Kiyoshi Kumata

Determination of quadratic nonlinear optical coefficient of AlxGa1−xAs system by the method of reflected second harmonics

The quadratic nonlinear optical coefficient in the AlGaAs system has been systematically measured as a function of the alloy composition at the fundamental wavelength of 1.064 μm by the method of reflected harmonics. The harmonic waves from the thin‐film samples are analyzed considering various interferences including multiple reflections. The experimental results show a reduction of the magnitude of the second‐harmonic coefficient with increasing Al content in the AlGaAs system. This tendency is consistent with Miller’s rule.

Optical third-harmonic generation in layered perovskite-type material (C10H21NH3)2PbI4

Abstract Optical third-harmonic generation has been investigated over a wide range of wavelengths on a layered perovskite-type material (C10H21NH3)2PbI4, which exhibits prominent two-dimensional exciton effects due to the “natural superlattice” structure. The measured nonlinear optical susceptibility χ(3)(−3ω, ω, ω, ω) shows large three-photon resonance to the lowest-energy exciton for the fundamental wavelength at 1.53 μm. The magnitude of χ(3) reaches 10−9 esu, which is comparable to the largest reported value on organic materials with one-dimensional conjugated π-electron structures.

Anomalous electro-absorption in the low-temperature phase of (C10H21NH3)2PbI4

Abstract Electro-absorption (EA) spectra have been measured on thin films of (C 10 H 21 NH 3 ) 2 PbI 4 , a layered perovskite-type material, over the lowest-energy exciton region at 300 K [room-temperature (RT) phase] and 77 K [low-temperature (LT) phase]. An anomalous EA signal has been observed for the LT phase, while the RT-phase EA signal exhibits a behavior characteristic of a normal exciton. The LT-phase EA signal with an anomalous line shape and phase may be related to a domain-like structure of unknown origin.

Magneto-optical effects of excitons in (C10H21NH3)2PbI4 under high magnetic fields up to 40 T

Abstract Magneto-absorption spectra have been measured over the lowest-energy exciton region of (C10H21NH3)2PbI4, a layered perovskite-type material, under high magnetic fields up to 40 T at 4.2 K. The magnetic field is applied perpendicular and parallel to the layer planes. An obvious splitting and a shift of the exciton lines are observed in the perpendicular-field configuration, whereas no change is detected up to 40 T in the parallel-field configuration. This characteristic phenomenon probably occurs as the result of strong two-dimensional confinement caused by the existence, in this material, of large steps of the band gap and the dielectric constant in combination with a very thin potential-well layer.

New method for determining the nonlinear optical coefficients of thin films

A new scheme for characterizing the quadratic optical nonlinearity of thin films grown on opaque substrates is proposed and demonstrated. This involved the measurement, as a function of the film thickness, of second‐harmonic waves reflected from a film surface. The d36 coefficient of a ZnSe‐on‐GaAs film is estimated by this method to be 33±7 pm/V at the fundamental wavelength of 1.06 μm, which agrees reasonably well with the known value for the bulk crystal.

Nonlinear Optical Coefficient of AlAs Thin Film on GaAs Substrate

We report the first measurement of the nonlinear optical coefficient, d14, at the fundamental wavelength of 1.06 µm, of AlAs grown by molecular beam epitaxy. The d coefficient is deduced from the intensities of second-harmonic waves reflected from an AlAs film grown on GaAs. Multiple reflections in the film and second-harmonic generation in the substrate are taken into account. The ratio |d14(AlAs)/d14(GaAs)| is found to be 0.23±0.06.