Bum Suk Zhao

Ulsan National Institute of Science and Technology | UNIST · Department of Chemistry

Mirrors for atoms and molecules are essential tools for matter-wave optics with neutral particles. Their realization has required either a clean and atomically smooth crystal surface, sophisticated tailored electromagnetic fields, nanofabrication, or particle cooling because of the inherently short de Broglie wavelengths and strong interactions of...

We report on a method of enhanced elastic and coherent reflection of 4He2 and 4He3 from a micro-structured solid surface under grazing incidence conditions. The van der Waals bound ground-state helium clusters exhibit fundamental quantum effects: 4He2, characterized by a single ro-vibrational bound state of 10-7 eV dissociation energy, is known to...

We report on an experimental test of Babinet's principle in quantum reflection of an atom beam from diffraction gratings. The He beam is reflected and diffracted from a square-wave grating at near grazing-incidence conditions. According to Babinet's principle the diffraction peak intensities (except for the specular-reflected beam) are expected to...

We study the effect of rotational state–dependent alignment in the scattering of molecules by optical fields. CS 2 molecules in their lowest few rotational states are adiabatically aligned and transversely accelerated by a nonresonant optical standing wave. The width of the measured transverse velocity distribution increases to 160 m/s with the fie...

Annulative π-extension chemistry provides a concise synthetic route to polycyclic arenes. Herein, we disclose a nondirected annulation approach of unactivated simple arenes. The palladium-catalyzed 2-fold C-H arylation event facilitates tandem C-C linkage relays to furnish fully benzenoid triphenylene frameworks using cyclic diaryliodonium salts. T...

We report on reflection and diffraction of beams of He and D2 from square-wave gratings of a 400−μm period and strip widths ranging from 10 to 200 μm at grazing-incidence conditions. In each case we observe fully resolved matter-wave diffraction patterns including the specular reflection and diffracted beams up to the second diffraction order. With...

Molecular beams of He and D₂ are scattered from a ruled diffraction grating in conical-mount geometry under grazing-incidence conditions. Fully resolved diffraction patterns as a function of detection angle are recorded for different grating azimuth angles and for two different kinetic energies of the particle beams. Variations in diffraction peak...

We enhance the optical dipole force acting on molecules by decreasing the molecules' rotational temperature and aligning the molecular axis with a linearly polarized nonresonant laser beam. The rotational temperature is decreased by increasing a source pressure from 2 to 81 bar. Using the effective polarizability directly pertaining to the optical...

The properties of molecule-optical elements such as lenses or prisms based on the interaction of molecules with optical fields depend in a crucial way on the molecular quantum state and its alignment created by the optical field. However, in previous experimental studies, the effects of state-dependent alignment have never been included in estimate...

Since de Broglie's work on the wave nature of particles, various optical phenomena have been observed with matter waves of atoms and molecules. However, the analogy between classical and atom/molecule optics is not exact because of different dispersion relations. In addition, according to de Broglie's formula, different combinations of particle mas...

We report on the rotational-state-dependent, transverse acceleration of CS_{2} molecules affected by pulsed optical standing waves. The steep gradient of the standing wave potential imparts far stronger dipole forces on the molecules than propagating pulses do. Moreover, large changes in the transverse velocities (i.e., up to 80 m/s) obtained with...

When a molecule is placed in a nonresonant laser field, the Stark interactions between the laser field and the induced molecular dipole result in a mechanical force on the molecule. This nonresonant dipole force is proportional to the intensity gradient of the laser, thus requiring a strong and focused pulsed laser for a sizable impact on the molec...

We report on the non-destructive scattering and diffraction of He, He2 and He3 from a plane ruled reflection grating. At grazing incidence the normal component of the particle’s wave-vector is sufficiently small to allow for quantum reflection at the attractive Casimir–van der Waals particle–surface interaction potential. Quantum reflection occurs...

The quantum interference of large molecules can be recorded in real time thanks to state-of-the-art nanofabrication and nano-imaging technologies.

We report on emerging beam resonances appearing in diffraction patterns of a helium atom beam reflected at grazing incidence from a grating. The plane ruled grating is mounted in an out-of-plane diffraction configuration. We present the measured angular diffraction patterns as a function of the atom's energy change along the grating normal. This pr...

Das Heliumdimer He2 ist das im Grundzustand am schwächsten gebundene, bekannte Molekül. Dass es ohne zu zerbrechen von einer Wand zurückprallt, widerspricht den Gesetzen der klassischen Physik. Ein Experiment am Fritz-Haber-Institut der Max-Planck-Gesellschaft hat nun gezeigt, dass Heliumdimere durchaus zerstörungsfrei zurückgestreut werden können....

Quantum reflection allows an atom or molecule to be reflected from a solid before it reaches the region where it would encounter the repulsive potential of the surface. We observed nondestructive scattering of the helium dimer (He(2)), which has a binding energy of 10(-7) electron volt, from a solid reflection grating. We scattered a beam containin...

We report coherent reflection of thermal He atom beams from various microscopically rough surfaces at grazing incidence. For a sufficiently small normal component k(z) of the incident wave vector of the atom the reflection probability is found to be a function of k(z) only. This behavior is explained by quantum reflection at the attractive branch o...

We report on the observation of emerging beam resonances, well known as Rayleigh-Wood anomalies and threshold resonances in photon and electron diffraction, respectively, in an atom-optical diffraction experiment. Diffraction of He atom beams reflected from a blazed ruled grating at grazing incidence has been investigated. The total reflectivity of...

We demonstrate one-dimensional (1D) focusing of a thermal helium atom beam by quantum reflection from a cylindrical concave quartz mirror at near-grazing incidence. The smallest width of the focus achieved is 1.8 μm, essentially limited by spherical aberration. The various effects that contribute to the finite focal width have been investigated. We...

The Institute of Physics (IOP) is a leading scientific society promoting physics and bringing physicists together for the benefit of all. It has a worldwide membership of around 40 000 comprising physicists from all sectors, as well as those with an interest in physics. It works to advance physics research, application and education; and engages wi...

A simple method to control molecular translation with a chemical reaction is demonstrated. Slow NO molecules have been produced by partially canceling the molecular beam velocity of NO$_2$ with the recoil velocity of the NO photofragment. The NO$_2$ molecules were photodissociated using a UV laser pulse polarized parallel to the molecular beam. The...

We observe high-resolution diffraction patterns of a thermal-energy helium-atom beam reflected from a microstructured surface grating at grazing incidence. The grating consists of 10-$\mu$m-wide Cr strips patterned on a quartz substrate and has a periodicity of 20 $\mu$m. Fully-resolved diffraction peaks up to the $7^{\rm th}$ order are observed at...

A photon as a particle has an energy and a momentum. In a matter-photon interaction, the matter and photons may exchange their momenta observing the momentum conservation law. The consequence of the momentum transfer from a photon to a matter particle is a mechanical force exerted on the particle. Several separation methods based on this force of l...

We produce a cool pulsed supersonic molecular beam of CaF radicals essentially without recourse to pumping. The radicals are generated by laser ablating a solid precursor target in a small ablation cell of volume of about 0.01  cm ³. The target is ablated through a 750 μm orifice by a pulsed Nd:YAG laser. The ablation plume supersonicall...

In molecule optics, a matter wave of molecules is manipulated by a molecule-optical component made out of external, typically radiative, fields. The molecule-optical index of refraction, n, for a nonresonant IR laser pulse focused onto a molecular beam can be obtained from the energy conservation and wave properties of molecules. Experimentally mea...

A molecular lens of the nonresonant dipole force formed by focusing a nanosecond IR laser pulse has been applied to benzene and CS2 molecular beams. Using the velocity map imaging technique for molecular ray tracing, characteristic molecular lens parameters including the focal length (f ), minimum beam width (W), and distance to the minimum beam wi...

A cylindrical molecular lens is formed by focusing a nanosecond IR laser pulse. Trajectories of a CS2 molecular beam deflected by the lens are traced using the velocity map imaging technique. The characteristic lens parameters including the focal length, minimum beam width, and distance to the minimum-width position are determined. The laser intens...

Summary form only given. We demonstrate the experimental tracing of a molecular beam passing through a cylindrical lens made of a non-resonant laser pulse. The beam of CS2 molecules was deflected by a focused laser pulse (1064 nm, 7 ns, peak intensity I0∼1012 W/cm2). We probed the deflection of molecular beam directly by using the velocity map imag...

We have identified quantum reflection as a mech-anism of coherent reflection from microscopically rough surfaces like, e.g., glass [1]. In quantum re-flection a wave packet is reflected at the attractive branch of the atom-surface potential. In contrast to classical mechanics there is no classical turning point resulting from a repulsive potential...