An enhanced technique of heterodyne detection for transient grating experiments has been developed. This technique features a very simple optical alignment because no lenses are used to focus beams on the samples. It was applied to a vapor-deposited gold thin film (thickness: 30 nm), and the detected signal was confirmed to consist of a heterodyne component based on the dependence of the signal intensity on the pump intensity. Furthermore, this technique was shown to provide easy control of the phase difference between the probe and reference beams.

Photocatalytic water splitting system using particulate semiconductor materials is a promising strategy for converting solar energy into hydrogen and oxygen. In particular, visible-light-driven ‘Z-scheme’ printable photocatalyst sheets are cost-effective and scalable. However, little is known about the fundamental photophysical processes, which are key to explaining and promoting the photoactivity. Here, we applied the pattern-illumination time-resolved phase microscopy for a photocatalyst sheet composed of Mo-doped BiVO₄ and Rh-doped SrTiO₃ with indium tin oxide as the electron mediator to investigate photo-generated charge carrier dynamics. Using this method, we successfully observed the position- and structure-dependent charge carrier behavior and visualized the active/inactive sites in the sheets under the light irradiation via the time sequence images and the clustering analysis. This combination methodology could provide the material/synthesis optimization methods for the maximum performance of the photocatalyst sheets.

Ultrafast transient reflecting grating (TRG) spectroscopy was applied to investigate the influence of various defect states on ultrafast carrier dynamics of up to 3 ps duration in an ion-implanted silicon surface region. The TRG spectra revealed the energy-state distribution of two kinds of defect states, and it was observed that photoexcited carriers were trapped in each state depending on annealing time. It was proposed that TRG spectroscopy can be used as an analytical method for characterizing defects in the surface region of semicondcutors.

Lead halide perovskites are attracting a great deal of interest for optoelectronic applications such as solar cells, LEDs, and lasers because of their unique properties. In solar cells, heat dissipation by hot carriers results in a major energy loss channel responsible for the Shockley–Queisser efficiency limit. Hot carrier solar cells offer the possibility to overcome this limit and achieve energy conversion efficiency as high as 66% by extracting hot carriers. Therefore, fundamental studies on hot carrier relaxation dynamics in lead halide perovskites are important. Here, we elucidated the hot carrier cooling dynamics in all-inorganic cesium lead iodide (CsPbI₃) perovskite using transient absorption spectroscopy. We observe that the hot carrier cooling rate in CsPbI₃ decreases as the fluence of the pump light increases and the cooling is as slow as a few 10 ps when the photoexcited carrier density is 7 × 10¹⁸ cm⁻³, which is attributed to phonon bottleneck for high photoexcited carrier densities. Our findings suggest that CsPbI₃ has a potential for hot carrier solar cell applications.