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

Abstract

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 α or β ( α X 2 and β X 2 ), utilizing a pulse train with their time interval of T rev com = βT rev α = αT rev β , where T rev α and T rev β are the rotational revival times of the isotopologues. We demonstrate experimentally that a train of four alignment pulses with their interval of T rev com (α = 14, β = 15) creates transiently aligned 14 N 2 and antialigned 15 N 2 just before T rev com /2 after the last alignment pulse and vice versa just after T rev com /2. Highly isotope-selective N 2 ionization is achieved at these timings with another femtosecond laser pulse, which induces the nonresonant 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 ( 15 N + 2 )/I ( 14 N + 2 ) ranges from 0.49 to 2.00, which is wider than the range obtained with a single alignment pulse [H. Akagi et al., Appl. Phys. B 109, 75 (2012)].

Quantum control of molecular rotation

“…Selective rotational excitation of molecules using a sequence of ultrashort laser pulses has experimentally been explored by [292], leading to the discrimination of isotopologues and of para-and ortho-isomers. Isotope-selective ionization with a specific train of femtosecond laser pulses was proposed by [293].…”

Exciting Molecules Close to the Rotational Quantum Resonance: Anderson Wall and Rotational Bloch Oscillations

“…The results presented in this work have immediate practical implications for numerous current experimental schemes using resonant laser kicking for enhanced molecular alignment, isotope-selective excitation, , and impulsive gas heating for Raman photoacoustics and controlling high-power optical pulse propagation in atmosphere . A particular question arising for several of these experiments is how one may circumvent the Anderson wall.…”

“…If a molecular rotor is kicked by laser pulses at a period that is a rational multiple of the rotational revival time, , its energy grows quadratically with the number of kicks; this is the so-called rotational quantum resonance. This effect is used in multiple current experiments employing resonant laser kicking for enhanced molecular alignment, isotope-selective excitation, , and impulsive gas heating for Raman photoacoustics and controlling high-power optical pulse propagation in atmosphere . The resonant growth of the molecular angular momentum is suppressed by centrifugal distortion, which causes Anderson localization beyond a critical value, J A , of the angular momentum, the Anderson wall.…”

Orientation and Alignment Dynamics of Polar Molecule Driven by Shaped Laser Pulses

“…Molecular alignment based selective approaches like; manipulation of selective components in isotropic mixtures [406] and spin selective alignment in isomers [407], rotational excitations within selective states [408], isotope selective ionization [409] have been proposed in literature. Several scattering processes have been controlled through molecular alignment [410][411][412][413].…”