Isotope-selective ionization utilizing field-free alignment of isotopologues with a train of femtosecond laser pulses

Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*

Physical Review A, 91(6), p.063416_1 - 063416_7, 2015/06

https://doi.org/10.1103/PhysRevA.91.063416

We propose a strategy of isotope-selective ionization for a binary mixture of isotopologues of homonuclear diatomic molecules, utilizing field-free alignment with a train of femtosecond laser pulses. Field-free alignment can be achieved simultaneously for two isotopologues consisting of two atoms with the same atomic mass number or , utilizing a pulse train with their time interval of T = T() = T(), where T() and T() are the rotational revival times of the isotopologues. We demonstrate experimentally that a train of four alignment pulses with their interval of T ( = 14, = 15) creates transiently aligned N and anti-aligned N just before T/2 after the last pulse, and vice versa just after T/2. Highly isotope-selective N ionization is achieved at these timings with another femtosecond laser pulse, which induces the non-resonant multiphoton ionization with the cross section remarkably depending on the angle between the molecular axis and the laser electric field direction. The ion yield ratio I(N)/I(N) ranges from 0.49 to 2.00, which is wider than the range obtained with single alignment pulse.

Numerical study on quantum walks implemented on the cascade rotational transitions in a diatomic molecule

Matsuoka, Leo; Kasajima, Tatsuya; Hashimoto, Masashi; Yokoyama, Keiichi

Journal of the Korean Physical Society, 59(4), p.2897 - 2900, 2011/10

https://doi.org/10.3938/jkps.59.2897

Vibration-selective coherent anti-Stokes Raman scattering with linearly chirped white-light pulses

Kasajima, Tatsuya; Yokoyama, Keiichi; Matsuoka, Leo; Yokoyama, Atsushi

Chemical Physics Letters, 485(1-3), p.45 - 48, 2010/01

https://doi.org/10.1016/j.cplett.2009.12.032

Isotope selective ionization of N isotopologues utilizing rotational coherence and angular dependent ionization

Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*

no journal, , 

In the present work, the isotope separation utilizing the rotational coherence is demonstrated experimentally for the first time, by the isotopically selective ionization of N isotopomers via the non-resonant multiphoton ionization process. A gas mixture of 14-N and 15-N was irradiated with a pair of linearly-polarized short laser pulses. The present experiment indicated that the ion yield ratioI(15N)/I(14N) can be changed in the range from 0.85 to 1.22, depending on the time delay between the two pulses.

Theoretical study on the cascade excitation based on pure rotational transition in diatomic molecules

Yokoyama, Keiichi; Matsuoka, Leo; Akagi, Hiroshi; Kasajima, Tatsuya; Tsubouchi, Masaaki

no journal, , 

Pure rotational transition shows evenly spaced line spectra, the rotational comb, when the molecule is diatomic and has a closed-shell electronic structure. Let us consider irradiating an optical frequency comb tuned to the rotational comb. We studied numerically the dynamics of the molecular rotation in such a irradiation. As a result, the dynamics was found to obey the diffusion equation within the quantum mechanics. Also, we found that an isotope-selective excitation based on this scheme is a novel example of coherent control effective even at high temperature.

A New scheme for the laser isotope separation applicable to heavy elements

Yokoyama, Keiichi; Matsuoka, Leo; Kasajima, Tatsuya; Tsubouchi, Masaaki; Hashimoto, Masashi

no journal, , 

Recent progress in laser science enables us precise manipulation of molecules by taking advantages of the wave nature of matter. These techniques are called coherent quantum control. Using coherent quantum control, a breakthrough in laser isotope separation may be realized. Actually, we proposed a novel scheme of isotope selective excitation, which is based on cascaded excitation of rotation in diatomic molecules. A numerical simulation done by solving a coupled Schroedinger equation for the cesium iodide molecule has shown that the separation factor reaches three orders of magnitude higher than that by the conventional scheme. The current status of the experimental demonstration undergoing in our institute will be introduced.

Isotope selection using intense laser induced molecular alignment and angle-dependent ionization

Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*

no journal, , 

We demonstrate the isotope selection with molecular alignment and angle-dependent ionization in intense laser fields. The 14-N2 and 15-N2 mixed gas is irradiated with a linearly polarized femtosecond laser pulse for creation of rotational wavepackets. After a certain delay when one of two isotopologues is aligned along the laser polarization direction, another linearly polarized femtosecond laser pulse is shined for ionization. It is confirmed that the ionization yield ratio between the two isotopologues can be changed as a function of the delay between the two laser pulses.

Improvement in selectivity of isotope-selective ionization utilizing molecular alignment and angular dependent ionization

Akagi, Hiroshi; Kasajima, Tatsuya*; Kumada, Takayuki; Itakura, Ryuji; Yokoyama, Atsushi; Hasegawa, Hirokazu*; Oshima, Yasuhiro*

no journal, , 

We are demostrating isotope-selective ionization of N and N isotopologues, utilizing molecular alignment and angular dependent ionization. In the present work, we used a train of four identical pulses with 125.7-ps interval to creating rotational wave packets in these isotopologues. We optimized the following experimental conditions to improve the isotope selectivity: mixing ratio of the gas sample, timing of pulse valve to introduce the gas sample into a vacuum chamber, laser beam diameters for the alignment and ionization pulses, and these peak intensities. As the results, we obtained the minimum of the ion yield ratio N/N (= 0.49) and the maximum (= 2.00).

Impulsive stimulated Raman transition of I in the B (0) state

Matsuoka, Leo; Yokoyama, Keiichi; Kasajima, Tatsuya; Yokoyama, Atsushi

no journal, , 

no abstracts in English

Numerical simulation on highly efficient isotope separation using terahertz wave

Yokoyama, Keiichi; Hashimoto, Masashi; Matsuoka, Leo; Kasajima, Tatsuya

no journal, , 

Enhancement of isotope separation by a phase-locked pulse train of terahertz wave is numerically demonstrated by solving close-coupling time-dependent Schroedinger equations. The terahertz wave is transform-limited and has the center frequency of 0.5 THz with the bandwidth of 0.55 THz FWHM. Individual pulse energy is 1.56 J. Irradiation of 16 such pulses to lithium chloride vapor is simulated at 70 K. At the pulse interval of 24.04 ps, the rotational state distribution of LiCl is largely displaced, while that of LiCl is not. Assuming multi-photon decomposition as a subsequent process, the enrichment factor is calculated and found to be enhanced by three orders of magnitude, while decomposition probability of the target isotope is kept up 0.3.