In order meet strong demands to realize "sustainable society", we have to develop power generation, energy efficient and energy storage green devices such as fuel cells, less power consumption non-volatile memories, and Li(Na) ion batteries. Synchrotron radiation, especially soft X-ray is a very powerful tool to analyze electronic structure of these devices with high spatial resolution and high energy resolution even under operation condition. In this seminar, I will show our latest results on operando soft X-ray emission spectroscopy of non-Pt cathode catalysts for PEFC and 70 nm photoelectron microscopy of Ni nanowire ReRAM, graphene FET, and  Li ion battery at the SPring-8 University-of-Tokyo beamline.

The Ultrafast Optics and X-Rays Division at DESY CFEL is currently pursuing two different technological approaches to generate intense sub-cycle waveforms. In this lecture, I will discuss the experimental schemes, the technological challenges and our experimental results on high-energy sub-cycle optical waveform synthesis based on (i) parametric amplification and (ii) induced-phase modulation in a gas-filled hollow-core fiber compressor.

First, a CEP-stable 3-channel multi-mJ sub-cycle parametric waveform synthesizer driven by a non-CEP-stable cryogenically cooled Ti:sapphire amplifier is discussed (see left photo above). In this system, a passively CEP-stable white-light seed continuum (0.5-2.5 µm) is split and amplified in three parallel parametric amplification channels (VIS NOPA, NIR DOPA, IR DOPA) up to the multi-mJ level. The amplified spectra support 1.9-fs FWHM waveforms. Preliminary FROG pulse-characterization results demonstrate the feasibility to recompress all three channels simultaneously close to the Fourier limit. Finally, the relative timing of the pulses can be locked with sub-cycle precision using balanced optical cross-correlators. Second, waveform synthesis relying on self-phase modulation (SPM) in hollow-core fiber (HCF) compressors represents a rather mature technology and has recently permitted the generation of sub-cycle pulses (covering 260-1100 nm). However, the energy throughput is typically limited to several tens or hundreds of µJ (depending on bandwidth) due to gas ionization. A potential solution out of this energy-scaling dilemma is the application of induced-phase modulation (IPM) based on the interaction between two (or more) copropagating optical pulses of different colors. I will discuss the advantages of our IPM synthesizer over SPM with respect to control over the spectral shape and bandwidth, as well as relieving the energy-scaling bottleneck in the UV region.

We foresee that our waveform synthesizers will become versatile tools for controlling strong-field interactions in matter, for attosecond pump-probe spectroscopy employing ultrashort pulses in the VIS/IR and XUV/soft-X-ray regions, and for the realization of bright coherent tabletop high-harmonic sources in the water-window region.

Research subjects:

Growth and characterization of nitride semiconductors by pulsed laser deposition (PLD)

Growth of magnetic oxide films by PLD and fabrication of tunneling magnetic resistance devices and resistance switching devices

in situ SR photoemission analysis of PLD-grown oxide thin films

SR analysis of carbon-related cathode catalysts for polymer electrolyte fuel cells

Development of 3-dimensional nano ESCA system with 70 nm spatial resolution and sub-100 meV energy resolution at the Univ-of-Tokyo outstation at SPring-8

SR analysis of novel cathode materials for Li ion battery