Development of Optical Parametric Oscillator Source for Investigating Two-Photon Excitation PDT

Abstract

PDT (photodynamic therapy) is one of the treatments of superficial early cancer. But PDT is not adapted to advanced cancers. The peak absorption wavelength of Talaporfin sodium (Laserphyrin®) is 405 nm. 405 nm light is not used for Laserphyrin® PDT because it does not penetrate into tissues deeply interfered with hemoglobin absorption and scattering attenuation in tissues. The next peak absorption wavelength 664 nm is used for Laserphyrin® PDT now. The penetration depth of 664 nm light in tissue is not enough for advanced cancers.Photoexcitation is usually performed by single-photon excitation at absorption wavelength. However, high peak power light can occur two-photon excitation. Since the absorption rate at 405 nm of Laserphyrin® is very high, the effect of two-photon excitation at 810 nm can be expected. Through the absorption rate at 664 nm of Laserphyrin® is smaller than at 405 nm, light scattering attenuation at 1328 nm in tissues is smaller than at 810 nm. Two-photon excitation PDT at 1328 nm might be expected.In this study, we investigate a feasibility of two-photon excitation PDT using near infrared light, and compared two-photon excitation PDT at 810 nm with at 1328 nm. We have developed Nd:YAG SHG pumped KTP-OPO that oscillate at both wavelength by replacing the output coupler and adjusting phase matching angle with high peak power. In this paper, we report KTP-OPO configuration and optical properties at 810 nm and 1328 nm. We have accomplished 200 kW peak power 20 ns pulse width 50 Hz repetition rate at both wavelengths.KeywordsPDT (photodynamic therapy)Talaporfin sodium (laserphyrin®)Single-photonTwo-photon