Seung Mook Lee

Picosecond pump-probe measurement of bandgap changes in SiO2/TiO2 one-dimensional photonic bandgap structures

A picosecond pump-probe nonlinear optical measurement is performed in SiO2/TiO2 one-dimensional photonic bandgap structures fabricated by a solgel method. Both high and low band edges were examined by varying the probe wavelengths and angle tuning was also employed to further clarify the mechanism of a nonlinear optical response. The third-order nonlinear optical response in one-dimensional photonic bandgap structures that comprise TiO2 films is responsible for the nonlinear optical transmissions at both bandgap edges, with an 8% decrease at the low-energy edge and a 4.5% increase at the high-energy edge for a 355 nm pump intensity of 430 MW/cm2.

Optical parametric spectral broadening of picosecond laser pulses in β-barium borate

We present that optical parametric luminescence generated near the degenerate point of a type I optical parametric tuning curve in β-BaB2O4 can be used as a spectrally broadened probe beam for a picosecond pump-probe spectroscopy. In particular, we show that it is possible to change the position of the central peak and spectral range in visible and infrared wavelengths by varying the incident angle of pump pulse with respect to the optical axis of barium borate crystal. The picosecond time-resolved diffuse-reflectance experiment is also performed in order to demonstrate usefulness of these spectrally broadened pulses as a probe source.