Katsuya Wakita

Intracavity Second-Harmonic Generation and Influence of Optical Loss of Organic Nonlinear Optical Materials

We propose two different methods to estimate the optical loss of organic nonlinear optical (NLO) materials, which significantly reduces the efficiency of intracavity second-harmonic generation. One method is the estimation of the optical loss from the intracavity optical power at 1064 nm. The optical loss of the 4-nitrophenol sodium (:Na) salt dihydrate (NPNa) crystal was 1.3 dB/cm, and that of the DNPNa crystal, in which the water of crystallization of NPNa was deuterated, was 0.15 dB/cm. Another method is the estimation of the optical absorption loss from a liquid, the molecular structure of which has the same particular structural groups as those of the organic NLO materials. This latter method is very useful when new organic NLO materials are designed. The optical absorption losses at 1064 nm for the particular structural groups of the benzene ring were found to increase in the following order: -Cl<-NO2<-CH3=-OCH3<-OC2H5<-NH2.

Second harmonic generation in the binary system of π-conjugated compounds

A large second harmonic generation (SHG) intensity, which was 60 times as large as that of urea was observed in a p‐nitroaniline(PNA)/N‐(p‐nitrophenyl)ethylenediamine (NPEN) system. This SHG intensity was related to the cooling rate for solidification. The optimum cooling rate for SHG intensity was in the range of 2–10 °C/s. X‐ray and thermal analysis done for this new system show that the hydrogen bond and the unique nonplanar structure of NPEN play an important role for SHG and its stability.

Second harmonic generation in binary systems of pi-conjugated compounds

A large Second Harmonic Generation (SHG) intensity which was 60 times as large as that of urea was observed in p-nitroaniline (PNA) I N-(p--nitrophenyl)ethylenediamine (NPEN) system. Results of X-ray and Scanning Electron Microscopy (SEM) analysis showed the new crystal structure. And this SHG intensity was related to cooling rate for solidification. The optimum cooling rate was in the range of 2°C/sec to 10°C/sec. Moreover, results of X-ray analysis and SHG measurements of similar binary systems showed that hydrogen bond and unique non- planar structure of NPEN played an important role for SHG and its stability.

Optical Second-Harmonic Generation of Tetrazole Derivatives

Second-harmonic generation (SHG) was investigated for 48 tetrazole compounds. Nine tetrazole compounds were found to generate second harmonic light upon irradiation with Nd:YAG laser light and to have an absorption edge of short wavelength below 350 nm.