We describe advances inlight pulse sources using semiconductor lasers and focus on the recent progress in light pulse generation and applications for multi-photon biomedical imaging. Studies on gain switching under fast and intensive pulsed excitation revealed the potential of the reliable generation of light pulses of a duration of several picoseconds. Combining gain-switched laser diodes (GSLDs) and optical amplifiers, we experimentally produced compact, highly functional light pulse sources and demonstrated that they enabled the world’s deepest in vivo multi-photon imaging of mouse brains. To further extend LD functionality, wealso developed a method for producing smooth-shaped subnanosecond light pulses utilizing a pulsed operation of a semiconductor laser amplifier instead of a GSLD. This light pulse source will be used for very high performance pulsed-mode super-resolution imaging. We also generated sub-picosecond light pulses with high-peak-power exceeding 1 megawatt by removing spontaneous emission noise during light amplification. This technology will enable the adoption of GSLDs for laser micro-processing applications.

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We describe an interesting optical nature of a broadband coherent radiation consisting of a highlydiscrete spectrum. We show that the amplitude and phase distributions among such highly-discrete spectral components can be almost arbitrarily manipulated by simply placing three fundamental optical elements (waveplate, polarizer, and dispersive plate) on an optical axis and then precisely controlling their thicknesses. We also briefly describe the physical mechanism behind such optical property. Furthermore, as a typical application of

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An optical frequency comb (OFC) has attracted attention in optical frequency metrology because the mode-resolved OFC spectrum can be used as a precise frequency ruler due to both broadband spectrum and narrow linewidth characteristics. However, other than optical frequency metrology, the application fields of OFC remain undeveloped. Another interesting aspect of OFC is an optical carrier with a huge number of discrete frequency channels because OFC is composed of a series of frequency spikes that are regularly separated by a repetition frequency in the broad spectral range. In this paper, we encode the line-image of a sample on the mode-resolved OFC spectrum by 1D spectral encoding. The resulting line-image-encoded OFC spectrum is acquired by a dual-comb spectrometer after passing through a confocal pinhole. Finally, the line image is decoded from the mode-resolved amplitude spectrum. The proposed method enables us to establish both confocality and line-field imaging under a scan-less condition.

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Stimulated Raman scattering (SRS) microscopy is a powerful method for the high-speed imaging of biological samples without labeling or staining. This method is based on the sensitive detection of molecular vibrational signatures probed by two-color picosecond pulses. This review introduces the principle and applications of SRS microscopy and explains various methods of SRS spectral imaging for discriminating different constituents.

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We demonstrate a simple method for realizing STAMP (Sequentially Timed All-optical Mapping Photography) in a compact 4f configuration utilizing spectral filtering: STAMP utilizing Spectral Filtering (SF-STAMP). SF-STAMP system consists of a diffractive optical element (DOE), a band-pass filter (BPF), and two Fourier transform lenses. SF-STAMP system works as a single-shot multispectral imaging system. Using a linearly frequency-chirped laser pulse, ultrafast 2D-burst imaging is realized. The number of multispectral images captured by a single shot is determined by the DOE, which is 25 in our current system. We capture ultrafast phenomena with sub-picosecond temporal resolution using a frequency-chirped Ti:sapphire laser pulse.

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The principle of coherent Raman spectroscopy in terahertz (THz) frequency region using frequencychirped optical pulses is explained. The examples of THz Raman spectroscopy for solid state (β -GaSe crystal) and liquid state materials (CCl4, DMSO/water mixture, aqueous solution of ZnBr2) are demonstrated. The advantage of this technique over the conventional one is the simplicity of the system.

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Since the inauguration in 2012, an X-ray Free Electron Laser (XFEL) facility SACLA has produced a number of significant achievements ranging in ultrafast chemistry, materials science, biology, and high energy density physics. A nano-focusing system produces intense XFEL pulses over 1020 W/cm2. The intense XFEL pulses, which are utilized as a pump source, not a conventional prove, have opened up studies of x-ray nonlinear phenomena. In the article, a nano-focusing system and its applications at SACLA are reported.

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The generation of an isolated attosecond pulse (IAP) has been pioneering new breakthroughs in the field of ultrafast science since the first measurement in 2001. Here, we review the recent technological advances in the IAP generation from the view point of ultrabroadband attosecond continua, which support sub-50-as pulse generation. We also introduce our studies for the IAP generation based on a high-intensity Ti:sapphire laser system. In particular, we report the generation of the attosecond supercontinuum spectrum with an extremely broad bandwidth of 70 eV at full width half maximum, which suggests the generation of 32-as pulse, based on the combination of the amplitude gating and the double optical gating schemes using the driving laser field with sub-two-cycle duration. Our approach will be a promising method for generating the shorter IAP that achieves an improved temporal resolution for investigating electron dynamics in unprecedented attosecond timescale.

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Nano-focusing of grating-coupled surface plasmon polariton (SPP) pulses along a tapered gold tip is simulated by a finite-differential time-domain (FDTD) method to optimize the diffraction grating structure fabricated on the tip. We experimentally demonstrate the enhancement of nanofocused ultrafast SPP pulse intensity with optimization in the wave front and the spectral phase of the incident femtosecond laser pulses to the grating structure. We also experimentally achieve ultrafast nonlinear imaging using the nanofocused ultrafast SPP pulse at the tip apex.

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Silicon is used as original material for solar cells and semiconductors. The material naturally exists in the surface of the earth, such as a desert or coast. We proposed an energy cycle using solar-pumped pulse lasers and base metals. Metals are used as an effective energy storage materials. Chemical energy is stored in metals when metal oxides are reduced. In this study, we succeeded in generating electricity for a long time by (metal) air cell using sintered metallurgical-grade Si nanopaste. Si oxide particles were reduced to Si nanoparticles by using high-repetitive laser pulses. The laser pulses should be converted from solar light using solar-pumped laser. Si pastes with the reduced Si nanoparticles were sintered by hot plate or laser. Nanostructure of sintered Si nanopaste (nano-polisycllicstalyne body) was analyzed by SEM, EDX, and XRD. Property for generating electricity using the air cells when connecting LED illuminator or motor were investigated.

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