Establishment of dynamic measurement technique of plasma induced subsurface reaction by using wavelength-tunable femtosecond fiber laser

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We have established the dynamic measurement technique of the plasma induced subsurface reaction by using the near-infrared wavelength tunable femtosecond fiber laser and the cavity ring-down spectroscopy.In order to realize the high sensitive measurements, we investigated the flatly or smoothly supercontinum(SC) pulse generation and the ultrashort-pulse generation of the SC pulse. On the basis of knowledge derived from the analysis, we designed the hybrid fibers which were constructed from plural fibers with different properties to realize the effective spectral broadening. A wideband of 1180-2100nm, flatly broadened, low-noise, and high-coherence SC generation has demonstrated in the three-stages hybrid fiber. Moreover, the optical pulse was effectively compresses through three-stages in the hybrid fiber. The 13-fs ultrashort-pulse generation has been demonstrated.In the cavity ring-down method that used the near-infrared wavelength tunable femtosecond pulse, high sensitivity and a high-speed detection method were indispensable. Therefore, the cavity ring-down method that used the detection method that consisted of an optical homodyne detecting technique, a differential amplification, and a digital filter was constructed. It succeeded in the measurement at the ring-down time by the cavity consisted of two high reflection mirrors that had reflectivity 99.8% or more within the range of wavelength 1200-1850nm, the femtosecond laser, and the high sensitivity detection method. The obtained ring-down time was shorter than the theory value. The cause of this difference is thought to be a divergence of the laser pulse. However, a ring-down time near the theory value can be obtained by the improvement of the coherence of the laser pulse by the optimization of the optical system etc. and the detection system.