1 state populated by ISC as well as from the optically prepared S1 state, are analyzed in detail. The alignment at the rotational revival time in the T1 state is found to be much smaller than that in the S1 state. Numerical calculations, using the molecular eigenstate basis and taking account of the angular momentum coupling, to model the transfer of coherence between the S1 and T1 states are presented. The calculated time dependence of signal strength and the axis alignment are found to be in excellent agreement with the observed profiles. The diminished alignment in T1 is explained by the angu...

Femtosecond time-resolved photoelectron imaging was applied to (1+2‘) resonance-enhanced multiphoton ionization of deuterated pyrazine. The resonances with the 3s and 3p Rydberg states and rotational dephasing on a picosecond time-scale were observed similarly with pyrazine-H4. The photoionization dynamics of pyrazine-D4 was found to be identical to that of H4 at the photoionization wavelength of 393 nm. No signature was observed of the influence of the superexcited states upon ionization.

Ultraviolet photodissociation dynamics of the NO dimer into NO(Α)+NO(Χ) in a supersonic molecular beam is studied by femtosecond pump-probe charged particle imaging. Time-resolved photoelectron imaging reveals that photoionization from the Franck–Condon region of the excited state(s) reaches vibrationally excited states of the NO dimer cation, resulting in spontaneous fragmentation into NO+NO+ even at the shortest pump-probe time delays. The corresponding photoelectron energy distribution extending up to more than 1 eV above the ionization threshold indicates a large structural difference between the dimer cation and the photoexcited neutral state. From the isotropic photoelectron distribution, this state is assigned to a valence state rather than a Rydberg state. The characteristic photoelectron distribution and also the small NO dimer ion signal vanish within 200 fs. In the same time the photoelectron image rapidly evolves from an almost isotropic distribution into an anisotropic one characteristic for ionization from the 3s Rydberg state of the NO dimer that is adiabatically correlated with the NO(Α)+NO(Χ) fragments. Time-resolved photoion imaging used to measure the translational energy release in the NO(Α)+NO(Χ) dissociation channel reveals that at least one of the fragments, most likely NO(Χ), has an inverted vibrational state distribution. The strong vibrational excitation is in qualitative agreement with a large structural change of the NO dimer in the excited state from the neutral ground state, which presumably involves excitation of the NO stretching vibration in the dimer.

The wavelength dependence of the electronic dephasing time in the optically excited state of the NO dimer has been measured by femtosecond pump–probe photoelectron imaging for the range of 200–235 nm. The observed dephasing time increased from 0.2 to 1 ps towards longer photoexcitation wavelengths. The 3s Rydberg state was formed with similar time constants for excitation wavelengths of λ

Ultrafast electronic dephasing from the S1(nπ*) state and the energetics of the n = 3 Rydberg states of pyridine were studied by time-resolved photoelectron imaging in conjunction with (1+2‘) resonance-enhanced multiphoton ionization (REMPI) via the S1 state. The lifetime at the S1 origin was determined to be 32 ± 5 ps from the decay of the total photoionization signal. Photoelectron energy and angular distributions observed for (1+2‘) REMPI clearly indicated that two-photon ionization from the S1 state is being enhanced by the resonance with singlet 3s(n-1) and 3p(n-1) Rydberg states that have not been clearly observed before. The electronic energies of the 3px(δ=0.57) and 3py(δ=0.50) Rydberg states were determined for the first time, to be 56 120 and 57 140 cm-1, respectively.

This paper is concerned with photoelectron imaging following one-color (2+1) and two-color (2+1′) resonance enhanced multiphoton ionization in the CO molecule. After the two-photon absorption step B 1Σ+ (v′=0)←←X 1Σ+ (v″=0) or B 1Σ+ (v′=1)←←X 1Σ+ (v″=0), the subsequent one-photon ionization X 2Σ+(v+)←B 1Σ+ (v′=0,1) shows deviations from the expected Δv=0 Franck–Condon propensity rule. The results are in good agreement with a previous study using time-of-flight photoelectron spectroscopy [Sha et al., J. Chem. Phys. 99, 4334 (1993)]. The experimental photoelectron kinetic energy spectra and their angular distributions are analyzed, and the essential role played by “superexcited” Rydberg states with an A 2Π ion core in this process is examined. Moreover, photoelectron imaging methods appear to be useful in extracting information about superexcited states.

Two-color and one-color resonance enhanced multiphoton ionization photoelectron spectroscopies (REMPI–PES) have been applied to Rydberg states (n=3) of jet-cooled pyrazine. The 3s and 3p members of Rydberg series converging to the ground state (n−1) of the cation and the 3s member of a Rydberg series converging to an excited state of the cation (π−1) were observed. The photoelectron angular distributions (PADs) measured via the 3s(n−1) state drastically differed for the two-color and one-color REMPI experiments. This behavior is ascribed to different molecular axis alignments created by the two-photon excitation schemes. The PADs were also used to discriminate between the different Rydberg series.

The OH(v′=4, N′=1) products of the photon-initiated reaction O(1D2)+H2(v=0)→OH(v′, N′)+H have been probed using Doppler-resolved laser induced fluorescence. The data are used to extract the product state-resolved differential cross-section and excitation function. The state-specific angular distribution displays pronounced forward–backward peaks with a bias for backward scattering. The experimental data are compared with the results of QCT calculations, using two alternative abinitio versions of the ground 11A′ potential energy surface, and a recent abinitio version ofthe first excited 11A″ potential energy surface, in order to assess its possible influence on the overall dynamics of the reaction.

We have investigated dielectric relaxation in aqueous ionic solutions by terahertz time-domain spectroscopy to elucidate the ionic hydration effect on the structure of water. Our finding suggests the dissolved ion induces the “structure breaking effect” which weakens the hydrogen bonding of water beyond the ion hydration shell.

We present high-resolution infrared absorption spectra of chloromethyl radical produced by in situ UV photolysis of chloroiodomethane isolated in solid parahydrogen. The radicals were stable over a few days in solid parahydrogen kept at 3.6 K. Analysis of the rotation-vibration spectra revealed that the radical exhibited quantized one-dimensional rotational motion about the C-Cl bond, while the ortho and para nuclear spin species were still clearly distinguishable in the spectra. Temporal change of the spectra indicated that the nuclear spin conversion between the ortho and para nuclear spin species of the radical in solid parahydrogen occurred in a time scale of a few hours at 3.6 K. It was also found that the nuclear spin conversion became significantly slower in a higher concentration of chloroiodomethane.

We developed a new contact grating device for terahertz (THz) pulse generation by optical rectification. The device was made from polycrystalline rutile TiO2 thin film in the grating region and an amorphous SiO2 layer deposited on a Mg-doped LiNbO3 crystal. Our calculations indicated that the TiO2 grating on the SiO2 layer would yield an increase in diffraction efficiency of up to 0.69. The prepared TiO2 thin film had a sufficient laser induced damage threshold (140 GW/cm2) to enable effective THz pulse generation. Using a prototype device, we demonstrated THz pulse generation and investigated the phase-matching conditions experimentally.

Clusters of tetracene molecules with different numbers of attached (Ar) N , (Ne) N and (H 2 ) N particles (N = 1-2000) are assembled inside superfluid He nanodroplets and studied via laser-induced fluorescence. The frequency shift of the fluorescence spectrum of the tetracene molecules is studied as a function of cluster size and pickup order of tetracene and cluster species. For (Ar) N and (Ne) N clusters, our results indicate that the tetracene molecules reside inside the clusters when tetracene is captured by the He nanodroplet before the cluster species; conversely, the tetracene molecules stay on the surface of the clusters when tetracene is captured after the cluster species. In the case of (H 2 ) N clusters, however, tetracene molecules reside inside the (H 2 ) N clusters irrespective of the pickup order. We conclude that (Ar) N and (Ne) N clusters are rigid at T = 0.38 K, while (H 2 ) N clusters of up to N = 2000 remain fluxional at the same temperature. The results may also indicate the occurrence of heterogeneous nucleation of the (H 2 ) N clusters, which is induced by the interaction with tetracene chromophore molecules.

We have numerically examined optimization of the experimentally achievable shapes of mid-infrared femtosecond laser pulses to construct elementary quantum gates using molecular rovibrational states of a single molecule. Instead of optimizing the electric field by optimal control theory, the method generally used in theoretical studies of coherent control, the transmittance and the phase shift of conventional pulse shapers were optimized in the frequency domain by a genetic algorithm. The target molecular system we examined was the rotation-vibration states of CO in the $X({^{1}\ensuremath{\Sigma}}^{+})$ ground electronic state. Although the existence of the rotational degrees of freedom makes the quantum gate operation complicated, high fidelity of over 0.95 was achieved for one-rovibrational-qubit systems, which indicates that a molecular quantum computer may be feasible for at least one-qubit calculations on a diatomic molecule. On the other hand, two-qubit calculations are more difficult to achieve in a single CO molecule using rotational and vibrational degrees of freedom as different qubits. The importance of the control of the rotational in addition to the vibrational wave packet in order to realize a molecular quantum computer is discussed.

We have designed and fabricated a contact grating device to increase diffraction efficiency on the basis of the principle of the Fabry–Perot resonator. The grating structure and layer thicknesses were carefully determined by considering the electric field strength in the device and the fabrication accuracy of the grating. The prototype device had a peak diffraction efficiency of 71% at an incident angle of 42°; these values were slightly different from the design values of 78% and 44.5°, respectively. Numerical calculations revealed that this deviation was caused by the fabricated grating structure. A higher terahertz power will be expected with a device as per the design.

We have developed a 1 kHz repetition picosecond laser system dedicated for intense terahertz (THz) pulse generation. The system comprises a chirped pulse amplification laser equipped with a Yb:YAG thin-disk amplifier. At room temperature, the Yb:YAG thin-disk regenerative amplifier provides pulses having energy of over 10 mJ and spectral bandwidth of 1.2 nm. The pulse duration achieved after passage through a diffraction grating pair compressor was 1.3 ps. By employing this picosecond laser as a pump source, THz pulses having a peak frequency of 0.3 THz and 4 µJ of energy were generated by means of optical rectification in an Mg-doped LiNbOsub3/subcrystal.

We calculated the photoelectron angular distribution (PAD) expected in the laboratory frame (LF PAD) for the ionization of ${\mathrm{N}}_{2}$ molecules that are aligned by an intense laser pulse. We consider two independent processes of the dynamical alignment of molecules in the electronic ground state by an intense femtosecond laser pulse $(g10\phantom{\rule{0.3em}{0ex}}\mathrm{TW}∕{\mathrm{cm}}^{2})$ and one-photon ionization or $(2+1)$ resonance-enhanced multiphoton ionization of the aligned molecules by a weak laser pulse $(l10\phantom{\rule{0.3em}{0ex}}\mathrm{GW}∕{\mathrm{cm}}^{2})$. We examined the variation of the LF PAD against the intensity of the alignment laser, durations of the alignment and ionization laser pulses, and the time delay between these pulses. The LF PAD obtained from the ionization of the aligned ensemble shows a semiquantitative agreement with the PAD in the molecular frame.

Photoelectron angular distributions in the laboratory frame (LF-PADs) from the A((2)sigma(+)) state of NO molecule were measured by femtosecond time-resolved photoelectron imaging with (1 + 1(')) resonance enhanced multiphoton ionization via the A state. High-precision measurements of the anisotropy parameters of LF-PADs were performed for the photoelectron kinetic energy from 0.03 to 1.05 eV as a function of the pump-probe delay time. The revival feature of the rotational wave packet on the A state was clearly observed in the time dependence of the photoelectron anisotropy parameters. By approximating the phase shifts of the photoelectron partial waves by the quantum defects in the high-lying Rydberg states using the multichannel quantum defect theory, the energy-dependent photoionization transition dipole moments were determined, for the first time, from time-dependent LF-PADs measured by time-resolved photoelectron spectroscopy.

We investigated liquid-sheet jets with controllable thickness for application to terahertz (THz) spectroscopy. Slit-type and colliding-jet nozzles were used to generate optically flat liquid jets. The thickness of the liquid sheet was determined precisely by spectral interference and THz time-domain-spectroscopy methods. By adjusting the collision angle of the colliding-jet nozzle, we could control the thickness of the liquid sheet from 50 to 120 μm.

Rotational wave packet revivals on an excited electronic state have been measured by femtosecond time-resolved photoelectron imaging for the first time. The first full revival at 82 ps of S1 (n,pi*) pyrazine was clearly observed in the time dependencies of the photoelectron intensity and the photoelectron angular distribution (PAD). The PAD, measured for laser aligned pyrazine, clearly reflects the different characters of pi* and 3s molecular orbitals.