High peak-intensity short pulse laser has the potential to be applied for ultrafast spectroscopy, nonlinear optical microscopy, and material processing. This special issue introduces the recent progress on shortpulse lasers for high-intensity.

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Compact lasers capable of producing kilowatt class peak power are highly preferable for various applications, including laser remote sensing, laser micromachining, and biomedical photonics. In this paper, we propose a high-peak-power wafer-level diode-pumped solid-state surface-emitting laser in which two cavities are optically coupled at a solid-state laser gain medium. The first cavity is for intra-pumping of ytterbium-doped yttrium-aluminum-garnet (Yb:YAG) with an electrically driven indium gallium arsenide (InGaAs) quantum well, and the second cavity consists of Yb:YAG and chromium-doped yttrium-aluminum- garnet (Cr:YAG) for passive Q-switching. The proposed laser produces pulses as short as 450 ps, and an estimated peak power of 57 kW with a laser chip dimension of only 1 mm 3.

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High-peak-power semiconductor lasers with sub-nanosecond pulse widths are crucial for various applications including eye-safe remote sensing and non-thermal focused ultrafine material processing. In this paper, we describe the recent progress of short-pulse, high-peak-power photonic-crystal surface-emitting lasers (PCSELs). First, we demonstrate PCSELs with 2D arranged saturable absorbers, which enable high-peak-power, short-pulse operation in the fundamental mode while suppressing lasing in higher-order modes. Second, we propose the concept of self-evolving PCSELs, where the lattice constant of the photonic crystal is spatially graded. In the proposed device, the spontaneous transition from a high-loss state to a low-loss state is induced even without saturable absorbers, leading to short-pulse generation with a 100-W-class peak power and 30-ps pulse width. Finally, we propose PCSELs based on simultaneous absorptive and radiative Q-switching, and demonstrate short-pulse generation with an even higher (~200 W) peak power.

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We describe a technology by which amplitude, phase, and polarization of an optical wave comprised of a highly-discrete spectrum are arbitrarily manipulated on a coaxial optical path. We also show generation of arbitrary optical amplitude waveforms in the continuous wave regime by employing such an optical technology. We briefly comment on how an attractive frontier can be opened by applying the arbitrary phase-manipulation technology to nonlinear optical processes.

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This review introduces a novel pulse generation method, the Mamyshev oscillator, which is based on the Mamyshev pulse re-amplification and pulse re-shaping, 2R generator with offset filtering for a high-intensity pulse. The advantage of Mamyshev oscillator is available to generate high pulse energy up to a couple of μJ and ultrashort pulse less than 50 fs. To date, high-intensity Mamyshev oscillators have been reported using large-core size fiber in various wavelengths. In contrast, because of offset filtering in the cavity, an external seed pulse is required to start the pulse generation in Mamyshev oscillator. For widespread use of the Mamyshev oscillator, the development of the self-start method is the issue to be resolved. Here, we introduce our recent study on developing the high-intensity Yb fiber Mamyshev oscillator using double-clad fiber, and the development of the self-start method in Mamyshev oscillator.

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This paper reviews the highly stable frequency-doubled Nd:YAG laser with sub-nanosecond pulse duration for optically synchronized optical parametric chirped-pulse amplification. 1064 nm seed pulses generated by a soliton self-frequency shift in a photonic crystal fiber from Ti:sapphire oscillator pulses were amplified to 200 mJ with a high stability of only less than 0.2% (RMS) by a diode-pumped fibers and Nd:YAG amplifiers. 532 nm pulses with an energy of 130 mJ were obtained with an external LBO doubler. The pulse duration could be extended to 490 ps by optimizing Nd:YAG crystal temperature. We also discuss the importance of suppressing timing jitter between the pump laser and signal laser for stabilizing Optical Parametric Chirped-Pulse Amplification (OPCPA) output, introduce timing jitter suppression methods and their accuracy, and describe the detail of the optically synchronized Nd:YAG pump laser.

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We report on the development of a high-power ytterbium (Yb)-based laser. This laser consists of an Ybfiber laser oscillator, a pulse stretcher based on chirped fiber Bragg grating, an Yb-doped potassium gadolinium tungstate regenerative amplifier, an Yb-doped yttrium aluminum garnet thin-disk regenerative amplifier, and a pulse compressor based on transmission gratings. After the pulse compressor, this laser produces 1030-nm optical pulses with a pulse energy of 20.6 mJ and a temporal duration of 923 fs at a repetition rate of 5 kHz, corresponding to an output power of 102.8 W. This laser source is designed to pump an infrared optical parametric amplifier (OPA) operating near degeneracy (~2060 nm) with an expected conversion efficiency of ~10%. This OPA would be a promising candidate for generating high harmonics in the soft x-ray beyond the water window region (280 ~ 540 eV).

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Monitoring of near-surface dust dispersion and wind flow are important from the perspective of health hazards and air pollution. To observe atmospheric flows near ground on small spatio-temporal scales, we are developing a low-coherence Doppler lidar. First, we evaluated the coherence dependence of light source by scattering light. Next, as a light source for the low coherence Doppler lidar, a bulk device and a pigtailed Distributed Feed Back Laser Diode (DFB-LD) devices were evaluated in terms of optical output and coherence length. Pigtailed DFB-LDs are suitable for low coherence Doppler lidar sources and provide an interference signal 30 dB larger than bulk device of DFB-LDs.

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