Motoi Ueda

Quartz revisits nonlinear optics: twinned crystal for quasi-phase matching [Invited]

The pioneering material utilized in first optical mixing revisits nonlinear optics with the cutting-edge polarity-control technology stress-induced twinning. Periodically twinned quartz with modulated polarity demonstrates quasi-phase-matched SHG emitting vacuum UV light at 193 nm.

Low phonon energies and wideband optical windows of La 2 O 3 -Ga 2 O 3 glasses prepared using an aerodynamic levitation technique

xLa2O3-(100 − x)Ga2O3 binary glasses were synthesized by an aerodynamic levitation technique. The glass-forming region was found to be 20 ≤ x ≤ 57. The refractive indices were greater than 1.92 and increased linearly with increasing x. The polarizabilities of oxide ions were estimated to be 2.16–2.41 Å3, indicating that the glasses were highly ionic. The glasses were transparent over a very wide range from the ultraviolet to the mid-infrared region. The widest transparent window among the oxide glasses was from 270 nm to 10 μm at x = 55. From the Raman scattering spectra, a decrease in bridging oxide ions and an increase in non-bridging oxide ions were confirmed to occur with increasing La2O3 content. The maximum phonon energy was found to be approximately 650 cm−1, being one of the lowest among oxide glasses. These results show that La2O3-Ga2O3 binary glasses should be promising host materials for optical applications such as lenses, windows, and filters over a very wide wavelength range.

Studies of High Index Immersion Lithography

High index immersion lithography is one of the candidates for next generation lithography technology following water immersion lithography. This technology may be most attractive for the industry since it is effective in raising resolution without seriously changing the chip making processes. This motivates us to continue to study further NA expansion although there are many challenges with respect to either high index fluid development or high index lens material development. In this paper, the current status of high index lithography development compared with the industrys requirements is discussed while considering design feasibility.

Vacuum ultraviolet light generation at 193 nm by quasi-phase-matched quartz

Coherent all-solid-state light source of a wavelength below 200nm is attracting a lot of attention for industrial applications such as semiconductor processing, eye surgery, and micro machining. Multi-stage wavelength conversion from a high power infrared solid-state laser is a promising solution. We have developed a technology for quasi-phasematching (QPM) in crystalline quartz that utilizes stress-induced twinning. In the present paper, we report a novel stressmaintaining module that suppresses back-switching of twinning and enables QPM-SHG in the vacuum ultraviolet (VUV) region. We demonstrated the fabrication of finest periodic twins with a period of 9.6 μm and performed QPM-SHG experiment. Vacuum ultraviolet 193.4 nm light of 17 mW was generated from 177 mW fundamental light. To the best of our knowledge, this is the shortest emission wavelength ever obtained with QPM technology.

VUV 193 nm emission from micro-twinned crystal quartz

VUV light at 193 nm was generated by second harmonic generation in quasi-phase-matched crystal quartz. Specially developed mechanical module stabilized a micron-scale twin structure realizing stable QPM wavelength converter to 193 nm.

Polarization dependence of SHG efficiency in periodically-twinned QPM quartz

We examined second harmonic generation efficiency depending on input polarization state of the fundamental wave in crystal-quartz wavelength converter. We found the optimum polarization state for efficient SHG at 532 nm.