Forming a gaseous crystal with three-fold symmetry
Recently, we proposed how to prepare a molecular ensemble with macroscopic three-fold symmetry, which can be regarded as a gaseous crystal with three-fold symmetry . By utilizing the special laser electric field trajectory with three-fold symmetry, which can be formed by superposing a counter-rotating circularly-polarized fundamental pulse and its second harmonic pulse, sample molecules with three-fold symmetry such as BX3 (X=F, Cl, Br, I) can be aligned with their three arms along (or in between) the laser electric fields with three-fold symmetry depending on the sign of the hyperpolarizability of the sample molecule. We are aiming at the first demonstration of the formation of a gaseous crystal with three-fold symmetry. The preparation of a molecular ensemble with macroscopic three-fold symmetry could be confirmed by observing the angular distributions of the fragment ions produced with circularly polarized femtosecond probe pulses. To observe those fragment ions produced in the circular polarization plane of the two-color pump pulse, they are to be first extracted by utilizing the ion optics technique and then to be projected onto the two-dimensional ion detector . The ion images on the detector plane are recorded by a CCD camera. We have already modified our experimental apparatus.
 H. Nakabayashi, W. Komatsubara, and Hirofumi Sakai, “Recipe for preparing a molecular ensemble with macroscopic three-fold symmetry,” Phys. Rev. A 99, 043420 (2019).
 K. Mizuse, K. Kitano, H. Hasegawa, and Y. Ohshima, Sci. Adv. 1, e1400185 (2015).