Element Selectivity in Second-Harmonic Generation of GaFeO3 by a Soft-X-Ray Free-Electron Laser

Abstract

Nonlinear optical frequency conversion has been challenged to move down to the extreme ultraviolet and x-ray region. However, the extremely low signals have allowed researchers to only perform transmission experiments of the gas phase or ultrathin films. Here, we report second harmonic generation (SHG) of the reflected beam of a soft x-ray free-electron laser from a solid, which is enhanced by the resonant effect. The observation revealed that the double resonance condition can be met by absorption edges for transition metal oxides in the soft x-ray range, and this suggests that the resonant SHG technique can be applicable to a wide range of materials. We discuss the possibility of element-selective SHG spectroscopy measurements in the soft x-ray range.

Ionothermal Synthesis of Metal Chalcogenides M2Ag3Sb3S7 (M = Rb, Cs) Displaying Nonlinear Optical Activity in the Infrared Region

“…In the last two decades, mid-far infrared (>2 μm, MFIR) nonlinear optical (NLO) materials have become increasingly important as coherent and tunable sources for both scientific research and technological applications, such as long-distance laser communication, molecular spectroscopy, and laser surgery therapy. [1][2][3][4][5][6][7][8] However, well-known UV and visible-region NLO materials such as metal borates, [9][10][11][12][13][14] metal phosphates, [15][16] and metal oxides [17][18] are restricted from use in the MFIR region because their metal−oxygen absorption bands (and their overtones) lower the efficiencies and optical transparencies. 19 Metal chalcogenides, on the other hand, have proven to be one of the best candidates for NLO materials in the MFIR regions, and so extensive efforts have been invested to discover new metal chalcogenides with useful MFIR NLO properties.…”

Ultrathin regime growth of atomically flat multiferroic gallium ferrite films with perpendicular magnetic anisotropy

“…This contact-free technique is frequently used to probe the breaking of inversion symmetry related to the onset of ferroic order such as spontaneous polarization in bulk crystals and thin films [25]. While the multiferroic properties of bulk GFO have been extensively studied by this technique [36][37][38][39][40][41], reports on SHG probing of the polar properties of GFO thin films are limited [20,42]. The allowed SHG components related to the polarization in GFO are set by its orthorhombic mm2 point group with five independent elements.…”

Electronic multipoles in second harmonic generation and neutron scattering

“…The recent advent of free-electron lasers (FELs) in the energy ranges from extreme ultraviolet to x rays allows us to explore these effects involving core-level resonances [25]. Yamamoto et al [26] measured SHG at the Fe 3p edge of gallium ferrate (GaFeO 3 ) using soft x-ray FEL radiation. Other nonlinear optical techniques observed in the extreme-ultraviolet and x-ray region include sum-frequency generation [27], four-wave mixing [28], and x-ray two-photon absorption [29].…”