Azo-polymer film twisted to form a helical surface relief by illumination with a circularly polarized Gaussian beam.

A helical surface relief can be created in an azo-polymer film simply by illuminating circularly polarized light with spin angular momentum and without any orbital angular momentum. The helicity of the surface relief is determined by the sign of the spin angular momentum. The illumination of circularly polarized light induces orbital motion of the azo-polymer to shape the helical surface relief as an intermediate form; a subsequent transformation to a non-helical bump-shaped relief with a central peak creates a final form with additional exposure time. The mechanism for the formation of such a helical surface relief was also theoretically analyzed using the formula for the optical radiation force in a homogeneous and isotropic material.

Degenerate Fermi gases of ytterbium.

Evaporative cooling was performed to cool fermionic 173Yb atoms in a crossed optical dipole trap. The large elastic collision rate leads to efficient evaporation and we have successfully cooled the atoms to 0.37+/-0.06 of the Fermi temperature, that is to say, to a quantum degenerate regime. In this regime, a plunge of evaporation efficiency was observed as a result of Fermi degeneracy.

High-resolution photoassociation spectroscopy of ultracold ytterbium atoms by using the intercombination transition.

We observed high-resolution photoassociation spectra of laser-cooled ytterbium (Yb) atoms in the spin-forbidden 1S0 - 3P1 intercombination line. The rovibrational levels in the 0u+ state were measured for red detunings of the photoassociation laser ranging from 2.9 MHz to 1.97 GHz with respect to the atomic resonance. The rotational splitting of the vibrational levels near the dissociation limit were fully resolved due to the sub-MHz linewidth of the spectra in contrast to previous measurements using the spin-allowed singlet transition. In addition, from a comparison between the spectra of 174Yb and those of 176Yb, a d-wave shape resonance for 174Yb is strongly suggested.

Spin-singlet Bose-Einstein condensation of two-electron atoms.

We report the observation of a Bose-Einstein condensation of ytterbium atoms by evaporative cooling in a novel crossed optical trap. Unlike the previously observed condensates, a ytterbium condensate is a two-electron system in a singlet state and has distinct features such as the extremely narrow intercombination transitions which are ideal for future optical frequency standard and the insensitivity to external magnetic field which is important for precision coherent atom optics, and the existence of the novel metastable triplet states generated by optical excitation from the singlet state.