극초단파 심자외선 빔라인 개발 및 광전자 홀로그래피에의 응용

DoctorMotion in the microcosm is extremely rapid. For instance, a chemical reaction can be completed in a few femtoseconds. Due to the extremely short time scale at which chemical reactions occur, only the initial and final products are known; the reaction pathways and intermediate products, on the other hand, remain unknown. To observe these ultrafast processes on their time scales, science requires measurement technology that is faster than the processes to be observed. Development of ultrashort pulsed laser technology enabled the detection of these processes in real time. For example, the so-called ”pump-probe” spectroscopy technique enables the tracking of ultrafast dynamics in atoms and molecules following the excitation with a short laser pulse called the pump pulse. A delayed second pulse, also known as the probe pulse, probes the current state of the evolving system. In this manner, by varying the time interval between the pump-probe pulses with multiple repetitions, a dynamical evolution of the system can be obtained. The available shortest pulse duration, however, was limited to capturing only nuclear dynamics with this technique. A new regime in ultrafast optical science called attosecond physics emerged at the turn of the 21st century. In the extreme ultraviolet regime, the high-order harmonic generation method has enabled previously unattainable ultrashort pulse durations of a few hundred attoseconds. Attosecond pulses enable us to probe dynamics beyond the Born-Oppenheimer approximation, in which electronic states are not stationary and influential. We need to investigate how nonstationary electronic states are coupled to nuclear motion and then understand how manipulating the electronic motion can be used to trigger the nuclei to move selectively, thereby implementing a chemical reaction pathway. To aid in our knowledge and control of ultrafast dynamics in a new paradigm, an intense few-cycle deep-ultraviolet beamline was built in conjunction with ultrashort near-infrared and extreme ultraviolet pulses enabling time-resolved studies using various combinations of these light sources

Attosecond Chemical Physics Beamline at POSTECH

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Generation of high-contrast, intense single-cycle pulses using a two-stage thin-solid-plate setup

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High-contrast, intense single-cycle pulses from an all thin-solid-plate setup

High-contrast, intense single-cycle pulses are highly desirable tools in ultrafast science, enabling highest temporal resolution, pushing matter to extreme conditions, and serving as drivers in petahertz electronics. In this Letter, we use thin solid plates in a double multi-plate supercontinuum configuration, delivering a broadband spectrum spanning from similar to 400 to similar to 4.000 nm at the -20 dB intensity level to produce a single-cycle pulse. We show that the spectral broadening by self-phase modulation with few-cycle pulses is more suitable for compression than the single-cycle limit than with multi-cycle pulses. The pulses are compressed to 2.6 fs pulses, close to the transform limit of 2.55 fs, with an energy of 0.235 mJ. They exhibit an excellent power stability of 0.5% rms over 3 h and a beam profile. The obtained single-cycle pulses can be utilized in many applications, such as generation of isolated attosecond pulses via high-order harmonic generation, investigation of ultrafast phenomena with extreme temporal resolution, or high-intensity laser-solid experiments. (C) 2020 Optical Society of America11Nsciescopu

Few-Cycle, μJ-Class, Deep-UV Source from Gas Media

Energetic, few-fs pulses in the deep-UV region are highly desirable for exploring ultrafast processes on their natural time scales, especially in molecules. The deep-UV source can be generated from gas media irradiated with few-cycle near-infrared laser pulses via a third-order frequency conversion process, which is a perturbative mechanism in a relatively weak field regime. In this work, we demonstrate that the deep-UV generation process is significantly affected by also even higher nonlinear processes, such as the ionization depletion of gas and plasma-induced spatiotemporal distortion of propagating light. In the experiment, by optimizing the deep-UV (3.6–5.7 eV) generation efficiency, the highest deep-UV energy of 1 μJ was observed from a moderately ionized 0.8-bar Ar gas target. The observed UV spectra exhibited frequency shifts depending on the experimental conditions—gas type, gas pressure, and the gas cell location—supporting the importance of the highly nonlinear mechanisms. The experimental observations were well corroborated by numerical simulations